Extended Radio Sources in Clusters of Galaxies Elizabeth Blanton University of Virginia

Collaborators Craig Sarazin (UVa) Brian McNamara (Ohio U.) Michael Wise (MIT) Noam Soker (U. Haifa at Oranim) David Helfand (Columbia U.) Michael Gregg, Robert Becker (UC Davis / LLNL)

Radio Sources in Clusters Radio sources and the X-ray emitting ICM have a profound effect on each other, as seen with Chandra. Radio sources blow bubbles in the ICM and the ICM confines and distorts the radio lobes. 70% of cooling flow clusters contain central cD galaxies with associated radio sources, and 20% of non-cooling flow clusters have radio-bright central galaxies. The fact that radio sources are distorted by dense ICM can be exploited to find high-z clusters using radio sources as tracers.

When the cooling time of gas (with T=temp. and n=density) is shorter than the Hubble time, or the time since the last major merger of the system, a cooling flow will be set up Excess peak in central surface brightness above a  -model profile Spatially resolved temperature gradients measured from X-ray spectra Cooling Flows

The Cooling Flow “Problem” Where does the cooling gas go? Central cD galaxies in cooling flows do emit blue light and exhibit massive star formation, however the star formation accounts for only ~ 1--10% of the expected gas derived from the X-ray predictions (as measured from Einstein, ROSAT, and ASCA) Both Chandra and XMM-Newton have revealed an apparent lack of the expected quantities of cooler gas below about kT < 1- 2 keV (~10 7 K) Radio sources are possible heaters (but not by strong shocks).

(Radio Contours, Burns [1990]) Abell 2052 Chandra ACIS-S3, 36 ksec, z=0.0348, 1’’ = 1 kpc (Blanton et al. [2001,2002])

Abell 262 (Radio Contours, Parma et al. [1986]) Chandra ACIS-S3, 28 ksec, z=0.0163, 1’’ = 0.5 kpc (Blanton et al. [2003])

Source of Pressure in Bubbles? Pressure measured in X-ray shells is an order of mag. higher than the equipartition pressure measured from the radio source. Magnetic field may be larger than equipartition value? Contribution from low-energy relativistic electrons? Very hot, diffuse thermal gas? Chandra spectral limits on temp. of thermal component are not very restrictive. Limit for A2052 from lack of Faraday depolarization is kT > 20 keV. May be able to observe very hot gas directly with XMM-Newton.

Buoyant Bubbles Perseus (Fabian et al. 2000) A2597 (McNamara et al. 2001) Buoyant bubbles have been seen in Perseus, A2597, and possibly A262. The density inside the radio cavities is much lower than the ambient gas, so we expect the bubbles formed by radio sources to be buoyant. These bubbles may transport very hot gas and magnetic fields into the ICM.

Total Spectrum / A2052 Cooling flow model kT low < 0.55 keV ( /-0.43 keV) kT high = / keV (approximately 3x lower than values measured from Einstein, ROSAT, and ASCA).

Can Radio Source Heating Offset the Cooling Flow (A2052)? Total energy output of the radio source, including the work done on compressing the gas is 5/2 PV = ergs With kT = 3 keV and = 42 Msun/yr, L cool = 3 x erg/s. If the repetition rate of the radio source is 10 8 yr (as with Perseus and A2597), E/t for the radio source is 3 x erg/s.

Radio Sources as Tracers of Distant Clusters Since the appearance of radio sources is affected by interaction with the ICM (confinement, distortion), we can use radio sources to locate distant clusters of galaxies that would be difficult to find in optical (b.c. of projection effects) or X-ray (b.c. of flux limits) surveys.

Some types of radio sources are more often found in clusters than others FR IIFR I / WATFR I (most often not in clusters) (most often in clusters)

Wide-angle tails (WATs) Usually associated with cD or central E galaxies. Usually not in cooling flows. May need a cluster merger to get the ram pressure from the ICM to bend the radio lobes. Should be good pointers to clusters. (Gomez et al. [1997], radio grayscale on ROSAT contours of A562)

FIRST Bent Doubles Blanton et al. (2001) 384 sources visually selected from the VLA FIRST survey Optically followed up (imaging and spectroscopy) Low-z complete sample showed that 50% of BDs are found in clusters, as revealed in the optical and X-ray High-z sample had an 80% success rate using radio and optical images Highest-z object was observed in optical and NIR, with spectra taken at Keck.

Radio overlaid onto K-band (KPNO 2.1m, IRIM). Radio exp. = 3 min. (VLA). Optical R-band image. Exp. = 2 hrs. (MDM 1.3m) z = 0.96 Cluster Blanton et al. (2003)

z = 0.96 Cluster 10 galaxies spectroscopically confirmed at z=0.96 with the Keck II and LRIS. Velocity dispersion: km/s Expected L X,bol ~ couple erg/s Scheduled with Chandra and XMM-Newton Keck II, K-band snapshot, central ~290 kpc

Conclusions Cluster central radio sources and X-ray-emitting ICM profoundly affect one another: the ICM confines and distorts radio lobes while the radio lobes blow bubbles in the ICM. Central radio sources are at least part of the solution to the problem with the standard cooling flow model (with additional contributions from, i.e., inhomogeneous abundances and conduction). Energy is released into the ICM and dispersed through buoyancy; strong shocks are not seen. Since distorted radio sources often attain their morphologies from interaction with the ICM, they can be used as tracers for distant clusters and groups of galaxies for studies of cosmology and galaxy evolution.