Faint millimeter NIKA2 dusty star-forming galaxies: finding the high-redshift population
arxiv(2024)
摘要
We develop a new framework to constrain the source redshift. The method
jointly accounts for the detection/non-detection of spectral lines and the
prior information from the photometric redshift and total infrared luminosity
from spectral energy distribution analysis. The method uses the estimated total
infrared luminosity to predict the line fluxes at given redshifts and generates
model spectra. The redshift-dependent spectral models are then compared with
the observed spectra to find the redshift. Results. We apply the aforementioned
joint redshift analysis method to four high-z dusty star-forming galaxy
candidates selected from the NIKA2 observations of the HLSJ091828.6+514223
(HLS) field, and further observed by NOEMA with blind spectral scans. These
sources only have SPIRE/Herschel photometry as ancillary data. They were
selected because of very faint or no SPIRE counterparts, as to bias the sample
towards the highest redshift candidates. The method finds the spectroscopic
redshift of 4 in the 5 NOEMA-counterpart detected sources, with z>3. Based on
these measurements, we derive the CO/[CI] lines and millimeter continuum fluxes
from the NOEMA data and study their ISM and star-formation properties. We find
cold dust temperatures in some of the HLS sources compared to the general
population of sub-millimeter galaxies, which might be related to the bias
introduced by the SPIRE-dropout selection. Our sources, but one, have short gas
depletion time of a few hundred Myrs, which is typical among high-z
sub-millimeter galaxies. The only exception shows a longer gas depletion time,
up to a few Gyrs, comparable to that of main-sequence galaxies at the same
redshift. Furthermore, we identify a possible over-density of dusty
star-forming galaxies at z=5.2, traced by two sources in our sample, as well as
the lensed galaxy HLSJ091828.6+514223. (abridged)
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