6426( 6) - 05/14/97 15:53 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6426 Version: 6 Check-in Date: 14-May-1997 15:45:23 1.Proposal Title: A Search For Multiple Images of QSOs Seen Through Damped Ly-alpha Absorbers ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COSMOLOGY GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: EMILIO FALCO SMITHSONIAN ASTROPHYSICAL OBSERVATORY CoI: Abraham Loeb Harvard University N CoI: Matthias Bartelmann Max-Planck Institut fuer Astrophysik N ------------------------------------------------------------------------------------ 6. Abstract We propose to obtain high-resolution images of a sample of QSOs with strong damped Ly-alpha absorption in their spectra. The observations would determine whether these QSOs are multiply imaged by gravitational lensing. It is widely believed that damped Ly-alpha absorption occurs in HI disks of spiral galaxies. Gravitational lensing is then inevitable for lines of sight passing close to the centers of these systems. For typical spiral galaxies, the resulting image separation is expected to be in the range 0.1''--0.5'' and can only be detected with HST at optical wavelengths. Because the neutral -hydrogen column density increases on average towards the center of galaxies, strong Ly-alpha absorption provides an efficient ``flag'' for gravitationally lensed QSOs with small image separations. Bartelmann & Loeb (1995, ApJ, in press) have shown that the frequency of multiple images is enhanced by 1--2 orders of magnitude in samples of QSOs with strong damped Ly-alpha absorption (N_ HI>~ 10^21 cm^-2), compared to the overall QSO population. For this proposal, we have selected those QSOs most likely to exhibit gravitational lensing, from the published list of QSOs with damped Ly-alpha absorption. If lensing is found in this QSO sample, it will have important cosmological implications. First, it will confirm the association of damped Ly-alpha systems with galactic potential wells. Second, the magnification bias associated with lensing would make the appearance of damped systems more likely, and therefore affect estimates of the neutral-hydrogen fraction in the Universe (Bartelmann & Loeb 1995). Third, the cosmological history of HI is linked to the process of galaxy formation and evolution (Lanzetta, Wolfe, & Turnshek 1995, ApJ, 440, 435). Finally, the lensing frequency provides a sensitive probe of the cosmological constant. ------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 2] Observations Description ------------------------ We have selected a sample of QSOs with damped Ly-alpha absorption from the literature. Table 1 shows the list of objects that would be most likely to exhibit multiple images. The table shows the QSO brightness, its redshift, the limits of the redshift interval surveyed for damped Ly-alpha absorption, the absorber redshift, its HI column density, and the estimated probability of occurrence of image splitting. The probability P is computed from the redshift interval surveyed for damped Ly-alpha absorption, the quasar brightness, the redshifts of the QSO and the damped Ly-alpha absorption, and the absorber column density, following Bartelmann & Loeb (1995). begintable begincenter QSO V z_QSO z_min z_max z_abs N P t_1 t_2 t_3 PG1329+412 16.30 1.935 0.485 0.632 0.519 6.31 49 5 15 3 2223-052 17.19 1.404 0.416 0.631 0.492 7.94 37 11 38 8 PG2112+059 15.52 0.466 0.111 0.451 0.204 2.51 10 20 7 21 0000-263 18.00 4.111 2.389 4.060 3.395 19.95 9 4 8 18 1209+093 18.50 3.297 2.175 3.254 2.581 25.12 7 7 14 15 PG0935+417 16.20 1.937 1.062 1.550 1.369 2.00 6 5 15 3 0058-292 18.47 3.093 1.778 3.052 2.673 15.85 6 7 14 15 0302-223 16.00 1.400 1.008 1.376 0.969 1.00 3 34 11 37 0347-382 17.30 3.228 2.044 3.186 3.025 6.31 2 12 43 9 129 105 165 129 B0218+35.7 20.00 0.94(?) - - 0.68 >= 10? 100 35 8 23 The proposed sample of QSOs with known damped Ly-alpha absorption, as well as the known lens, B0218+35.7. For a given QSO, V is its apparent V magnitude, z_QSO is its redshift, z_min and z_max are the boundaries of the redshift interval surveyed for damped Ly-alpha absorption, z_abs is the absorber redshift, N its HI column density, P is the estimated probability for the occurrence of a multiple image of the QSO, given these redshifts, the QSO brightness, and the column density of the absorption, and t_i, with i = 1, 2, 3 is the exposure time in minutes that we estimated with FOCSIM for filters F175W, F342W and F480LP, respectively (in combination with neutral- density filters F2ND, F4ND and F6ND wherever necessary). The absorption system in 0302-223 consists of three damped Ly - alpha systems separated by about 5000 km/s. This may indicate that the absorbers are part of a larger system, like a filament, which by its additional mass might increase the chance of lensing. For B0218+35.7, z_QSO is tentatively based on possible absorption lines because its spectrum is that of a BL Lac (Browne et al. 1993); N is a rough estimate, because as of yet there is no measurement. endcenter endtable We propose to observe the sample of QSOs shown in Table 1 with three filters, F175W, F342W and F480LP. An initial estimate of colors of possible lensed images would aid the interpretation, and because the sample is bright, the total time requested remains small, even with three filters, which also help to fill out the orbits efficiently. The initial lensing signature that we will search for is multiple images, most likely pairs, with separations <1''. With this observed sample in hand, we plan to proceed to propose spectroscopic follow-up observations with HST. We estimated imaging exposures for each QSO with FOCSIM. We assumed that the QSO spectrum is a continuum with slope ~ -0.5 (Francis et al. 1991, ApJ 373, 465). Thus, we neglected line absorption, which is further in the blue than the limits of our filters for the redshifts involved, and the flux in emission lines that would only add a small upward correction to our flux estimates. For each object, we calculated the exposure time necessary to reach S/N ~ 30, or a dynamic range for image flux ratios of ~ 3.7 mag. It was necessary to include neutral - density filters F2ND, F4ND and F6ND in various combinations with F175W, F342W and F480LP, to maintain count rates at acceptable levels. We also propose to obtain a low -resolution, objective-prism (FUVOP) spectrum of B0218+357, to determine directly the HI column density of the lens. We propose to orient the dispersion axis so as to simultaneously disperse (but spatially separate) both images of the quasar, to measure their individual UV spectra. We found it necessary to include F275W and F1ND in the optical path, to maintain acceptable count rates; we estimated a total of about 40 minutes would suffice to obtain a spectrum with S/N > 50, again based on the FOCSIM simulations. We trimmed most of our exposure times to fit all of our observations in the 10 orbits that we were allotted. In particular, we eliminated several of the F175W exposures where, as pointed out by the TAC, the QSO light would be absent due to the Ly- alpha absorption. Although it would still be interesting to try to detect any lensing galaxies, we opted for eliminating the F175W exposures for sample QSOs with Ly-alpha absorption at redshifts > 1. The TAC also pointed out that 0000- 263 and 0347-382 were observed previously with HST. However, the archived observations are only pre-refurbishment, were between 100 and 350 seconds long, and were conducted at best under coarse lock. Therefore, the extant data are not very useful. Because 0347-382 had the lowest lensing probability and we were short on orbits, we decided to eliminate it from our sample. We decided however to keep 0000-263, to obtain a much improved image with FOC. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- We plan to conduct ground-based follow-up observations of interesting candidates wherever possible, to confirm the occurrence of lensing. SAO reference number: P3554-9-95 ------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: ------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PG1329+412 GALAXY, QSO, Lyman RA=13H 31M 41.13S +/- 0.03S, J2000 Z=1.930 V = 16.3+/-0.1 Alpha Cloud, DEC=+41D 01' 58.0" +/- 0.5" Gravitational Lens 2 2223-052 GALAXY, QSO, Lyman RA=22H 25M 47.321S +/- 0.03S, J2000 Z=1.404 V = 17.2+/-0.1 Alpha Cloud, DEC=-04D 57' 01.4" +/- 0.5" Gravitational Lens 3 PG2112+059 GALAXY, QSO, Lyman RA=21H 14M 52.51S +/- 0.03S, J2000 Z=0.466 V = 15.5+/-0.1 Alpha Cloud, DEC=+06D 07' 42.5" +/- 0.5" Gravitational Lens 4 0000-263 GALAXY, QSO, Lyman RA=00H 03M 22.87S +/- 0.03S, J2000 Z=4.098 V = 18.0+/-0.1 Alpha Cloud, DEC=-26D 03' 17.0" +/- 0.5" Gravitational Lens 5 1209+093 GALAXY, QSO, Lyman RA=12H 11M 34.90S +/- 0.03S, J2000 Z=3.297 V = 18.5+/-0.1 Alpha Cloud, DEC=+09D 02' 22.8" +/- 0.5" Gravitational Lens 6 PG0935+417 GALAXY, QSO, Lyman RA=09H 38M 57.02S +/- 0.03S, J2000 Z=1.937 V = 16.2+/-0.1 Alpha Cloud, DEC=+41D 28' 21.3" +/- 0.5" Gravitational Lens 7 0058-292 GALAXY, QSO, Lyman RA=01H 01M 04.57S +/- 0.03S, J2000 Z=3.093 V = 18.5+/-0.1 Alpha Cloud, DEC=-28D 58' 01.1" +/- 0.5" Gravitational Lens 8 0302-223 GALAXY, QSO, Lyman RA=03H 04M 49.82S +/- 0.03S, J2000 Z=1.400 V = 16.0+/-0.1 Alpha Cloud, DEC=-22D 11' 52.0" +/- 0.5" Gravitational Lens 9 B0218+35.7 GALAXY, QSO, Lyman RA=02H 21M 05.44S +/- 0.03S, J2000 Z=0.940 V = 20.0+/-0.1 Alpha Cloud, DEC=+35D 56' 13.9" +/- 0.5" Gravitational Lens 6426( 6) - 05/14/97 15:53 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 101 PG1329+412 FOC/96 IMAGE 512X512 F4ND,F1ND PIXEL=25x25 1 10 M ,F342W ------------------------------------------------------------------------------------------------------------------------------------ 102 PG1329+412 FOC/96 IMAGE 512X512 F2ND,F1ND PIXEL=25x25 1 568 S ,F480LP ------------------------------------------------------------------------------------------------------------------------------------ 103 PG1329+412 FOC/96 IMAGE 512X512 F2ND,F1ND PIXEL=25x25 1 14 M END ORBIT MAX DUR 15M MIN ,F175W DUR 13M ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 201 2223-052 FOC/96 IMAGE 512X512 F2ND, PIXEL=25x25 1 970 S F175W ------------------------------------------------------------------------------------------------------------------------------------ 202 2223-052 FOC/96 IMAGE 512X512 F2ND, PIXEL=25x25 1 6 M F480LP ------------------------------------------------------------------------------------------------------------------------------------ 203 2223-052 FOC/96 IMAGE 512X512 F4ND, PIXEL=25x25 1 440 S F342W ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 7] Visit: 03 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 ------------------------------------------------------------------------------------------------------------------------------------ 301 PG2112+059 FOC/96 IMAGE 512X512 F6ND, PIXEL=25x25 1 10 M F342W ------------------------------------------------------------------------------------------------------------------------------------ 302 PG2112+059 FOC/96 IMAGE 512X512 F4ND, PIXEL=25x25 1 10 M F175W ------------------------------------------------------------------------------------------------------------------------------------ 303 PG2112+059 FOC/96 IMAGE 512X512 F4ND, PIXEL=25x25 1 548 S F480LP ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 8] Visit: 04 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 ------------------------------------------------------------------------------------------------------------------------------------ 401 0000-263 FOC/96 IMAGE 512X512 F1ND, PIXEL=25x25 1 20 M F480LP ------------------------------------------------------------------------------------------------------------------------------------ 402 0000-263 FOC/96 IMAGE 512X512 F4ND, PIXEL=25x25 1 950 S F342W ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 9] Visit: 05 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 ------------------------------------------------------------------------------------------------------------------------------------ 501 1209+093 FOC/96 IMAGE 512X512 F2ND,F1ND PIXEL=25x25 1 1060 S ,F342W ------------------------------------------------------------------------------------------------------------------------------------ 502 1209+093 FOC/96 IMAGE 512X512 F1ND, PIXEL=25x25 1 1080 S F480LP ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 10] Visit: 06 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 ------------------------------------------------------------------------------------------------------------------------------------ 601 PG0935+417 FOC/96 IMAGE 512X512 F2ND,F1ND PIXEL=25x25 1 20 M ,F480LP ------------------------------------------------------------------------------------------------------------------------------------ 602 PG0935+417 FOC/96 IMAGE 512X512 F4ND,F1ND PIXEL=25x25 1 1060 S ,F342W ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 11] Visit: 07 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 ------------------------------------------------------------------------------------------------------------------------------------ 701 0058-292 FOC/96 IMAGE 512X512 F2ND,F1ND PIXEL=25x25 1 20 M ,F342W ------------------------------------------------------------------------------------------------------------------------------------ 702 0058-292 FOC/96 IMAGE 512X512 F1ND, PIXEL=25x25 1 965 S F480LP ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 12] Visit: 08 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 ------------------------------------------------------------------------------------------------------------------------------------ 801 0302-223 FOC/96 IMAGE 512X512 F4ND, PIXEL=25x25 1 1180 S F480LP ------------------------------------------------------------------------------------------------------------------------------------ 802 0302-223 FOC/96 IMAGE 512X512 F6ND, PIXEL=25x25 1 965 S F342W ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 13] Visit: 09 Visit Requirements: ORIENT 301D TO 81D 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 ------------------------------------------------------------------------------------------------------------------------------------ 901 B0218+35.7 FOC/96 IMAGE 512X512 F2ND, PIXEL=25x25 1 900 S F342W ------------------------------------------------------------------------------------------------------------------------------------ 902 B0218+35.7 FOC/96 IMAGE 512X512 F175W PIXEL=25x25 1 1045 S ------------------------------------------------------------------------------------------------------------------------------------ 903 B0218+35.7 FOC/96 IMAGE 512X512 F130LP, 2750 PIXEL=25x25 1 2641 S POS TARG 0, -3.7 PRISM1 ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 14] Visit: 56 Visit Requirements: On Hold Comments: Additional Comments: Auto-repeat of Visit 06 after previous failure. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 651 PG0935+417 FOC/96 IMAGE 512X512 F2ND,F1ND PIXEL=25x25 1 20 M ,F480LP ------------------------------------------------------------------------------------------------------------------------------------ 652 PG0935+417 FOC/96 IMAGE 512X512 F4ND,F1ND PIXEL=25x25 1 1060 S ,F342W ------------------------------------------------------------------------------------------------------------------------------------ 6426( 6) - 05/14/97 15:53 - [ 15] Summary Form for Proposal 6426 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters PIXEL=25x25 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COSMOLOGY ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements END ORBIT MAX DUR 15M MIN DUR 13M ORIENT 301D TO 81D POS TARG 0, -3.7 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F4ND,F1ND,F342W F2ND,F1ND,F480LP F2ND,F1ND,F175W F2ND,F175W F2ND,F480LP F4ND,F342W F6ND,F342W F4ND,F175W F4ND,F480LP F2ND,F1ND,F342W F2ND,F342W F130LP,PRISM1 ------------------------------------------------------------------------------------------------------------------------------------ Target Names PG1329+412 2223-052 PG2112+059 0000-263 1209+093 PG0935+417 0058-292 0302-223 B0218+35.7 ------------------------------------------------------------------------------------------------------------------------------------