CHAMPSDSSA ivo://nasa.heasarc/champsdssa NASA/GSFC HEASARC Constantin et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source The combination of the Sloan Digital Sky Survey (SDSS) and the Chandra Multiwavelength Project (ChaMP; Green et al. 2004, ApJS, 150, 43) currently offers the largest and most homogeneously selected sample of nearby galaxies for investigating the relations between X-ray nuclear emission, nebular line emission, black hole masses, and the properties of the associated stellar populations. The authors provide X-ray spectral fits and valid uncertainties for all the galaxies with counts ranging from 2 to 1325 (mean 76, median 19). They present in their paper novel constraints that both X-ray luminosity L<sub>X</sub> and X-ray spectral energy distribution bring to the galaxy evolutionary sequence HII -> Seyfert/Transition Object -> LINER -> Passive suggested by optical data. In particular, the authors show that both L<sub>X</sub> and Gamma, the slope of the power law that best fits the 0.5 - 8 keV spectra, are consistent with a clear decline in the accretion power along the sequence, corresponding to a softening of their spectra. This implies that, at z ~ 0, or at low-luminosity active galactic nucleus (AGN) levels, there is an anticorrelation between Gamma and L/L<sub>Edd</sub>, opposite to the trend which is exhibited by high-z AGN (quasars). The turning point in the Gamma - L/L<sub>Edd</sub> LLAGN + quasars relation occurs near Gamma ~ 1.5 and L/L<sub>Edd</sub> ~ 0.01. Interestingly, this is identical to what stellar mass X-ray binaries exhibit, indicating that the authors have probably found the first empirical evidence for an intrinsic switch in the accretion mode, from advection-dominated flows to standard (disk/corona) accretion modes in supermassive black hole accretors, similar to what has been seen and proposed to happen in stellar mass black hole systems. The anticorrelation the authors find between Gamma and L/L<sub>Edd</sub> may instead indicate that stronger accretion correlates with greater absorption. Therefore, the trend for softer spectra toward more luminous, high-redshift, and strongly accreting (L/L<sub>Edd</sub> >~ 0.01) AGNs/quasars could simply be the result of strong selection biases reflected in the dearth of type 2 quasar detections. The cross-match of all ChaMP sky regions imaged by Chandra/ACIS with the SDSS DR4 spectroscopic footprint results in a parent sample of 15,955 galaxies on or near a chip and a subset of 199 sources that are X-ray detected. Among those, only 107 sources have an off-axis angle (OAA) Theta <0.2 degrees and avoid ccd=8 due to high serial readout noise; these 107 objects comprise the main sample that the authors employ for this study and that are listed in this table. The authors performed direct spectral fits to the X-ray counts distribution using the full instrument calibration, known redshift, and Galactic 21-cm column nH<sub>Gal</sub>. Source spectra were extracted from circular regions with radii corresponding to energy encircled fractions of ~90%, while the background region encompasses a 20 arcsec annulus, centered on the source, with separation 4 arcsecs, from the source region. Any nearby sources were excised, from both the source and the background regions. The spectral fitting was done via yaxx ('Yet Another X-ray eXtractor': Aldcroft 2006, BAAS, 38, 376), an automated script that employs the CIAO Sherpa tool. Each spectrum was fitted in the range 0.5 - 8 keV by two different models: (1) a single power law plus absorption fixed at the Galactic 21-cm value (model 'PL'), and (2) a fixed power law of photon index Gamma = 1.9 plus intrinsic absorption of column nH (model 'PLfix'). For the nine objects with more than 200 counts, the authors employed a third model in which both the slope of the power law and the intrinsic absorption were free to vary (model 'PL_abs'). This table was created by the HEASARC in January 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/705/1336/">CDS Catalog J/ApJ/705/1336/</a> file table1.dat. This is a service provided by NASA HEASARC . 2009ApJ...705.1336C https://heasarc.gsfc.nasa.gov/W3Browse/all/champsdssa.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=champsdssa& GET text/xml 180 99999 true 340.84625 -9.51805556 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=champsdssa GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_champsdssa&Action=More+Options&Action=Parameter+Search&ConeAdd=1 SDSS 0.0166666666666667 X-ray public champsdssa CHAMP/SDSS Nearby Low-Luminosity AGN Catalog name ChaMP X-Ray Source Identification (CXOMP JHHMMSS.s+DDMMSS) meta.id;meta.main char nullable ra Right Ascension of the ChaMP X-Ray Source degree pos.eq.ra;meta.main double nullable dec Declination of the ChaMP X-Ray Source degree pos.eq.dec;meta.main double nullable sdss_id SDSS Unique Object Identifier meta.id char nullable sdss_ra Right Ascension of the SDSS Object degree pos.eq.ra double nullable sdss_dec Declination of the SDSS Object degree pos.eq.dec double nullable redshift Spectroscopic Redshift src.redshift double nullable counts Net 0.5-8keV Source Counts ct phot;em.X-ray double nullable flux X-Ray Flux (0.5-8keV) erg/s/cm^2 phot.flux;em.X-ray double nullable log_lx Logarithm X-Ray Luminosity (0.5-8keV) in erg/s log(erg/s) phys.luminosity;em.X-ray double nullable opt_class Optical Spectral Classification src.class char nullable "__x_ra_dec" System unit vector column double nullable "__y_ra_dec" System unit vector column double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable off_axis Chandra Off-Axis Angle arcmin instr.offset double nullable nh Best-Fit YAXX Intrinsic Column Density cm^-2 phys.columnDensity double nullable spectral_index Best-Fit YAXX Power-Law Index {Gamma} spect.index;em.X-ray double nullable nh_gal Galactic Hydrogen Column Density cm^-2 phys.columnDensity double nullable spectral_index_pos_err Positive 1-Sigma Uncertainty in {Gamma} stat.error;em.X-ray;spect.index double nullable target_flag Flag [I] Indicates Intended Chandra PI Target meta.code char nullable exposure Vignetting-Corrected Exposure Time (s) s time.duration;obs.exposure double nullable class Browse Object Classification src.class short nullable spectral_index_neg_err Negative 1-Sigma Uncertainty in {Gamma} stat.error;em.X-ray;spect.index double nullable nh_neg_err Negative 1-Sigma Uncertainty in Best-Fit YAXX Intrinsic Column Density cm^-2 stat.error;phys.columnDensity double nullable nh_limit Limit Flag for Hydrogen Column Density meta.code;phys.columnDensity char nullable lii Galactic Longitude of the ChaMP X-Ray Source degree pos.galactic.lon double nullable nh_pos_err Positive 1-Sigma Uncertainty in Best-Fit YAXX Intrinsic Column Density cm^-2 stat.error;phys.columnDensity double nullable bii Galactic Latitude of the ChaMP X-Ray Source degree pos.galactic.lat double nullable