Radio Mode Feedback in Giant Elliptical Galaxies

Paul Nulsen (CfA), Christine Jones (CfA), William Forman (CfA), Eugene Churazov (MPA),

Laurence David (CfA), Brian McNamara (Waterloo),Steven Murray (CfA)

Radio Galaxies in the Chandra Era

AGN Outbursts in Giant EllipticalsIn an AGN outburst, jets inflate radio lobes

displace surrounding gas drive shocks

In a hot atmospherelobes make X-ray “cavities”shocks cause breaks in surface

brightnessReview McNamara & Nulsen (2007)

M84 (Finoguenov & Jones 2001)

NGC 4552 (Machacek et al. 2006)NGC 4636 (Jones et al. 2002)

Outbursts are seen in the hot (X-ray emitting) atmospheres of

galaxy clustersgalaxy groupsisolated

ellipticals

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Radio Galaxies in the Chandra Era

Range of Scales

NGC 5813, z = 0.0066, 1 arcmin ≈ 9.3 kpc

Dominant member of a subgroup of the NGC 5846 group (Mahdavi et al. 2005).

Most energetic outburst known is MS0735.6+7421 (McNamara et al. 2005)

Centre of 4.5 keV cluster (Gitti et al. 2007)

z = 0.216, 1 arcmin ≈ 210 kpc

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Radio Galaxies in the Chandra Era

Impact of AGN OutburstsOutbursts occur in systems with short central cooling times (tcool < H0

-1, often < 109 yr).

Average outburst powers in clusters similar to radiative losses (Bîrzan et al. 2004; Dunn & Fabian 2006; Rafferty et al. 2006).

-> AGN feedback (radio mode, eg Croton et al. 2006) can prevent cooling and star formation.

But some systems with short cooling times show no signs of an outburst.

Also shock formation requires intermittency.

-> Outbursts are intermittent

Require an unbiased, complete sample to measure mean power, intermittency, etc.

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Rafferty et al. (2006)

Radio Galaxies in the Chandra Era

Nearby Elliptical Galaxy SampleJones et al. (in prep.) have collected X-ray data for a sample of ≈ 160 nearby elliptical galaxies (expanded from Beuing et al. 1999; O’Sullivan et al. 2001).

After removal of point sources and unresolved emission from X-ray binaries, 109 show X-ray emission from diffuse hot gas.

Of these, 27 have signs of AGN outbursts (cavities and/or shocks) - underestimated. AGN jet powers determined using methods of Bîrzan et al. (2004), Rafferty et al. (2006):

energy input per cavity taken as pV3 age estimates: tsonic, tbuoy, trefill

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Radio Galaxies in the Chandra Era

AGN Heating vs CoolingCavity power vs cooling power for elliptical galaxies with outbursts.

tsonic – blue, tbuoy – red, trefill – green

Cooling power is LX(r < rcool), where tcool(rcool) = 7.7 Gyr (look back time to z = 1).

Dashed lines show Pcav = LX(rcool), forenergy inputs of 1pV, 4pV and 16pV per cavity (top to bottom).

…cavities detected in only 25% of galaxies with hot gas.

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Radio Galaxies in the Chandra Era

AGN Heating vs CoolingCavity power vs cooling power for elliptical galaxies with outbursts.

tsonic – blue, tbuoy – red, trefill – green

Cooling power is LX(r < rcool), where tcool(rcool) = 7.7 Gyr (look back time to z = 1).

Dashed lines show Pcav = LX(rcool), forenergy inputs of 1pV, 4pV and 16pV per cavity (top to bottom).

…cavities detected in only 25% of galaxies with hot gas.

Correct UGC 408 by setting distance from center to semimajor axis of cavity.7/9/08

Radio Galaxies in the Chandra Era

AGN Heating vs CoolingCavity power vs cooling power for elliptical galaxies with outbursts.

tsonic – blue, tbuoy – red, trefill – green

Cooling power is LX(r < rcool), where tcool(rcool) = 7.7 Gyr (look back time to z = 1).

Dashed lines show Pcav = LX(rcool), forenergy inputs of 1pV, 4pV and 16pV per cavity (top to bottom).

…cavities detected in only 25% of galaxies with hot gas.

AGN dominates

Cooling dominates

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Radio Galaxies in the Chandra Era

Global EnergeticsIntermittent – compare powers for whole sample (109 galaxies with hot gas):

Total cavity powers (1pV per cavity):Psonic = 2.6×1043 erg s-1, Pbuoy = 2.9×1043 erg s-1, Prefill = 1.5×1043 erg s-1.

Total cooling power for 109 galaxies:LX,cool = 8.7×1043 erg s-1.

Ratio of totals, <LX,cool>/<Pcav> = 3.3, 3.0, 5.6 (sonic, buoy, refill).

Enthalpy of cavity dominated by relativistic gas is 4pV.

Add extra energy in shocks, sound, particles, etc.

Cavities are under-counted.

-> Very plausibly: time averaged AGN power can balance cooling in these galaxies, soradio mode feedback can limit star formation in nearby gE sample

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Radio Galaxies in the Chandra Era

Energetics vs Size

Order by cooling power, LX(rcool).

Ratio of cumulative cooling power (LX,cool) to cumulative cavity power (Pcav) plotted vs LX,cool:

For energy of 4pV per cavity, mean AGN power matches or exceeds cooling power over full range.

Noisy (intermittent) but broadly consistent with a constant ratio, independent of cooling power (size).

4

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Radio Galaxies in the Chandra Era

Duty Cycle vs Size

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Cumulative fraction of gE’s with outbursts vs cooling power.

For 107 galaxies, 27/107 ≈ 0.25.

Cumulative values consistent with fixed fraction of 0.25 for whole sample.

Marked range is ±1σ for binomial samples with p = 0.25.

Radio Galaxies in the Chandra Era

Conclusions• AGN outbursts can occur in any elliptical galaxy at the center

of a hot atmosphere• Outbursts are intermittent, on ~1/4 of the time, with average

power close to cooling power• Radio mode AGN feedback can limit cooling and star

formation in these galaxies, as well as in clusters

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