ULXNGCAT - Ultraluminous X-Ray Sources in Nearby Galaxies Catalog

Overview

One hundred and seven ultraluminous X-ray sources (ULXs) with 0.3-10.0 keV luminosities in excess of 10³⁹ erg s^-1 are identified in a complete sample of 127 nearby galaxies. The sample includes all galaxies within 14.5 Mpc above the completeness limits of both the Uppsala Galaxy Catalogue and the Infrared Astronomical Satellite survey. The galaxy sample spans all Hubble types, a four-decade range in mass, 7.5 < log (M/M_sun) < 11.4, and in star formation rate, 0.0002 < SFR(M_sun yr^-1) <= 3.6. ULXs are detected in this sample at rates of one per 3.2 x 10¹⁰ M_sun, one per ~0.5 M_sun yr^-1 star formation rate, and one per 57 Mpc³ corresponding to a luminosity density of ~2 x 10³⁷ erg s^-1 Mpc^-3. At these rates, the authors estimate as many as 19 additional ULXs remain undetected in fainter dwarf galaxies within the survey volume. An estimated 14 objects, or 13%, of the 107 ULX candidates are expected to be background sources. The differential ULX luminosity function shows a power-law slope alpha ~ -0.8 to -2.0 with an exponential cutoff at ~20 x 10³⁹ erg s^-1 with precise values depending on the model and on whether the ULX luminosities are estimated from their observed numbers of counts or, for a subset of candidates, from their spectral shapes. Extrapolating the observed luminosity function predicts at most one very luminous ULX, L_X ~ 10⁴¹ erg s^-1, within a distance as small as 100 Mpc. The luminosity distribution of ULXs within the local universe cannot account for the recent claims of luminosities in excess of 2 x 10⁴¹ erg s^-1, requiring a new population class to explain these extreme objects.

Catalog Bibcode

2011ApJ...741...49S

References

A Complete Sample of Ultraluminous X-Ray Source Host Galaxies
   Swartz D.A., Soria R., Tennant A.F., Yukita M.
  <Astrophys. J., 741, 49 (2011)>
  =2011ApJ...741...49S

Provenance

This table was created by the HEASARC in November 2011 based on an electronic version of Table 1 from the reference paper that was obtained from the ApJ web site.

Parameters

Name
The name of the ULX candidate. The HEASARC created this parameter using the usual Dictionary of Nomenclature of Celestial Objects format, viz., the prefix '[SST2011]" for Swartz, Soria, Tennant 2011 and the J2000.0 equatorial coordinates of the source.

RA
The Right Ascension of the ULX candidate in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.01 seconds of time in the original table. The accuracy of this is estimated to be ~0.3 arcseconds for a Chandra source (3-5 digit ObsID value) or ~1.5 arcseconds for an XMM-Newton source (10 digit ObsID value).

Dec
The Declination of the ULX candidate in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.1 arcseconds in the original table. The accuracy of this is estimated to be ~0.3 arcseconds for a Chandra source (3-5 digit ObsID value) or ~1.5 arcseconds for an XMM-Newton source (10 digit ObsID value).

LII
The Galactic Longitude of the ULX candidate.

BII
The Galactic Latitude of the ULX candidate.

Galaxy_Name
The designation of the putative ULX host galaxy.

Distance
The distance to the putative ULX host galaxy, in megaparsecs. Distances to target galaxies were taken from the critically assessed values used previously in the ULX catalog of Swartz et al. (S04: 2004, ApJS, 154, 519). Otherwise, distances were taken from the recent NED compilation of redshift-independent distances in the following order of preference listed in Section 3.1 of the reference paper: Cepheid period-luminosity relation from the Hubble Key Project results, other Cepheid-based distances, surface brightness fluctuations, the tip of the red giant branch, globular cluster luminosity functions, brightest stars, and the Tully-Fisher relation. Targets not included in the redshift-independent NED compilation or in S04 were assigned distances as listed in the Nearby Galaxies Catalogue (Tully 1988) or, finally, from flow-corrected redshift distances listed in NED, preferring the values corrected for Local Group motions over those using only a single-attractor Virgocentric flow model.

Radial_Fraction
The separation of the ULX candidate from the center of the host galaxy, expressed as a fraction F_D25_of the deprojected galaxy radius in units of half of the major isophotal angular diameter measured at the surface brightness level of 25.0 mag arcsec^-2 in blue light.

ObsID
The observation identifier (ObsID) of the Chandra or XMM-Newton pointing, where 3-5 digit numbers refer to Chandra observations and 10 digit numbers refer to XMM-Newton pointings.

Counts
The aperture-corrected X-ray source counts within the detection bandpass: 0.3-6.0 keV for Chandra sources (3-5 digit ObsID values) or 0.5-4.5 keV for XMM-Newton sources (10 digit ObsID values).

SNR
The X-ray detection signal-to-noise ratio.

Lx_Cts
The unabsorbed 0.3-10.0 keV luminosity of the source, in erg s^-1, assuming that it is at the distance of the galaxy, estimated from the source counts in the original detection bandpass and using a fixed conversion rate calculated assuming an absorbed power-law spectrum of Gamma = 1.7 and the Galactic column density in the direction of the source.

Lx_Fit
The unabsorbed 0.3-10.0 keV luminosity of the source, in erg s^-1, assuming that it is at the distance of the galaxy, estimated from model fits to the X-ray spectral energy distribution. For sources with >130 counts detected in any observation, this is either newly calculated herein (see Section 3.5 of the reference paper for the full details) or taken from published results in the literature. For results taken from the literature, the intrinsic luminosities were converted from the originally published energy range to the 0.3-10.0 keV bandpass and, where needed, scaled to the distances adopted herein. PIMMS was used for the bandpass conversion and to scale from observed to intrinsic (unabsorbed) fluxes where needed if spectral model fit parameters were provided. The references to published spectral modeling results are listed in the ref_source parameter (q.v.).

Ref_Source
This parameter contains a number that indicates the reference from which the spectral fit results for the ULX candidate (quoted in the lx_fit parameter) are taken. The references are coded as follows:

       1: Feng & Kaaret 2009, ApJ, 696, 1712;
       2: Roberts et al. 2004, MNRAS, 349, 1193;
       3: Walton et al. 2011, MNRAS, 414, 1011;
       4: Sutton et al. 2011, Astron. Nachr., 332, 362.

Contact Person

Questions regarding the ULXNGCAT database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: Thursday, 24-May-2012 10:52:12 EDT