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CHANSNGCAT - Chandra ACIS Survey for X-Ray AGN in Nearby Galaxies

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Overview

The authors searched the public archive of the Chandra X-ray Observatory as of 2016 March and assembled a sample of 719 galaxies within 50 Mpc with available Advanced CCD Imaging Spectrometer observations. By cross-correlation with the optical or near-infrared nuclei of these galaxies, 314 of them are identified to have an X-ray active galactic nucleus (AGN). The majority of them are low-luminosity AGNs and are unlikely X-ray binaries based upon their spatial distribution and luminosity functions. The AGN fraction is around 60% for elliptical galaxies and early-type spirals, but drops to roughly 20% for Sc and later types, consistent with previous findings in the optical. However, the X-ray survey is more powerful in finding weak AGNs, especially from regions with active star formation that may mask the optical AGN signature. For example, 31% of the H II nuclei are found to harbor an X-ray AGN. For most objects, a single power-law model subject to interstellar absorption is adequate to fit the spectrum, and the typical photon index is found to be around 1.8. For galaxies with a non-detection, their stacked Chandra image shows an X-ray excess with a luminosity of a few times 1037 erg/s on average around the nuclear region, possibly composed of faint X-ray binaries. This paper reports on the technique and results of the survey; in-depth analysis and discussion of the results were to be reported in forthcoming papers, e.g., She et al. (2017, ApJ, 842, 131).

The sample was assembled based on Chandra/ACIS observations that were publicly available as of 2016 March. The authors first generated a full list of ACIS observations, and then searched in the NASA/IPAC Extragalactic Database (NED) for galaxies within 50 Mpc whose nuclear positions were less than 8 arcminutes from the aim point of any Chandra observation. The adopted distances were taken from NED, in the following order of priority: surface brightness fluctuations, Cepheid variables, tip of the red giant branch, Type Ia supernovae, the fundamental plane, Faber-Jackson relation, Tully-Fisher relation. If more than one reference is available for the distance by the same means, the latest one is selected, unless otherwise specified. Whenever possible, the authors obtain positions of the galaxy nuclei based on measurements from near-infrared images, which suffer from less obscuration by dust or confusion from young star-forming regions. Most of the data come from the Two-Micron All Sky Survey (2MASS) extended source catalog (Skrutskie et al. 2006, AJ, 131, 1163), or NED otherwise. In a few cases, the NED positions come from radio observations. The authors discarded galaxies whose nuclear positions in NED were obtained from X-ray observations.


Catalog Bibcode

2017ApJ...835..223S

References

Chandra survey of nearby galaxies: the catalog.
    She R., Ho L.C., Feng H.
   <Astrophys. J., 835, 223-223 (2017)>
   =2017ApJ...835..223S    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in September 2017 based upon the CDS Catalog J/ApJ/835/223 files table1.dat, table2.dat and table4.dat.

Parameters

Source_Number
A unique identification number for each nearby galaxy in this catalog.

Name
The name of the galaxy.

Distance
The distance of the galaxy, in Mpc, taken from NED. See the Overview above for more details on how these distances were selected.

RA
The Right Ascension of (the nucleus of) the galaxy in the selected equinox. (See the Overview above for more details on how the positions were selected). This was given in J2000.0 equatorial coordinates to a precision of 0.01 seconds of time in the original table.

Dec
The Declination of (the nucleus of) the galaxy in the selected equinox. (See the Overview above for more details on how the positions were selected). This was given in J2000.0 equatorial coordinates to a precision of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of (the nucleus of) the galaxy.

BII
The Galactic Latitude of (the nucleus of) the galaxy.

Nuclear_Class
Classification of the nuclear optical spectrum, as described in Section 3 of Ho et al. (1997, ApJS, 112, 315), where 'H' means H II nucleus, 'S' means Seyfert nucleus, 'L' means LINER, and 'T' means transition object. The number attached to the class letter designates the type (1.0, 1.2, 1.5, 1.8, 1.9, and 2); quality ratings are given by ':' and '::' for uncertain and highly uncertain classification, respectively. Two classifications are given for some ambiguous cases, where the first entry corresponds to the adopted choice (e.g., 'L2/S2' means that the object is most likely a LINER 2, but may actually be a Seyfert 2).

Hubble_Type
The Hubble type of the galaxy, taken from NED.

Class
The HEASARC Browse object classification, based on the Hubble type.

Sigma
The central velocity dispersion, sigma, of the galaxy, in km s-1. There are 419 galaxies in this sample that have published central stellar velocity dispersions: 249 objects from the Palomar survey (Ho et al. 2009, ApJS, 183, 1), 163 objects from the HyperLeda database (see CDS Cat. VII/237), and 7 objects from Gue (2006, MNRAS, 366, 480).

Sigma_Error
The uncertainty in the central velocity dispersion, sigma, of the galaxy, in km s-1.

Log_L_Halpha
The logarithm of the H-alpha luminosity of the galaxy, in erg s-1, from the Palomar survey (Ho et al. 1997, ApJS, 112, 315; 2003, ApJ, 583, 159). The typical uncertainty is 10-30%. In some cases (entries with non-blank values of the related log_l_halpha_flag parameter), the quoted value is more uncertain, or is a lower or upper limit to the actual value.

Log_L_Halpha_Flag
This flag parameter indicates that the quoted value of log_l_halpha is more than usually uncertain, or is a lower or upper limit to the actual value, as follows:

    Value  Significance

      b     an uncertainty of 30-50%
      c     an uncertainty of 100%
      L     a 3-sigma lower limit
      u     a 3-sigma upper limit
  

Log_Blackhole_Mass
The logarithm of the central black hole mass, MBH, in the galaxy, in solar masses. This is estimated using the MBH - sigma relation. More details are given in the reference paper.

Log_Blackhole_Mass_Lower
The lower limit to the logarithm of the central black hole mass, MBH, in the galaxy, in solar masses.

Log_Blackhole_Mass_Upper
The upper limit to the logarithm of of the central black hole mass, MBH, in the galaxy, in solar masses.

NH_Gal
The Galactic absorption column density, NH,0, in H atoms cm-2.

ObsID
The Chandra ACIS observation identifier, ObsID.

Instrument
The instrument in the focal plane for the Chandra observation: ACIS-S or ACIS-I.

Exposure
The exposure time of the Chandra observation, in seconds.

Offset
The offset from the nearest point-like X-ray source to the optical/infrared (in a few cases, radio) position of the galaxy nucleus, in arcseconds.

AGN_Flag
This flag parameter is set to 'Y' if the authors consider that the specified galaxy has an AGN, else is set to 'N'.

Hardness_Ratio_0
The Chandra ACIS hardness ratio, HR0, of the X-ray source identified as the AGN, where HR0 = (CH - CM - CS)/C_T), where CS, CM, CH, and CT are the counts in the soft band (0.3 - 1.0 keV), the counts in the medium band (1.0 - 2.0 keV), the counts in the hard band (2 - 8 keV), and the counts in the full band (0.3 - 8 keV), respectively.

Hardness_Ratio_0_Error
The uncertainty in the Chandra ACIS hardness ratio, HR0, of the X-ray source identified as the AGN.

Hardness_Ratio_1
The Chandra ACIS hardness ratio, HR1, of the X-ray source identified as the AGN, where HR1 = (CM - CS)/C_T), where CS, CM, CH, and CT are the counts in the soft band (0.3 - 1.0 keV), the counts in the medium band (1.0 - 2.0 keV), the counts in the hard band (2 - 8 keV), and the counts in the full band (0.3 - 8 keV), respectively.

Hardness_Ratio_1_Error
The uncertainty in the Chandra ACIS hardness ratio, HR1, of the X-ray source identified as the AGN.

Hardness_Ratio_2
The Chandra ACIS hardness ratio, HR2, of the X-ray source identified as the AGN, where HR2 = (CH - CM)/C_T), where CS, CM, CH, and CT are the counts in the soft band (0.3 - 1.0 keV), the counts in the medium band (1.0 - 2.0 keV), the counts in the hard band (2 - 8 keV), and the counts in the full band (0.3 - 8 keV), respectively.

Hardness_Ratio_2_Error
The uncertainty in the Chandra ACIS hardness ratio, HR2, of the X-ray source identified as the AGN.

NH_From_HR
The intrinsic absorption column density towards the X-ray source, as inferred from its hardness ratio, in H atom cm-2 (not populated if no X-ray emission was detected).

NH_From_HR_Lower
The lower limit to the intrinsic absorption column density towards the X-ray source, as inferred from its hardness ratio, in H atoms cm-2.

NH_From_HR_Upper
The upper limit to the intrinsic absorption column density towards the X-ray source, as inferred from its hardness ratio, in H atoms cm-2.

Flux
The inferred observed flux of the X-ray source in the 2-10 keV energy band, in erg cm-2 s-1 (not populated if no X-ray emission was detected).

Flux_Lower
The 90% confidence lower limit to the inferred observed flux of the X-ray source in the 2-10 keV energy band, in erg cm-2 s-1.

Flux_Upper
The 90% confidence upper limit to the inferred observed flux of the X-ray source in the 2-10 keV energy band, in erg cm-2 s-1.

Log_Lx
The logarithm of the luminosity of the X-ray source in the 2-10 keV energy band, in erg s-1 (not populated if no X-ray emission was detected).

Log_Lx_Lower
The 90% confidence lower limit to the luminosity of the X-ray source in the 2-10 keV energy band, in erg s-1.

Log_Lx_Upper
The 90% confidence upper limit to the luminosity of the X-ray source in the 2-10 keV energy band, in erg s-1.

Log_Lx_Note
This flag parameter can include a note on the derivation of the X-ray luminosity or, for sources suffering from pileup, a coded reference. The reference codes and abbreviations are as follows:

       Ref.1 = Ebrero et al. (2011, A&A, 535A, 62),
       Ref.2 = De Rosa et al. (2012, MNRAS, 420, 2087),
       Ref.3 = Cappi et al. (2006, A&A, 446, 459),
       Ref.4 = Shu et al. (2010, ApJ, 713, 1256),
       Ref.5 = Iyomoto et al. (1998, ApJ, 503, 168),
       Ref.6 = Ptak et al. (2004, ApJ, 606, 173),
       Ref.7 = Weaver et al. (1999, ApJ, 520, 130),
       Ref.8 = Guainazzi et al. (2010, MNRAS, 406, 2013),
       Ref.9 = Evans et al. (2004, ApJ, 612, 786).
       Fit   = luminosity from spectral fitting
       HR    = luminosity from hardness ratio
       G1.8  = luminosity from assumption of spectral index Gamma=1.8 with
               Galactic NH,0
  

Spectral_Model
The best-fit spectral model for the X-ray source, using the following abbreviations (see reference paper for more details):

    PL   = powerlaw
    ME   = thermal plasma component (mekal)
    VME  = vmekal
    PABS = pcfabs
    BB   = cool black-body component (bbody)
    G    = Gaussian (for iron K-alpha line) component in XSPEC
  

Spectral_Norm_Cpt1
The logarithm of the normalization of the power-law component for the best-fit spectral model to the X-ray source, in photon keV-1 cm-2 s-1.

Log_L_Cpt1
The logarithm of the 0.3-10 keV luminosity of the power-law component for the best-fit spectral model to the X-ray source, in erg s-1.

Spectral_Norm_Cpt2
The logarithm of the normalization of the mekal or bbody component for the best-fit spectral model to the X-ray source, if available. It is equal to (1.0e-14/[4*pi*D2]) * Integral(ne*nH*dV) for a mekal component, where D is the distance to the source in cm, and ne and nH are the electron and hydrogen densities in cm-3, respectively. It is equal to L39/D102 for a bbody (black-body) component, where L39 is the source luminosity in units of 10+39 erg s-1, and D10 is the distance to the source in units of 10 kpc.

Log_L_Cpt2
The logarithm of the 0.3-10 keV luminosity of the mekal or bbody component for the best-fit spectral model to the X-ray source, in erg s-1, if available.

NH
The inferred intrinsic absorption column density for the best-fit spectral model to the X-ray source, in H atoms cm-2.

NH_Lower
The lower limit to the inferred intrinsic absorption column density for the best-fit spectral model to the X-ray source, in H atoms cm-2.

NH_Upper
The upper limit to the inferred intrinsic absorption column density for the best-fit spectral model to the X-ray source, in H atoms cm-2.

Spectral_Index
The power-law photon index, gamma, for the best-fit spectral model to the X-ray source.

Spectral_Index_Lower
The lower limit to the power-law photon index for the best-fit spectral model to the X-ray source. In a few cases, the errors are not available due to poor statistics.

Spectral_Index_Upper
The upper limit to the power-law photon index for the best-fit spectral model to the X-ray source. In a few cases, the errors are not available due to poor statistics.

Temperature
The temperature of the mekal or bbody component for the best-fit spectral model to the X-ray source, in keV, if available.

Temperature_Lower
The lower limit to the temperature of the mekal or bbody component for the best-fit spectral model to the X-ray source, in keV, if available.

Temperature_Upper
The upper limit to the temperature of the mekal or bbody component for the best-fit spectral model to the X-ray source, in keV, if available.

Fit_Chi_Squared
The Chi-squared of the best-fit spectral model to the X-ray source.

Fit_DoF
The number of degrees of freedom of the best-fit spectral model to the X-ray source.

Ref_Spectrum
This parameter can contain a note on the spectral fitting or a reference for piled-up sources, as follows:

       Ref.1 = Ebrero et al. (2011, A&A, 535A, 62),
       Ref.2 = De Rosa et al. (2012, MNRAS, 420, 2087),
       Ref.3 = Cappi et al. (2006, A&A, 446, 459),
       Ref.4 = Shu et al. (2010, ApJ, 713, 1256),
       Ref.5 = Iyomoto et al. (1998, ApJ, 503, 168),
       Ref.6 = Ptak et al. (2004, ApJ, 606, 173),
       Ref.7 = Weaver et al. (1999, ApJ, 520, 130),
       Ref.8 = Guainazzi et al. (2010, MNRAS, 406, 2013),
       Ref.9 = Evans et al. (2004, ApJ, 612, 786).
       Fit   = luminosity from spectral fitting
       HR    = luminosity from hardness ratio
       G1.8  = luminosity from assumption of Gamma=1.8 with Galactic NH,0
   {Gamma} fixed = spectral index was fixed in the fit
  

Contact Person

Questions regarding the CHANSNGCAT database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Wednesday, 27-Sep-2017 15:17:22 EDT