7271( 7) - 08/08/97 11:35 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7271 Version: 7 Check-in Date: 08-Aug-1997 11:34:28 1.Proposal Title: Molecular Hydrogen in the Damped LyAlpha Absorber of Q1331+170 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle QUASAR ABSORPTION LIN GO 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: JILL BECHTOLD UNIVERSITY OF ARIZONA CoI: Mr. Jian Ge Steward Observatory, University of Arizona N CoI: Dr. David Meyer Northwestern University N ------------------------------------------------------------------------------------ 6. Abstract We wish to search for the Lyman and Werner absorption lines of molecular hydrogen (rest LambdaLambda = 1104 to 911 Angstrom) associated with the well-studied damped LyAlpha and 21-cm absorber at z=1.776 in Q1331+170. The rare detection of C I absorption in this system, along with features in the IUE spectrum consistent with the expected H_2 spectrum, make this the most promising redshift system for such a search. After detecting H_2, we plan to measure the relative population in the individual rotation states. The J = 0, 1, 2, 3 states will yield the kinetic temperature of the gas, while the weak J = 4 and higher states will measure (or limit) the local UV radiation field and hydrogen density. The recent detection of C I^* has been used to measure the cosmic microwave background temperature at z=1.776, and test the validity of the Big Bang model. The observed population of the fine structure levels of C I can be explained entirely by the expected CMB radiation, with surprisingly strong limits on local sources of excitation. The H_2 spectrum will enable us to check this result, by allowing us to make an independent estimate of the rate of UV and collisional pumping of the C I^* levels. ------------------------------------------------------------------------------------ 7271( 7) - 08/08/97 11:35 - [ 2] Observations Description ------------------------ For estimating exposure times, we used the STIS simulator, and the flux measured with IUE, f_Lambda(3100Angstrom)= 2times10^-15 ergs s^-1 cm^-2 AA^-1. The IUE flux agrees perfectly with the extrapolation of the fitted optical power law and normalization reported by Uomoto (1984, ApJ, 284:497), which predicts f_Lambda(3100Angstrom)= 2.1times10^- 15 ergs s^-1 cm^-2 AA^-1, and so there appears to be no problem with the IUE flux calibration. The optical and UV continuum of Q1331+17 has not varied in the many years it has been observed (e.g. O'Brien et al., 1988, MNRAS, 233, 845); Bechtold last obtained spectrophotometry of Q1331+170 in April 1996. The simulated spectra used the output tables from the STIS www simulator, so have proper signal-to-noise as a function of wavelength. The exposure time per orbit was estimated as follows. We use the 0.2 wide arcsecond slit, in order to obtain high spectral resolution, while minimizing overhead for acquisition. The visibility for the declination of our target is 52 minutes per orbit. We use the 9+8+10 minute acquisition sequence for the first orbit, and 6 minute re-acquisition for subsequent orbits. For each 8 orbit visit, the first orbit yields 17m of exposure, orbits 2,4,6,8 yield 45 minutes, and orbits 3,5,7 yield 41 minutes (taking wavecals every other orbit, and including 8 minutes of overhead for the first exposure and 1 minute for subsequent exposures). Thus, in every 8 orbits we obtain 320 minutes of exposure. We request two 8-orbit visits, for a total of 38,400 seconds of exposure on the source. With the E230M grating, in 16 orbits, we will obtain a signal-to-noise of 7.5, 7.6, 6.4 per resolution element at 2600, 2800, 3000 Angstrom. In 8 orbits, we would obtain signal-to- noise of 5.3, 5.4, 4.5 at 2600, 2800, 3000 Angstrom. In Figure 3, we show a simulated spectrum obtained in 8, 16 and 24 orbits, respectively. We include a simulated LyAlpha forest spectrum (with nominal LyAlpha forest parameters for lines extending to logN(HI)=12.2 cm^-2) and the expected H_2 spectrum for the z_abs=1.7765 system, as in Figure 2. Since line confusion is a worry, we plot also the expected positions of Lyman and metal lines for the known metal absorbers (z_abs = 1.7765, 1.3284, 0.7443, 0.7454). In 8 orbits, if f_H_2sim5*10^-6 we will just barely be able to detect molecular hydrogen, and will easily detect it if f> 0.04. We ask, however, for 16 orbits, in order to make sure we have an interesting limit, and to try to measure the J=4 levels if the H_2 column is high. In figure 3, the spectrum with 24 orbits shows clearly the J=4 levels, so even if we can't see them in 16, it may be possible to request a modest number of orbits later to improve the spectrum sufficiently, when we have a better idea of N(H_2). Note, that our simulations have assumed typical ISM values for temperature, density and UV field. If the density for the Q1331+170 system is as low as the Songaila et al. results imply, then collisional de-excitation will not be as important, and the J=4 lines will be relatively stronger. They will also be stronger if the UV radiation field is higher than in the ISM. Finally, we can co-add the regions around several bands to improve our limits on the J=4 lines. Therefore in 16 orbits we have a good chance of detecting the J=4 lines if the f_H_2 is high, and will put an excellent limit on f_H_2 if it is low. HST is required for these observations, since all of the Lyman and Werner lines of H_2 are shortward of 3150 Angstrom. noindent Figure 3. Enlargement of spectrum, simulated for signal-to-noise attained in 8, 16, 24 orbits, for f_H_2=4times10^-2 and level populations matching those observed in ISM line-of-sight to EpsilonPer. Real Time Justification ----------------------- None. The PI and co-I's have extensive optical spectroscopy of Q1331+170 obtained at the MMT and KPNO 4m, including echelle spectra extending to 3140 Angstrom; Keck HIRES spectra also exist. These data will be used to identify metal and Lyman series lines in the STIS spectrum. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7271( 7) - 08/08/97 11:35 - [ 3] Data Distribution Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7271( 7) - 08/08/97 11:35 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 Q1331+170 Galaxy, QUASAR RA=13H 33M 35.80S +/- 0S,DEC=16D 2000.0 V = 16.71 49' 02.54" +/- 0",PLATE-ID=01TF B-V = 0.13 7271( 7) - 08/08/97 11:35 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 Q1331+170 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 1.0 S ONBOARD ACQ for 2-4 CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 Q1331+170 STIS/C ACQ/PEA 0.2X0.2 MIRROR 1 1.0 S ONBOARD ACQ for 3 CD K ------------------------------------------------------------------------------------------------------------------------------------ 3 Q1331+170 STIS/N ACCUM 0.2X0.2 E230M 2707 1 32.0 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 4 Q1331+170 STIS/N ACCUM 0.2X0.2 E230M 2707 2 42.0 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7271( 7) - 08/08/97 11:35 - [ 6] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 Q1331+170 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 1.0 S ONBOARD ACQ for 2-4 CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 Q1331+170 STIS/C ACQ/PEA 0.2X0.2 MIRROR 1 1.0 S ONBOARD ACQ for 3 CD K ------------------------------------------------------------------------------------------------------------------------------------ 3 Q1331+170 STIS/N ACCUM 0.2X0.2 E230M 2707 1 35.0 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 4 Q1331+170 STIS/N ACCUM 0.2X0.2 E230M 2707 2 42.0 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7271( 7) - 08/08/97 11:35 - [ 7] Summary Form for Proposal 7271 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category QUASAR ABSORPTION LINES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ for 2-4 ONBOARD ACQ for 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names Q1331+170 ------------------------------------------------------------------------------------------------------------------------------------