Matching of DR4 to HST data

This page contains (links to) four files correlating DR4 and the HST exposure time catalogue. Note however that there are several caveats below which should be taken into account - especially for the matching to the spectroscopic data.

Spectroscopic targets with HST observations

First there are two files correlating the spectroscopic data housed herein with all HST exposures from 1993 to the present (the catalogue used was complete up to 1st of March 2005 according to the MAST page, starting with 1993.

For each HST exposure the field-of-view of the instrument was used to define a radius. This was taken to be sqrt(2) times half the side-length of the FOV (the average where the FOV was rectangular) to allow for rotation. In other words, rotation was not taken rigorously into account. Thus there are quite likely a few matches that in reality are on the edge or just outside the field of view of the image. Also for WFPC-2 observations, the FOV was assumed square so there is a approximately 20% chance that any WFPC-2 matches are not real.

The total number of matches is 52 - so of course it would be possible to check everything by hand, but the preview function in the archives isn't usually good enough for this so this has not been done. Hopefully this is anyway a good starting point for those that would want to know and I will be very happy to receive corrections!

The two files are:

• hst_ids_and_configs.dat.gz. This file has one line for each object in the main sample for DR4 outlined here. The file contains information of whether an HST observation containing the object exists.

  The format is simple. The first column gives the index into the DR4 catalogues and the following the instrument configuration used and the HST Dataset name. As an example:

   28175  ACS/WFC[J8NP09010] ACS/WFC[J8NP09030] ACS/WFC[J8NP09040]
  

  says that that object number 28175 (PID=335, MJD=52000, FID=35) lies in the field of three ACS WFC exposures with dataset IDs J8NP09010, J8NP09030 and J8NP09040, which can be used to request the data from the various archives.

• The other file is spec_matches.dat.gz which is the inverse of the previous. It contains one line for each of the HST observations used for these correlations. The format is:

    Column #1: A counter
    Column #2: The HST dataset name
    Column #3 and subsequent: The SDSS targets that are within the FOV
              of this HST dataset. The number is the index in our catalogues.
  

Matching of the entire SDSS DR4 to the HST Exposure Time Catalogue

The previous is the most useful information when using the galaxy sample, but in many other situations you might either want to know whether an HST observation has SDSS imaging or whether a particular SDSS image has further HST information. This is achieved by the files included here.

What I did to construct these files was to interrogate the DR4 Footprint server for each position in the HST Exposure Catalogue. Thus this list is an underestimate of the total number of intersections of the SDSS with the HST exposure time catalogue, because HST observations with their center outside the FOV of an SDSS image are not included. This shouldn't be a huge effect though!

So, the files:

• hst_aec_to_sdss.dat.gz contains a lookup table from the HST Dataset name to SDSS Run, rerun etc. The format is:

    Column #1: HST Dataset name
    Column #2: HST Instrument configuration
    Column #3: The number of matches in the SDSS Footprint.
    Column #4: The Run number of the match to the SDSS
    Column #5: The Rerun
    Column #6: The CamCol
    Column #7: The Field
    Column #8: ROWC of the center of the HST observation
    Column #9: COLC 
  
  If there is more than one match, then column 10-15 are repeats of 4-9
  for the second match and so on
  

  There are two HST observations (of the same location) with six matches in the SDSS. This is the largest number.
• sdss_run_to_aec.dat.gz provide the inverse of this file. It contains a lookup from SDSS run, rerun, camcol, field to HST exposures. The format is as follows:

    Column #1: Run-Rerun-Camcol-Field
    Column #2: The number of HST observations in this SDSS observation
    Column #3: The HST dataset name
    Column #4: The HST instrument configuration used.
    Column #5: Like Column #3 
    Column #6: Like Column #4
  etc.
  

  The maximum number of HST datasets per SDSS run, rerun, camcol, field combination is 4491. This does of course not mean that there are 4491 unique HST observations of this place!!