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The evolving role of radio-AGN feedback
Philip Best IfA Edinburgh
Cambridge, 5th Sept 2013

Sunday, October 6, 2013


Motivation
"AGN feedback" is currently postulated to explain many issues in galaxy evolution

Supernovae & ionising background

(Radio) AGN

In particular, recurrent radio-loud AGN activity is thought to be responsible for the latter two, and hence a strong driver of the "quenching" of massive galaxies. But

· · ·

Black-hole - bulge mass relation Avoidance of over-production of massive galaxies "Old, red and dead" appearance of massive ellipticals

· · ·

what type of radio-AGN activity? how and when is the radio-AGN activity triggered? how does this radio-AGN activity evolve over cosmic time?

Sunday, October 6, 2013


"Standard" quasar-like AGN
"Standard" AGN have:

· · · · ·

Luminous accretion disk (with X-ray corona) Bright line emission (ionised by disk) Dusty obscuring torus (emits in IR/sub-mm) Orientation-dependent observed properties Sometimes, extended radio jets

Sunday, October 6, 2013


Another class of AGN
Other AGN, exemplified by weak radio sources, don't fit this scheme:

Sunday, October 6, 2013


Another class of AGN
Other AGN, exemplified by weak radio sources, don't fit this scheme: - No strong emission lines
(Hine & Longair 1979)

Sunday, October 6, 2013


Another class of AGN
Other AGN, exemplified by weak radio sources, don't fit this scheme: - No strong emission lines - No IR torus emission - No accretion-related X-ray emission

Sunday, October 6, 2013


Another class of AGN
Other AGN, exemplified by weak radio sources, don't fit this scheme: - No strong emission lines - No IR torus emission - No accretion-related X-ray emission - Only evidence of AGN activity is the jet

Sunday, October 6, 2013


Why different AGN?
Accretion models predict a change in the nature of accretion flows at low fractions of Eddington:
Merloni & Heinz 2008

· · ·

high accretion - optically thick, geometrically thin disk; strong radiative emission, sometimes also with jets low accretion - advection dominated accretion flow; most energy comes out as jets in "kinetic" mode. cf. microquasar modes

Sunday, October 6, 2013


Local radio AGN populations
Best & Heckman 2012, MNRAS, 421, 1569

· · ·

Cross-matched SDSS DR7 with radio catalogues

-

sample of >18,000 radio sources

Classify all radio galaxies as high- or low excitation
use SDSS emission line ratios (where possible) use [OIII] 5007 line equivalent width

Both classes are found over most of the range of luminosity, but low-excitation (radiatively inefficient) sources dominate at low powers.

Sunday, October 6, 2013


Mass dependence of radio-AGN classes
Janssen et al 2013

The fraction of galaxies that host low-excitation radio sources is a very strong function of galaxy mass. The fraction of galaxies that host high excitation sources varies only weakly with mass, and less on radio power; these are similar to optical AGN It is the radiatively inefficient LERGs that have the strong mass-dependence (and also other properties, e.g. red colours) indicative of "maintenance mode" feedback
Sunday, October 6, 2013


Testing accretion mode picture
Best & Heckman 2012, MNRAS, 421, 1569

Estimate the Eddington-scaled accretion luminosities of all of the classified radio-AGN as

f

Edd

= L / LEdd = (L

rad

+L

mech)

/ LEdd

· · ·

Estimate black hole masses from velocity dispersions Calculate radiative luminosity, scaling from [OIII] 5007

-

corrected for reddening using H

/H

line ratio

calibrated using quasars (cf. Heckman et al 2004) estimates from "X-ray cavities" and from minimum energy

Estimate mechanical (jet) luminosity from radio luminosity

Sunday, October 6, 2013


Accretion modes of low-z RGs

Best & Heckman 2012, MNRAS, 421, 1569

Putting together radiative and mechanical luminosities and black hole mass estimates for the SDSS radio sample, we determine Eddington-scaled accretion luminosities (± 0.8 dex / source)

· ·

Clear dichotomy between two source classes. Good match to the theoretical expectations of advection dominated accretion flows setting in below few % Eddington

the

Sunday, October 6, 2013


Origin of different classes?
`Standard' AGN (`quasar-mode' or `radiative' or `cold-mode' or HERG....) fuelled through `standard' accretion disks

· · · · ·

need a plentiful supply of cold gas mergers/interactions or secular evolution origin for gas

`Other' radio sources (LERG, or `radio-mode', or `hot-mode' or `radiatively inefficient'....) fuelled at low rate via ADAF
low rate can be supplied by cooling hot gas in galaxy/cluster halo offers possibility of radio-AGN feedback cycle in local Universe, time-averaged radio-AGN energetic output is sufficient to (over-?) balance radiative cooling from halo

Sunday, October 6, 2013


Cosmic evolution of radio-AGN
To determine the evolving importance of radio-AGN feedback we need to measure cosmic evolution of the LERG population We combined 8 radio source samples at 0.5
Sunday, October 6, 2013


Cosmic evolution of radio-AGN
Best et al 2013, in prep

This has allowed us to derive the luminosity functions of the two separate populations, to compare with the local RLFs

High-excitation (efficient) AGN evolve by factor ~7 at all powers LERGs show no evolution at low power, but like HERGs at high-P
Sunday, October 6, 2013


Cosmic evolution of radio-AGN
Best et al 2013, in prep

Samples large enough to separate the radiatively inefficient AGN (LERGs) into two sub-slices in redshift. LERG space densities decline at z > 0.7.

Sunday, October 6, 2013


Evolving radio-AGN heating rate
Converting radio luminosity functions into heating rates, assuming the local relation, the "feedback" energetic output of radio-AGN peak at z~0.5 and then declines.

Sunday, October 6, 2013


Summary · · · · · ·
Not all AGN follow the "standard" accretion disk picture. A population of low accretion rate, radiatively inefficient, radio sources, dominates the low-luminosity end of RLF These sources are in massive galaxies, and are probably fuelled directly or indirectly from the hot gas halo. Low luminosity radio source activity is highly-recurrent with a fast duty cycle, especially in the most massive gals In the local Universe the energetic output (over-?) balances cooling rates, leading to feedback cycle. The cosmic radio-AGN heating rate increases out to z~0.5, but then peaks and declines to higher redshift.

Sunday, October 6, 2013