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Federico Marulli, Dipartimento di Astronomia, Università di Bologna
Modeling AGN properties in Modeling AGN properties in the local Universethe local Universe
Federico MarulliDipartimento di Astronomia
Università degli Studi di Bologna
Modeling active galactic nuclei: ongoing problems for the faint-end of Modeling active galactic nuclei: ongoing problems for the faint-end of the luminosity functionthe luminosity function
F.Marulli, E.Branchini, L.Moscardini, M.Volonteri (MNRAS,375,649) F.Marulli, E.Branchini, L.Moscardini, M.Volonteri (MNRAS,375,649)
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
ContentsContents
Aim of this work Compare the predictions of standard theoretical models to the most recent observational
data at low redshifts (z<2)
Observational data Luminosity function (LF) Clustering
Theoretical models Semi-analytic methods Standard assumption: QSO emission triggered by galaxy mergers
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
General feauturesGeneral feautures QSOs first discoveries: Schmidt,
Greenstein&Matthews in the early 60’s
Accretion of mass onto supermassive black holes as the power mechanism for QSOs emission (Lynden Bell 1969)
Supermassive black holes are a ubiquitous constituent of spheroids in nearby galaxies (Kormandy&Richstone 1995)
The QSO population evolves with cosmic time: the QSO space density above a given luminosity increases by a factor of ~50 from the present to z~2.5, then decreases to z~5 (for istance Richards et al. 2006)
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
BH scale relationsBH scale relations
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
AGN bolometric luminosity AGN bolometric luminosity functionfunction
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
Semi-analytic modelSemi-analytic modelMethodMethod
Assumptions Hierarchical structure formation: EPS model (Monte Carlo procedure) QSO phenomenon is triggered by halo-halo major mergers (P:=0.1) BHs seeds: M=150 Msun, z=20, Mhalo=1.6e7 Msun (3.5 σ)
Kind of accretion Coalescence of BH binary (neglected) Gas accretion
E1:
E2:
B: early stage of super critical accretion (Bondi-Hoyle; z>12)
H: AGN feedback is included following the outcome
of recent hydrodynamical simulations of galactic mergers
haloaccr MM
5caccr vkM 05.0)1(15.0)( zzkk
6107
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
Semi-analytic modelSemi-analytic modelMethodMethod
Data and equations
220 binary merger trees of parent halos with masses in the range (1.43e11,1e15 Msun)
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Federico Marulli, Dipartimento di Astronomia, Università di Bologna
Semi-analytic modelSemi-analytic modelLuminosity functionLuminosity function
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
Semi-analytic modelSemi-analytic modelLuminosity functionLuminosity function
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
Semi-analytic modelSemi-analytic modelLuminosity functionLuminosity function
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
Semi-analytic modelSemi-analytic modelBiasing functionBiasing function
Federico Marulli, Dipartimento di Astronomia, Università di Bologna
ConclusionsConclusions We confirm the success of simple semi-analytic models in reproducing both the AGN
bolometric LF at 1 < z ≤ 2, i.e. around the peak of activity, and their clustering, quantified by the biasing function, at z ≤ 2
As pointed out by several previous analyses, problems occur at lower redshifts, where hierarchical models systematically overestimate the number density of bright AGNs and underestimate the faint ones
Comparing bolometric LFs rather than the optical or hard X-rays ones allows to spot significant discrepancies already at moderate redshifts z~1, i.e. earlier than what was found in previous analyses (e.g. Marulli et al. 2006)
The underestimating of faint AGNs looks like a serious problem that we have tried to tackle
by assuming a time-dependent Eddington ratio, as suggested by the outcome ofthe hydrodynamical simulations by Hopkins et al. 2005
→ hierarchical models in which accretion is driven only by major mergers cannot describe the local properties of AGNs, and accretion episodes not triggered by such mergers are likely necessary