Dark Matter Fraction in z~1 Star-Forming Galaxies

Abstract

We present a observational study of the dark matter fraction in 225 rotation supported star-forming galaxies at $z\approx 0.9$ having stellar mass range: $9.0\le log(M_{\ast }{\mathrm{M}}_{\odot })\le 11.0$ and star formation rate: $0.49\le log\left(SFR[{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}]\right)\le 1.77$. This is a sub sample of KMOS redshift one spectroscopic survey (KROSS) previously studied by \citet{GS20}. The stellar masses ($M_{\ast }$) 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${}_{\hat{I}}\pm$ luminosities. The total gas masses ($M_{gas}$) are determined by scaling relations of molecular and atomic gas \citep[][respectively] {Tacconi2018, Lagos2011}. The dynamical masses ($M_{dyn}$) are directly derived from the rotation curves (RCs) at different scale lengths (effective radius: $R_e$, $\sim 2R_e$ and $\sim 3R_e$) and then the dark matter fractions ($f_{DM}=1-M_{bar}/M_{dyn}$) at these radii are calculated. We report that at $z\sim 1$ only a small fraction ($\sim 5\%$) of our sample has a low ($<20\%$) DM fraction within $\sim$ 2-3 $R_e$. The majority ($>72\%$) of SFGs in our sample have dark matter dominated outer disks ($\sim 5-10$ kpc) in agreement with local SFGs. Moreover, we find a large scatter in the fraction of dark matter at a given stellar mass (or circular velocity) with respect to local SFGs, suggesting that galaxies at $z\sim 1$, a) span a wide range of stages in the formation of stellar disks, b) have diverse DM halo properties coupled with baryons.

Accepted for publication in A&A (in press)