University of Virginia, College and Graduate School of Arts and Sciences

X-ray Astronomy and Clusters of Galaxies Group

Overview

The X-ray Astronomy and Clusters of Galaxies Group does both observational and theoretical work related to X-ray astronomy and the physics of clusters of galaxies, galaxies, X-ray binaries, and compact objects.

Personnel

Faculty, scientists and staff involved in our group include:

Undergraduate students working in this group include:

  • Bridget Andersen
  • Avery Bailey
  • Eli Golub
  • Renatto Mazzei

Recent Research Projects and Papers

Shocks and Radio Relics in Clusters of Galaxies: Cluster radio relics are diffuse radio sources in clusters of galaxies not associated with any active galaxy. Radio relics and cluster radio halos are only found in clusters undergoing mergers. Using X-ray observations, we have found that several clusters with radio relics have merger shocks at the outer edge of the relic. We argue that the relativistic electrons in the relics are (re)accelerated by the merger shocks. Clusters with radio relics and merger shocks include Abell3667 (above), Paper II, Paper I, the Coma relic. This project involves collaborations with scientists at many other institutions.

X-ray Binary Populations in Galaxies: Chandra X-ray observations are being used to study the X-ray binary populations in many galaxies, including Cen A (right). These studies show that the LMXBs in globular clusters have a different luminosity function than in the field, (Paper 2), (Paper 3). In the S0 galaxy NGC 1380 (below), a very bright Ultra-Luminous X-ray binary (ULX) was found in a globular cluster, probably only the second clear case.

IC Hard X-rays from Clusters: We have searched for hard X-rays from inverse Compton (IC) emission from relativistic electrons in clusters with radio halos and relics using the Suzaku and Swift satellites. We used the Hard X-ray Detector on Suzaku to set limits on the IC from the Coma Coma cluster which were three times lower than previous detections or limits. One possibility was that the IC emission in Coma was too extended to be seen easily with Suzaku. However, we also used the BAT telescope on Swift and combined data from several years of observing to show that the hard X-ray emission from Coma is due to the thermal gas and has the same spatial distribution. Also using the BAT telescope on Swift, we did a survey of all of the HIFLUGCS clusters (the brightest X-ray clusters on the sky). We did not detect any individual clusters, but did detect IC by stacking all the observations of all clusters with radio halos or relics. Most of this work was led by Dr. Dan Wik, former U.Va. grad student, now an NPP Fellow at NASA-Goddard.

SLAM Simulations of Cluster Mergers: The Simulation Library for Astrophysical cluster Mergers (SLAM) is a suite of 156 high resolution merrger simulations of clusters of galaxies. The simulation treat both collisionless particle (dark matter and galaxies) and the intracluster gas. They are being used to analyze the physics of mergers. Also, their X-ray and SZ observational properties have been calculated at many timesteps and for many viewing angles. This project is led by Dr. Marios Chatzikos, former U.Va. grad student, now a post-doc at the University of Kentucky.

Cool Gas, AGN Feedback, and Star Formation in Cool Core Clusters: The role of cool gas, feedback from central radio galaxies, and star formation in the central regions of cool core clusters is being investigated using X-ray observations with Chandra, radio observations with the VLA, GMRT, and millimeter telescopes, optical/UV observations with HST and ground=-based observatories, and IR observations with Spitzer and Herschel. This involves a number of very large internation collaborations. Objects studieds include Abell 2597, (Paper 2), Abell 2052, (Paper 2), Abell 133, Herschel observations of a sample of BCGs, (Paper 2), Chandra observations of the HIFLUGCS sample, and individual ellipticals, (Paper 2)

High Resolution SZ Images of Clusters: The highest spatial resolution SZ images of clusters of galaxies are being made with the MUSTANG and MUSTANG1.5 bolometer arrays on the Green Bank Telescope (GBT). The Sunyaev-Zel'dovich (SZ) effect involves the inverse Compton scattering of photons from the Cosmic Microwave Background (CMB) by hot electrons in the intracluster gas. Since the thermal SZ effect gives the integral of the pressure through a cluster, high resolution images show regions of violent dynamical activity, such as shocks. In RXJ1347-1145 and MACS0744, shocks are seen; the shock in MACS0744 had previously been detected in X-ray or SZ images. In MACS J0717.5+3745, a high pressure region (possible shock) is associated with the unusual radio relic. We also have a moderately significant detection of the kinetic SZ effect from the rapidly infalling B subcluster.