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CHANULXCAT - Chandra Archive Of Galaxies Ultraluminous X-Ray Source Catalog

HEASARC
Archive

Overview

One hundred fifty-five (the abstract in the paper erroneously states the number to be 154) discrete, non-nuclear, ultraluminous X-ray (ULX) sources, with spectroscopically determined intrinsic X-ray luminosities greater than 10^39 erg/s, have been identified in 82 galaxies that were observed with Chandra's Advanced CCD Imaging Spectrometer (ACIS). Positions, X-ray luminosities, and spectral and timing characteristics of these ULXs are contained in this table. Eighty-three percent of ULX candidates have spectra that can be described as absorbed power laws with mean index Gamma = 1.74 and column density N_H = 2.24 x 10^21 atoms cm^-2, or ~5 times the average Galactic column. About 20% of the ULXs have much steeper indices indicative of a soft, and likely thermal, spectrum. The locations of ULXs in their host galaxies are strongly peaked toward their galaxy centers. The deprojected radial distribution of the ULX candidates is somewhat steeper than an exponential disk, indistinguishable from that of the weaker sources. About 5%-15% of ULX candidates are variable during the Chandra observations (which average 39.5 ks). Comparison of the cumulative X-ray luminosity functions of the ULXs to Chandra Deep Field results suggests ~25% of the sources may be background objects, including 14% of the ULX candidates in the sample of spiral galaxies and 44% of those in elliptical galaxies, implying the elliptical galaxy ULX population is severely compromised by background active galactic nuclei. Correlations with host galaxy properties confirm the number and total X-ray luminosity of the ULXs are associated with recent star formation and with galaxy merging and interactions. The preponderance of ULXs in star-forming galaxies as well as their similarities to less-luminous sources suggest they originate in a young but short-lived population such as the high-mass X-ray binaries, with a smaller contribution (based on spectral slope) from recent supernovae. The number of ULXs in elliptical galaxies scales with host galaxy mass and can be explained most simply as the high-luminosity end of the low-mass X-ray binary population.

Catalog Bibcode

2004ApJS..154..519S

References

The ultraluminous X-ray source population from the Chandra archive of galaxies.
    Swartz D.A., Ghosh K.K., Tennant A.F., Wu K.
   <Astrophys. J. Suppl. Ser., 154, 519-539 (2004)>
   =2004ApJS..154..519S

Provenance

This table was created by the HEASARC in March 2007 based on CDS catalog J/ApJS/154/519 file table2.dat.

Parameters

Galaxy_Name
The name of the galaxy in which the ULX lies or is projected against.

Name
The name for the X-ray source using the '[SGT2004]' prefix and the truncated J2000.0 coordinates (JHHMMSS.ss+DDMMSS.s), as recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Spect_Shape
A parameter describing the X-ray spectrum, generally the power-law index, found from the best-fit absorbed (ACISABS and PHABS components) XSPEC-specific power-law model called PEGPWRLW, unless the parameter spect_shape_flag is non-blank, in which case it is the black body or thermal emission-line temperature.

Spect_Shape_Pos_Err
The upper (positive) error in the value of the spectral parameter.

Spect_Shape_Neg_Err
The lower (negative) error in the value of the spectral parameter.

Spect_Shape_Flag
This parameter flags cases where the spectral parameter is not the power-law index, as follows:

   b: it is the disk-blackbody model inner disk temperature, kT_inner, in keV.
   c: it is the thermal emission-line model temperature, kT, in keV.
  

NH
The equivalent hydrogen absorption column density, in H-atoms/cm^2, from the best-fit model.

NH_Pos_Err
The upper (positive) error in the value of the equivelent hydrogen column Density, in H-atoms/cm^2.

NH_Neg_Err
The lower (negative) error in the value of the equivelant hydrogen column density, in H-atoms/cm^2.

Chi_Squared
The chi-squared value of the best-fit model.

DoF
The number of degrees of freedom of the best-fit model.

Lx_Obs
The observed X-ray luminosity of the source in the 0.5 to 8.0 keV energy band, in erg/s, derived from the observed best-fit model flux and the adopted distance to the galaxy in whose direction it lies (given in Table 1 of the reference paper), i.e., the implicit assumption has been made that the source lies at the same distance as the galaxy.

Lx_Obs_Error
The uncertainty in the observed X-ray luminosity, in erg/s.

Lx
The intrinsic (absorption-corrected) X-ray luminosity of the source in the 0.5 to 8.0 keV energy band, in erg/s, derived from the corresponding best-fit model flux and the adopted distance to the galaxy in whose direction it lies (given in Table 1 of the reference paper), i.e., the implicit assumption has been made that the source lies at the same distance as the galaxy.

Lx_Error
The uncertainty in the intrinsic X-ray luminosity, in erg/s.

Lx_Flag
This flag parameter is set to 'd' if the intrinsic luminosity is less than 10^39 erg/s when the X-ray spectrum is fit using a thermal emission-line model.

Hardness_Ratio_1
The hard to medium energy color (hardness ratio) C_HM of the X-ray source. Colors are defined using the background-substracted X-ray counts in the following energy bands: S = the counts in the (0.5 - 1.0 keV) band, M in the (1.0 - 2.0 keV) band, and H in the (2.0 - 8.0 keV) band. Thus, the total (0.5 - 8.0 keV) band counts T = S + M + H, and C_HM = (H - M)/T.

Hardness_Ratio_2
Ths medium to soft energy color (hardness ratio) C_MS of the X-ray source. Colors are defined using the background-substracted X-ray counts in the following energy bands: S = the counts in the (0.5 - 1.0 keV) band, M in the (1.0 - 2.0 keV) band, and H in the (2.0 - 8.0 keV) band. Thus, the total (0.5 - 8.0 keV) band counts T = S + M + H, and C_MS = (M - S)/T.

Prob_Constant
The Kolmogorov-Smirnov probability P_KS that the X-ray source was constant. The authors consider that sources with P_KS <= 0.001 are significantly variable, and that those with 0.001 <= P_KS <= 0.04 are likely to be variable. For the ULX candidates, there are 7 (4.5%) and 22 (14.3%) of the sources, respectively, below these two thresholds.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 14-Mar-2007