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MOXC - Massive Star-Forming Regions Omnibus X-Ray Catalog

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Overview

This table contains the Massive Star-forming Regions (MSFRs) Omnibus X-ray Catalog (MOXC), a compendium of X-ray point sources from Chandra/ACIS observations of a selection of MSFRs across the Galaxy, plus 30 Doradus in the Large Magellanic Cloud. MOXC consists of 20,623 X-ray point sources from 12 MSFRs with distances ranging from 1.7 kpc to 50 kpc, and comprises Table 3 of the reference paper. In their paper, the authors show the morphology of the unresolved X-ray emission that remains after the cataloged X-ray point sources are excised from the ACIS data, in the context of Spitzer and WISE observations that trace the bubbles, ionization fronts, and photon-dominated regions that characterize MSFRs. In previous work, they have found that this unresolved X-ray emission is dominated by hot plasma from massive star wind shocks. This diffuse X-ray emission is found in every MOXC MSFR, clearly demonstrating that massive star feedback (and the several-million-degree plasmas that it generates) is an integral component of MSFR physics.

The Chandra observations used for the Massive Star-forming Regions Omnibus X-ray Catalog (MOXC) are summarized in Table 2 of the reference paper and have dates ranging from 2000-04-03 to 2013-01-31 for the 12 MSFRs: the 7 MYStIX targets NGC 6334, NGC 6357, M 16, M 17, W 3, W 4 and NGC 3576, and the 5 "beyond-MYStIX" targets G333.6-0.2, W 51A, G29.96-0.02, NGC 3603 and 30 Doradus.

A similar table to MOXC for other MYStIX targets was presented by Kuhn et al. (2013, ApJS, 209, 27, available as the HEASARC MYSTIXXRAY table). The main difference between that table and the MOXC version is that the present authors have chosen to omit absorption-corrected X-ray source luminosities from the XPHOT algorithm (Getman et al. 2010, ApJ, 708, 1760) herein, because those quantities are given in Broos et al. (2013, ApJS, 209, 32, available as the HEASARC MYSTIXMPCM table) for relevant MYStIX X-ray sources (those classified as pre-main sequence stars). For beyond-MYStIX targets, the authors chose to postpone XPHOT calculations until the X-ray sources were classified, since XPHOT estimates are only appropriate for pre-MS stars. The XPHOT code is available (Getman et al. 2012, Astrophysics Source Code Library, record ascl.soft12002) if others wish to use it on MOXC sources.

All photometric quantities in this table are apparent (not corrected for absorption). The HEASARC has used prefixes 'fb_', 'sb_' and 'hb_' (replacing the suffixes '_t', '_s' and '_h' used in the reference paper) on the names of the X-ray photometric quantities which designate the full (total, 0.5 - 8 keV), soft (0.5 - 2.0 keV) and hard (2-8 keV) energy bands. Correction for finite extraction apertures is applied to the ancillary reference file (ARF) calibration products (see Broos et al. 2010, ApJ, 714, 1582, Section 5.3); the total_counts and counts quantities characterize the extraction and are not aperture-corrected. The only calibrated quantities presented are the apparent photon fluxes, in units of photon cm-2 s-1 (see Broos et al. 2010, ApJ, 714, 1582, Section 7.4), and estimates for the apparent energy fluxes, in units of erg cm-2 s-1 (Getman et al. 2010, ApJ, 708, 1760).


Catalog Bibcode

2014ApJS..213....1T

References

The Massive Star-Forming Regions Omnibus X-ray Catalog.
    Townsley L.K., Broos P.S., Garmire G.P., Bouwman J., Povich M.S.,
    Feigelson E.D., Getman K.V., Kuhn M.A.
   <Astrophys. J. Suppl. Ser., 213, 1 (2014)>
   =2014ApJS..213....1T

Provenance

This table was created by the HEASARC in October 2014 based on CDS Catalog J/ApJS/213/1 files table3.dat (the MOXC X-ray Source Catalog) and table6.dat (the list of MOXC sources in previously published Chandra catalogs).

HEASARC Implementation

There was one source in Table 6 of the reference paper, 'CXOU J172403.37-341400.8', which was not in Table 3, the main MOXC X-ray source table. This source is not included in this HEASARC representation of MOXC.

Parameters

SFR_Name
The designation of the massive star-forming region. See Table 1 of the reference paper for more information on the MSFRs. These names and the internal source labels identify Chandra pointings; they do not necessarily convey membership in astrophysical clusters.

Name
The IAU-style J2000 position-based source designation, e.g., 'CXOU JHHMMSS.ss+DDMMSS.s', with the prefix 'CXOU' standing for Chandra X-ray Observatory, Unregistered. Notice that these designations are non-standard according to the guidelines of the Dictionary of Nomenclature of Celestial Objects, which suggests that they should be of the form 'CXOU JHHMMSS.s+DDMMSS', i.e., with lower-precision coordinates.

Internal_Name
The source designation used within the project for an X-ray source in a particular MSFR.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates to an accuracy of 10-6 degrees (0.0036 arcseconds) in the original reference. Source positions are computed using a subset of each source's extractions chosen to minimize the position uncertainty (Broos et al. 2010, ApJ, 714, 1582, Sections 6.2 and 7.1).

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates to an accuracy of 10-6 degrees (0.0036 arcseconds) in the original reference. Source positions and their uncertainties are computed using a subset of each source's extractions chosen to minimize the position uncertainty (Broos et al. 2010, ApJ, 714, 1582, Sections 6.2 and 7.1).

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The radius of the 1-sigma positional error circle around the source position, in arcseconds. Source positions and their uncertainties are computed using a subset of each source's extractions chosen to minimize the position uncertainty (Broos et al. 2010, ApJ, 714, 1582, Sections 6.2 and 7.1).

Pos_Algorithm
The particular algorithm which was used to estimate the source position: "AE correlation", "AE mean data", "AE reconstruction" or "eye". The algorithms used are described in Section 7.1 of Broos et al. (2010, ApJ, 714, 1582, hereafter B10).

Prob_No_Src_Min
The smallest of the 3 band-dependent 'no-source' probabilities (p-values), fb_prob_no_src,sb_prob_no_src and hb_prob_no_src.

FB_Prob_No_Src
The probability for the 'no-source' hypothesis in the full 0.5-8.0 keV band, i.e., the p-value as described in B10, Section 4.3. In statistical hypothesis testing, the p-value is the probability of obtaining a test statistic at least as extreme as the one that was actually observed when the null hypothesis is true.

SB_Prob_No_Src
The probability for the 'no-source' hypothesis in the soft 0.5-2.0 keV band, i.e., the p-value as described in B10, Section 4.3. In statistical hypothesis testing, the p-value is the probability of obtaining a test statistic at least as extreme as the one that was actually observed when the null hypothesis is true.

HB_Prob_No_Src
The probability for the 'no-source' hypothesis in the hard 2.0-8.0 keV band, i.e., the p-value as described in B10, Section 4.3. In statistical hypothesis testing, the p-value is the probability of obtaining a test statistic at least as extreme as the one that was actually observed when the null hypothesis is true.

Single_Ks_Prob
The smallest p-value for the one-sample Kolmogorov-Smirnov statistic under the no-variability null hypothesis within a single observation. See B10, Section 7.6 for a description of the variability metrics.

Merged_Ks_Prob
The smallest p-value for the one-sample Kolmogorov-Smirnov statistic under the no-variability null hypothesis for the merged observations. See B10, Section 7.6 for a description of the variability metrics and caveats regarding possible spurious indications of variability using the merged_ks_prob metric.

Nominal_Exposure
The total nominal exposure time for the X-ray source in the merged observations, in seconds.

Frac_Expo
The fraction of the total nominal exposure time that the X-ray source was observed. Due to dithering over inactive portions of the focal plane, a Chandra source is often not observed during some fraction of the nominal exposure time. (See http://cxc.harvard.edu/ciao/why/dither.html.) The reported quantity is the value of FRACEXPO produced by the CIAO tool mkarf.

Rate_In_3x3_Cell
ACIS suffers from a non-linearity at high count rates known as photon pile-up, described in Section 3.2 of the reference paper. The parameter rate_in_3x3_cell is an estimate of the observed 0.5-8 keV count rate, in counts per frame, falling on an event detection cell of size 3x3 ACIS pixels, and centered on the source position. When its value exceeds 0.05 counts per frame, the reported source properties may be biased by pile-up effects. See Table 4 in the reference paper for a list of MOXC sources with significant pile-up.

Num_Obs_Extracted
The total number of observations of the source that were extracted.

Num_Obs_Merged
The number of observations of the source that were merged so as to estimate its photometric properties.

Frac_Expo_Discard
The fraction of exposures that were discarded in the merging of the observations for the source.

Off_Axis_Min
The smallest off-axis angle ThetaLo of the X-ray source among the merged observations, in arcminutes.

Off_Axis
The average off-axis angle Theta of the X-ray source among the merged observations, in arcminutes.

Off_Axis_Max
The largest off-axis angle ThetaHi of the X-ray source among the merged observations, in arcminutes.

PSF_Fraction
The average PSF fraction at 1.5 keV for the X-ray source in the merged observations.

Aperture_Area
The average aperture area for the X-ray source in the merged observations, in units of the number of pixels of 0.492 by 0.492 arcseconds in size.

Afterglow_Fraction
The suspected afterglow fraction. Since the extracted event data are lightly cleaned to avoid removing legitimate X-ray events from bright sources (B10, Section 3), some background events arising from an effect known as "afterglow" (http://cxc.harvard.edu/ciao/why/afterglow.html) will remain and may contaminate source extractions, despite careful procedures to identify and remove them during data preparation. After extraction, the authors attempted to identify afterglow events using the tool ae_afterglow_report (see the AE manual at http://www.astro.psu.edu/xray/acis/acis_analysis.html) and report the fraction of extracted events attributed to afterglow in this parameter.

FB_Total_Counts
The observed total-band (0.5-8 keV) total counts in the X-ray source in the merged apertures.

SB_Total_Counts
The observed soft-band (0.5-2 keV) total counts in the X-ray source in the merged apertures.

HB_Total_Counts
The observed hard-band (2-8 keV) total counts in the X-ray source in the merged apertures.

Bck_Scaling
The scaling of the background extraction (See B10, Section 5.4) for the X-ray source.

FB_Bck_Counts
The observed 0.5-8 keV counts in the merged background regions.

SB_Bck_Counts
The observed 0.5-2 keV counts in the merged background regions.

HB_Bck_Counts
The observed 2-8 keV counts in the merged background regions.

FB_Counts
The net (background-subtracted) 0.5-8 keV counts in the merged apertures for the X-ray source.

FB_Counts_Neg_Err
The 1-sigma negative error in the full-band counts for the X-ray source. The 68%-confidence intervals for the net counts quantities were estimated by the CIAO tool aprates (http://asc.harvard.edu/ciao/ahelp/aprates.html). The HEASARC calculated the negative error using the lower bound value given in the original table and the value of the corresponding counts parameter.

FB_Counts_Pos_Err
The 1-sigma positive error in the full-band counts for the X-ray source. The 68%-confidence intervals for the net counts quantities were estimated by the CIAO tool aprates (http://asc.harvard.edu/ciao/ahelp/aprates.html). The HEASARC calculated the positive error using the upper bound value given in the original table and the value of the corresponding counts parameter.

SB_Counts
The net (background-subtracted) 0.5-2 keV counts in the merged apertures for the X-ray source.

SB_Counts_Neg_Err
The 1-sigma negative error in the soft-band counts for the X-ray source. The 68%-confidence intervals for the net counts quantities were estimated by the CIAO tool aprates (http://asc.harvard.edu/ciao/ahelp/aprates.html). The HEASARC calculated the negative error using the lower bound value given in the original table and the value of the corresponding counts parameter.

SB_Counts_Pos_Err
The 1-sigma positive error in the soft-band counts for the X-ray source. The 68%-confidence intervals for the net counts quantities were estimated by the CIAO tool aprates (http://asc.harvard.edu/ciao/ahelp/aprates.html). The HEASARC calculated the positive error using the upper bound value given in the original table and the value of the corresponding counts parameter.

HB_Counts
The net (background-subtracted) 2-8 keV counts in the merged apertures for the X-ray source.

HB_Counts_Neg_Err
The 1-sigma negative error in the hard-band counts for the X-ray source. The 68%-confidence intervals for the net counts quantities were estimated by the CIAO tool aprates (http://asc.harvard.edu/ciao/ahelp/aprates.html). The HEASARC calculated the negative error using the lower bound value given in the original table and the value of the corresponding counts parameter.

HB_Counts_Pos_Err
The 1-sigma positive error in the hard-band counts for the X-ray source. The 68%-confidence intervals for the net counts quantities were estimated by the CIAO tool aprates (http://asc.harvard.edu/ciao/ahelp/aprates.html). The HEASARC calculated the positive error using the upper bound value given in the original table and the value of the corresponding counts parameter.

FB_Arf_Value
The mean 0.5-8 keV ancillary response file (ARF) value, in units of cm2 count photon-1. The ARF in ACIS data analysis represents both the effective area of the observatory and the fraction of the observation for which data were actually collected for the source (the frac_expo parameter).

SB_Arf_Value
The mean 0.5-2 keV ancillary response file (ARF) value, in units of cm2 count photon-1. The ARF in ACIS data analysis represents both the effective area of the observatory and the fraction of the observation for which data were actually collected for the source (the frac_expo parameter). #

HB_Arf_Value
The mean 2-8 keV ancillary response file (ARF) value, in units of cm2 count photon-1. The ARF in ACIS data analysis represents both the effective area of the observatory and the fraction of the observation for which data were actually collected for the source (the frac_expo parameter). #

FB_Median_Energy
The median energy of the observed spectrum of the X-ray source, in the 0.5-8 keV band, in keV. This is the AE quantity ENERG_PCT50_OBSERVED, the median energy of extracted events, corrected for background events (B10, Section 7.3).

SB_Median_Energy
The median energy of the observed spectrum of the X-ray source, in the 0.5-2.0 keV band, in keV. This is the AE quantity ENERG_PCT50_OBSERVED, the median energy of extracted events, corrected for background events (B10, Section 7.3).

HB_Median_Energy
The median energy of the observed spectrum of the X-ray source, in the 2-8 keV band, in keV. This is the AE quantity ENERG_PCT50_OBSERVED, the median energy of extracted events, corrected for background events (B10, Section 7.3).

FB_Obs_Photon_Flux
The incident photon flux in the total (0.5-8 keV) band, in photon cm-2 s-1. This is the net counts over the product of the mean effective area in this band (the fb_arf_value) and the nominal exposure time (See B10, Section 7.4).

SB_Obs_Photon_Flux
The incident photon flux in the soft (0.5-2 keV) band, in photon cm-2 s-1. This is the net counts over the product of the mean effective area in this band (the sb_arf_value) and the nominal exposure time (See B10, Section 7.4).

HB_Obs_Photon_Flux
The incident photon flux in the hard (2-8 keV) band, in photon cm-2 s-1. This is the net counts over the product of the mean effective area in this band (the hb_arf_value) and the nominal exposure time (See B10, Section 7.4).

FB_Obs_Flux
The apparent (observed) 0.5-8 keV energy flux of the source, in erg cm-2 s-1, defined as the sum of the maximum apparent energy flux in the soft band and the maximum apparent energy flux in the hard band.

SB_Obs_Flux
The apparent (observed) 0.5-2.0 keV energy flux of the source, in erg cm-2 s-1, defined as 1.602 x 10-9 (erg keV-1) times the corresponding photon flux times the median energy in this band (Getman et al. 2010, ApJ, 708, 1760, Section 2.2).

HB_Obs_Flux
The apparent (observed) 2-8 keV energy flux of the source, in erg cm-2 s-1, defined as 1.602 x 10-9 (erg keV-1) times the corresponding photon flux times the median energy in this band (Getman et al. 2010, ApJ, 708, 1760, Section 2.2).

Prev_Cat_Source_Number
The previously published Chandra Catalog source identifier, if there was one. Chandra catalogs for the five MOXC targets listed in Table 5 of the reference paper (reproduced below) have been published previously:

          Table 5: Previously Published Chandra Catalogs of MOXC Targets

  Target         Reference                                   Astrometric offset
                                                            RA(J2000) Dec(J2000)
                                                                  (arcsec)

   NGC 6334      Feigelson et al. (2009, AJ, 138, 227)        0.01   0.02
   NGC 6357      Wang et al.      (2007, ApJS, 168, 100)      0.06   0.01
   Eagle Nebula  Guarcello et al. (2012, ApJ, 753, 117)      -0.06   0.01
   M17           Broos et al.     (2007, ApJS, 169, 353)      0.01   0.03
   30 Doradus    Townsley et al.  (2006, AJ, 131, 2164)      -0.09   0.13
  
The astrometric offsets are the adjustment to the published coordinates required for the best alignment with the MOXC coordinates.

For NGC 6334 and M16, the ACIS ObsIDs used here are identical or similar to those used in the earlier studies, but MOXC uses slightly (for NGC 6334) or substantially (for M16) different analysis methodologies. For the other targets in Table 5, MOXC uses deeper ACIS data (or covers a wider field with more ACIS pointings) than what was available in earlier studies. For the reader's convenience, the authors have matched those previously published catalogs for these targets to the MOXC catalog, using a simple algorithm (Section 8 in Broos et al. 2010) in which the maximum acceptable separation between a MOXC source and a published counterpart is based on the individual source position errors, assuming Gaussian distributions, scaled so that ~99% of true associations should be identified as matches. When multiple sources in the published catalog satisfy the match criterion, the closest one was adopted as the actual match.

Prev_Cat_Name
The previously published Chandra Catalog J2000.0 position-based source name, e.g., 'CXOU JHHMMSS.ss+DDMMSS.s', with the prefix 'CXOU' standing for Chandra X-ray Observatory, Unregistered. Notice that these designations are non-standard according to the guidelines of the Dictionary of Nomenclature of Celestial Objects, which suggests that they should be of the form 'CXOU JHHMMSS.s+DDMMSS', i.e., with lower-precision coordinates.

Prev_Cat_Moxc_Offset
The offset between the MOXC and previously published source positions, in arcseconds. Prior to matching, the authors estimated and removed small astrometric offsets between the MOXC catalogs and the previously published catalog coordinate systems (see Table 5 reproduced above). This step removes systematic catalog offsets; it is a very small effect for the published catalogs considered here, but the authors include this step in all catalog matching because these systematic offsets can be quite large and will result in mismatches (and serious confusion in the literature) if not eliminated before matching.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 15-Oct-2014