6462( 6) - 03/03/99 10:04 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6462 Version: 6 Check-in Date: 03-Mar-1999 10:04:01 1.Proposal Title: Is IRAS 15307+3252 Gravitationally Lensed ? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 6 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Lee Armus California Institute of Technology CoI: Prof. Baruch T. Soifer California Institute of Technology N CoI: Dr. Gerry Neugebauer California Institute of Technology N CoI: David Hogg California Institute of Technology N ------------------------------------------------------------------------------------ 5. Abstract At a redshift of z=0.93, IRAS 15307+3252 is the most luminous object discovered in the IRAS all sky survey. While optical ground-based images show only a single source at the radio position, deep near-infrared observations reveal that IRAS 15307+3252 has one, and possibly two nearby companions within a radius of 2''. These may be galaxies interacting with IRAS 15307+3252. Alternatively, the IRAS 15307+3252 system (in analogy with IRAS 10214+4724) may be gravitationally lensed by a foreground galaxy. We propose to image IRAS 15307+3252 with the WFPC2 to understand the true nature of this ultraluminous infrared source. Using the F450W and F791W filters will allow us to determine the UV-optical colors of the components. If IRAS 15307+3252 is a merger in progress, the HST data will reveal a wealth of detail on the interaction, such as the brightnesses, sizes, and colors of tidal features, and the possible presence of star forming (proto-globular) clusters. On the other hand, if IRAS 15307+3252 is lensed, the HST data will allow us to create a detailed model of the lens and the source. With this model we will be able to estimate the mass and velocity dispersion of the lensing galaxy, as well as the size and true luminosity of the source. In addition, these data will allow us to more accurately estimate the lensing rate among luminous IRAS galaxies, and therefore understand their true redshift distribution. ------------------------------------------------------------------------------------ 6462( 6) - 03/03/99 10:04 - [ 2] Observations Description ------------------------ Our observing time request is for WFPC2 PC observations of IRAS 15307+3252 in the F450W and F791W filters. The flux densities at the observed wavelengths of 4400Angstrom and 7000Angstrom (0.044mJy and 0.070mJy, respectively) have been taken from C94 and used with the WFPC2 Exposure Time Calculator Tool to estimate the required exposure times. We wish to obtain a signal-to-noise ratio of > 25 at 1/100 the level of the primary nucleus flux density as measured by C94. This will allow not only a confident detection of all three nuclei in the system, but a search for faint, resolved emission around the primary as well as structure within the central 0.5''. To achieve these goals in the F450W filter will require 2300 seconds of on source time. To achieve these goals in the F791W filter will require an on source time of 1700 seconds. A full orbit (2520 sec on source) with the F791W filter will allow a detection of an object with 1/1000 the flux density of the primary at a signal-to-noise ratio of ~5. Including time for guide star acquisition and overheads, we therefore request 1 orbit per filter, or a total of 2 orbits to complete the project. Note that 1 orbit exposure per filter would achieve a signal-to-noise ratio of >5 per pixel even if all the flux of the primary were spread out over the central 2-3''. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 6462( 6) - 03/03/99 10:04 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 FSC15307+325 GALAXY, ULTRALUMINOUS RA=15H 30M 44.6S +/- 1.0", B1950 Z = 0.93 F(4400)=6.8+/-1.1e-17 2 IR GAL DEC=32D 52' 57" +/- 1.0" F(7000)=4.3+/-0.8e-17 Comments: This position is 7 arcseconds north of the VLA position of the galaxy. Since there is a suitable psf star approximately 20 arcseconds north of the galaxy, this 7 arcsecond offset will allow both the galaxy and the psf to be on the chip at all times. 6462( 6) - 03/03/99 10:04 - [ 4] Visit: 01 Visit Priority: 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 FSC15307+32 WFPC2 IMAGE PC1 F791W DITHER-TYPE=LINE,CR-SPLIT=no 1 900 S GS ACQ SCENARIO SINGLE 52 ------------------------------------------------------------------------------------------------------------------------------------ 2 FSC15307+32 WFPC2 IMAGE PC1 F791W 1 140 S 52 ------------------------------------------------------------------------------------------------------------------------------------ 3 FSC15307+32 WFPC2 IMAGE PC1 F450W DITHER-TYPE=LINE,CR-SPLIT=no 1 1000 S 52 ------------------------------------------------------------------------------------------------------------------------------------ 4 FSC15307+32 WFPC2 IMAGE PC1 F450W 1 140 S 52 ------------------------------------------------------------------------------------------------------------------------------------ 6462( 6) - 03/03/99 10:04 - [ 5] Summary Form for Proposal 6462 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters DITHER-TYPE=LINE CR-SPLIT=no ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO SINGLE ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F791W F450W ------------------------------------------------------------------------------------------------------------------------------------ Target Names FSC15307+3252 ------------------------------------------------------------------------------------------------------------------------------------