1,721,079 research outputs found
Host galaxies of luminous z? 0.6 quasars: Major mergers are not prevalent at the highest AGN luminosities
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Setting firmer constraints on the evolution of the most massive, central galaxies from their local abundances and ages
No full textThere is still much debate surrounding how the most massive, central galaxies in the local universe have assembled their stellar mass, especially the relative roles of in situ growth versus later accretion via mergers. In this paper, we set firmer constraints on the evolutionary pathways of the most massive central galaxies by making use of empirical estimates on their abundances and stellar ages. The most recent abundance matching and direct measurements strongly favour that a substantial fraction of massive galaxies with Mstar>3 × 1011?M? reside at the centre of clusters with mass Mhalo>3 × 1013?M?. Spectral analysis supports ages >10 Gyr, corresponding to a formation redshift zform>2. We combine these two pieces of observationally based evidence with the mass accretion history of their host dark matter haloes. We find that in these massive haloes, the stellar mass locked up in the central galaxy is comparable to, if not greater than, the total baryonic mass at zform. These findings indicate that either only a relatively minor fraction of their present-day stellar mass was formed in situ at zform, or that these massive, central galaxies form in the extreme scenario where almost all of the baryons in the progenitor halo are converted into stars. Interestingly, the latter scenario would not allow for any substantial size growth since the galaxy's formation epoch either via mergers or expansion. We show our results hold irrespective of systematic uncertainties in stellar mass, abundances, galaxy merger rates, stellar initial mass function, star formation rate and dark matter accretion histories
Super-massive Black Holes: the missing link in galaxy evolution
Full text linkThe aim of this thesis is to investigate the key points concerning the evolution of the local Super-massive Black Hole (SMBH) population and to understand the origin of the links the SMBH have with their host spheroidal galaxies and dark matter (DM) halos. In fact the tight correlations observed among the SMBH mass, the photometric and dynamical properties of the host galaxy and DM halo, suggest that these systems must have co-evolved during time building up together.
The study of the statistical mass distribution of the local SMBH population and galaxies and their link with the overall AGN statistics are fundamental tools to get important physical insights on the basic average features of SMBH evolution.
Any galaxy formation model must compare with such findings. For this purpose I have worked with the semi-analytical code developed by Granato et al. (2004) to physically model SMBH evolution in galaxies and DM halos, compare model results with empirical derivations and make predictions. In particular, my work has been primarily to tune the parameters and also try to arrange minor modifications, where needed, in order to cope with the variety of the numerous empirical data the model can successfully account for
A matter of measurement: rotation velocities and the velocity function of dwarf galaxies
No full textThe velocity function derived from large-scale surveys can be compared with the predictions of ? cold dark matter (?CDM) cosmology, by matching the measured rotation velocities Vrot of galaxies to the maximum circular velocity of dark matter (DM) haloes Vmax. For Vrot < 50 kms?1, a major discrepancy arises between the observed and ?CDM velocity functions. However, the manner in which different observational measures of Vrot are associated with Vmax is not straightforward in dwarf galaxies. We instead relate galaxies to DM haloes using the empirical baryon-mass to halo-mass relation, and show that different observational measures of Vrot result in very different velocity functions. We show how the W50 velocity function, i.e. using the H i profile linewidth at 50 per cent of peak H i flux to measure Vrot, can be reconciled with a ?CDM cosmology. Our semi-empirical methodology allows us to determine the region of rotation curves that are probed by H i measurements (RHI), and shows that the Vrot of dwarfs are generally measured at a fraction of Rmax, explaining their tendency to have rising rotation curves. We provide fitting formulae for relating RHI and Reff (the effective radius) to the virial radius of DM haloes. To continue to use velocity functions as a probe of ?CDM cosmology, it is necessary to be precise about how the different measures of rotation velocity are probing the mass of the DM haloes, dropping the assumption that any measure of rotational velocity can be equally used as a proxy for Vmax
Interpreting the possible break in the black hole-bulge mass relation
Full text linkRecent inspections of local available data suggest that the almost linear relation between the stellar mass of spheroids (Msph) and the mass of the super massive black holes (BHs), residing at their centres, shows a break below Msph ~ 1010 Msun, with a steeper, about quadratic relation at smaller masses. We investigate the physical mechanisms responsible for the change in slope of this relation, by comparing data with the results of the semi-analytic model of galaxy formation MORGANA, which already predicted such a break in its original formulation. We find that the change of slope is mostly induced by effective stellar feedback in star-forming bulges. The shape of the relation is instead quite insensitive to other physical mechanisms connected to BH accretion such as disc instabilities, galaxy mergers, active galactic nucleus (AGN) feedback, or even the exact modelling of accretion on to the BH, direct or through a reservoir of low angular momentum gas. Our results support a scenario where most stars form in the disc component of galaxies and are carried to bulges through mergers and disc instabilities, while accretion on to BHs is connected to star formation in the spheroidal component. Therefore, a model of stellar feedback that produces stronger outflows in star-forming bulges than in discs will naturally produce a break in the scaling relation. Our results point to a form of co-evolution especially at lower masses, below the putative break, mainly driven by stellar feedback rather than AGN feedback
Selection bias in dynamically-measured super-massive black hole samples: dynamical masses and dependence on Sérsic index
No full textSemi-empirical models of galaxy formation and evolution
No full textWe provide a review on semi-empirical models of galaxy formation and evolution. We present a brief census of the three main modeling approaches to galaxy evolution, namely hydrodynamical simulations, semi-analytic models, and semi-empirical models (SEMs). We focus on SEMs in their different flavors, i.e. interpretative, descriptive and hybrid, discussing the peculiarities and highlighting virtues and shortcomings for each of these variants. We dissect a simple and recent hybrid SEM from our team to highlight some technical aspects. We offer some outlook on the prospective developments of SEMs. Finally, we provide a short summary of this review
The evolution of the M_BH-sigma relation inferred from the age distribution of local early-type galaxies and active galactic nuclei evolution
No full textWe utilize the local velocity dispersion function (VDF) of spheroids, together with their inferred age distributions, to predict the VDF at higher redshifts (0 < z lsim 6), under the assumption that (1) most of the stars in each nearby spheroid formed in a single episode and, (2) the velocity dispersion ? remained nearly constant afterward. We assume further that a supermassive BH forms concurrently with the stars, and within ±1 Gyr of the formation of the potential well of the spheroid, and that the relation between the mass of the BH and host velocity dispersion maintains the form M BH vprop ?? with ? ? 4, but with the normalization allowed to evolve with redshift as vprop(1 + z)?. We compute the BH mass function associated with the VDF at each redshift, and compare the accumulated total BH mass density with that inferred from the integrated quasar luminosity function (LF; the so-called So?tan argument). This comparison is insensitive to the assumed duty cycle or Eddington ratio of quasar activity, and we find that the match between the two BH mass densities favors a relatively mild redshift evolution, with ? ~ 0.33, with a positive evolution as strong as ? gsim 1.3 excluded at more than 99% confidence level. A direct match between the characteristic BH mass in the VDF-based and quasar LF-based BH mass functions also yields a mean Eddington ratio of ? ~ 0.5-1 that is roughly constant within 0 lsim z lsim 3. A strong positive evolution in the M BH-? relation is still allowed by the data if galaxies increase, on average, their velocity dispersions since the moment of formation due to dissipative processes. If we assume that the mean velocity dispersion of the host galaxies evolves as ?(z) = ?(0) × (1 + z)–?, we find a lower limit of ? gsim 0.23 for ? gsim 1.5. The latter estimate represents an interesting constraint for galaxy evolution models and can be tested through hydro simulations. This dissipative model, however, also implies a decreasing ? at higher z, at variance with several independent studie
Massive black holes in galactic nuclei: theory and simulations
No full textMassive black holes are fundamental constituents of our cosmos, from the Big Bang to today. Understanding their formation from cosmic dawn, their growth, and the emergence of the first, rare quasars in the early Universe remains one of our greatest theoretical and observational challenges. Hydrodynamic cosmological simulations self-consistently combine the processes of structure formation at cosmological scales with the physics of smaller, galaxy scales. They capture our most realistic understanding of massive black holes and their connection to galaxy formation and have become the primary avenue for theoretical research in this field. The space-based gravitational wave interferometer, LISA, will open up new investigations into the dynamical processes involving massive black holes. Multi-messenger astrophysics brings new exciting prospects for tracing the origin, growth and merger history of massive black holes across cosmic ages
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