X-ray Signatures of Feedback in Intracluster Gas

Megan Donahue

Michigan State University

Collaborators: Mark Voit, Ken Cavagnolo, Steven Robinson, Don Horner (GSFC)

X-ray Signatures of Feedback

• Metals in the ICM

• The ICM Luminosity - Temperature relationship.

• ICM entropy profiles and ICM bubbles.

Clusters of galaxies

• Most massive, gravitationally-bound structures in the universe (~1015 Mo)

• Hot gas outweighs the stars by a factor ~10

• Dark matter outweighs the baryons by a factor ~ 8.

ICM enriched on all scales

• 22 clusters w/Beppo-SAX

• Consistent Fe abundances

• Central excess consistent w/production

by BCG. DeGrandi et al. 2001; 2004

ICM enriched at high redshift

• Little evolution seen between z=0.3-1.3.

Tozzi et al. 2003; Ettori, et al. 2005

Abundance Patterns (Tamura et al. 2004)

• [Si/Fe], [S/Fe] solar • [O/Fe] 0.4-0.7 solar in core of

cool clusters; solar elsewhere.

• No trend with T > 2 keV• Consistent with Ia and core-

collapse supernova yields + star formation rates scaled from the field.

(See ASCA results in Baumgartner et al. astro-ph/0309166 for contrary view.)

XMM EPIC & RGS spectra, 22 clusters

ICM Luminosity - Temperature Relation

Gravity-only physics predicts L ~ T2.

Allowing radiation to cool the gas modifies the relation.

e.g. Voit & Bryan 2001

Galaxy Formation and the ICM

• Cooling and condensation into stars brings the L-T relation into agreement w/observations.

• However, cooling alone produces too many stars (Rees & White 1978; Balogh 2001).

• Star formation contributes metals and energy to the ICM: this feedback alone may regulate star formation in most galaxies.

Galaxy Formation and the ICM: Questions

• Even with feedback from star formation, simulations still predict too much star formation in central dominant galaxies (e.g. Kravtsov 2005).

• Feedback in “cooling flows”: the ICM in the centers of most X-ray clusters are radiating too brightly to be supported without additional energy input.

“Cooling Flows”

• Clusters with short central cooling times (tc<tH).

• Regular, relaxed, luminous X-ray clusters with peaked central X-ray surface brightness.

• Fairly common, often with central radio sources and H nebulae in their cores.

• The radiation losses must be stabilized by feedback.

Observed “cooling flow”

spectra (XMM)

• Peterson et al. 2003

• FeXVII and other lines from 1 keV gas not present.

• Two-temperature or “truncated” cooling flow (at ~T/3 - T/2)

Cluster gas cools…

• Temperature gradients from Chandra and XMM observations.

• Mass cooling rates closer to star formation rates.

• Gas cooler than ~1 keV not seen or is very faint.

• The cooling times are still short.• What keeps this gas from cooling further?

Hydra Az=0.0522

50 kpc

Radio Sources & Cluster Cores• Can AGN balance radiative

cooling in cluster cores?• Bubbles in the ICM:

(McNamara, Sarazin, Blanton)• Heating occurs, but it’s not clear

how the AGN compensates for radiative losses.

• AGN may be the primary culprit in quenching the cooling in cluster cores: but how to tell?

Abell 2052z=0.0353

50 kpc

Radio-quiet cluster cores

Peres et al. 1998:• 23 clusters with cooling rates > 100 solar masses/year• 13: emission line nebulae & strong central radio source• 2: strong central radio source but no optical line

emission (A2029, A3112)• 3: emission lines but weak central radio source. (A478,

A496, A2142)• 5: no emission lines and little or no radio activity.

(A644, A1650, A1651, A1689, A2244)

Radio-quiet cluster cores

Peres et al. 1998:• 23 clusters with cooling rates > 100 solar

masses/year• 13: emission line nebulae & strong central radio

source• 2: strong central radio source but no optical line

emission (A2029, A3112)• 3: emission lines but weak central radio source.

(A478, A496, A2142)• 5: no emission lines and little or no radio activity.

(A644, A1650, A1651, A1689, A2244)

Chandra Observations

• Chose 2 symmetric, relaxed clusters without radio sources, A1650 and A2244.

• ACIS-S observations sufficient to obtain >150,000 counts for radial deprojection of spectra and surface brightness.

• Temperature and metallicity gradients measured at lower resolution than density gradient.

A2244 & A1650

• Feedback free?

• Radio quiet -- upper limits or detections a factor of 30 or more below the others

• Z = 0.095 and 0.085

• KT ~ 5-6 keV

What might have been:

• Fossil radio lobes and/or X-ray cavities suggestive of earlier radio activity.

• Temperature gradients sufficient to quench cooling via conduction.

• Very low central entropy values, suggesting that these clusters are on the verge of a heating episode.

What is• No fossil lobes out to

~100 kpc

A1650

A2244

Donahue, et al. 2005

What is

• No temperature gradients: limited, if any, conduction.

Donahue, et al. 2005

Entropy

• Specific entropy (Tn-2/3) is more closely related to heating and cooling than temperature alone.

S = (Heat)/T = (3/2) Nk[ ln(Tn-2/3)] – Only radiative cooling can reduce entropy– Only heat input (e.g. shocks) can increase entropy– Compression in a gravitational potential changes T but not

Tn-2/3 (adiabatic).– S is directly related to tcool (small S(T), short tcool)– Convective stability condition: dS/dr > 0

• Cooling time tc = (14 Gyr) (S/81 keV cm2)3/2 (TkeV)-1

Entropy Gradients

• Cool cores with feedback evidence show a remarkable consistency in their entropy profiles:

• S(r) = S0 + (r/r1)

– S0 ~ 10 keV cm2

~ 0.9 - 1.3

• is about what one expects as a result of structure formation outside the core (but not necessarily inside the core).

• Almost all have non-zero S0.

Interpretation of profiles

• Similarity of profiles could be used to argue against episodic heating.

• No evidence for entropy inversions r > 10 kpc: suggests energy injection can’t just happen at the center.

• Entropy floors, small entropy inversions, bubbles show current energy injection.

Iron Gradients

• Significant iron gradients, increasing toward the core measured in most of these systems.

• The presence of a gradient suggests lack of disturbance (e.g. major mergers.)

Quasi-stable core gas?

What do we see?• High central entropy! 35-50 keV cm2

What do we see?• T~5-6 keV => tcool > 109 years

Comparison

LR vs. Central Entropy LR vs. Power-Law Slope

Significant Iron Gradients

What happened?

• These cluster cores have not yet cooled to low entropy, and will trigger an outburst in the future.

OR

• The AGN in these clusters have a very low duty cycle, requiring enormous energy injection by AGN in the past.

Do radio jets heat the ICM?

Perseus Cluster & 3C 84 Sound Waves in Perseus

10 kpc

Dramatic Heating Events

MS0735 (McNamara et al.) Hydra A (Nulsen et al.)

AGN Heating in Groups

Radio-loud groups (circles) tend toward the low-L, high-T side of L-T relation

Croston et al. 2004

Chandra Entropy Profiles

Core entropy profiles very regular

Entropy inversions are minor and lie atr < 10 kpc

Episodic Heating

t 108 yr (K / 10 keV cm2)3/2 (T / 5 keV)-1

• Heating episodes required every ~108 yr• Central entropy level remains near input

level for most of duty cycle• Central entropy input cannot greatly

exceed 10-20 keV cm2

Entropy Jump Condition

K2 + 0.84 K1

K - 0.16 K1

v2

3(4)2/3

v2

3(4)2/3

Core Density Structure

Core density profile: (r) ~ 1/r

(r) = r (r)

~ 3 x10-3 g cm-2

Zones of AGN Heating for r ~ const.

• Luminosity dominated: L ~ r2v3

K ~ 29 keV cm2 L452/3 3

-4/3

• Energy dominated: E ~ r3v2

K ~ 22 keV cm2 E59 3-5/3 r10

-4/3

• Bubble dominated: E ~ Vbub |dP/dr| r

K ~ 6 keV cm2 E59 3-5/3 (r/rinj)-0.18 r10

-4/3

Chandra Entropy Profiles

Core entropy profiles very regular

Entropy inversions are minor and lie atr < 10 kpc

Beyond the Core (r2 ~ const)

• Sustained Luminosity: L ~ r2v3

v ~ 1600 km s-1 L461/3 (T/5 keV)

-1/3

K / K ~ 0.4 L462/3 (T/5 keV)-5/3

Beyond the Core (r2 ~ const)

• Sustained Luminosity: L ~ r2v3

v ~ 1600 km s-1 L461/3 (T/5 keV)

-1/3

K / K ~ 0.4 L462/3 (T/5 keV)-5/3

Preserves shape of original K profile!

Entropy Profiles

• Cooling:

Breaks self-similarity

Its entropy scale determines M-T, L-T relations• Feedback:

Prevents overcoolingWhat elevates entropy at large radius?

• Core Profiles:

Suggest AGN heating (~1045 erg s-1 , ~108 yr)Extended outburst can elevate entire profile

AGN heating?

• Yes!

• AGN are almost certainly the primary stabilizing mechanisms for cooling cores at z~0.

Next Work

• Complete entropy profile extraction on other radio quiet clusters (almost done).

• Test idea that cooling rates ~ star formation rates with RGS and Astro E-2 spectra (faint Fe XVII and O VII lines should be present.)

• Test deprojection assumptions with realistic hydro simulations.

Conclusions• Recent ICM abundance measurements show

enrichment throughout the cluster.• ICM abundance evolution since z~1.3 slow;

consistent with supernova rates.• Central entropies of nearby clusters with short

central cooling times are higher in clusters without radio sources.

• Cooling and star formation explain the ICM L-T relation (at least at high T).

• AGN are required to complete the story to regulate star formation in cDs and stabilize cool core clusters.