Project highlights
Since the seminal discovery, more than ten years ago (Magorrian et al. 1998), of the presence of SMBH (M_BH>10^6 Msun) in the nuclei of virtually all galaxies, it has been realised that Active Galactic Nuclei (AGN) are not exotic phenomena occurring in a small fraction of galaxies, but rather a key ingredient of their formation and evolution. Support for this hypothesis comes from several observational evidences, and in particular: i) the match between the mass function of BHs grown through AGN phases and that observed in local galaxies (Marconi et al. 2004; Shankar et al. 2004); ii) the cosmological “downsizing” of both nuclear activity and star formation (Ueda et al. 2003; Fiore et al. 2003; Cowie et al. 1996); iii) the fact that spheroid properties of local galaxies are correlated with the mass of the BH in their centre (the so-called “local scaling relations", Ferrarese & Merrit 2000; Gebhardt et al. 2000). Despite the progress made in recent years, often sparse and not always conclusive, we do not yet have a clear consistent picture of when did BH start to accrete, which growth modes occur, in what systems, and under what conditions.
In particular, according to the most popular models of Active Galactic Nuclei (AGN) and galaxies co-evolution, starburst galaxies, unobscured quasars and inactive (and quenched) galaxies represent the different phases of an evolutionary sequence reproducing the most massive galaxies observed in the Universe. In this context, gas flows in the form of energetic out outflows are postulated to play a pivotal role in this process, given that they regulate both accretion and ejection of material onto and from the SMBH and can propagate momentum and energy over a wide spatial scale, acting on the fuel from which new stars form and stopping the host galaxy growth
The "eEASy" project has been funded to shed light on this important topic, exploiting X-ray, optical, infrared and millimeter data from different multi-wavelength surveys. Below we report the main results obtained within the project, and the references to related/relevant works. The most important results are based on three nights of Near Infrared Spectroscopic observations at the ESO Very Large Telescope for the use of the highly demanded X-shooter instrument (ESO program 090.A-0830(A), PI: M. Brusa, February 2013) and on follow-up observations with VLT/SINFONI and the Plateau de Bure Interferometer.
Outline:
Powerful ionised outflows in luminous quasars
The effects of feedback from luminous Quasars
The molecular gas content of quasars in the feedback phase
The importance of high resolution (adaptive optics) observations
The incidence of ionised/neutral AGN outflows and gas plasma properties
Black hole masses of obscured AGN
The next generation of X-ray surveys
Identifications of X-ray sources: path to eROSITA
Powerful (ionised) outflows in luminous quasars
Brusa, Bongiorno, Cresci et al. 2015 (MNRAS 446, 2394):
"X-shooter reveals powerful outflows in z~1.5 X-ray selected obscured quasi-stellar objects (QSOs)"
This paper presents the X-shooter observations of a sample of 10 luminous, X-ray obscured QSOs at z~1.5 from the XMM-COSMOS survey, expected to be caught in the transitioning phase from starburst to AGN-dominated systems. Thanks to its large wavelength coverage, X-shooter allowed us to determine accurate redshifts from the presence of multiple emission lines for the targets for which we had only a photometric redshift estimate, with an 80 per cent success rate, significantly larger than what is observed in similar programs of spectroscopic follow-up of red QSOs. We report the detection of broad and shifted components in the [O III]4959,5007 complexes for six out of eight sources with these lines observable in regions free from strong atmospheric absorptions. The full width at half-maximum (FWHM) associated with the broad components are larger than the average value observed in Sloan Digital Sky Survey type 2 AGN samples at similar observed [O III] luminosity. This may be seen as an indication that the color selection applied to our X-ray sample is effective in picking up objects with FWHM larger than the average values. In contrast, the measured FWHM are similar to those observed for QSO/ultraluminous infrared galaxies systems for which the presence of kpc scale outflows has been revealed through integral field unit spectroscopy, and can be considered a clear evidence that the proposed selection does efficiently work in order to pick up objects experiencing outflowing winds. Although the total outflow energetics (inferred under reasonable assumptions) may be consistent with winds accelerated by stellar processes, we favour an AGN origin for the outflows given the high outflow velocities observed (v>1000 km/s) and the presence of strong winds also in objects undetected in the far-infrared. Overall, we were able to directly reveal, for the first time, the presence of winds of ionised gas fuelled by the AGN emission in this class of rare sources.
Figure: FWHM (broad component) of the broad 5007 Å line against the total [O III ] 5007 luminosity. In both panels the X-shooter targets are marked with blue circles. Our results are compared with known literature samples of star-forming systems (both ULIRGs and star forming galaxies; upper panel) and Sey2 and type 2 QSOs (lower panel), as labelled. The black filled circle in the upper panel represents the average for a population of 30 massive star-forming galaxies at z∼ 1.6 (Kashino et al. 2013). The magenta square in the lower panel represents the result from the stacked spectrum of ∼110 XMM-COSMOS type 2 QSOs with spectra available from the zCOSMOS 20k survey in the range z=0.5–0.9, without any pre-selection on their optical/IR colours. The plot shows that the objects for which we detect a broad component have FWHM larger than the average value observed in SDSS type 2 AGN samples at similar observed [O III] luminosity (see pinkish-grey and green points). This may be seen as an indication that the colour selection applied to our X-ray sample is effective in picking up objects with FWHM larger than the average values.
Perna, Brusa, Cresci et al. 2015 (A&A 574, A82):"Galaxy-wide outflows in z~1.5 luminous obscured QSOs revealed through NIR slit-resolved spectroscopy"For the two brightest sources of the X-shooter sample (XID2028 and XID5321) we performed slit-resolved spectroscopy to study in more details the complex emission and absorption line kinematics. We were able to detect outflow extended out to ~10 kpc from the central black hole (BH), both as blueshifted and redshifted emissions in spectra extracted in lateral aperture from the one centered on the QSOs. We also detect kpc scale outflows in the [OII] emission lines and in the neutral gas component, traced by the sodium D and magnesium absorption lines, confirming that a substantial amount of the outflowing mass may be in the form of neutral gas. The measured gas velocities and the outflow kinetic powers, inferred under reasonable assumptions on the geometry and physical properties of these two systems, favor an AGN origin for the observed winds, in agreement with the results obtained in Brusa et al. (2015).
Figure: XID2028 (left) and XID5321 (right) X-Shooter spectra of the regions a, b, c, centered on [OIII] 5007. The red and orange lines indicate the best fit solutions that reproduce the line profiles according to a non-parametric approach. The Gaussian components are shown with arbitrary normalization in order to ease the visualization. The dotted lines mark the wavelength of [OIII] 5007 at the systemic redshift. The lower panels show the 2D spectra, indicating the apertures used to extract the 1D spectra seen in the upper panels. Red to blue colors represent increasing flux. Extended vertical structures, like the one at 1242 nm ( ight), delineate strong sky features and are indicated in the 1D spectra as shaded areas. Clearly, flux associated with fast [O III] emitting gas is observed also outside the central aperture, in one preferential direction, and extending up to ~10 kpc in size.See also:
Cicone, Brusa et al. 2018, "The largely unconstrained multiphase nature of outflows in AGN host galaxies",
Nature Astronomy 2, 176
Vietri et al. 2018, "The WISSH quasars project. IV. Broad line region versus kiloparsec-scale winds", A&A 617, A81
Cresci et al. 2017, "The MUSE view of He 2-10: no AGN ionization but a sparkling starburst", A&A 604, A101
Talia, Brusa et al. 2017, "AGN-enhanced outflows in star-forming galaxies at 1.7<z<4.6: the low-ionization gas perspective", MNRAS 471, 4527
Bischetti et al. 2017, "The WISSH Quasars Project I:Powerful ionized outflows in hyper-luminous quasars", A&A 598, 122
Kakkad et al. 2016, "Tracing outflows in the AGN forbidden region with SINFONI", A&A 591, A148
Carniani et al. 2015, "Ionised outflows in z~2.4 quasar host galaxies", A&A 591, A148
The effects of feedback from luminous Quasars
Cresci, Mainieri, Brusa et al. 2015 (ApJ 799, 82):
"Blowin' in the Wind: Both "Negative" and "Positive" Feedback in an Obscured High-z Quasar"
The works on X-shooter data generated a follow-up paper on one of the brightest sources, XID2028. Spatially resolved near IR spectroscopy with ESO/SINFONI in the H and J bands unambiguously resolved the wind seen in X-shooter data up to a 10 kpc scale. For the first time, thanks also to the availability of deep HST data, "positive" feedback effects in triggering new episodes of star-formation have been revealed.
XID2028 therefore represents the first direct detection of outflow induced star formation in a radio-quiet AGN, as well as the first example of both types of feedback simultaneously at work in the same galaxy. This result show that these mechanisms are in action not only in powerful radio galaxies with relativistic jets, but also in less extreme objects during an obscured QSO phase that is thought to be a common step in the evolutionary sequence of star forming galaxies.Figure: Schematic view of the geometry of the XID2028. The high velocity material is sweeping the gas suppressing star formation in a cavity along the core of the outflow (“negative feedback”), but also triggering star formation by outflow induced pressure at the edges (“positive feedback”).
Cimatti, Brusa, Talia et al. 2013 (ApJL 779, 13):
"Active Galactic Nucleus Feedback at z~2 and the Mutual Evolution of Active and Inactive Galaxies"
The X-shooter related works explored the accretion and host galaxies properties, and feedback effect in luminous QSOs. The work presented in Cimatti, Brusa et al. (2013), instead, explores the morphologies of moderate luminosity AGN from the GOODS survey. On the basis of deep X-ray data and optical spectra, and a detailed morphological analysis, we probed the role of AGN feedback in the morphological transformation of galaxies hosting low-luminosity active nuclei at z~2. In particular, we show that at z ~ 2.2, the ultraviolet spectra of active galaxies show possible gas outflows with velocities up to about -500 km s-1, which are observed neither in inactive systems at the same redshift, nor at lower redshifts. Such outflows indicate the p
resence of gas that can move faster than the escape velocities of active galaxies. These results suggest that feedback from moderately luminous AGNs (log LX < 44.5 erg s-1) played a key role at z >~
2 by contributing to outflows capable of ejecting part of the interstellar medium. Figure: The stacked GMASS spectra (R∼600) at z=1.7-3 (upper panel) and z=1-1.7 (lower panel) placed at the systemic reference defined by photospheric lines. Red and blue spectra relate to inactive and active galaxies, respectively. Evidences of outflows in the low ionization gas component are observed only at high redshift and in the X-ray selected sample (absorption lines around SIII and CII are asymmetric and blueshifted)
See also:
Fiore et al. 2017,"AGN wind scaling relations and the co-evolution of black holes and galaxies", A&A 601, A143
Bongiorno et al. 2016,"AGN host galaxy mass function in COSMOS: is AGN feedback responsible for the mass- quenching of galaxies?", A&A 588, A78
Balmaverde et al. 2016, "Is there any evidence that ionized outflows quench star formation in type 1 quasars at z < 1?", A&A 585, A148
Carniani et al. 2016, "Fast outflows and star formation quenching in quasar host galaxies", A&A 582, A28
Cresci et al. 2015, "The MAGNUM survey: positive feedback in the nuclear region of NGC 5643 revealed by MUSE", A&A 582, A63
The molecular gas content of quasars in the feedback phase
Brusa, Feruglio, Cresci et al. 2015 (A&A 578, A11):
"Evidence for feedback in action from the molecular gas content in the z~1.6 outflowing QSO XID2028"
We observed with the Plateau de Bure Interferometer the obscured quasar XID2028, for which the presence of an ionized outflow has been unambiguously signalled by NIR spectroscopy. The detection of 12CO(3-2) emission in this source allows us to infer the molecular gas content and compare it to the ISM mass derived from the dust emission. The star formation efficiency (~100) and gas mass (Mgas = 2.1-9.5 × 1010 M⊙) inferred from the CO(3-2) line suggest that the ISM/gas content of XID2028 is significantly lower than expected for its observed stellar mass, specific SFR and redshift, based on the most up-to-date calibrations (with gas fraction <20% and depletion timescale <340 Myr). Overall, the constraints we obtain from the far infrared and millimeter data suggest that we are observing QSO feedback able to remove the gas from the host. The measure of the intensity of the CO(3-2) emission in XID2028 represents a first step towards a mapping experiment using high spatial resolution to study the morphology and the kinematics of the molecular gas reservoir and of the clumpy structures in the SF regions seen in HST and SINFONI maps.
Sensitive ALMA observations of XID2028 (Cycle 3; data obtained in June 2016), coupled with high spatial resolution NIR imaging obtained with LUCI+ARGOS@LBT (commissioning phase), subsequently confirmed the depletion of the gas reservoir, and revealed the molecular outflow, with mass outflow rate comparable with the ionised component. XID2028 is therefore the first QSO at high-z in which a multi-phase spatially resolved outflow has been detected (Brusa et al. 2018). Figure: The depletion timescale plotted versus the sSFR-excess for galaxies (grey) and AGN (colored) samples compared with the values obtained for XID2028 (blue, green and red) under different assumptions. All quantities are normalized to the expected values for normal and Starburst galaxies predicted by the calibration presented in Sargent et al. (2014). The black line traces the expected variation (median) with sSFR for a MS spiral galaxy with identical mass and redshift as XID2028 (see Sargent et al. 2014). The step at sSFR~4 reflects the transition from the main sequence locus to the sSFR-regime where high-SFE Starbursts dominate. XID2028 lies a factor 2 to 10 below the black line. I.e. it shows significant lower gas fraction and depletion timescale than those expected for the properties of its host galaxy.
See also:
Brusa et al. 2018, "Molecular outflow and feedback in the obscured quasar XID2028 revealed by ALMA", A&A 612, A29
Talia et al. 2018, "ALMA view of a massive spheroid progenitor: a compact rotating core of molecular gas in an AGN host at z = 2.226", MNRAS 476, 3956
Perna, Sargent, Brusa et al. 2018, "The molecular gas content in obscured AGN at z > 1", A&A in press, arXiv:1807.03378
Carniani et al. 2017, "AGN feedback on molecular gas reservoirs in quasars at z~2.4", A&A 605, 105
Kakkad, Mainieri, Brusa et al. 2017, "ALMA observations of cold molecular gas in AGN hosts at z∼1.5 - Evidence of AGN feedback?", MNRAS 468, 4205
Feruglio et al. 2014, "Gas reservoir of a hyper-luminous QSO at z=2.6, A&A 565, 91
The importance of high resolution (adaptive optics) observations
Brusa, Perna, Cresci et al. 2016 (A&A 588, A58):
"A fast ionised wind in a Star Forming-Quasar system at z∼1.5 resolved through Adaptive Optics assisted near-infrared data"
From the analysis of both galaxies and AGN samples at z~1-3, it is becoming clear that powerful outflows may be very common in AGN hosts. High-resolution and high S/N observations are needed to uncover the physical properties of the wind through kinematic analysis. We exploited VLT/VIMOS, VLT/SINFONI, and Subaru/IRCS adaptive optics (AO) data to study the kinematic properties on the scale of the host galaxy of XID5395; this galaxy is a luminous, X-ray obscured starburst/quasar (SB-QSO) merging system at z ~ 1.5, detected in the XMM-COSMOS field, associated with an extreme [O II] emitter. We propose that [O II] EW as large as >150 Å in X-ray selected AGN may be an efficient criterion to isolate objects associated with the short, transition phase of "feedback" in the AGN-galaxy co-evolutionary path. This criterion may complement other diagnostics that have been proposed in the past to isolate such rare objects in X-ray samples, such as those based on the observed red colours of the hosts. The achieved spatial resolution (few kpc) allowed us to resolve all the components of the SB-QSO system. Our analysis reveals complexities and asymmetries in and around the nucleus of XID5395. The velocity field measured via non-parametric analysis points to different kinematic components with maximum blueshifted and redshifted velocities up to ≳ 1300 km s-1 that are not spatially coincident with the nuclear core.
These extreme velocities and spatial location can be explained by the presence of fast moving material. We also spectroscopically confirm the presence of a merging system at the same redshift as the AGN host. We then discuss how this system will likely evolve into an unobscured QSO, as suggested from all the observational evidences, including the observed compact radio emission. Figure: Contours of the Subaru/IRCS H -band (blue) and K-band (magenta) emission from Subaru/IRCS overlaid on the [O III]5007 channel map obtained integrating the SINFONI datacube on the line core. All contours and colour level starts from 3 sigma with steps of +2, as labelled. Spatial scale is given in arcsec. The [O III] systemic emission is overall symmetric, except for a plume extending beyond 0.5" (4.5 kpc) in the north-west direction, corresponding to a merger galaxy.
To uncover the kinematics and physical properties of the winds, high-resolution and high S/ N observations, such as those presented in this work, are needed. In the next few years the ESO Large Programme SUPER (a SINFONI Survey for Unveiling the Physics and Evolution of Radiative feedback, PI: V. Mainieri; 280 hours) will undertake this task by targeting, with the needed resolution and depth, a sample of 40 AGN at z~2.
We also obtained ALMA Cycle 4, 5 and 6 data on XID5395, XID5321 (another obscured QSO from the Brusa+2015a sample) and for the SUPER targets to study the molecular gas content in these peculiar systems at comparable (0.3") spatial resolution. Analysis is ongoing.
See also:
Perna, Brusa, Salvato et al. 2015, "SINFONI spectra of heavily obscured AGNs in COSMOS: evidence of outflows in a MIR/O target at z∼ 2.5", A&A 583, A72
The incidence of ionised/neutral AGN outflows and gas plasma properties
Perna, Lanzuisi, Brusa, Mignoli & Cresci 2017a (PaperI: A&A 603, A99)
An X-ray/SDSS sample. I. Multi-phase outflow incidence and dependence on AGN luminosity
Perna, Lanzuisi, Brusa, Cresci & Mignoli 2017b (PaperII: A&A 606, A96)
An X-ray/SDSS sample. II. AGN-driven outflowing gas plasma properties
In these two companions works we presented the analysis of a large spectroscopic sample of X-ray detected SDSS AGNs at z<0.8 with a high signal-to-noise ratio in the [O III].5007 line to unveil the faint wings of the emission profile associated with AGN-driven outflows.
In PaperI, we derived the incidence of ionized (~40%) and atomic (<1%) outflows covering a wide range of AGN bolometric luminosity from 1042 to 1046 erg/s and we showed a well-defined positive trend between outflow velocity and LX, for the first time, over a range of 5 order of magnitudes, finding that in the QSO-luminosity regime and at logMBH > 108 Msun the fraction of AGNs with outflows becomes >50%. We interpret our results about X-ray bolometric corrections and outflow incidence in cold and ionized phases in the context of an evolutionary sequence allowing two distinct stages for the feedback phase: first, an initial stage characterized by X-ray/optical obscured AGNs, in which the atomic gas is still present in the ISM and the outflow processes involve all the gas components and, second, a later stage associated with unobscured AGNs, in which the line of sight has been cleaned and the cold components have been heated or exhausted.
Figure: Doubly ionised oxygen Vmax non-parametric velocity estimator versus [O III] luminosity (left), intrinsic 2-10 keV X-ray luminosity (central), and black hole mass (right) for the BL AGN subsample. Red/yellow and red/cyan dots represent average gas and stellar maximum velocities in bin of luminosity andMBH.The mild increase of the stellar Vmax with AGN power tracers is reasonably related to the fact that more powerful, luminous and massive AGN are hosted in more massive systems. The figure shows that the increasing gravitational broadening cannot explain the stronger positive trend observed in the velocity of the ionised gas.
Taking advantage of the spectroscopic analysis results presented in Paper I, in Paper II we analyse stacked spectra and sub-samples of sources with high signal-to-noise temperature- and density-sensitive emission lines to derive the plasma properties of the outflowing ionized gas component, which play a crucial role for the determination of mass outflow rates and related energetics.We derived, for the first time, median values for electron temperature (Te~1.7x104 K) and density (ne~1200 cm-3) of outflowing gas from medium-size samples (.30 targets) and stacked spectra of AGNs.
We cautioned that the usually assumedelectron density (ne = 100 cm-3) in ejected material might result in relevant overestimates of flow mass rates and energetics and, as a consequence, of the e.ffects of AGN-driven outflows on the host galaxy.
Figure: Median stacked spectrum around the doubly ionized oxygen emission lines obtained combining the spectra of faint/obscured sources with evidence of ionized outflows. Red curve represents the best-fit result we obtained fitting simultaneously the emission lines displayed. Green Gaussians represent the narrow (NC) and broad line region components (BC), blue profiles mark the outflow components (OC). The stacked spectrum allowed us to study the profile of the faint [OIII]4363 line, and to derive the electron temperature for the outflowing gas through standard diagnostics.
See also:
Concas, Popesso, Brusa, Mainieri, Erfanianfar & Morselli 2017, "Light breeze in the Local Universe", A&A 606, A36
Menzel, Merloni, Nandra, Brusa, Salvato & Coffey 2018,in preparation
Black hole masses of obscured AGN
Bongiorno, Maiolino, Brusa et al. 2014 (MNRAS 443, 2077 ):
"The MBH-M* relation for X-ray-obscured, red QSOs at 1.2 < z < 2.6"
BH masses and accretion rates have been measured for a sample of 21 X-ray selected obscured QSOs (5/21 sources, ~20%, have data from the X-shooter run) through virial methods applied to the Halpha line. This represented, at the time, the largest sample published in the literature for this class of sources.
From optical/IR multicomponent spectral energy distribution fitting we have derived the stellar mass of their host galaxies and their star formation rates. We find a strong trend of the MBH-M* relation with the BH mass, i.e. less massive objects are scattered below and above the local relation, while the most massive ones are mainly located above it. We also studied the evolution of these sources on the MBH-M* plane compared to a sample of optically blue type-1 QSOs and we find that obscured red QSOs show a ratio of MBH to M* that increases with redshift which is consistent with or slightly lower than what has been found for blue QSOs. This is consistent with the scenario that luminous, X-ray selected obscured AGN trace the brief evolutionary phase at the end of the rapid BH growth and immediately preceding the classical blue QSOs typically sampled in optical surveys.Figure: Redshift evolution of Gamma(z), the offset measured for our sample from the local MBH−M∗ relation. Different colours and symbols correspond to different subsamples (blue circles refer to X-shooter targets) while light grey symbols show a comparison sample of type-1, blue QSOs from Merloni et al. (2010). The average values and errors binned in four redshift bins for obscured QSOs (red) and blue QSOs (blue) are reported in the upper panel. Right-hand panel: histogram of the blue (grey histogram) and red (red shaded histogram) QSOs populations in the common redshift range (1.2<z<2.0). See also:
Onori F. et al. 2017a, "Detection of faint broad emission lines in type 2 AGN: I. Near infrared observations and spectral fitting", MNRAS 464, 1783
Onori F. et al. 2017b, "Detection of faint broad emission lines in type 2 AGN: II. On the measure of the BH mass of type 2 AGN and the unified model", MNRAS 468, L97
Ricci F. et al. 2017, "Detection of faint broad emission lines in type 2 AGNs - III. On the MBH-σ⋆ relation of type 2 AGNs", MNRAS 471, L41
La Franca F. et al. 2015, "Virial Black Hole mass estimates in low luminosity or obscured AGN: calibration and application to NGC 4395 and MCG 01-24-12", MNRAS 449, 1526;
X-ray AGN winds
Lanzuisi, Perna, Comastri et al. 2016 (A&A 590, A77):
"NuSTAR reveals the extreme properties of the super-Eddington accreting supermassive black hole in PG 1247+267" PG1247 is the most luminous QSO in the SDSS at z~2 and offers the unique possibility to study in great detail the X-ray spectrum of a luminous QSO at such early epochs. New black hole mass estimates (Perna et al. 2014) also point to a relatively small SMBH (Log(M_BH)=8.9 Msun). This implies that the source is in a rare, strongly super-Eddington accreting phase (Edd~10). Massive outflows are naturally expected during these super-Eddington accretion episodes (Zubovas & King 2012) owing to the intense radiation pressure associated with these events. Archival XMM data show a prominent hump at rest-frame energies of ~12-24 keV. We obtained Nustar data for this interesting source in order to study its peculiar X-ray spectrum. The combination of Nustar and XMM, covering a broad energy range, is crucial in order to disentangle between different models of X-ray continuum emission, able to explain the observed hump (i.e. reflection vs. absorption). The absorption model interpretation (left panel) is strengthen by the presence of an absorption feature above the Fe 6.4keV k\alpha line (right panel). Such absorption features are currently interpreted as evidence of mildly relativistic ionized disk winds, accelerated by the intense radiation pressure of the accretion SMBH, and observable in X-ray spectra in the form of blue-shifted high ionization Fe lines. These winds are thought to be ultimately responsible for the launching of ionized and molecular outflows on much larger scales through shocks caused by the interaction between the fast AGN wind and the interstellar medium. Deeper XMM data are required in order to characterize the disk wind physical properties in this luminous QSO observed at the peak of SMBH accretion and SF history. A Swift-XRT monitoring is ongoing (PI: Lanzuisi), with the aim of studying the strong long-term X-ray variability of the source, that reflects into spectral changes which can affect the interpretation of the continuum emission.
We also obtained pilot XMM-observations of two SDSS galaxies with [OIII] outflows aimed to investigate their X-ray properties and, possibly, the presence of X-ray winds and therefore to establish a connection of the winds phenomena.
Figure: Left: The best fit model of the XMM (red) and Nustar data (blue). The absorption model is able to explain the observed broad band spectrum with a primary power-law, modified by a ionized, dense (N_H=10^24 cm^-2) absorber, partially covering (CF=0.5) the nuclear emission. Right: Rest-frame residuals in the Fe Kα line region, after fitting with a simple power law. The gray dashed lines mark the expected neutral Fe, FeXXV, and FeXXVI Kα emission line energies.See also:
Vignali C., et al. 2015, " The XMM Deep survey in the CDF-S. IX. An X-ray outflow in a luminous obscured quasar at z~1.6", A&A 583, 141
Dadina et al. 2016, "XMM-Newton reveals a Seyfert-like X-ray spectrum in the z = 3.6 QSO B1422+231", A&A 592, A104
Compton Thick AGN Census
Lanzuisi, Perna et al. 2015 (A&A 578, A12):
"The most obscured AGN in the COSMOS field"
Highly obscured AGN are common in nearby galaxies, but are difficult to observe beyond the local Universe, where they are expected to significantly contribute to the black hole accretion rate density. Furthermore, Compton-thick (CT) absorbers (NH ≳ 1024 cm-2) suppress even the hard X-ray (2-10 keV) AGN nuclear emission, and therefore the column density distribution above 1024 cm-2 is largely unknown. We present the identification and multi-wavelength properties of a heavily obscured (NH ≳ 1025 cm-2), intrinsically luminous (L2-10 > 1044 erg s-1) AGN at z = 0.353 in the COSMOS field. Several independent indicators, such as the shape of the X-ray spectrum, the decomposition of the spectral energy distribution and X-ray/[NeV] and X-ray/6 μm luminosity ratios, agree on the fact that the nuclear emission must be suppressed by a ≳1025 cm-2 column density. The host galaxy properties show that this highly obscured AGN is hosted in a massive star-forming galaxy, showing a barred morphology, which is known to correlate with the presence of CT absorbers. Finally, asymmetric and blueshifted components in several optical high-ionization emission lines indicate the presence of a galactic outflow, possibly driven by the intense AGN activity (LBol/LEdd = 0.3-0.5).
Such highly obscured, highly accreting AGN are intrinsically very rare at low redshift, whereas they are expected to be much more common at the peak of the star formation and BH accretion history, at z ~ 2-3. We demonstrate that a fully multi-wavelength approach can recover a sizable sample of such peculiar sources in large and deep surveys such as COSMOS. Figure: Rest frame, broad-band SED of XID-392. In blue we show the stellar emission, in red the AGN torus emission, and in magenta the SF dust emission. b) Unfolded XMM-Newton (black) and Chandra (red) spectra of XID-392. The best-fit model (magenta) is composed of a thermal component (green) and an obscured torus template (blue). c) SDSS optical spectrum of XID-392. The most prominent emission lines are labelled. The grey area masks a region of bad-sky subtraction. d) [NeV]3346,3426 and [FeVII]6086 lines decom position. The green curve represents the narrow component, while the blue curve represents the broadened asymmetric component, associated with the outflow. The red curve is the sum of the two components. The dotted lines represent the systemic redshift, estimated from the continuum and the stellar absorption lines.
See also:
Zappacosta et al. 2018, "The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample", ApJ 854, 33
Lanzuisi et al. 2018, "The Chandra Cosmos Legacy Survey: Compton Thick AGN at high redshift ", MNRAS 480, 2578
Lanzuisi 2017, "X-ray selection of Compton Thick AGN at high redshift ", AN in press
Lanzuisi et al. 2015, "Compton Thick AGN in the XMM-COSMOS survey ", A&A 573, A137
AGN host galaxies properties
Rodighiero, Brusa, et al. 2015 (ApJ 800, L10):
"Relationship between Star Formation Rate and Black Hole accretion at z=2: the different contributions in quescient, normal and starburst galaxies"
We investigate the co-evolution of the black hole accretion rate (BHAR) and the star formation rate (SFR) in z=1.5-2.5 galaxies displaying a greater diversity of star-forming properties compared to previous studies. By combining X-ray stacking and far-IR photometry of stellar mass-limited samples of normal star-forming, starburst, and quiescent/quenched galaxies in the COSMOS field, we corroborate the existence of a strong correlation between the BHAR and stellar mass (M*) for normal star-forming galaxies, though we find a steeper relation than previously reported. We find that starbursts show a factor of three enhancement in BHAR compared to normal SF galaxies (against a factor of six excess in SFR), while quiescents show a deficit of a factor times 5.5 at a given mass.
One possible interpretation of this is that the starburst phase does not coincide with cosmologically relevant BH growth. Contrary to studies based on smaller samples, we find that the BHAR/SFR ratio of main-sequence(MS) galaxies is not mass invariant, implying faster BH growth in more massive galaxies at z~2. Furthermore, BHAR/SFR during the starburst is a factor of two lower than in MS galaxies, at odds with the predictions of hydrodynamical simulations of merger galaxies that foresee a sudden enhancement of LX/SFR during the merger. Finally, we estimate that the bulk of the accretion density of the universe at z~2 is associated with normal star-forming systems, with only ~6% and ~11% associated with starburst and quiescent galaxies, respectively.Figure: Comparison of our results with predictions of hydro-dynamical models that simultaneously follow star formation and the growth of black holes during a galaxy–galaxy merger. (a): evolution of the SFR with time. The temporal window where (SFR)/(SFR pre-merger)is larger than a factor of 4 for all models is marked by the two vertical dot-dashed lines. (b) Evolution of the X-ray luminosity with time. (c) Evolution of the X-ray luminosity to SFR ratio, as a function of time. Two different values of the virial velocity of the collisional galaxies are considered in the di Matteo et al. (2005) model (160 km s−1; black lines, and 320 km s−1; magenta lines). Our results are presented as a red rectangle for the pre-merger phase (corresponding to our MS normal star-forming sources) and as a blue region for the merger phase (i.e., our starburst sample).
See also:
Lanzuisi et al. 2017, "AGN vs. host galaxy properties in the COSMOS field ", A&A 602, A123
Delvecchio et al. 2015, "Mapping the average AGN accretion rate in the SFR-M∗ plane for Herschel selected galaxies at 0< z <2.5", MNRAS 449, 373
The next generation of X-ray surveys
X-ray extragalactic surveys are ideal laboratories for the study of the evolution and clustering of a AGN. Usually, a combination of deep and wide surveys is necessary to create a complete picture of the population. Deep X-ray surveys provide the faint population at high redshift, while wide surveys provide the rare bright sources. The team has been involved in three of the major, next steps in terms of wide area coverage of the X-ray sky developed in the years 2014-2016, notably:
- The Chandra-COSMOS Legacy survey (PI: Civano)
- The XXL survey (PI: Pierre), complemented by dedicated SDSS spectroscopic coverage within the BOSS project
- The Stripe82-X survey (PI: LaMassa/Urry)
We are also involved in the Chandra survey of the Ultra Deep Subaru (UDS) field (PI: Kocevski/Hasinger), awarded in 2015 and currently ongoing.
Marchesi, Civano, Elvis, Salvato, Brusa et al. 2015 (ApJ 817, 34):
"THE OPTICAL COUNTERPARTS OF THE CHANDRA COSMOS LEGACY SURVEY "
We present the catalog of optical and infrared counterparts of the Chandra COSMOS-Legacy Survey, a 4.6 Ms Chandra program on the 2.2 deg2 of the COSMOS field, combination of 56 new overlapping observations obtained in Cycle 14 with the previous C-COSMOS survey. In this Paper we report the i, K, and 3.6 μm identifications of the 2273 X-ray point sources detected in the new Cycle 14 observations. We use the likelihood ratio technique to derive the association of optical/infrared (IR) counterparts for 97% of the X-ray sources. We also update the information for the 1743 sources detected in C-COSMOS, using new K and 3.6 μm information not available when the C-COSMOS analysis was performed.
The final catalog contains 4016 X-ray sources, 97% of which have an optical/IR counterpart and a photometric redshift, while ≃54% of the sources have a spectroscopic redshift. The full catalog, including spectroscopic and photometric redshifts and optical and X-ray properties described here in detail, is available online. We study several X-ray to optical (X/O) properties: with our large statistics we put better constraints on the X/O flux ratio locus, finding a shift toward faint optical magnitudes in both soft and hard X-ray band. We confirm the existence of a correlation between X/O and the the 2-10 keV luminosity for Type 2 sources. We extend to low luminosities the analysis of the correlation between the fraction of obscured AGNs and the hard band luminosity, finding a different behavior between the optically and X-ray classified obscured fraction. Figure: X-ray flux vs. i-band total magnitude, for all X-ray sources with an i -band counterpart. The black dashed lines de fine the so-called “ soft locus” and “ hard locus” of AGNs along the correlation X/O=0±1. Red circles are AGNs ( LX> 10 42 erg s−1, darker scalecolor indicates higher source density), blue squares are sources with LX<1042erg s−1 and cyan stars are stars. Black solid lines represent the region including 90% of the Chandra COSMOS-Legacy AGN population.Menzel et al. 2016 (MNRAS 457, 110):"A Spectroscopic Survey of X-ray Selected AGN in the Northern XMM-XXL field"This paper presents a survey of X-ray-selected AGN with optical spectroscopic follow-up in a ~18 deg2 area of the equatorial XMM-XXL north field. A sample of 8445 point-like X-ray sources detected by XMM-Newton was matched to optical (Sloan Digital Sky Survey, SDSS) and infrared (IR; WISE) counterparts. We followed up 3042 sources brighter than r = 22.5 mag with the SDSS Baryon Oscillation Spectroscopic Survey (BOSS) spectrograph. The spectra yielded a reliable redshift measurement for 2578 AGN in the redshift range z = 0.02-5.0, with 0.5-2 keV luminosities ranging from 1039-1046 erg s- 1. This is currently the largest published spectroscopic sample of X-ray-selected AGN in a contiguous area. The BOSS spectra of AGN candidates show a distribution of optical line widths which is clearly bimodal, allowing an efficient separation between broad- and narrow-emission line AGN. The former dominate our sample (70 per cent) due to the relatively bright X-ray flux limit and the optical BOSS magnitude limit. We classify the narrow-emission line objects (22 per cent of the full sample) using standard optical emission line diagnostics: the majority have line ratios indicating the dominant source of ionization is the AGN. A small number (8 per cent of the full sample) exhibit the typical narrow line ratios of star-forming galaxies, or only have absorption lines in their spectra. We term the latter two classes `elusive' AGN, which would not be easy to identify correctly without their X-ray emission.
We also compare X-ray (XMM-Newton), optical colour (SDSS) and and IR (WISE) AGN selections in this field. X-ray observations reveal, by far, the largest number of AGN. The overlap between the selections, which is a strong function of the imaging depth in a given band, is also remarkably small. We show using spectral stacking that a large fraction of the X-ray AGN would not be selectable via optical or IR colours due to host galaxy contamination. A substantial fraction of AGN may therefore be missed by these longer wavelength selection methods. Figure: Venn diagram of X-ray, optical (XDQSO) and infrared (Assef et al. 2013) AGN selections in the XMM-XXL north: We indicate the flux depths for eRASS:8 and eRASS:1 of eROSITA, the reliable fraction (dashed line) and number ofAGN in each intersection
LaMassa et al. 2016 (ApJ 817, 172):
"THE 31 DEG2 RELEASE OF THE STRIPE 82 X-RAY SURVEY: THE POINT SOURCE CATALOG"
With this paper, we release the next installment of the Stripe 82 X-ray survey point-source catalog, which sums up to 31.3 deg2 of the Sloan Digital Sky Survey (SDSS) Stripe 82 Legacy field. In total, 6181 unique X-ray sources are significantly detected with XMM-Newton (>5σ) and Chandra (>4.5σ). This catalog release includes data from XMM-Newton cycle AO 13, which approximately doubled the Stripe 82X survey area. The flux limits of the Stripe 82X survey are 8.7 × 10-16 erg s-1 cm-2, 4.7 × 10-15 erg s-1 cm-2, and 2.1 × 10-15 erg s-1 cm-2 in the soft (0.5-2 keV), hard (2-10 keV), and full bands (0.5-10 keV), respectively. We matched the X-ray source lists to available multi-wavelength catalogs, including updated matches to the previous release of the Stripe 82X survey; 88% of the sample is matched to a multi-wavelength counterpart. Due to the wide area of Stripe 82X and rich ancillary multi-wavelength data, including coadded SDSS photometry, mid-infrared WISE coverage, near-infrared coverage from UKIDSS and VISTA Hemisphere Survey, ultraviolet coverage from GALEX, radio coverage from FIRST, and far-infrared coverage from Herschel, as well as existing ˜30% optical spectroscopic completeness, we are beginning to uncover rare objects, such as obscured high-luminosity active galactic nuclei at high-redshift. The Stripe 82X point source catalog is a valuable data set for constraining how this population grows and evolves, as well as for studying how they interact with the galaxies in which they live.
Figure: Left: K-corrected (rest-frame) soft-band (0.5-2 keV) luminosities as a function of redshift for the Stripe 82X (red diamonds), COSMOS-Legacy (blue asterisks), and CDFS (black crosses) sources. At every redshift, an increase in survey area preferentially identifies higher-luminosity sources. Right: Normalized distribution of k -corrected soft-band luminosities for Stripe 82X compared with COSMOS and CDFS: t he wide-area coverage of Stripe 82X which probes a large effec tive volume of the Universe, enables the rare, highest luminosity quasars to be uncovered, complementing the parameter spac e explored by small- to moderate-area surveys. In both plots, only the sou rces identified with redshifts are plotted, representing 30 % of the Stripe 82X sample (which currently has only spectroscopic redshifts) and 91% and 96% of the CDFS and COSMOS-Legacy sample, respect ively, where both spectroscopic and photometric redshifts are available
See also:
Kocevksi et al. 2018, "X-UDS: The Chandra Legacy Survey of the UKIDSS Ultra Deep Survey Field", ApJS 236, 48
Civano et al. 2016, "The Chandra COSMOS Legacy survey: overview and point source catalog", ApJ 819, 62
Marchesi, Lanzuisi et al. 2016, "The Chandra COSMOS-Legacy Survey: Source X-Ray Spectral Properties, ApJ 830, 100
Pierre et al. 2016, "The XXL survey. I. Scientific motivations - XMM-Newton observing plan - Follow-up observations and simulation programme", A&A 592, A1
Fotopoulou et al. 2016, "The XXL survey. VI. The 1000 brightest X-ray point sources"", A&A 592, A1
Hsu, Salvato, Nandra, Brusa et al. 2014, "CANDELS/GOODS-S, CDFS, ECDFS: Photometric Redshifts For Normal and for X-Ray- Detected Galaxies", ApJ 796, 60
Luminosity functions works based on these catalogs or previous versions of the source lists:
Fotopoulou et al. 2016, "5-10 keV luminosity function at 0.01< z <4.0", A&A 687, A142
Miyaji, Hasinger, Salvato, Brusa et al. 2015, "Detailed Shape and Evolutionary Behavior of the X-ray Luminosity Function of Active Galactic Nuclei", ApJ 804, 104
AGN Infancy
Vito, Gilli, Vignali, Comastri, Brusa, Cappelluti & Iwasawa, 2014 (MNRAS 445, 3557):
"The hard X-ray luminosity function of high-redshift (3<z<5) active galactic nuclei "
We present the hard-band (2-10 keV) X-ray luminosity function (HXLF) of the 0.5-2 keV band selected AGN at high redshift. We have assembled a sample of 141 AGN at 3<z<5 from X-ray surveys of different size and depth, in order to sample different regions in the Lx-z plane. The HXLF is fitted in the range logLx~43-45 with standard analytical evolutionary models through a maximum likelihood procedure. The evolution of the HXLF is well described by a pure density evolution, with the AGN space density declining by a factor of ~10 from z=3 to 5. A luminosity-dependent density evolution model which, normally, best represents the HXLF evolution at lower redshift, is also consistent with the data,
but a larger sample of low-luminosity (logLx<44), high-redshift AGN is necessary to constrain this model. We also estimated the intrinsic fraction of AGN obscured by a column density logNH>23 to be 0.54+/-0.05, with no strong dependence on luminosity. This fraction is higher than the value in the Local Universe, suggesting an evolution of the luminous (Lx>1044 erg s-1) obscured AGN fraction from z=0 to z>3. Figure: Obscured AGN fraction as a function of luminosity.
Filled points are results from this work. The dotted, dot-dashed, long-dashed and short-dashed lines are the predictions from the X-ray background synthesis models by Shi et al. (2013), Akylas et al. (2012), Treister et al. (2009) and Gilli et al. (2007), respectively, computed at the median of the considered redshift range.The open symbols represent the obscured AGN fraction measured in a local (z<0.3) sample of AGN. The comparison between the high-z (z>3) and low z (z<0.3) populations suggests an increase of the average obscuration in AGN at high redshifts
See also:
Marchesi, Civano, Elvis, Salvato, Brusa et al. 2016, "The Chandra COSMOS Legacy survey: the z>3 sample", ApJ 827, 150
Morselli et al. 2014, "Primordial environment of super massive black holes: large scale galaxy overdensities around z~6 quasars with LBT", A&A 568, 1
Identifications of X-ray sources: path to eROSITA
LaMassa, Civano, Brusa et al. 2016 (ApJ 818, 88):
"On R-W1 as a diagnostics to discover obscured active galactic nuclei in wide area X-ray surveys"
Capitalizing on the all-sky coverage of WISE and the 35% and 50% sky coverage from Sloan Digital Sky Survey and Pan-STARRS, respectively, we explore the efficacy of mR (optical) - m3.4μm (mid-infrared), hereafter R-W1, as a color diagnostic to identify obscured supermassive black hole accretion in wide-area X-ray surveys. We use the ~16.5 deg2 Stripe 82 X-ray survey data as a test bed to compare R-W1 with R-K, an oft-used obscured AGN selection criterion, and examine where different classes of objects lie in this parameter space. Most stars follow a well-defined path in R - K versus R-W1 space. We demonstrate that optically normal galaxies hosting X-ray AGN at redshifts 0.5<z<1 can be recovered with an R-W1>4 color cut, while they typically are not selected as AGN based on their W1-W2 colors. Additionally, different observed X-ray luminosity bins favor different regions in R-W1 parameter space: moderate-luminosity AGN (logLx=43-44 erg s-1) tend to have red colors, while the highest-luminosity AGN (logLx>45 erg s-1) have bluer colors;
higher spectroscopic completeness of the Stripe 82X sample is needed to determine whether this is a selection effect or an intrinsic property. Finally, we parameterize X-ray obscuration of Stripe 82X AGN by calculating their hardness ratios (HRs) and find no clear trends between HR and optical reddening. Our results will help inform best-effort practices in following up obscured AGN candidates in current and future wide-area, shallow X-ray surveys, including the all-sky eROSITA mission.
Figure: R−W1 as a function of X-ray hardness ratio forStripe 82X sources in 4 redshift ranges from z=1 to z>2, as labeled. The dashed line denotes the Chandra HR that corresponds to NH= 1022 cm−2 for the median redshift of the sub-sample, where HRs greater than this value indicate larger amounts of X-ray obscuration. No trends between optical reddening ndX-ray obscuration are apparent
See also:
Salvato et al. 2018, "Finding counterparts for all-sky X-ray surveys with NWAY: a Bayesian algorithm for cross-matching multiple catalogues", MNRAS 473, 4973
Dwelly, Salvato, Merloni, Brusa et al. 2017, "SPIDERS: Selection of spectroscopic targets using AGN candidates detected in all-sky X-ray surveys", MNRAS 469, 1065
Kolodzig, Gilfanov, Sunyaev, Sozonov & Brusa, 2013, "AGN and QSOs in the eROSITA All-Sky Survey – Part I: Statistical properties ", A&A 819, 62
