Galaxy evolution through infrared and submillimeter spectroscopy: Measuring star formation and black hole accretion with JWST and ALMA

Abstract

Rest-frame mid-to far-infrared (IR) spectroscopy is a powerful tool to study how galaxies formed and evolved, because a major part of their evolution occurs in heavily dust enshrouded environments, especially at the so-called Cosmic Noon (i.e. at 1<z<3). Using the calibrations of IR lines, recently updated with Herschel and Spitzer spectroscopy, we predict the expected fluxes of lines and features, with the aim to measure the star formation (SF) rate and the Black Hole Accretion (BHA) rate in intermediate to high redshift galaxies. On the one hand, the launch of the James Webb Space Telescope (JWST) in a short time, together with its mid-IR spectroscopic capability, will allow us for the first time a deep investigation of both the SF and the BHA obscured processes as a function of cosmic time. We make an assessment of the spectral lines and features that can be detected by JWST-MIRI in galaxies and Active Galactic Nuclei up to redshift z ∼ 3. We confirm the fine-structure lines of [MgIV]4.49µm and [ArVI]4.53µm as good BHA rate tracers for the 1 z 3 range, and we propose the [NeVI]7.65µm line as the best tracer for redshifts of z 1.5. We suggest the use of the [ArII]6.98µm and [ArIII]8.99µm lines to measure the SF rate, for z 3 and z 2, respectively, while the stronger [NeII]12.8µm exits the JWST-MIRI spectral range above z 1.2. At higher redshifts, the PAH features at 6.2µm and 7.7µm can be observed at z 3 and z 2.7, respectively. On the other hand, rest-frame far-IR spectroscopy is currently being collected in high redshift galaxies (z 3) since a few years with the Atacama Large Millimeter Array (ALMA). The observability of far-IR lines from ALMA depends on the frequency at which the line is redshifted, the higher the frequency the most difficult is observing the line, because of the decrease of atmospheric transmission. We confirm that the [CII]158µm line is a good tracer of the SF rate and can in most cases (0.9 z 2 and 3 z 9) be observed, and we propose the use of the combination of [OIII]88µm and [OI]145µm lines as an alternative SF rate tracer, that can be detected above z 3. We emphasize the importance of using multifeature analysis to measure both BHA and SFR, since individual tracers can be strongly dependent on the local ISM conditions and vary from source to source. We conclude, however, that the current and foreseen facilities will not be able to cover properly the peak of the obscured SF and BHA activities at the Cosmic Noon of galaxy evolution and a new IR space telescope, actively cooled to obtain very good sensitivities, covering the full IR spectral range from about 10µm to 300µm, will be needed.