Presentation on theme: "Sep 3, 2008NVOSS 20081 VO Analysis Using Local Utilities Mike Fitzpatrick NOAO."— Presentation transcript:
Sep 3, 2008NVOSS VO Analysis Using Local Utilities Mike Fitzpatrick NOAO
Sep 3, 2008NVOSS Introduction Well use various VO tools in an attempt to re-create a Tully-Fisher relation using data queries. Well do this using command-line and desktop tools. –When presented in the 2006 NVOSS this was done using web-based tools Well skip the detailed work needed to make real science out of this.
Sep 3, 2008NVOSS Whats a Tully-Fisher Relation? A (empirical) correlation of the luminosity and maximum rotation velocity of a spiral galaxy. The bigger a galaxy is, the faster it rotates. So, if you know the rotation velocity you can make assumptions using T-F about its intrinsic brightness. You compare this with the apparent magnitude and you have a measure of its distance.
Sep 3, 2008NVOSS What Do We Need? 1.Some measure of the rotational velocity –HI emission lines can give us this 2.A selection of spiral galaxies with photometry 3.A method to correct for the inclination 4.A method to convert magnitude to luminosities using the disance modulus: M = constant - 10log 10 V max
Sep 3, 2008NVOSS Finding Velocities Do a Registry query for HI % voregistry -R -t catalog HI The digitalHIarchive looks like what we need, lets see if it has the columns we require: % voregistry -meta digitalHIarchive Note: The RC3 Catalog also contains HI data, see how thisexercise would differr using that as the resource.
Sep 3, 2008NVOSS Finding Velocities This is a fairly small catalog, so lets download it using an all-sky query: % vodata -O HI -V digitalHIarchive From the metadata we know this table has positions, morph type, velocities, and semi- major/minor axis (needed for inclination), save only these columns : % stilts tpipe HI.xml \ cmd=select morphtype==1 \ cmd=keepcols ra dec a b vhelio wf50 \ out=spirals.xml
Sep 3, 2008NVOSS Finding Photometry The SDSS is a good resource for photometry of galaxies We can start with a query for SDSS resources: % voregistry -R -t catalog sdss We notice a Russian service offering the PhotObjAll and PhotTag tables as a Cone Service. These are nice, but not fast enough for this demo. Lets see if one of the SDSS Cone searches gives us a magnitude: % voregistry -meta SDSS-DR4 From this service we can get ugriz magnitudes
Sep 3, 2008NVOSS Finding Photometry Now lets query for the SDSS data given the positions we have for the Sa galaxies: % vodata -O dr4 -1 SDSS_DR4 spirals.xml -rs 3 -mt 3 Why the -mt 3 flag? –The task runs multiple threads and we can overwhelm the server and get bogus results. This flag says run only three threads. For our 327 positions we get 125 results from SDSS Why the -1 flag? –We want to collect the results into one final table
Sep 3, 2008NVOSS What Do We Have Now? The file spirals.xml is a VOTable that has our Sa galaxies with the velocity information. The file dr4.csv has photometry of those galaxies that overlap SDSS. We need to combine these, and add information (e.g. inclination)
Sep 3, 2008NVOSS Combining Tables We use STILTS to match the tables and produce a combined output table: % stilts tmatch2 in1=spirals.xml in2=dr4.csv ifmt2=csv\ matcher=sky \ values1="RA Dec" \ values2="POS_EQ_RA_MAIN POS_EQ_DEC_MAIN" params="2" \ out=combined.xml
Sep 3, 2008NVOSS Plotting Results We now have all the columns necessary to plot a very simply Tully-Fisher relation To plot the results, use TOPCAT to load the final table % topcat final.xml Bring up the graph window, and plot absMag vs logcorW