AGORA Working Groups and Paper Groups

        - Description:  We will provide a package of common physics for cosmological simulations.  Participants to the Project will agree to a minimal set of common input parameters, from the initial stellar mass function to the metal yield, and to the ionizing ultraviolet background.  Gas cooling tables as a function of density, temperature, metallicity, and UV background (or redshift) will be provided over the next six weeks or so to all Project participants for code implementation.  [authored by Madau]

        - Participants:  Tom Abel, Oscar Agertz, Peter Behroozi, Greg Bryan, Daniel Ceverino, Fabrice Durier, Richard Gerber, Nick Gnedin, Oliver Hahn, Cameron Hummels, Ji-hoon Kim, Andrey Kravtsov, Mike Kuhlen, Piero Madau, Lucio Mayer, Daisuke Nagai, Ken Nagamine, Jose Onorbe, Brian O'Shea, Joel Primack, Tom Quinn, Brant Robertson, Douglas Rudd, Sijing Shen, Britton Smith, Romain Teyssier, Matthew Turk, James Wadsley

        - Leader:  Piero Madau

        - Description:  The goal is to generate initial conditions for an isolated MW-like galactic disk.  We use for that purpose an older version of the MakeDisk code written by Volker Springel to generate quasi-equilibrium 4 component systems (dark halo, stellar bulge, stellar disk, gas disk).  We will provide on a web repository several files containing initial particle coordinates and velocities that everybody will be able to download.  For more information about the data we will provide, visit the WG-II page on Project Workspace.  The repository address will be given as soon as possible.  [authored by Teyssier]

        - Participants:  Oscar Agertz, Robert Feldmann, Nathan Goldbaum, Phil Hopkins, Shigeki Inoue, Ji-hoon Kim, Andrey Kravtsov, Sam Leitner, Hui Li, Lucio Mayer, Johnny Powell, Joel Primack, Tom Quinn, Justin Read, Yves Revaz, Wolfram Schmidt, Romain Teyssier, Sebastian Trujillo-Gomez, Hector Velazquez, James Wadsley

        - Leader:  Romain Teyssier

        - Description:  We will provide initial conditions for high-resolution cosmological zoom-in simulations targeted at eight different types of halos.  Four different halo masses: 1e10, 1e11, 1e12, 1e13 Msun at z=0, and two different types of merger histories per each mass: violent (i.e. with multiple major mergers) and quiescent (i.e. with few major mergers).  A strong isolation criterion will be imposed to select target halos; that is, 3 Rvir radius circle of the halo being simulated must not intersect 3 Rvir radius circle of any halo with half or more of its mass at redshift 0.  Common initial conditions will be generated with MUSIC which supports most of the participating codes.  The initial conditions including MUSIC parameter files will be posted on the workspace webpage as soon as possible.  [authored by Kim]

        - Participants:  Tom Abel, Oscar Agertz, Daniel Ceverino, Jun-Hwan Choi, Jan Engels, Robert Feldmann, Oliver Hahn, Phil Hopkins, Shigeki Inoue, Ji-hoon Kim, Hui Li, Daisuke Nagai, Jose Onorbe, Brian O'Shea, Wolfram Schmidt, Kyle Stewart

        - Leader:  Ji-hoon Kim and Oliver Hahn

        - Description:  This working group will focus on defining repeatable, quantitative and physically-meaningful comparisons of simulation results.  Additionally, tools will be identified and developed to support making these comparisons.  [authored by Turk]

        - Participants:  Tom Abel, Peter Behroozi, Jun-Hwan Choi, Richard Gerber, Nathan Goldbaum, Cameron Hummels, Shigeki Inoue, Ji-hoon Kim, Alexander Knebe, Chris Moody, Daisuke Nagai, Jose Onorbe, Joel Primack, Douglas Rudd, Erik Sanchez, Britton Smith, Robert Thompson, Matthew Turk

        - Leader:  Matthew Turk

        - Description:  This working group will examine how well different numerical methods agree on the structure and evolution of an isolated galactic disk. Starting from simple assumptions regarding the gas (e.g., an isothermal equation of state) we will incrementally increase the level of sophistication by including gas cooling and heating, star formation and feedback. The goal is to quantify in what manner the numerical methods differ given the similar input physics. At each step of the study, effort will go into quantifying the density and temperature structure of the ISM, as well as what level of turbulence is generated in the disk, and how sensitively this depends on numerical resolution. As star formation occurs in the high density tail of the density distribution, we will investigate how to appropriately match refinement strategies in AMR codes to the choice of force softening and minimum smoothing kernel size in SPH codes. By adopting a simple prescription for star formation in all methods, we will compare the resulting star formation rates (SFR) as well as Σ_gas − Σ_SFR (Kennicutt - Schmidt) relations to relevant observations (e.g., Bigiel et al. 2008). The effect of a commonly agreed upon stellar feedback model will subsequently be investigated. A strong focus will here lie on understanding how the input efficiency in the star formation recipe relates to actual star formation efficiency “measured” via the Kennicutt - Schmidt relation, and quantifying the properties of outflows (mass loading, velocity and gas phase structure, etc.). This will ultimately aid in interpreting the results in other working groups, and serve as a way of calibrating star formation and feedback models for different numerical models.  [authored by Agertz]

        - Participants:  Oscar Agertz, Peter Behroozi, Samantha Benincasa, Michael Butler, Daniel Ceverino, Fabrice Durier, Robert Feldmann, John Forbes, Richard Gerber, Nick Gnedin, Oleg Gnedin, Nathan Goldbaum, Luca Graziani, Javiera Guedes, Alexander Hobbs, Phil Hopkins, Amit Kashi, Daisuke Kawata, Ben Keller, Ji-hoon Kim, Andrey Kravtsov, Sam Leitner, Nir Mandelker, Lucio Mayer, Ken Nagamine, Brian O'Shea, Joel Primack, Tom Quinn, Justin Read, Rok Roskar, Wolfram Schmidt, Raffaella Schneider, Sijing Shen, Claudio Soriano, Robert Thompson, Dylan Tweed, Hector Velazquez, James Wadsley

        - Leader:  Oscar Agertz and Romain Teyssier

        - Description:  This working group will simulate and compare a Mvir ~ 1e10 Msun galactic halo in a (5 comoving Mpc/h)^3 cosmological box using all participating codes. The main purpose of this comparison is, as a tradeoff of using a small size box, to make possible for all codes involved reach high spatial and mass resolution in order to test different implementations of baryon physics in a cosmological context (for recent similar studies see Simpson et al. 2012; Governato et al. 2012; Zolotov et al. 2012; Arraki et al. 2012). First dark matter-only simulations will be run to test the cosmological initial condition of a dwarf-sized galaxy and to guarantee that there is no “contamination” by lower-resolution particles in the subsequent baryon runs. In addition, before running the more expensive hydrodynamic simulations, a minimum convergence criterion for all codes will be defined based on mass accretion history, evolution of the density profile, and evolution of the subhalo population. Our goal is to test the effects of feedback on the dark matter distribution and understand the factors that control the gas content, SFR, and stellar mass of dwarf galaxies in order to provide a better theoretical framework for interpreting observations (Geha et al. 2006; Strigari et al. 2008; Kormendy et al. 2009; Oh et al. 2011; Kirby et al. 2011; Geha et al. 2012).  [authored by Onorbe]

        - Participants:  Kenza Arraki, Peter Behroozi, Greg Bryan, Sukanya Chakrabarti, Fabrice Durier, Jonathan Freundlich, Luca Graziani, Javiera Guedes, Jason Jaacks, Daisuke Kawata, Dusan Keres, Ji-hoon Kim, Mike Kuhlen, Shijie Li, Ken Nagamine, Jose Onorbe, Brian O'Shea, Joel Primack, Justin Read, Emilio Romano-Diaz, Raffaella Schneider, Sijing Shen, Christine Simpson, Matteo Tomassetti, Sebastian Trujillo-Gomez, Dylan Tweed, Hector Velazquez, John Wise, Adi Zolotov

        - Leader:  Jose Onorbe

        - Description:  The focus of this working group will be to investigate the effects of baryonic physics on the structure of the simulated galaxies’ dark matter halos. The current literature in this field describes a variety of such effects, often contradictory to each other. For example, adiabatic contraction (Blumenthal et al. 1986; Gnedin et al. 2004) has been shown to steepen the central dark matter density profile in numerical simulations (e.g., Zemp et al. 2012), but on the other hand repeated episodes of supernova-driven outflows can lead to a flattening of the profile and a reduction of the central density (creating a “core”; Read & Gilmore 2005; Mashchenko et al. 2006; Pontzen & Governato 2012; Teyssier et al. 2013, but see also Garrison-Kimmel et al. 2013). Central baryonic condensation may make dark matter subhalos more resilient to tidal disruption, increasing their abundance (Romano-Diaz et al. 2010), while the increased tidal forces due to interactions with the stellar disk could enhance the disruption rate, especially if the subhalos’ density profile has been flattened by feedback processes (Read et al. 2006b; Penarrubia et al. 2010; Zolotov et al. 2012). It is clear that the magnitude, and often even the sign, of the baryonic effects on dark matter depends sensitively on what physics is included in the simulations and on the numerical details of its implementation. Using the AGORA simulations, we intend to systematically investigate these dependencies and to settle some of the following questions: 1) How much adiabatic contraction is there, and is it well described by existing analytical prescriptions? How does this depend on time, and the mass and accretion history of the halo? 2) Is there evidence for the formation of a dark matter core, and how much does it depend on numerical resolution and the feedback implementation? How much can the circular velocity curves be lowered, and can baryonic physics resolve the “Too Big to Fail” problem (Boylan-Kolchin et al. 2011, 2012; Brooks et al. 2013)? 3) Is there evidence for a dark disk, and how does it depend on merger history (Lake 1989; Read et al. 2008, 2009)? 4) Does baryonic mass accretion track dark matter mass accretion? If not, how and why does it differ (van de Voort et al. 2011; Faucher-Giguere et al. 2011; Kuhlen et al. 2013b)? 5) How much does baryonic physics alter the shapes of halos and their spins (Dubinski 1994; Kazantzidis et al. 2004; Debattista et al. 2008; Zemp et al. 2012; Bryan et al. 2013)? 6) Do we see evidence for a dark matter density displacement from the galaxy’s dynamical center (Kuhlen et al. 2013a)?  [authored by Kuhlen]

        - Participants:  Tom Abel, Peter Behroozi, Javiera Guedes, Mike Boylan-Kolchin, Jonathan Freundlich, Oleg Gnedin, Daisuke Kawata, Mike Kuhlen, Piero Madau, Annalisa Pillepich, Joel Primack, Justin Read, Miguel Rocha, Ramin Skibba

        - Leader:  (Miguel Rocha and Mike Kuhlen)

        - Description:  This working group will study the evolution of satellite galaxies as a function of various host halo and satellite properties, and across different treatments of feedback and reionization. Major emphases will be on how baryonic processes affect the interpretation of the observed properties of dwarf satellites in the Local Group. Because the highest-resolution region near the AGORA target halos will include many satellites, the AGORA simulations will enable us to address the following questions: 1) What are the relative impacts of environmental versus internal processes on the evolution of satellite galaxies? We will study the impact of tidal and ram pressure stripping, reionization, and stellar and supernova feedback on the morphology, star formation history, and stellar abundances of satellites. 2) How do the central dark matter density profiles of satellites depend on its luminosity and star formation history? This will address how different feedback implementations influence possible dark matter “core” formation in low-luminosity satellites. Our results will be compared with the dynamical studies of the Milky Way’s dwarf spheroidals (dSphs) which finds that the larger ones have dark matter cores of several hundred pc (Battaglia et al. 2008; Walker & Penarrubia 2011; Amorisco & Evans 2012, but see also Wolf & Bullock 2012). 3) How do satellites’ mass loss rates via tidal stripping vary with orbital histories, infall masses, host halo mass, and satellite dark matter profiles (Penarrubia et al. 2010; Zolotov et al. 2012; Di Cintio et al. 2012)? By studying how the number of luminous satellites predicted to survive to z = 0 varies with these parameters we will address the missing satellite problem (Moore et al. 1999; Klypin et al. 1999) and the “Too Big to Fail” problem. 4) We will study the number of low-mass halos formed and amount of baryons accreted onto such halos before reionization, to determine how many of these “pre-reionizaton fossils” host luminous satellite galaxies today and if they can make up some fraction of the Milky Way’s ultrafaint dSphs (Bovill & Ricotti 2011; Simpson et al. 2012). 5) We will consider which processes are most important for setting the size and mass of the smallest observable galaxies (e.g. Efstathiou 1992, 2000; Susa & Umemura 2004; Read et al. 2006a).  [authored by Zolotov]

        - Participants:  Peter Behroozi, Sukanya Chakrabarti, Oleg Gnedin, Javiera Guedes, Ji-hoon Kim, Mike Boylan-Kolchin, Mike Kuhlen, Piero Madau, Lucio Mayer, Annalisa Pillepich, Joel Primack, Justin Read, Miguel Rocha, Christine Simpson, Ramin Skibba, Hector Velazquez, Adi Zolotov

        - Leader:  Adi Zolotov

        - Description:  Using high-resolution hydrodynamic simulations, this working group will follow the formation and evolution to z = 0 of 1e11 and 1e12 Msun galaxies in their cosmological environments: 1) We will juxtapose our resulting simulations to explore which models best match observations and why; to this end, the simulation outputs will be post-processed to produce synthetic observations so as to enable analysis of the kinematic and structural properties of the galaxies from an observer’s viewpoint (e.g., Governato et al. 2010; Guedes et al. 2011; Brooks et al. 2011; Munshi et al. 2012). Using the radiative transfer code SUNRISE (Jonsson 2006), we will create mock images of the galaxies in a range of filters. These images will be used to calculate surface brightness profiles, derive bulge-to-disk ratios using GALFIT (Peng et al. 2002), and study surface brightness breaks (e.g., Pohlen & Trujillo 2006; Bakos et al. 2008). 2) Further analysis using the yt suite will enable the production of rotation curves, fitting to the Tully-Fisher and M∗−Mvir relations, and investigation of the origin and accretion mode of gas and stars in the halo, thick/thin disks, and bulge of the galaxies (e.g., Keres et al. 2005; Christensen et al. 2012; Guedes et al. 2013; Bird et al. 2013). 3) In addition, we will address the source of metallicity gradients in the disk, the role of stellar migration, and the evolution of bars in these systems. Direct comparison between the various simulations while focusing on what agreements with observations are found, will reveal the galactic characteristics common across different hydrodynamic solvers and subgrid models, while isolating us from differences such as initial condition and halo mass.  [authored by Guedes and Hummels]

        - Participants:  Oscar Agertz, Peter Behroozi, Daniel Ceverino, Jun-Hwan Choi, Romeel Dave, Maria Emilia De Rossi, Fabrice Durier, Robert Feldmann, Oleg Gnedin, Javiera Guedes, Cameron Hummels, Shigeki Inoue, Jason Jaacks, Daisuke Kawata, Dusan Keres, Ji-hoon Kim, Andrey Kravtsov, Sam Leitner, Lucio Mayer, Daisuke Nagai, Ken Nagamine, Brian O'Shea, Joel Primack, Justin Read, Brant Robertson, Emilio Romano-Diaz, Rok Roskar, Sijing Shen, Ramin Skibba, Britton Smith, Kyle Stewart, Robert Thompson, Matteo Tomassetti

        - Leader:  Cameron Hummels (and Javiera Guedes)

        - Description:  This working group will focus on the mass, metals and energy exchange between galaxies and their surroundings, and the roles of galactic outflows in regulating star formation, in determining galactic properties, and in enriching the CGM. Multi-wavelength observations are being used to study the complex, multi-phase structure of the galactic outflows which are ubiquitous in star-forming galaxies (Veilleux et al. 2005, and references therein). Also, absorption studies of the primordial and metal ions within several hundred kpc around galaxies at both low and high redshift (e.g., Prochaska & Hennawi 2009; Chen et al. 2010; Steidel et al. 2010; Tumlinson et al. 2011; Rubin et al. 2012; Werk et al. 2012) continue to provide increasingly detailed maps of the chemical, ionization, thermodynamic and kinematic states of the CGM. Comparisons of the observed CGM and outflows with the ones in simulations have shown to be fruitful (e.g., Fumagalli et al. 2011; Shen et al. 2012, 2013; Hummels et al. 2013). The AGORA simulations, with their high resolution, various hydrodynamic methods, and a wide range halo masses, will provide a large and unbiased sample for such comparisons. The following questions will be investigated: 1) The extent, spacial distribution, and kinematics of heavy elements in the CGM, and how these properties evolve with time and change with galaxy mass and star formation history. 2) The properties of outflows (e.g., mass loading, velocity, temperature, and co-exsistence of different phases) and their dependence on feedback processes and gas cooling. 3) The role of galactic outflows on star formation and galaxy morphology, and whether outflows degenerate with respect to other physical mechanisms of galaxy formation. 4) The effect of outflows on gas inflows and the observational detection of inflows. 5) The sensitivity of the above aspects to the numerical methods being used, in particular between Eulerian and Lagrangian methods.  [authored by Shen]

        - Participants:  Greg Bryan, Daniel Ceverino, Jun-Hwan Choi, Romeel Dave, Colin DeGraf, Fabrice Durier, John Forbes, Jonathan Freundlich, Michele Fumagalli, Javiera Guedes, Alexander Hobbs, Phil Hopkins, Cameron Hummels, Amit Kashi, Dusan Keres, Sam Leitner, Piero Madau, Ken Nagamine, Justin Read, Wolfram Schmidt, Sijing Shen, Britton Smith, Kyle Stewart, James Wadsley

        - Leader:  Sijing Shen

        - Description:  This working group will focus on scientific questions related to high-redshift galaxies at different galaxy mass scales: 1) Gas kinematics. Particular attention will be paid to understand the origins of rotation-dominated and dispersion-dominated galaxies and their mass dependencies. The mock Hα data cubes (Robertson & Bullock 2008; Ceverino et al. 2012) will be compared with integral field unit observations of high-redshift galaxies (Genzel et al. 2006; Law et al. 2007, 2009; Fo ̈rster Schreiber et al. 2009). 2) Violent disk instability (Dekel et al. 2009b; Agertz et al. 2009; Ceverino et al. 2010). The main goal is to study the turbulence and its origin in clumpy, gas-rich galaxies, as well as the clumps properties in varying feedback scenarios (Genel et al. 2012; Hopkins et al. 2012). 3) Cold flows and their importance for gas accretion into galaxies (Birnboim & Dekel 2003; Keres et al. 2005; Dekel & Birnboim 2006; Brooks et al. 2009; Dekel et al. 2009a; van de Voort & Schaye 2012). We will examine the clumpiness of the cold streams, and their detectability as Lyman-α blobs (Goerdt et al. 2010), Lyman-limit systems (Fumagalli et al. 2011; Shen et al. 2013), damped Lyman-α systems (Nagamine et al. 2010; Yajima et al. 2012), or metal-line absorbers (Goerdt et al. 2012; Shen et al. 2013). H I gas distribution around galaxies in general will also be studied. 4) Galactic properties at high redshift. We will characterize the effect of different feedback models on galaxy properties, such as mass in stars and gas, and the SFRs at different redshifts. These properties will be compared with results from abundance matching models (Behroozi et al. 2012; Moster et al. 2013). 5) Mock observations. Synthetic images of the simulated galaxies will be compared in different bands with the observed ones in high-redshift surveys (e.g., CANDELS; Grogin et al. 2011).  [authored by Ceverino]

        - Participants:  Tom Abel, Oscar Agertz, Peter Behroozi, Daniel Ceverino, Jun-Hwan Choi, Romeel Dave, Maria Emilia De Rossi, Fabrice Durier, Jan Engels, Jonathan Freundlich, Michele Fumagalli, Nick Gnedin, Oleg Gnedin, Luca Graziani, Javiera Guedes, Shigeki Inoue, Jason Jaacks, Dusan Keres, Ji-hoon Kim, Andrey Kravtsov, Mike Kuhlen, Sam Leitner, Piero Madau, Ken Nagamine, Brian O'Shea, Joel Primack, Brant Robertson, Emilio Romano-Diaz, Raffaella Schneider, Sijing Shen, Robert Thompson, Matteo Tomassetti, John Wise

        - Leader:  Daniel Ceverino

        - Description:  This working group will investigate the properties of gas in simulated galaxies across mass, redshift, and numerical method. This analysis will divide into three categories: 1) We will inspect the density and temperature structure of the simulated ISM and compare with observations. Compared structural properties will include gas profiles (Bigiel et al. 2010; Kravtsov 2012), gas morphology (e.g., H I holes and shapes; Weisz et al. 2009), gas power spectra (Elmegreen et al. 2001; Dutta et al. 2013), as well as gas distribution functions and phase partition of the ISM (i.e., mass fraction is in molecular gas, cold H I, warm H I, and ionized gas). 2) The analysis will scrutinize the connection between star formation, feedback and gas properties. We will compare simulations with the observed Kennicutt-Schmidt relation at various scales and redshifts (e.g., Bigiel et al. 2008 for inner galaxies, Bigiel et al. 2010 for outer galaxies, and Bolatto et al. 2011 for dwarf galaxies; see also Kim et al. 2012), explore how feedback disperses dense gas (e.g., McKee & Ostriker 2007), and report how these processes impact the structure, stability and dynamics of the gas disk. 3) Finally we will describe the simulated gas disks in their broader cosmological context. Specifically, we will characterize how gas fractions, metallicity gradients, and velocity dispersions vary with redshift and mass (Haynes et al. 1999; Tacconi et al. 2012; Swinbank et al. 2012a,b), how different star formation laws affect the onset of star formation in galaxies (Rafelski et al. 2011; Christensen et al. 2012; Kuhlen et al. 2012a; Thompson et al. 2013), and how cosmological accretion modifies the ISM compared to galaxies simulated in isolation.  [authored by Leitner]

        - Participants:  Oscar Agertz, Daniel Ceverino, Charlotte Christensen, Robert Feldmann, John Forbes, Nick Gnedin, Oleg Gnedin, Nathan Goldbaum, Luca Graziani, Cameron Hummels, Amit Kashi, Daisuke Kawata, Dusan Keres, Andrey Kravtsov, Sam Leitner, Piero Madau, Lucio Mayer, Ken Nagamine, Brian O'Shea, Brant Robertson, Emilio Romano-Diaz, Raffaella Schneider, Sijing Shen, Robert Thompson, Matteo Tomassetti, James Wadsley

        - Leader:  (Sam Leitner)

        - Description:  This working group will investigate the effect that including a SMBH subgrid model has on the overall dynamics of a galaxy across different simulation codes. Employing a SMBH subgrid model for accretion and feedback (e.g., Springel et al. 2005a; Booth & Schaye 2009; Kim et al. 2011; Choi et al. 2012) will provide interesting science for both the isolated disks, where the black hole will start already at a typical SMBH mass and therefore exert a strong effect on the dynamics of the central region, and for the cosmological galaxies, where it will start as a seed of negligible mass but co-evolve with the galaxy as it forms. In particular: 1) We will study the role that different subgrid implementations and modes of the SMBH feedback have on galactic properties including SFR, stellar morphology, the MBH−σbulge (Gebhardt et al. 2000; Ferrarese & Merritt 2000) relation, and the M_BH−M_bulge (Magorrian et al. 1998; Haring & Rix 2004) relation. These properties will also provide observational benchmarks against which to infer the success of the subgrid model in each code. 2) The interplay between star formation and black hole growth, and the relative strength between stellar feedback and SMBH feedback across the lifetime of the simulated galaxies will also be a priority.  [authored by Hobbs] 

        - Participants:  Tom Abel, Colin DeGraf, Fabrice Durier, Jonathan Freundlich, Alexander Hobbs, Phil Hopkins, Amit Kashi, Ben Keller, Ji-hoon Kim, Lucio Mayer, Daisuke Nagai, Rick Newton, Brian O'Shea, Chris Power, Justin Read, Romain Teyssier

        - Leader:  Alexander Hobbs