Chandra observations of the central region of Abell 3112

1
Chandra observations of the central region of
Abell 3112

• M. Takizawa (Yamagata Univ.)
• C. L. Sarazin, E. L. Blanton (Univ. of Virginia)
• G. B. Taylor (NRAO)

2
Introduction

• We have a lot of unsolved problems about the
  cluster center.
• Radiative cooling (cooling flows)
• Where is cold gas ?
• What will cooled gas be ?
• Does gas really cools ?
• Interactions with radio bubbles
• Do they supply enough energy ?
• Do they supply magnetic field ?
• How do they interact ?
• Thermal conduction
• Is it reduced from the Spitzsers value ?
• What mechanism reduces it ?
• Does it transport enough energy from outside the
  cooling flow region ?

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Abell 3112

• ROSAT and EXOSAT imaging observations detected a
  very strong cooling flow
• dM/dt 400 solar mass /yr
• tcool 2 Gyr
• rcool 250 kpc
• Radio point source (PKS 0316-444) in the center.
• z 0.0746
• 1 1.94 kpc with H050 km s-1 Mpc-1
• No detailed observations about the inner
  structure of the cooling flow region

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X-ray Observations and Data Reduction

• 2001 May 24 (7257 sec) Sep. 15 (17496sec)
• A few short periods with background flair were
  found and removed. ?Total exposure 21723 sec
• Data from only ACIS-S3 (back illuminated CCD)
  were analyzed.
• Roll angles were different between the two
  observations. We merged them using the positions
  of bright point sources.
• Exposure maps and background data are generated
  for each observation separately, and then merged.

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Radio Observations and Data Reduction

• 1996 October 18
• Very Large Array (VLA)
• a center frequency of 1320 MHz
• Angular resolution of 6.9 1.5 arcsec

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Adaptively smoothed X-ray Image
0.3 10.0 keV The image has been
background subtracted and exposure corrected.
On large scales, the cluster is quite symmetric
and there appears to be no substrcture.
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Central 50 70 region

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Radio vs X-ray residual component
We fitted the image with a concentric elliptical
isophotal model to get a residual component. Obs.
Data elliptical isophotal model residual
Excess emission (black) appears to surround the
radio lobes. Probable interaction between ICM
and radio lobes Interacting region is limited to
very central region (r 10) c.f. rcool120
Gray scale residual (X-ray) Contours 1.32 GHz
(radio)
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Temperature and abundance profile
Abundance
Temperature
Solid crosses when the absorption is allowed to
vary. Dashed crosses when the absorption is
fixed to the Galactic value.
Clear temperature decrease and abundance increase
towards the center.
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Locally Determined Mass Deposition Rate
The data were fitted with MEKAL MKCFLOW
Total mass deposition rate 44.4652.07-32.50
solar mass/yr This value is much lower than that
derived from ROSAT and EXOSAT imaging analysis
(400 solar mass/yr).
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Globally Determined Mass Deposition Rate
Total Spectrum (rlt157) The data are fitted with
MEKAL MKCFLOW , where the Tlow in MKCFLOW is
allowed to vary.
The mass deposition rate is comparable with the
former (ROSAT, EXOSAT) results. However, the Tlow
in MKCFLOW is not very low.
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Cooling vs Conduction

• Isobaric cooling time.
• tcool8.51010 yr (np/10-3cm-3)-1 (T/108K) ½
• Cooling tends to enhance temperature gradient.
• Thermal conduction tends to reduce temperature
  gradient.
• t cond9.1106 yr (ne/10-3cm-3) (lT/100kpc)2
  
  (T/108K)-5/2
  (ln?/40)
• where?lTT/(dT/dr)?Spitzers
  conductivity is used?
• Which is more effective, cooling or conduction?

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Radial profile of cooling time and thermal
conduction timescale
tcool
Circles cooling time Squares conduction time
tcond
Inside cooling radius (tcool lt 2.01010 yr),
conduction time is comparable or shorter than
cooling time.
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Physical status of the cooling flow region

• The central radio source affects ICM only very
  close to the center (20 kpc).
• (c.f. rcool 250 kpc)
• tcoolgttcond . However, the temperature gradient
  do exits.
• Conduction is reduced from the Spitzers value by
  some physical mechanisms.
• Tlow is not very low (?2keV).
• Some heating sources (reduced heat conduction,
  high energy proton from AGN, or others?)

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Summary

• We analyzed the Chandra data of the central
  region of Abell 3112.
• In large scales, ICM is distributed quite
  smoothly and symmetrically. There appears to be
  no substructures.
• The central radio source probably interacts with
  the surrounding ICM. However, the interaction is
  limited to the region very close (10) to the
  central radio source.
• ICM is cooling significantly as a whole, but in
  only a limited temperature range (?2keV).
• Our results strongly suggest that thermal
  conduction is reduced from the Spitzers value.