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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). Introduction. We have a lot of unsolved problems about the cluster center. Radiative cooling (cooling flows) Where is cold gas ?
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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)
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 Spitzser’s value ? • What mechanism reduces it ? • Does it transport enough energy from outside the cooling flow region ?
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 H0=50 km s-1 Mpc-1 • No detailed observations about the inner structure of the cooling flow region
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.
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
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.
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. rcool～120” Gray scale: residual (X-ray) Contours: 1.32 GHz (radio)
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.
Locally Determined Mass Deposition Rate The data were fitted with MEKAL + MKCFLOW Total mass deposition rate: 44.46+52.07-32.50 solar mass/yr This value is much lower than that derived from ROSAT and EXOSAT imaging analysis (～400 solar mass/yr).
Globally Determined Mass Deposition Rate Total Spectrum (r<157”): 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.
Cooling vs Conduction • Isobaric cooling time. tcool=8.5×1010 yr (np/10-3cm-3)-1 (T/108K) ½ • Cooling tends to enhance temperature gradient. • Thermal conduction tends to reduce temperature gradient. t cond=9.1×106 yr (ne/10-3cm-3)(lT/100kpc)2 (T/108K)-5/2 (lnΛ/40) where、lT=T/(dT/dr)、Spitzer’s conductivity is used。 • Which is more effective, cooling or conduction?
Radial profile of cooling time and thermal conduction timescale tcool Circles: cooling time Squares: conduction time tcond Inside cooling radius (tcool < 2.0×1010 yr), conduction time is comparable or shorter than cooling time.
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) • tcool>tcond . However, the temperature gradient do exits. • Conduction is reduced from the Spitzer’s value by some physical mechanisms. • Tlow is not very low (≧～2keV). • Some heating sources （reduced heat conduction, high energy proton from AGN, or others?）
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 Spitzer’s value.