Abstract
We consider the capabilities of current and future large facilities operating
at 2\,mm to 3\,mm wavelength to detect and image the CII 158\,$\mu$m line
from galaxies into the cosmic "dark ages" ($z 10$ to 20). The CII line
may prove to be a powerful tool in determining spectroscopic redshifts, and
galaxy dynamics, for the first galaxies. We emphasize that the nature, and even
existence, of such extreme redshift galaxies, remains at the frontier of open
questions in galaxy formation. In 40\,hr, ALMA has the sensitivity to detect
the integrated CII line emission from a moderate metallicity, active
star-forming galaxy $Z_A = 0.2\,Z_ødot$; star formation rate (SFR) =
5\,$M_ødot$\,yr$^-1$, at $z = 10$ at a significance of 6$\sigma$. The
next-generation Very Large Array (ngVLA) will detect the integrated CII line
emission from a Milky-Way like star formation rate galaxy ($Z_A =
0.2\,Z_ødot$, SFR = 1\,$M_ødot$\,yr$^-1$), at $z = 15$ at a significance
of 6$\sigma$. Imaging simulations show that the ngVLA can determine rotation
dynamics for active star-forming galaxies at $z 15$, if they exist. Based
on our very limited knowledge of the extreme redshift Universe, we calculate
the count rate in blind, volumetric surveys for CII emission at $z 10$
to 20. The detection rates in blind surveys will be slow (of order unity per
40\,hr pointing). However, the observations are well suited to commensal
searches. We compare CII with the OIII 88$\mu$m line, and other ancillary
information in high $z$ galaxies that would aid these studies.
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