The interstellar medium of quiescent galaxies and its evolution with time

¹ Cosmic Dawn Center (DAWN), Copenhagen, Denmark
e-mail: geoma@space-dtu.dk
² DTU-Space, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
³ Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, 2100 Copenhagen Ø, Denmark
⁴ Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso, Chile
⁵ CEA, IRFU, DAp, AIM, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, CNRS, 91191 Gif-sur-Yvette, France
⁶ Istituto Nazionale di Astrofisica, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁷ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁸ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
⁹ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA

Received: 23 August 2020
Accepted: 18 December 2020

Abstract

We characterise the basic far-IR properties and the gas mass fraction of massive (⟨log(M_*/M_⊙)⟩ ≈ 11.0) quiescent galaxies (QGs) and explore how these evolve from z = 2.0 to the present day. We use robust, multi-wavelength (mid- to far-IR and sub-millimetre to radio) stacking ensembles of homogeneously selected and mass complete samples of log(M_*/M_⊙)≳10.8 QGs. We find that the dust to stellar mass ratio (M_dust/M_*) rises steeply as a function of redshift up to z ∼ 1.0 and then remains flat at least out to z = 2.0. Using M_dust as a proxy of gas mass (M_gas), we find a similar trend for the evolution of the gas mass fraction (f_gas), with z > 1.0 QGs having f_gas ≈ 7.0% (for solar metallicity). This f_gas is three to ten times lower than that of normal star-forming galaxies (SFGs) at their corresponding redshift but ≳3 and ≳10 times larger compared to that of z = 0.5 and local QGs. Furthermore, the inferred gas depletion time scales are comparable to those of local SFGs and systematically longer than those of main sequence galaxies at their corresponding redshifts. Our analysis also reveals that the average dust temperature (T_d) of massive QGs remains roughly constant (⟨T_d⟩ = 21.0 ± 2.0 K) at least out to z ≈ 2.0 and is substantially colder (ΔT_d ≈ 10 K) compared to that of SFGs. This motivated us to construct and release a redshift-invariant template IR SED, that we used to make predictions for ALMA observations and to explore systematic effects in the M_gas estimates of massive, high-z QGs. Finally, we discuss how a simple model that considers progenitor bias can effectively reproduce the observed evolution of M_dust/M_* and f_gas. Our results indicate universal initial interstellar medium conditions for quenched galaxies and a large degree of uniformity in their internal processes across cosmic time.