! Proposal 6652, submission 1 ! PI: Chris Impey ! Received Fri Feb 16 14:52:55 EST 1996 ! From: ndinshaw@as.arizona.edu ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6652,v 3.1 1996/02/19 20:31:45 pepsa Exp $ ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6652,v 3.1 1996/02/19 20:31:45 pepsa Exp $ ! ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Sleiman ! Phone: 410-338-4753 , E-mail: sleiman@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: archive-0685.impey.prop ! Date generated: Fri Dec 22 18:16:49 EST 1995 ! Proposal_Information ! Section 4 Title: Imaging the Gravitational Lens System 1422+231 Proposal_Category: GO Scientific_Category: COSMOLOGY Cycle: 6 Investigators PI_name: Chris Impey PI_Institution: University of Arizona CoI_Name: Craig Foltz CoI_Institution: Multiple Mirror Telescope Observatory Contact: ! Y or N (designate at most one contact) CoI_Name: Laird Close CoI_Institution: University of Arizona Contact: ! Y or N (designate at most one contact) CoI_Name: Jens Hjorth CoI_Institution: Institute of Astronomy Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) The gravitational lens system 1422+231 offers the exciting prospect of a direct measure of the Hubble constant. This system has important advantages compared to the more well- studied double quasar (0957+561). First, the background quasar at z = 3.62 is a strong and compact radio source which is known to be a radio variable, and for which evidence for rapid optical variations exists. Second, there are four quasar images giving a large number of model constraints from measures of image position, image magnification, and time delay. Finally, successful models show the primary deflector to be a single galaxy (shear is contributed by two other galaxies in the field), so that the interpretation is not compromised by the unknown distribution of dark matter in a cluster potential. Cycle 4 spectroscopy with the FOS has yielded identical spectra for the four quasar components, confirming the system as a gravitational lens. Cycle 4 imaging with the FOC has yielded the first clear detection of the lensing galaxy. As a step towards the eventual measure of the Hubble constant, we propose multicolor UBVRI imaging with the Planetary Camera, with a deep exposure in the sensitive I(814W) filter. The data will yield the colors, structure and morphology of the lens and the two shearing galaxies, as well as a census of other deflectors and lensing screens along the line-of-sight to the quasar. Individual exposures from the deep I(814W) image will be used to characterize the intrinsic optical variations of the quasar. Questions ! Free format text (please update) Observing_Description: Observations of the deflector in a system where the lensing galaxy lies within 1 arcsecond of quasar images 100 times brighter can only be carried out with the HST. This proposal requests 19 orbits with the Planetary Camera in Cycle 6. The Planetary Camera provides the best combination of sensitivity and spatial resolution for these observations. Of the total time request of 19 orbits, 12 will be devoted to a deep I band image of the 1422+231 system. The visibility per orbit is 53 minutes, and after allowing for guide star acquisition, each orbit will be be comprised of four WFPC2 exposures (two CR-split overheads per orbit). The total integration time is 2000 seconds on the first orbit of a visit, and 2200 seconds on the second and subsequent orbits of a visit. Three visits are assumed in total. The table above gives the aperture magnitudes for the lens measured with the FOC in its high spatial resolution F/96 mode. Only the U and V magnitudes are measured quantities, the other colors are derived by assuming the typical colors of an elliptical galaxy at z = 0.64. The next six lines give the surface brightness in mag arcsec^-2 over six different regions of the lens. The last six lines give the signal to noise ratio with the Planetary Camera assuming the integration times listed at the top of the table. All calculations used the new WFPC estimator available on the World Wide Web connection at STScI. The galaxy is of course very faint in the ultraviolet, but the proposed number of orbits gives a comfortable detection of the core of the lensing galaxy in all five wavebands. Combined with the ground-based H and K magnitude, a sensitive assessment of the stellar populations is possible. Since the nearby shearing galaxies G2 and G3 are at least 1 magnitude brighter than the lens, the color information for them will be superior. .25truecm Structure of the Lens:\ \ \ The model of the 1422+231 system requires a mass for the lens. Mass is difficult to measure directly for a distant galaxy, but the colors and surface photometry will yield important constraints. Assuming the lens is an elliptical galaxy, the scaling relationships of Kormendy (1977, Ap.J., 218, 333) give a good estimate of the expected structure. With an effective (or half-light) radius of 10 kpc (equivalent to 1.6", and appropriate to the inferred luminosity of the lens), the surface brightness at the effective radius is 22.8 B mag arcsec^-2. Applying a (1+z)^4 correction to observed surface brightness and assuming elliptical colors gives the surface brightness at r_e, 3r_e, and 5r_e in the table above. The corresponding signal to noise values are for a summation over an annulus 1.6" (or +/-0.5 r_e) wide at each radius. The lens is too faint in U and B for effective surface photometry. In V and R, the radial profile is detected out to 3r_e and 5r_e respectively. In the deep sum of the I exposures, the lens should be detectable out to large distances from the nucleus, and with high signal to noise within 3 effective radii. At 3r_e, a feature of 10\% contrast will be detectable over a patch of 12 pixels. This corresponds to structure of 0.5 kpc at the redshift of the lens. In other words, the deep I image will offer comparable information to the ground-based images of ellipticals at low redshift. .25truecm Ultra-Deep Imaging:\ \ \ The coadded sum of the I images, representing 7.2 hours of integration in the F814W filter, will give an ultra-deep image of the 1422+231 field. This will allow a search for other faint galaxies and potential lensing screens near the line of sight to the quasar. The summed exposure of 26000 seconds will give a signal to noise of 7 for point sources at I = 27.5. The deep image will give a signal to noise of 7 for galaxies with an effective surface brightness Mu(I) = 26 mag arcsec^-2 distributed over r = 0.3". This represents an isophote of 5\% of sky brightness, which is easily achievable without using superskyflats. By comparison with the Medium Deep Survey (Driver et al. 1995, Ap.J., 453, in press), and allowing for the lower surface brightness sensitivity of the Planetary Camera compared to the Wide Field Camera, we estimate a a galaxy sample complete to I = 23. This will allow a search for a potential cluster at the redshift of the lens down to the equivalent of 4 magnitudes fainter than L_* (about M_ V = -16). By the argument given previously, it will be sensitive to all galaxies out to the redshift of the quasar brighter than L_*/20 for q_0 = 0.5 or L_* for q_0 = 0.05. .25truecm Quasar Variability:\ \ \ An additional experiment is made possible by the deep I band image that is being used for surface photometry of the lens. There is evidence from high quality ground-based optical images that the quasar is variable on a timescale of hours. While in principle it is difficult to distinguish between intrinsic variations and microlensing, in practice the quasar components A,B, and C are 3-4 h^-1_100 kpc from the galaxy, so the optical depth to microlensing should be small. If this result is confirmed, a campaign to measure the A/B time delays (Delta t predicted to be ~ 4 hours) and the A/C and B/C time delays (Delta t predicted to be ~ 1 day) is likely to be successful. We note that VLA monitoring has detected intrinsic variations on a timescale of weeks, but the phase stability of the VLA is insufficient to measure variations of <= 10\% on shorter timescales. By contrast, each individual 7 or 8 minute exposure that goes into the deep I band image will detect quasar component D with signal to noise of 100 (I = 20.5), allowing the detection of intrinsic variations of 4-5\% or greater. Assuming that the 12 orbits are divided into two closely separated visits, there will be a total of 48 individual measurements covering time spacings from 90 minutes to several days. The characterization of the intrinsic variability of the quasar is a key step in the eventual determination of the Hubble constant. Real_Time_Justification: The 1422+231 system is a prime target for an eventual measure of the Hubble constant because it is a bright quasar and a strong radio source. The combined optical, infrared and radio data will yield a web of new constraints on lens models which are already quite sophisticated. The following ground-based observations are underway or planned to support the HST observations : o One of us (L. Close) has recently imaged the 1422+231 system at the diffraction limit of the Steward Observatory 90-inch telescope using the FASTTRAC rapid tip- tilt IR camera system. The resulting images, with a resolution of 0.2 arcseconds, clearly show the lens, and yield H and K magnitudes. Now that the technical obstacles to this type of imaging have been resolved, we plan an intensive monitoring campaign next spring. o One of us (J. Hjorth) has recently detected variations in the quasar brightness on a timescale of hours using the Nordic Optical Telescope (NOT). This facility has the routine capability of obtaining 0.4-0.5 arcsecond resolution, which is sufficient to accurately model the brightnesses of components A,B, and C. These observations will continue more intensively next year. o Monitoring with the VLA at 8.4 GHz and 15 GHz is continuing this year, conducted by Alok Patnaik. Preliminary analysis of the first 16 epochs shows that the quasar is indeed variable. The source is also known to be variable in radio polarization, so time delay measurements can be performed with 3 Stokes parameters. MERLIN observations at 23 GHz have been scheduled to look for variability as well. o VLBI observations at 1.7 GHz and 5 GHz have clearly resolved core and jet structure in components A,B, and C. Further observations with the VLBA have been proposed to look for proper motion in the components. The VLBI structures can put additional constraints on the lens models, from image parities and image magnification matrices. Hogg and Blandford (1994) have noted that the absolute expansion speeds could exceed ~ 100c or ~ 9 mas yr^-1. The achievable data set for this system constitutes a formidable set of constraints on lens models: radio and optical positions and magnifications, optical time delays and radio time delays in three Stokes parameters, positions and structural parameters of the lens and the two shearing galaxies G2 and G3, and radio image parities and proper motions. The key missing ingredient is the velocity dispersion of the lens itself. Unfortunately, although HST provides good separation of the lens from the nearby quasar light, the expected count rate for the lens galaxy is lower than the FOS dark count, making the observations very difficult with existing HST instrumentation, and essentially impossible from the ground. The requirement for a velocity disperison measurement accurate to 15\% is a spectrum with signal-to-noise ~15 at redshifted MgI or the G band at a resolution of 200-250 kms^-1 (the predicted velocity dispersion of 210 kms^-1 implies stellar absorption features with a Gaussian FWHM of 490 kms^-1). We plan to apply for observations with STIS in Cycle 7 to make the vital spectroscopic measurement of the lens. Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: QSO1424P231-B Alternate_Names: PKS Description: Galaxy, Quasar Position: RA = 14H 24M 38.094S +/- 0.004S, DEC = +22D 56' 00.59" +/- 0.05" Equinox: 2000 RV_or_Z: Z = 3.62 Flux: B = 18.4 +/- 0.2 B-V = 1.7 Comments: SUBARCSECOND GRAVITATIONAL LENS COMPONENT B, VLBI RADIO POSITION ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 1 Exposure_Number: 1 Target_Name: QSO1424P231-B Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 3 Time_Per_Exposure: 600S Special_Requirements: EXPAND Exposure_Number: 2 Target_Name: QSO1424P231-B Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 3 Time_Per_Exposure: 600S Special_Requirements: EXPAND Exposure_Number: 3 Target_Name: QSO1424P231-B Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F791W Wavelength: Optional_Parameters: Number_of_Iterations: 3 Time_Per_Exposure: 600S Special_Requirements: EXPAND Exposure_Number: 4 Target_Name: QSO1424P231-B Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F791W Wavelength: Optional_Parameters: Number_of_Iterations: 3 Time_Per_Exposure: 600S Special_Requirements: EXPAND Data_Distribution ! 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