Use Case: Searching for Data available for the bright galaxy M51. (Aladin, SIMBAD, VizieR , Topcat, VOSpec)

  • Search for images of the bright galaxy M51 in Aladin.
  • Try the various image servers: The Aladin image server, Skyview and Sloan Digitial Sky Survey
  • Try the 'all VO' access (selecting image servers) - Note the method for selecting images at a given sky location. Clicking in the image puts a tick in the selection boxes of the available data.
  • Make a colour composite image using the RGB tool.
  • Use the multi-view windows to manage the various images you have in the 'stack'
  • Try the 'match' button at the bottom of the image window to align the image for synchronized zooming
  • Try the transparency control for viewing images overlaid on each other
  • Overlay as SIMBAD identifications using the SIMBAD link in the Server selector window

- Try 'with no filter' for a simple listsing of the IDs
- Try with 'Simbad filter' (colorized) to see how the same info can be presented in detail
(optional - open the 'properties' window for the Simbad plane to see or edit the filter)

  • Filtering of sources can also be done interactively with Topcat. Start Topcat, and send the SIMBAD plane to Topcat (right-click on the plane in the stack, and 'Broadcast selected tables to..'
  • View the table values in Topcat. Make a plot of the positions and try the area selection tools to select a number of points in the plot. Note how the selected subset may be transmitted back to Aladin to highlight sources from the original Simbad plane.
  • Make a subset of the brightest HII regions, and send the table back to Aladin using the Topcat 'Interop' menu
  • Search for spectra available in the VO with the 'all VO' button in the server selector window.
  • Find spectra available from the Hubble Space Telescope, and view the positions of the spectra (and sometimes thespectral slit aperture) on the image. Make a plane containing all the spectra positions, and cross match these with the positions of the HII regions.
  • Start VOSpec ( Web Start: ) and display some of the spectra, by clicking on the spectra in the server selector window, and 'Load in -> VOSpec'.
  • Check VizieR for more detailed catalogues of HII emitting regions in M51. This can be done via Aladinor via the more detailed VizieR interface.
  • (Advanced - compile a list of bright HII regions in M51 and query VizieR with this list

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) 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) to find the non-matches
  • cross-match with quasars and/or AGN catalogue(s)
  • 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

-- MarkAllen - 15 Jun 2009

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Topic revision: r1 - 15 Jun 2009 - MarkAllen
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