The X-Ray Binary Population in M33. I. Source List and Luminosity Function

In this paper we present the source list for three Chandra observations of the Local Group galaxy M33. The observations are centered on the nucleus and on the star-forming region NGC 604. We detect a total of 261 sources in an area of ~0.2 deg2 down to a flux limit of 3 × 10-16 ergs s-1 cm-2, which corresponds to a luminosity of ~2 × 1034 ergs s-1 at a distance of 840 kpc. From the source list we construct the luminosity functions of sources observed in M33. If we take into account background contamination, the luminosity functions are consistent with those of other star-forming galaxies. In addition, the combination of X-ray color analysis and the existence of "blue" optical counterparts strongly indicates that the X-ray point-source population in M33 consists of young objects. Above 3 × 1035 ergs s-1 there are few X-ray sources in the locus of the X-ray hardness ratio diagram that is generally populated by low-mass X-ray binaries.

[1]  Xu Zhou,et al.  SED, age distribution and evolutionary history of M 33 , 2004 .

[2]  V. La Parola,et al.  Spectral Variability of the Nucleus of M33 in a Chandra/ACIS Observation , 2003 .

[3]  H. Ford,et al.  Star clusters in M 33 - IV. A new survey from deep HST images , 2001 .

[4]  An Atlas of H(alpha) Emitting Regions in M33: A Systematic Search for SS433 Star Candidates , 1995 .

[5]  Frank Haberl,et al.  The X-ray view of M 33 after ROSAT , 2001 .

[6]  F. Haberl,et al.  ROSAT HRI catalogue of X-ray sources in the SMC region , 2000, astro-ph/0009390.

[7]  M. Tsujimoto,et al.  A Study of the Populations of X-Ray Sources in the Small Magellanic Cloud with ASCA , 2000, astro-ph/0002167.

[8]  P. Massey,et al.  Evolved Massive Stars in the Local Group. II. A New Survey for Wolf-Rayet Stars in M33 and Its Implications for Massive Star Evolution: Evidence of the “Conti Scenario” in Action , 1998 .

[9]  T. Wyder,et al.  The Hii Regions of M33. II. A Photometric Catalog of 1272 Newly Identified Emission Regions , 1999 .

[10]  Peter A. R. Ade,et al.  American Astronomical Society Meeting , 2004 .

[11]  F. Haberl,et al.  ROSAT HRI catalogue of X-ray sources in the LMC region ? , 2000, astro-ph/0002318.

[12]  Marat Gilfanov,et al.  High mass x-ray binaries as a star formation rate indicator in distant galaxies , 2002 .

[13]  Philip Kaaret,et al.  Classifying X-Ray Sources in External Galaxies from X-Ray Colors , 2003 .

[14]  P. Massey.  Evolved Massive Stars in the Local Group. I. Identification of Red Supergiants in NGC 6822, M31, and M33 , 1998 .

[15]  R. Di Stefano,et al.  X-Ray Point Sources in the Central Region of M31 as Seen by Chandra , 2002, astro-ph/0203243.

[16]  Thomas J. Chester,et al.  The 2MASS Large Galaxy Atlas , 2001 .

[17]  T. Markert,et al.  X-ray observations of M33 with the high resolution imager on the Einstein Observatory , 1983 .

[18]  J. Dickey,et al.  H I in the Galaxy , 1990 .

[19]  D. Hatzidimitriou,et al.  XMM-Newton survey of the Local Group galaxy M 33 – catalogue results and global properties , 2004, Proceedings of the International Astronomical Union.

[20]  Jr.,et al.  Chandra Multiwavelength Project. II. First Results of X-Ray Source Properties , 2003, astro-ph/0308493.

[21]  B. Madore,et al.  New Cepheid distances to nearby galaxies based on BVRI CCD photometry. II, The Local Group galaxy M33 , 1991 .

[22]  A. Zezas,et al.  Identifying X-ray Sources in Bulge and Disk Galaxies , 2001, astro-ph/0206127.

[23]  R. Sunyaev,et al.  The Milky Way in X-rays for an outside observer , 2001, astro-ph/0109239.

[24]  R. Di Stefano,et al.  Chandra Studies of the X-Ray Point Source Luminosity Functions of M31 , 2003 .

[25]  The spiral galaxy M33 mapped in the FIR by ISOPHOT. A spatially resolved study of the warm and cold dust. , 2003, astro-ph/0306558.

[26]  A. M. Read,et al.  The second ROSAT PSPC survey of M 31 and the complete ROSAT PSPC source list , 2001 .

[27]  P. Massey,et al.  The UV-brightest Stars of M33 and Its Nucleus: Discovery, Photometry, and Optical Spectroscopy , 1996 .

[28]  K. Long,et al.  A Deep X-Ray Image of M33 , 1996 .

[29]  D. Burrows,et al.  Determination of Confidence Limits for Experiments with Low Numbers of Counts , 1991 .

[30]  G. Trinchieri,et al.  The X-ray spectra of galaxies. I - Spectral fits of individual galaxies and X-ray colors , 1992 .

[32]  B. Madore,et al.  A catalog of blue and red supergiants in M33 , 1993 .

[33]  Marat Gilfanov,et al.  Low-mass X-ray binaries as a stellar mass indicator for the host galaxy , 2004 .

[34]  R. Corradi,et al.  Accurate positions of candidate planetary nebulae in M 33 , 2001 .

[35]  Tod R. Lauer,et al.  M33: A Galaxy with No Supermassive Black Hole , 2001, astro-ph/0107135.

[36]  A. Collura,et al.  Variability of the X-ray sources in M33 , 1989 .

[37]  H. Ford,et al.  Star Clusters in M33. I. Detection, Morphology, and Photometry , 1999 .

[38]  N. Gehrels.  Confidence limits for small numbers of events in astrophysical data , 1986 .

[39]  N. Duric,et al.  A New Sample of Radio-selected and Optically Confirmed Supernova Remnants in M33 , 1999 .

[40]  R. Humphreys,et al.  On the stellar content and structure of the spiral galaxy M33. , 1980 .

[41]  The DIRECT Project: Catalogs of Stellar Objects in Nearby Galaxies. I. The Central Part of M33 , 2000, astro-ph/0012208.

[42]  T. Oosterbroek,et al.  BeppoSAX spectroscopy of the luminous X-ray sources in M33 , 2001, astro-ph/0101057.

[43]  G. Fabbiano,et al.  Chandra X-Ray Observations of NGC 1316 (Fornax A) , 2002, astro-ph/0206369.

[44]  P. Massey,et al.  Hot, luminous stars in selected regions of NGC 6822, M31, and M33 , 1995 .

[45]  Edward Colbert,et al.  Old and Young X-Ray Point Source Populations in Nearby Galaxies , 2003, astro-ph/0305476.

[46]  F. R. Harnden,et al.  Chandra Multiwavelength Project. I. First X-Ray Source Catalog , 2003, astro-ph/0308492.

[47]  D. M. Alexander,et al.  The Chandra Deep Field North Survey. XIII. 2 Ms Point-Source Catalogs , 2003, astro-ph/0304392.

[48]  Giovanni Peres,et al.  Morphology and spectral characteristics of the X-ray emission of M33 , 1988 .

[49]  Jonathan C. McDowell,et al.  A Chandra Survey of Nearby Spiral Galaxies. I. Point Source Catalogs , 2005 .