Dusty star-forming galaxies with LABOCA 870um obs.
Short Name:
J/ApJ/862/96
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present images obtained with LABOCA of a sample of 22 galaxies selected via their red Herschel SPIRE colors. We aim to see if these luminous, rare, and distant galaxies are signposting dense regions in the early universe. Our 870{mu}m survey covers an area of ~1deg^2^ down to an average rms of 3.9mJy/beam, with our five deepest maps going 2x deeper still. We catalog 86 dusty star-forming galaxies (DSFGs) around our "signposts," detected above a significance of 3.5{sigma}. This implies a 100+/-30% overdensity of S_870_>8.5mJy (or L_FIR_=6.7x10^12^-2.9x10^13^L_{sun}_) DSFGs, excluding our signposts, when comparing our number counts to those in "blank fields." Thus, we are 99.93% confident that our signposts are pinpointing overdense regions in the universe, and 95% [50%] confident that these regions are overdense by a factor of at least >=1.5x[2x]. Using template spectral energy distributions (SEDs) and SPIRE/LABOCA photometry, we derive a median photometric redshift of z=3.2+/-0.2 for our signposts, with an inter-quartile range of z=2.8-3.6, somewhat higher than expected for 850{mu}m selected galaxies. We constrain the DSFGs that are likely responsible for this overdensity to within |{delta}_z_|<=0.65 of their respective signposts. These "associated" DSFGs are radially distributed within (physical) distances of 1.6+/-0.5Mpc from their signposts, have median star formation rates (SFRs) of ~(1.0+/-0.2)x10^3^M_{sun}_/yr (for a Salpeter stellar initial mass function) and median gas reservoirs of ~1.7x10^11^M_{sun}_. These candidate protoclusters have average total SFRs of at least ~(2.3+/-0.5)x10^3^M_{sun}_/yr and space densities of 9x10^-7^Mpc^-3^, consistent with the idea that their constituents may evolve to become massive early-type galaxies in the centers of the rich galaxy clusters we see today.
Intergalac. medium opacity from Lyman-break galaxies
Short Name:
J/AJ/160/37
Date:
08 Dec 2021
Publisher:
CDS
Description:
We measure the effective opacity ({tau}_eff_) of the intergalactic medium from the composite spectra of 281 Lyman-break galaxies in the redshift range 2<~z<~3. Our spectra are taken from the COSMOS Ly{alpha} Mapping And Tomographic Observations survey derived from the Low Resolution Imaging Spectrometer on the W.M. Keck I telescope. We generate composite spectra in two redshift intervals and fit them with spectral energy distribution (SED) models composed of simple stellar populations. Extrapolating these SED models into the Ly{alpha} forest, we measure the effective Ly{alpha} opacity ({tau}_eff_) in the 2.02<~z<~2.44 range. At z=2.22, we estimate {tau}_eff_=0.159{+/-}0.001 from a power-law fit to the data. These measurements are consistent with estimates from quasar analyses at z<2.5 indicating that the systematic errors associated with normalizing quasar continua are not substantial. We provide a Gaussian processes model of our results and previous {tau}_eff_ measurements that describes the steep redshift evolution in {tau}_eff_ from z=1.5-4.
