6524( 5) - 03/28/96 08:38 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6524 Version: 5 Check-in Date: 28-Mar-1996 08:36:01 1.Proposal Title: WFPC2 Mapping of Dust Obscuration and Stellar Populations in Starburst Galaxies. ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle GALAXIES & CLUSTERS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Daniela Calzetti Space Telescope Science Institute CoI: Ralph C. Bohlin Space Telescope Science Institute N CoI: Donald R. Garnett University of Minnesota N CoI: Anne L. Kinney Space Telescope Science Institute N CoI: Claus Leitherer Space Telescope Science Institute Y CoI: Thaisa Storchi-Bergmann Instituto de Fisica, Universidade Federal N Rio Grande do Sul ------------------------------------------------------------------------------------ 6. Abstract We propose to obtain WFPC2 narrow and broad band filter images of the nearby starburst galaxy NGC5253. The galaxy starburst regions are resolved with HST, and we will map the spatial distribution of the massive stars and the ionized gas, in order to study how disruptive is the onset of a burst of star formation in a `quiescent' galactic environment, and how the subsequent evolution of the region is affected. Characteristics such as the inhomogeneity of the dust obscuration, the clumpiness and the age of the starforming regions, the spatial variation of the star formation rate, and the spatial coincidence between the ionizing stars and the ionized gas will be investigated. Where available, HST archival images of the target will be used in conjunction with the observations. The ultraviolet and high spatial resolution capabilities of the WFPC2 are essential for the success of the proposed research. ------------------------------------------------------------------------------------ 6524( 5) - 03/28/96 08:38 - [ 2] Observations Description ------------------------ The FOV of each WF Camera is about 1^ .2, which corresponds to a spatial scale of 1.7 kpc at a distance of 5 Mpc. This scale matches the typical extent of a burst of star formation (~ 1 kpc across). The WF pixel size of 0^ .1 corresponds to 2.4 pc, implying that regions down to about 6-7 pc can be resolved. The broad band UV filter F255W and optical filters F555W and F814W will map the stellar content of the galaxies. The F255W filter covers the wavelength region 2300-2900 Angstrom, where the WFPC2 throughput is still high; the Cameras' efficiency drops sharply only below 2100 Angstrom. The F255W is then the bluest UV filter which can be used with high efficiency. It has an almost negligible red leak: the contamination of the UV flux for a star with spectral type K0 is only 3.5\\%. Our UV-detected stars and star clusters will be typically bluer than a K0 spectral type. The intrinsic magnitudes and colors of young stellar clusters in the WFPC2 passbands will be derived from spectral synthesis models to compare with the observed colors. The three filters have been selected to cover a large wavelength range to disentangle the effects of dust obscuration. From the comparison of intrinsic and observed colors and magnitudes, we will derive the reddening and the physical properties of the clusters. The narrow band images F487N and F656N will map the distribution of the ionized gas via the H Alpha(Lambda6563) emission and the spatial variations of the dust obscuration via the H Alpha/H Beta\\ ratios. Subtraction of the stellar continuum from the narrow band filters will be obtained using the broad band images. A detailed study of the hot star content of the galaxies requires the detection of O and early B stars down to spectral types B1-B2 in the F255W filter. Main sequence B1-B2 stars have M_2500~-3.5, which at the distance modulus = 28 of our target corresponds to m_2500=24.5. At these wavelengths, the sky has typical brightness m_2500=31 mag/pix in the WF camera. A S/N=3 per WF pixel (equal S/N>5 for the source) for a point source with m_2500=24.5 is obtained in 70 minutes, taking into account the noise produced by 4 read-outs (section 6 of the WFPC2 Manual). The HST archival images of NGC 5253 (R. Fesen, private communication) obtain the same S/N in 110 minutes, with 9 read-outs. These images are slightly dithered. The nucleus of the galaxy is placed in the WF3 Camera.The images will become non-proprietary in June 1996, and we will use them as integral part of our program. Our observations in the other filters will closely match, in pointing and orientation, the UV images. The depth of the UV images is matched by the two optical broad band filters, F547M and F814W, with much shorter exposures. In these filters the sky has magnitudes V=28 mag/pix and I=27.5 mag/pix. For the background due to unresolved stars in the host galaxies, we will assume the conservative estimate of about 26 mag/pix in both filters. Exposure times of 20 minutes and 15 minutes in F547M and F814W, respectively, give S/N=3 per WF pixel for stars of V=I=25.8, with 2 read -outs per filter. From our spatially integrated optical spectra (over a region 10^prime *20^ ) the typical nebular fluxes are: F(hbeta)~10^-14 erg/sec/cm^2/arcsec^2 and F(halpha)=4*10^-14 erg/sec/cm^2/arcsec^2. These average values are very conservative, since nebular gas is clumped around hot star clusters. The H Beta\\ and H Alpha\\ emission will be mapped with the F487N and the F656N filters, respectively. The F656N filter is narrow enough that the NII(6584 Angstrom) emission will be outside the band at the redshift of all the galaxies (see Table 1). Calculations for exposure times of emission lines follow from section 6.5 of the WFPC2 manual. A H Alpha\\ flux 50 times fainter than the above average value will be detected in the F656N filter with S/N=3 over an area 0.2^prime *0.2^ in 50 minutes. With the same amount of time and over the same area, a S/N=3 will be attained in the F487N filter for a H Beta\\ flux about 4 times fainter than the average value. In both calculations, the noise from three read-outs has been included. With a typical target orbital visibility of 52^m, 5 orbits per galaxy are required for guide star acquisition, instrument set-ups, and sequence exposures. Since we will be using archival F255W images for NGC 5253, only 3 orbits are needed to observe this galaxy in the remaining filters. The proposed investigation requires a total of 13 orbits. Real Time Justification ----------------------- There are no special requirements. No supporting observations are required. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6524( 5) - 03/28/96 08:38 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6524( 5) - 03/28/96 08:38 - [ 4] TARGET LIST a) 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= 2000 V=+404 V = 10.9 IRREGULAR,STARBURST -31D 38' 26.0" +/- 3" B-V = 0.43 6524( 5) - 03/28/96 08:38 - [ 5] Visit: 01 Visit Requirements: ORIENT 80D TO 90D 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 NGC5253 WFPC2 IMAGE WF3-FIX F487N 4865 CR-SPLIT=NO 1 1200S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC5253 WFPC2 IMAGE WF3-FIX F487N 4865 CR-SPLIT=NO 1 1300S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC5253 WFPC2 IMAGE WF3-FIX F656N 6564 CR-SPLIT=NO 1 500S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC5253 WFPC2 IMAGE WF3-FIX F656N 6564 CR-SPLIT=NO 1 1500S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC5253 WFPC2 IMAGE WF3-FIX F814W 7920 CR-SPLIT=NO 1 400S ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC5253 WFPC2 IMAGE WF3-FIX F814W 7920 CR-SPLIT=NO 1 180S ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC5253 WFPC2 IMAGE WF3-FIX F547M 5470 CR-SPLIT=NO 1 200S ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC5253 WFPC2 IMAGE WF3-FIX F547M 5470 CR-SPLIT=NO 1 600S ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC5253 WFPC2 IMAGE WF3-FIX F547M 5470 CR-SPLIT=NO 1 200S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC5253 WFPC2 IMAGE WF3-FIX F547M 5470 CR-SPLIT=NO 1 600S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 13 NGC5253 WFPC2 IMAGE WF3-FIX F814W 7920 CR-SPLIT=NO 1 180S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 14 NGC5253 WFPC2 IMAGE WF3-FIX F814W 7920 CR-SPLIT=NO 1 400S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC5253 WFPC2 IMAGE WF3-FIX F656N 6564 CR-SPLIT=NO 1 500S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 16 NGC5253 WFPC2 IMAGE WF3-FIX F656N 6564 CR-SPLIT=NO 1 1100S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 17 NGC5253 WFPC2 IMAGE WF3-FIX F487N 4865 CR-SPLIT=NO 1 1300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 18 NGC5253 WFPC2 IMAGE WF3-FIX F487N 4865 CR-SPLIT=NO 1 1300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 6524( 5) - 03/28/96 08:38 - [ 6] Summary Form for Proposal 6524 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 80D TO 90D POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F487N F656N F814W F547M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC5253 ------------------------------------------------------------------------------------------------------------------------------------