paper

Fast Outflows Identified in Early Star-Forming Galaxies at

arXiv:1904.03106 · doi:10.3847/1538-4357/ab49fe

Abstract

We present velocities of galactic outflows in seven star-forming galaxies at 5-6 with stellar masses of . Although it is challenging to observationally determine the outflow velocities, we overcome this by using ALMA [CII]158 m emission lines for systemic velocities and deep Keck spectra with metal absorption lines for velocity profiles available to date. We construct a composite Keck spectrum of the galaxies at 5-6 with the [CII]-systemic velocities, and fit outflow-line profiles to the SiII1260, CII1335, and SiIV1394,1403 absorption lines in the composite spectrum. We measure the maximum (90%) and central outflow velocities to be $v_\rm{max}=700^{+180}_{-110}\ \rm{km\ s^{-1}}$ and $v_\rm{out}= 400^{+100}_{-150}\ \rm{km\ s^{-1}}$ on average, respectively, showing no significant differences between the outflow velocities derived with the low to high-ionization absorption lines. For , we find that the $v_\rm{max}$ value of our 5-6 galaxies is 3 times higher than those of galaxies and comparable to galaxies. Estimating the halo circular velocity $v_\rm{cir}$ from the stellar masses and the abundance matching results, we investigate a $v_\rm{max}$-$v_\rm{cir}$ relation. Interestingly, $v_\rm{max}$ for galaxies with shows a clear positive correlation with $v_\rm{cir}$ and/or the galaxy star formation rate over 0-6 with a small scatter of dex, which is in good agreement with theoretical predictions. This positive correlation suggests that the outflow velocity is physically related to the halo circular velocity, and that the redshift evolution of $v_\rm{max}$ at fixed is explained by the increase in $v_\rm{cir}$ toward high redshift.

arXiv comment13 pages, 7 figures, 4 tables; Accepted for publication in ApJ

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