We Must Preserve Hubble given its Unique Complementarity to Webb, Roman, and Euclid

Abstract

We present compelling arguments -- focusing on galaxy science -- for preserving the main imagers and operational modes of the Hubble Space Telescope (HST) for as long as is technically feasible, to assure maximum complementarity to the James Webb Space Telescope (JWST), Roman, and Euclid. HST was designed to work well over the 0.1-1.6 $\mu$m wavelength range, and its unique UV-optical performance has fundamentally contributed to our understanding of galaxy assembly and the Cosmic Star Formation History (CSFH). While star-formation started at redshifts $z \gtrsim 10$, when the universe was less than 500 Myr old, the CSFH did not peak until $z \simeq 1.9$ (i.e., about 10 Gyr ago), and has steadily declined since that time. Hence, at least half of all stars in the universe formed it in the last 10 Gyrs where HST provides its unique rest-frame UV view of unobscured young, massive stars tracing cosmic star-formation, as well as unobscured Active Galactic Nuclei (AGN). HST thus uniquely probes (unobscured) young, hot, massive stars and AGN in galaxies, while JWST, Euclid and Roman reveal more advanced stages of older stellar populations, as well as relatively short-lived phases where galaxies produce and shed a lot of dust from intense star-formation, dusty AGN, and the very high redshift universe ($z \gtrsim 10$) not accessible by HST. HST is thus highly complementary to these other facilities, all of which took decades to build to ensure decades of operation. To maximize return on investment in these facilities, ways will need to be found to operate HST imaging instruments in all relevant modes for as long as possible into the JWST and Roman missions.