6570(  4) - 10/22/96 08:54  - [  0]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      6570
                                                       Version: 4
                                                       Check-in Date: 21-Oct-1996
                                                                      15:59:14

1.Proposal Title:
High-Redshift Galaxies and Their Contribution to the Ionizing Background
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2. Scientific Category   3. Proposal For  4. Cycle
INTERSTELLAR MEDIUM         GO               6
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5. Investigators
                                                                                     Contact?
    PI: Mauro Giavalisco                  THE OBSERVATORIES OF CIW
   CoI: Ray Weymann                       The Observatories of the Carnegie             Y
                                          Institution
   CoI: Simon Lilly                       University of Toronto                         N

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6. Abstract

We propose objective-prism spectroscopy with the FOC-F/96 + FUVOP of a well-
controlled sample of 10 blue galaxies at redshifts ~ 1, to study their UV spectral
energy distribution, from shortward of the Lyman limit to longward of Ly-alpha. Aim
of the project is to investigate on 1) the contribution by star-forming galaxies at
half the Hubble time to the ionizing background; 2) the star-formation activity in
these galaxies. This data bears on several key issues, including galaxy formation
and evolution, the physical state of gas in protogalaxies and the degree of
ionization of the QSO absorption systems. The sample is selected from the
statistically-complete Canada-France Redshift Survey for having I_AB<22 and (U-
I)_AB<1.4, corresponding to the color of a present-day Sbc galaxy, and includes
galaxies in the range 0.8<~ z<~ 1.1. Among these there are the blue galaxies with
peculiar morphology and enhanced star-formation activity which dominate the faint
counts. Several reasons suggest that these galaxies could be important contributors
of UV ionizing radiation. From the FOC UV data we will measure, or set tight limits
on, the flux of ionizing photons, and, by combining the UV spectra of the galaxies
with existing optical spectroscopy, photometry and WFPC2 morphology, will obtain
quantitative information on the initial mass-function, star-formation rate and
structure of the ISM, which is essential to reconstruct the evolutionary history of
the faint blue galaxies to the present epoch.
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  Observations Description
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     centerline 1. Why HST? We want to carry out spectroscopy of relatively faint
     galaxies at redshifts z<~ 1, covering the wavelength range from shortward of
     the Lyman break to longward of Ly-alpha, approximately LambdaLambda 1500--2500
     Angstrom. Our galaxies have apparent magnitudes in the range 21<~ m_V<~ 23 with
     very blue f_Nu spectra (spectral indexes in the range 0<Alpha<1). This
     corresponds to typical fluxes of ~ 10^-16 erg s^-1 cm^-2 AA^-1 in the above
     wavelength range. Therefore, the use of HST in this project is necessary to
     provide UV wavelength coverage with sufficient sensitivity. centerline 2.
     Feasibility The necessary signal- to-noise (S/N), and therefore number of
     orbits, to achieve the scientific goals of this proposal is imposed by the need
     to: (i) obtain a S/N redward of the Lyman limit adequate to study the hot
     stellar population and (ii) to explore the Lyman discontinuity with sufficient
     depth to be able to put interesting constraints (in the case of non detection
     of flux shortward of the redshifted 912 Angstrom\\ wavelength) on the
     contribution of these galaxies to the ionizing background. We have estimated
     that a fraction of up ~ 10-15 \\% of the flux redward of the Lyman
     discontinuity can be expected at wavelengths blueward of it due to escaping
     ionizing photons. If we want to put interesting upper limits on such a flux a
     SN of at least 30 at ~ 1700 Angstrom\\ should be reached. Warren Hack of the
     FOC team at ST ScI has kindly simulated for us FOC F/96 + FUVOP observations of
     our sample galaxies using the FOC prism package. This package contains the most
     recent calibrations of the camera and its accuracy has been tested to be well
     the within 10 \\% level. Using the photometric data (magnitudes and colors)
     available for our galaxies, the simulations have shown that SN~ 30 per
     resolution element at Lambda 1700 Angstrom\\ is reached in ~ 10^4 seconds of
     total integration for the faintest and reddest of our sources. With the same
     integration time, the bluest and brightest galaxies will be observed with SN~
     60. Assuming a typical visibility window of 40 minutes per orbit, 4 orbits per
     target will meet our minimum requirements of SN for the faintest objects and
     exceed them for the brightest. With a sample of 10 galaxies, the total length
     of the program sums up to 40 orbits. We explicitely note that excellent
     sensitivity of this experiment will largely improve on any past measurements of
     ionizing photons from star-forming galaxies. This is largely due to the high
     redshifts of the targets, which shifts the Lyman discontinuity to a wavelength
     region where the FOC has a good throughput and the prism a relatively low
     dispersion. The scientific impact that our limits can place will be large.

  Real Time Justification
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     None None

  Calibration Justification
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  Additional Comments
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  Data Distribution

  Media:           8MM
  Blocking Factor: 10
  Ship To:         PI_Address
  Ship Via:        UPS
  Email:                                                              ,
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                                                6570(  4) - 10/22/96 08:54  - [  1]

TARGET LIST    a) Fixed Targets
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Tar|   Target   |         Target        |            Target              |Coord   | Radial |             Flux data
No |    Name    |       Description     |           Position             |Eqnx    |  Vel.  |
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11  GAL-CFRS-00- GALAXY, High z Gal,     RA=00H 02M 28.92S +/- 1.0", DEC= 2000     Z=0.951  V = 21.54+/-0.05
    0137         Starburst               -00D 41' 43" +/- 1.0"                              V-I = 0.36+/-0.1

12  GAL-CFRS-14- GALAXY, High z Gal,     RA=14H 18M 07.32S +/- 1.0",      2000     Z=0.986  V = 22.13+/-0.05
    0438         Starburst               DEC=+52D 26' 48.8" +/- 1.0"                        V-I = 0.74+/-0.1

13  GAL-CFRS-14- GALAXY, High z Gal,     RA=14H 18M 00.90S +/- 1.0",      2000     Z=1.038  V = 22.22+/-0.05
    0600         Starburst               DEC=+52D 32' 38.4" +/- 1.0"                        V-I = 0.69+/-0.1

14  GAL-CFRS-14- GALAXY, High z Gal,     RA=14H 17M 50.53S +/- 1.0",      2000     Z=0.875  V = 21.77+/-0.05
    0899         Starburst               DEC=+52D 27' 45.6" +/- 1.0"                        V-I = -0.11+/-0.1

15  GAL-CFRS-22- GALAXY, High z Gal,     RA=22H 17M 55.75S +/- 1.0",      2000     Z=1.1003 V = 22.13+/-0.05
    0579         Starburst               DEC=+00D 22' 07.8" +/- 1.0"                        V-I = 0.42+/-0.1

                                                6570(  4) - 10/22/96 08:54  - [  2]

Visit: 01
     Visit Requirements:  <none>
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
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Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|             Optional            |Num|  Time |       Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|            Parameters           |Exp|       |     Requirements
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11       GAL-CFRS-00 FOC/96 IMAGE   256X102 PRISM1   1300-28                                   8   1200 S  EXPAND
         -0137                      4                00
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                                                6570(  4) - 10/22/96 08:54  - [  3]

Visit: 02
     Visit Requirements:  <none>
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
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Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|             Optional            |Num|  Time |       Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|            Parameters           |Exp|       |     Requirements
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12       GAL-CFRS-14 FOC/96 IMAGE   256X102 PRISM1   1300-28                                   8   1200 S  EXPAND
         -0438                      4                00
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                                                6570(  4) - 10/22/96 08:54  - [  4]

Visit: 03
     Visit Requirements:  <none>
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
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Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|             Optional            |Num|  Time |       Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|            Parameters           |Exp|       |     Requirements
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15       GAL-CFRS-22 FOC/96 IMAGE   256X102 PRISM1   1300-28                                   8   1200 S  EXPAND
         -0579                      4                00
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                                                6570(  4) - 10/22/96 08:54  - [  5]

Visit: 04
     Visit Requirements:  <none>
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
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Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|             Optional            |Num|  Time |       Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|            Parameters           |Exp|       |     Requirements
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13       GAL-CFRS-14 FOC/96 IMAGE   256X102 PRISM1   1300-28                                   8   1200 S  EXPAND
         -0899                      4                00
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                                                6570(  4) - 10/22/96 08:54  - [  6]

Visit: 05
     Visit Requirements:  <none>
     On Hold Comments:    <none>
     Additional Comments: <none>


Exposures
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Exposure|   Target  |Instr | Oper. | Aper  |Spectral|Central|             Optional            |Num|  Time |       Special
 Number |    Name   |Config| Mode  |or FOV |Element |Waveln.|            Parameters           |Exp|       |     Requirements
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14       GAL-CFRS-14 FOC/96 IMAGE   256X102 PRISM1   1300-28                                   8   1200 S  EXPAND
         -0600                      4                00
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                                                6570(  4) - 10/22/96 08:54  - [  7]

            Summary Form for Proposal  6570

  Item                         Used in this proposal
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  Configurations               FOC/96
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  Opmodes                      IMAGE
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  Proposal Category            GO
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  Scientific Category          INTERSTELLAR MEDIUM
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  Special Requirements         EXPAND
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  Spectral Elements            PRISM1
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  Target Names                 GAL-CFRS-00-0137 GAL-CFRS-14-0438 GAL-CFRS-22-0579 GAL-CFRS-14-0899 GAL-CFRS-14-0600
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