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M51CXO2 - M 51 Deep Chandra ACIS X-Ray Point Source Catalog

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Overview

The authors obtained a deep X-ray image of the nearby galaxy M 51 using the Chandra X-Ray Observatory. Here the catalog of X-ray sources detected in these observations is presented, while an overview of the properties of the point-source population is provided in the reference paper. The authors find 298 sources within the D25 radii (the apparent major isophotal galactic radii measured at or reduced to the surface brightness level muB = 25.0 B-mag per square arcsecond) of NGC 5194 and NGC 5195, of which 20% are variable, a dozen are classical transients, and another half dozen are transient-like sources. The typical number of active ultraluminous X-ray sources in any given observation is ~5, and only two of those sources persist in an ultraluminous state over the 12 years of observations. Given reasonable assumptions about the supernova remnant population, the luminosity function is well described by a power law with an index between 1.55 and 1.7, only slightly shallower than that found for populations dominated by high-mass X-ray binaries (HMXBs), which suggests that the binary population in NGC 5194 is also dominated by HMXBs. The luminosity function of NGC 5195 is more consistent with a low-mass X-ray binary dominated population.

This deep study of M51 is composed of 107 ks of archival Chandra observations, to which the authors added another 745 ks of observations. The Chandra ObsIDs and parameters of all of the observations used in this study (which span from June 2000 to October 2012) are given in Table 2 of the reference paper. All of the observations were made with the ACIS-S array. The authors used the ACIS Extract software package (AE) to perform the photometry. For each source, AE extracted a source region whose size and shape were based on the local PSF, and a background region whose size and shape were based on the size of the local PSF and the location of nearby sources. Source properties were then calculated in a standard manner. Of particular importance in this analysis is the prob_no_source parameter, which is the probability that one could measure the observed count rate in the absence of a source. The authors took a source to be significant only if this parameter was < 5 x 10-6. At this probability threshold, one would expect a single spurious source per field, or roughly 1.5 spurious sources within the D25 regions. As they used the same value in their analysis of M83 (Long et al. 2014, ApJS, 212, 21, the source catalog from which is available in the HEASARC database as the M83CXO table), the two catalogs are directly comparable.


Catalog Bibcode

2016ApJ...827...46K

References

A deep Chandra ACIS survey of M51.
    Kuntz K.D., Long K.S., Kilgard R.E.
   <Astrophys. J., 827, 46-46 (2016)>
   =2016ApJ...827...46K    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in January 2017 based on CDS Catalog J/ApJ/827/46 files table4.dat, table5.dat and table6.dat.

Parameters

Source_Number
A running number for the X-ray source in order of increasing J2000.0 Right Ascension.

Name
The name of the X-ray source using the 'CXOKM51' prefix followed by 'Xnnn', where 'CXO' stands for Chandra X-ray Observatory, 'K' for Kuntz, M51 for M51 (NGC 5194/5195), 'X' indicates X-ray source and nnn is the source number. These names were created by the HEASARC using a general style format 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 tables.

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 tables.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The 1-sigma statistical positional uncertainty, in arcseconds.

Exposure
The total exposure time at the Chandra X-ray source position, in seconds (converted by the HEASARC from the ks units that were used in the original table).

Count_Rate
The broad-band (0.35-8.0 keV) count rate of the X-ray source, in counts per second. This is the mean value over all exposures. This was converted by the HEASARC from the ct/ks units that were used in the original table.

Count_Rate_Error
The uncertainty in the broad-band (0.35-8.0 keV) count rate of the X-ray source, in counts per second. This was converted by the HEASARC from the ct/ks units that were used in the original table.

Hardness_Ratio_1
The hardness Ratio HR1, (M-S)/T, of the Chandra X-ray source, where S, M and T are the photon fluxes in the soft (0.35-1.1 keV), medium (1.1-2.6 keV) and total (0.35-8.0 keV) bands, respectively.

Hardness_Ratio_1_Error
The uncertainty in the hardness ratio (M-S)/T.

Hardness_Ratio_2
The hardness Ratio HR2, (H-M)/T, of the Chandra X-ray source, where M, H and T are the photon fluxes in the medium (1.1-2.6 keV), hard (2.6-8.0 keV) and total (0.35-8.0 keV) bands, respectively.

Hardness_Ratio_2_Error
The uncertainty in the hardness ratio (H-M)/T.

Photon_Flux_1
The 0.35-8.0 keV (T band) photon flux of the Chandra X-ray source, in photon cm-2 s-1, based on the time-averaged spectrum of the source that was produced by AE. The conversion of source counts to flux of an X-ray source depends on the assumed X-ray spectrum and, for soft sources, the absorbing column density. The authors assumed a power-law source with a photon index of 1.9 and a foreground Milky Way absorption column of 2 x 1020 cm-2. This choice of spectrum is appropriate for compact binaries and background AGNs, and is typical of that chosen for other studies of the X-ray properties of normal galaxies

Photon_Flux_1_Error
The uncertainty in the corresponding photon flux of the Chandra X-ray source, in photon cm-2 s-1.

Photon_Flux_2
The 0.35-1.1 keV (S band) photon flux of the Chandra X-ray source, in photon cm-2 s-1, based on the time-averaged spectrum of the source that was produced by AE. The conversion of source counts to flux of an X-ray source depends on the assumed X-ray spectrum and, for soft sources, the absorbing column density. The authors assumed a power-law source with a photon index of 1.9 and a foreground Milky Way absorption column of 2 x 1020 cm-2. This choice of spectrum is appropriate for compact binaries and background AGNs, and is typical of that chosen for other studies of the X-ray properties of normal galaxies.

Photon_Flux_2_Error
The uncertainty in the corresponding photon flux of the Chandra X-ray source, in photon cm-2 s-1.

Photon_Flux_3
The 1.1-2.6 keV (M band) photon flux of the Chandra X-ray source, in photon cm-2 s-1, based on the time-averaged spectrum of the source that was produced by AE. The conversion of source counts to flux of an X-ray source depends on the assumed X-ray spectrum and, for soft sources, the absorbing column density. The authors assumed a power-law source with a photon index of 1.9 and a foreground Milky Way absorption column of 2 x 1020 cm-2. This choice of spectrum is appropriate for compact binaries and background AGNs, and is typical of that chosen for other studies of the X-ray properties of normal galaxies.

Photon_Flux_3_Error
The uncertainty in the corresponding photon flux of the Chandra X-ray source, in photon cm-2 s-1.

Photon_Flux_4
The 2.6-8.0 keV (H band) photon flux of the Chandra X-ray source, in photon cm-2 s-1, based on the time-averaged spectrum of the source that was produced by AE. The conversion of source counts to flux of an X-ray source depends on the assumed X-ray spectrum and, for soft sources, the absorbing column density. The authors assumed a power-law source with a photon index of 1.9 and a foreground Milky Way absorption column of 2 x 1020 cm-2. This choice of spectrum is appropriate for compact binaries and background AGNs, and is typical of that chosen for other studies of the X-ray properties of normal galaxies.

Photon_Flux_4_Error
The uncertainty in the corresponding photon flux of the Chandra X-ray source, in photon cm-2 s-1.

Photon_Flux_5
The 0.5-2.0 keV band photon flux of the Chandra X-ray source, in photon cm-2 s-1, based on the time-averaged spectrum of the source that was produced by AE. This band is typically used in the construction of luminosity functions. The conversion of source counts to flux of an X-ray source depends on the assumed X-ray spectrum and, for soft sources, the absorbing column density. The authors assumed a power-law source with a photon index of 1.9 and a foreground Milky Way absorption column of 2 x 1020 cm-2. This choice of spectrum is appropriate for compact binaries and background AGNs, and is typical of that chosen for other studies of the X-ray properties of normal galaxies.

Photon_Flux_5_Error
The uncertainty in the corresponding photon flux of the Chandra X-ray source, in photon cm-2 s-1.

Photon_Flux_6
The 2.0-8.0 keV band photon flux of the Chandra X-ray source, in photon cm-2 s-1, based on the time-averaged spectrum of the source that was produced by AE. This band is typically used in the construction of luminosity functions. The conversion of source counts to flux of an X-ray source depends on the assumed X-ray spectrum and, for soft sources, the absorbing column density. The authors assumed a power-law source with a photon index of 1.9 and a foreground Milky Way absorption column of 2 x 1020 cm-2. This choice of spectrum is appropriate for compact binaries and background AGNs, and is typical of that chosen for other studies of the X-ray properties of normal galaxies

Photon_Flux_6_Error
The uncertainty in the corresponding photon flux of the Chandra X-ray source, in photon cm-2 s-1.

Lx
The average 0.35-8.0 keV (T band) luminosity of the Chandra X-ray source, in erg s-1. The X-ray luminosity is calculated from the energy flux in the 0.35-8.0 keV band, assuming that it is located at the 7.6 Mpc distance of NGC 5194 and 5195.

Lx_Error
The statistical uncertainty in the total 0.35-8.0 keV luminosity of the Chandra X-ray source, in erg s-1.

Tw2004_Source_Number
The source number of the object in Terashima and Wilson (2004, ApJ, 601, 735): the Chandra source catalog from this reference is available in the HEASARC database as the M51CXO table.

Tw2004_Flag
This parameter flags the location of the source and is taken from Terashima and Wilson (2004, ApJ, 601, 735). The codes have the following meanings:

      Value   Association   Name in Simbad (and Alt_Name in M51CXO table)

       a      NGC 5194      "[TW2004] NGC 5194 NN";
       b      NGC 5195      "[TW2004] NGC 5195 NN";
       o      other         "[TW2004] Source NN".
  

Kcg2005_Name
The name of the object in the Kilgard et al. (2005, ApJS, 159, 214) source catalog. The authors recovered all but three of the sources listed by Kilgard et al. (2005). Source CXOU J132957.4+471613 appears to be one of a pair of sources in the Kilgard et al. list that form a single source within the present list. Kilgard's source CXOU J132958.4+471548 is Terashima's source 5 in NGC 5195 (his J132958.4+471547) and is the only source from the Terashima & Wilson (2004) list that was not detected in this work.

Mck2007_Source_Number
The source number of the corresponding radio source in the Maddox et al. (2007, AJ, 133, 2559) list.

Multiwavelength_IDs
Identifier(s) of multiwavelength counterpart source in the optical (SDSS: the objID number) or radio (FIRST). In the region with SDSS imaging but not SDSS photometry, the authors merely note the existence of optical sources within the Chandra PSF (such cases are labeled as "SDSS Visual".

SDSS_Type
The SDSS extension-based object type: "STR" for stellar (point-like) and "GAL" for galaxy (extended).

Source_Type
The authors' object type classification, as follows:

      FGS = foreground star;
      GAL = galaxy;
      HAB = H-alpha bubble;
        S = stellar (point like, but not necessarily a star);
      SFR = star-forming region;
       SN = historical supernova.
  

Galaxy_Code
This parameter flags sources according to which galaxy against which they are projected: A = NGC 5194; B = NGC 5195.

Long_Term_Var_Bands
The presence of long-term source variation, i.e., of variation between the individual observations used in this study is flagged by the energy band(s) in which the variation was detected: S, M, H, T, s or h.

         S: 0.35-1.1 keV,
         M: 1.1-2.6 keV,
         H: 2.6-8.0 keV,
         T: 0.35-8.0 keV,
         s: 0.5-2.0 keV,
         h: 2.0-8.0 keV.
  
Note that sources in the outer regions of the field may not have measured long-term variation due to lack of multi-epoch coverage.

Med_Term_Var_Bands
The presence of medium-term source variation, i.e., of variation between observations in epoch E (the 7 Chandra observations made between September 12, 2012 and October 10, 2012) is flagged by the energy band(s) in which the variation was detected: S, M, H, T, s or h.

         S: 0.35-1.1 keV,
         M: 1.1-2.6 keV,
         H: 2.6-8.0 keV,
         T: 0.35-8.0 keV,
         s: 0.5-2.0 keV,
         h: 2.0-8.0 keV.
  

Notes
Additional notes on the source. When the source is marked as having source_type = "FGS", the notes contain information about the proper motion. When the source is marked as source_type = "HAB", the notes contain information about the H-alpha morphology. Objects previously noted as ULXs are noted here, even if they are not persistent. Transient and "drop-out" sources are noted.


Contact Person

Questions regarding the M51CXO2 database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 9-Jan-2017