9144( 2) - 02/15/01 15:58 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9144 Version: 2 Check-in Date: 15-Feb-2001 15:57:33 1.Proposal Title: Calibrating Star Formation: The Impact of Environment ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Daniela Calzetti Space Telescope Science Institute CoI: Prof John S. Gallagher III Wisconsin University N CoI: Mr Christopher J. Conselice Space Telescope Science Institute N CoI: Ms Nicole L. Homeier Wisconsin University N ------------------------------------------------------------------------------------ 5. Abstract One missing piece for placing star formation within the broader context of galaxy evolution is the quantification of the feedback mechanisms between a starburst and its host galaxy. We propose to obtain WFPC2 UV, V, and I broad-band and HAlpha, OIII, SII, and HBeta emission line images of three nearby, sub-L^*, starburst galaxies to: map the young stellar populations and star clusters, locate the obscuring dust clouds, and diagnose conditions in the ionized ISM. Our sample is carefully selected to probe a range of environments for the host galaxy, from isolated to group-interacting, for constant morphology, luminosity and metallicity. The galaxies are all closer than ~4 Mpc, giving ~2 pc resolution with the WF so we can chart the detailed structure of each starburst. This project is designed to: (a) establish whether starbursts are large-scale coherent or chaotic processes by investigating the presence of sequential/propagating star formation; and (b) explore the influence of the external environment on the evolution of the starburst. For this purpose we will measure: (1) the recent star formation history of both stellar clusters and young diffuse population; (2) the dust distribution; and (3) the structures in the shocked and photo-ionized gas. This study will provide a physical basis, in terms of energetics, evolution, and internal structures, for the interpretation of blue galaxies at intermediate and high redshifts. ------------------------------------------------------------------------------------ 9144( 2) - 02/15/01 15:58 - [ 2] Observations Description ------------------------ 1. Sample Selection and Definition. Our sample (Table 1) is selected to best meet our science goals while, at the same time, maximally exploit existing WFPC2 images in the HST Archive. The three dwarfs have active starbursts in their centers with SFRs per unit kpc^2 between 100 and 1000 times the averages in normal disk galaxies. In order to separate the effects of galaxy--galaxy interations from other factors, the targets have been selected with very similar galactic morphology, luminosity, and metallicity. They are also at comparable distances, in order to minimize differences in the physical size resolved by HST. NGC3077 is a member of the M81 group, and forms a triplet with M81 and M82. It is connected to M81 by a ~50 kpc HI bridge 1. NGC5253 is in pair- interaction with M83, at a separation of ~140 kpc. NGC4214 is an isolated starburst, which we will use as a no-interaction template. We are not considering rich galaxy clusters, where tidal disruption of the dwarf galaxy could dominate over other effects (Lopez-Cruz et al. 1997, ApJ, 475, L97). Two of the galaxies, NGC4214 and NGC5253, have been already extensively observed with HST (Table 2); we only request two narrow-band images for each galaxy, to complement the archival HST images with the missing ionized gas emission observations. beginscriptsize begintableh begincenter Table 1: Targets Propertiesendcenter begintabularlrrrrrrrl Name & Morph. & v_H^a & D^b & a*b^c & M_B^d &O/H^e & SFR^f & Comments , & & (km/s) & (Mpc) & (arcmin) & & & M_\odot/yr & , NGC3077 & I0/Im & 14 & 3.5 & 5.4*4.5 & -17.4 & 8.6 & 0.1 &Dwarf Starburst, M81 group, NGC4214 & IABm & 291 & 3.9 & 8.5*6.6 & -17.7 & 8.2 & 0.9 & Isolated Dwarf Starburst, NGC5253 & Im & 404 & 3.7 & 5.0*1.9 & -17.6 & 8.2 & 0.5 & Dwarf Starburst, M83 companion, endtabular Notes: ^a Recession velocity. ^b Distance. ^c Angular sizes of the major and minor axis. ^d Absolute blue magnitude. ^e Oxygen abundance, 12+log(O/H). ^f Star Formation Rate, from the HAlpha nebular emission. endtable endscriptsize 2. Strategy. We have already successfully applied this observing strategy to the galaxies M83 (GO-8234, Calzetti et al. 2000) and, using some of the filters, NGC5253 (GO-6524, Calzetti et al. 1997). The ionized gas emitting region is sim80--90^ in size in each galaxy 8, 21, perfectly matched to the Field-of- View of a WF chip. At the typical distance of our galaxies (Table 1), 1 WF pixel corresponds to 1.8 pc, sufficient to resolve young stellar clusters, which have half-light radii ~3 pc 22, 8. Photometry and colors of the the stellar population underlying the starburst will be provided by the other WFPC2 chips, and we will use the information to subtract this component from the starburst population. NGC4214 will be observed in HBeta and SII, and NGC5253 in OIII and SII. NGC3077 will be observed in the mid-UV (3, 000 Angstrom), V, and I filters, and in HBeta, OIII(5007), HAlpha, and SII(6717, 6731) (Table 2). The OIII will map the sub- arcsec distribution and intensity of gas photoionized by the most active star forming regions, and SII will trace the shock and low-ionization structures, and the SNRs 31. The OIII/HBeta vs. SII/HAlpha will discriminate shocked from low-ionization structures 5. For this type of study the OIII/HAlpha ratio 16 is inadequate because of its high sensitivity to dust reddening, which increasingly affects the youngest regions. As we already did for NGC5253 8, we will construct for NGC3077 and NGC4214 HBeta/HAlpha ratio maps to trace the dust reddening distribution of the ionized gas, which we will convert to reddening corrections for the stellar population via the recipe of Calzetti et al. (1997). These corrections will remove the age-reddening degeneracy from the stellar populations. At a ~3.5--4 Mpc distance, WFPC2 resolves the stellar clusters, but not the individual stars (except the brightest). We will thus derive ages of the starburst population(s) by comparing the reddening-corrected mid-UV, V, and I color-magnitude and color-color diagrams, and the number of ionizing photons from HAlpha with stellar population synthesis models (e.g., Starburst99, Leitherer et al. 1999, ApJS, 123, 3), a technique we successfully employed for NGC5253. The mid-UV flux at 3000 Angstrom is dominated by stars with M>5 M_\odot, probing star formation averaged over ~100 Myr with weak dependence on the metallicity and the IMF details 13. The V band maps the older stars, while the I band probes the red supergiants. The HAlpha emission maps the star formation over <10 Myr. Our proposed observations will map the age and age variations of the diffuse and clustered young stellar population in NGC3077 and NGC4214, in the range 0--1 Gyr and 0--100 Myr, respectively. The precision will be Deltaage/age=0.2--0.3 for the clusters and Deltaage/age=0.4-- 0.5 for the diffuse population 8, which is adequate for drawing a coherent picture of the star formation history in the starbursts. beginscriptsize begintableh begincenter Table 2: Existing and Requested HST Imagesendcenter begintabularlrrr Name & Archival Images & Requested Observations^a & Total Orbits , NGC3077 &None & F300W(1.0), F547M (0.4), F814W (0.3), F487N(1.6), & 6 , & & F656N(0.3), F502N(0.6), F673N(1.4) & , NGC4214 & F170W, F336W, F555W, F814W, & F487N(1.0), F673N(1.0) & 2, & F502N(OIII), F656N(HAlpha)& & , NGC5253^b & F170W, F255W, F547M, F814W, & F502N(0.7), F673N(1.3) & 2, & F656N(HAlpha), F487N(HBeta) & & , & & Grand Total & 10, endtabular Notes: ^a Requested orbits (including overheads) for each filter are indicated in parenthesis. ^b The following observations of NGC5253 were obtained as part of our own program GO-6524 (P.I.: Calzetti): F547M, F814W, F656N, F487N. We also have ground-based J, H, K images of this galaxy, and archival HST/NICMOS J, H, K, and PaAlpha data are available. endtable endscriptsize 3. Narrow-Band Imaging. The narrow-band filters F487N, F502N, F656N, and F673N will map the line emission of HBeta4861Angstrom, OIII5007Angstrom, HAlpha6563Angstrom+NII6548Angstrom, and SII6717, 6731Angstrom in these low- redshift objects. The (existing or proposed) broad-band images will be used for the continuum subtraction, a very successful method with WFPC2 thanks to its photometric stability 8, 6. Contamination of the HAlpha image from the NII6584Angstrom line emission in NGC3077 is not a concern as the metal line falls in the red wing of the F656N filter, thus contributing less than 1 total flux. We request to reach relatively faint surface brightnesses in HAlpha and HBeta, in order to use them for dust reddening correction of the stellar continuum. For the line emission of OIII and SII we request a more modest depth, to map the small-scale emission structure in the high surface brightness regions in the starburst; for the large-scale structure, we will use our (existing or planned) ground-based images. The average surface brightnesses of the nebular emission lines are F(hbeta)=5*10^-15, F(OIII)=5times10^-15, F(halpha)=2*10^-14, and F(SII)=10^-15 in units of erg s^-1 cm^-2 arcsec^-2, as derived from our ground-based images and/or large-aperture spectroscopy of the galaxies. These average values are conservative estimates, since the nebular gas will be clumped (and thus brighter) on small scales. Taking into account the contamination of the underlying stellar continuum, S/N=5--6 per pixel is achieved in 2, 500-- 3500 sec for HBeta and 500 sec for HAlpha (CR-SPLIT). For OIII and SII we request 1, 300 sec and 2, 500--3, 000 sec of exposure (CR- SPLIT), respectively, which will achieve S/N=3-- 3.5 per pixel for the average surface brightness (from the WFPC2 WWW exposure times calculator). 4. Broad- Band Imaging. The WFPC2 F300W, F547M, and F814W filters will be employed as mid -UV, ~V, and ~I for NGC3077. The three filters are selected to avoid strong emission lines in the passbands (e.g., HAlpha and OIII). The F300W is the best compromise between throughoput and dynamical range for the massive stars. It has a small red leak, which is not a concern for this project, since we aim at mapping young stellar populations. We select to use WFPC2 F300W imaging over the (more efficient) STIS UV imaging, because the STIS FOV is a factor of ~10 smaller in area than the active region in NGC3077, and would require ~3--4 times more exposure time to map it. The maximum tolerable uncertainty in the ages requires to determine colors of stellar clusters and diffuse population with an accuracy of ~0.2 mag. Drawing experience from our previous HST observations of NGC5253 and M83, and rescaling to NGC3077, we can achieve such accuracy with a 5 Sigma surface brightness detection limit of ABsimeq19.5 mag arcsec^-2 at 3000 Angstrom, 5500 Angstrom, and 8000 Angstrom, where the constant surface brightness with wavelength takes into account the blue spectral energy distribution of the starburst. This limit correponds to a 5 Sigma detection for a cluster of 2 main sequence B1-B2 stars at the distance of NGC3077 (V~25). S/N=5 per pixel for such magnitudes is obtained with exposures of 2400 sec in F300W, 800 sec in F547M, and 700 sec in F814W (CR-SPLIT). 5. IN SUMMARY, with a typical target orbital visibility of 52^m, a total of 10 orbits are required for guide star acquisitions, instrument set-ups, and sequence exposures. The 10 orbits are split between targets and filters as detailed in Table 2. Real Time Justification ----------------------- None. None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9144( 2) - 02/15/01 15:58 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5253 GALAXY, AMORPHOUS RA=13H 39M 56.00S +/- 0.5S, DEC= J2000 V=+404 V = 10.9 IRREGULAR, STARBURST -31D 38' 26.0" +/- 3", PLATE- B-V = 0.43 ID=02IZ Coordinate Source: GSC_SURVEY_PLATE 2 NGC4214 GALAXY, MAGELLANIC RA=12H 15M 39.78S +/- 0.2S, J2000 V=+291 V = 9.78 IRREGULAR, STARBURST DEC=36D 19' 37.5" +/- 1", PLATE- B-V = 0.46 ID=00Y2 Coordinate Source: GSC_SURVEY_PLATE 3 NGC3077 GALAXY, MAGELLANIC RA=10H 03M 19.16S +/- 0.2S, J2000 V=+14 V = 9.85 IRREGULAR, STARBURST DEC=68D 44' 01.3" +/- 1", PLATE- B-V = 0.76 ID=00M9 Coordinate Source: GSC_SURVEY_PLATE Comments: Center of Pa-alpha emission from NICMOS imaging. 9144( 2) - 02/15/01 15:58 - [ 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 NGC5253 WFPC2 IMAGE WF3-FIX F502N 5012 CR-SPLIT=NO 1 200 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC5253 WFPC2 IMAGE WF3-FIX F502N 5012 CR-SPLIT=NO 1 600 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC5253 WFPC2 IMAGE WF3-FIX F673N 6732 1 1200 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 50 NGC5253 WFPC2 IMAGE WF3-FIX F502N 5012 CR-SPLIT=NO 1 260 S POS TARG +0.5,+0.5 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 60 NGC5253 WFPC2 IMAGE WF3-FIX F502N 5012 CR-SPLIT=NO 1 800 S SAME POS AS 50 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 70 NGC5253 WFPC2 IMAGE WF3-FIX F673N 6732 CR-SPLIT=NO 1 1200 S SAME POS AS 50 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 9144( 2) - 02/15/01 15:58 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 110 NGC4214 WFPC2 IMAGE WFALL F487N 4865 CR-SPLIT=NO 1 1000 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 120 NGC4214 WFPC2 IMAGE WFALL F673N 6732 1 1200 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 130 NGC4214 WFPC2 IMAGE WFALL F487N 4865 1 1200 S POS TARG +0.5,+0.5 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 140 NGC4214 WFPC2 IMAGE WFALL F673N 6732 CR-SPLIT=NO 1 1100 S SAME POS AS 130 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 9144( 2) - 02/15/01 15:58 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 210 NGC3077 WFPC2 IMAGE WF3-FIX F300W 2943 1 1600 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 220 NGC3077 WFPC2 IMAGE WF3-FIX F300W 2943 CR-SPLIT=NO 1 800 S POS TARG 0.5, 0.5 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 230 NGC3077 WFPC2 IMAGE WF3-FIX F547M 5476 CR-SPLIT=NO 1 600 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 240 NGC3077 WFPC2 IMAGE WF3-FIX F814W 7921 CR-SPLIT=NO 1 300 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 250 NGC3077 WFPC2 IMAGE WF3-FIX F487N 4865 1 1400 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 300 NGC3077 WFPC2 IMAGE WF3-FIX F502N 5012 CR-SPLIT=NO 1 350 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 310 NGC3077 WFPC2 IMAGE WF3-FIX F502N 5012 CR-SPLIT=NO 1 600 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 320 NGC3077 WFPC2 IMAGE WF3-FIX F673N 6732 1 1400 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 350 NGC3077 WFPC2 IMAGE WF3-FIX F656N 6564 CR-SPLIT=NO 1 300 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 360 NGC3077 WFPC2 IMAGE WF3-FIX F656N 6564 CR-SPLIT=NO 1 800 S Comments: default positioning ------------------------------------------------------------------------------------------------------------------------------------ 370 NGC3077 WFPC2 IMAGE WF3-FIX F673N 6732 CR-SPLIT=NO 1 1400 S POS TARG +0.5,+0.5 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 9144( 2) - 02/15/01 15:58 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 400 NGC3077 WFPC2 IMAGE WF3-FIX F547M 5476 CR-SPLIT=NO 1 600 S POS TARG +0.5,+0.5 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 410 NGC3077 WFPC2 IMAGE WF3-FIX F814W 7921 CR-SPLIT=NO 1 400 S SAME POS AS 400 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 420 NGC3077 WFPC2 IMAGE WF3-FIX F487N 4865 CR-SPLIT=NO 1 1300 S SAME POS AS 400 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 450 NGC3077 WFPC2 IMAGE WF3-FIX F502N 5012 CR-SPLIT=NO 1 800 S POS TARG +0.5,+0.5 EXPAND MAX DUR 900 S Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 460 NGC3077 WFPC2 IMAGE WF3-FIX F656N 6564 CR-SPLIT=NO 1 800 S SAME POS AS 450 ------------------------------------------------------------------------------------------------------------------------------------ 470 NGC3077 WFPC2 IMAGE WF3-FIX F487N 4865 CR-SPLIT=NO 1 700 S SAME POS AS 450 Comments: Get (5, 5) pixels away to identify hot pixels ------------------------------------------------------------------------------------------------------------------------------------ 9144( 2) - 02/15/01 15:58 - [ 8] Summary Form for Proposal 9144 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WF3-FIX WFALL ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG +0.5,+0.5 SAME POS AS 50 SAME POS AS 130 POS TARG 0.5, 0.5 SAME POS AS 400 POS TARG +0.5,+0.5 EXPAND MAX DUR 900 S SAME POS AS 450 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F502N F673N F487N F300W F547M F814W F656N ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC5253 NGC4214 NGC3077 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 5012 6732 4865 2943 5476 7921 6564 ------------------------------------------------------------------------------------------------------------------------------------