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CHNGPSCLIU - Chandra ACIS Survey of Nearby Galaxies X-Ray Point Source Catalog

HEASARC
Archive

Overview

The Chandra data archive is a treasure trove for various studies, and in this study the author exploits this valuable resource to study the X-ray point source populations in nearby galaxies. By 2007 December 14, 383 galaxies within 40 Mpc with isophotal major axes above 1 arcminute had been observed by 626 public ACIS observations, most of which were for the first time analyzed by this survey to study the X-ray point sources. Uniform data analysis procedures were applied to the 626 ACIS observations and led to the detection of 28,099 point sources, which belong to 17,559 independent sources. These include 8700 sources observed twice or more and 1000 sources observed 10 times or more, providing a wealth of data to study the long-term variability of these X-ray sources. Cross-correlation of these sources with galaxy isophotes led to 8,519 sources within the D25 isophotes of 351 galaxies, 3,305 sources between the D25 and 2 * D25 isophotes of 309 galaxies, and an additional 5,735 sources outside the 2 * D25 isophotes of galaxies.

This survey has produced a uniform catalog, by far the largest, of 11,824 X-ray point sources within 2 * D25 isophotes of 380 galaxies. Contamination analysis using the log N-log S relation shows that 74% of the sources within the 2 * D25 isophotes above 1039 erg s-1, 71% of the sources above 1038 erg s-1, 63% of the sources above 1037 erg s-1, and 56% of all sources are truly associated with the galaxies. Meticulous efforts have identified 234 X-ray sources with galactic nuclei of nearby galaxies. This archival survey leads to 300 ultraluminous X-ray sources (ULXs) with LX in the 0.3-8 keV band >= 2 x 1039 erg s-1 within the D25 isophotes, 179 ULXs between the D25 and the 2 * D25 isophotes, and a total of 479 ULXs within 188 host galaxies, with about 324 ULXs truly associated with the host galaxies based on the contamination analysis. About 4% of the sources exhibited at least one supersoft phase, and 70 sources are classified as ultraluminous supersoft sources with LX (0.3-8 keV) >= 2 x 1038 erg s-1. With a uniform data set and good statistics, this survey enables future works on various topics, such as X-ray luminosity functions for the ordinary X-ray binary populations in different types of galaxies, and X-ray properties of galactic nuclei.

This table contains the list of 17,559 'independent' X-ray point sources that was contained in table 4 of the reference paper. As the author notes in Section 5 of this paper, there are 341 sources projected within 2 galaxies with overlapping domains which are listed for both galaxies. The 5,735 sources lieing outside the 2* D25 isophotes of the galaxies are also included in this table. For these sources, the X-ray luminosities are computed as if they were in a galaxy of that group, which may or may not be the case; thus, they may not be their 'true' luminosities, but are listed for the purposes of comparison.


Catalog Bibcode

2011ApJS..192...10L

References

Chandra ACIS Survey Of X-Ray Point Sources in 383 Nearby Galaxies I.
The Source Catalog
    Liu, J.
   <Astrophys. J. Suppl. Ser., 192, 10 (2011)>
   =2011ApJS..192...10L

Provenance

This table was created by the HEASARC in March 2011 based on the electronic version of Table 4 of the reference paper which was obtained from the Astrophysical Journal web site.

Parameters

Group_Number
This number identifies the set of ACIS observations that were analyzed together for the particular field in which the X-ray source was located. The groups are defined and the included observations are listed in Table 2 of the reference paper. The author placed the 626 ACIS observations into 320 groups based on the proximity of the pointings. The observations in the same group have overlapping fields of view and are suitable to be studied together. There are 48 groups with two ACIS observations, and 45 groups with three and more observations. The latter includes the M33 group observed 28 times over six years, the M101 group observed 26 times over five years, and the PGC 3598 group observed 21 times over eight months.

Name
The name of the Chandra ACIS X-ray point source using the convention recommended by the CDS Dictionary of Nomenclature of Celestial Objects, viz., 'CXOU JHHMMSS.s+DDMMSS', and replacing the higher precision form used in the original reference, viz., 'CXOJHHMMSS.sss+DDMMSS.ss'.

RA
The Right Ascension of the Chandra ACIS X-ray point source in the selected equinox. This was given (implicitly in the original name field) in J2000.0 equatorial coordinates to a precision of 0.001 seconds of time.

Dec
The Declination of the Chandra ACIS X-ray point source in the selected equinox. This was given (implicitly in the original name field) in J2000.0 equatorial coordinates to a precision of 0.01 arcseconds.

LII
The Galactic Longitude of the Chandra ACIS X-ray point source.

BII
The Galactic Latitude of the Chandra ACIS X-ray point source.

Error_Radius
The X-ray source positional uncertainty, in arcseconds, computed using the scheme of Kim et al. (2004, ApJS, 150, 19).

Alt_Name
An alternative name for the Chandra ACIS X-ray point source explicitly included the galaxy name and a source number sequence based on the maximum detection significance, e.g., 'NGC 598-X1' is the most significant X-ray source associated with the galaxy NGC 598.

Nuclear_Offset
The offset of the Chandra ACIS X-ray point source from the nucleus of the galaxy specified in the alt_name parameter, in arcminutes.

Nuclear_Offset_R25
The offset of the Chandra ACIS X-ray point source from the nucleus of the galaxy specified in the alt_name parameter, in multiples of the elliptical radius R25 along the great arc connecting the galactic nucleus and the X-ray source.

Distance
The distance to the X-ray point source, assumed to be the same as that of the galaxy with which it has been associated, in Mpc.

Obs_Over_Detect
The number of times that the source was observed compared to the number of times that it was detected, e.g., '2/1' means that it was observed twice, but detected only once.

Lx_Max
The maximum computed luminosity of the X-ray source in all of its detections in the 0.3-8.0 keV energy band, in erg/s, using the quoted distance and the flux calculated from the count rate as described in Section 3.5 of the reference paper.

Flux
The average computed flux of the X-ray source in all of its detections in the 0.3-8.0 keV energy band, in erg/s/cm2, using the count rate to flux calculation as described in Section 3.5 of the reference paper.

Flux_Max_To_Min
The ratio of the maximum to minimum X-ray flux Fmax/Fmin given as a variability indicator. Fmax is the maximum 0.3-8 keV flux from all detections and Fmin is the minimum flux from all detections and upper limits in the same band. The ratio is unity without quoted errors if the values of Fmax and Fmin are the same.

Flux_Max_To_Min_Pos_Err
The upper limit uncertainty in the Fmax/Fmin flux ratio.

Flux_Max_To_Min_Neg_Err
The lower limit uncertainty in the Fmax/Fmin flux ratio.

SNR_Max
The maximum detection significance of the X-ray source.

Counts_Max
The maximum photon counts of the X-ray source among all of its detections.

Phase_Statistics
The statistics for supersoft/quasisoft/hard/dim phases in the X-ray source. For example, s2 means supersoft in two observations, q3 means quasisoft in three observations, h4 means hard in four observations, and d1 means too dim (below 10 counts) in one observations.

Var_Flag
The statistics for variability within single observations by the Kolmorogov-Smirnov (K-S) criterion. For example, 'v:3' means that the source was variable by the K-S criterion (i.e., PKS < 0.01, more than 10 counts, and the background fraction is <10%) in three observations.

Source_Note
A note on the source type and/or identification, where 'ULX' means an ultraluminous X-rsy source, 'ULS' an ultraluminous supersoft source, and '(NGC598)' means that the source has been identified as the nucleus of the given galaxy.

Here, ULXs are defined as those non-nuclear sources with maximum LX (0.3-8keV) above 2 x 1039 erg s-1. These sources are further classified as '1ULX' if they are within the D25 isophotes of the host galaxies, and as '2ULX' if they are outside the D25 isophotes but within the 2 * D25 isophotes of the host galaxies. In addition, extreme ULXs with maximum LX (0.3-8keV) above 1040 erg s-1 are designated as 'EULX'. These definitions lead to 300 1ULXs (including 47 1EULXs), 179 2ULXs (including 27 2EULXs), and a total of 479 ULXs within 188 host galaxies.

234 of the 390 galactic nuclei observed in this survey have been identified as X-ray sources with luminosities ranging from 2 x 1036 to 2 x 1042 erg s-1 using the methodology discussed in Section 7 of the reference paper.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 9-Mar-2011