0 Assigned ID: 2831 ----- Attempting Submission 1 (Tue Mar 22 17:12:18 GMT 2022) ----- HST Phase I Proposal 2831 successfully submitted. Receipt: # 2831-1 ----- Attempting Submission 2 (Wed Mar 23 14:21:05 GMT 2022) ----- 0 ----- Attempting Submission 1 (Thu Jul 14 12:04:28 GMT 2022) ----- HST Phase II Proposal 17225 successfully submitted. Receipt: # 17225-1 ----- Attempting Submission 2 (Thu Jul 14 12:35:55 GMT 2022) ----- The (Ir)Regularities of Dust Attenuation in Star Forming Galaxies While dust constitutes a small fraction of a galaxy's interstellar medium, it has an outsized impact on its spectral energy distribution (SED) by reddening and attenuating the light from stars. The effects of dust are degenerate with those of the galaxy's star formation history, because stellar populations of different ages can be subject to different levels of attenuation in the presence of patchy dust. We propose to separate the variations of the ultraviolet-to-nearIR (UV-to-NIR) dust attenuation from those of the star formation history in star-forming galaxies, by leveraging the multi-wavelength and high resolution capabilities of HST. We will complement archival HST data with new ACS and WFC3 broad and narrow-band imaging to probe the SEDs of the stars and the hydrogen recombination lines of H-alpha and Pa-beta to model the spatially-resolved stellar populations, gas emission, and dust in five nearby galaxies hosting central starbursts. The five starbursts are selected based on their global far-infrared and UV emission properties, which deviate from those of typical starbursts in the local Universe, making them puzzling outliers. FUV (1600 Angstrom) to NIR (~1.6 micron) SEDs of individual star clusters and HII regions will provide necessary constraints to separate variations of stellar ages in patchy dust from variations of the shape and normalization of the dust attenuation curve. Our study will provide a benchmark for dust attenuation corrections directly applied to UV-to-NIR SEDs. This will remain the only viable option to derive physical parameters for the large high-redshift galaxy surveys produced by the JWST, Roman, Euclid, and ELTs. Target Selection: Our targets are selected to be starbursts with IRX values 2 sigma or more below those of the IRX-beta relation marked by the SB curve and to span a range in beta, to probe the attenuation curve along the locus marked by the SMC curve. We impose a distance limit of 10 Mpc to achieve spatial resolution better than 5 pc with HST. Observational Set--Up and Exposure Times. Instrument/filter combinations are chosen to complete the archival datasets and cover the full FUV-H range for each target. Our template source is a 5000 M_sun, 4 Myr old star cluster with a conservative A_V=1.5~mag (F(1600)=2.5x10-1 ~erg/s/cm^2/AA and Sigma(Pa-beta)=2x10^-16 erg/s/cm^2/arcse$^2 at 4.5 Mpc distance). ACS/SBC 2x2 mosaics in F150LP are planned for NGC4214 and NGC5236 to cover the UV--emitting starburst regions, while one pointing only is required for NGC3351. S/N=5 is expected to be achieved for the above template cluster in 600 s per mosaic tile in NGC4214 and NGC5236 and in 2,400 s for NGC3351 (located at twice the distance of the other two galaxies). WFC3/UVIS observations for NGC3351 (F218W), NGC4214 and NGC5236 (F275W), and NGC5253 (F657N+F547M) will be obtained with S/N>=10 for our template cluster in 2,500 s (F218W), 2,000 s (F275W), 2,000 s (F657N). WFC3/IR observations will be obtained for NGC5474 in F110W, F128N, F160W, with S/N>=10 in 900 s, 2300 s, and 900 s, respectively. F547M and F110W are observed with S/N>20 to ensure that the subtraction of the stellar continuum from the narrow-band filter does not dominate the noise budget. Each WFC3 exposure is divided into 3-4 dither patterns to remove CRs and fill the chip gap. The WFC3 UV/U and H-alpha exposures include 20 s post--flash. The S/N in the FUV is sufficient to discriminate between individual attenuation slopes to >5 sigma; the combination of SBC/F150LP, WFC3/F218W (or F225W) and F275W separates mean UV slopes from effects of the 2175 A bump to >10 sigma. The PI, Daniela Calzetti, is an expert on star formation and dust obscuration. She has extensive experience with HST imaging data, and both stellar population and dust modeling, from the UV to the IR. She has modeled spectral energy distributions of both whole galaxies and regions within galaxies. She has been/is the PI of multiple HST programs, including the Cycle 21 Treasury project LEGUS (Legacy ExtraGalactic UV Survey). Andrew Battisti is an expert in characterizing the dust attenuation curves of galaxies and in modeling galaxy spectral energy distributions at both high and low redshift from the UV to the far-infrared. He is a specialist of the spectral energy distribution fit code MAGPHYS, and has contributed improvements to the code. Irene Shivaei has extensive experience in studying dust properties of high-redshift galaxies at z~1-3. In particular, she investigates UV to far-IR spectral energy distribution and rest-frame optical spectra of z~2 galaxies to put constraints on the shape and normalization of dust attenuation curve in typical high-redshift star-forming galaxies and how the attenuation curve varies in different galaxy populations. As a member of JWST extragalactic GTO teams, her insight and expertise in the evolution of dust and gas will be beneficial to this project in the era of JWST and ELTs. Shivaei has experience with HST observations and data. Linda Smith is an expert on young star clusters, H II regions and starburst spectral synthesis. She is an experienced HST observer, particularly in the UV, and is part of the LEGUS collaboration. Elena Sabbi has nearly 20 years of expertise with HST photometry in crowded fields with ACS, NICMOS, WFPC2 and WFC3. Over this period of time Sabbi led several successful HST programs, including the Hubble Tarantula Treasury Project and the recent Galaxy UV Legacy Project, and the stellar photometry of the Legacy ExtraGalactic UV Survey. Sabbi is an established expert in star and cluster formation and evolution. Sean Linden has multi-year expertise in multiwavelength modeling of star clusters in dusty environments, including cluster populations in ultraluminout infrared galaxies. Galaxies 6 false false true false false false false false SUPPORTED GALAXY SPIRAL STARBURST This object was generated by the targetselector and retrieved from the NED database. Coordinates slightly (<0.5") updated using HST imaging. J2000 J2000 GALAXY SPIRAL STARBURST This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY MAGELLANIC IRREGULAR STARBURST This object was generated by the targetselector and retrieved from the NED database. J2000 J2000 GALAXY AMORPHOUS IRREGULAR STARBURST This object was generated by the targetselector and retrieved from the NED database. J2000 J2000 GALAXY SPIRAL STARBURST This object was generated by the targetselector and retrieved from the NED database. J2000 J2000 ACS/SBC Imaging No No F150LP WFC3/UVIS Imaging No No F218W ACS/SBC Imaging No No F150LP WFC3/UVIS Imaging No No F275W ACS/SBC Imaging No No F150LP WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F657N WFC3/UVIS Imaging No No F547M WFC3/IR Imaging No No F128N WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.179 LINE 0.116 false false 63.65 4 20.02 ACS-SBC-DITHER-BOX 1 false POS-TARG DITHER 0.173 LINE 2.414 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 3 false POS-TARG MOSAIC 28.801 LINE 32.957 false true 264.24 4 90.0 ACS-SBC-MOSAIC-BOX 4 false POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 5 false The scheduling data was generated by CASM 30.3. 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Extrapolation from F275W to F150LP uses most unfavorable case that source has a Lambda^(-2) spectral shape. The scheduling data was generated by CASM 30.3. 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CASM was run in Phase II mode. 1687999745000 85.0 (Tic-Visit :proposal-id 17225 :visit-id "03" :proposal-version -1 :trans-version "20220516" :date "14-Jul-2022 07:56:54.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "28" :si-bright-earth-limb-angle 20.0 :data-volume 74064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17225 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17225 :visit-id "03" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2763 :al-overhead-at-end 0 :internal-dur-at-end 117 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3165 :pcs-gap 0 ) true 1 0 The bright area in this galaxy has been already observed in SBC/F125LP (HST-GO-11579). Brightest pixel has flux: 3.615E-16 erg/s/cm^2/A. The scheduling data was generated by CASM 30.3. 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