Hot and Cold Gas Accretion Modes and Feedback Processes in Radio-

loud Active Galaxies

Dan Evans (Harvard)Martin Hardcastle (U. Hertfordshire)

Judith Croston (U. Hertfordshire)

Standard Picture of Radio-Loud AGN• Luminous accretion disk surrounded by “torus”• X-ray continuum emission in the nuclei of RL AGN consists of:

– “Radio-quiet” accretion-related component– “Radio-loud” jet-related component

Which dominates the X-ray emission?

The Fanaroff-Riley Dichotomy

Is the dichotomy• Environmental?

• Interaction of the jet with ambient medium either causes the jet to decelerate (FRI) or propagate supersonically to large distances (FRII)

• Intrinsic?• Properties of the central engine govern large-scale

morphology (FRI/FRII)

Low- and High-Excitation Radio Galaxies

• FRIs are almost entirely low-excitation

• Significant population of low-excitation FRIIs at 0.1<z<0.5

• Encompass all NLRGs and BLRGs

• Almost entirely FRIIs• A handful of FRIs, too

Based on strength of high-excitation lines , e.g., [OIII] (Laing et al. 1994)

3CRR z<0.5 Sample Results• Chandra observations of the nuclei of

40/86 z<0.5 3CRR sources• X-ray emission of LERGs is dominated by a

parsec-scale jet, with little or no intrinsic absorption

• X-ray emission of HERGs is dominated by an accretion flow and is heavily absorbed (except BLRGs)

• Each HERG also has an unabsorbed component of X-ray emission jet origin

• See Evans et al. (2006, ApJ, 642, 96); Hardcastle et al. (2006, MNRAS, 370, 1893)

e.g. 3C 264(LERG FRI)

e.g. 3C 403(HERG FRII)

Jet

Jet Accn

Where is the torus in LERGs?• Cannot determine presence or

absence of torus directly• Assume there exists a ‘hidden’

accretion component obscured by a torus of intrinsic absorption 1023 atoms cm-2

• Find upper limits to luminosity of accretion-related emission

• Data don’t exclude luminosities of LX,acc ~ 1039-1041 ergs s-1 (X,Edd ~ 10-7-10-5)

• Substantially lower than HERGs, LX,acc ~ 1043-1044 ergs s-1

(X,Edd ~ 10-3-10-2)• Implies accretion flow radiatively

inefficient (e.g., ADAF)e.g. 3C 274 (M87)

Accr

etion

Jet

Luminosities

White = LERG Red = NLRGGreen = BLRG; Blue = quasarCircle => FRI

Line goes through FRII NLRG

Limits assume NH = 1023 cm-2

• For a given 178-MHz radio power, LERGs produce significantly less radiative accretion luminosity

• Pointing to a dichotomy in the excitation properties of AGN? i.e., not a nuclear F-R dichotomy

Speculation: Hot vs. Cold Accretion

Bondi accretion vs. jet power in nearby cluster-center radio galaxies (Allen et al 06)

Hi-excLow-exc

Esin et al. (1997);Körding, Falcke, & Markoff (2002)

Accretion flow

Jet

mEddmcrit m

LX Low state

High state

• Fundamentally different accretion mode in LERGs and HERGs

• HERG features (disk, torus, etc.) require cold fuel

• Could LERG features (radiatively inefficient accretion, ADAF) require a hot gas supply?

• Could all LERG be powered by ‘hot-mode’ accretion and all HERG by ‘cold-mode’?

• Discussed in detail by Hardcastle et al. (2007, astro-ph/0701857)

Allen et al. (2006)

Testing Hot-Mode Accretion

Compare Bondi accretion power

with jet power

Testing Hot-Mode Accretion

Black hole mass vs. K-band bulge luminosity for spirals and ellipticals (Marconi & Hunt 2003)

Compare Bondi accretion power

with jet power

Testing Hot-Mode Accretion

• Assume central environment of all sources is similar to 3C 31

• Good approximation for LERGs• HERGs likely to have less galaxy-

scale gas (Croston et al. in prep.)

Density as a function of radius for model fits to X-ray observations of 3C31 (Hardcastle et al. 2002)Compare Bondi

accretion power

with jet power

Testing Hot-Mode Accretion

Compare Bondi accretion power

with jet power

1) Inflating cavitiese.g. Allen et al. (2006)

2) Models of jet deceleratione.g. Laing et al. (2002)

3) Willott et al. (1999) relation

• FRI sources (circled) lie close to the line of equality, as expected from earlier calculations

• Many LERG FRIIs lie close to the line too• The majority of HERGs are a long way away from being able to be powered

by hot-mode accretion --> additional (cold) gas needed

Bondi rates

• Both FRI and FRII kpc-scale structures can be produced by nuclei with low accretion luminosity (LERGs)

• Conversely, FRIs and FRIIs can be produced by HERGs

• FRI/FRII dichotomy entirely due to environment and jet power

• Excitation dichotomy controlled by accretion mode

3C 388 (LERG FRII)Kraft et al. (2006)

Cen A (HERG FRI)Kraft et al. (2002)

• True ‘feedback’ between AGN and hot phase requires the AGN to be controlled by the hot phase. Only directly possible in hot mode

• In cold mode accretion the radio source can blow away its atmosphere without affecting its fuel supply

• Consistent with observations of FRIIs in poor environments which show work done/energy stored comparable to total thermal energy of atmosphere 3C 33 (HERG FRII)

Kraft et al. (2007)

• Hot-mode sources need massive central black holes and a good supply of hot gas – they will tend to inhabit the most massive galaxies in relatively rich environments

• Cold-mode sources’ power comes from accretion of cold gas so they can inhabit poorer systems. Merger activity important

• Qualitatively good agreement with known facts

3C 66B (LERG FRI)Croston et al. (2003)

Cen A (HERG FRI)

Summary

• The excitation of an AGN is a vital parameter in unification schemes

• X-ray emission of LERGs is unabsorbed and dominated by a parsec-scale jet

• X-ray emission of HERGs is heavily absorbed and accretion-related

• Bondi accretion of hot gas sufficient to power LERGs• Bondi accretion of hot gas insufficient to power HERGs• Additional supply of cold gas need to power HERGs• The Fanaroff-Riley dichotomy remains a consequence of the

interaction between the jet and the environment

Luminosity-Luminosity Correlations

JetJet

• Consider LX and LR

• Considerable scatter• Strong LX-LR correlation for

unabsorbed X-ray components

• Suggests X-ray emission affected by beaming in same manner as radio

• Origin of X-ray emission in pc-scale jet (outside any torus)

• Components with NH ~ 1023 lie above trendline

• As does 3C 390.3, unobscured BLRG

• All have Fe K lines• Accretion-dominated and

surrounded by a torus

• HERGs are dominated by these components

Luminosity-Luminosity Correlations

NH ≤ 5 x 1022

Jet