16513( 8) - 25-Oct-2022 16:48:15 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16513 Version: 8 Check-in Time: 25-Oct-2022 16:48:15 STScI Edit Number: 2 Title The resolved PAH properties at low metallicity ------------------------------------------------------------------------------------ Type Cycle GO 28 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Julia Christine Roman-Duval Space Telescope Science Institute Y CoI: Dr. Bruce T. Draine Princeton University N CoI: Dr. Karl D. Gordon Space Telescope Science Institute N CoI: Dr. Aleksandra Hamanowicz Space Telescope Science Institute N CoI: Dr. Christopher Clark Space Telescope Science Institute N CoI: Dr. Martha L. Boyer Space Telescope Science Institute N CoI: Dr. Karin Marie Sandstrom University of California - San Diego N CoI: Dr. Benjamin F. Williams University of Washington N CoI: Dr. Jeremy Chastenet Ghent University N ------------------------------------------------------------------------------------ Abstract The NIR-MIR SED of galaxies is dominated by spectral features from polycyclic aromatic hydrocarbon (PAH) molecules fluorescing in regions illuminated by FUV photons. In low metallicity systems (Z < 0.2 Zo), previous studies with Spitzer have revealed a substantial deficiency in the emission and abundance of PAHs, the origin of which remains unexplained due to the lack of deep, resolved, multi-band photometry or spectroscopy. We will obtain NIRCam and MIRI imaging to observe the 3.3, 7.7, and 11.3 micron PAH features in dusty star-forming regions in two low metallicity galaxies, IC 1613 (15% solar) and Sextans A (8% solar). Additionally, we will obtain HST/WFC3 imaging with F275W, F336W, F475W, and F814W to complement the JWST observations. The HST observations will allow us to derive extinction maps, which will be used to normalize the PAH abundance to that of big grains. To obtain the extinction maps, we will fit the NUV-NIR SED of thousands of stars in the HST and JWST images with the BEAST code (Gordon+2016) in order to constrain the stellar mass, age and dust extinction (A_V) toward each sight-line. A_V measurements toward individual stars will be combined on the sky to produce the extinction maps. The observations will allow us to 1) estimate the PAH properties, particularly their abundance, ionized fraction, and size distribution; and 2) correlate those properties with other tracers of the ISM, such as the star formation rate density, the distance and UV spectrum of massive stars, the distance to PAH-producing stellar sources, the ISM column density of gas and dust, and gas-phase abundances. By observing how the PAH properties and abundance vary with environment, we will constrain the mechanisms responsible for the formation, destruction, excitation, and low abundance of PAHs in those poorly shielded low metallicity environments. Since JWST will measure star formation rates as low as 10 Mo/yr from PAH emission at the peak of cosmic star formation at redshift z~2 when the average metallicity of the universe was about 10% solar, it is crucial that we deepen our physical understanding of PAHs at low metallicity. ------------------------------------------------------------------------------------ Observations Description 16513( 8) - 25-Oct-2022 16:48:15 - [ 2] ------------------------ This program will obtain WFC3/UVIS imaging of the dusty star-forming regions in IC 1613 (15% solar) in order to map extinction. The filters (F275W, F336W, F475W, F814W) were selected to cover the NUV-optical stellar + dust SEDs so as to disentangle stellar mass from reddening. This program is designed to support JWST GO-2391 (a joint JWST-HST program). The HST NUV-optical imaging will complement the NIRCam and MIRI imaging. We will obtain single fields centered on the dustiest star-forming regions where PAH emission was previously detected with Spitzer. We will use the WFC3-UVIS-GAP-LINE dither to cover the chip gap for the most sensitive filters for which we are getting 2 exposures (F475W, F814W). We do not expect saturation in those filters. We will use a custom box dither pattern (a hydrid pattern covering the gap and providing sub-pixel sampling) for the less sensitive filters that require 4 exposures (F275W, F336W). The parameters of the custom dither pattern are explained in the associated comments. Exposure times were computed to reach a S/N of 10 for A5 stars with A_V = 1. ------------------------------------------------------------------------------------ 16513( 8) - 25-Oct-2022 16:48:15 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 IC-1613 GALAXY, MAGELLANIC RA=01H05M0.9264S, J2000 V = 9.9 IRREGULAR, STAR FORMING DEC=+02D09'16.21" REGION Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 16513( 8) - 25-Oct-2022 16:48:15 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-GAP-LINE Pattern_Purpose MOSAIC Number_Of_Points 2 Point_Spacing 2.414 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 85.759 Angle_Between_Sides Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 2.414 Line_Spacing 0.1448 Coordinate_Frame POS-TARG Pattern_Orient 85.759 Angle_Between_Sides 38.92 Center_Pattern NO Pattern_Comments: For the custom dither pattern, the coordinates of the 4 points are (-2.25, -30.25), (2.25, 30.25), (-0.25, 27.75), (-4.75, -32.75). The first line is the same as the WFC3-UVIS-GAP-LINE, and the second line is parallel to the first, with the points offset by -2.5 pix in x and -2.5 pix in y. Using the a11, b10, and b11 coefficients given in the ISR https://www.stsci.edu/files/live/sites/www/files/home/hst/instrumentation/wfc3/documentati on/instrument-science-reports-isrs/_documents/2010/WFC3-2010-09.pdf, we get the parameters of the dither pattern: Point spacing = sqrt( (4.5a11)**2 + (4.5b11 + 60.5b10)**2)) = 2.41 arcsec (same as gap line, that makes sense) Line spacing = sqrt( (2.5a11)**2 + (2.5b10 + 2.5b11)**2) = 0.1448 arcsec (not the same as the uvis box line spacing) Pattern orient alpha = arctan( (60.5b10 + 4.5b11)/(4.5a11)) = 85.758 deg (same as gap line, expected) Gamma = arctan ( (2.5b10 + 2.5b11)/(-2.5a11) ) = -46.84 deg Angle between sides = beta = alpha + gamma = 38.92 deg. ------------------------------------------------------------------------------------------------------------------------------------ 16513( 8) - 25-Oct-2022 16:48:15 - [ 5] 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 IC-1613 WFC3/UVI ACCUM UVIS F475W FLASH=19 1 20 S (20 S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 IC-1613 WFC3/UVI ACCUM UVIS F475W FLASH=6 1 560 S PATTERN 1 2 S (1120 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 IC-1613 WFC3/UVI ACCUM UVIS F814W FLASH=2 1 520 S PATTERN 1 3 S (1040 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 IC-1613 WFC3/UVI ACCUM UVIS F275W FLASH=18 1 580 S PATTERN 2 4 S (2320 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 IC-1613 WFC3/UVI ACCUM UVIS F336W FLASH=18 1 580 S PATTERN 2 5 S (2320 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 | ------------------------------------------------------------------------------------------------------------------------------------ IC-1613 1 WFC3/UVI ACCUM UVIS F475W none none none none 1 N/A S IC-1613 2 WFC3/UVI ACCUM UVIS F475W 1 none none none 1 N/A S IC-1613 2 WFC3/UVI ACCUM UVIS F475W 2 none none none 1 N/A S IC-1613 3 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 N/A S IC-1613 3 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 N/A S IC-1613 4 WFC3/UVI ACCUM UVIS F275W 1 none none none 2 N/A S IC-1613 4 WFC3/UVI ACCUM UVIS F275W 2 none none none 2 N/A S IC-1613 4 WFC3/UVI ACCUM UVIS F275W 3 none none none 2 N/A S IC-1613 4 WFC3/UVI ACCUM UVIS F275W 4 none none none 2 N/A S IC-1613 5 WFC3/UVI ACCUM UVIS F336W 1 none none none 3 N/A S 16513( 8) - 25-Oct-2022 16:48:15 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ IC-1613 5 WFC3/UVI ACCUM UVIS F336W 2 none none none 3 N/A S IC-1613 5 WFC3/UVI ACCUM UVIS F336W 3 none none none 3 N/A S IC-1613 5 WFC3/UVI ACCUM UVIS F336W 4 none none none 3 N/A S 16513( 8) - 25-Oct-2022 16:48:15 - [ 7] Visit: 02 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 IC-1613 WFC3/UVI ACCUM UVIS F475W FLASH=19 1 20 S (20 S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 IC-1613 WFC3/UVI ACCUM UVIS F475W FLASH=6 1 560 S PATTERN 1 2 S (1120 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 IC-1613 WFC3/UVI ACCUM UVIS F814W FLASH=7 1 520 S PATTERN 1 3 S (1040 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 | ------------------------------------------------------------------------------------------------------------------------------------ IC-1613 1 WFC3/UVI ACCUM UVIS F475W none none none none 1 N/A S IC-1613 2 WFC3/UVI ACCUM UVIS F475W 1 none none none 1 N/A S IC-1613 2 WFC3/UVI ACCUM UVIS F475W 2 none none none 1 N/A S IC-1613 3 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 N/A S IC-1613 3 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 N/A S 16513( 8) - 25-Oct-2022 16:48:15 - [ 8] Visit: 03 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 IC-1613 WFC3/UVI ACCUM UVIS F475W FLASH=19 1 20 S (20 S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 IC-1613 WFC3/UVI ACCUM UVIS F475W FLASH=6 1 560 S PATTERN 1 2 S (1120 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 IC-1613 WFC3/UVI ACCUM UVIS F814W FLASH=7 1 520 S PATTERN 1 3 S (1040 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 | ------------------------------------------------------------------------------------------------------------------------------------ IC-1613 1 WFC3/UVI ACCUM UVIS F475W none none none none 1 N/A S IC-1613 2 WFC3/UVI ACCUM UVIS F475W 1 none none none 1 N/A S IC-1613 2 WFC3/UVI ACCUM UVIS F475W 2 none none none 1 N/A S IC-1613 3 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 N/A S IC-1613 3 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 N/A S 16513( 8) - 25-Oct-2022 16:48:15 - [ 9] Summary Form for Proposal 16513 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=18, FLASH=19, FLASH=2, FLASH=6, FLASH=7 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 2, PATTERN 1 3, PATTERN 2 4, PATTERN 2 5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F275W, F336W, F475W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names IC-1613 ------------------------------------------------------------------------------------------------------------------------------------