8360(  2) - 12/18/98 16:46  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      8360
                                                       Version: 2
                                                       Check-in Date: 18-Dec-1998
                                                                      16:45:06

1.Proposal Title:
How Opaque Are Spiral Galaxies?
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2. Proposal For  3. Cycle
AR               8
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4. Investigators
                                                                                     Contact?
    PI: Ron J. Allen                      Space Telescope Science Institute
   CoI: Dr. Rosa A. Gonzalez              Space Telescope Science Institute             N
   CoI: Dr. Harry C. Ferguson             Space Telescope Science Institute             N
   CoI: Dr. Daniela Calzetti              Space Telescope Science Institute             N
   CoI: Prof. Nino Panagia                Space Telescope Science Institute             N

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5. Abstract

Using HST Archival images in a previous modest AR program, we have developed a new
method to calibrate the effects of crowding and confusion from foreground structure
on the counts of background galaxies seen through a foreground system. This new
method, the Synthetic Field Method, permits us to establish the area-averaged amount
of extinction through the entire thickness of the foreground galaxy. No assumptions
about the spatial distribution of the obscuring material in the foreground system or
about its reddening law are required. We now propose to exploit this method by
applying it to deep Archival images of all 17 nearby spiral galaxies obtained
earlier with the HST/WFPC2 in the Cepheid distance scale programs. Applying the
method to this large sample of spirals will permit us: (1) to decrease the
fundamental uncertainty in our results owing to field-to-field variations in the
surface number density of the background galaxies, and (2) to begin quantifying the
differences in extinction between arms and inter-arm regions, and between the inner
and outer parts of spiral galaxy disks. The results of this project will provide the
largest study to date of TOTAL extinction in spiral galaxies using background
illuminating objects.
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  Data Distribution

  Paper Products:  NO
  Media:           ELECTRONIC
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:
  Email:
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                                                8360(  2) - 12/18/98 16:46  - [  2]

            Summary Form for Proposal  8360

  Item                         Used in this proposal
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  Proposal Category            AR
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