[Surveys -- Oral ]

The Chandra ACIS Survey of M33 (ChASeM33): A Chandra Legacy Program

Ralph Tuellmann, Harvard-Smithsoninan Center for Astrophysics
Terrance J. Gaetz (CfA), Paul P. Plucinsky (CfA), Knox S. Long (STSci), William P. Blair (JHU), P. Frank Winkler (Middlebury College), Benjamin Williams (University of Washington), Kip Kuntz (JHU/GSFC), David Helfand (Columbia University), John P. Hughes (Rutgers University), and the ChASeM33 team

ChASeM33, the Chandra ACIS Survey of M33, with a total exposure time of 1.4Ms and a limiting sensitivity of ~2e34erg/s, covers about 70\% of the D25 isophote and is the deepest, high angular resolution X-ray survey of the nearest face-on spiral galaxy to date. More than 650 X-ray sources were detected whose positions, nature, and source statistics are reported in the final ChASeM33 source catalog. Among these sources are more than 60 X-ray counterparts to previously identified SNRs, which means that we have more than doubled the number of known X-ray SNRs in M33. In at least two cases the X-ray spectrum seems to be dominated by ejecta from core collapse SNe.We also report the first detections of two eclipsing high-mass X-ray binaries and seven new transient sources in M33. In one of the X-ray binaries, M33 X-7, the compact object seems to be a black hole with a mass >9M_solar. Besides the point source population, extended sources such as the two most luminous giant HII regions, NGC604 and IC131, are also studied.NGC604 shows the typical soft X-ray spectrum expected from such regions, whereas IC131 appears to be extremely different as it contains a diffuse emission region (~200 pc across) with a hard X-ray spectrum. This spectrum is difficult to explain in the context of the standard wind-blown bubble models. Even if some of the emission is non-thermal, it is not clear what mechanism can produce non-thermal X-rays on such large scales.Moreover, results from the ChASeM33 source catalog are used to explore the large-scale distribution of the purely diffuse X-ray emission in M33. Even with these numerous applications the potential of ChASeM33 is far from being exhausted. This survey will be relevant for future M33 studies and certainly form an important part of Chandra's legacy.