Sofía A. Cora

Effects of AGN feedback on ΛCDM galaxies

ABSTRACT We study the effects of Active Galactic Nuclei (AGN) feedback on the formation andevolution of galaxies by using a combination of a cosmological N-body simulation ofthe concordance Λ cold dark matter (ΛCDM) paradigm and a semi-analytic modelof galaxy formation. This model is an improved version of the one described by Cora(2006), which now considers the growth of black holes (BHs) as driven by (i) gasaccretion during merger-driven starbursts and mergers with other BHs, (ii) accretionduring starbursts triggered by disc instabilities, and (iii) accretion of gas cooled fromquasi-hydrostatic hot gas haloes. It is assumed that feedback from AGN operatesin the later case. The model has been calibrated in order to reproduce observationalcorrelations between BH mass and mass, velocity dispersion, and absolute magnitudesofthe galaxybulge. AGN feedback hasa strongimpact on reducing oreven suppressinggas cooling, an effect that becomes important at lower redshifts. This phenomenonhelpsto reproducethe observedgalaxyluminosityfunction(LF) inthe opticalandnearIR bands at z = 0, and the cosmic star formation rate and stellar mass functions over awide redshift range (0 . z . 5). It also allows to have a population of massive galaxiesalready in place at z & 1, which are mostly early-type and have older and redderstellar populations than lower mass galaxies, reproducing the observed bimodalityin the galaxy colour distribution, and the morphological fractions. The evolution ofthe optical QSO LF is also reproduced, provided that the presence of a significantfraction of obscured QSOs is assumed. We explore the effects of AGN feedback duringstarbursts finding that, in order to obtain a good agreement with observations, theseneed to be strong enough to expell the reheated gas away from the galaxy halo.We also test new, recent prescriptions for dynamical friction time-scales, and findthat they produce an earlier formation of elliptical galaxies, and a larger amount ofdisc instabilites, which compensate the change in the merger frequency such that theproperties of z = 0 galaxies remain almost unaffected.Key words: galaxies: evolution - galaxies: formation - galaxies: statistics - quasars:general

Chemical evolution using smooth particle hydrodynamical cosmological simulations – I. Implementation, tests and first results

We develop a model to implement metal enrichment in a cosmological context based on the hydrodynamical AP3MSPH code described by Tissera, Lambas and Abadi (1997). The star formation model is based on the Schmidt law and has been modified in order to describe the transformation of gas into stars in more detail. The enrichment of the interstellar medium due to supernovae I and II explosions is taken into account by assuming a Salpeter Initial Mass Function and different nucleosynthesis models. The different chemical elements are mixed within the gaseous medium according to the Smooth Particle Hydrodynamics technique. Gas particles can be enriched by different neighbouring particles at the same time. We present tests of the code that assess the effects of resolution and model parameters on the results. We show that the main effect of low numerical resolution is to produce a more effective mixing of elements, resulting in abundance relations with less dispersion. We have performed cosmological simulations in a standard Cold Dark Matter scenario and we present results of the analysis of the star formation and chemical properties of the interstellar medium and stellar population of the simulated galactic objects. We show that these systems reproduce abundance ratios for primary and secondary elements of the interstellar medium, and the correlation between the (O/H) abundance and the gas fraction of galaxies. We find that star formation efficiency, the relative rate of supernovae II to supernovae I and life-time of binary systems as well as the stellar nucleosynthesis

Metal enrichment of the intracluster medium: a three‐dimensional picture of chemical and dynamical properties

We develop a model for the metal enrichment of the intracluster medium (ICM) that combines a cosmological non-radiative hydrodynamical N-body/SPH (smoothed particle hydrodynamic) simulation of a cluster of galaxies, and a semi-analytic model of galaxy formation. The novel feature of our hybrid model is that the chemical properties of the diffuse gas in the underlying simulation are dynamically and consistently generated from stars in the galaxies. We follow the production of several chemical elements, provided by low- and intermediate-mass stars, core collapse and Type Ia supernovae. We analyse the spatial distribution of metals in the ICM, investigate the way in which the chemical enrichment proceeds and use iron emissivity as a tracer of gas motions. The similar abundance patterns developed by O and Fe indicate that both types of supernovae pollute the ICM in a similar fashion. Their radial abundance profiles are enhanced in the inner 100 h -1 kpc in the last Gyr because of the convergence of enriched gas clumps to the cluster centre; this increment cannot be explained by the metal ejection of cluster galaxies which is quite low at the present epoch. Our results support a scenario in which part of the central intracluster gas comes from gas clumps that, in the redshift range of z ∼ 0.2 to 0.5, have been enriched to solar values and are at large distances from the cluster centre (from ∼1 to 6 h -1 Mpc) moving at very high velocities (from ∼1300 to 2500 km s -1 ). The turbulent gas motions within the cluster, originated in the inhomogeneous gas infall during the cluster assembly, are manifested in emission-weighted velocity maps as gradients that can be as large as ∼1000 km s -1 over distances of a few hundred kpc. Gradients of this magnitude are also seen in velocity distributions along sightlines through the cluster centre. Doppler shifting and broadening suffered by the Fe K α 6.7-keV emission line along such sightlines could be used to probe these gas large-scale motions when they are produced within an area characterized by high iron line emissivity.

On the dynamical origin of the ICM metallicity evolution

We present a study on the origin of the metallicity evolution of the intra-cluster medium (ICM) by applying a semi-analytic model of galaxy formation to N-body/smoothed particle hydrodynamic (SPH) non-radiative numerical simulations of clusters of galaxies. The semi-analytic model includes gas cooling, star formation, supernovae feedback and metal enrichment, and is linked to the diffuse gas of the underlying simulations so that the chemical properties of gas particles are dynamically and consistently generated from stars in the galaxies. This hybrid model lets us have information on the spatial distribution of metals in the ICM. The results

Black hole spin and radio loudness in a Λ cold dark matter universe

We use a combination of a cosmological N-body simulation of the concordance A cold dark matter paradigm and a semi-analytic model of galaxy formation to investigate the spin development of central supermassive black holes (BHs) and its relation to the BH host galaxy properties. In order to compute BH spins, we use the a model of Shakura & Sunyaev and consider the King et al. warped disc alignment criterion. The orientation of the accretion disc is inferred from the angular momentum of the source of accreted material, which bears a close relationship to the large-scale structure in the simulation. We find that the final BH spin depends almost exclusively on the accretion history and only weakly on the warped disc alignment. The main mechanisms of BH spin-up are found to be gas cooling processes and disc instabilities, a result that is only partially compatible with Monte Carlo models where the main spin-up mechanisms are major mergers and disc instabilities; the latter results are reproduced when implementing randomly oriented accretion discs in our model. Regarding the BH population, we find that more massive BHs, which are hosted by massive ellipticals, have higher spin values than less massive BHs, hosted by spiral galaxies. We analyse whether gas accretion rates and BH spins can be used as tracers of the radio loudness of active galactic nuclei (AGN). We find that the current observational indications of an increasing trend of radio-loud AGN fractions with stellar and BH mass can be easily obtained when placing lower limits on the BH spin, with a minimum influence from limits on the accretion rates; a model with random accretion disc orientations is unable to reproduce this trend. Our results favour a scenario where the BH spin is a key parameter to separate the radio-loud and radio-quiet galaxy populations.

Chemoarchaeological downsizing in a hierarchical universe: impact of a top-heavy IGIMF

Fil: Gargiulo, Ignacio Daniel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico La Plata. Instituto de Astrofisica de La Plata; Argentina; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

The bright end of the colour-magnitude relation of cluster galaxies

We investigate the origin of the colour-magnitude relation (CMR) followed by early-type cluster galaxies by using a combination of cosmological N-body simulations of cluster of galaxies and a semi-analytic model of galaxy formation (Lagos, Cora & Padilla 2008). Results show good agreement between the general trend of the simulated and observed CMR. However, in many clusters, the most luminous galaxies depart from the linear fit to observed data displaying almost constant colours. With the aim of understanding this behaviour, we analyze the dependence with redshift of the stellar mass contributed to each galaxy by different processes, i.e., quiescent star formation, and starburst during major/minor and wet/dry mergers, and disk instability events. The evolution of the metallicity of the stellar component, contributed by each of these processes, is also investigated. We find that the major contribution of stellar mass at low redshift is due to minor dry merger events, being the metallicity of the stellar mass accreted during this process quite low. Thus, minor dry merger events seem to increase the mass of the more luminous galaxies without changing their colours.

Host galaxy–active galactic nucleus alignments in the Sloan Digital Sky Survey Data Release 7

We determine the intrinsic shapes and orientations of 27,450 type I and II active galactic nucleus (AGN) galaxies in the spectroscopic sample of the SDSS DR7, by studying the distribution of projected axis ratios of AGN hosts. Our aim is to study possible alignments between the AGN and host galaxy systems (e.g. the accretion disc and the galaxy angular momentum) and the effect of dust obscuration geometry on the AGN type. We define control samples of non-AGN galaxies that mimic the morphology, colour, luminosity and concentration distributions of the AGN population, taking into account the effects of dust extinction and reddening. Assuming that AGN galaxies have the same underlying three-dimensional shape distribution as their corresponding control samples, we find that the spiral and elliptical type I AGN populations are strongly skewed toward face-on galaxies, while ellipticals and spirals type II AGN are skewed toward edge-on orientations. These findings rule out random orientations for AGN hosts at high confidence for type I spirals (delta chi^2~230) and type II ellipticals (delta chi^2~15), while the signal for type I ellipticals and type II spirals is weaker (delta chi^2~3 and delta chi^2~6, respectively). We obtain a much stronger tendency for the type II spirals to be edge-on when just high [OIII] equivalent width (EW) AGN are considered, suggesting that >20% of low [OIII] EW edge-on type II AGN may be missing from the optical sample. Galactic dust absorption of the broad-line region alone cannot explain the observed inclination angle and projected axis ratio distributions of type I and II Seyfert types, implying that obscuration by a small-scale circumnuclear torus is necessary. These results favour a scenario in which the angular momentum of the material which feeds the black hole retains a memory of its original gas source at least to some small, non-negligible degree.

Calibration of semi-analytic models of galaxy formation using particle swarm optimization

Fil: Ruiz, Andres Nicolas. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Instituto de Astronomia Teorica y Experimental; Argentina. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina

Properties of submillimetre galaxies in a semi-analytic model using the ‘Count Matching’ approach: application to the ECDF-S

We present a new technique for modeling submillimeter galaxies (SMGs): the “Count Matching” approach. Using lightcones drawn from a semi-analytic model of galaxy formation, we choose physical galaxy properties given by the model as proxies for their submillimeter luminosities, assuming a monotonic relationship. As recent interferometric observations of the Extended Chandra Deep Field South show that the brightest sources detected by single-dish telescopes are comprised by emission from multiple fainter sources, we assign the submillimeter fluxes so that the combined LABOCA plus bright-end ALMA observed number counts for this field are reproduced. After turning the model catalogs g iven by the proxies into submillimeter maps, we perform a source extraction to include the effects of the observational process on the recovered counts and galaxy properties. We fin d that for all proxies, there are lines of sight giving counts consistent with those derived f rom LABOCA observations, even for input sources with randomized positions in the simulated map. Comparing the recovered redshift, stellar mass and host halo mass distributions for model SMGs with observational data, we find that the best among the proposed proxies is that i n which the submillimeter luminosity increases monotonically with the product between dust mass and SFR. This proxy naturally reproduces a positive trend between SFR and bolometric IR luminosity. The majority of components of blended sources are spatially unassociated.