6592( 5) - 05/24/96 15:05 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6592 Version: 5 Check-in Date: 24-May-1996 14:59:59 1.Proposal Title: The Distribution and Evolution of Lyman- Alpha Forest Cloud Sizes ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle INTERGALACTIC MEDIUM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Craig Foltz Multiple Mirror Observatory CoI: Chris Impey Steward Observatory N CoI: Nadine Dinshaw Steward Observatory Y CoI: Ray Weymann Observatories of the Carnegie Institution N of Washington CoI: Simon Morris Dominion Astrophysical Observatory N ------------------------------------------------------------------------------------ 6. Abstract Our ongoing program to measure the sizes of Ly-alpha\ forest clouds by looking for common absorption in close pairs of quasars using FOS UV spectroscopy (GO Programs 5320 and 6100) has yielded dramatic and unexpected results: (1) Observations of the pair Q0107-025A,B (z_em ~eq 0.95) give a firm and model-independent lower limit on the transverse size of the absorbers of more than 300 kpc and suggest a characteristic radius of the clouds of ~ 600 ,h^-1 kpc (h = 100 kms Mpc^-1; q_0 = 0.5) at 0.5 <= z <= 0.9. (2) Similar observations of the higher redshift pair LB 9605 (z_ em = 1.834) and LB 9612 (z_ em = 1.898) imply a characteristic radius of about half that inferred at lower redshift. Together with ground-based observations, these results imply an evolution of cloud radii with redshift, with the characteristic size of the Ly-alpha\ absorbers decreasing with increasing redshift. (3) Evidence is also found for a possible dependence of cloud radii on column density, with the high column density clouds being larger in extent than the lower column density clouds. Additional observations of these quasars, as well as a third quasar LBQS 0107-0232 within 3' of Q0107-025A,B, will establish whether the correlation with column density is real, further constrain the size of the clouds at two different redshift ranges, and probe cloud sizes on scales up to 1 Mpc. ------------------------------------------------------------------------------------ 6592( 5) - 05/24/96 15:05 - [ 2] Observations Description ------------------------ The proposed observations will improve the S/N of the spectra of the quasars Q0107-025A,B and LBQS 0107-0232, as well as LB 9605 and 9612, to a limiting rest equivalent width limit of 0.12 Angstrom in the wavelength region greater than 1800 Angstrom. beginenumerate em Improved S/N in the spectra of Q0107-025 A,B and LBQS 0107-0232 in the range 1600 - 2300 Angstrom. Figure reffig-0107 shows the FOS/RD G190H data acquired in Cycle 4 GO Program 5320. New observations are required to raise the S/N to about 25 at 1800 Angstrom, sufficient to yield a 5 Sigma rest equivalent width limit of about 0.12 Angstrom. This will approximately double the number of significant lines detected above W_0 > 0.12 Angstrom. An added consequence of the improved S/N is that we will be able to measure more reliable central wavelengths and equivalent widths in the critical wavelength region shortward of 2100 Angstrom, the observed wavelength of the Ly -alpha\\ emission in LBQS 0107-0232. Exposure times for Q0107- 025 A,B were calculated based on the measured S/N and limiting rest equivalent widths of the Cycle 4 data. The required integration time is 220 minutes. Including overheads for guide-star and target acquisitions, we request 6 orbits for A and 5 for B. The difference in B_J magnitude between Q0107-0232 and Q0107-025A is well-known from the LBQS plates to be 0.3 +/- 0.1 mag (barring variability). From the S/N realized in the GO 5320 observations of Q0107-025A, using this magnitude difference and assuming that both quasars have the same spectral slope (consistent with the optical data) we estimate that 590 minutes of integration (15 orbits) will give S/N equal to that of the improved Q0107-025A,B spectra. We are obtaining 410 min of LBQS 0107-0232 in Cycle 5, so we are asking for 180 min (5 orbits) in Cycle 6. em Improved S/N in the spectra of Q0107-025 A,B in the range 2300 - 3270 Angstrom. Count rates were estimated from Table 1.2.2 in the FOS Instrument Handbook by extrapolating the GO program 5320 fluxes to longer wavelengths. In order to achieve the same rest equivalent width limit (0.12 Angstrom), we are aiming for with the G190H grating, we estimate requiring 130 minutes of integration time. We are obtaining 65 min in Cycle 5, so only another 65 min (2 orbits) are required in Cycle 6. em Improved S/N in the spectra of LB 9605 and 9612 in the range 2300 - 3270 Angstrom. The S/N achieved in Cycle 4 GO program 5631 was 10 at 2500 Angstrom and 24 at its maximum in both LB 9605 and 9612. In order to acheive a rest equivalent width limit of W_0 = 0.12 Angstrom over the entire wavelength region, we will need 145 minutes on LB 9605 and 65 minutes on LB 9612 which is obtainable in 4 and 2 orbits respectively. endenumerate Accurate wavelength calibration is critical for our program since it limits the precision of the velocity difference measurements of Ly-alpha lines between the lines of sight. We therefore specify that a comparison exposure be taken upon each visit to a target and after a grating change. We have taken these exposures into account in calculating the required number of orbits. We are currently obtaining FOS observations in Cycle 5 (GO Program 6100) of a third bright quasar, LBQS 0107-0232 (z_ em = 0.728, B_J = 18.4) which lies within a few arcminutes of Q0107-025A,B. These three quasars form a triangle with sides projected on the sky of 1min point44, 2min point00 and 2min point93 (see Figure reffig-map). Although LBQS 0107-0232 is at lower redshift than the other two quasars, the separations are larger so that observations in the range from 1600 - 2100 Angstrom will probe distance scales up to nearly 1 Mpc, i.e. comparable to the current upper limits on cloud sizes at z~eq2.5. We are also extending our observations of Q0107- 025A,B redward to cover forest lines out to the Ly-alpha emission line using the G270H grating on FOS. These data will cover the range from 2300 - 3200 Angstrom and will eliminate any ambiguity in the lines which are presently identified as Ly-alpha but could possibly be Ly-beta. Spectroscopic observations of LB 9605, 9612 in the wavelength region 3150 to 5500 Angstrom\\ at a resolution of better than 1 Angstrom\\ will be made with the Multiple Mirror Telescope. These observations will overlap the G270H spectra and will cover the critical region just shortward of the Ly-alpha\\ emission lines of the quasars. These observations will also allow us to identify any metal-line absorption systems. vspace.1in o We have already obtained MMT spectra of Q0107-025A,B from 3200 Angstrom\\ to longward of the Mg II Lambda 2798 emission line in order to search for metal- line systems. vspace.1in o In a complementary program (GTO 5170), we have obtained GHRS G140L spectra of Q0107- 025A,B and begun a survey of galaxies near the lines of sight to the quasars in an attempt to identify galaxies responsible for the Ly-alpha\\ absorption. The ground-based observations were made with the prime focus spectrograph COSMIC on the 200 inch Hale telescope. More ground-based spectroscopy of candidate galaxies are being obtained for this program at the Canada-France-Hawaii and Hale Telescopes to deeper magnitudes. An unexpected result of program GTO 5170 with interesting implications is the strong Lyman limit system detected in the GHRS G140L spectrum of Q0107-025B at z ~eq 0.4 which is missing (or very much weaker) in Q0107-025A, although Civ absorption is present at that redshift in both quasars. We have thus far failed to identify a galaxy which can plausibly be associated with the Lyman limit system. Real Time Justification ----------------------- Calibration Justification ------------------------- The success of this proposal relies on whether the absorption features in one quasar can be unambiguously identified as common (or not) to those in the other quasar in the pair. This demands accurate zero-point calibration of the wavelength scale. According to Papers I and II of the HST Quasar Absorption Line Key Project, the rms scatter in the zero point is about 0.5 ang (60-80 km/sec) in the G190H and G270H gratings. The offsets can be determined from the Galactic absorption lines, however in calibrating the G190H spectra only the Al II 1670 line is suitable and is not always well detected. Therefore one wavelength calibration frame following an exposure at each grating for each of the quasars is requested. We will not need a calibration frame for every exposure because the relative zero-point shifts between exposures of a given quasar can be calculated by cross-correlating the individual exposures of the same quasar. Note that the GO 5320 observations achieved an uncertainty in the difference in wavelengths between the members of a common pair of about 40 km/sec because the observations of the two quasars used the same guide star, thereby minimizing the uncertainty in the relative positioning of the two quasars in the spectrograph aperture. We request that the same procedure be used for the G270H observations of Q0107-025 A,B, i.e. the same guide stars should be used for both observations. Additional Comments ------------------- ------------------------------------------------------------------------------------ 6592( 5) - 05/24/96 15:05 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6592( 5) - 05/24/96 15:05 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 Q0107-025A Galaxy, Lyman Alpha RA = 01H 10M 13.146S +/- 0.1S, J2000 Z=0.956 V = 18.2 Cloud DEC = -02D 19' 54.05" +/- 1.0", PLATE-ID = 00WM Comments: COMPONENT A OF QUASAR PAIR Q0107-025A,B 2 Q0107-025B Galaxy, Lyman Alpha RA = 01H 10M 16.316S +/- 0.1S, J2000 Z=0.952 V = 17.4 Cloud DEC = -02D 18' 52.81" +/- 1.0", PLATE-ID = 00WM Comments: COMPONENT B OF QUASAR PAIR Q0107-025A,B 3 Q0107-0232 Galaxy, Lyman Alpha RA = 01H 10M 14.47S +/- 0.1S, 2000 Z=0.728 V = 18.5 Cloud DEC = -02D 16' 58.9" +/- 1.0", PLATE-ID = 00WM 6592( 5) - 05/24/96 15:05 - [ 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 Q0107-025A FOS/RD ACQ/BIN 4.3 MIRROR 1 62.6 S ONBOARD ACQ FOR 2-7 ARY Comments: USE SAME GUIDE STARS ------------------------------------------------------------------------------------------------------------------------------------ 2 Q0107-025A FOS/RD ACCUM 1.0 G190H 1590-23 1 25 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 3 Q0107-025A FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 4 Q0107-025A FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 5 Q0107-025A FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 6 Q0107-025A FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 7 Q0107-025A FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 8 WAVE FOS/RD ACCUM 1.0 G190H 1590-23 1 DEF 12 Comments: DO NOT CHANGE GRATING POSITION BETWEEN EXPOSURES ------------------------------------------------------------------------------------------------------------------------------------ 6592( 5) - 05/24/96 15:05 - [ 6] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: USE SAME GUIDE STARS AS IN VISIT 1 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 9 Q0107-025B FOS/RD ACQ/BIN 4.3 MIRROR 1 32.7 S ONBOARD ACQ FOR 10-14 ARY Comments: USE SAME GUIDE STARS AS FOR TARGET 1 ------------------------------------------------------------------------------------------------------------------------------------ 10 Q0107-025B FOS/RD ACCUM 1.0 G190H 1590-23 1 26 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 11 Q0107-025B FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 12 Q0107-025B FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 13 Q0107-025B FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 14 Q0107-025B FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 15 WAVE FOS/RD ACCUM 1.0 G190H 1590-23 1 DEF 12 Comments: DO NOT CHANGE GRATING POSITION BETWEEN EXPOSURES ------------------------------------------------------------------------------------------------------------------------------------ 16 Q0107-0232 FOS/RD ACQ/BIN 4.3 MIRROR 1 100.6 S ONBOARD ACQ FOR 17-18 ARY Comments: USE SAME GUIDE STARS ------------------------------------------------------------------------------------------------------------------------------------ 17 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590-23 1 25 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 18 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 19 WAVE FOS/RD ACCUM 1.0 G190H 1590-23 1 DEF 12 Comments: DO NOT CHANGE GRATING POSITION BETWEEN EXPOSURES ------------------------------------------------------------------------------------------------------------------------------------ 6592( 5) - 05/24/96 15:05 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 20 Q0107-0232 FOS/RD ACQ/BIN 4.3 MIRROR 1 100.6 S ONBOARD ACQ FOR 21-27 ARY Comments: USE SAME GUIDE STARS ------------------------------------------------------------------------------------------------------------------------------------ 21 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590-23 1 25 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 22 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 23 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 24 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 25 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 26 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 27 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590-23 1 40 M 12 ------------------------------------------------------------------------------------------------------------------------------------ 28 WAVE FOS/RD ACCUM 1.0 G190H 1590-23 1 DEF 12 Comments: DO NOT CHANGE GRATING POSITION BETWEEN EXPOSURES ------------------------------------------------------------------------------------------------------------------------------------ 6592( 5) - 05/24/96 15:05 - [ 8] Summary Form for Proposal 6592 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERGALACTIC MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2-7 ONBOARD ACQ FOR 10-14 ONBOARD ACQ FOR 17-18 ONBOARD ACQ FOR 21-27 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G190H ------------------------------------------------------------------------------------------------------------------------------------ Target Names Q0107-025A WAVE Q0107-025B Q0107-0232 ------------------------------------------------------------------------------------------------------------------------------------