7422( 3) - 06/12/97 16:34 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7422 Version: 3 Check-in Date: 12-Jun-1997 16:31:39 1.Proposal Title: NICMOS observations of the gravitational lens 1608+656 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COSMOLOGY GO 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: ANTHONY READHEAD CALTECH CoI: Ger de Bruyn Netherlands Foundation for Radio Astronomy N CoI: Ignas Snellen University of Leiden N CoI: Richard Schilizzi University of Leiden N CoI: Chris Fassnacht California Institute of Technology Y CoI: Roger Blandford California Institute of Technology N CoI: Tim Pearson California Institute of Technology N CoI: Donna Womble California Institute of Technology N CoI: Steve Myers University of Pennsylvania N CoI: Ian Browne Jodrell Bank, University of Manchester N CoI: Neal Jackson Jodrell Bank, University of Manchester N CoI: Sunita Nair Jodrell Bank, University of Manchester N CoI: Peter Wilkinson Jodrell Bank, University of Manchester N CoI: Leon Koopmans University of Groningen N ------------------------------------------------------------------------------------ 6. Abstract We request NICMOS observations of the gravitational lens system 1608+656 in order to measure the light distribution of the lens while minimizing the effects of extinction. This information is needed to refine the lens mass model -- required if the system is to be used to determine H_0. The 1608+656 system is one of the 5 lenses found so far in the Cosmic Lens All-Sky Survey and is the most promising one to use for H_0 determination. Our systematic follow-up has given both the lens and source redshifts, z=0.63 and z=1.39, respectively. We have also made extensive VLA and VLBA observations and have been granted time to monitor the system for time delays. What we now need is a well constrained model of the lens and this is the prime motivation for the present proposal. Our WFPC2 observations show spectacular optical arcs produced by the imaging of the extended radio galaxy. These arcs sample the lens potential at many points and thus produce many constraints on the mass model, providing information unavailable in even very high resolution (1 mas) radio images. However, the lens as seen with WFPC2 has two peaks separated by 0.7 arcsec suggesting either two galaxies or more likely a single galaxy containing dust. The NICMOS image will show if there is really a single lensing galaxy and give the distribution of starlight (which we can relate to mass) substantially free from the effects of dust. ------------------------------------------------------------------------------------ 7422( 3) - 06/12/97 16:34 - [ 2] Observations Description ------------------------ The observation is aimed at imaging a relatively faint galaxy (V ~ 22.6) in the presence of fairly bright lensed images. We require reasonably high dynamic range, resolution of about 0.2 arcsec and a wavelength far enough into the infrared to significantly reduce the dust censorship compared that at 814nm in our previous WFPC2 observation. Tradeoffs between these considerations dictate a wavelength of about 1.6micron; shorter wavelengths improve resolution but worsen the dust constraint, and longer wavelengths impose unacceptable penalties in thermal background and resolution. We therefore propose to use the F160W filter with camera 1 in order to fully sample the point spread function. Our measurements of the lensing galaxy with WFPC2 at 814 nm yield a flux of 6.7 e-18 erg/cm^2/sAngstrom/arcsec^2 for the brightest part of the lensing galaxy and 8.1 e-19 erg/cm^2/s/Angstrom/arcsec^2 for the possible second galaxy. Using typical I - H colors for galaxies at z = 0.63 (G. Neugebauer, private communication), we estimate that in the F160W band, the peaks in the emission will have flux densities of 1.3 e-3 and 6.5 e-4 Jy arcsec^-2, respectively. We would be able to reach a signal to noise level of 10:1 in only a few hundred seconds, but our science goals demand knowledge of the details of the light distribution, not just of the areas of peak brightness. By integrating for approximately 5.5 hr on source, and using the MULTIACCUM mode, we will achieve noise levels of ~ 0.003 mJy without saturating the brightest pixels. Because 1608+656 is in the CVZ, we require only four orbits for this observation. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7422( 3) - 06/12/97 16:34 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 GAL- GALAXY,GRAVITATIONAL RA=16H 9M 13.96S +/- J2000 F(1.6)=2.4e-17 1609+6532 LENS,RADIO GALAXY 0.1",DEC=65D 32' 28.0" +/- 0.1",PLATE-ID=034O Comments: The flux is at 1.6 microns and is in units of erg/cm^2/sec/Ang. The position of the object is from a radio survey. The GSC coordinates (Plate 034O) are 16:09:13.85 65:32:28.11 7422( 3) - 06/12/97 16:34 - [ 4] Visit: 01 Visit Requirements: CVZ On Hold Comments: Additional Comments: This visit has several exposures arranged in a quasi-dither pattern, in order to shift the position of the object on the chip and to minimize the effects of bad areas on the chip. The reason a standard dither wasn't chosen was to avoid tying up all the lenghty exposures in one pattern. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GAL-1609+65 NIC1 MULTIAC NIC1 F160W SAMP-SEQ=STEP256,NSAMP=25 1 DEF 32 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 GAL-1609+65 NIC1 MULTIAC NIC1 F160W SAMP-SEQ=STEP256,NSAMP=25 1 DEF POS TARG 1.0,0.0 32 CUM Comments: "Manual dither" to shift position of target on chip. ------------------------------------------------------------------------------------------------------------------------------------ 3 GAL-1609+65 NIC1 MULTIAC NIC1 F160W SAMP-SEQ=STEP256,NSAMP=25 1 DEF POS TARG 0.0,1.0 32 CUM Comments: "Manual dither" to shift position of target on chip. ------------------------------------------------------------------------------------------------------------------------------------ 4 GAL-1609+65 NIC1 MULTIAC NIC1 F160W SAMP-SEQ=STEP256,NSAMP=25 1 DEF POS TARG -1.0,0.0 32 CUM Comments: "Manual dither" to shift position of target on chip. ------------------------------------------------------------------------------------------------------------------------------------ 5 GAL-1609+65 NIC1 MULTIAC NIC1 F160W SAMP-SEQ=STEP256,NSAMP=25 1 DEF POS TARG 0.0,-1.0 32 CUM Comments: "Manual dither" to shift position of target on chip. ------------------------------------------------------------------------------------------------------------------------------------ 6 GAL-1609+65 NIC1 MULTIAC NIC1 F160W SAMP-SEQ=STEP128,NSAMP=25 1 DEF POS TARG 1.0,1.0 32 CUM Comments: "Manual dither" to shift position on chip. ------------------------------------------------------------------------------------------------------------------------------------ 7 GAL-1609+65 NIC1 MULTIAC NIC1 F160W SAMP-SEQ=STEP128,NSAMP=16 1 DEF POS TARG -1.0,-1.0 32 CUM Comments: "Manual dither" to shift position on chip. ------------------------------------------------------------------------------------------------------------------------------------ 7422( 3) - 06/12/97 16:34 - [ 5] Summary Form for Proposal 7422 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC1 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SAMP-SEQ=STEP256 NSAMP=25 SAMP-SEQ=STEP128 NSAMP=16 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COSMOLOGY ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ POS TARG 1.0,0.0 POS TARG 0.0,1.0 POS TARG -1.0,0.0 POS TARG 0.0,-1.0 POS TARG 1.0,1.0 POS TARG -1.0,-1.0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W ------------------------------------------------------------------------------------------------------------------------------------ Target Names GAL-1609+6532 ------------------------------------------------------------------------------------------------------------------------------------