Chandra ACIS Survey of M33 (ChASeM33): A First Look

Abstract

We present an overview of the Chandra ACIS Survey of M33 (ChASeM33): A Deep Survey of the Nearest Face-on Spiral Galaxy. The 1.4 Ms survey covers the galaxy out to R % 180 (%4 kpc). These data provide the most intensive, high spatial resolution assessment of the X-ray source populations available for the confused inner re- gions of M33. Mosaic images of the ChASeM33 observations show several hundred individual X-ray sources as well as soft diffuse emission from the hot interstellar medium. Bright, extended emission surrounds the nucleus and is also seen from the giant H ii regions NGC 604 and IC 131. Fainter extended emission and numerous individual sources appear to trace the inner spiral structure. The initial source catalog, arising from $2/3 of the expected sur- vey data, includes 394 sources significant at the 3 confidence level or greater, down to a limiting luminosity (absorbed) of $1:6 ; 1035 ergs sÀ1 (0.35Y8.0 keV). The hardness ratios of the sources separate those with soft, thermal spectra such as supernova remnants from those with hard, nonthermal spectra such as X-ray binaries and background active galactic nuclei. Emission extended beyond the Chandra point-spread function is evident in 23 of the 394 sources. Cross-correlation of the ChASeM33 sources against previous catalogs of X-ray sources in M33 re- sults in matches for the vast majority of the brighter sources and shows 28 ChASeM33 sources within 1000 of super- nova remnants identified by prior optical and radio searches. This brings the total number of such associations to 31 out of 100 known supernova remnants in M33.