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Register a new userModelling Galaxy and AGN Evolution in the IR: Black Hole Accretion versus Star-Formation Activity
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Added by
Carlotta Gruppioni Dr.
Publication date
2011
fields
Physics
and research's language is
English
Authors
C. Gruppioni
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We present a new backward evolution model for galaxies and AGNs in the infrared (IR). What is new in this model is the separate study of the evolutionary properties of the different IR populations (i.e. spiral galaxies, starburst galaxies, low-luminosity AGNs, unobscured type 1 AGNs and obscured type 2 AGNs) defined through a detailed analysis of the spectral energy distributions (SEDs) of large samples of IR selected sources. The evolutionary parameters have been constrained by means of all the available observables from surveys in the mid- and far-IR (source counts, redshift and luminosity distributions, luminosity functions). By decomposing the SEDs representative of the three AGN classes into three distinct components (a stellar component emitting most of its power in the optical/near-IR, an AGN component due to hot dust heated by the central black hole peaking in the mid-IR, and a starburst component dominating the far-IR spectrum) we have disentangled the AGN contribution to the monochromatic and total IR luminosity emitted by the different populations considered in our model from that due to star-formation activity. We have then obtained an estimate of the total IR luminosity density (and star-formation density - SFD - produced by IR galaxies) and the first ever estimate of the black hole mass accretion density (BHAR) from the IR. The derived evolution of the BHAR is in agreement with estimates from X-rays, though the BHAR values we derive from IR are slightly higher than the X-ray ones. Finally, we have simulated source counts, redshift distributions and SFD and BHAR that we expect to obtain with the future cosmological Surveys in the mid-/far-IR that will be performed with JWST-MIRI and SPICA-SAFARI.
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We present a new suite of hydrodynamical simulations and use it to study, in detail, black hole and galaxy properties. The high time, spatial and mass resolution, and realistic orbits and mass ratios, down to 1:6 and 1:10, enable us to meaningfully compare star formation rate (SFR) and BH accretion rate (BHAR) timescales, temporal behaviour and relative magnitude. We find that (i) BHAR and galaxy-wide SFR are typically temporally uncorrelated, and have different variability timescales, except during the merger proper, lasting ~0.2-0.3 Gyr. BHAR and nuclear (<100 pc) SFR are better correlated, and their variability are similar. Averaging over time, the merger phase leads typically to an increase by a factor of a few in the BHAR/SFR ratio. (ii) BHAR and nuclear SFR are intrinsically proportional, but the correlation lessens if the long-term SFR is measured. (iii) Galaxies in the remnant phase are the ones most likely to be selected as systems dominated by an active galactic nucleus (AGN), because of the long time spent in this phase. (iv) The timescale over which a given diagnostic probes the SFR has a profound impact on the recovered correlations with BHAR, and on the interpretation of observational data.
We use a suite of hydrodynamical simulations of galaxy mergers to compare star formation rate (SFR) and black hole accretion rate (BHAR) for galaxies before the interaction (stochastic phase), during the `merger proper, lasting ~0.2-0.3 Gyr, and in the `remnant phase. We calculate the bi-variate distribution of SFR and BHAR and define the regions in the SFR-BHAR plane that the three phases occupy. No strong correlation between BHAR and galaxy-wide SFR is found. A possible exception are galaxies with the highest SFR and the highest BHAR. We also bin the data in the same way used in several observational studies, by either measuring the mean SFR for AGN in different luminosity bins, or the mean BHAR for galaxies in bins of SFR. We find that the apparent contradiction or SFR versus BHAR for observed samples of AGN and star forming galaxies is actually caused by binning effects. The two types of samples use different projections of the full bi-variate distribution, and the full information would lead to unambiguous interpretation. We also find that a galaxy can be classified as AGN-dominated up to 1.5 Gyr after the merger-driven starburst took place. Our study is consistent with the suggestion that most low-luminosity AGN hosts do not show morphological disturbances.
We present a study of the star formation and central black hole accretion activity of the galaxies hosted in the two nearby (z$sim$0.2) rich galaxy clusters Abell 983 and 1731. Aims: We are able to quantify both the obscured and unobscured star formation rates, as well as the presence of active galactic nuclei (AGN) as a function of the environment in which the galaxy is located. Methods: We targeted the clusters with unprecedented deep infrared Spitzer observations (0.2 mJy @ 24 micron), near-IR Palomar imaging and optical WIYN spectroscopy. The extent of our observations ($sim$ 3 virial radii) covers the vast range of possible environments, from the very dense cluster centre to the very rarefied cluster outskirts and accretion regions. Results: The star forming members of the two clusters present star formation rates comparable with those measured in coeval field galaxies. The analysis of the spatial arrangement of the spectroscopically confirmed members reveals an elongated distribution for A1731 with respect to the more uniform distribution of A983. The emerging picture is compatible with A983 being a fully evolved cluster, in contrast with the still actively accreting A1731. Conclusions: The analysis of the specific star formation rate reveals evidence of on-going galaxy pre-processing along A1731s filament-like structure. Furthermore, the decrease in the number of star forming galaxies and AGN towards the cluster cores suggests that the cluster environment is accelerating the ageing process of galaxies and blocking further accretion of the cold gas that fuels both star formation and black hole accretion activity.
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Large extragalactic surveys allow us to trace, in a statistical sense, how supermassive black holes, their host galaxies, and their dark matter halos evolve together over cosmic time, and so explore the consequences of AGN feedback on galaxy evolution. Recent studies have found significant links between the accretion states of black holes and galaxy stellar populations, local environments, and obscuration by gas and dust. This article describes some recent results and shows how such studies may provide new constraints on models of the co-evolution of galaxies and their central SMBHs. Finally, I discuss observational prospects for the proposed Wide-Field X-ray Telescope mission.
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