Dust and gas in star-forming galaxies at z ~ 3

Extending galaxy uniformity to 11.5 billion years^⋆

¹ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Mariesvej 30, 2100 Copenhagen, Denmark
e-mail: magdis@dark-cosmology.dk
² Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, 15236 Athens, Greece
³ Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
⁴ Space Science & Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
⁵ CEA, Laboratoire AIM, Irfu/SAp, 91191 Gif-sur-Yvette, France
⁶ Aix-Marseille Univ., CNRS, LAM, Laboratoire d’Astrophysique de Marseille, 13013 Marseille, France
⁷ INAF Observatory of Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy
⁸ Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Falmer, Brighton BN1 9QH, UK
⁹ Instituto de Astrofisica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
¹⁰ Universidad de La Laguna, Dpto. Astrofisica, 38206 La Laguna, Tenerife, Spain
¹¹ NOAO, 950 N. Cherry Avenue, Tucson, AZ 85719, USA
¹² National Astronomical Observatories of China, Chinese Academy of Sciences, 100012 Beijing, PR China
¹³ China-Chile Joint Center for Astronomy, Chinese Academy of Sciences, Camino El Observatorio, 1515 Las Condes, Santiago, Chile
¹⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Received: 25 April 2017
Accepted: 15 May 2017

Abstract

We present millimetre dust emission measurements of two Lyman-break galaxies at z ~ 3 and construct for the first time fully sampled infrared spectral energy distributions (SEDs), from mid-IR to the Rayleigh-Jeans tail, of individually detected, unlensed, UV-selected, main sequence (MS) galaxies at z = 3. The SED modelling of the two sources confirms previous findings, based on stacked ensembles, of an increasing mean radiation field ⟨ U ⟩ with redshift, consistent with a rapidly decreasing gas metallicity in z> 2 galaxies. Complementing our study with CO[J = 3 → 2] emission line observations, we have measured the molecular gas mass reservoir (M_H2) of the systems using three independent approaches: 1) CO line observations; 2) the dust to gas mass ratio vs. metallicity relation; and 3) a single band, dust emission flux on the Rayleigh-Jeans side of the SED. All techniques return consistent M_H2 estimates within a factor of two or less, yielding gas depletion time-scales (τ_dep ≈ 0.35 Gyr) and gas-to-stellar mass ratios (M_H2/M_∗ ≈ 0.5−1) for our z ~ 3 massive MS galaxies. The overall properties of our galaxies are consistent with trends and relations established at lower redshifts, extending the apparent uniformity of star-forming galaxies over the last 11.5 billion years.