Dark matter fraction in z  ∼  1 star-forming galaxies

¹ SISSA International School for Advanced Studies, Via Bonomea 265, 34136 Trieste, Italy
e-mail: 7.gaurisharma@gmail.com
² GSKY, INFN-Sezione di Trieste, via Valerio 2, 34127 Trieste, Italy
³ IFPU Institute for Fundamental Physics of the Universe, Via Beirut, 2, 34151 Trieste, Italy
⁴ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Wien, Austria

Received: 10 February 2021
Accepted: 27 May 2021

Abstract

Context. The study of dark matter (DM) across cosmic timescales is essential for understanding galaxy formation and evolution. Recent observational studies show that further back in time (z > 0.5), rotation-supported, star-forming galaxies (SFGs) begin to appear to be DM deficient compared to local SFGs.

Aims. We present an observational study of the DM fraction in 225 rotation-supported, SFGs at z ≈ 0.9; these SFGs have stellar masses in the range 9.0 ≤ log(M_* M_⊙) ≤ 11.0 and star formation rates 0.49 ≤ log(SFR[M_⊙ yr⁻¹]) ≤ 1.77.

Methods. We studied a subsample of the KMOS Redshift One Spectroscopic Survey (KROSS) studied by Sharma et al. (2021, MNRAS, 503, 1753). The stellar masses (M_*) of these objects were previously estimated using mass-to-light ratios derived from fitting the spectral energy distribution of the galaxies. Star formation rates were derived from the H_α luminosities. In this paper, we determined the total gas masses (M_gas) by the scaling relations of molecular and atomic gas (Tacconi et al. 2018, ApJ, 853, 179; Lagos et al. 2011, MNRAS, 418, 1649, respectively). We derived the dynamical masses (M_dyn) from the rotation curves (RCs) at different scale lengths (effective radius: R_e, ∼2 R_e and ∼3 R_e) and we then calculated the DM fractions (f_DM = 1 − M_bar/M_dyn) at these radii.

Results. We report that at z ∼ 1 only a small fraction (∼5%) of our sample has a low (<20%) DM fraction within ∼2 − 3R_e. The majority (>72%) of SFGs in our sample have outer disks (∼5−10 kpc) dominated by DM, which agrees with local SFGs. Moreover, we find a large scatter in the fraction of DM at a given stellar mass (or circular velocity) with respect to local SFGs, suggesting that galaxies at z ∼ 1 span a wide range of stages in the formation of stellar disks and have diverse DM halo properties coupled with baryons.