The uncertain interstellar medium of high-redshift quiescent galaxies: Impact of methodology

TL;DR

This study revisits FIR observations of high-redshift quiescent galaxies, revealing that dust mass estimates are highly sensitive to methodology, which complicates understanding star formation quenching processes.

Contribution

It demonstrates the impact of different FIR data extraction and conversion methods on dust mass estimates in high-redshift QGs, highlighting methodological uncertainties.

Findings

Dust mass estimates vary significantly with extraction method.

High dust fractions in early QGs remain plausible.

Methodological choices can alter dust fraction estimates by up to an order of magnitude.

Abstract

How much gas and dust is contained in high-redshift quiescent galaxies (QGs) is currently an open question with relatively few and contradictory answers, as well as important implications for our understanding of the nature of star formation quenching processes at cosmic noon. Here we revisit far-infrared (FIR) observations of the REQUIEM-ALMA sample of six z = 1.6 - 3.2 QGs strongly lensed by intermediate-redshift galaxy clusters. We measured their continuum emission using priors obtained from high resolution near-infrared (NIR) imaging, as opposed to focusing on point-source extraction, converted it into dust masses using a FIR dust emission model derived from statistical samples of QGs, and compared the results to those of the reference work. We find that, while at least the most massive sample galaxy is indeed dust-poor, the picture is much more nuanced than previously reported. In particular, these more conservative constraints remain consistent with high dust fractions in early QGs. We find that these measurements are very sensitive to the adopted extraction method and conversion factors: the use of an extended light model to fit the FIR emission increases the flux of detections by up to 50% and the upper limit by up to a factor 6. Adding the FIR-to-dust conversion, this amounts to an order of magnitude difference in dust fraction, casting doubts on the power of these data to discriminate between star formation quenching scenarios. Unless these are identified by other means, mapping the dust and gas in high-redshift QGs will continue to require somewhat costly observations.