Programme

Cold gas in and around galaxies plays a key role in galaxy quenching. I will discuss recent simulation results on the gas contents of galaxies and their halos from star-forming to quenched. Galaxy formation simulations constrained to give similar stellar growth properties can yield dramatically different predictions for the HI and H2 contents in >L* galaxies, making it both an interesting barometer for tracking quenching as well as a key discriminant between current models. I will further highlight the role played by the CGM in quenching galaxies, and some of the formidable challenges in modelling how the baryon cycle operates throughout massive halos to enact quenching.

The connection between halo gas acquisition through the circumgalactic medium (CGM) and galaxy star formation has long been studied. In this series of two papers, we put this interplay within the context of the galaxy environment on large scales (several hundreds of kpc). We use the IllustrisTNG-100 simulation to demonstrate that the large-scale environment modulates the circumgalactic gas angular momentum, resulting in either enhanced or suppressed star formation inside a galaxy. In the former case, the large-scale environment around a star-forming galaxy is often responsible for triggering new episodes of star formation. Such an episodic star formation pattern is well synced with a pulsating motion of the circumgalactic gas, which, on the one hand receives angular momentum modulations from the large-scale environment, yielding in-spiralling gas to fuel the star-forming reservoir, while, on the other hand, is affected by the feedback activities from the galaxy centre. As a result, a present-day star-forming galaxy may have gone through several cycles of star-forming and quiescent phases during its evolutionary history, with the circumgalactic gas carrying out a synchronized cadence of "breathing in and out" motions out to ~100 kpc. In the latter case for present-day quenched galaxies, both the large-scale environments and the ambient CGM have always had higher angular momenta throughout their evolutionary history since at least z=2, in comparison to those around present-day star-forming disk galaxies. This angular momentum modulation results in less efficient gas inflow into the central star-forming gas reservoirs. A sufficiently high CGM angular momentum, as inherited from the larger-scale environment, is thus an important factor in keeping a galaxy quenched, once it is quenched. The process above naturally renders two key observational signatures: (1) a coherent rotation pattern existing across multiple distances from the large-scale galaxy environment, to the circumgalactic gas, to the central stellar disk; and (2) a possible anti-correlation between galaxy star-formation rates and orbital angular momenta of interacting galaxy pairs or groups.

The classic theoretical picture of the galaxy merger life cycle predicts three key phases: triggered star formation, enhanced black hole accretion and finally (as a result of feedback from the former two processes) the quenching of star formation. The first two of these three phases have been well documented observationally. However, the quenching of star formation in the post-merger phase remains untested. Indeed, recent simulations have even called into question whether galaxy mergers are actually an effective quenching mechanism. By comparing the incidence of post-starburst galaxies, which identify the recent and rapid cessation of star formation, in a large sample of late-stage mergers and a control dataset, we can (for the first time) empirically answer the long-standing question of whether mergers quench star formation.

Post-starburst galaxies (PSBs) are prototypes for rapid galaxy quenching, yet recent detections of a significant ISM in many PSBs challenges theoretical predictions. How PSBs' star formation is halted through feedback and how they evolve afterward are consequential for galaxy models. We present high-resolution ALMA observations of several PSBs, revealing that their molecular gas is exceptionally compact, rivaling ULIRGs. We find gas turbulent pressures >100x higher than found in typical galaxies, implying some continuous injection of feedback. Yet, despite their high surface densities, these turbulent reservoirs exhibit highly inefficient star formation and little true dense gas, inferred from lines such as HCN and HCO+. These results paint a coherent picture of systems in which star formation was rapidly truncated, but in which the ISM was not completely expelled. Compact nuclear reservoirs of molecular fuel remain, but are supported against collapse by some form of turbulent heating.

Galaxy mergers have been long considered a major pathway for quenching star formation - but observational evidence for this paradigm has been elusive. However, many of the simulations that predicted this widespread merger-quenching implemented aggressive quasar-like feedback which ejected much of the galactic gas reservoir. More modern simulations, motivated by reproducing the observed properties of galaxies, implement more gentle feedback, which could potentially give very different results for mergers.

In this talk, I will present esults from a study that uses a large statistical sample of mergers selected from the IllustrisTNG (TNG) simulation to test whether mergers really do lead to widespread quenching. We find that quenching is very rare in descendants of TNG star-forming post-mergers and that in these cases the halt of star formation is due to gas removal caused by AGN kinetic feedback. Despite quenching does not commonly occur immediately after coalescence, we find that quenching occurs in post-mergers at twice the rate than in a control sample (i.e. post-merger galaxies that are matched in redshift, stellar mass, SFR, black hole mass and environment), thus suggesting that mergers do promote the cessation of star formation in some TNG post-mergers. To gain more insights into the impact of mergers on quenching, we also show results from the analysis of other cosmological simulations (Illustris and EAGLE) that implement different models to regulate black hole accretion and AGN feedback.

One of the proposed mechanisms for the quenching of massive galaxies is negative feedback from AGN. This theory is built into the subgrid models of modern cosmological simulations and is a crucial element in their ability to accurately reproduce the high-mass end of the galactic stellar mass function. However, direct observational evidence of this negative feedback on a population scale is lacking. Indeed, observations typically find that luminous AGN are preferentially located in gas-rich, star forming galaxies. Some observational papers have consequently suggested that this is in conflict with what would be expected from negative AGN feedback models. This has led to speculation in many observational studies that AGN feedback may not be as important as we thought, or as the simulations suggest.

To address this apparent tension, I will present our investigation into the impact of AGN feedback on host galaxy properties in three of the current generation of cosmological simulations (IllustrisTNG, EAGLE and SIMBA), along with post-processed models for molecular hydrogen gas masses.We perform tests similar to those frequently used by observers, such as searching for trends between AGN luminosity and star formation rate or molecular gas fraction, comparing AGN-selected sources to main sequence galaxies, and calculating quenched and gas-depleted fractions for the AGN host galaxies.

Despite the three simulations having very different feedback models, we find that they are in qualitative agreement, and predict: (i) no strong negative trends between AGN luminosity and galaxy properties; (ii) that both high-luminosity (L_bol > 10^44 erg/s) and high-Eddington ratio (>1%) AGN are preferentially located in galaxies with high molecular gas fractions and sSFR; and (iii) that the gas-depleted and quenched fractions of AGN host galaxies are lower than a control sample of non-active galaxies. These results are in qualitative agreement with observational samples at z=2 and z=0 and show that such findings are not in tension with the presence of effective AGN feedback. I will also present quantifiable differences between the predictions from the simulations, which could allow us to observationally test the different subgrid feedback models and improve our understanding of the role of AGN in the quenching of massive galaxies.

Understanding how galaxies cease to form stars represents an outstanding challenge for all galaxy evolution theories. The ``star formation quenching'' can be related to a complex interplay of phenomena such as the AGN activity, the influence of large-scale dynamics, or the environment in which galaxies live in. All this information is available from the Integral Field Unit (IFU) CALIFA survey (Sanchez et al. 2016) which provides kpc-resolved measurements of stellar population and ionized gas emission lines for a representative sample of local Universe galaxies. However, disentangling the dominant quenching mechanisms is impossible without knowledge of the conditions of the molecular gas, the raw fuel of star formation. With this aim, we are assembling the Extragalactic Database for Galaxy Evolution (EDGE, Bolatto et al. 2017) which, to date, consists of a homogenized CO line dataset for more than 700 CALIFA targets observed with the CARMA, APEX, ACA, GBT, and LMT telescopes. Through the EDGE-CALIFA dataset, we have noticed that galaxies at different stages of their evolution show approximately similar molecular gas quantities and that the star formation efficiency (SFE) in the remaining cold gas reservoir is what modulates their retirement, with lower efficiencies corresponding to more quiescent galaxies (Colombo et al. 2020). Causes for the altered SFE (compared to the average value in star-forming disks) are diverse and span from the influence of bar and merger (Utomo et al. 2017, Chown et al. 2019) to the incremented shear (Colombo et al. 2018), and the presence of bulge (Villanueva et al. 2021). Nevertheless, the molecular gas appears really reduced in the regions influenced by the AGN activity (Ellison et al. 2020). Through the combination of integrated and kpc-resolved CO measurements provided by EDGE, we have observed that star formation fundamental relations are equivalent whether measured integrating across the whole galaxy or on kpc-scale. This implies that the main physical processes that regulate star formation operate on kpc-scale. Nevertheless, galaxy interactions, galactic-wide outflows, and the ignition of an AGN do influence star formation, but they do not seem to have a direct effect galaxy-wide (Sanchez et al. 2021). Additionally, on kpc-scale, SFR in galaxies appear modulated by the hydrostatic mid-plane pressure (Barrera-Ballesteros et al. 2021) which indicates that SFR is self-regulated by momentum injection from supernovae explosions.

Identifying and understanding the physical mechanisms responsible for star formation quenching are key challenges in modern astronomy. For instance, black hole feedback has been widely implemented as the key recipe to quench star formation in massive galaxies in modern semi-analytic models and hydro-dynamical simulations. As the theoretical details surrounding the accretion and feedback of black holes continue to be refined, various feedback models have been implemented across simulations, with notable differences in their outcomes. Yet, most of these simulations have successfully reproduced some observations, such as stellar mass function and star formation rate density in the local Universe. I will first present recent observations on the cold gas in galaxies at various stages of their evolution. Then I will show the use of these observations as critical tests of star formation and black hole feedback models in simulations, and discuss the implications.

The star formation can be halted either through the removal of the gas reservoir or the suppression of the star formation efficiency. Probing the star formation rate relative to the gas content of galaxies thus provides crucial insight into the physical mechanisms that are responsible for quenching. In this talk, I will summarize our current understanding of the gas content in galaxies that are on the star-forming main sequence (SFMS) and in those that depart from the SFMS based on both the integrated and spatially-resolved observations of molecular gas. In particular, I will highlight how the resolved observations help characterize the quenching mode. And finally, I will comment on the importance of having dense gas (e.g., HCN, HCO+) observations for further constraining the physics of quenching.

While great progress has been made in understanding how galaxies evolve over time, a self-consistent explanation for the diffuse gaseous halos surrounding galaxies (the circumgalactic media,CGM) and its impact on galaxy evolution still eludes us. Characterizing the detailed physical properties of the CGM is essential for making new progress. In my talk, I will highlight recent results from our space- and ground-based observational studies of the CGM around a diverse population of galaxies and discuss what they teach us about the nature of the CGM. Our work shows that despite their quiescence, massive red and dead galaxies host as much cool gas in their CGM as star-forming L* galaxies, contrary to theoretical expectation that their CGM is predominantly hot (T>10^6 K). Furthermore, large variations in gas metallicities, elemental abundance ratios, and densities within the CGM of quenched galaxies indicate that the CGM is a multiphase mixture of gas with different enrichment histories. In particular, the observed elemental abundance ratios of the gas indicate that the inner CGM is significantly influenced by feedback from Type Ia supernovae, whereas gas in the outer CGM (>100 kpc) likely originates from accretion from the intergalactic medium. Finally, I will present initial results from a new study on how galaxy environment influences the gas properties of massive quiescent galaxies on both small (~kpc, ISM) and large (~100 npc, CGM) scales. These new observational results provide critical insights into the interplay between accretion and feedback in massive galaxies, which is critical to understanding how quenching impacts galaxies and the CGM over cosmic time.

This is an important question because massive quiescent galaxies at high-redshift have historically driven forward our understanding of galaxy formation and evolution. Numerous spectroscopic confirmations have shown that these galaxies do exist at z>3, however the measured number densities are still highly uncertain and depend on photometrically selected samples. Massive quiescent galaxies at high-redshift evolve rapidly and so constraining hydrodynamical simulations with precise number densities is critical.

The deepest ground based spectroscopy of quiescent galaxies in this redshift range (our work of Schreiber_2018) targeted 24 photometrically pre-selected quiescent galaxy candidates (z>3, stellar mass>2E10 Msun selection) with MOSFIRE/Keck. Here only 12 galaxies were spectroscopically confirmed, 3 of which were highly uncertain, leaving a possible 12 quiescent galaxies still unconfirmed - many with continuum detections and no emission lines. Thus even with this deep data the confirmed number density is up to 100% uncertain. Furthermore while the unconfirmed galaxies are the fainter ones in the quiescent galaxy candidate sample they are not necessarily the least massive. They could simply be older, which at 3<z<4 would place them as the earliest to form (perhaps z>6).

With JWST/NIRSPEC we are observing the remaining 15 uncertain or unconfirmed quiescent galaxy candidates. The first spectra were secured recently. Analysis of the spectra will confirm or deny the redshifts and the ages of the galaxies, hence tracing the epoch at which the first massive galaxies form.

Chemical composition is a powerful tracer of the star formation history of galaxies. Spectroscopic surveys have given us access to detailed analysis of the stellar populations of passive galaxies and are pushing our knowledge of the chemical make-up of star-forming galaxies at low and high-redshift. Connecting star-forming and passive populations across cosmic time, and therefore drawing a coherent picture of the quenching process, remains, however, a difficult task. A theoretical famework is needed, which correctly reproduces both the cosmic star formation and chemical evolution history. In this review talk I will discuss recent observational work and draw a connection to the predictions of both analytical models and hydrodynamical simulations. Despite lingering systematic uncertainties, I aim to show that studying the chemical make-up of stars and gas in galaxies may shine new light on the timescale of the quenching process. In particular, I will show how the relation between stellar mass, star formation rate and metallicity may be interpreted in this context. Finally, I will summarize the role of future facilities aimed at obtaining spectroscopy of intermediate and high-redshift galaxies and the opportunities they offer to draw a coherent chemical evolution history of the Universe.

We developed a new methodology to reconstruct reliable non-parametric Star Formation Histories (SFHs) from full spectral fitting using the penalized pixel fitting code pPXF (Cappellari, 2017), and by adopting a bootstrapping re-sampling scheme in combination with weight regularization. We have applied this technique to 10,000 MaNGA SDSS galaxies and explored the SFHs as a function of galactocentric radius, host galaxy properties like stellar mass, star-formation state, and central/satellite classification. In particular we have explored the variation of radial quenching of star formation as a function of local, global and environmental galactic properties with high statistical significance.

Very interestingly, our technique has also provided additional information about accretion or lack thereof. Indeed, our analysis of MaNGA galaxies indicates the existence of young metal-poor populations (YMPP) in some populations of galaxies, likely tracing stars formed by the recent accretion of metal-poor gas. Our spatially resolved analysis reveals cases of both centrally concentrated and extended YMPP.

Finally, depending on the JWST schedule and data availability, I may be able to present some of the very first results on galaxy quenching at high redshift from the first observations obtained within the JWST NIRSpec GTO programme, and by using an adapted version of the methodology described above.

Since the turn of the 21st Century, we have developed a detailed understanding of the local, present-day galaxy population. However, significant uncertainties remain as to how these galaxies formed across the 14-billion-year span of cosmic history. One surprising result is the downsizing trend, in which the stellar populations of more-massive local galaxies are found to be older than their less-massive counterparts, in stark contrast to the hierarchical assembly of dark matter halos. This has been accompanied by the progressive discovery of massive, apparently fully evolved, galaxies at increasingly high redshifts, with log(M*/M_sol) ~ 11 passive galaxies now spectroscopically confirmed as early as z = 4. In this talk, I will discuss current and future efforts to constrain the star-formation histories (SFHs) and stellar metallicities of massive quiescent galaxies, from the end of the peak epoch of cosmic star formation at z ~ 1, all the way back to the first billion years of cosmic history.

I will begin by discussing results from the VANDELS survey and subsequent KMOS follow-up in the rest-frame optical. Combined, these provide high-SNR rest-frame UV-optical continuum spectroscopy for a mass-complete sample of massive quiescent galaxies at z >~ 1 for the first time, allowing detailed studies of their SFHs and metallicities to precisely understand when and how quickly these galaxies quenched. I will also discuss the upcoming 200-night Multi-Object Optical and Near-Infrared Spectrograph (MOONS) extragalactic GTO program MOONRISE, which will provide huge statistical samples of high-SNR spectra at z > 1, revolutionising the study of star formation, chemical enrichment and quenching at cosmic noon.

Finally, I will discuss massive, quiescent galaxies at the highest redshifts, focusing on the upcoming revolution we can expect as a result of James Webb Space Telescope data. We now know the first massive quiescent galaxies must have reached their considerable masses, then quenched their star formation activity, during the first billion years of cosmic history. Objects of this nature are extremely challenging to accommodate within our current understanding of galaxy formation physics, and even Lambda-CDM cosmology, given that massive, early galaxies place a lower bound on the halo mass function. I will discuss two JWST Cycle 1 programmes that will provide new insights into the number densities and astrophysical origins of massive quiescent galaxies at z > 3. The first, of which I am PI, is an extremely deep spectroscopic study of the earliest known massive quiescent galaxy, at z ~ 4.7. The second is the PRIMER large treasury program, which will deliver unprecedentedly deep near-infrared imaging over a 400 square arcmin area in the COSMOS and UDS fields.

In this talk I will discuss the physics of the multiphase gas in local active galaxies and the impact of the Active Galactic Nucleus (AGN) on the host galaxy evolution.

AGNs can generate winds and jets that interact with the host galaxy interstellar medium (ISM), potentially altering both the star formation and the nuclear gas accretion. I will focus on the warm ionized and cold molecular phases of the ISM in the nearby AGN NGC2992, using MUSE/VLT and ALMA data to probe the kinematics and interaction of the different gas phases, over a broad range of physical scales. I will present a detailed dynamical modeling of the gas component through which we can reconstruct the distribution and kinematics of the multiphase discs, winds and their interaction, from nuclear out to several kp-scale.

By exploiting spatially resolved MUSE multi-line diagnostics, we are able to derive the best estimate of the velocity field, the spatial distribution, and electron density and therefore properly quantify the ionized mass across the disc, narrow line region (NLR) and outflow, and the ionized outflow energetics.

JVLA data of NGC2992 clearly shows the presence of a compact radio jet, of which we study the interaction with the gas in the host galaxy disc and ionized cones, probing the impact of the AGN mechanical feedback. Indeed there is a growing awareness that jets in so-called 'radio-quiet' galaxies, such as NGC2992, can have a significant effect on the ISM.

Finally I will discuss the extension of this analysis to a larger sample of hard X-ray selected nearby AGN drawn from the INTEGRAL-IBIS AGN catalog.

In recent years, an explosion of photometric and spectroscopic studies has revealed an undoubtable quenched galaxy population at z>3, hinting at the first episodes of quenching in the early universe. These quenched galaxies are massive, compact, and many exhibit signs of recent or even ongoing star formation, implying that many of them recently underwent a period of star formation cessation. Methods used to find and select these galaxies in photometric catalogs so far have been adopted from lower redshift, which may not be optimal for finding recently quenched galaxies in particular. In this talk, I will present a new method for finding and selecting quiescent galaxies at z>2 in photometric data using rest frame colours, and highlight some results of its application to the latest COSMOS catalog.

Observational constraints on the build-up of the red sequence have largely been limited to photometric studies of deep fields. Here, I utilize the novel DESI SV1 Bright Luminous Red Galaxy (LRGs) spectroscopic sample, leveraging its deep (∼ 3 hour/galaxy) spectra to characterize the growth of the massive galaxy population at 0.4 < z < 1.3. I use Prospector to infer non-parametric star formation histories of ∼ 18, 000 LRGs and identify a significant population of younger, post-starburst galaxies that have recently joined the quiescent population. We find that the number density of young quiescent galaxies is steadily rising as a function of redshift, and by z=0.8 galaxies which formed >10% of their stellar mass in the past Gyr represent ~2% of the massive (log(M/Msun)>11.2) galaxy population. Additionally, I will show that the 290 galaxies we select at 1 < z < 1.3 represent the largest spectroscopic sample of post-starburst galaxies at that epoch. I will highlight my upcoming HST/SNAP program that will measure morphologies and merger rates for this population.

Post-starburst galaxies (PSBs) have recently and rapidly quenched their star-formation, making them an important population for understanding the processes that cause galaxies to transition from star-forming late-type galaxies to quiescent early-type galaxies. However, the recent discovery of large cold gas reservoirs in PSBs calls into question the theory that galaxies must expel or exhaust their gas to become quiescent. To better understand the mechanisms that quench star formation, we analyze a sample of 14 nearby (z < 0.1) PSBs with spatially resolved optical IFU data from the MaNGA survey and with matched resolution ALMA observations of 12CO(1-0). This unique sample allows us to study the molecular gas and star-formation properties on kpc scales and increases the total number of PSBs with resolved gas measurements by a factor of 3. We find centrally concentrated molecular gas morphologies, with ~75% of the molecular gas contained within 3-sigma of the beam size, on average. We also see a diversity in the alignments of the kinematic axes of the stellar, ionized and molecular gas components, which depend on whether the post-starburst spaxels are centrally concentrated. We compare the molecular gas and star-formation rate surface densities of the post-starburst regions of galaxies in our sample to other star-forming galaxies and PSBs and find that star-formation tends to be suppressed in our PSBs with central post-starburst regions in particular. While the post-starburst regions in some of our galaxies are gas-poor with typical star-formation efficiencies, others display typical star-forming gas fractions with greatly reduced star-formation efficiencies. Overall, our results point to a major event disrupting the gas in these post-starbursts, driving it inwards and resulting in centrally concentrated gas reservoirs with varied kinematics that form stars at a suppressed rate.

The galaxies in massive clusters are by and large red and dead. Massive clusters are home to abundant dark matter and hot baryon gas and thus where complex physical processes take place, making the question difficult to answer. One useful approach to tackle this issue is to constrain the quenching timescales of galaxies. This is because each quenching process works with a different quenching timescale. In this work, we take a novel approach to constrain the quenching timescale of cluster galaxies. First, with cosmological simulation data, we investigate how the time since infall of galaxies is distributed on the phase-space diagram, a plot of distance versus velocity of galaxies. We see a clear hint that each region on the phase-space diagram can predict the times since infall of observed galaxies (Rhee et al. 2017). Secondly, we extend this idea by applying the prediction to observed cluster galaxies. We statistically connect the SFR distribution of the observed galaxies with the time since infall distribution of simulated galaxies located at the same position of the phase-space diagram. This leaves a mean behavior of SFR of galaxies as a function of their time since infall. We then measure the quenching timescales of galaxies from the relation. We confirm that cluster galaxies generally follow the delayed-then-rapid quenching pattern (Rhee et al. 2020): (1) the e-folding time for quenching is roughly 3 Gyr before infall, (2) the pace of quenching is maintained roughly for 2 Gyr during the first crossing time, and (3) quenching becomes more dramatic after the delay time (~1 Gyr as the e-folding time). We conclude that the gentle mode of quenching during the delay time mainly affects the hot and neutral gas component of galaxies, with which SFR of galaxies is not severely affected, and then strong ram pressure causes cluster galaxies to be red and dead. Therefore, a clear red sequence of cluster galaxies is the product of a special quenching pattern of SFR of galaxies.

Given the complexity of the star formation histories of galaxies, it is not trivial to pinpoint the exact physical mechanisms responsible for the decline of the cosmic star formation activity from z ~ 2 to z ~ 0. By far, integral field spectroscopy (IFS) surveys such as MaNGA and SAMI have helped shed light on the physical processes at play by studying the spatially resolved star formation activity of galaxies at z ~ 0. These studies suggest that galaxies typically quench 'inside-out', while those residing in dense environments tend to quench 'outside-in'. This motivates a further investigation into the evolution of star formation activity at higher redshifts, with the Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey - a MUSE Large Program - extending the regime towards intermediate redshifts (z ~ 0.3). In this talk, I will be introducing the MAGPI survey and early results with the MAGPI data on the spatially resolved star formation activity of galaxies. In particular, I will present radial profiles of star formation rate (SFR) densities and metallicities of galaxies of different global star-forming states and compare them with those from z ~ 0 studies.

I will present a state-of-the-art analysis of the Stellar Mass Function (SMF) of passive galaxies from z~5 to the nearby Universe.

At low z (z<3), the combination of the CANDELS and the Hubble Frontier Fields programs allows the extension of previous analyses by an order of magnitude down in stellar mass. Thanks to this data set, the deepest available until the first JWST data, the typical low-mass upturn in the passive (UVJ-selected) SMF, indicative of environmental quenching processes, is for the first time observed up to z~2.5.

At higher z (z>3), I will present the SMF of a statistically meaningful sample of passive galaxies selected by means of photometric technique based on SED fitting, adopting a probabilistic approach. This technique was ad-hoc developed to overcome the limitations associated with the standard UVJ selection at high redshift, and its accuracy and reliability had been demonstrated by means of ALMA observations probing the lack on on-going star formation. I will show that the SMF of passive galaxies undergoes a strong evolution around z~4, indicating that we are witnessing the emergence of the passive population at this epoch, i.e. we are looking at the epoch when a substantial amount of quenching took place.

Quenching is intuitively understood as a total cessation in star formation. However, we now identify a full spectrum of the levels of quenching that includes the transitional stages. Therefore, it is common to consider as quenching (and fully quenched) the galaxies that scatter below the main sequence and have low specific SFRs. What makes the use of sSFR to inform us of the degree of quenching confounding is that sSFR will go down as the galaxy ages and accumulates stellar mass even if it maintains its star-forming capacity (e.g., the number of star forming regions and their total SFR). In this talk, I will discuss an alternative conceptualization of quenching (or more broadly, of the level of SF activity) that is based on the SFR surface density, which is largely decoupled from past star formation and therefore more indicative of the mechanisms regulating the star formation. I will show the evolution of the SFRD "main sequence" obtained from state-of-the art SED fitting at 0<z<2.5 and discuss why it looks different from the evolution of the traditional, (s)SFR main sequence.

The star-formation and chemical-enrichment histories of galaxies are known to follow well-defined trends with stellar mass, which are testified by the z~0 archaeological records of the relations between stellar mass and mean stellar age and metallicity, respectively. With the advent of the integral-field spectroscopy (IFS), these "global" relations have been found to have "local" counterparts in the relations between stellar-mass surface density and the local mean stellar age and metallicity. In my talk I will present the results of a series of works (Zibetti et al. 2017, 2020, Zibetti & Gallazzi 2022), based on the CALIFA IFS survey, pointing at the fundamental role of local stellar mass density in establishing the evolutionary paths for quenching and for the chemical enrichment. In particular, we find that 1kpc-scale regions follow two sequences: an old ridge with old ages irrespective of stellar-mass surface density µ*, and a young sequence along which the age increases with µ*, indicating a strong link between density growth and suppression of the SFR. The relative weight of these two regimes is largely determined by the total stellar mass of the galaxy, with regions in massive galaxies predominantly living in the old ridge and, vice versa, regions in the less massive populating the young sequence. Local stellar metallicity displays a steep increase with µ*, but, quite surprisingly, this relation is the same for old-ridge and young-sequence regions. While this result appears at odds with the global mass-metallicity relations of star-forming and passive galaxies, respectively, being substantially different (e.g. Peng et al. 2015), we can reconcile this apparent discrepancy by considering the different distribution in µ* (i.e. the different structure) of star-forming and passive galaxies. We conclude that any attempt to understand galaxy quenching and the baryonic cycle of galaxies requires understanding and modelling the (transformations of) structure and the growth of stellar-mass surface density.

Stars are fossils that retain the history of their host galaxies. Elements heavier than helium are created inside stars and are ejected when they die. Elements heavier than iron (such as gold) are also produced by neutron star mergers. From the spatial distribution of elements in galaxies, it is therefore possible to constrain star formation and chemical enrichment histories of the galaxies. This approach, Galactic Archaeology, has been popularly used for our Milky Way Galaxy with a vast amount of data from Gaia and multi-object spectrographs. This approach can also be applied to external galaxies thanks to integral field units. Mass-metallicity relations and metallicity radial gradients have been observed and compared with theoretical predictions, namely, hydrodynamical simulations incorporating detailed chemical enrichment. Elemental abundances can give more stringent constraints, but the available observations are limited, and are only for alpha/Fe ratios in early-type galaxies and for N/O of star-forming galaxies up to z~2; these observations will be expanded for higher redshifts with JWST, as well as for other elemental abundances with ALMA.

Star-forming galaxies can be transformed into passive systems by a multitude of processes that quench star formation, such as the halting of cold gas accretion (starvation) or the rapid removal of gas in AGN-driven outflows. However, it remains unclear which processes are the most significant, primary drivers of the star-forming - passive bimodality. Leveraging on the statistical power of the SDSS-IV MaNGA galaxy survey, we analyse both the global and spatially-resolved chemical properties of thousands of local star-forming, green valley and passive galaxies to investigate how galaxy quenching depends on mass and environment, and how quenching operates on a radial basis within galaxies. By integrating all the light in each MaNGA galaxy out to 1.5 - 2.5 R_e, we find that the significant difference in the global stellar metallicities of passive galaxies and their star-forming progenitors implies that for galaxies at all masses, quenching must have involved an extended phase of starvation. In order to best match the observed properties of local passive galaxies, some form of gas ejection has to be introduced in our models, with outflows becoming increasingly more important with decreasing stellar mass. Additionally, by dividing each MaNGA galaxy into a series of 0.5 R_e-wide annuli, we further find that passive galaxies are in fact substantially more metal-rich than star-forming galaxies at all radii, with the stellar metallicity difference between star-forming and passive galaxies decreasing with increasing radial distance. Therefore, while starvation plays a relatively prominent role in quenching the central regions of galaxies, it plays an increasingly less important role in quenching the outskirts of galaxies, as galactic outflows and gas stripping begin to dominate the quenching process.

We present changes in stellar population age scaling relations for quiescent galaxies from intermediate redshift (0.60 < z < 0.76) using the LEGA-C Survey to low redshift (0.014 < z < 0.10) using the SAMI Galaxy Survey. Specifically, we study how the spatially-integrated global age of individual quiescent galaxies vary in the mass--size plane, using the stellar mass and a dynamical mass proxy derived from the virial theorem. Despite there being a strong correlation between age and surface density (M/R^2) at low redshifts, we find no correlation between age and surface density at 0.60 < z < 0.76. We consider this change with redshift in the age-surface density relation in the context of the redshift evolution of the star-forming and quiescent mass--size relations, and find our results are consistent with galaxies forming more compactly at higher redshifts and remaining compact throughout their evolution. Furthermore, galaxies appear to quench at a characteristic surface density that decreases with decreasing redshift, so that galaxies forming and evolving at higher redshifts reach a higher surface density before quenching compared to low-redshift star-forming galaxies. The z=0 age--surface density relation is therefore a result of building up the quiescent and star-forming populations with galaxies that formed at a range of redshifts and therefore a range of surface densities. Our work further establishes the strong interdependence between quenching and internal galaxy structure, and places constraints on models for quenching mechanisms.

For decades, we have been trying to solve the causality dilemma of “which came first: quenching or galaxy transformation?"

With the wealth of data from photometric and spectroscopic galaxy surveys at high-redshift, combined with extensive IFS surveys at low-redshift, we should be in a position to answer this question once and for all. Yet, many questions on how galaxy structure, kinematics, and morphology are related to quenching still exist. In this talk I will go over the observational evidence that links the rate of star-formation to the intrinsic stellar properties of galaxies. Specifically, I will present a summary of recent results on how galaxy structure evolves from high redshift to the present day, which process are most likely to transform galaxies from rotationally supported to dispersion dominated, and how these processes are connected to quenching.

We introduce a novel machine learning method for analyzing the dependence of star formation quenching on galaxy and environmental parameters. Our machine learning technique is highly effective at extracting causality (not merely correlation) from models, and hence is of great value in the analysis of observational data (where causality is generally hidden). We apply this technique to three of the largest observational galaxy surveys (SDSS, MaNGA and CANDELS), as well as to a leading semi-analytic model (LGalaxies). In observations, we demonstrate that central galaxy quenching is governed primarily by global (galaxy-wide) physics and is most strongly connected with the conditions at the very center of massive galaxies (especially central velocity dispersion and bulge mass). Interestingly, these results are precisely predicted by models of Active Galactic Nucleus (AGN) feedback. This strongly suggests that supermassive black holes play a fundamental role in determining the fate of galaxies - once a black hole reaches a critical mass, it shuts down accretion of gas into the system, ending star formation forever.

I will present results on massive star-forming galaxies at z~1-3 from spatially- and spectrally-resolved surveys --- particularly KMOS^3D, SINS/zC-SINF, NOEMA^3D, and from ALMA observations. This population is likely to quench in the near future, thus providing key constraints on the "pre-quenching" nature of galaxies during the epoch when the massive quiescent population is rapidly building up. Together these surveys provide constraints on the gas and star formation distributions and kinematics for ~800 star-forming galaxies at "cosmic noon," spanning the full population at the massive end of the star-forming main sequence. I will emphasize the significance of the quantity and distribution of gas and star formation, the link between kinematics and the emergence of galaxy structure, and the role of outflows. I will also highlight the first evidence at this epoch of motions tracing efficient gas transport in action. These motions are likely tracing the growth of bulges in-situ, as well as potential feeding of supermassive black holes, that then leads to AGN feedback. Finally, I will outline exciting prospects with the new VLT/ERIS AO-assisted near-infrared IFU, with the upgraded IRAM/NOEMA sub-millimeter interferometer, synergies with JWST, and in the further future with ELT/MICADO and HARMONI.

Stellar kinematics hold the record of the mass assembly history of galaxies. We use a Gauss-Hermite expansion of the velocity distribution to measure h4, a proxy for the excess kurtosis and a measure of orbital anisotropy. Using 1-d spectroscopy from the SAMI, MAGPI and LEGA-C surveys, we find independent correlations with stellar mass and with the rotation-to-dispersion ratio, both in the local Universe (SAMI) as well as at redshift 0.7 (LEGA-C). We further find that quiescent galaxies have systematically larger h4 than coeval star-forming galaxies, pointing to a larger radial anisotropy for quiescent systems and to yet another link between stellar kinematics and the star-formation status of galaxies.

Leveraging the long baseline in cosmic time provided by our data, we study the evolution of h4 in massive, quiescent galaxies across the last 6 billion years. For these massive systems, h4 increases with cosmic time, even more so after controlling for stellar mass. Qualitatively, this increase is consistent with the observed evolution in galaxy shape and rotation-to-dispersion ratio, both pointing to quiescent galaxies becoming rounder and with higher dispersion. Crucially, the observed evolution in h4 cannot be caused by progenitor bias, because quiescent galaxies have larger h4 than star-forming galaxies. Therefore this change in the quiescent population must be due to individual galaxies evolving after becoming quiescent, most likely due to dry mergers.

These results open a new avenue to study the mass assembly history of galaxies, leveraging 1-d spectroscopy from the upcoming generation of large single-fibre surveys. Depending on the data availability, we could present preliminary results from the JWST GTO program.

Recent observational studies indicate that bulge-dominated galaxies exhibit suppressed star formation rates (SFRs) compared to disc-dominated galaxies with similar gas reservoirs, often attributed to a low star formation efficiency (SFE). Dynamical suppression, where star formation is inhibited because shear from the bulge induces turbulence in the gas and stabilises the gas disc against fragmentation, offers an explanation for low SFEs without invoking feedback from active galactic nuclei. The effectiveness of dynamical suppression has been demonstrated in isolated galaxy simulations and a couple of idealised cosmological zoom-in simulations. It has been predicted that even Milky Way-mass galaxies could have already been impacted by dynamical suppression for the past 4-5 Gyr.

I will present a sample of 14 Milky Way-mass galaxies drawn from the EMP-Pathfinder suite of cosmological zoom-in simulations. For each galaxy the initial conditions were evolved self-consistently across cosmic time with two different sub-grid star formation prescriptions: one with an environmentally-dependent, turbulence-based SFE, the other with a constant SFE. These simulations are ideally suited to explore the impact of dynamical suppression on L* galaxies (in addition to allowing a systematic exploration of how an environmentally-dependent SFE influences galaxy evolution in a cosmological context).

I show that despite the similar stellar mass at z=0, the SFRs and star formation histories differ significantly between the galaxies evolved with different star formation models. However, contrary to expectations, the galaxies evolved with the dynamics-dependent SFE are even more star-forming at z=0 than their constant SFE counterparts. The SFR differences are driven by differences in the galaxies' cold gas content and their gas fractions are too high for dynamical suppression to be effective. This supports the idea that dynamical suppression may act in concert with other mechanisms to keep gas-poor bulge-dominated galaxies quiescent, but is unlikely to quench galaxies by itself.

Recent observations have identified a population of high-redshift massive galaxies that experienced a remarkably rapid quenching. This raises fundamental questions related to the quenching process: Are all galaxies at high redshift experiencing rapid quenching? Is rapid quenching caused by AGN feedback and/or mergers? Are cosmological hydrodynamical simulations able to reproduce the observations? We look for analogs of rapidly quenching galaxies in the IllustrisTNG simulation, and find a promising population. While quenching in IllustrisTNG is due to AGN feedback by construction, in many of these galaxies it is also associated with merger-triggered starbursts. These centrally concentrated starbursts leave a unique signature on the age gradient which is qualitatively consistent with the observations. We then analyze new absorption-line spectroscopy of rapidly quenching galaxies at z~2, which we use to derive precise measurements of the star formation history and the quenching timescale. By comparing our measurements to the properties of simulated galaxies in IllustrisTNG, we are able to gain new insight on the physical nature of rapid quenching.

Outflows driven by active galactic nuclei (AGN) are widely accepted to play a key role in shaping the evolution of the host galaxy and are invoked by galaxy evolutionary models to quench the star formation (SF) in massive galaxies. However, decisive evidence of negative feedback in action is still lacking. To further investigate this, a first step can be to understand how effective the coupling between the energy released by the AGN and the galactic interstellar medium (ISM) is, that is how AGN winds are accelerated on galaxy scales. The 'wind feedback' scenario predicts a nuclear ultra-fast outflow (UFO) to shock against the galactic ISM, leading on kpc scales to either a massive and powerful energy-driven outflow, or a low-mass momentum-driven wind. In this perspective, multiwavelength observations are crucial to obtain a full multi-phase and multi-scale description of AGN winds: from X-rays, where UFOs are typically detected, to the optical, NIR and mm bands used to trace large-scale, multiphase outflows especially through IFS observations. It is important to study outflows both in detail at low redshift, and at high redshift, with primary focus on epochs close to the peak of both AGN and SF activity histories (z~2), where negative feedback is expected to be more effective.

In this talk I will review the known association between UFOs and large-scale outflows, and highlight the recent results on the large-scale ionised outflows detected in four UFO-host quasars: two nearby objects observed with MUSE, and two more distant systems at z~1.5 observed with SINFONI. These four quasars along with the other few well-studied AGN with both secure UFO and extended (ionised/atomic/molecular) outflow detections constitute a first representative sample to finally test the predictions of wind feedback models. The overall good compatibility of observations with models warmly suggests the strict link between nuclear and galaxy-scales winds.

The QSOFEED project is gathering multi-wavelength observations of a sample of 48 nearby (z~0.1), luminous type-2 quasars (QSO2s) to enhance our understanding of the impact AGN driven outflows have on different gas phases in the ISM and how that in turn impacts stellar populations. Key results from the QSOFEED project to date include our spatially resolved investigation into the interplay between the young stellar populations (YSPs; ages <100 Myr) and the kinematics of the warm ionised outflows in the well-studied type 2 quasar Markarian 34. Utilising IFS data, we demonstrate a spatial correlation between the outer edges of the approaching side of the outflow and an enhancement in the proportion of the YSP flux, suggesting that the outflow is responsible for triggering star formation in this region. In regions with more highly disrupted gas kinematics, we find that the proportion of YSP flux is consistent with that found outside the outflow region, suggesting that the increased disruption is preventing a similar enhancement in star formation from occurring. Our analysis suggests that Mrk 34 is an example of quasar driven outflows simultaneously producing both `positive' and `preventive' feedback, further demonstrating the complex nature of the relationship between quasars and their host galaxies. Exploring the cold molecular gas phase, we have also mapped, for the first time, the gas content traced by the 2-1 line of CO, and adjacent continuum emission, of 7 QSO2s in the QSOFEED sample. The ALMA observations, with an angular resolution of ~0.2 arcsec (370 pc), reveal molecular outflows that are mostly coplanar with the CO disks These outflows represent 0.2-0.7% of the QSO2s total molecular gas mass and have maximum velocities of 200-350 km/s , radii from 0.4 to 1.3 kpc, and outflow mass rates of 8-6 Msun/yr. These outflow properties are intermediate between those of the mild molecular outflows measured for Seyfert galaxies and the fast and energetic outflows shown by ultra-luminous infrared galaxies. This suggests that it is not only AGN luminosity that drives massive molecular outflows. Other factors such as jet power, coupling between winds, jets, and/or ionized outflows and the CO disks, and amount or geometry of dense gas in the nuclear regions might also be relevant. Thus, although we do not find evidence for a significant impact of quasar feedback on the total molecular gas reservoirs and star formation rates, it appears to be modifying the distribution of cold molecular gas in the central kiloparsec of the galaxies.

Abstract: TBD

Cosmological models of galaxy formation suggest that massive gas outflows driven by stellar and AGN feedback play a key role in shaping the star formation efficiency of galaxies. Such outflows are expected to be particularly important at high redshift (z~1-3), during the peak of the cosmic SF and AGN activity. We test this ejective feedback scenario by investigating the demographic of kpc-scale outflows in a sample of 141 star-forming galaxies at 1.2 < z < 2.6 observed within the KMOS (K-band Multi-Object Spectrograph) LEnsed galaxies Velocity and Emission line Review, KLEVER. Combining small gravitationally lensed galaxies with more massive galaxies, we explore the kinematics of the ionised gas (traced by Hbeta, [OIII], Halpha, [NII] and [SII]) in an exceptional range of stellar masses, log(M/Msun) between 8.1 and 11.4, pushing outflow studies to stellar masses down to the dwarf regime. Comparing our observations with the expectation of a simple rotating disk model, we find that: (1) ionised gas outflows are statistically present in very massive galaxies, log(M/Msun)>10.8; (2) the AGN activity is the main source of ionisation suggesting that AGN may be the primary force behind the gas flows; (3) ionised gas outflows are rare in low mass galaxies, where the ionised flux is dominated by the gas in the galactic disk; (4) the winds have very low mass loading factors, accounting for less than 2% of the global mass loading factor expected on IllustrisTNG50. I will discuss the implications of our results on theoretical models of galaxy formation.

I will present the work by Varma et al. (2021) in which we investigate the relation between structural transformations and quenching in the TNG50 simulation in the observational plane. We generate mock images with the properties of the CANDELS survey and derive Sersic parameters and optical rest-frame morphologies as usually done in the observations. We first show that the simulation reproduces the observed evolution of the abundances of different galaxy morphological types of star-forming and quiescent galaxies as well as observed scaling relations such as the mass-size relation up to z~3. We then explore how the observed relations are built-up across cosmic time.

I will in particular focus on the following key results:

1. Galaxies increase their observed central stellar mass density and transform in morphology from irregular/clumpy systems to normal Hubble-type systems in the Star Formation Main Sequence at a characteristic stellar mass

2. This morphological transformation is tightly connected to the activity of the central Super Massive Black Holes. Ejective feedback from the SMBH leads to the quenching of star-formation, along with a simultaneous growth in central density, partly due to the fading of stellar populations

3. The simulation predicts therefore that quiescent galaxies have higher stellar central densities than star-forming galaxies for the same SMBH mass, which disagrees with alternative models, and may potentially be in tension with some observations

Feedback processes play a crucial role in galaxy formation, regulating star formation both in the low-mass and high-mass regimes. In the common theoretical model, the low-mass end is thought to be suppressed by stellar feedback whilst the high-mass end is hypothesised to be regulated by AGN feedback. In this talk, I will summarise how these feedback processes have been incorporated into theoretical cosmological models, including hydrodynamical and semi-analytical simulations. In particular, I will discuss the different implementations of stellar and AGN feedback, and how these feedback mechanisms may act to enhance or suppress one another. I will also outline how observational studies have guided and challenged these theoretical models and whether the inclusion of additional components, such as AGN in low-mass galaxies or cosmic rays, may be necessary to reproduce observations.

Cosmological hydrodynamical simulations have become a key tool to understand the physics of galaxy quenching, which for central galaxies is typically attributed to AGN feedback. There is however some confusion about how quenching works in the simulations. I will discuss which aspects are effectively built into the models and which ones are emerging, which features are mostly numerical in origin, which rarely mentioned ingredients are critical, and which often mentioned ingredients may not be. An important but underappreciated question that I will also discuss, is why the quenching mass scale is similar to the mass at which galaxies begin to acquire haloes of hot, hydrostatic gas.

Cosmological simulations predict that AGN feedback is responsible for suppressing the growth of massive galaxies and is believed to be a key process in reproducing basic properties of galaxies (such as luminosity function, the black hole--spheroid relationships, galaxy sizes, galaxy colour bi-modality). There have been a number of studies that have suggested an anti-correlation between ionised outflows (traced with [O III] in IFU data) and star formation (traced using H-alpha in IFU data) in the host galaxies of high-luminosity AGN. However, the H-alpha line as a tracer of star formation is susceptible to obscuration by dust, therefore this anti-correlation between star formation and outflows might be caused by dust obscuration, rather than SF suppression.

Therefore, we have utilized the largest sample of AGN observed with IFU at high redshift (the KASHz survey) to select AGN with high-quality IFU data, to map both the H-alpha and [OIII] kinematics, and that also have ancillary ALMA (870 micron) data, to map the dust. We verified that the ALMA 870 micron observations are not contaminated by AGN emission using UV-Radio SED fitting. This combination enables us to map both the obscured and unobscured star-formation as well as any AGN-driven outflows in the host galaxies of these AGN. Using this unique sample of AGN, with a range of luminosities, we have compared the location and sizes of the obscured and unobscured star-forming regions and the star-formation rate inferred from each tracer. We conclude that in order to map all-star formation in host galaxies, we must use multiple tracers. Furthermore, using these star formation tracers and the [OIII] data, we see no evidence of AGN driven outflows instantaneously suppressing star formation in moderate luminosity AGN.

Additionally, I will present a re-assessment of the flagship examples of suppression of star-formation by AGN-driven outflows in the aforementioned papers. Using our own techniques and comprehensive assessments of the total star-formation with both obscured and unobscured star formation tracers, I will address the question: Do powerful AGN really suppress star formation?

Understanding the physical processes responsible for ceasing star formation in galaxies is one of the most important unresolved questions in the field of galaxy evolution. We investigate how star formation is brought to a halt in local, massive, central galaxies by comparing Sloan Digital Sky Survey (SDSS) observations with three state-of-the-art hydrodynamical cosmological simulations - EAGLE, Illustris and IllustrisTNG. We address the complex nature of quenching by combining machine learning techniques with partial correlation analysis to determine which galactic property is the most predictive of quenching. We find that the supermassive black hole mass (MBH) is the most powerful parameter in determining whether a galaxy is star-forming or quenched - a statement which is true for all three implementations of AGN feedback in the simulations. Remarkably, this prediction is precisely confirmed in the SDSS observations, where we infer MBH from a variety of calibrations for ~230 000 local galaxies.

We further show that the observed correlations between quiescence and parameters like stellar mass, halo mass or black hole accretion rate result from the connection between these properties and MBH. Moreover, we find that the black hole accretion rate (which linearly translates to AGN luminosity) is almost irrelevant for quiescence, explaining why observations of optically selected AGN struggle to find evidence for AGN feedback driven quenching in action.

Finally, we infer molecular gas masses from the reddening of the SDSS spectra to characterise the mode of operation of the AGN feedback. We find that both gas fraction and star formation efficiency (SFE) decrease upon transition to quiescence in the observable Universe. In simulations, we find similar qualitative trends in IllustrisTNG, while the quiescent population in Illustris shows hints of elevated SFEs, disagreeing with the observations. We then repeat our machine learning experiment and classify galaxies into star-forming and quenched, asking which of the two - gas fraction or SFE are more predictive of quiescence. We find that for both the SDSS and IllustrisTNG galaxies, the classification is primarily determined by SFE, in contrast with Illustris, where gas fraction is a more predictive parameter between the two. We conclude that black holes can successfully quench star formation through a combination of heating and turbulence injection into the interstellar medium.

Heating from relativistic jets launched from active galactic nuclei (AGN) is thought to be an important mechanism that contributes to the quenching of star formation in massive galaxies. We implement a black hole (BH) spin evolution and AGN jet feedback model into the SWIFT smoothed particle hydrodynamics code. We test out the jets in hydrodynamical simulations with a single jet episode, first focusing on self-similar jets, and then on jet-inflated bubbles and their interactions with an idealized intracluster medium (ICM). We then perform more realistic simulations of galaxy groups and clusters with self-consistent jet feedback. The accretion of the BH is determined from the properties of the gas surrounding it, and the jet power also depends on a realistic, spin-dependant efficiency. The jet direction varies with the spin of the BH, resulting in natural reorientation and precession. Our low-mass system, representing a galaxy group, is quenched by a strong jet episode triggered by a cooling flow, and it is kept quenched by a low-power jet fed from hot halo accretion. In more massive systems (galaxy clusters), hot halo accretion is insufficient to quench the galaxies, or to keep them quenched after the first cooling episode, unless jet efficiencies are very high (approaching 100 per cent). Instead, these galaxies experience multiple episodes of cooling, star formation and jet feedback. In the most massive system we simulate, representing a massive galaxy cluster, star formation rates of hundreds of solar masses per year are reached during cooling flows which last 0.1 to 1 Gyr. The same cooling flows also trigger jets with powers matching the highest-power jets observed. The jets subsequently shut off the cooling flows which triggered them, as well as any associated star formation. We find that jets effectively heat and quench the haloes even if they are launched along a fixed axis. Jet-inflated bubbles draw out low-entropy and high-metallicity gas, which forms dense, cooling filaments. The existence of these cold filaments is in agreement with observations of galaxy clusters. Based on idealized simulations, we conclude that the filaments play an important role in the feedback cycle.

TBD

Tracing the relative contribution of AGN and stellar feedback processes across cosmic time is soon to be within our reach with rest-frame optical-to-UV spectroscopy available with JWST. With the star-forming locus in the BPT shifting towards the AGN cloud at z~2 (Steidel+14), and low-metallicity AGN occupying similar regions (e.g. Feltre+16), deriving the AGN contribution will require simultaneous modelling of AGN and HII region line emission. This fitting provides both HII and NLR gas properties (logU, metallicity N/O etc). Additionally, deriving AGN contribution from emission lines provides a sensitive probe of the accretion disc emission in a wavelength range inaccessible by other means in Type-II AGN. I will present the integration of the Feltre, Charlot & Gutkin 2016 AGN narrow-line region line emission models into BEAGLE (Chevallard & Charlot 2016), a Bayesian spectral and SED fitting code. BEAGLE already incorporates the HII nebular emission models of Gutkin, Charlot & Bruzual 2016, meaning that we now have the ability to perform simultaneous HII and NLR fits. To test the models and fitting technique we fit to a) BEAGLE-simulated galaxies with range of AGN contribution to the line fluxes and b) a sample of X-ray selected Type-II AGN with SDSS DR7 spectra, as well as measuring HeII for a large sample of SDSS AGN to determine their ionisation state. I will present these studies as well as prospects for identifying and measuring NLR metallicities of high redshift AGN with JWST.

I will present a critical evaluation of the physical process of galaxy quenching, and the corresponding rise of the quiescent galaxy population, from the perspective of the IllustrisTNG simulations. The supermassive black hole feedback model of TNG produces a population of quenched galaxies already at early times (z>2) due to the rapid onset of efficient black hole activity. It is simultaneously ejective and preventative in nature. Corresponding signatures are imprinted in the gaseous outflows, the circumgalactic medium, the galaxy ISM itself, as well as in the stellar population properties. I will contrast several key observables against data, and outline future expectations for massive quiescent galaxies based on these simulations.

One of the long-standing problems in astrophysics concerns the process that regulates star formation in galaxies. Only a small fraction (<10-20%) of baryonic matter in a galaxy halo is currently in stars, indicating that galaxies have been fairly inefficient in forming stars from their available reservoir of gas across the cosmic time. Yet, the primary mechanisms responsible for regulating star formation in galaxies are still unclear and debated. Theoretical models offer a wide range of solutions to this problem, relying on the physics of gas, stars, and black holes as the so-called “feedback”. Observational studies are required to test these models and provide evidence for their range and applicability. In this review talk, I will discuss recent observational works and discuss the impact of supernova- and AGN-driven outflows on the host galaxy and the surrounding environment.

I will present a wide-ranging overview of results on the physics of galaxy quenching, primarily based on FIRE simulations. The base FIRE simulations include resolved ISM physics and feedback from all the main known stellar processes (core collapse and Type Ia supernovae; winds from young and evolved stars; and radiative feedback via photoionization and radiation pressure) in a cosmological environment. Recent FIRE simulations implement a variety of additional processes, including magnetic fields, cosmic rays from stellar populations, and multi-channel AGN feedback (AGN winds and jets; AGN radiative feedback; and AGN cosmic rays). I will summarize what we have learned from these simulations about what quenches galaxies and what does not. I will also comment on the role and interplay of different physical scales, ranging from the nuclear regions of galaxies to the circumgalactic medium, in driving galaxy evolution around the quenching mass scale ~L*.

It is well-established that feedback plays a pivotal role in regulating the instantaneous star formation efficiency of galaxies (i.e. the Kennicutt-Schmidt law) and driving the gas outflows which regulate the total baryonic matter reservoirs in galactic disks and enrich the circum-galactic and intergalactic mediums. However, despite tremendous progress in replicating these feedback effects in zoom-in cosmological simulations, the non-linear combination of different feedback mechanisms (e.g. radiation, SN, and AGN) remains ambiguous and, at best, sensitive to the simulation setup. Regardless, the success of zoom-in simulations in reproducing the observable galaxy properties (in particular, the Stellar Mass to Halo Mass relation) suggests that a comprehensive picture of the non-linear combination of feedback mechanisms in regulating the star formation histories of galaxies is close to emerging. In this talk, I compare the relative contribution of different feedback mechanisms as drawn from various zoom-in simulations and setups. I discuss their relative importance in driving the metallicity evolution, regulating the instantaneous star formation efficiency, and quenching the galaxies. Moreover, I determine the empirical dataset required to break the degeneracies between the contribution of different feedback mechanisms.

A plethora of observations point to strong trends between environment and star formation activity, kinematic morphology, colours of galaxies, etc, which are interpreted as the environment playing a key role in aiding the quenching of satellite galaxies and nurturing morphological transformations. How the environment leads to such trends is however an area in which galaxy formation simulations do not agree on. For example, the effect of pre-processing, recycling of gas that has been removed from galaxies, the effect of active galactic nuclei of the central galaxy on nearby satellites, etc, are areas of intense research. During this talk I will discuss areas of consensus and disagreement of how environment leads to quenching between different hydrodynamical simulations, and how future observations can help provide much needed constraints.

We present results from MUSE spatially-resolved spectroscopy of 21 post-starburst galaxies in the centers of 8 clusters from z~0.3 to z~0.4. We measure spatially resolved star-formation histories (SFHs), the time since quenching and the fraction of stellar mass assembled in the past 1.5 Gyr. The SFHs display a clear enhancement of star-formation prior to quenching for 16 out of 21 objects, with at least ~10% (and up to more than 50%) of the stellar mass being assembled in the past 1.5 Gyr and and time since quenching ranging from less than 100 Myrs to ~800 Myrs. By mapping these quantities in the MUSE data, we analyze the quenching patterns of the galaxies. Most galaxies in our sample have quenched their star-formation from the outside-in or show a side-to-side/irregular pattern, both consistent with quenching by ram-pressure stripping. Only three objects show an inside-out quenching pattern, all of which are at the high-mass end of our sample. At least two of them currently host an active galactic nucleus. In two post-starbursts, we identify tails of ionized gas indicating that these objects had their gas stripped by ram pressure very recently. Post-starburst features are also found in the stripped regions of galaxies undergoing ram-pressure stripping in the same clusters, confirming the link between these classes of objects. Our results point to ram-pressure stripping as the main driver of fast quenching in these environments, with active galactic nuclei playing a role at high stellar masses.

The CGM around galaxies today is filled by ambient hot gas, but speckled with reservoirs of cooler gas clouds. This cold CGM gas could be sourced from ram pressure stripping (RPS) of infalling satellite galaxies, or its condensation could be triggered by the passage of satellite galaxies. Moreover, recent observations from the GASP and LoTSS collaborations suggest ongoing star formation in the tails and increased AGN fractions in the centers of galaxies undergoing RPS, i.e., jellyfish galaxies. Using the IllustrisTNG simulations, we utilize the Zooniverse citizen science project Cosmological Jellyfish to study the evolution of these galaxies. First we describe the demographics of the TNG jellyfish and comment on the relative frequency and duration of the jellyfish phase. Next we quantify when and where the cold gas is stripped, finding that galaxies on average take ~a few Gyrs to lose 90% of their cold gas mass. Moreover, a majority of the gas is stripped at large distances (>0.1 Rvir) from the central galaxy or cluster center. Simultaneously, some satellites undergo bursts of star formation and black hole growth upon interacting with the ambient host gas, before eventually quenching their star formation. In the next steps, we track the cold gas clouds until z=0, determining how much of the stripped gas remains cold/triggers condensation in the CGM or falls onto the central galaxy, potentially refueling its star formation.

In 2020, Wang & Lilly introduced the star formation change parameter SFR_79, defined to be the ratio of the star formation rate (SFR) averaged within the last 5 Myr (SFR_7) to the SFR averaged within the last 800 Myr (SFR_9). It is based on the equivalent widths of Halpha emission and Hdelta absorption and provides an interesting insight into the recent star formation histories of galaxies, telling us whether a galaxy currently has an enhanced or a suppressed SFR with respect to its 800 Myr - average. Investigating roughly 1000 spatially resolved galaxies from the MaNGA survey, Wang & Lilly used the parameter to extensively study how the SFR of Main Sequence galaxies varies over time, to assess the relative strength of fluctuations on different timescales and to relate that to the star formation efficiency of regions of galaxies as traced by the stellar mass surface density.

In our current work, we re-calibrate the star formation change parameter, optimising it for galaxies below the Main Sequence and for spectra with low signal-to-noise ratio and measure it for almost 300'000 galaxies selected from the Sloan Digital Sky Survey. With this large sample we confirm the basic results concerning Main Sequence galaxies that have been published by Wang & Lilly and then move on to study galaxies below the Main Sequence.

In particular, we find that the median log(SFR) is remarkably constant (~0) for galaxies within ~0.4 dex of the SFR_9-based Main Sequence, indicating as many galaxies increasing their SFR as decreasing it. We then discuss the evidence that for galaxies more than ~0.4 dex below the SFR_9-based Main Sequence, the median log(SFR_79) systematically deviates to negative values, indicating a declining SFR on average, i.e. recent and ongoing quenching.

More generally, we extensively explore and discuss the calibration and meaning of the star formation change parameter for galaxies below the Main Sequence, the limits of its applicability and whether and how an excess of objects with negative log(SFR_79) in the galaxy population can be related to quenching. We argue that SFR_79 provides an instructive and promising framework to study both time-variations in the SFR of star-forming galaxies as well as quenching processes and timescales.

Galaxy-galaxy mergers play an integral role in galaxy evolution, in particular triggering drastic changes in the star formation activity and gas mass of their constituents. Extensive integral field spectroscopy (IFS) surveys have allowed us to characterize these changes on a kpc-scale for the first time with large merger samples, revealing that though on average mergers boost star formation, the radial extent of that enhancement can vary significantly between mergers. The diversity of merger induced star formation prompts an essential follow-up question: is merger-triggered star formation driven by an enhanced reservoir of gas in interacting galaxies, or a heightened rate at which gas is converted into stars? To answer this question, I investigate the resolved star formation and gas properties of 31 merging galaxies from the ALMaQUEST (ALMA-MaNGA QUEnching and STar formation) survey. ALMaQUEST measured spatially resolved CO(1-0) emission with the Atacama Large Millimeter Array (ALMA) for 46 MaNGA galaxies, allowing for direct comparison between molecular gas surface density maps from ALMA and star formation surface density maps from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) IFS survey. An ALMaQUEST follow up program targeted 20 galaxies at different stages of interaction such that, in combination with 11 mergers from the original ALMaQUEST sample, we can examine the interplay between gas and star formation at different stages of the merging process. I will show how key resolved scaling relations between star formation, stellar mass, and molecular gas differ for mergers compared to non-interacting galaxies in ALMaQUEST. By directly comparing offsets in resolved scaling relations I quantify whether star-formation in a merger is primarily driven by enhanced star-formation efficiency or gas fraction, and investigate how global and resolved galaxy properties lead to one mechanism dominating within a merger.

Both observational and theoretical studies suggest that stellar bars accelerate the quenching process in galaxies, after a pronounced burst of star formation in the central regions. While this can be easily seen when studying galaxies in relatively isolated environments, such kind of analysis takes a higher degree of complexity when cluster galaxies are considered, due to the variety of interactions that can potentially occur in denser environments. We use IFU MUSE data from the survey GASP (GAs Stripping Phenomena in galaxies with MUSE), to study the combined effect of the presence of a stellar bar and of ram pressure on the spatially resolved properties of stellar populations of cluster-members ram-pressure stripped galaxies. We found that galaxies that are going through ram pressure have a higher increase of star formation activity in the central region compared to galaxies that are not affected by this process. If the galaxies that go through ram pressure are barred, the increase in star formation activity is stronger, which means that the presence of a stellar bar in a galaxy that is going through ram pressure accelerates the consumption of gas in the galaxy. The most extreme cases of increased star formation activity that we find are in those barred galaxies that are the peak of ram pressure. We also find a trend in that the greater the length of the bar the larger the region with enhanced stellar formation activity. Finally, taking into account only face-on galaxies (a necessary requirement to identify the bar) we found that more than 80% of the galaxies with AGN activity host a stellar bar, being all of them strongly affected by ram-pressure stripping.

In this talk, I will model the stellar populations of thousands of nearby galaxies from SDSS-IV MaNGA to constrain their quenching epochs and timescales. I will show evidence that central galaxies quench earlier and more rapidly if they assembled in dark-matter halos that are massive and old. This results suggests that central galaxy assembly and halo growth are closely connected, a possible signal galaxy assembly bias. On the other hand, satellite galaxies assembled their stellar populations earlier and more rapidly than centrals of similar stellar mass. In agreement with recent work on SDSS-I samples, this result is more pronounced in higher mass halos and at closer cluster-centric distances. Although massive satellites may quench as a result of internal processes, their detailed evolution appears subject to unique environment-driven effects.

In recent years, on the topic of the bimodal distribution of blue, star-forming spirals and red, quenched ellipticals, many possible mechanisms have been proposed that halt star-formation in spirals and eventually transform them into quenched ellipticals, but quantitative evidence is lacking that informs on the relative importance between the mechanisms. Recently it has been recognised that stellar metallicity might be a useful aid to distinguish different quenching mechanisms, due to its imprint on the 'fossil record' of post-quenched galaxies. Following careful analysis of hydrodynamic simulations as proof-of-concept, I have found that 9/14 post-starburst galaxies observed with the MaNGA IFU survey experienced a statistically significant increase in stellar metallicity during the starburst. This finding matches the picture described by gas-rich major merger driven starbursts, with limited external inflow of less enriched gas and significant internal gas recycling before outflows occur, allowing for the rapid rise in stellar metallicity during the starburst. The use of an evolving metallicity model also allows for more accurate recovery of total stellar mass, SFR, etc, crucial for improved measurements of scaling relationships such as gas-to-stellar mass and star formation efficiency.

Clusters of galaxies are fantastic laboratories for understanding the physics of black holes feedback. In this talk, I will review the current state of this field while focussing on the evolution of such feedback over the last 10 billion years. I will also present new results on how machine learning can (and will) play a vital role in our understanding of black hole feedback for the next decades.

The most massive galaxies place the most stringent constraints on models of galaxy formation and evolution. The MAGAZ3NE (Massive Ancient Galaxies At Z > 3 NEar-infrared) Keck MOSFIRE survey has returned the largest spectroscopically-confirmed sample of Ultra-Massive Galaxies (UMGs; photometrically selected as log(M*) > 11.1) and their environments at 3<z<4. I will present results from this survey, including the unexpected and surprising discovery of "XMM-2599", a monster galaxy discovered at z=3.49 which formed most of its stars in a huge frenzy when the Universe was less than 1 billion years old, and then quenched by the time the Universe was only 1.8 billion years old. I will also present "MAGAZ3NE J095924+022537", a spectroscopically-confirmed protocluster around a spectroscopically-confirmed quiescent UMG at z = 3.37. Notably, and in marked contrast to protoclusters previously reported at this epoch which have been found to contain predominantly star-forming members, this protocluster contains an elevated fraction of quiescent galaxies relative to the coeval field. This high quenched fraction provides a striking and important counterexample to the seeming ubiquitousness of star-forming galaxies in protoclusters at z > 2 and suggests, rather, that protoclusters exist in a diversity of evolutionary states in the early Universe.

I will also present results from the GCLASS (Gemini CLuster Astrophysics Spectroscopic Survey) and GOGREEN (Gemini Observations of Galaxies in Rich Early ENvironments) surveys, which together consist of deep, multiwavelength photometry and extensive Gemini GMOS spectroscopy of 26 systems ranging in halo mass from small groups to massive clusters at 0.8 < z < 1.5. Collectively, these powerful surveys are allowing us to place new constraints on the location and timescale of quenching and, in concert with both hydro-simulations and semi-analytic models, identify the role of environment in shaping galaxy transformation over cosmic time.

The quenching of star formation in cluster satellite galaxies is preceded by a decline in their cold gas content. It is well established that the cold gas in the outskirts of galaxies, which is predominantly atomic hydrogen, is stripped during their infall. However, a non-negligible amount of both atomic (HI) and molecular (H2) hydrogen can survive in their centre, continuing to fuel star formation for a few billion years. Understanding how (and if) the remaining gas is affected by the environment is key to understanding how galaxies in clusters are quenched. I will present new results from the Virgo Environment Traced in CO (VERTICO) survey, a large ALMA program delivering homogeneous molecular gas observations of Virgo cluster galaxies that span a range of environmental influences. Combined with existing HI observations, I will present the first study of the ISM properties of cluster galaxies at ~650 pc scales. I will show how environmental effects shape the distribution and content of the surviving HI and H2, and how these changes are reflected in the physical state of the gas. I will conclude by discussing how these results can help us better understand how star formation is ultimately quenched in clusters of galaxies.

It is now firmly established that galaxy clusters play a significant role in quenching star formation of member galaxies. A likely driver of this environmental quenching is ram pressure stripping (RPS), where satellite galaxies orbiting through the intracluster medium have their gas reserves removed, eventually leading to a reduction in star formation. In my talk I will introduce a new sample of ~150 jellyfish galaxies undergoing RPS in nearby groups and clusters. These galaxies are identified on the basis of one-sided radio continuum tails identified at 144MHz with LOFAR. I will discuss the relative frequency of jellyfish galaxies as a function of host halo mass - ranging from low-mass groups to massive clusters. I will present resolved spectral index maps (LOFAR+VLA) of RPS tails in the Coma cluster, which provide information on the stripping history as well as the presence (or lack thereof) of ongoing star formation in these tails. This will also include multi-frequency LOFAR imaging of a spectacular 100 kpc tail observed behind the nearby group galaxy, NGC 2276. Finally, I will make the case that RPS is not solely associated with reduced star formation but often (temporarily) enhances star formation in cluster galaxies. This enhanced star formation in confined to the "leading side" of the galaxy, opposite to the direction of the stripped tail. Together these results make significant steps in understanding the details of RPS, which in turn contributes important information to our understanding of star formation quenching in dense environments.