Search for ULX sources and X-ray binaries in nearby (e.g. D<10 Mpc) galaxies (uses TOPCAT, Aladin).

ULXs (Ultra-Luminous X-ray sources) are X-ray sources that are less luminous than AGN but more luminous than any known stellar process (Lx > 10^39 erg/sec)

  • tip: launch Aladin first , then TOPCAT; launch TOPCAT with a larger memory buffer; try java -Xmx512M -jar topcat-full.jar

  • load the NED-1D galaxy catalogue. A .csv (coma-separated values) version of the catalogue can be found here: NED-1D.csv

  • the RA and Dec are in sexadecimals; convert RA, Dec to decimal: select Table Columns and then Add new sky coordinate column based on existing one; get rid of the multiple entries using the option match one

  • optional : apply a filter in distance (e.g. D<10 Mpc) using TOPCAT (the stricter the criterion, the smaller the number of objects!) and send the filtered nearby galaxies catalogue to Aladin

  • this catalogue does not contain any information about the size of the objets; load the hyperLeda catalogue in Aladin [(VII/237/pgc) from All Vizier (this might take a while as it contains about a million objects; place the cursor on the plane as it loads to get an idea of the number of objects still to be loaded); cross-match the two catalogues and send the match back to TOPCAT; add new column with radius in arcmin: pow(10.,$diameter_column)*0.1/2

  • you can now delete the hyperLEDA plane in order to save memory; then load the 2XMMi catalogue (0.2-12 keV band) in Aladin (IX/40), which gives the calibrated fluxes for sources; send it to TOPCAT and cross-correlate (match two; "Sky with Errors"; "1&2"; "All Matches") the 2XMMi with the nearby galaxies catalogue using the new radius and the X-ray position uncertainty (ePOS) as errors

  • add new column with the luminosity Lx for the point like sources from the calibrated flux and distance to each galaxy, i.e. Lx = 4*pi*D^2*fx = (do the math!) 50.078+2*log10($distance_column)+log10($fx_column)

  • filter those sources with Lx >= 1e39 erg/s (our ULX candidates)

  • plot Lx vs cross-correlation separation: most objects are at very low offsets, therefore X-ray emission most probably comes from the nucleus; some objects are clearly off; keep those above a given separation which you can select based on the separation distribution

  • send the catalogue to Aladin keeping only the X-ray coordinates

  • cross-match with X-ray binaries table(s) [e.g. J/ApJS/157/59] to find the non-matches

  • cross-match with quasars and/or AGN catalogue(s) [e.g. QORG: J/A+A/427/387/master]

  • find images of the galaxies, plot the positions of the AGN and ULX candidates; verify their separation as well as from the galaxy centre

  • find existing ULX catalogues to confirm candidates (e.g. J/ApJ/452/739]

-- MarkAllen - 08 July 2009

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Topic revision: r3 - 08 Jul 2009 - MarkAllen
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