The Scaling Relations of Galaxies in the Infrared

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

Observations with the new Atacama Large Millimeter-submillimeter Array (ALMA) facility, and with the next generation James Webb Space Telescope (JWST), will soon enable measurement of the star formation rate and the total available mass of gas contained in galaxies at high redshifts, providing critical information for studies of the growth of galaxies across cosmic time. These two measurements are made using different regions of the galaxy's spectrum. This work will determine how the numbers are related, and whether there are meaningful causal connections. This is essential to understanding how reliably these sorts of studies can actually derive physical parameters for the observed galaxies. The project has an integrated educational component: (1) summer research opportunities for undergraduate students from the surrounding area, exposing them to cutting-edge research; and (2) research experiences for teachers from local middle and elementary schools, helping to align them with the new "content driven" testing standards set by the State of Massachusetts, and with the requirements of the national Next Generation Science Standards. The synergy between ALMA and JWST will return the star formation rate (SFR) and gas mass (M_gas) of galaxies across the full range of luminosity and physical parameters at high redshifts, thus shedding light on the efficiency of star formation and the growth of galaxies as a function of cosmic time. Commonly, the SFR is derived from the "blue" side of the infrared spectral energy distribution (IR SED) of the dust, while M_gas is derived from the "red" side of the IR SED. However, the dichotomy between "blue" and "red" sides is artificial, and IR colors and monochromatic luminosities show correlations with each other. If there are underlying covariances, then they may be either helpful or detrimental to the use of the IR SED for deriving physical parameters. This project will determine such covariances, including their strengths, and establish whether they are physical (causal correlations) or trivial (such as some common cause) in nature. Bayesian inference methods applied to the ALMA and other archives will uncover and investigate covariances, to (1) investigate the correlation between mid-IR and far-IR/mm colors in a sample of nearby galaxies; (2) establish how well, and under what assumptions, physical models of dust emission account for the observed color-color correlation; and (3) establish whether the IR SED color-color correlation implies covariance between luminosities. The results will provide prescriptions for application to high redshift galaxies, specifically, recipes for deriving unbiased SFRs and M_gas from the IR SED and for extrapolating missing IR SED data in distant galaxies where issues of completeness, depth, and confusion become important. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.