! Proposal 6462, submission 1 ! PI: Dr. Lee Armus ! Received Fri Feb 9 13:31:45 EST 1996 ! From: lee@mop.caltech.edu ! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /data1/proposals/st/cyc6/phase2/6462.prop ! Generated by PREPROCESSOR, version 6.0e ! Date: Thu Feb 8 14:53:05 PST 1996 Proposal_Information Title: Is IRAS 15307+3252 Gravitationally Lensed ? Proposal_Category: GO Scientific_Category: COSMOLOGY Cycle: 6 Investigators PI_Name: Dr. Lee Armus PI_Institution: California Institute of Technology CoI_Name: Prof. Baruch T. Soifer CoI_Institution: California Institute of Technology Contact: CoI_Name: Dr. Gerry Neugebauer CoI_Institution: California Institute of Technology Contact: CoI_Name: David Hogg CoI_Institution: California Institute of Technology Contact: 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. Questions Observing_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: Fixed_Targets Target_Number: 1 Target_Name: FSC15307+3252 Alternate_Names: Description: GALAXY,ULTRALUMINOUS IR GAL, Position: RA=15H 30M 44.6S +/- 1.0",DEC=32D 52' 57" +/- 1.0" Equinox: B1950 RV_or_Z: Z = 0.93 RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: F(4400)=6.8+/-1.1e-17 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. Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 1 Target_Name: FSC15307+3252 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F791W Wavelength: Optional_Parameters: DITHER-TYPE=LINE,CR-SPLIT=no Number_of_Iterations: 1 Time_Per_Exposure: 900S Special_Requirements: Comments: Exposure_Number: 2 Target_Name: FSC15307+3252 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F791W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 140S Special_Requirements: Comments: Exposure_Number: 3 Target_Name: FSC15307+3252 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F450W Wavelength: Optional_Parameters: DITHER-TYPE=LINE,CR-SPLIT=no Number_of_Iterations: 1 Time_Per_Exposure: 1000S Special_Requirements: Comments: Exposure_Number: 4 Target_Name: FSC15307+3252 Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F450W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 140S Special_Requirements: Comments: Data_Distribution ! 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