extragalactic_workflow.html

Extragalactic workflow

Left side of the workflow tree, case with spectra; show existing data

Aim: show column manipulation, show interface to display spectra

click on "Load", target CDFS, radius = 30'
click on "Data Tree"
load V-band WFI preview image of whole CDFS as background
load file fields.xml which includes known type 2 source (with FORS2 spectrum)
select all sources on image to be able to see IDs
open e.g. ACS F850LP box, then open version1.0 (this are the 5-epoch, stacked images), close WFI
select source 27, click, this checks box on sector 23
open version 1.0 for other filters, show checked boxes in those as well
hit submit and download all checked boxes (typically 3 ACS images F435W, F775W, F850LP)
close ACS
make RGB of ACS images
zoom out, point out they are mostly blue, show tiny size of ACS image compared to WFI
compact some planes in folder (right click on stack, "create new folder", then put them in)
load X-ray catalogue (829 sources, 503 in HDFN, 326 in CDFS); Vizier Catalogs (emphasize), type Alexander in author box, "SUBMIT" click (once), then add /cdfs (otherwise one gets everything), then SUBMIT (MAKE SURE TO HAVE WFI IMAGE SELECTED BEFORE DOING THAT)
now overlay the FOV of GOODS-ACS-HST data and show how one can see which X-ray sources are or not in the GOODS area; then select a few sources on the image and show the catalog entries
need to create hardness ratio HR from soft- (S) and hard-band (H) fluxes
load script hr.ajs which gets rid of double upper limits, sets HR = 1.0 for upper limits in soft-band, sets HR = -1.0 for upper limits in hard band, and then derive HR = (H-S)/(H+S) by adding a new column to catalog; in the future, we will also calculate errors on HR and perhaps select only sources with small errors
here we are using a new feature which adds a column to a catalog (VOTable)
script makes HR filter, turn filter on (click), the "properties" button allows one to export plane with filtered sources
load script abs.ajs, turn it on to select absorbed sources defined as HR >= -0.2, turn HR filter OFF, then again the "properties" button allows one to export plane with filter sources
rename plane as "absorbed"
load szokoly_cat.xml, a catalog of sources which have been observed by VLT/FORS2 with redshift information produced by the CDFS team; we need this information to derive the X-ray powers
we now access the data which went into the making of this catalog using Simple Spectrum Access (SSA)
to get to the spectra we use the "SSA for VLT/FORS" button under the VOdemo button, then SUBMIT; this gives access to science-ready spectra produced by the CDFS team (Szokoly et al. 2004) and the GOODS team at ESO using the SSA standard for THE FIRST TIME in a VO environment
this loads the spectra into the tree, and one can see them all with their position angles (needs cursor on top level "SSA server for VLT/FORS spectra" in the tree); zoom in a little to be able to see the slits on the objects in the ACS image
right click on same text in the tree to create a catalog plane for spectra (might need to change color by using the "properties" button)
to get to the spectra one selects a region and then clicks on the "spectrum" link; this sends off a request to ESO, retrieves the FITS file and displays it
display spectrum named "CDF_27" as example of narrow-line, i.e., type 2, source; we do this by going to the ACS RGB image, select all sources by dragging the box, making sure that only the spectra catalog plane is on, and click the SPECTRUM link of source 27; this is the z = 3.064 type 2 QSO prototype discovered by the CDFS team, Norman et al. (2002); (point out narrow Lyman_alpha and C IV); pan in twice
display spectrum named "CDF_011" as example of broad-line, i.e., type 1, QSO at z ~ 2.6; in this case click directly from the tree since this source is not in the ACS field
cross match the absorbed sources (use as first catalog) against the Szokoly catalog (use as second catalog) to get redshifts and then powers; this service is run at CDS
load script lxcalc.ajs to calculate X-ray powers
VOPlot of Lx vs. HR (HR_tab1 parameter, then log Y); say that anything above ~ 10^43 erg/s has to be an AGN; we follow Szokoly et al. and define type-2 QSOs as sources with hard X-ray power > 10^44 erg/s; select them in VOPlot as follows: 1. click on "mode" 2. select points mode 3. drag box from top left; the corresponding sources are highlighted in the image, clicking gives access to the catalog information
now on to the discovery part!

Right side of the workflow tree, case without spectra; discovering new sources

Aim: show cross-match plug-in, use statistical methods to discover faint type-2 QSO candidates, mention ASTROGRID tool & Hyper-z

start with the catalog of absorbed sources
we want to use the correlation between fx/fi and Lx for known type-2 QSO (Fiore et al. 2003) to estimate their X-ray power; note that this way of estimating the X-ray power only works for type-2 sources
run ACE on the ACS F775W image to get I-band fluxes (load first configuration file F775W-v1-config.ace):

select F775W image
select ACE from plug-in, "open" and load F775W-v1-config.ace, select "I" in the pull down menu, click "extract"
this tells the CDS server in Strasbourg to send the image to ACE in Cambridge and then returns to the user the output catalog whose sources are automatically overlaid

in the future we should exclude ACS sources with S/N_I < 5 (need to find out why parameter FLUXERR_ISO is not available; then one could define S/N = FLUX_ISO/FLUXERR_ISO)
run the cross-match plugin on the absorbed sample and the ACS I catalog, threshold = 1.5", first X-ray, second ACS
rename the plane to XO_match
add new column with I flux = (10^((-0.4*I_ACS)-8.912))*2,400; then calculate log(fx(2-8 keV)/fi)-15.0 (because the flux units for the X-ray fluxes are 10^-18 W/m^2/s); then estimate log Lx = log(fx(2-8 keV)/fi)+43.45; do this by loading script lx.ajs
we find 2 candidates in this little tile; out of these, one is the type 2 QSO at z = 3.064 already known, the other one is a new type 2 QSO candidate
what we have done here by hand for a small tile we have also done off-line for the full GOODS mosaics, in both fields; ASTROGRID has in fact now a service which takes the ACS images and runs SEXtractor on them, producing catalogs, and then running Hyper-z on them to generate photometric redshifts; this is a perfect VO application of distributed computing and VO workflow; at present the service only uses the 4 ACS bands and therefore is good only for 2.5 <~ z <~ 3.5 but it will be soon expanded
load catalog zphot-out-cdfs.xml; you can see the catalog of photo-z overlaid over the CDFS field for ~ 32,000 sources; zoom in to show that the type-2 prototype has photo-z ~ 3.8 (compared to 3.05)
using this process we find 64 new type 2 sources, of these 41 have Lx > 10^44 erg/s and therefore qualify as type 2 QSO (we have checked that all these sources have fx/fi values way above those typical of galaxies). Sixteen of these are in the CDFS area, compared to the 6 previously known (increase of more than a factor of 2). Our method recovers all of these sources! In the HDFN we find 25 new type 2 sources, compared to 3 previously known; again our method recovers all of these sources. I ~ 25 (R ~ 26), therefore beyond optical spectroscopy.
plot of Lx vs HR for the newly discovered sources in the CDFS region