Gathering Galaxy Distances in Abundance with Roman Wide-Area Data

TL;DR

This paper discusses leveraging the Roman Space Telescope's wide-area survey capabilities to measure galaxy distances using the surface brightness fluctuation method, aiming to improve cosmological parameter estimates and galaxy property measurements.

Contribution

It proposes an optimized survey strategy with specific filter choices and coverage plans to efficiently gather high-quality galaxy distance data at large scales.

Findings

Potential to measure distances to thousands of galaxies out to hundreds of Mpc.

Independent estimate of the Hubble constant with negligible statistical error.

Competitive constraints on the parameter S8 for cosmology.

Abstract

The extragalactic distance scale is fundamental to our understanding of astrophysics and cosmology. In recent years, the surface brightness fluctuation (SBF) method, applied in the near-IR, has proven especially powerful for measuring galaxy distances, first with HST and now with a new JWST program to calibrate the method directly from the tip of the red giant branch (TRGB). So far, however, the distances from space have been gathered slowly, one or two at a time. With the Roman Space Telescope, we have the opportunity to measure uniformly high-quality SBF distances to thousands of galaxies out to hundreds of Mpc. The impact of these data on cosmology and galaxy studies depends on the specifics of the survey, including the filter selection, exposure depth, and (especially) the sky coverage. While the baseline HLWAS survey in four filters plus the grism would yield useful data, the impact would be limited by the relatively small area. A more optimal approach would concentrate on the most efficient passband (F146), adopt an exposure time sufficient to measure good quality distances well out into the Hubble flow, and then maximize the sky coverage within the total time constraints. Grism observations over the same area can provide the needed information on redshifts and spectral energy distributions for compact sources, while colors for larger objects can be obtained from lower resolution surveys. The proposed plan will enable accurate determination of the physical properties of thousands of nearby galaxies, an independent measure of the Hubble constant $H_0$ with negligible statistical error, and competitive constraints on $S_8{\,=\,}\sigma_8(\Omega_m/0.3)^{0.5}$. The resulting data set will be a phenomenal resource for a wide range of studies in astrophysics and cosmology.