x-ray signatures of feedback in intracluster gas
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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.