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Register a new userA Very Deep Chandra Observation of Abell 2052: Bubbles, Shocks, and Sloshing
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Elizabeth L. Blanton
Publication date
2011
fields
Physics
and research's language is
English
Authors
E. L. Blanton
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We present first results from a very deep (~650 ksec) Chandra X-ray observation of Abell 2052, as well as archival VLA radio observations. The data reveal detailed structure in the inner parts of the cluster, including bubbles evacuated by the AGNs radio lobes, compressed bubble rims, filaments, and loops. Two concentric shocks are seen, and a temperature rise is measured for the innermost one. On larger scales, we report the first detection of an excess surface brightness spiral feature. The spiral has cooler temperatures, lower entropies, and higher abundances than its surroundings, and is likely the result of sloshing gas initiated by a previous cluster-cluster or sub-cluster merger. Initial evidence for previously unseen bubbles at larger radii related to earlier outbursts from the AGN is presented.
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We present results from a deep Chandra observation of Abell 2052. A2052 is a bright, nearby, cooling flow cluster, at a redshift of z=0.035. Concentric surface brightness discontinuities are revealed in the cluster center, and these features are consistent with shocks driven by the AGN, both with Mach numbers of approximately 1.2. The southern cavity in A2052 now appears to be split into two cavities with the southernmost cavity likely representing a ghost bubble from earlier radio activity. There also appears to be a ghost bubble present to the NW of the cluster center. The cycle time measured for the radio source is approximately 2 x 10^7 yr using either the shock separation or the rise time of the bubbles. The energy deposited by the radio source, including a combination of direct shock heating and heating by buoyantly rising bubbles inflated by the AGN, can offset the cooling in the core of the cluster.
We present an analysis of the Chandra X-ray observation of Abell 2052, including large scale properties of the cluster as well as the central region which includes the bright radio source, 3C 317. We present temperature and abundance profiles using both projected and deprojected spectral analyses. The cluster shows the cooling flow signatures of excess surface brightness above a beta- model at the cluster center, and a temperature decline into the center of the cluster. The heavy element abundances initially increase into the center, but decline within 30 arcsec. Temperature and abundance maps show that the X-ray bright shells surrounding the radio source are the coolest and least abundant regions in the cluster. The mass-deposition rate in the cooling flow is 26 < Mdot < 42 Msun/yr. This rate is ~ a factor of three lower than the rates found with previous X-ray observatories. Based on a stellar population analysis using imaging and spectra at wavelengths spanning the far UV to the NIR, we find a star formation rate of 0.6 Msun/yr within a 3 arcsec radius of the nucleus of the central cluster galaxy. Total and gas mass profiles for the cluster are also determined. We investigate additional sources of pressure in the X-ray holes formed by the radio source, and limit the temperature of any hot, diffuse, thermal component which provides the bulk of the pressure in the holes to kT > 20 keV. We calculate the magnetic field in the bright-shell region and find B ~ 11 muG. The current luminosity of the central AGN is L_X = 7.9 x 10^41 erg/s, and its spectrum is well-fitted by a power-law model with no excess absorption above the Galactic value. The energy output from several radio outbursts, occurring episodically over the lifetime of the cluster, may be sufficient to offset the cooling flow near the center. (Abridged)
We present an analysis of a 72 ks Chandra observation of the double cluster Abell 1644 (z=0.047). The X-ray temperatures indicate the masses are M500=2.6+/-0.4 x10^{14} h^{-1} M_sun for the northern subcluster and M500=3.1+/-0.4 x10^{14} h^{-1} M_sun for the southern, main cluster. We identify a sharp edge in the radial X-ray surface brightness of the main cluster, which we find to be a cold front, with a jump in temperature of a factor of ~3. This edge possesses a spiral morphology characteristic of core gas sloshing around the cluster potential minimum. We present observational evidence, supported by hydrodynamic simulations, that the northern subcluster is the object which initiated the core gas sloshing in the main cluster at least 700 Myr ago. We discuss reheating of the main clusters core gas via two mechanisms brought about by the sloshing gas: first, the release of gravitational potential energy gained by the cores displacement from the potential minimum, and second, a dredging inwards of the outer, higher entropy cluster gas along finger-shaped streams. We find the available gravitational potential energy is small compared to the energy released by the cooling gas in the core.
Recent X-ray observations of galaxy clusters have shown that there is substructure present in the intracluster medium (ICM), even in clusters that are seemingly relaxed. This substructure is sometimes a result of sloshing of the ICM, which occurs in cool core clusters that have been disturbed by an off-axis merger with a sub-cluster or group. We present deep Chandra observations of the cool core cluster Abell 2029, which has a sloshing spiral extending radially outward from the center of the cluster to approximately 400 kpc at its fullest extent---the largest continuous spiral observed to date. We find a surface brightness excess, a temperature decrement, a density enhancement, an elemental abundance enhancement, and a smooth pressure profile in the area of the spiral. The sloshing gas seems to be interacting with the southern lobe of the central radio galaxy, causing it to bend and giving the radio source a wide-angle tail (WAT) morphology. This shows that WATs can be produced in clusters that are relatively relaxed on large scales. We explore the interaction between heating and cooling in the central region of the cluster. Energy injection from the active galactic nucleus (AGN) is likely insufficient to offset the cooling, and sloshing may be an important additional mechanism in preventing large amounts of gas from cooling to very low temperatures.
We present the first X-ray dedicated study of the galaxy cluster A795 and of the Fanaroff-Riley Type 0 hosted in its brightest cluster galaxy. Using an archival 30 ks textit{Chandra} observation we study the dynamical state and cooling properties of the intracluster medium, and we investigate whether the growth of the radio galaxy is prevented by the surrounding environment. We discover that A795 is a weakly cool core cluster, with an observed mass deposition rate $lessapprox 14,$ M$_{odot}$yr$^{-1}$ in the cooling region (central $sim$66 kpc). In the inner $sim$ 30 kpc we identify two putative X-ray cavities, and we unveil the presence of two prominent cold fronts at $sim$60 kpc and $sim$178 kpc from the center, located along a cold ICM spiral feature. The central galaxy, which is offset by 17.7 kpc from the X-ray peak, is surrounded by a multi-temperature gas with an average density of $n_{text{e}} = 2.14 times 10^{-2}$ cm$^{-3}$. We find extended radio emission at 74-227 MHz centered on the cluster, exceeding the expected flux from the radio galaxy extrapolated at low frequency. We propose that sloshing is responsible for the spiral morphology of the gas and the formation of the cold fronts, and that the environment alone cannot explain the compactness of the radio galaxy. We argue that the power of the two cavities and the sloshing kinetic energy can reduce and offset cooling. Considering the spectral and morphological properties of the extended radio emission, we classify it as a candidate radio mini-halo.
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