Article

# Detecting Star Formation in Brightest Cluster Galaxies with GALEX

(Impact Factor: 5.99). 06/2010; 719(2). DOI: 10.1088/0004-637X/719/2/1844
Source: arXiv

ABSTRACT

We present the results of GALEX observations of 17 cool core (CC) clusters of galaxies. We show that GALEX is easily capable of detecting star formation in brightest cluster galaxies (BCGs) out to $z\ge 0.45$ and 50-100 kpc. In most of the CC clusters studied, we find significant UV luminosity excesses and colors that strongly suggest recent and/or current star formation. The BCGs are found to have blue UV colors in the center that become increasingly redder with radius, indicating that the UV signature of star formation is most easily detected in the central regions. Our findings show good agreement between UV star formation rates and estimates based on H$\alpha$ observations. IR observations coupled with our data indicate moderate-to-high dust attenuation. Comparisons between our UV results and the X-ray properties of our sample suggest clear correlations between UV excess, cluster entropy, and central cooling time, confirming that the star formation is directly and incontrovertibly related to the cooling gas. Comment: 39 pages, 11 figures; accepted for publication in The Astrophysical Journal. Figure quality reduced to comply with arXiv file size requirements

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##### Article: On the Origin of the Extended Halpha Filaments in Cooling Flow Clusters
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The Astrophysical Journal 08/2010; 721(2). DOI:10.1088/0004-637X/721/2/1262 · 5.99 Impact Factor
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##### Article: Far Ultraviolet Emission in the A2597 and A2204 Brightest Cluster Galaxies
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ABSTRACT: We use the Hubble Space Telescope Advanced Camera for Surveys (ACS)/Solar Blind Channel (SBC) and Very Large Telescope (VLT) Focal Reducer/low dispersion Spectrograph (FORS) cameras to observe the brightest cluster galaxies (BCGs) in Abell 2597 and Abell 2204 in the far-ultraviolet (FUV) F150LP and optical U, B, V, R, I Bessel filters. The FUV and U-band emission is enhanced in bright, filamentary structures surrounding the BCG nuclei. These filaments can be traced out to 20 kpc from the nuclei in the FUV. Excess FUV and U-band light is determined by removing emission due to the underlying old stellar population and mapped with 1-arcsec spatial resolution over the central 20-kpc regions of both galaxies. We find the FUV and U excess emission to be spatially coincident, and a stellar interpretation requires the existence of a significant amount of 10 000–50 000 K stars. Correcting for nebular continuum emission and dust intrinsic to the BCG further increases the FUV to U-band emission ratio and implies that stars alone may not suffice to explain the observations. However, lack of detailed information on the gas and dust distribution and extinction law in these systems prevents us from ruling out a purely stellar origin. Non-stellar processes, such as the central active galactic nucleus, scattering, synchrotron and Bremsstrahlung emission are investigated and found to not be able to explain the FUV and U-band measurements in A2597. Contributions from non-thermal processes not treated here should be investigated. Comparing the FUV emission to the optical Hα line emitting nebula shows good agreement on kpc-scales in both A2597 and A2204. In concordance with an earlier investigation by O’Dea et al. (2004), we find that O stars can account for the ionizing photons necessary to explain the observed Hα line emission.
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