Understanding the Role of Massive Stars in Galaxies at Cosmic Noon in a Legacy Spectroscopic Field

0 Assigned ID: 5399 ----- Attempting Submission 1 (Tue Mar 26 12:45:20 GMT 2024) ----- HST Phase I Proposal 5399 successfully submitted. Receipt: # 5399-1 ----- Attempting Submission 2 (Tue Mar 26 18:19:08 GMT 2024) ----- HST Phase I Proposal 5399 successfully submitted. Receipt: # 5399-2 ----- Attempting Submission 3 (Tue Mar 26 21:39:37 GMT 2024) ----- We are planning for 11 orbits of ACS imaging: 4 in f606w and 7 in f814. We split these into 2-3 orbit visits to help with scheduling. All of the imaging is done for the same target with PA requirment needed to fit all of the galaxies of interest in the ACS FOV. We use the same dither pattern for all the orbits, one large dither to cover the chip-gap and a sub-pattern 2pt sub-pixel line to help with subpixel sampling and cosmic ray rejection. Updated orient constraints based on TTRB Decision -887363424 ----- Attempting Submission 1 (Thu Aug 15 15:13:03 GMT 2024) ----- HST Phase II Proposal 17714 successfully submitted. Receipt: # 17714-1 ----- Attempting Submission 2 (Thu Apr 24 15:11:14 GMT 2025) ----- Understanding the Role of Massive Stars in Galaxies at Cosmic Noon in a Legacy Spectroscopic Field We propose to use new HST/ACS imaging in F606W and F814W to create high spatial resolution rest-UV maps for z~2 star-forming galaxies in the field surrounding luminous quasar Q2343+125. This field stands out in terms of spectroscopic investment, with deep (~10 hr) rest-UV spectra from Keck/LRIS, deep (~2-10 hr) rest-optical spectra from Keck/MOSFIRE, and ultra-deep (~30 hr) rest-optical and rest-NIR spectra from JWST/NIRSpec. This unique combination enables a detailed accounting of the ionizing spectra of massive stars using direct observations of their rest-UV continua and myriad HII emission lines spanning rest-frame ~0.3-1.1 micron. The proposed imaging will allow us to study the rest-UV morphology of these galaxies for the first time, thereby addressing two outstanding questions related to the distribution of massive stars in high-z galaxies: First, we will investigate the connection between ionization conditions and galaxy morphology. This study will serve as a bridge to understanding this connection at even higher redshifts, where knowledge of how the clustering of massive stars affects galaxies' ionizing output is urgently needed to determine their contribution to cosmic reionization. Second, we will use these data to provide improved guidance to the community about how best to combine space- and ground-based spectroscopy, which are often observed at very different spatial scales. A comparatively small investment of HST time will significantly enhance the legacy value of one of richest spectroscopic datasets of distant galaxies ever assembled and provide novel constraints on the properties of massive stars--and their impact on galaxies--at Cosmic Noon and beyond. We propose to obtain rest-UV imaging in two filters (F606W and F814W) over the footprint of the CECILIA JWST NIRSpec/MSA observations. The principal scientific goals of these observations are to perform resolved SED fitting and determine the rest-UV morphologies of z = 2 galaxies (Sec. 2) and improve slit-loss corrections (Sec. 3). We choose the F606W and F814W filters as they sample the rest-UV continuum from rest wavelength = 1500- 3000 angstrom of the targeted galaxies at z = 2 (see Fig. 1). We require two bands, in addition to the rest- optical F140W observations obtained as part of HST C24 GO 14620, in order to perform resolved SED fitting and study the relationship between ionization conditions and the distribution of star formation with a galaxy. Multiple bands are needed to successfully break the degeneracy between dust attenuation and star formation in the rest-UV (e.g., Miller et al., 2022). The parent galaxy sample has a median RAB = 24.58, with an interquartile range of R band mage = 24.12 - 25.01 at a median z = 2.4. The median semi-major (half-light) axis is 0.26 arcsec, with an axis ratio of b/a = 0.6. In order to perform resolved SED fitting and calculate accurate slit-loss corrections, we require a S/N per pixel of > 5 out to the effective radius. This corresponds to an integrated S/N > 20, above the suggested benchmark of S/N = 15 for traditional morphological analysis (e.g., Shibuya et al., 2015). Using the median properties of our sample and the HST/ACS ETC, we find that achieving this S/N requires 13 ks and 22 ks in the F606W and F814W filters, respectively. The orbital visibility of our target field is 52 min, so we request a total of 11 orbits: 4 in F606W and 7 in F814W PI Dr. Tim Miller is an expert in studying galaxy morphology and resolved stellar populations at Cosmic Noon, focusing on using HST and JWST imaging data. Co-PI Dr. Allison Strom and Co-I Dr. Gwen Rudie are Co-PIs of the Cycle 1 JWST program CECILIA (JWST GO 2593), and Co-Is Dr. Noah Rogers, Dr. Ryan Trainor, and Caroline von Raesfeld are actively involved in the data reduction and analysis. CECILIA has already delivered novel results based on the extremely deep rest-optical spectra of these galaxies, see Strom et al. (2023) and Rogers et al. (2024). Co-PIs Strom and Co-Is Rudie and Trainor also have extensive experience working with the Keck Baryonic Structure Survey (KBSS), which is the parent sample for CECILIA and comprises deep Keck/LRIS and Keck/MOSFIRE spectra of the galaxies targeted by the current proposal. In particular, Strom is an expert in determining slit-loss corrections, having developed the original MOSFIRE slit-loss correction technique for KBSS. Co-I Trainor led the previous HST/WFC3-IR program (C24 GO 14620) to create a deep F140W mosaic of the Q2343 field and performed the analysis to measure galaxy luminosities and morphologies in the rest-frame optical continuum. Co-PIs Strom and Co-Is Rogers, Rudie, Trainor, and von Raesfeld are experts in using emission line spectroscopy to study the gas properties and ionizing photon production of galaxies at z~2. Rogers and Strom are experts in gas-phase metallicity measurements. Rudie is an expert in studying the CGM. Trainor is an expert in studying the effects of massive stars and stellar feedback in galaxies. Von Raesfeld is an expert in using photoionization modeling to understand emission line strengths in high-z galaxies. Galaxies Stellar Populations and the Interstellar Medium 6 false false false false false false SUPPORTED GALAXY QUASAR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W POS-TARG DITHER DITHER 2 3.034 ACS-WFC-DITHER-LINE false false 0.149 2 85.29 POS-TARG ACS-WFC-DITHER-LINE 34.25 2

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