8107( 9) - 04/28/00 14:07 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8107 Version: 9 Check-in Date: 28-Apr-2000 14:06:51 1.Proposal Title: What is the Nature of the Cold Medium in Cooling Flow Clusters? Clues from L-alpha ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Christopher ODea Space Telescope Science Institute CoI: Dr. Stefi Baum Space Telescope Science Institute N CoI: Dr. Ari Laor Technion - Israel Institute of Technology N CoI: Dr. Anton Koekemoer Space Telescope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract X-ray spectra of a significant fraction of cooling flow (CF) clusters of galaxies indicate the presence of large columns of ``cold'' absorbing material. The physical nature of the absorbing medium remains a mystery. Searches for H I in this medium using the 21 cm hyperfine structure line, and for molecular gas traced by CO yielded null results at the required levels. The LyAlpha absorption cross section is >= 10^7 times larger than for the 21 cm line, and it can therefore be used as a much more sensitive probe of H I in clusters. This method was applied to the Perseus CF cluster using a medium resolution (~ 250 km s^-1) HST spectrum, yielding an upper limit on the H I column about three orders of magnitude smaller than implied by X- ray spectra. We propose to obtain higher resolution (~ 40 km s^-1), spatially extended spectra of the Ly-alpha\ emission line filaments in three CF clusters with the brightest known LyAlpha fluxes. These spectra will allow us to probe H I columns about 10^7 smaller than deduced from the excess X-ray absorption in these clusters (>= 10^20 cm^-2), and thus put very strong constraints on the nature of the cold absorbing medium and its covering factor. If substantial amounts of cold gas do exist in the ICM, this would have important implications for our understanding of cooling flows, the physics of the ICM, galaxy formation and evolution, and LyAlpha forest systems. ------------------------------------------------------------------------------------ 8107( 9) - 04/28/00 14:07 - [ 2] Observations Description ------------------------ For each of the three clusters, we aim to obtain a high- dispersion long-slit spectrum in the Ly-alpha\ line, using the FUV-MAMA detector with the first- order G140M grating, together with the 52 * 0arcs1 slit. We desire to obtain a combination of sufficient kinematic resolution and sufficient S/N per resolution element to allow us to distinguish between the models shown in Figure 2. Thus, we choose the 52 * 0arcs1 slit rather than the 52 * 0arcs05 slit -- assuming a conservative scenario, in which the Ly-alpha\ emission is extended and uniform across the slit aperture, the 52 * 0arcs1 slit will provide a spectral resolution with FWHM of order ~ 45 kms, which is sufficient for our purpose. Since the expected FWHM of the Ly-alpha\ emission is of order ~ 250 kms\ (based on previous spectroscopic studies of these and other clusters), we will resolve this with ~ 5 resolution elements. Our aim is to obtain sufficient S/N across this part of the profile to allow interesting constraints to be placed on the amount of Ly-alpha\ absorption. Assuming an approximately Gaussian line profile for the Ly-alpha emission, we thus require a total of ~ 100 counts under the entire line profile, in order to obtain >~ 10 counts per resolution element in Ly-alpha\ for the emission within the FWHM part of the profile. We calculate here the exposure time required to obtain this number of counts in each spatial resolution element along the slit (~ 0arcs1), making the conservative assumption that the Ly-alpha\ emission is distributed uniformly across the entire spatial extent of the line-emitting region. We find that we can obtain this number in a maximum of 2 orbits per object, as shown in the following table. At the redshifts of these clusters the cluster <~\ line is well separated from geocoronal <~\ and in the latter two clusters geocoronal will not be in the G140M spectrum at all. begintableh captionREQUIRED EXPOSURE TIME begintabularlccccc Object & z & <~\ flux^a & Max. extent & <~\ SB^b & T (s) , A426 & 0.0183 & 6.8 & 4" * 5" & 3.4 & 5000 , A1795 & 0.0632 & 3.6 & 3" * 4" & 3.0 & 4600 , A2597 & 0.0818 & 4.0 & 3" * 3" & 4.4 & 3400 , endtabular, ^a In units of 10^-13 ergs cm^-2 s^-2, as observed with IUE (Hu 1992)., ^b In units of 10^-14 ergs cm^-2 s^-2 arcsec^-2. endtable Thus, we require two orbits per cluster to carry out spectroscopy in one position angle using the STIS FUV-MAMA detector with the first-order G140M grating, together with the 52 * 0arcs1 slit. There are no HST emission line images for A1795 and the H Alpha\ and OIILambda 3727 images for A426 and A2597 may not correspond well to the <~\ morphology because of the strong sensitivity of <~\ to dust. We need to determine the morphology of <~\ with HST with the same resolution as our long-slit spectra in order to locate the optimum slit position and to assist in interpreting our spectroscopic results. Thus, we propose to spend one orbit for each object to obtain an image in Ly-alpha, together with an off-band continuum image using the FUV-MAMA. For A426, onband = 25MAMA and offband=F25SRF2, and for A1795 and A2597 onband=F25SRF2 and offband=F25QTZ. Given the <~\ surface brightnesses, and the conservative assumption of uniform brightness, in a single orbit we expect to obtain S/N of a few in a 2* 2 pixel box for the three clusters. This is sufficient to identify the brighter portions of the nebula. The spectroscopic observations of each source will begin with a 6 min guide-star acquisition followed by a 6 min target acquisition and a second 6 min acq/peak for the 52* 0.1 slit. For NGC1275 which has a bright nucleus, we will peak up on the object itself. For the remaining sources we will peak up on a nearby bright star and then slew to our target galaxy. We will use the existing WFPC2 observations to determine accurate offsets. Real Time Justification ----------------------- None. All three clusters have well defined X-ray absorbing columns (Allen & Fabian 1997) and sensitive 21 cm HI observations (Jaffe 1990; Sijbring 1993; O'Dea Etal\ 1994b, 1995). Under program 6717 we have obtained WFPC2 F410M images of the redshifted OIILambda 3727 line in the central emission line nebula in A2597. We are also scheduled to obtain low spectral resolution STIS UV and optical spectra to study the ionization of the nebula. These observations will complement the high velocity <~\ spectra proposed here. Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ 8107( 9) - 04/28/00 14:07 - [ 3] Data Distribution Paper Products: YES Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8107( 9) - 04/28/00 14:07 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 A426-NUC GALAXY, Elliptical, RA=03H 19M 48.16S +/- 0.05S, J2000.0 Z=0.0175 SURF(V) = 17.0 Radio Galaxy, CLUSTER DEC=+41D 30' 42.1" +/- 0.5", 6 E(B-V) = 0.0 OF GALAXIES, Rich PLATE-ID=02RZ Cluster, BCM Coordinate Source: Comments: Target for EARLY ACQUISITION IMAGE 2 A426-SPEC GALAXY, Elliptical, RA=03H 19M 48.16S +/- 0.05S, J2000.0 Z=0.0175 SURF(V) = 17.0 Radio Galaxy, CLUSTER DEC=+41D 30' 42.8" +/- 0.5", 6 E(B-V) = 0.0 OF GALAXIES, Rich PLATE-ID=02RZ Cluster, BCM 3 A1795-STAR STAR RA=13H 48M 50.5038S +/- 0.0005S, J2000.0 Z=0.0 V = 17.2 DEC=+26D 35' 08.130" +/- 0.005", E(B-V) = 0.0 PLATE-ID=019J 4 A1795-NUC GALAXY, Elliptical, RA=13H 48M 52.43S +/- 0.05S, J2000.0 Z=0.0632 SURF(V) = 20.0 Radio Galaxy, CLUSTER DEC=+26D 35' 34.0" +/- 0.5", 6 E(B-V) = 0.0 OF GALAXIES, Rich PLATE-ID=019J Cluster, BCM Coordinate Source: Comments: Target for EARLY ACQUISITION IMAGE 5 A1795-SPEC GALAXY, Elliptical, RA-OFF=+2.0645S +/- 0.0005S, DEC J2000.0 Z=0.0632 SURF(V) = 20.0 Radio Galaxy, CLUSTER -OFF=+25.685" +/- 0.005", FROM 3 6 E(B-V) = 0.0 OF GALAXIES, Rich Cluster, BCM 6 A2597-STAR STAR RA=23H 25M 18.33S +/- 0.05S, J2000.0 Z=0.0 V = 15.6 DEC=-12D 07' 48.9" +/- 0.5", V-I = 2.3 PLATE-ID=00WQ 7 A2597-NUC GALAXY, Elliptical, RA=23H 25M 19.82S +/- 0.05S, J2000.0 Z=0.0822 SURF(V) = 19.7 Radio Galaxy, CLUSTER DEC=-12D 07' 26.4" +/- 0.5", B-V = 1.08 OF GALAXIES, Rich PLATE-ID=00WQ Cluster, BCM Coordinate Source: Comments: Target for EARLY ACQUISITION IMAGE 8 A2597-SPEC GALAXY, Elliptical, RA=23H 25M 19.82S +/- 0.05S, J2000.0 Z=0.0822 SURF(V) = 19.7 Radio Galaxy, CLUSTER DEC=-12D 07' 26.4" +/- 0.5", B-V = 1.08 OF GALAXIES, Rich PLATE-ID=00WQ Cluster, BCM Coordinate Source: Comments: The RA and DEC are nominal, and can only be finalized after we obtain data from the EARLY ACQUISITION IMAGE. 8107( 9) - 04/28/00 14:07 - [ 5] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: VISIT 1 IS AN EARLY ACQUISITION TO DETERMINE SLIT ORIENT AND LOCATIONS FOR VISIT 2. THEREFORE WE REQUEST THAT IT BE SCHEDULED AS EARLY AS POSSIBLE. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 A426-NUC STIS/C ACCUM 50CCD MIRROR CR-SPLIT=2 1 120 S POS TARG -23.00, 0.00 CD ------------------------------------------------------------------------------------------------------------------------------------ 2 A426-NUC STIS/F TIME-TA 25MAMA MIRROR BUFFER-TIME=120 1 1000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 A426-NUC STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=120 1 1000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8107( 9) - 04/28/00 14:07 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 145D TO 145D ORIENT 325D TO 325D On Hold Comments: Additional Comments: Visit 2 requires contiguous orbits, in order to avoid compromising the science objectives. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 A426-SPEC STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 1 S CD P Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 A426-SPEC STIS/C ACQ/PEA 52X0.1 MIRROR 1 3 S CD K Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 3 A426-SPEC STIS/F TIME-TA 52X0.1 G140M 1222 BUFFER-TIME=120 1 2050 S UV-MAM G A Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 4 A426-SPEC STIS/F TIME-TA 52X0.1 G140M 1222 BUFFER-TIME=120 1 2850 S UV-MAM G A Comments: Orbit 2 ------------------------------------------------------------------------------------------------------------------------------------ 8107( 9) - 04/28/00 14:07 - [ 7] Visit: 03 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: VISIT 3 IS AN EARLY ACQUISITION TO DETERMINE SLIT ORIENT AND LOCATIONS FOR VISIT 4. THEREFORE WE REQUEST THAT IT BE SCHEDULED AS EARLY AS POSSIBLE. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 A1795-NUC STIS/C ACCUM 50CCD MIRROR CR-SPLIT=2 1 120 S POS TARG 0.00, -15.00 CD ------------------------------------------------------------------------------------------------------------------------------------ 2 A1795-NUC STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=120 1 1000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 A1795-NUC STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=120 1 1000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8107( 9) - 04/28/00 14:07 - [ 8] Visit: 04 Visit Priority: Visit Requirements: ORIENT 67D TO 67D ORIENT 247D TO 247D On Hold Comments: Additional Comments: Visit 4 requires contiguous orbits, in order to avoid compromising the science objectives. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 A1795-STAR STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 5 S CD P Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 A1795-STAR STIS/C ACQ/PEA 52X0.1 MIRROR 1 15 S CD K Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 3 A1795-SPEC STIS/F TIME-TA 52X0.1 G140M 1272 BUFFER-TIME=120 1 1700 S UV-MAM G A Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 4 A1795-SPEC STIS/F TIME-TA 52X0.1 G140M 1272 BUFFER-TIME=120 1 2800 S UV-MAM G A Comments: Orbit 2 ------------------------------------------------------------------------------------------------------------------------------------ 8107( 9) - 04/28/00 14:07 - [ 9] Visit: 05 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: VISIT 5 IS AN EARLY ACQUISITION TO DETERMINE SLIT ORIENT AND LOCATIONS FOR VISIT 6. THEREFORE WE REQUEST THAT IT BE SCHEDULED AS EARLY AS POSSIBLE. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 A2597-NUC STIS/C ACCUM 50CCD MIRROR CR-SPLIT=2 1 120 S CD ------------------------------------------------------------------------------------------------------------------------------------ 2 A2597-NUC STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=120 1 1000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 A2597-NUC STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=120 1 1000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8107( 9) - 04/28/00 14:07 - [ 10] Visit: 06 Visit Priority: Visit Requirements: ON HOLD FOR 5 On Hold Comments: Data from VISIT 6 are required in order to finalize the ORIENT and SLIT LOCATION for Visit 6. Additional Comments: Visit 6 requires contiguous orbits, in order to avoid compromising the science objectives. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 A2597-STAR STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 1 S SEQ 1-4 NON-INT CD P Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 A2597-STAR STIS/C ACQ/PEA 52X0.1 MIRROR 1 3 S CD K Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 3 A2597-NUC STIS/C ACCUM 50CCD MIRROR CR-SPLIT=2 1 100 S CD Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 4 A2597-SPEC STIS/F TIME-TA 52X0.1 G140M 1321 BUFFER-TIME=120 1 1500 S UV-MAM G A Comments: Orbit 1 ------------------------------------------------------------------------------------------------------------------------------------ 5 A2597-SPEC STIS/F TIME-TA 52X0.1 G140M 1321 BUFFER-TIME=120 1 2800 S UV-MAM G A Comments: Orbit 2 ------------------------------------------------------------------------------------------------------------------------------------ 8107( 9) - 04/28/00 14:07 - [ 11] Summary Form for Proposal 8107 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD 25MAMA F25SRF2 F28X50LP 52X0.1 F25QTZ ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM TIME-TAG ACQ ACQ/PEAK ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2 BUFFER-TIME=120 ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG -23.00, 0.00 ORIENT 145D TO 145D ORIENT 325D TO 325D POS TARG 0.00, -15.00 ORIENT 67D TO 67D ORIENT 247D TO 247D ON HOLD FOR 5 SEQ 1-4 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names A426-NUC A426-SPEC A1795-NUC A1795-STAR A1795-SPEC A2597-NUC A2597-STAR A2597-SPEC ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1222 1272 1321 ------------------------------------------------------------------------------------------------------------------------------------