14102( 2) - 23-Jul-2015 09:55:04 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14102 Version: 2 Check-in Time: 23-Jul-2015 09:55:04 STScI Edit Number: 0 Title The II Zw 40 Supernebula: 30 Doradus on Steroids ------------------------------------------------------------------------------------ Type Cycle GO 23 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Claus Leitherer Space Telescope Science Institute Y CoI: Dr. Janice C. Lee Space Telescope Science Institute N CoI: Dr. Emily Levesque University of Washington N ------------------------------------------------------------------------------------ Abstract We propose COS G140L spectroscopy of the enigmatic nearby blue compact dwarf galaxy II Zw 40. The galaxy hosts a nuclear super star cluster with a luminosity 10 times that of 30 Doradus, the most powerful giant HII region in the Local Group. The super star cluster has been suggested to be the ionizing source of a "supernebula" detected via its free-free radiation in the radio. The physical conditions, however, are much more complex, as demonstrated by the detection of the nebular He II and the mid-infrared line of [O IV] 25.9. These lines are unlikely to be related to hot stars and require a different powering source. II Zw 40 shares many similarities with the related blue compact dwarfs NGC 5253 and Henize 2-10, both of which have been studied extensively with HST, yet no ultraviolet spectroscopy has ever been obtained for II Zw 40. This small 4-orbit proposal will provide the necessary UV data to study the massive-star content directly. We will determine reddening, age, and the stellar initial mass function and perform a comparison with the local benchmark 30 Doradus. In particular we will investigate whether the hot stars are able to power the supernebula and the nebular high-excitation lines. Our modeling will utilize the latest generation of stellar evolutionary tracks with and without stellar rotation. If the stars fall short in terms of spectral hardness and luminosity, II Zw 40 may become the second candidate for a central black hole in a young starburst after Henize 2-10. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will use COS with the G140L (1105) grating to collect R ~ 3000 spectra in the wavelength range ~1120 A - 2150 A of the nuclear super star cluster of II Zw 40. Our target is labeled SSC-N in Figure 1. It is essentially a point source. Therefore the COS resolution will not be degraded. SSC-N accounts for ~90% of the total H-alpha luminosity of the nuclear clusters. SSC-S is south of SSC-N outside the radio supernebula. Its H-alpha luminosity is an order of magnitude lower than that of SSC-N. It will not be in the COS aperture. We carefully considered the trades between the G130M and G140L gratings, in particular for the 1105 and 1280 settings for G140L. Both gratings provide comparable S/N over the wavelengths of interest when rebinned to the same spectral resolution. Our choice is mainly driven by wavelength coverage in as few settings as possible. This argues in favor of G140L. As for 1105 vs. 1280, we opted for the former in order to have continuous coverage rather than a gap 14102( 2) - 23-Jul-2015 09:55:04 - [ 2] around Lyman-alpha. The proposed G140L data with R ~ 3000 and S/N > 10 in the wavelength range ~1120 A - 2150 A will allow us to study the stellar populations, the ISM kinematics and the dust properties. II Zw 40 has reliable GALEX data; therefore UV fluxes for estimating exposure times and evaluating target acquisition strategies are available. Essentially all the UV flux is concentrated in the central super star cluster, which will be fully encompassed by the circular 2.5" COS aperture. The 1500 A fluxes (column 8 of Table 1) were obtained from the GALEX magnitudes. As a consistency check, we also verified these fluxes by extrapolating the fluxes measured in optical spectra to the UV. We require a minimum S/N of 10 over most of the wavelength range. This is based on our prior extensive experience with HST UV spectra of star-forming galaxies. S/N = 10 will allow us to analyze the strong stellar-wind profiles and compare them with population synthesis models, model nebular Lyman-alpha, measure the outflow properties of the ISM from interstellar absorption lines, and determine the dust properties from the continuum shape. We will acquire the galaxies with a standard MIRROR-A NUV imaging acquisition, followed by time-tagged FUV spectra with the G140L grating using the 1105 setting. Accounting for all the overhead due to guide-star acquisitions and reacquisitions, target acquisition, detector/grating overhead and exposure times to reach S/N = 10 - 20, we find that four orbits are needed (column 9 of Table 1). The average orbit duration assumed is 3200 s. ------------------------------------------------------------------------------------ 14102( 2) - 23-Jul-2015 09:55:04 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 UGCA-116 GALAXY, EMISSION LINE RA=05H55M42.6450S +/- 0.3", J2000 Z = V = 11.46 +/- 0.5 F(1500)=6e-16 NEBULA, KNOT, STAR DEC=+03D23'32.23" +/- 0.3" 0.00263 FORMING REGION, STARBURST Reference Frame: Other: SIMBAD Extended: YES Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 14102( 2) - 23-Jul-2015 09:55:04 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 UGCA-116 COS/NUV ACQ/IMA PSA MIRRORA 1 15 S (15 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 UGCA-116 COS/FUV TIME-TA PSA G140L 1105 FP-POS=1, BUFFER-TIME=9000 1 2520 S G (2520 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 UGCA-116 COS/FUV TIME-TA PSA G140L 1105 FP-POS=2, BUFFER-TIME=9000 1 2920 S G (2920 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 UGCA-116 COS/FUV TIME-TA PSA G140L 1105 FP-POS=3, BUFFER-TIME=9000 1 2920 S G (2920 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 UGCA-116 COS/FUV TIME-TA PSA G140L 1105 FP-POS=4, BUFFER-TIME=9000 1 2920 S G (2920 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ UGCA-116 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE UGCA-116 2 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G UGCA-116 3 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G UGCA-116 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G UGCA-116 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G 14102( 2) - 23-Jul-2015 09:55:04 - [ 5] Summary Form for Proposal 14102 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=9000, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names UGCA-116 ------------------------------------------------------------------------------------------------------------------------------------