12467( 4) - 19-Jul-2011 10:45:54 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12467 Version: 4 Check-in Time: 19-Jul-2011 10:45:54 STScI Edit Number: 0 Title Probing ISM in the Stellar Disk of Dwarf Galaxy GQ1042+0747 ------------------------------------------------------------------------------------ Type Cycle GO 19 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Sanchayeeta Borthakur The Johns Hopkins University CoI: Prof. Todd Tripp University of Massachusetts N CoI: Dr. David V. Bowen Princeton University N CoI: Dr. Joseph Meiring University of Massachusetts N CoI: Dr. Timothy M. Heckman The Johns Hopkins University N CoI: Prof. Min S. Yun University of Massachusetts N CoI: Dr. Donald G. York University of Chicago N ------------------------------------------------------------------------------------ Abstract QSO-galaxy pairs with small impact parameters of few kpcs are very rare. The QSO-galaxy pair J104257.5+074850.5-GQ1042 is a unique system that presents us with the opportunity to study the stellar disk of an extragalactic source using a background QSO at an impact parameter of 1.7 kpc. In addition, the background QSO is bright in the UV as well as radio frequencies, thus allowing us to probe the cold (21 cm HI) gas as well as warmer components enveloping it. Taking advantage of the radio brightness of the quasar, we have obtained high spectral (0.3 km/s) and spatial (parsec-scale) resolution data and detected a very narrow (3.6 km/s) absorber of column density of ~1x10^20 cm^{-2}. We found significant variations in the optical depth within the cloud (cloud of size ~14x27 pc). We request HST time to observe this QSO-galaxy pair with COS for a pilot study to check for presence of any Lyman limit system and estimate the HI column density. This study aims to probe the warmer phases of gas associated with the cold 21 cm absorber. This will provide us with a good understanding of multi-phase ISM cloud structures in this dwarf spiral galaxy. This system is one of the few galaxies outside our local group where we can study the ISM within the stellar disk at such small scales. This makes it an excellent test bed for ISM theories in dwarf galaxies and for studying how (if real) ISMs of smaller galaxies differ from those of bigger galaxies such as the Milky Way. ------------------------------------------------------------------------------------ Observations Description ------------------------ GQ1042 is a unique dwarf galaxy with a background UV bright QSO behind its stellar disk thus enabling us to study the ISM in its disk. In this pilot project we aim to check if there is any Lyman limit system in the FUV range. This in turn will prove if a high-resolution UV study is possible. Our primary goal is to understand the ISM of the dwarf-isolated galaxy, GQ1042. The purpose of this pilot project is to find out the following: 1. If future high-resolution COS observations of this target is feasible. 2. The strength of the Lyman-alpha transition associated with the target. The strength of this transition when put together with the available 21cm radio observations of the gas will provide us with the spin temperature of the gas. 12467( 4) - 19-Jul-2011 10:45:54 - [ 2] The project uses COS FUV grating G140L for 1 orbit in order to achieve the above mentioned goals. The 2221sec observations for the QSO with FUV of 20.15 +/- 0.22 mags at 1225 A (Ly-alpha of foreground galaxy) will result in a S/N >6 (COS.sp.201236). As a safety check, a magnitude higher source (i.e FUV = 19.15 mag) when observed for 2221 secs will yield 229 cts/s for the entire detector (COS.sp.201237). For the target acquisition we use NUV MIRROR A imaging setting for 34 secs, based on the ETC estimate (ID: 201202) for the QSO with NUV=19.75 +/-0.1 mags or 19.85 mags in the worst case scenario based on error estimate. This exposure will have a count rate for the entire detector of 826 cts/s and for the brightest pixel 6 cts/s. To check the safety of the aquisition exposures, we estimate the counts for an exposure of 34 secs for a source 1 mag brighter, i.e NUV=18.75 +/- 0.1 mags or 18.65 mags including the error margin, to 20 cts/s for the brightest pixel and 923 cts/s for the entire detector. Hence, we conclude that both the exposures are within safe limits for the detectors. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12467( 4) - 19-Jul-2011 10:45:54 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SDSSJ104257. GALAXY, LSB, QSO RA=10H42M57.5888S +/- 0.1", J2000 Z = V = 19.5 GALEX FUV = 20.15+/-0.22 mags, 58+074850.5 DEC=+07D48'50.53" +/- 0.1" 2.666 NUV = 19.75+/-0.10 mags Reference Frame: ICRS Comments: Coordinates taken from DR7 of SDSS. ------------------------------------------------------------------------------------------------------------------------------------ 12467( 4) - 19-Jul-2011 10:45:54 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: 1 orbit of G140L. The QSO lies behind a low surface brightness galaxy. GALEX FUV flux is recorded at the position of the QSO, and this observation is designed to test whether the FUV flux arises from the QSO (or, instead, from the galaxy). Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SDSSJ104257 COS/NUV ACQ/IMA PSA MIRRORA 1 34 S .58+074850. GE 5 ------------------------------------------------------------------------------------------------------------------------------------ 2 SDSSJ104257 COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2111, FP-POS=4 1 2221 S .58+074850. G 5 Comments: The amount of time on-target is small. We therefore include no additional FP-SPLITs. ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ SDSSJ104257.58+0748 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A 50.5 GE SDSSJ104257.58+0748 2 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A 50.5 G 12467( 4) - 19-Jul-2011 10:45:54 - [ 5] Summary Form for Proposal 12467 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=2111, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names SDSSJ104257.58+074850.5 ------------------------------------------------------------------------------------------------------------------------------------