sep 3, 2008nvoss 20081 vo analysis using local utilities mike fitzpatrick noao
TRANSCRIPT
Sep 3, 2008NVOSS 2008 1
VO Analysis UsingLocal Utilities
Mike FitzpatrickNOAO
Sep 3, 2008NVOSS 2008 2
Introduction
• We’ll use various VO tools in an attempt to re-create a Tully-Fisher relation using data queries.
• We’ll do this using command-line and desktop tools.– When presented in the 2006 NVOSS this was done
using web-based toolshttp://nvotwiki.stsci.edu/twiki/pub/Main/NVOSS3CourseNotes/scienceApplications3.html
• We’ll skip the detailed work needed to make real science out of this.
Sep 3, 2008NVOSS 2008 3
What’s 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 2008 4
What’s a Tully-Fisher Relation?
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Top: Abell 1367
Bottom: Fornax
Sep 3, 2008NVOSS 2008 5
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 inclination4. A method to convert magnitude to
luminosities using the disance modulus:
M = constant - 10log10Vmax
Sep 3, 2008NVOSS 2008 6
Finding Velocities
• Do a Registry query for ‘HI’% voregistry -R -t catalog HI
• The ‘digitalHIarchive’ looks like what we need, let’s 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 2008 7
Finding Velocities
• This is a fairly small catalog, so let’s download it using an all-sky query:
% vodata -O HI -V digitalHIarchive 0.0 0.0 180
• 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 2008 8
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. Let’s 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 2008 9
Finding Photometry
• Now let’s 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 2008 10
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 2008 11
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 2008 12
Adding Columns
We use STILTS once again:
% stilts tpipe in=combined.xml out=final.xml \
cmd="addcol axratio 'b/a'" \
cmd="addcol cossqi '(axratio*axratio-0.4)/(0.96)'" \ cmd='addcol inclination "acos ( sqrt ( cossqi ) )"' \ cmd='addcol logcorW "log10(wf50/sin(inclination))"' \ cmd="addcol distance 'vhelio/70.0'" \ cmd="addcol absMag 'phot_sdss_i-
5*log10(distance*1000000/10.0 )'"
Sep 3, 2008NVOSS 2008 13
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
Sep 3, 2008NVOSS 2008 14
Plotting Results