9134( 3) - 09/18/01 16:47 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9134 Version: 3 Check-in Date: 18-Sep-2001 16:46:48 1.Proposal Title: Giant H II Regions and the Connection with Starbursts and Diffuse Ionized Gas ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Donald Garnett University of Arizona ------------------------------------------------------------------------------------ 5. Abstract Giant H II regions in nearby galaxies are an intermediate link between energetic starbursts in distant galaxies and local star-forming complexes in the solar neighborhood. They provide an opportunity to study the connection between massive star formation regions, ionized supershells, and the diffuse ionized gas that pervades many star-forming galaxies. Although giant H II regions have been modeled extensively, key questions remain unresolved: (1) what is the connection between the giant H II region and the diffuse ionized gas? (2) how do Wolf-Rayet stars influence the observed spectrum of the H II region? (3) is there significant leakage of ionizing radiation from giant H II regions into the ISM? (4) are the observed emission line ratios and ionization structure consistent with predictions based on stellar photon fluxes? One important key to answering these questions is high resolution imaging of giant H II regions and the surrounding regions. Here I propose an imaging study of one of the nearest giant H II regions, NGC 604 in the spiral galaxy M33 with the WFPC-2. This object has extensive archival WFPC-2 imaging in broad-band filters and some emission lines. I will obtain new imaging in other important diagnostic lines (e.g. O II, S III, and HBeta) to provide a more accurate picture of the ionization structure, and compare the emission-line imaging with the known stellar populations and ionization modeling. ------------------------------------------------------------------------------------ 9134( 3) - 09/18/01 16:47 - [ 2] Observations Description ------------------------ The signal/noise estimates given below are based on the surface brightnesses of features observed in the archival F656N data and emission-line ratios measured by Di az et al. (1987; MNRAS 226, 19) for NGC 604. The WFPC2 Exposure Time Calculator was used to estimate the necessary exposure times. I assumed a visibility period of 53 minutes, minus ~ 10 minutes per orbit for acquisitions and overheads. This leaves approximately 2500 seconds per orbit available for exposures. The F656N image is a combination of two exposures of 1100 seconds each. I measured HAlpha surface brightnesses from seventeen positions in the bright inner nebula and in the diffuse gas 30-60 arcsec from the central region. For the diffuse gas, the surface brightnesses were in the range (1- 9)times10^-14 ergs cm^-2 s^-1 arcsec^-2. The S/N for these regions ranged from about 20 to > 100. The brightest regions in the central H II region had HAlpha surface brightnesses in the range (2-3)times10^-13 ergs cm^-2 s^-1 arcsec^-2. For purposes of exposure estimates we will consider only the DIG component - if the DIG has sufficient S/N the H II region will be very well exposed. Di az et al. (1987) measured values of HBeta/HAlpha ~ 0.25 (not corrected for reddening). From the ETC, we find that 3 orbits of exposure in F487N will yield S/N ~ 6-50 per pixel for the DIG component. This will be sufficient to provide good estimates of interstellar reddening for the bulk of the bright DIG. O II 3727/HAlpha was measured to be in the range 0.3-0.5 for the H II region by Di az et al. This ratio is expected to be much larger in the diffuse ionized gas; Galarza et al. (1999) typically observed O II/HAlpha in the range 0.5-1.5. We make the conservative assumption that O II/HAlpha = 0.5. In this case the ETC calculates that 6 non-CR-SPLIT exposures of 2500 seconds each in F375N will yield S/N ~ 3-25 per pixel for the DIG. I expect the actual S/N to be higher in many cases. The H II region-DIG interface will certainly be well-exposed. The Di az et al. spectra have S III 9532/HAlpha ratios in the range 0.15-0.30. Atmospheric water vapor absorption makes accurate measurement of S III 9532 difficult. Based on these values, the ETC calculates that 3 orbits of exposure in F953N will yield S/N ~ 4-35 per pixel for the diffuse gas. Again, in all three filters the bright central H II region and the brighter component of the diffuse gas will be well-exposed. The ionized gas complex is elongated and extends onto all four CCD frames in the archival data. To ensure that as much of the diffuse gas as possible is imaged, I will use the same pointing and orientation as the archival images. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9134( 3) - 09/18/01 16:47 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC604 EXT-MEDIUM, HII REGION, RA=01H 34M 34.97S +/- 1", J2000 SURF-LINE(3727)=2.5+/-2e-14 EXT-CLUSTER, OB DEC=30D 47' 10.0" +/- 1" SURF-LINE(4861)=1.25+/-1e-14 ASSOCIATION SURF-LINE(9532)=1.0+/-0.8e-14 Coordinate Source: HST_IMAGE Comments: Position and orientation to be the same as observations from program GO-5773. This is necessary to cover the same structures in NGC 604 as the archived data, since the target fills the WFPC2 field. 9134( 3) - 09/18/01 16:47 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 71D TO 75D On Hold Comments: Additional Comments: ORIENT of 73+/-2 is chosen to reproduce the pointing of the WFPC2 images from program 5773. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC604 WFPC2 IMAGE WFALL-F F487N CR-SPLIT=NO,ATD-GAIN=7 3 2700 S IX ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC604 WFPC2 IMAGE WFALL-F F658N 1 2600 S SAME POS AS 10 IX ------------------------------------------------------------------------------------------------------------------------------------ 9134( 3) - 09/18/01 16:47 - [ 5] Visit: 02 Visit Priority: Visit Requirements: SAME ORIENT AS 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC604 WFPC2 IMAGE WFALL-F F375N ATD-GAIN=7,CR-SPLIT=NO 3 2700 S IX ------------------------------------------------------------------------------------------------------------------------------------ 9134( 3) - 09/18/01 16:47 - [ 6] Visit: 03 Visit Priority: Visit Requirements: SAME ORIENT AS 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC604 WFPC2 IMAGE WFALL-F F375N ATD-GAIN=7,CR-SPLIT=NO 3 2700 S IX ------------------------------------------------------------------------------------------------------------------------------------ 9134( 3) - 09/18/01 16:47 - [ 7] Visit: 04 Visit Priority: Visit Requirements: SAME ORIENT AS 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC604 WFPC2 IMAGE WFALL-F F953N ATD-GAIN=7 3 2600 S IX ------------------------------------------------------------------------------------------------------------------------------------ 9134( 3) - 09/18/01 16:47 - [ 8] Summary Form for Proposal 9134 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ATD-GAIN=7 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 71D TO 75D SAME POS AS 10 SAME ORIENT AS 01 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F487N F658N F375N F953N ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC604 ------------------------------------------------------------------------------------------------------------------------------------