The impact of AGN on their host galaxies

35 Pages·2013·7.3 MB·English

by  Davo Alexander

The impact of AGN on their host
galaxies

David Alexander (Durham)
Talk Overview

Introduction and Motivation�

AGN-star formation connection in distant Universe
(need to account for AGN varabiliity)�
�

Do AGNs suppress star formation?�
(need for good source statistics)

�
�
Do we see large-scale outflows in distant AGNs?�
(need more observations!)
Why investigate the impact of AGN on host galaxy?

M /M ~10-3
bh sph
AGN!
y
t
i
v
i
t
c
a

N
G
A

:
r
e
v
i
r
D

]
s
s
a
m

H
B
!
Star formation
[
[Spheroid mass] Driver: Star formation (gas accretion)
See also, for example, Magorrian et al. (1998); Ferrarese & Merritt (2000); Gebhardt et
Haring & Rix (2004)!
al. (2000); Tremaine et al. 2002; Marconi & Hunt (2003); Gultekin et al. (2009)!
Both star formation and AGN activity driven by
cold gas – so why any surprise of a connection?

Star formation: collapse of cold
molecular cloud

AGN activity: accretion of (originally
cold) gas onto a black hole

There is plenty of cold gas over ~10 kpc scales in active galaxies �
– the potential to form stars and grow the central black hole
The surprise: the huge difference in size scales

Black Hole!
Accretion disk:!
<0.01 pc!
Large-scale galaxy
environment (most of the gas)!
Of order ~10 pc!
(region of BH influence)!
Any connection between the black hole
Of order ~1-10 kpc!
and the galaxy is over size scales of ~6-9
orders of magnitude!!
Black-hole-galaxy: ~109 difference in size scale (grape-Earth) – how can
one know about or influence the other?
A leading contender: outflows/winds driven by the AGN

Springel et al. (2005)!
Alexander & Hickox (2012)!
Di Matteo et al. (2005)
The potential impact of AGN activity can be simply assessed by
considering the amount of energy it takes to build a massive black hole

:
2
E = fM c
BH BH
Where f is the mass-to-energy efficiency conversion. �
For a 108 solar mass black hole, E ~2x1061 ergs for f=0.1

BH
Compare this to the binding energy of the galaxy spheroid

:
2
0.4M
Sph
E ≈
Sph
R
Sph
For M ~1011 solar masses and R ~4 kpc, E ~1059 ergs

Sph Sph Sph

If ~1% of the mass accretion is released in an outflow and couples to the
host-galaxy gas then the galaxy spheroid could be unbound

!
Important component I won’t directly focus on

Mechanical outflows: may be responsible
for suppressing production of most
massive galaxies by heating the gas

Bower et al. (2006)!
Low accretion rate systems and
by definition not active.
The impact of AGN activity on the host galaxy:�
the key components