! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! Id: 6524 ! ! For help call your Program Coordinator: Mutchler ! Phone: 410-338-1321 , E-mail: mutchler@stsci.edu Proposal_Information Title: WFPC2 Mapping of Dust Obscuration and Stellar Populations in Starburst Galaxies. Proposal_Category: GO Scientific_Category: GALAXIES & CLUSTERS Cycle: 6 Investigators PI_name: Daniela Calzetti PI_Institution: Space Telescope Science Institute CoI_Name: Ralph C. Bohlin CoI_Institution: Space Telescope Science Institute Contact: ! Y or N (designate at most one contact) CoI_Name: Donald R. Garnett CoI_Institution: University of Minnesota Contact: ! Y or N (designate at most one contact) CoI_Name: Anne L. Kinney CoI_Institution: Space Telescope Science Institute Contact: ! Y or N (designate at most one contact) CoI_Name: Claus Leitherer CoI_Institution: Space Telescope Science Institute Contact: Y ! Y or N (designate at most one contact) CoI_Name: Thaisa Storchi-Bergmann CoI_Institution: Instituto de Fisica, Universidade Federal Rio Grande do Sul Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) 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. Questions ! Free format text (please update) Observing_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: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: NGC5253 Alternate_Names: Description: GALAXY,AMORPHOUS IRREGULAR,STARBURST Position: RA=13H 39M 56.00S +/- 0.5S, DEC=-31D 38' 26.0" +/- 3" Equinox: 2000 RV_or_Z: V=+404 Epoch: Flux: V=10.9 B-V=0.43 Visits ! Section 6 Visit_Number: 1 Visit_Requirements: ORIENT 80D TO 90D ! Section 7.1 Exposure_Number: 1 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F487N Wavelength: 4865 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: Exposure_Number: 2 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F487N Wavelength: 4865 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: Exposure_Number: 3 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F656N Wavelength: 6564 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Exposure_Number: 4 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F656N Wavelength: 6564 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1500S Special_Requirements: Exposure_Number: 5 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F814W Wavelength: 7920 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 400S Special_Requirements: Exposure_Number: 6 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F814W Wavelength: 7920 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 180S Special_Requirements: Exposure_Number: 7 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F547M Wavelength: 5470 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 200S Special_Requirements: Exposure_Number: 8 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F547M Wavelength: 5470 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 600S Special_Requirements: Exposure_Number: 11 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F547M Wavelength: 5470 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 200S Special_Requirements: POS TARG 0.5,0.5 ! Section 7.2 Exposure_Number: 12 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F547M Wavelength: 5470 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 600S Special_Requirements: POS TARG 0.5,0.5 ! Section 7.2 Exposure_Number: 13 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F814W Wavelength: 7920 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 180S Special_Requirements: POS TARG 0.5,0.5 ! Section 7.2 Exposure_Number: 14 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F814W Wavelength: 7920 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 400S Special_Requirements: POS TARG 0.5,0.5 ! Section 7.2 Exposure_Number: 15 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F656N Wavelength: 6564 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: POS TARG 0.5,0.5 Exposure_Number: 16 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F656N Wavelength: 6564 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1100S Special_Requirements: POS TARG 0.5,0.5 Exposure_Number: 17 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F487N Wavelength: 4865 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 0.5,0.5 Exposure_Number: 18 Target_Name: NGC5253 Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F487N Wavelength: 4865 Optional_Parameters: CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 0.5,0.5 Data_Distribution ! Defaults indicated; change if desired Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 ! Only astronomers with very old 9- ! track tape drives should consider ! a blocking factor of 1 Ship_To: PI_Address ! STSCI or PI_Address or ! PI Address from Phase I is: ! ! 3700 San Martin Drive ! Baltimore ! 21218 ! ! Ship_Via: UPS ! UPS (2-day) or OVERNIGHT ! Overnight shipping done at PI expense Recipient_Email: ! Needed if Ship_To: is not PI_Address !