The uncertain interstellar medium of high-redshift quiescent galaxies: Impact of methodology by Raphaël Gobat et al. on Tuesday 29 November

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.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.14131v1