Exploring the Evolution of Star Formation and Dwarf Galaxy Properties with JWST/MIRI Serendipitous Spectroscopic Surveys

Abstract

The James Webb Space Telescope ’s Medium Resolution Spectrometer (MRS), will offer nearly two orders of magnitude improvement in sensitivity and >3×  improvement in spectral resolution over our previous space-based mid-IR spectrometer, the Spitzer IRS. In this paper, we make predictions for spectroscopic pointed observations and serendipitous detections with the MRS. Specifically, pointed observations of Herschel sources require only a few minutes on source integration for detections of several star-forming and active galactic nucleus lines, out to z  = 3 and beyond. But the same data will also include tens of serendipitous 0 ≲  z  ≲ 4 galaxies per field with infrared luminosities ranging ∼10 6 –10 13 L ☉ . In particular, for the first time and for free we will be able to explore the L IR  < 10 9 L ☉ regime out to z  ∼ 3. We estimate that with ∼ 100 such fields, statistics of these detections will be sufficient to constrain the evolution of the low- L end of the infrared luminosity function, and hence the star formation rate function. The above conclusions hold for a wide range in the potential low- L end of the IR luminosity function, and account for the PAH deficit in low- L , low-metallicity galaxies.