The GADOT Galaxy Survey: Dense Gas and Feedback in Herschel-Selected
  Starburst Galaxies at Redshifts 2 to 6
  We report the detection of 23 OH+(1-0) absorption, emission, or
P-Cygni-shaped lines and CO(9-8) emission lines in 18 Herschel-selected z=2-6
starburst galaxies with ALMA and NOEMA, taken as part of the Gas And Dust Over
cosmic Time (GADOT) Galaxy Survey. We find that the CO(9-8) luminosity is
higher than expected based on the far-infrared luminosity when compared to
nearby star-forming galaxies. Together with the strength of the OH+ emission
components, this may suggest that shock excitation of warm, dense molecular gas
is more prevalent in distant massive dusty starbursts than in nearby
star-forming galaxies on average, perhaps due to an impact of galactic winds on
the gas. OH+ absorption is found to be ubiquitous in massive high-redshift
starbursts, and is detected toward 89% of the sample. The majority of the
sample shows evidence for outflows or inflows based on the velocity shifts of
the OH+ absorption/emission, with a comparable occurrence rate of both at the
resolution of our observations. A small subsample appears to show outflow
velocities in excess of their escape velocities. Thus, starburst-driven
feedback appears to be important in the evolution of massive galaxies in their
most active phases. We find a correlation between the OH+ absorption optical
depth and the dust temperature, which may suggest that warmer starbursts are
more compact and have higher cosmic ray energy densities, leading to more
efficient OH+ ion production. This is in agreement with a picture in which
these high-redshift galaxies are "scaled-up" versions of the most intense
nearby starbursts.
