Fast Outflows Identified in Early Star-Forming Galaxies at $z = 5-6$

Understand

We present velocities of galactic outflows in seven star-forming galaxies at $z=$5-6 with stellar masses of $M_* \sim10^{10.1}\ \rm{M_\odot}$.

• Although it is challenging to observationally determine the outflow velocities, we overcome this by using ALMA [CII]158 $\mu$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 $z=$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.