ADS: Weiss et al. 2013
arXiv: Weiss et al. 2013
This paper describes the results from an ALMA Cycle 0 program to measure the redshifts of the SPT galaxies. We did this by observing each galaxy in almost all of ALMA’s 3mm band (Band 3), looking to detect rotational transitions of carbon monoxide. Since the frequencies of the CO lines are very well known and are the brightest lines available at these frequencies, if we can detect more than one line, we know the redshift of the galaxy. Knowing the redshift opens up a wide variety of possible further projects – basically anything that targets a spectral line requires knowledge of the redshift. We ended up detecting at least one line in 90% of the galaxies we targeted, making it the most complete sample yet observed.
We also aimed to determine the intrinsic redshift distribution (i.e., how the galaxies are distributed as a function of distance from earth), and described possible biases and selection effects in our sample. For example, our sample is gravitationally lensed, and we discovered our galaxies at a longer wavelength (1.4mm) than other samples (from 250 to 870um, usually). We found that our sources are distributed to higher redshifts (farther away) than other samples which relied on detecting galaxies at radio frequencies before attempting to measure redshifts. Meanwhile, we determined that lensing probably doesn’t significantly affect the redshift distribution beyond z > 2 unless the galaxies rapidly become smaller at higher redshifts, which there is little evidence for.