12005( 2) - 28-Aug-2009 15:23:03 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12005 Version: 2 Check-in Time: 28-Aug-2009 15:23:03 STScI Edit Number: 0 Title Unveiling the Dusty Starburst Galaxy Hosting GRB080607 ------------------------------------------------------------------------------------ Type Cycle GO/DD 17 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Hsiao-Wen Chen University of Chicago CoI: Prof. Joshua S. Bloom University of California - Berkeley N CoI: Prof. Jason X. Prochaska University of California - Santa Cruz N CoI: Dr. M. Dessauges-Zavadsky Observatoire de Geneve N CoI: Prof. Max Pettini University of Cambridge N CoI: Mr. Daniel A. Perley University of California - Berkeley N ------------------------------------------------------------------------------------ Abstract GRB 080607 at redshift z = 3.0363 is a unique case of a highly extinguished (A_V ~ 3 mag) afterglow that was yet sufficiently bright for high-quality spectroscopy. The ISM properties revealed by our afterglow spectrum are unprecedented among GRB host galaxies, including an enormous dust and gas surface mass density (~ 400 M_sun/pc^2), the first detection of CO molecules, and roughly solar metallicity. Contrary to the common expectation of GRBs occurring preferentially in low-mass and low-metallicity environments, the observed large metal and dust content, together with the mass-metallicity relation known for z=2-3 galaxies, imply that the host galaxy is massive and intrinsically luminous. Identifying the host galaxy of this event is critical for connecting our spectroscopy to the rest of the poorly-understood dark burst population with suppressed optical afterglow light. Despite our large investments in optical and NIR imaging at ground-based telescopes to date, the host of GRB 080607 has eluded detection to an unobscured limiting UV luminosity of ~ 0.07 L*. The lack of bright emission suggests that the dust seen in the afterglow spectrum reflects the global dust content throughout the host ISM. Otherwise, it would imply the presence of highly metal-enriched regions in a low-mass galaxy, challenging the validity of our current understanding of star formation at high redshift. The low sky background and high spatial resolution make HST and WFC3/IR the only instrument available to unveil the morphology and stellar counterpart of the dusty host galaxy of GRB 080607. Here we request Director's Discretionary time to obtain deep near-infrared images of the field surrounding GRB 080607, using WFC3 and the IR channel with the F160W filter. The proposed imaging program will allow us to investigate whether the host of GRB 080607 is a dusty luminous galaxy or a faint dwarf galaxy with patchy dust clouds, and to examine the significance of dust enshrouded star formation at z~3. The extraordinary ISM properties observed around GRB 080607 have stimulated a considerable amount of interest not only in the GRB community but also among observers and theorists who study star formation both in the nearby universe and at high redshift. We believe the proposed WFC3/IR imaging data will have high impact in the broader astrophysics community. ------------------------------------------------------------------------------------ 12005( 2) - 28-Aug-2009 15:23:03 - [ 2] Observations Description ------------------------ We aim to obtain deep near-infrared images of the field surrounding GRB080607 at redshift z=3.036, using the IR channel in Wide Field Camera 3 (WFC3) with the F160W filter. At z=3, the observed F160W band corresponds to rest-frame 4000 Ang. Our early-time afterglow spectrum has revealed a large amount of dust (A_V ~ 3 mag) and chemically enriched ISM of near solar metallicity in the host galaxy. The observed large metal and dust content, together with the mass-metallicity relation known for star-forming galaxies at z=2-3, imply that the host galaxy is massive and intrinsically luminous. However, because of the substantial extinction, we expect the host galaxy to be faint in the F160W bandpass. We estimate that an L* galaxy at z=3 with E(B-V)=0.8 dust extinction would have AB(F160W)=27.3. To improve the spatial sampling of distant faint galaxies, we adopt the WFC3-IR-DITHER-BOX-MIN dither pattern with sub-integer pixel offsets. The host galaxy will be identified based on its coincident position with the optical transient. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12005( 2) - 28-Aug-2009 15:23:03 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 GRB080607 EXT-MEDIUM, ABSORPTION RA=12H59M48.2400S +/- 0.5", J2000 V = 29 +/- 0.5 LINE SYSTEM - DEC=+15D55'5.74" +/- 0.5" EXTRAGALACTIC Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 12005( 2) - 28-Aug-2009 15:23:03 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 12005( 2) - 28-Aug-2009 15:23:03 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GRB080607 WFC3/IR MULTIAC IR-FIX F160W NSAMP=15, SAMP-SEQ=STEP100 1 DEF PATTERN 1 1 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 GRB080607 WFC3/IR MULTIAC IR-FIX F160W NSAMP=15, SAMP-SEQ=STEP100 1 DEF PATTERN 1 2 CUM ------------------------------------------------------------------------------------------------------------------------------------ 3 GRB080607 WFC3/IR MULTIAC IR-FIX F160W NSAMP=15, SAMP-SEQ=STEP100 1 DEF PATTERN 1 3 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GRB080607 1 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 1 N/A CUM GRB080607 1 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 1 N/A CUM GRB080607 1 WFC3/IR MULTIAC IR-FIX F160W 3 none none none 1 N/A CUM GRB080607 1 WFC3/IR MULTIAC IR-FIX F160W 4 none none none 2 N/A CUM GRB080607 2 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 2 N/A CUM GRB080607 2 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 2 N/A CUM GRB080607 2 WFC3/IR MULTIAC IR-FIX F160W 3 none none none 3 N/A CUM GRB080607 2 WFC3/IR MULTIAC IR-FIX F160W 4 none none none 3 N/A CUM GRB080607 3 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 3 N/A CUM GRB080607 3 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 4 N/A CUM GRB080607 3 WFC3/IR MULTIAC IR-FIX F160W 3 none none none 4 N/A CUM GRB080607 3 WFC3/IR MULTIAC IR-FIX F160W 4 none none none 4 N/A CUM 12005( 2) - 28-Aug-2009 15:23:03 - [ 6] Summary Form for Proposal 12005 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=15, SAMP-SEQ=STEP100 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 1 2, PATTERN 1 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W ------------------------------------------------------------------------------------------------------------------------------------ Target Names GRB080607 ------------------------------------------------------------------------------------------------------------------------------------