9380( 4) - 02/12/02 14:20 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9380 Version: 4 Check-in Date: 12-Feb-2002 14:19:47 1.Proposal Title: Determination of Extragalactic Extinction Laws at UV wavelengths with gravitationally-lensed QSOs ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Evencio Mediavilla Instituto de Astrofisica de Canarias CoI: Dr. Emilio Falco Smithsonian Astrophysical Observatory N CoI: Dr. Santiago Arribas Space Telescope Science Institute N CoI: Dr. Christopher Kochanek Smithsonian Astrophysical Observatory N CoI: Dr. Veronica Motta Instituto de Astrofisica de Canarias N CoI: Dr. Jose Mu\~noz Instituto de Astrofisica de Canarias N ------------------------------------------------------------------------------------ 5. Abstract The study of extragalactic extinction laws is of paramount importance as it plays a key role in galaxy evolution, as well as for the determination of the cosmological parameters, for example using SNe. We propose to utilize a new technique based on flux measurements of gravitationally lensed, multiply-imaged QSOs to estimate the extinction law of the lensing galaxy. Here we propose a pilot project of STIS observations of the doubly-imaged QSO SBS 0909+532 with a separation between images of 1.1 arcsec. Our goal would be to determine the extinction law at UV wavelengths in the lens galaxy (z=0.83). In a study that is the first of this type, we have obtained ground-based Integral Field Spectroscopy (IFS) data in the region of the 2175Angstrom\ PAH bump for SBS 0909+532. Our proposed observations will allow us to complete and extend the extinction law farther in the UV. Such observations would be impossible from the ground because they extend too far into the UV, and HST is the only instrument available with the necessary spatial resolution and sensitivity. ------------------------------------------------------------------------------------ 9380( 4) - 02/12/02 14:20 - [ 2] Observations Description ------------------------ SBS 0909+532 is a doubly-imaged QSO (see figure 1). We propose to obtain HST low resolution UV spectroscopy of the two images simultaneously. For our proposed observations we prefer STIS/CCD/G230LB, G430L versus ACS/HRC/PR200L for two main reasons: a) The ACS configuration provides a spectral resolution ranging from 205 (at 1800 Angstrom) to 18 (at 3500 Angstrom), and even lower at longer wavelengths. This is too low for us to obtain a true extinction curve, especially if the effects of the emission lines (which may be different for images A and B) need to be removed. b) The ACS configuration has a more limited dynamic range as a consequence of the compression of the spectrum with wavelength (i.e. the linear dispersion changes dramatically with wavelength). In fact, for a redshifted QSO SED similar to that of SBS 0909+523, the number of counts per pixel at Lambda = 2000 Angstrom\ is about 400 times smaller than at Lambda = 5000 Angstrom. Therefore the number of counts expected for image A at 5000 Angstrom\ is about 1000 times larger than this of image B at 2000 Angstrom. Contrary for the STIS configuration the ratio is only 15. noindent Spectral resolution and coverage: Low resolution (R ~ 500- 700) suffices to estimate in great detail the extinction law, maximizing sensitivity and spectral coverage. For the present study the most relevant spectral range is about 2000-4000 Angstrom, which covers the region of the 2175Angstrom\ PAH bump and extends well into the UV (note that z for the lens galaxy is ~ 0.8). This spectral range is covered by two gratings, G230LB and G430L. In addition, the G430L extends the observed range farther to the visible wavelengths (upto 5700 Angstrom) allowing good overlap with our ground based optical integral field spectroscopic data. noindent Slit width: A slit 0.2 (0.5) arcsec width will allow us good spectrophotometric quality. noindent Slit PA: The slit position angle should be 116.77 or 296.77 degrees in order to observe image A and B simultaneously. noindent Exposure times: The faintest image, SBS 0909+532B (V=17.66), will determine the required exposure time. We will need a S/N of 50 in the region around the 2175 Angstrom\ PAH bump (which appears in 2900-4000 Angstrom \ considering the redshift of the lens galaxy. According to the spectroscopic STIS-ETC, with the G230LB grating we will need an exposure time of about 10000 sec, for obtaining that S/N at 3000 Angstrom, assuming a redshifted QSO SED similar to that of SBS0909 +532. This total exposure time considers the fact that it should be divided into ~ 10 individual exposures of ~ 1000 sec each (i.e. CR=10 was used in the ETC) to guarantee a good cosmic ray rejection minimizing readout noise (c.f. STIS handbook for cycle 11, page 119). Taking into account the visibility of this object (56 minutes per orbit), and the guide star acquisition, target acquisition, and exposure overheads (HST primer for Cycle 11, pages 46-54), this can be accommodated in 4 orbits. Following a similar reasoning for G430L we will need ~ 4000 sec (for S/N=50 at 3400 Angstrom), which fits well within 2 orbits. Therefore, a total number of 6 orbits is required. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9380( 4) - 02/12/02 14:20 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SBS0909+532A GALAXY, GRAVITATIONAL RA=09H 13M 1.10S +/- 1", DEC=52D J2000 V = 16.4 -OFFSET LENS 59' 28.37" +/- 1", PLATE-ID=021E E(B-V) = 0.19+/-0.06 Coordinate Source: HST_IMAGE Comments: double, component A (V=16.76+/-0.26), use A as the offset reference 2 SBS0909+532A GALAXY, GRAVITATIONAL R=0.55276000000000003", J2000 V = 16.4 +B LENS PA=116.7737D, FROM 1, PLATE- E(B-V) = 0.19+/-0.06 ID=021E Coordinate Source: HST_IMAGE Comments: double, components A (V=16.76+/-0.26), B (V=17.66+\- 0.14), separation 1.11" Orient the slit to include both components 9380( 4) - 02/12/02 14:20 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.55 Coordinate_Frame POS-TARG Pattern_Orient 90 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 9380( 4) - 02/12/02 14:20 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 160.77D TO 162.77D ORIENT 340.77D TO 342.77D 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 SBS0909+532 STIS/C ACQ F28X50L MIRROR 1 2 S A-OFFSET CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 SBS0909+532 STIS/C ACCUM 52X0.5 G430L 4300 CR-SPLIT=3 1 1650 S PATTERN 1 2 A+B CD ------------------------------------------------------------------------------------------------------------------------------------ 3 SBS0909+532 STIS/C ACCUM 52X0.5 G230LB 2375 CR-SPLIT=4 1 4000 S PATTERN 1 3 A+B CD ------------------------------------------------------------------------------------------------------------------------------------ 9380( 4) - 02/12/02 14:20 - [ 6] Summary Form for Proposal 9380 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=3 CR-SPLIT=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 160.77D TO 162.77D ORIENT 340.77D TO 342.77D PATTERN 1 2 PATTERN 1 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G430L G230LB ------------------------------------------------------------------------------------------------------------------------------------ Target Names SBS0909+532A-OFFSET SBS0909+532A+B ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4300 2375 ------------------------------------------------------------------------------------------------------------------------------------