0 Assigned ID: 752 ----- Attempting Submission 1 (Fri Mar 06 20:38:27 GMT 2020) ----- HST Phase I Proposal 752 successfully submitted. Receipt: # 752-1 ----- Attempting Submission 2 (Fri Mar 06 23:34:00 GMT 2020) ----- How did the most massive galaxies in the Universe form? Deep HST/ACS imaging has shown that a giant cluster galaxy in formation, the enigmatic Spiderweb Galaxy, is rapidly forming stars in-situ from a large reservoir of cold molecular gas across the intra-cluster medium. This proved to be the first observational support for predictions that giant cluster galaxies may condense out of accreted cold gas early in the history of the Universe. If this mode of in-situ star formation is common among massive high-z galaxies, then this may require us to revise our ideas about star formation and the early build-up of galaxies. We propose to analyze 12 orbits of WFC3 data of the one other Spiderweb-like galaxy for which deep 2-color imaging is available in the archive, namely 4C 41.17. This spectacular proto-cluster system is observed at z~4, which is the epoch where cosmic gas accretion peaks. The HST and complementary ALMA data show indications for filamentary accretion of cold gas, as well as diffuse star formation on scales of >100 kpc. Our goal is to carefully analyze the web of gas and young stars that make up the CGM/ICM, in order to gain new insights into the role that in-situ star formation plays in the early evolution of the most massive galaxies. The team of Dr. Emonts, Prof. Lehnert, and Dr. Yoon has an effective and long-standing collaboration, with sufficient expertise in HST imaging. They also have supervised three undergraduate students over the past year who were involved in their research at NRAO. The relatively close distance between NRAO Charlottesville and STScI will allow Dr. Emonts, Dr. Yoon, and their students to visit STScI when needed for optimizing the archival HST data for this project. Dr. Bjorn Emonts is an Associate Scientist at NRAO. He is an expert in radio interferometry and the ALMA data analysis that is complementary to this HST proposal. He also has a long track record of studying proto-cluster radio galaxies and the molecular CGM/ICM. He has some previously experience with optical ground-based imaging, and is currently reducing and analyzing low-surface-brightness continuum and H-alpha imaging of nearby radio galaxies from PI projects at the GTC 10m telescope. Dr. Emonts is a long-term student mentor for the National Astronomy Consortium (NAC) that serves undergraduate students from underrepresented groups in STEM, and he and Dr. Yoon are actively supervising students from both the nearby University of Virginia and other institutes. Prof. Matthew Lehnert works at the IAP in Paris, and is an expert in the use of HST. He has a long career involving studies of high-z galaxies and proto-clusters. His HST expertise for this project is evident from his leading work on the rest-frame UV imaging of high-z quasars (Lehnert et al. 1999, ApJS, 124, 11; Lehnert et al 1999, ApJS, 123, 351). Prof. Lehnert's experience regarding both the observations and theoretical aspects of similar projects will guarantee a successful completion of this small HST AR project. Dr. Ilsang Yoon is an Assistant Scientist at NRAO. He is an expert on radio interferometry and the complementary ALMA data analysis, as well as on modeling galaxy morphology structure. Dr. Yoon is a member of the Great Observatories All-sky LIRG Survey (GOALS) team and is actively supervising undergraduate students. Intergalactic Medium and the Circumgalactic Medium Galaxies 0 Regular false false false false false SUPPORTED