Galactic population in cosmological hierarchical models

2007/2008Il lavoro di ricerca è stato orientato allo studio delle proprietà delle strutture su grande scala dell'Universo. In particolar modo si sono studiate le proprietà ottiche e fisiche di popolazioni sintetiche di galassie in ammassi di galassie in ambito cosmologico all'interno dello scenario gerarchico. Abbiamo affrontato il problema della formazione galattica seguendo due approcci complementari. Una linea di ricerca svolta è stata indirizzata allo studio della popolazione galattica in ammassi di galassie, utilizzando simulazioni idrodinamiche cosmologiche. A tale scopo si sono analizzate simulazioni realizzate con il codice Tree+SPH GADGET2 (Springel 2005) che include processi fisici quali cooling, formazione stellare ed un trattamento dettagliato dei processi di arricchimento chimico associato ai processi di nucleosintesi stellare (Tornatore et al. 2007). Dall'analisi comparata delle osservazioni tra le proprietà ottiche e fisiche di galassie in ammasso ed i risultati di codici spettro-fotometrici applicati alle simulazioni realizzate, è possibile trarre importanti informazioni sulla formazione e sull'evoluzione della componenente barionica tutta ed in particolar modo della popolazione galattica. In particolar modo sono state confrontate le proprietà fisiche e luminosità ottiche e infrarosse delle osservazioni con quelle delle galassie predette dai modelli numerici identificate tramite l'utilizzo di software specifici per il riconoscimento di sottostrutture gravitazionalmente legate (Saro et al. 2006). Sempre nell'ambito di questa linea di ricerca abbiamo studiato i processi coinvolti nella formazione delle galassie centrali d'ammasso ad alto redshift () (Saro et al. 2009), comparando le predizioni numeriche con le più recenti osservazioni ottenute tramite telescopi spaziali (Miley et al. 2006, Hatch et al. 2007), includendo in maniera autoconsistente nel calcolo delle luminosità l'assorbimento da polvere, la quale gioca un ruolo cruciale in regioni ad alto tasso di formazione stellare. Altro aspetto dell'attività di ricerca è stato rivolto allo studio ed al confronto delle predizioni delle proprietà della popolazione galattica in ammassi di galassie attraverso due diversi metodi d’indagine: simulazioni idrodinamiche cosmologiche dirette e modelli semianalitici (SAM), nei quali la popolazione galattica è invece riprodotta tramite apposite ”ricette” a partire dall’analisi dei “merging trees” degli aloni di materia oscura (p.es. De Lucia et al. 2006). Tali metodi presentano vantaggi e svantaggi complementari. Se da un lato infatti le simulazioni dirette permettono uno studio più accurato della dinamica e di seguire in dettaglio la fisica al prezzo però di enormi costi computazionali, dall'altro i modelli semianalitici permettono uno studio dello spazio dei parametri ed una statistica irragiungibile tramite le sole simulazioni. Parte di tale ricerca è stata svolta anche presso il Max Planck Institute for Astrophysics (MPA) di Garching (Monaco) in Germania in collaborazione con Klaus Dolag e Gabriella de Lucia grazie ad una borsa europea EARA - Marie Curie della durata di tre mesi, successivamente estesa per ulteriori due mesi. Lo scopo di quest’indagine si sviluppa su due fronti: confrontare le predizioni dei modelli semianalitici basati su merger trees di simulazioni con fisica diversa e confrontare le predizioni dei modelli semianalitici con quelle che si ottengono direttamente dalle simulazioni. Da un lato, infatti, confrontando le predizioni del modello semianalitico basato su merger trees di simulazioni di sola Dark Matter con le predizioni dello stesso modello semianalitico basato però su merger trees di simulazioni di Dark Matter e Gas, possiamo quantificare e valutare quanto considerare o trascurare processi fisici quali la pressione d'ariete modifichi l'evoluzione e la dinamica della popolazione galattica (Saro et al. 2008). Dall'altro, il confronto tra la popolazione galattica predetta direttamente da simulazioni idrodinamiche cosmologiche e quella predetta dai modelli semianalitici basati sugli stessi merger trees, permette di capire meglio i limiti e le differenze tra queste due tecniche nello studio della formazione di galassie in ambito cosmologico. In particolare tale confronto è stato effettuato con una fisica “semplificata” per poter quantificare l'importanza delle singole assunzioni. Nella fattispecie abbiamo considerato solo cooling e star formation, ed abbiamo trascurato processi fisici quali l'arrichimento chimico e il feedback. In questo modo sono state messe in luce le differenti trattazioni del cooling, della formazione stellare e degli effetti mareali nella creazione di una popolazione stellare intracluster (Saro et al. 2009, in prep).XXI Ciclo198

Cosmological simulations of black hole growth: AGN luminosities and downsizing

In this study, we present a detailed, statistical analysis of black hole growth and the evolution of active galactic nuclei (AGN) using cosmological hydrodynamic simulations run down to $z=0$. The simulations self-consistently follow radiative cooling, star formation, metal enrichment, black hole growth and associated feedback processes from both supernovae typeII/Ia and AGN. We consider two simulation runs, one with a large co-moving volume of $(500\ \mathrm{Mpc})^3$and one with a smaller volume of$(68\ \mathrm{Mpc})^3$but with a by a factor of almost 20 higher mass resolution. Consistently with previous results, our simulations can widely match observed black hole properties of the local Universe. Furthermore, our simulations can successfully reproduce the evolution of the bolometric AGN luminosity function for both the low-luminosity and the high-luminosity end up to$z=3.0$. In addition, the smaller but higher resolution run is able to match the observational data of the low bolometric luminosity end at higher redshifts$z=3-4$. We also perform a direct comparison with the observed soft and hard X-ray luminosity functions of AGN, including an empirical correction for a torus-level obscuration, and find a similarly good agreement. These results nicely demonstrate that the observed "anti-hierarchical" trend in the AGN number density evolution (i.e. the number densities of luminous AGN peak at higher redshifts than those of faint AGN) is self-consistently predicted by our simulations. Implications of this downsizing behaviour on active black holes, their masses and Eddington-ratios are discussed. Overall, the downsizing behaviour in the AGN number density as a function of redshift can be mainly attributed to the evolution of the gas density in the resolved vicinity of a (massive) black hole. (shortened)Comment: 24 pages, 15 figures, 1 table, accepted for publication in MNRAS, the analysis is updated using a simulation run with a cosmological volume of (500Mpc)^3 containing 2*1,564^3 particle

Cosmology dependency of halo masses and concentrations in hydrodynamic simulations

We employ a set of Magneticum cosmological hydrodynamic simulations that span over $15$ different cosmologies, and extract masses and concentrations of all well-resolved haloes between $z=0-1$ for critical over-densities $\Delta_\texttt{vir}, \Delta_{200c}, \Delta_{500c}, \Delta_{2500c}$ and mean overdensity $\Delta_{200m}.$ We provide the first mass-concentration (Mc) relation and sparsity relation (i.e. $M_{\Delta1} - M_{\Delta2}$ mass conversion) of hydrodynamic simulations that is modelled by mass, redshift and cosmological parameters $\Omega_m, \Omega_b, \sigma_8, h_0$ as a tool for observational studies. We also quantify the impact that the Mc relation scatter and the assumption of NFW density profiles have on the uncertainty of the sparsity relation. We find that converting masses with the aid of a Mc relation carries an additional fractional scatter ($\approx 4\%$) originated from deviations from the assumed NFW density profile. For this reason we provide a direct mass-mass conversion relation fit that depends on redshift and cosmological parameters. We release the package hydro\_mc, a python tool that perform all kind of conversions presented in this paper.Comment: 17 pages, 11 figures, accepted at MNRAS, hydro_mc URL https://github.com/aragagnin/hydro_m

Cosmological constraints from abundance, weak-lensing and clustering of galaxy clusters: application to the SDSS

The clustering of galaxy clusters is a powerful cosmological tool, which can help to break degeneracies between parameters when combined with other cosmological observables. We aim to demonstrate its potential in constraining cosmological parameters and scaling relations when combined with cluster counts and weak lensing mass information, using as a case study the redMaPPer cluster catalog derived from the Sloan Digital Sky Survey (SDSS). We extend the analysis of number counts and weak lensing signal performed by Costanzi et al. 2019a, with the addition of the real-space 2-point correlation function. We derive cosmological and scaling relation posteriors for all the possible combinations of the three observables to assess their constraining power, parameter degeneracies, and possible internal tensions. We find no evidence for tensions between the three data set analyzed. We demonstrate that the inclusion of the cluster clustering statistic can greatly enhance the constraining power of the sample thanks to its capability of breaking the $\Omega_{\rm m} - \sigma_8$ degeneracy characteristic of cluster abundance studies. In particular, for a flat $\Lambda$CDM model with massive neutrinos, we obtain $\Omega_{\rm m}=0.28 \pm 0.03$ and $\sigma_8 = 0.82 \pm 0.05$, a 33% and 50% improvement compared to the posteriors derived combining cluster abundance and weak lensing analyses. Our results are consistent with cosmological posteriors from other cluster surveys, as well as with Planck CMB results and DES-Y3 galaxy clustering and weak-lensing analysis.Comment: 15 pages, 10 figure

Impact of Weak Lensing Mass Calibration on eROSITA Galaxy Cluster Cosmological Studies -- a Forecast

We forecast the impact of weak lensing (WL) cluster mass calibration on the cosmological constraints from the X-ray selected galaxy cluster counts in the upcoming eROSITA survey. We employ a prototype cosmology pipeline to analyze mock cluster catalogs. Each cluster is sampled from the mass function in a fiducial cosmology and given an eROSITA count rate and redshift, where count rates are modeled using the eROSITA effective area, a typical exposure time, Poisson noise and the scatter and form of the observed X-ray luminosity-- and temperature--mass--redshift relations. A subset of clusters have mock shear profiles to mimic either those from DES and HSC or from the future Euclid and LSST surveys. Using a count rate selection, we generate a baseline cluster cosmology catalog that contains 13k clusters over 14,892~deg$^2$ of extragalactic sky. Low mass groups are excluded using raised count rate thresholds at low redshift. Forecast parameter uncertainties for $\Omega_\mathrm{M}$, $\sigma_8$ and $w$ are 0.023 (0.016; 0.014), 0.017 (0.012; 0.010), and 0.085 (0.074; 0.071), respectively, when adopting DES+HSC WL (Euclid; LSST), while marginalizing over the sum of the neutrino masses. A degeneracy between the distance--redshift relation and the parameters of the observable--mass scaling relation limits the impact of the WL calibration on the $w$ constraints, but with BAO measurements from DESI an improved determination of $w$ to 0.043 becomes possible. With Planck CMB priors, $\Omega_\text{M}$ ($\sigma_8$) can be determined to $0.005$ ($0.007$), and the summed neutrino mass limited to $\sum m_\nu < 0.241$ eV (at 95\%). If systematics on the group mass scale can be controlled, the eROSITA group and cluster sample with 43k objects and LSST WL could constrain $\Omega_\mathrm{M}$ and $\sigma_8$ to 0.007 and $w$ to 0.050.Comment: 28 pages, 13 figur

Photometric and clustering properties of hydrodynamical galaxies in a cosmological volume: results at z=0

In this work, we present results for the photometric and clustering properties of galaxies that arise in a LambdaCDM hydrodynamical simulation of the local universe. The present-day distribution of matter was constructed to match the observed large scale pattern of the IRAS 1.2-Jy galaxy survey. Our simulation follows the formation and evolution of galaxies in a cosmological sphere with a volume of ~130^3 (Mpc/h)^3 including supernova feedback, galactic winds, photoheating due to an uniform meta-galactic background and chemical enrichment of the gas and stellar populations. However, we do not consider AGNs. In the simulation, a total of ~20000 galaxies are formed above the resolution limit, and around 60 haloes are more massive than ~10^14 M_sun. Luminosities of the galaxies are calculated based on a stellar population synthesis model including the attenuation by dust, which is calculated from the cold gas left within the simulated galaxies. Environmental effects like colour bi-modality and differential clustering power of the hydrodynamical galaxies are qualitatively similar to observed trends. Nevertheless, the overcooling present in the simulations lead to too blue and overluminous brightest cluster galaxies (BCGs). To overcome this, we mimic the late-time suppression of star formation in massive halos by ignoring recently formed stars with the aid of a simple post-processing recipe. In this way we find luminosity functions, both for field and group/cluster galaxies, in better agreement with observations. Specifically, the BCGs then follow the observed luminosity-halo mass relation. However, in such a case, the colour bi-modality is basically lost, pointing towards a more complex interplay of late suppression of star formation than what is given by the simple scheme adopted.Comment: Typos corrected. Replaced to match published version. 12 pages, 12 figures. To appear in MNRA

The cool side of Lyman Alpha Emitters

We extend a previous study of Lyman Alpha Emitters (LAEs) based on hydrodynamical cosmological simulations, by including two physical processes important for LAEs: (a) Lyman Alpha and continuum luminosities produced by cooling of collisionally excited HI in the galaxy, (b) dust formation and evolution; we follow these processes on a galaxy-by-galaxy basis. HI cooling on average contributes 16-18% of the Lyman Alpha radiation produced by stars, but this value can be much higher in low mass LAEs and further increased if the HI is clumpy. The continuum luminosity is instead almost completely dominated by stellar sources. The dust content of galaxies scales with their stellar mass, M_{dust} is proportional to M_*^0.7 and stellar metallicity, Z_*, such that M_{dust} is proportional to Z_*^1.7. As a result, the massive galaxies have Lyman Alpha escape fraction as low as f_alpha=0.1, with a LAE-averaged value decreasing with redshift such that it is (0.33,0.23) at z =(5.7,6.6). The UV continuum escape fraction shows the opposite trend with redshift, possibly resulting from clumpiness evolution. The model successfully reproduces the observed Lyman Alpha and UV luminosity functions at different redshifts and the Lyman Alpha equivalent width scatter to a large degree, although the observed distribution appears to be more more extended than the predicted one. We discuss possible reasons for such tension.Comment: 9 pages, accepted for publication in MNRA

Forming intracluster gas in a galaxy protocluster at a redshift of 2.16

Galaxy clusters are the most massive gravitationally bound structures in the Universe, comprising thousands of galaxies and pervaded by a diffuse, hot intracluster medium (ICM) that dominates the baryonic content of these systems. The formation and evolution of the ICM across cosmic time1 is thought to be driven by the continuous accretion of matter from the large-scale filamentary surroundings and energetic merger events with other clusters or groups. Until now, however, direct observations of the intracluster gas have been limited only to mature clusters in the later three-quarters of the history of the Universe, and we have been lacking a direct view of the hot, thermalized cluster atmosphere at the epoch when the first massive clusters formed. Here we report the detection (about 6σ) of the thermal Sunyaev-Zeldovich (SZ) effect2 in the direction of a protocluster. In fact, the SZ signal reveals the ICM thermal energy in a way that is insensitive to cosmological dimming, making it ideal for tracing the thermal history of cosmic structures3. This result indicates the presence of a nascent ICM within the Spiderweb protocluster at redshift z = 2.156, around 10 billion years ago. The amplitude and morphology of the detected signal show that the SZ effect from the protocluster is lower than expected from dynamical considerations and comparable with that of lower-redshift group-scale systems, consistent with expectations for a dynamically active progenitor of a local galaxy cluster

Synthesizing Stellar Populations in South Pole Telescope Galaxy Clusters. I. Ages of Quiescent Member Galaxies at 0.3 < z < 1.4

Using stellar population synthesis models to infer star formation histories (SFHs), we analyze photometry and spectroscopy of a large sample of quiescent galaxies that are members of Sunyaev–Zel'dovich (SZ)-selected galaxy clusters across a wide range of redshifts. We calculate stellar masses and mass-weighted ages for 837 quiescent cluster members at 0.3 < z < 1.4 using rest-frame optical spectra and the Python-based Prospector framework, from 61 clusters in the SPT-GMOS Spectroscopic Survey (0.3 < z < 0.9) and three clusters in the SPT Hi-z cluster sample (1.25 < z < 1.4). We analyze spectra of subpopulations divided into bins of redshift, stellar mass, cluster mass, and velocity-radius phase-space location, as well as by creating composite spectra of quiescent member galaxies. We find that quiescent galaxies in our data set sample a diversity of SFHs, with a median formation redshift (corresponding to the lookback time from the redshift of observation to when a galaxy forms 50% of its mass, t50) of z = 2.8 ± 0.5, which is similar to or marginally higher than that of massive quiescent field and cluster galaxy studies. We also report median age–stellar mass relations for the full sample (age of the universe at t50 (Gyr) = 2.52 (±0.04)–1.66 (±0.12) log10(M/1011M⊙)) and recover downsizing trends across stellar mass; we find that massive galaxies in our cluster sample form on aggregate ∼0.75 Gyr earlier than lower-mass galaxies. We also find marginally steeper age–mass relations at high redshifts, and report a bigger difference in formation redshifts across stellar mass for fixed environment, relative to formation redshifts across environment for fixed stellar mass

A Gradual Decline of Star Formation since Cluster In-fall: New Kinematic Insights into Environmental Quenching at 0.3 <z<< z < 1.1

The environments where galaxies reside crucially shape their star formation histories. We investigate a large sample of 1626 cluster galaxies located within 105 galaxy clusters spanning a large range in redshift ($0.26 < z < 1.13)$. The galaxy clusters are massive (M$_{500} \gtrsim 2\times10^{14}$M$_{\odot}$), and are uniformly selected from the SPT and ACT Sunyaev-Zel'dovich (SZ) surveys. With spectra in-hand for thousands of cluster members, we use galaxies' position in projected phase space as a proxy for their in-fall times, which provides a more robust measurement of environment than quantities such as projected cluster-centric radius. We find clear evidence for a gradual age increase of the galaxy's mean stellar populations ($\sim$ 0.71 $\pm$ 0.4 Gyr based on a 4000 $\r{A}$ break, $\rm D_{\rm n}4000$) with the time spent in the cluster environment. This environmental quenching effect is found regardless of galaxy luminosity (faint or bright) and redshift (low-$z$ or high-$z$), although the exact stellar age of galaxies depends on both parameters at fixed environmental effects. Such a systematic increase of $\rm D_{\rm n}4000$ with in-fall proxy would suggest that galaxies that were accreted into hosts earlier were quenched earlier, due to longer exposure to environmental effects such as ram pressure stripping and starvation. Compared to the typical dynamical time scales of $1-3$ Gyr of cluster galaxies, the relatively small age increase ($\sim$ 0.71 $\pm$ 0.4 Gyr) found in our sample galaxies seems to suggest that a slow environmental process such as starvation is the dominant quenching pathway. Our results provide new insights into environmental quenching effects spanning a large range in cosmic time ($\sim 5.2$ Gyr, $z=0.26$--1.13) and demonstrate the power of using a kinematically-derived in-fall time proxy.Comment: 22 pages, 9 figures, 3 tables. Accepted for publication by Ap