Modeling AGN properties in the local Universe
Federico Marulli
Dipartimento di Astronomia
Università degli Studi di Bologna
Modeling active galactic nuclei: ongoing problems for the faint-end of
the luminosity function
F.Marulli, E.Branchini, L.Moscardini, M.Volonteri (MNRAS,375,649)
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Contents

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 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 relations
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
AGN bolometric luminosity function
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Semi-analytic model
Method

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: M accr  M halo
  7 10 6

E2: M accr  k  vc

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
5
k  k ( z )  0.15(1  z )  0.05
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Semi-analytic model
Method

Data and equations
220 binary merger trees of parent halos with masses in the range (1.43e11,1e15 Msun)
 t
1 
M BH (t  t )  M BH (t ) exp  
f Edd (t )

 t Edd
L

f Edd (t ) M Edd c 2



 L 
dt AGN
|  | tQ  9 
d log L
 10 L 

1
df Edd (t ) f Edd
(t )  M Edd c 2 



dt
|  | tQ  109 L 
 AGN
beff ( z ) 

 DM


0
b( M halo , z ) ( M halo ( LB  Lmin, B ), z )dM halo


0
 ( M halo ( LB  Lmin, B ), z )dM halo
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Semi-analytic model
Luminosity function
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Semi-analytic model
Luminosity function
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Semi-analytic model
Luminosity function
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Semi-analytic model
Biasing function
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Conclusions

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 of
the hydrodynamical simulations by Hopkins et al. 2005
→ hierarchical models in which accretion is driven only by major mergers cannot describe the
likely
local properties of AGNs, and accretion episodes not triggered by such mergers are
necessary
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
LQSO-Mhalo
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
Mbh-σ
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
VHM plots
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
N(M)
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna
VHM equations
dN
1 M 0 1 d c d M2
( z  z0 ) 
z
1.5
dM
2 M S dz dM
S   M2 ( z )   M2 0 ( z0 )
 ( M halo )
N QSO ( M halo ) 
dN / dM halo
Federico Marulli, Dipartimento di
Astronomia, Università di Bologna