9399( 2) - 01/31/02 16:35 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9399 Version: 2 Check-in Date: 31-Jan-2002 16:34:23 1.Proposal Title: Insights into Elliptical Galaxy Formation from HST Imaging of Shell Galaxies ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: David Carter Liverpool John Moores University CoI: Dr. Terry Bridges Anglo-Australian Observatory N CoI: Dr. George Hau European Southern Observatory N CoI: Dr. Marc Balcells IAC, Tenerife N CoI: Dr. Carlos DelBurgo MPIA, Heidelberg N ------------------------------------------------------------------------------------ 5. Abstract We propose to use ACS to carry out an imaging survey of the cores of shell galaxies. Key to understanding several aspects of shell formation is to determine how far in do shells exist. Photometric detection from the ground is limited by seeing and sampling to radii of at best R ~ 10 - 15 arcsec. In velocity maps derived from high spatial resolution long-slit and integral-field ground-based spectra we have found shell-like features with distinct kinematics in several shell galaxy cores (R ~ 3 - 5 arcsec ~ 1 kpc). Hence we believe that shells may extend further in than previously known. HST provides the spatial resolution and sampling needed to map out shells in the pronounced surface brightness gradients of elliptical galaxy cores. The data will allow us to detect and map inner shells, to measure their colors, to establish their dynamics with the help of ground-based kinematics, to compare the inner surface brightness profiles of shell and non-shell ellipticals, and to measure the mass and distribution of the dust. Where shells are found, combined spatial and velocity information will establish the orbital structure of shell- producing merger debris on the basis of data, and will allow useful checks of the models for formation of shell systems in early-type galaxies. ------------------------------------------------------------------------------------ 9399( 2) - 01/31/02 16:35 - [ 2] Observations Description ------------------------ We have selected a sample of 12 shell galaxies with cz < 4000 km/s from the catalogues from ground-based imaging by Malin & Carter (1983), Schweizer & Seitzer (1992), and Turnbull (1999). Prieur (1988b) classifies shell galaxies into 3 types based upon the shell morphology, and it is important that our sample represents all types. We include 5 Type I systems (aligned major axis shell systems, phase wrapped; NGC 596, NGC 1344, NGC 3923, NGC 5982 and NGC 7600); 3 Type II systems (shells all around the galaxy, spatially wrapped; NGC 474, NGC 2865 and NGC 3051), and 4 of the more complicated Type III systems which show both types of shells (NGC 1549, NGC 1553, NGC 2300 and NGC 7626). Thus our sample is a representative selection of the nearest shell galaxies. The benefits of the program do not derive from working on a complete sample but rather from obtaining quality HST data for nearby objects that are well studied from ground imaging and spectroscopy. For all of these galaxies we have high quality ground-based imaging data, all are known to have shells at large radius. Obviously dusty galaxies (Cen A type systems) have been omitted from the sample as dust would complicate the data analysis and make shell detection more difficult. Our goal is to to investigate the shell systems inside 20 arcsec radius, where detailed work on shell profiles and colours is impossible from ground based images with typically 1 arcsec seeing. Shell and galaxy background surface brightnesses will vary from object to object, but from the data of Turnbull et al. (1999) we calculate the signal-to-noise for a shell at radius 10 arcsec. Extrapolating the shell surface brightnesses inwards we estimate that the shell will have a surface brightness of R = 24.0 mag/sq arcsec, and the galaxy has a surface brightness of R = 19.0 mag/sq arcsec ( Fig. 2). Furthermore, from the shapes and sizes of kinematic shells ( Fig. 1), we estimate that we will be able to average over arc regions of at least 3 arcsec * 0.3 arcsec (360 WFC pixel). For the majority of our targets the visibility period per orbit is between 52 and 53 minutes, in one case (NGC 2300) it is 59 minutes. We propose to split each orbit into 2 CCD exposures for cosmic ray rejection. This should prevent the nuclei of the galaxies saturating, before completing the Phase II process we will check the exact central surface brightness of each galaxy, to verify whether we need to use CR- SPLIT=3 rather than 2 to avoid saturation. For each orbit the overheads are: 6 minutes guide star acquisition, 6.5 minutes instrument overheads (4 mins for the first exposure and 2.5 min for the second). Science exposures are therefore 39.5 - 40.5 mins in most cases. Using the signal values provided by the ACS Exposure Time Calculator, we find that in one orbit per filter, in filter F606W, we obtain 1.158 x 10^4 photons from the shell, 1.413 x 10^5 from the sky and 1.158 x 10^6 from the background galaxy in 39 minutes in our 360 pixel strip. Using the values of dark current and readout noise given by the Exposure Time Calculator, we obtain a signal to noise ratio of 10.0. Similarly in filter F814W we obtain a signal to noise ratio of 10.8. So in one orbit per galaxy we obtain surface brightness to 0.1 magnitude in each passband, and colour to 0.14 magnitude. These values will vary betwen galaxies and between shells, but we believe this calculation to be representative, and also to provide an indication of the limits that we will be working to in this experiment. We cannot provide a precise estimate of the shell surface brightnesses as this programme is designed in part to detect the shells in the first place. ACS is our instrument of choice, it allows us to measure colours (whereas STIS only allows unfiltered imaging). In addition to their diagnostic value, colours allow us to quantify and model the effect of dust on our observations. The larger field of view of ACS also allows us to determine, model and subtract the background galaxy surface brightness which is vital for accurate colour and surface brightness measurements of the shells. Our analysis techniques will build upon those developed over many years to measure surface brightnesses of shells form ground-based images (e.g. Prieur 1988, Forbes & Thomson 1992), but modified to take account of recent developments, for instance by modelling the surface brightness profiles of the underlying galaxy with the ``nuker law'' profile of Lauer et al. (1995) and Sersic profiles (Caon et al. 1993) rather than de Vaucouleurs' or Hubble's laws. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9399( 2) - 01/31/02 16:35 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3923 GALAXY, ELLIPTICAL RA=11H 51M 1.8S +/- 2", DEC=-28D J2000 V = 1788 B = 10.80+/-0.10 48' 22" +/- 2" Coordinate Source: OTHER_SOURCE 2 NGC2865 GALAXY, ELLIPTICAL RA=09H 23M 30.1S +/- 2", DEC=- J2000 V = 2627 B = 12.57+/-0.14 23D 9' 43" +/- 2" Coordinate Source: OTHER_SOURCE 3 NGC1344 GALAXY, ELLIPTICAL RA=03H 28M 19.2S +/- 2", DEC=- J2000 B = 11.27+/-0.10 31D 4' 4" +/- 2" Coordinate Source: OTHER_SOURCE 4 NGC7626 GALAXY, ELLIPTICAL RA=23H 20M 42.3S +/- 2", DEC=08D J2000 V = 3405 B = 12.16+/-0.13 13' 2" +/- 2" Coordinate Source: OTHER_SOURCE 5 NGC474 GALAXY, ELLIPTICAL RA=01H 20M 6.7S +/- 2", DEC=03D J2000 V = 2372 B = 12.37+/-0.13 24' 55" +/- 2" Coordinate Source: OTHER_SOURCE 6 NGC5982 GALAXY, ELLIPTICAL RA=15H 38M 39.9S +/- 2", DEC=59D J2000 V = 3017 B = 12.04+/-0.13 21' 21" +/- 2" Coordinate Source: OTHER_SOURCE 9399( 2) - 01/31/02 16:35 - [ 4] Visit: 01 Visit Priority: Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC3923 ACS/WF ACCUM WFC F814W CR-SPLIT=2 1 16.3 M C ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC3923 ACS/WF ACCUM WFC F606W CR-SPLIT=2 1 19 M C ------------------------------------------------------------------------------------------------------------------------------------ 9399( 2) - 01/31/02 16:35 - [ 5] Visit: 02 Visit Priority: Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC2865 ACS/WF ACCUM WFC F814W CR-SPLIT=NO 1 2 M C ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC2865 ACS/WF ACCUM WFC F814W CR-SPLIT=2 1 14 M C ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC2865 ACS/WF ACCUM WFC F606W CR-SPLIT=2 1 17 M C ------------------------------------------------------------------------------------------------------------------------------------ 9399( 2) - 01/31/02 16:35 - [ 6] Visit: 03 Visit Priority: Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC1344 ACS/WF ACCUM WFC F814W CR-SPLIT=NO 1 2 M C ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1344 ACS/WF ACCUM WFC F814W CR-SPLIT=2 1 14 M C ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC1344 ACS/WF ACCUM WFC F606W CR-SPLIT=2 1 17.7 M C ------------------------------------------------------------------------------------------------------------------------------------ 9399( 2) - 01/31/02 16:35 - [ 7] Visit: 04 Visit Priority: Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC7626 ACS/WF ACCUM WFC F606W CR-SPLIT=2 1 19 M C ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC7626 ACS/WF ACCUM WFC F814W CR-SPLIT=2 1 16 M C ------------------------------------------------------------------------------------------------------------------------------------ 9399( 2) - 01/31/02 16:35 - [ 8] Visit: 05 Visit Priority: Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC474 ACS/WF ACCUM WFC F814W CR-SPLIT=2 1 16 M C ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC474 ACS/WF ACCUM WFC F606W CR-SPLIT=2 1 19 M C ------------------------------------------------------------------------------------------------------------------------------------ 9399( 2) - 01/31/02 16:35 - [ 9] Visit: 06 Visit Priority: Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC5982 ACS/WF ACCUM WFC F814W CR-SPLIT=2 1 17 M C ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC5982 ACS/WF ACCUM WFC F606W CR-SPLIT=2 1 21.9 M C ------------------------------------------------------------------------------------------------------------------------------------ 9399( 2) - 01/31/02 16:35 - [ 10] Summary Form for Proposal 9399 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC3923 NGC2865 NGC1344 NGC7626 NGC474 NGC5982 ------------------------------------------------------------------------------------------------------------------------------------