6802( 3) - 02/29/96 10:46 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6802 Version: 3 Check-in Date: 29-Feb-1996 10:44:47 1.Proposal Title: COSMOLOGY WITH THE MEDIUM DEEP SURVEY ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COSMOLOGY GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Prof. Richard Griffiths Johns Hopkins University CoI: Richard Ellis Institute of Astronomy, U. Cambridge N CoI: Gerard Gilmore Institute of Astronomy, U. Cambridge N CoI: Richard Green NOAO N CoI: John Huchra Smithsonian Astrophysical Observatory N CoI: Kavan Ratnatunga Johns Hopkins University N ------------------------------------------------------------------------------------ 6. Abstract Parallel MDS exposures have provided unique high resolution images which clearly supplement the primary HST surveys. For statistical programs in extragalactic and Galactic astronomy, source counts parameterized by morphology, magnitude, color, scale-length and orientation constitute an invaluable database for long term programs in cosmology, galaxy evolution and Galactic structure. We have already demonstrated fundamental progress in each of these areas during Cycle 4, with ongoing progress in Cycle 5. Highlights include the following results: (i) the observation of non-evolving and evolving (irregular) galaxy populations, the latter explaining the faint blue excess, (ii) the diversity of the irregular populations, (iii) the bulk of the familiar Hubble sequence was in place at z ~ 0.5, (iv) the universe was dwarf-rich at z ~ 0.3-0.5, (v) the discovery of weak galaxy-galaxy shear and constraints on massive halos, (vi) constraints on Omega and Lambda using ellipticals, (vii) a low evolution of the `major merger' rate, (viii) detection of faint compact nuclei in 6\% of field galaxies at moderate z, (ix) discovery of HST- unique gravitational lenses which are powerful cosmological probes, (x) a bimodal color distribution in M87 globulars. With the level of progress and publications now well established, we request expansion of these exciting programs into Cycle 6, with an emphasis on the extraction of cosmological parameters. ------------------------------------------------------------------------------------ 6802( 3) - 02/29/96 10:46 - [ 2] Observations Description ------------------------ MDS OBSERVING STRATEGY FOR CYCLE 6 In a stack of four half- orbit exposures totalling 7500s, the magnitude limits for reliable measurements of individual objects are 26.5 mag for point sources and 26 mag for typical galaxies in I (F814W), and about 0.5 mag fainter in V (F606W) -- see Fig. 6. At fainter levels, we observe sky fluctuations that can be resolved into individual galaxies, but measurements of their structural parameters are less reliable. For the same exposure, star-galaxy separation can be achieved to 25.5 mag in V, compared to a ground-based separation limit of V ~ 22 mag. Longer exposures would not gain substantially in limiting magnitudes, although they could improve star-galaxy separation and measurement of structural parameters, both of which are limited by photon counting noise. For B (F450W) we estimate the detection limits to be about 0.5 mag brighter, and the star-galaxy separation limit about 1 mag brighter than in V. With the experience from previous cycles, we propose to continue with the following strategy: (i) It is vital that as much parallel time as possible continue to be used for WFPC2 exposures in broad passbands so as to maximize HST scientific productivity. Results from the MDS have vindicated the effort expended in the development of parallel operations, which increase the overall observing efficiency of HST by ~ 50\\%. We continue to emphasize the use of WFPC2 in parallel mode at every opportunity for exposure times greater than 600 s. In particular, multi-orbit exposures in each band are needed for all aspects of the Medium Deep Survey: galaxy morphology vs. color, the search for compact nuclei, rare object morphology, the detection of faint stars, gravitational lenses, etc. The MDS team at JHU has worked closely with STScI in the development of ``crafting rules'' for the optimisation of the MDS and GTO parallel surveys. (ii) LOW PRIORITY: For the shorter exposures, the scientific productivity of the Survey has been enhanced by biasing use of WFPC2 at high galactic latitudes as far as possible into the I-band. The I-band has the greatest space-advantage with respect to ground- based observations, by virtue of the elimination of the atmospheric hydroxyl bands and the resulting factor of ~ 10 reduction in sky background (~eq 22.3 mags arcsec^-2 at 8930Angstrom at the NEP). footnote The Cycle 5 TAC recommended that those parallel orbits not allocated to the MDS should be used for exposures in the same filters so as to generate a uniform database -- this recommendation has not been followed by STScI. Analysis of the UV-exposures taken instead by STScI shows no publishable result. (iii) LOW PRIORITY: For up to 3 exposures, we retain our plan of using the I-band, with the addition of the V-band for 4 exposures or more (2 C-R split orbits or 4 orbits without C-R split ). A minimum of 2 exposures in each filter is required to make a stack free of cosmic rays. (iv) HIGH PRIORITY: For pointings of 6 or more orbits with C-R split (9 non-split), which we expect to continue to constitute the most interesting part of the Survey, the I- V-bands will still be used, but with B- band imaging added to get color information, and especially to isolate bluer structures. In Cycle 6, we propose to obtain extra color information in the near-UV (F255W) on a subset (at least two or three) of the deepest low b survey fields exceeding 6 orbits. (v) HIGH PRIORITY: HST Calibration exposures on bright stars will provide the opportunity for repeated observations and will also provide an annular coverage that will be used for correlation studies of faint galaxies, as a function of galaxy type and structure or morphology. We expect a few calibration fields to be available eventually for this purpose. begintable def\\mk#1 ^ #1 vbox 5pt plus 2pt centerline Table 1: Explanation of types of observations \\medskip to hsize # && # noalign 1pt Depth & N. Orbits & \\# expected & Filtersmka &Multispan3 Limiting magnitude & & per cycle & & Detection & Disk/bulge & Morphology noalign Shallow & 1--3 & 200 & I & 25 & 23 & 21 Medium & 4--5 & 50 & VI mkb & 26.5/26 & 25/24 & 23/22 Deep & > 6 & 30 & BVI mkc & 26/26.5/26 & 24/25/24 & 22/23/22 noalign 1pt -5pt begindescription 0pt vspace-0.27in itema) For WFPC2, I is F814W; V is F606W; B is F450W; U is F255W itemb) At low galactic latitudes, B will be used instead of V itemc) At low galactic latitudes, U will be added for the longest pointings vspace-7mm enddescription endtable WFPC2 will thus be used for parallel observations at every opportunity for exposure times greater than 600 s in random fields at b > 10^ o , with an assumed average observing time of 2500 s per orbit; in these fields, exposure times less than 600 s are unlikely to be very valuable for faint galaxy work. However, at lower latitudes, and within nearby galaxies, shorter integrations are extremely useful. Single filter exposures/orbit will be split wherever possible for detection of particle radiation background (~2 - 3 events per CCD sec^-1, depositing typically 100-1000 electrons) The Observing Strategy summarized in Table 1 will provide a balanced overall parallel program while satisfying the requirements on the total number of fields and filter combinations for the science objectives of the MDS (Table 2). The final assignments and filter choices will depend on the distribution of orbits in the Cycle 6 GO primary pointings. We will continue to work with STScI personnel to optimize the program and filter usage. The scientific goals of the MDS and the expected number of exposures necessary to achieve them are summarized in Table 2. begintable def\\mk#1 ^ #1 vbox centerline Table 2: MDS Projects and Observational Requirements for Cycles 6 et seq. \\medskip tohsize # 4pt plus 2pt & # & #& #& #& #& #& # 0pt noalign 1pt Project & Type of objects & \\# obj. & \\# per & I_ lim & V_ lim & Fields & Statusmkc & and observationsmka & reqd.mkb & field & & & reqd. & noalign noalignnoindent Extragalactic: Number and structural parameters Number counts & V and I phot & 10000 & 200 & 24 & 26 & 50 M & A Number counts vs. type & Morphology & 3000 & 25 & 22 & -- & 120 S & A Deep Number counts & V and I phot & 10000 & 500 & 26 & 27 & 20 D & C6 Color vs. mag and type & E/S class, V-I & 2000 & 200 & 24 & 26 & 10 M & A BVI colors vs. morphology & Morph, BVI & 500 & 25 & 22 & 24 & 20 D & C6/LT Size distribution & All galaxies & 10000 & 500 & 26 & -- & 20 S & A Size vs. color & V-I & 10000 & 200 & 24 & 26 & 50 M & A Lambda, Omega from E's & E/S, V-I, size & 1000 & 5 & 23 & 26 & 200 M & LT Weak grav. shear & E/S + bkgd. obj. & 3000 & 70 & 23 & 26 & 400 M & LT noalign\\medskip phantom Extragalactic: Merging, pairing and angular correlation function (CF) Parents/satellites (Delta m<4 ) & Morph, V-I & 500 & 6 & 20 & 22 & 80 M & LT Color gradients of parents & BVI & 200 & 6 & 20 & 22 & 30 D & LT Color of major mergers & BVI & 100 & 3 & 22 & 24 & 30 D & LT Galaxy pairs & Pairs ( d ~ 1'') & 500 & 3 & 23 & -- & 150 M & C6 Pairing vs. type, color & Pairs, color, E/S & 1000 & 3 & 23 & 25 & 300 M & LT CF vs. type - bright end & E/S class & 10000 & 25 & 22 & -- & 400 S & C6/LT CF vs. type - faint end & E/S class & 20000 & 200 & 24 & -- & 100 S & A noalign\\medskip phantom Extragalactic: Properties of rare objects Quad grav lenses & Well-resolved ellipticals & 20 & 0.03 & 23 & 24 & 600 M & LT AGN/compact nuclei & Well- resolved galaxies & 200 & 2-3 & 21 & 23 & 80 M & C6/LT Colors of above & BVI of above & 50 & 2 & 20 & 22 & 25 D & LT Unusual Starforming gal. & Morph, BVI & 200 & ~1 & 23 & 25 & 200 M & LT Shreds (low SB fragments) & V-I , good depth & 100 & 1--2 & 24 & 26 & 100 M & C6 Compact objects & BVI photometry & 200 & 3 & 22 & 23 & 70 D & LT noalign\\medskip noindent Galactic: Structure and stellar populations of the Galaxy Luminous mass density & Faint stars at b > 30^ o & 50 & 1 & 23 & 26 & 50 M & C6 LF of K- M dwarfs & Faint star counts vs. b & 2000 & 20 & 23 & 26 & 100 M & LT Spheroid turnoff & Faint stars at b > 30^ o & 200 & 1 & 22 & 26 & 200 M & LT Galactic length scales & Star counts at b < 20^ o & 10000 & 100 & 24 & 26 & 100 M & LT noalign 1pt begindescription =0pt vspace -0.27in itema) Morphology indicates detailed morphological classification and disk/bulge separation for spirals; E/S indicates automated classification into bulge- dominated and disk-dominated galaxies by model fits; B, V, I stand for F450W, F606W, F814W respectively. vspace-2mm itemb) Fields required are divided into S(hallow), M(edium), and D(eep) according to Table 1; because of our observing strategy, a field of greater depth can also be used. vspace- 2mm itemc) Status is A (achieved) if data are already in hand (Sep 1, 1995); C5/6 if we expect to acquire the data by the end of Cycle 5/6 resp. at current rate (see table below); LT (long term) if data are not expected by the end of Cycle 6. These estimates include reasonable use of archival and HDF data. enddescription endtable \\medskip DATA ANALYSIS 0.05in Our results reinforce the need for a well organized and centralized MDS team which collates the parallel images with the objective of executing statistical studies which can only be realized using the whole parallel database. We have clearly demonstrated our progress in this regard by establishing at JHU a MDS database of over 15,000 objects from WF/PC in cycle 1 --3 and over 20,000 objects from WFPC2 in Cycle 4: these catalogs have been posted to STEIS, the largest catalogs thus far compiled using HST. We have demonstrated a continuing ability to keep up with the high data volume, having recalibrated and completed the object catalogs from all Cycle 1--4 data footnoteIn separate Archival Research proposals, we have proposed to perform similar analyses on the primary and GTO parallel data. (a third of all WFC data) in Cycle 4. Continuation of the MDS is the only feasible means by which the conclusive cosmological results can be extracted on any reasonable timescale from the whole database. The funding supplied to the MDS team has been used very effectively to develop the required non-standard software applicable to HST data and to solve the problems associated with a large dataset consisting of fields with exposures of varying depths, varying multiplicity within filters and various problems associated with scattered earthlight, etc. Thirty-seven MDS papers have been published or submitted to refereed journals (see Bibliography). We have established the MDS database and developed a detailed Working Group plan over the past several years. All Cycle 1--4 data have been recalibrated using the MDS super-sky flat fields and other improvements in calibrations which resulted in a gain of at least 0.3 mag in sensitivity for cy 1--3 (R94a), and all the data have been processed, searched and objects parameterized. The resulting calibration files for WF/PC and WFPC2 have been made publicly available on STEIS, together with the complete object catalog -- the HST MDS Catalog from WF/PC. Real Time Justification ----------------------- vspace-3mm None vspace-2mm GROUND-BASED OBSERVATIONS 0.05in To optimize the use of HST, we have undertaken an extensive program of ground-based follow-up work, recognizing the importance of complementary redshifts and spectral data for at least a complete subsample of the MDS data (to Sept 1995, a total of ~ 130 redshifts from Cycle 4 data have been measured: 64 from KPNO, 31 from WHT, ~ 20 -- 30 from MMT, 9 from Keck). Near infrared, radio, and additional broadband and narrow band optical imaging, etc., is also being supplied from the ground, especially for the small number of high galactic latitude areas that have or will receive multiple orbit observations. We plan to continue to invest at least two nights of 4m-class optical telescope time for each of a selected set of WFPC2 frames for multiaperture spectroscopy to V~ 23, using instruments such as the low dispersion multi-object spectrographs at the KPNO 4m, and the integral field spectrographs planned for the WHT and CFHT (R. Marzke of DAO is a collaborator for the follow-up spectroscopy). The mismatch between the WFPC2 field and that of the multi-object spectrographs is ameliorated to the maximum extent possible in our follow-up work, i.e. we can optimize the selection of HST objects for spectroscopy once the image has been processed. For the WHT, KPNO 4m and AAT we have made multi- slit masks with 8--12 slits for each WFPC field with less than 10 days lead-time. We have repeated this with up to 3 masks per field, and on several occasions measured about 30 spectra in a single WFPC2 field, or ~8--10 objects per square arcmin. We also take advantage of the a priori knowledge of the accurate location of the HST galaxy core (and/or H-II regions) from astrometry on the WFPC2 images. The median scale-length of MDS galaxies is 0.3''--0.4'' (C95), so that in good seeing, we can optimize the multi-slit spectrograph throughput by using 0.5''-0.75'' slits, thereby optimizing the number of measured redshifts per unit time. We will typically use half a night for additional multicolor photometry, and half a night for near infrared imaging (UKIRT) for full ground-based optical support. These observing times have been exceeded for several fields observed in Cycle 4. Such data give us the redshift-color- size, etc. correlations that allow us to understand our larger data set in terms of galaxy type vs. redshift. Altogether, about 100 nights of optical telescope time over a 3 to 5 year follow-up period are realistic goals for our team, and thus we should be able to optimize the usefulness of a significant fraction of the MDS data base. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6802( 3) - 02/29/96 10:46 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6802( 3) - 02/29/96 10:46 - [ 4] TARGET LIST c)Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ PAR CLUSTER OF GALAXIES ABS_II > 10D ------------------------------------------------------------------------------------------------------------------------------------ 6802( 3) - 02/29/96 10:46 - [ 5] Visit: 01 Visit Requirements: PARallel 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 PAR WFPC2 IMAGE WFALL F814W 1 20M ------------------------------------------------------------------------------------------------------------------------------------ 6802( 3) - 02/29/96 10:46 - [ 6] Summary Form for Proposal 6802 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COSMOLOGY ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PARallel ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PAR ------------------------------------------------------------------------------------------------------------------------------------