6408( 15) - 09/11/96 14:09 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6408 Version: 15 Check-in Date: 11-Sep-1996 13:48:48 1.Proposal Title: NGC1569 as a Local Probe of Galaxy Evolution at High Redshift -- Part 2: Spectroscopy ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Galaxies & Clusters GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: CLAUS LEITHERER SPACE TELESCOPE SCIENCE INSTITUTE CoI: Mark Clampin Space Telescope Science Institute N CoI: Guido De Marchi Space Telescope Science Institute N CoI: Laura Greggio Universita di Bologna N CoI: Antonella Nota Space Telescope Science Institute N CoI: Monica Tosi Osservatorio di Bologna N ------------------------------------------------------------------------------------ 6. Abstract We propose to perform a case study of the star-formation history and chemical evolution of the irregular galaxy NGC1569 over the past 500\ Myr. This galaxy may be the closest local analogues to faint blue galaxies at high redshift. The interstellar medium in NGC1569 is expelled and forms a large- scale outflow due to the effects of stellar winds and supernovae. The stellar content of stars with masses above 3\ M_\odot has been derived by comparing CMD's based on Cycle 5 WFPC2 images and theoretical CMD's computed stochastically. The youngest and most massive stars are concentrated in super star clusters, whose content will be investigated via integrated ultraviolet spectra taken with the FOS in Cycle 6. The Cycle 6 spectroscopy and Cycle 5 imagery combined will allow us to derive the complete star- formation history. The energy input into the ISM will be calculated and compared to the energetics of the superwind. The chemical enrichment will be computed, and the mass in heavy elements lost via the superwind will be estimated. We will evaluate the status of NGC1569 with respect to other irregular galaxies in the local universe and its relation to blue galaxies at high redshift. ------------------------------------------------------------------------------------ Observations Description ------------------------ Even with a relatively flat IMF, stars with masses above 10 M_\\odot hardly contribute to the optical continuum and their spectral features are correspondingly weak. The situation improves dramatically in the UV at wavelengths below 3000 Angstrom where massive stars display a variety of strong stellar absorption lines. Our main goal is to use HST FOS spectra to model and interpret the integrated UV spectra of starbursts in terms of a massive stellar population. We need S/N = 20 in the continuum to detect and model age- and IMF- sensitive stellar absorption lines of the brightest super star cluster in NGC1569 (named NGC1569-A by O'Connell et al.). This value is based on our experience with previous modeling of IUE and HST data. Lower S/N makes it difficult to resolve spectral lines which are blends of stellar and interstellar contributions. The spectral resolution of the FOS data (200\\ km\\ s^-1 FWHM) is sufficient to resolve the stellar wind lines, so that meaningful fits to the observed profiles using our models will be possible. In contrast, the IUE data would be inadequate to achieve our goal (both in terms of S/N and resolution). The UV absorption-lines in starburst galaxies will be of three types: stellar wind lines, stellar photospheric lines, and interstellar lines. Stellar wind lines will be easily recognizable because they are broad (2000\\ km\\ s^-1), blueshifted (by >1000\\ km\\ s^-1), and sometimes have a P-Cygni profile. We expect the resonance lines of Si IV Lambda1400 and C IV Lambda1550 to be the most prominent wind features (see Figure 1). These lines will be observed with grating G130H on the blue side of the FOS. We used the fluxes of NGC1569-A observed by O'Connell et al. and the continuum shape of the published IUE spectrum to calculate exposure times. We expect 0.08 counts s^-1 diode at 1400\\ Angstrom, i.e. S/N = 20 is reached in 90 minutes. Since NGC1569-A is somewhat evolved, spectral features due to B stars are expected as well. These features are prominent at wavelengths between 1800\\ Angstrom and 3000\\ Angstrom (cf. Kinney et al. 1993). The strongest lines will be due to Al III Lambda1860 and Mg II Lambda2800. They form partly in low- velocity stellar winds and photospheres. We will observe these lines with gratings G190H and G270H, both on the red side of the FOS. The expected count rates at 1900 and 2800\\ Angstrom are 0.6 and 7.0 counts s^-1 diode, respectively. S/N = 20 is reached in 11 and 1 minutes, respectively. We will also utilize the continuum slope in the ultraviolet to constrain the interstellar extinction. NGC1569 has a relatively high foreground extinction. We will derive the reddening in the ultraviolet from the spectroscopic data. We will use the 0.3'' aperture of the FOS. O'Connell et al. derived core diameters of 0.2'' (where 20\\% of the peak value is reached). The chosen aperture will still encompass the total light of NGC1569-A, but minimize contamination by the surrounding field population. The observations with all three gratings can be completed in 3 CVZ orbits. Relation to theoretical models. The observations will be interpreted with population synthesis and galaxy evolution models derived independently at Baltimore and Bologna. The two codes are based on entirely different stellar evolution models (Geneva vs. Padova). This will allow us to evaluate potential error sources in stellar evolution models. The imaging data will mainly be used to construct empirical CMD's for comparison with the models of Tosi et al., We will also generate two- color diagrams to monitor the time evolution of the galaxies using the models published by Leitherer & Heckman (1995). The spectroscopic data will be modeled with the method of Leitherer et al. (1995). The overall goal is to establish the SF history of the cluster and field population and predict the return of heavy elements and energy into the ISM. We will check for consistency with the energetics of the superwinds. At the same time we will predict the mass loss in heavy elements due to the winds. The enrichment of the IGM by the superwind cannot be studied observationally: even if an abundance analysis of the superwinds were technically feasible, the enriched material could not be detected optically due to the 2-component structure of the galactic wind. The shocked stellar wind and SN material is at temperatures of sim10^8 K (Suchkov et al. 1994), and therefore not detectable at optical wavelengths, where only the blown-out ISM of the galaxy can be traced. Therefore our proposed study provides the unique opportunity to infer superwind abundances semi-empirically, i.e. by combining observed properties of the stellar population with theoretical models for galaxy evolution. Real Time Justification ----------------------- NGC1569 is a CVZ target. No supporting observations are planned. We will retrieve ground-based results from the literature (e.g. spectrophotometry of individual H II regions, kinematical data of the outflow) and include them in our analysis. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6408( 15) - 09/11/96 14:09 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1569A EXT-CLUSTER, OPEN RA=4H 26M 3.7S +/- 0.3S, DEC=64D 1950 V = 12.0 CLUSTER 44' 29.0" +/- 2", PLATE-ID=01MS B-V = 0.0 6408( 15) - 09/11/96 14:09 - [ 2] Visit: 01 Visit Requirements: ORIENTation 230D TO 230D; CVZ 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 NGC1569A FOS/RD ACQ/PEA 4.3 MIRROR SCAN-STEP-Y=1.23,SEARCH-SIZE-X=1, 1 2 S ONBOARD ACQ FOR 2 K SEARCH-SIZE-Y=3 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1569A FOS/RD ACQ/PEA 1.0 MIRROR SCAN-STEP-X=0.61,SCAN-STEP-Y=0.61 1 2 S ONBOARD ACQ FOR 3 K ,SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1569A FOS/RD ACQ/PEA 0.5 MIRROR SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29 1 3 S ONBOARD ACQ FOR 4 K ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC1569A FOS/RD ACQ/PEA 0.3 MIRROR SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 1 4 S ONBOARD ACQ FOR 5-6 K ,SEARCH-SIZE-X=4,SEARCH-SIZE-Y=4 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC1569A FOS/RD ACCUM 0.3 G190H 1 23 M ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC1569A FOS/RD ACCUM 0.3 G270H 1 7 M ------------------------------------------------------------------------------------------------------------------------------------ 6408( 15) - 09/11/96 14:09 - [ 3] Visit: 02 Visit Requirements: ORIENTation 230D TO 230D; CVZ 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 NGC1569A FOS/BL ACQ/PEA 4.3 MIRROR SCAN-STEP-Y=1.23,SEARCH-SIZE-X=1, 1 2 S ONBOARD ACQ FOR 2 K SEARCH-SIZE-Y=3 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1569A FOS/BL ACQ/PEA 1.0 MIRROR SCAN-STEP-X=0.61,SCAN-STEP-Y=0.61 1 2 S ONBOARD ACQ FOR 3 K ,SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1569A FOS/BL ACQ/PEA 0.5 MIRROR SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29 1 3 S ONBOARD ACQ FOR 4 K ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC1569A FOS/BL ACQ/PEA 0.3 MIRROR SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 1 4 S ONBOARD ACQ FOR 5 K ,SEARCH-SIZE-X=4,SEARCH-SIZE-Y=4 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC1569A FOS/BL ACCUM 0.3 G130H 1 122.5 M ------------------------------------------------------------------------------------------------------------------------------------ 6408( 15) - 09/11/96 14:09 - [ 4] Summary Form for Proposal 6408 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCAN-STEP-Y=1.23 SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SEARCH-SIZE-Y=2 SEARCH-SIZE-X=3 SEARCH-SIZE-Y=4 SEARCH-SIZE-X=6 SCAN-STEP-Y=0.29 SEARCH-SIZE-X=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Galaxies & Clusters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENTation 230D TO 230D; CVZ ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 3 ONBOARD ACQ FOR 4 ONBOARD ACQ FOR 5-6 ONBOARD ACQ FOR 5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G190H G270H G130H ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC1569A ------------------------------------------------------------------------------------------------------------------------------------