Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 4402c Report Date: 09-May-96:19:36 Version: ********** Check-in Date: ********** 1.Proposal Title: A STUDY OF THE ARCSECOND GRAVITATIONAL LENS 1422+321 CYCLE3HIGH ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID QUASARS & AGN GO Sub Category GRAVITATIONAL LENSES ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Chris D. Impey STEWARD OBSERVATORY USA 602-621-6522 ------------------------------------------------------------------------------------ 7. Abstract We propose spectroscopy and imaging of the four components of the candidate gravitational lens 1422+231. This is the brightest of the few known examples of subarcsecond multiply imaged quasars. It was selected from a survey of 1750 flat spectrum radio sources which should be particularly effective at finding subarcsecond lenses. With V = 16.5 (all components) and z = 3.62, this is one of the most apparently luminous objects in the universe. Spectroscopy of optical counterparts to the four radio components will clearly establish whether or not the system is a gravitational lens, and imaging with the FOC is very likely to identify the lens, even if it is a highly subluminous galaxy. Contamination due to spilled light is not a problem for the brightest three components, and for the faintest component, we will measure contamination due to the other three components with an offset sky exposure. A system with four components offers the prospect of a large number of constraints on the lensing model. Moreover, the radio sources are compact and highly polarized, and so very likely to be variable. 1422+231 could therefore be used in a VLA or VLBA monitoring campaign to derive a new estimate of the Hubble constant using up to three time delays. Confirmation of the lens can only be done from space. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 9.01 par: 0 10. Num targs pri: 5 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 4402c PI: Chris D. Impey Proposal Title: A STUDY OF THE ARCSECOND GRAVITATIONAL LENS 1422+321 CYCLE3HIGH ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Chris D. Impey STEWARD OBSERVATORY USA Craig B. Foltz MULTIPLE MIRROR TELESCOPE USA Ian W. Browne NUFFIELD RADIO ASTRONOMY UNITED KING X LABORATORIES Alok R. Patnaik NUFFIELD RADIO ASTRONOMY UNITED KING X LABORATORIES Irwin Shapiro HARVARD SMITHSONIAN CENTER FOR USA ASTROPHYSICS Adam Reiss HARVARD SMITHSONIAN CENTER FOR USA ASTROPHYSICS ------------------------------------------------------------------------------------ 3. Description of proposed observations. We propose two observations of the candidate gravitational lens 1422+231. The first is spectroscopy of individual radio components A, B, C, and D using the FOS red side with grating G570H which gives wavelength coverage from 4600 to 6800 Angstroms. Exposure times are calculated assuming that the system is indeed a lens, and that the optical fluxes scale with the radio fluxes. Fluxes for the sum of A+B+C are taken from Figure 2. The 0.3 arcsec circular aperture will be used; any larger and the components will not be separated, any smaller is not practical with the degraded PSF of the HST. An integration time of 1500 seconds will give a S/N = 15 per resolution element in the continuum at 4800 Angstroms for components A and B, and 3000 seconds will give S/N = 14 for component C. High S/N spectra of A, B, and C are essential to confirm the lens hypothesis. High redshift quasars generally have similar continuum shapes, and there is already one case of an (unlensed) quasar pair with virtually identical spectra and a small velocity difference (Djorgovski et al. 1987, Ap.J., 321, L17). Limited S/N has so far hampered the interpretation of one other subarcsecond lens (Bahcall et al. 1992, in press); we note however that 1208+101 is considerably fainter than our candidate system. If D is a lens component, an integration time of 6200 seconds will be used to get a S/N = 7 in the putative Lyman-alpha line, allowing a clear- cut test of this fourth component. The PSF will give contamination between spectra of the different components, but it is generally small. A and B are contaminated by 5%, and C is contaminated 12% by the sum of A and B. The contamination of D is severe, the expected flux is increased by 200% by the sum of A plus B plus C. We therefore will take a "sky" exposure at a position which is on the opposite side of A+B from D, to determine the amount of spilled light directly. Although the PSF has azimuthal varations of 30-40%, this procedure, plus the high S/N we will obtain on A,B, and C, will allow us to unequivocally determine whether or not D has Lyman-alpha with the same equivalent width as components A, B, and C. The exposure times are slightly amended from phase 1 to conform to a smaller amount of spacecraft time. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The small separation of the components of this candidate gravitational lens system mean that observations from HST are essential for these observations. The overall extent of the radio source is 1.3 arcsec, the separation between A and B is 0.5 arcsec, and the separation between B and C is 0.8 arcsec (see Figure 1). While imaging of 1422+231 might be possible from the ground under the very best conditions, FOC observations still offer substantial advantages. Since the PSF gives a core of 10% of the image flux with a FWHM of only 0.07 arcsec, the bright components A, B, and C are expected to be well separated. Moreover, the presence of three bright point sources in the field means that image deconvolution will be well constrained, which is an advantage in the search for the lens. Confirmation of the 1422+231 system as a gravitational lens relies mostly on spectroscopy of components A, B, and C. The capabilities of HST in making this observation are unique, no ground-based facility can compete. Successful HST confirmation of the lens system will lead to important ground-based follow-up at radio wavelengths. The lens conponents are well separated with the VLA or VLBA, and are compact and polarized. Compactness and high polarization implies that they are also highly likely to be variable. A radio monitoring program offers the exciting possibility of a new geometric determination of the Hubble Constant, in a system where up to three time delays can be measured. Figure 2 shows the flux density of the sum of the three brightest components A, B, and C. The FOS exposure time calculations are based on the assumption that the relative fluxes of all four components is given by their relative radio fluxes (this assumption is confirmed by recent, unpublished imaging of the system in the near infrared). Count rates are calculated at two wavelength, in the middle of the continuum shortward of Lyman- alpha at 4800 Angstroms, and at the half power of the Lyman-alpha line around 5700 Angstroms. The calculated count rates for components A, B, C, and D are 0.18, 0.18, 0.088, and 0.0044 ct/s/diode at 4800 Angstroms, and 0.60, 0.60, 0.30, and 0.015 ct/s/diode at 5700 Angstroms (this assumes that all the components have Lyman-alpha with the same equivalent width). The exposure times are calculated to give S/N = 15 for components A (1500 sec), B (1500 sec), and C (3000 sec), and to give S/N = 7 at half power of the predicted Lyman-alpha line in component D (6200 sec). ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Real time interactive acquisition of the first of the four gravitational len images is required. The necessity for this scarce resource was confirmed in consultations with the FOS support scientists and the USB technical assistant for this program, and was recognized in the internal Phase 1 review of this proposal. The requirement is based on the fact that the four lens images are contained within an area of only 1 arcsecond, and three of them are of similar brightness. The VLBI radio positions are extremely accurate (better than 50 milliarcseconds absolute), and the field is visually distinctive, so real time recognition and centering should be straightforward. The 0.3 arcsecond FOS aperture is required to meet the scientific goals of the project. Having acquired the first of the four images, the other three can be located by offsetting. The differential positions of the four components are known to better than 10 milliarcseconds. Acquisition now being done with a blind pointing from an offset star. Page 4 ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. Standard calibration of the FOS spectra and FOC images is requested. The PI and MMT co-I have extensive experience in spectroscopic reduction and anaylsis. The most critical issue in the spectroscopic part of this proposal is the issue of contamination between the quasar images due to the degraded PSF of the HST. We will calculate this effect from the FOC images directly, but will check the contamination of the faintest component D directly with an "off" exposure with the FOS, designed to directly measure the contamination in the spectrum of D due to spilled light from the brighter quasar components. We will use standard image deconvolution techniques on the FOC images, guided by the three bright and (presumably) unresolved point sources (components A,B,C). The PSF has a sufficiently sharp core that all four components will be well separated. One graduate student at the University of Arizona will be involved in the reduction and analysis. ------------------------------------------------------------------------------------ 9. Description of previous HST work. a. List HST program numbers and titles: GO Program 2524 "Spectropolarimetry of Bright Quasars" - not related GO Program 3732 "Spectropolarimetry of Bright Quasars" - not related GO Program 3648 "Imaging of BL Lac Host Galaxies and Environments" - not related b. Summarize the main results obtained from previous related programs: GO Program 2524 - Cycle 1, data received and reduced, paper in preparation GO Program 3732 - Cycle 2, data received and reduced, paper in preparation GO Program 3648 - Cycle 2, data recieved and is currently being reduced ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). The University of Arizona will provide central computing services (hard disks, networks, tape drives) in support of this project. One undergraduate will be able to work on this project through funds provided by the Arizona Space Grant. We will also be supported by the University of Arizona in follow-up ground-based activities, such as VLA and VLBA monitoring of the radio lens components for brightness variations that could lead to a new determination of the Hubble constant. ------------------------------------------------------------------------------------ 11. Address Information Name: CHRIS D. IMPEY Category: PI Institution: Steward Observatory Address: STEWARD OBSERVATORY UNIVERSITY OF ARIZONA City: TUCSON State: AZ Zip Code: 85721 Country: USA Telephone: 602-621-6522 Telex (or e-mail): 467175 ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 4402c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 QSO1424P231- E, 314, 323 RA = 14H 24M 38.094S +/- 2000 Z=3.62 1 B = 18.4 +/- 0.2 B PKS 0.004S, 2 B-V = 1.7 DEC = +22D 56' 00.59" +/- 3 F-LINE(1216) = 5 +/- 1 E-15 0.05", Comments: SUBARCSECOND GRAVITATIONAL LENS COMPONENT B, VLBI RADIO POSITION UPDATED COORDS WILL COME FROM WFPC IMAGES IN 5080. ACQUIRE B THEN OFFSET TO OTHER COMPONENTS ------------------------------------------------------------------------------------------------------------------------------------ 2 QSO1424P231- E, 314, 323 RA-OFF = 0.028S +/- 0.002S, 2000 Z=3.62 1 B = 18.4 +/- 0.2 A PKS DEC-OFF = 0.320" +/- 0.010", 2 B-V = 1.7 FROM 1 3 F-LINE(1216) = 5 +/- 1 E-15 Comments: SUBARCSECOND GRAVITATIONAL LENS COMPONENT A, VLBI RADIO POSITION ACQUIRED BY OFFSET FROM COMPONENT B ------------------------------------------------------------------------------------------------------------------------------------ 3 QSO1424P231- E, 314, 323 RA-OFF = -0.024S +/- 0.002S, 2000 Z=3.62 1 B = 19.1 +/- 0.2 C PKS DEC-OFF = -0.750" +/- 2 B-V = 1.7 0.010", 3 F-LINE(1216) = 2 +/- 1 E-15 FROM 1 Comments: SUBARCSECOND GRAVITATIONAL LENS COMPONENT C, VLBI RADIO POSITION ACQUIRED BY OFFSET FROM COMPONENT B ------------------------------------------------------------------------------------------------------------------------------------ 4 QSO1424P231- E, 314, 323 RA-OFF = 0.068S +/- 0.002S, 2000 Z=3.62 1 B = 22.4 +/- 0.2 D PKS DEC-OFF = -0.810" +/- 2 B-V = 1.7 0.010", 3 F-LINE(1216) = 12 +/- 5 E-17 FROM 1 Comments: SUBARCSECOND GRAVITATIONAL LENS COMPONENT D, VLBI RADIO POSITION ACQUIRED BY OFFSET FROM COMPONENT B ------------------------------------------------------------------------------------------------------------------------------------ 5 QSO1424P231- E, 314, 323 RA-OFF = -0.068S +/- 0.002S, 2000 Z=3.62 1 B = 22.6 +/- 0.2 OFF PKS DEC-OFF = 0.810" +/- 0.010", 2 B-V = 1.7 FROM 1 3 F-LINE(1216) = 8 +/- 5 E-17 Comments: SUBARCSECOND GRAVITATIONAL LENS MEASURE CONTAMINATION OF D ACQUIRED BY OFFSET FROM COMPONENT B ------------------------------------------------------------------------------------------------------------------------------------ 6 OFFSET-STAR A RA = 14H 24M 37.6S +/- 2000 1 V = 18.1 +/- 0.2, TYPE=K0V 0.04S, DEC = +22D 55' 44.0" +/- 0.5", Comments: OFFSET STAR. UPDATED COORDS WILL BE PRIVDED BASED ON WFPC EARLY ACQ IMAGE IN 5080. ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4402c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 OFFSET-STAR FOS/RD ACQ/ 4.3 MIRROR SCAN-STEP- 1 4.5S 1 1 CYCLE 3 / 1-6 PEAK Y=1.43 ONBOARD ACQ FOR SEARCH-SIZE-X=1 1.1 SEARCH-SIZE-Y=3 REQ UPDATE / 1-6 Comments: COORDS AND EXP. TIME MAY BE UPDATED BASED ON EARLY ACQ IMAGES IN PROP 5080. ------------------------------------------------------------------------------------------------------------------------------------ 1.1 OFFSET-STAR FOS/RD ACQ/ 1.0 MIRROR SCAN-STEP- 1 22.0S 1 1 ONBOARD ACQ FOR PEAK Y=0.707 1.2 SEARCH-SIZE-X=6 SEARCH-SIZE-Y=2 SCAN-STEP- X=0.707 Comments: COORDS AND EXP. TIME MAY BE UPDATED BASED ON EARLY ACQ IMAGES IN PROP 5080. ------------------------------------------------------------------------------------------------------------------------------------ 1.2 OFFSET-STAR FOS/RD ACQ/ 0.5 MIRROR SCAN-STEP- 1 35.0S 1 1 ONBOARD ACQ FOR PEAK Y=0.354 1.3 SEARCH-SIZE-X=3 SEARCH-SIZE-Y=3 SCAN-STEP- X=0.354 Comments: COORDS AND EXP. TIME MAY BE UPDATED BASED ON EARLY ACQ IMAGES IN PROP 5080. ------------------------------------------------------------------------------------------------------------------------------------ 1.3 OFFSET-STAR FOS/RD ACQ/ 0.3 MIRROR SCAN-STEP- 1 49.0S 1 1 ONBOARD ACQ FOR 2- PEAK Y=0.144 6 SEARCH-SIZE-X=3 SEARCH-SIZE-Y=3 SCAN-STEP- X=0.144 Comments: COORDS AND EXP. TIME MAY BE UPDATED BASED ON EARLY ACQ IMAGES IN PROP 5080. ------------------------------------------------------------------------------------------------------------------------------------ 2 QSO1424P231 FOS/RD ACCUM 0.3 G570H 1 1500S 35 1 1 SEQ 2-6 NO GAP -B Comments: COORDS MAY BE UPDATED BASED ON EARLY ACQ IMAGES IN PROP 5080. S/N AT 6000 ANGSTROMS BLOCKING FILTER WG 375 ------------------------------------------------------------------------------------------------------------------------------------ 3 QSO1424P231 FOS/RD ACCUM 0.3 G570H 1 1500S 35 1 1 -A Comments: S/N AT 6000 ANGSTROMS BLOCKING FILTER WG 375 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4402c [ 7] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 4 QSO1424P231 FOS/RD ACCUM 0.3 G570H 1 3000S 35 1 1 -C Comments: S/N AT 6000 ANGSTROMS BLOCKING FILTER WG 375 ------------------------------------------------------------------------------------------------------------------------------------ 5 QSO1424P231 FOS/RD ACCUM 0.3 G570H 1 6200S 8 1 1 -D Comments: S/N AT 6000 ANGSTROMS BLOCKING FILTER WG 375 ------------------------------------------------------------------------------------------------------------------------------------ 6 QSO1424P231 FOS/RD ACCUM 0.3 G570H 1 3000S 8 1 1 -OFF Comments: S/N AT 6000 ANGSTROMS BLOCKING FILTER WG 375 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 4402c [ 8] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCAN-STEP-Y=1.43 SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=0.707 SEARCH-SIZE-X=6 SEARCH-SIZE-Y=2 SCAN-STEP-X=0.707 SCAN-STEP-Y=0.354 SEARCH-SIZE-X=3 SCAN-STEP-X=0.354 SCAN-STEP-Y=0.144 SCAN-STEP-X=0.144 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 9.01 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category QUASARS & AGN ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category GRAVITATIONAL LENSES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 3 / 1-6; ONBOARD ACQ FOR 1.1; REQ UPDATE / 1-6 ONBOARD ACQ FOR 1.2; ONBOARD ACQ FOR 1.3; ONBOARD ACQ FOR 2-6; SEQ 2-6 NO GAP; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G570H ------------------------------------------------------------------------------------------------------------------------------------ Target Names QSO1424P231-B PKS QSO1424P231-A QSO1424P231-C QSO1424P231-D QSO1424P231-OFF OFFSET-STAR ------------------------------------------------------------------------------------------------------------------------------------