CHANSNGCAT ivo://nasa.heasarc/chansngcat NASA/GSFC HEASARC She et al. 2026-04-03 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Galaxy 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 10<sup>37</sup> 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. This table was created by the HEASARC in September 2017 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/835/223">CDS Catalog J/ApJ/835/223</a> files table1.dat, table2.dat and table4.dat. This is a service provided by NASA HEASARC . 2017ApJ...835..223S https://heasarc.gsfc.nasa.gov/W3Browse/all/chansngcat.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=chansngcat& GET text/xml 180 99999 true 141.54804167 -76.62633333 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=chansngcat GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_chansngcat&Action=More+Options&Action=Parameter+Search&ConeAdd=1 CHANDRA 0.0166666666666667 X-ray public chansngcat Chandra ACIS Survey for X-Ray AGN in Nearby Galaxies nh Extragalactic Absorption Column Density cm^-2 phys.columnDensity double nullable hardness_ratio_0_error Error in H0 stat.error;phot.flux;arith.ratio;em.X-ray double nullable log_blackhole_mass_lower Lower Limit of Logarithm of Black Hole Mass log(Solar_Mass) phys.mass;stat.min double nullable log_l_halpha_flag Flag Indicates Note Regarding Logarithm of H-Alpha Luminosity meta.code;phys.luminosity;em.line.Halpha char nullable fit_dof Degrees of Freedom of Fit stat.fit.dof short nullable spectral_model Best-Fit Model meta.code;spect;meta.modelled char nullable nh_gal Galactic Absorption Column Density cm^-2 phys.columnDensity double nullable bii Galactic Latitude degree pos.galactic.lat double nullable class Browse Object Classification src.class short nullable fit_chi_squared Chi-Squared of Fit stat.fit.chi2 double nullable log_lx Logarithm of 2-10keV Luminosity log(erg/s) phys.luminosity;em.X-ray double nullable hardness_ratio_0 Hardness Ratio H0: (Hard-Soft-Medium)/Full phot.flux;arith.ratio;em.X-ray double nullable spectral_index_upper Upper Limit in Power-Law Photon Index spect.index;stat.max double nullable source_number Sequential Identification Number for Each Source in the Catalog meta.id;src short nullable temperature_lower Lower Limit in Temperature keV 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