Near-infrared MOSFIRE Spectra of Dusty Star-forming Galaxies at 0.2 < z < 4

Abstract

We present near-infrared and optical spectroscopic observations of a sample of 450 and 850 μm-selected dusty star-forming galaxies (DSFGs) identified in a 400 arcmin 2 area in the COSMOS field. Thirty-one sources of the 114 targets were spectroscopically confirmed at z 0.2 4 < < , identified primarily in the near-infrared with Keck MOSFIRE and some in the optical with Keck LRIS and DEIMOS. The low rate of confirmation is attributable both to high rest-frame optical obscuration in our targets and limited sensitivity to certain redshift ranges. The median spectroscopic redshift is z 1.55 0.14 spec á ñ =  , comparable to z 1.50 0.09 phot á ñ =  for the larger parent DSFG sample; the median stellar mass is 4.9 101.4The high-quality photometric redshifts available in the COSMOS field allow us to test the robustness of photometric redshifts for DSFGs. We find a subset (11 31 35 » %) of DSFGs with inaccurateor non-existent photometric redshifts; these have very distinct spectral energy distributions from the remaining DSFGs, suggesting a decoupling of highly obscured and unobscured components. We present a composite rest-frame 4300-7300 Å spectrum for DSFGs, and find evidence of 200±30 km s −1 gas outflows. Nebular line emission for a subsample of our detections indicate that hard ionizing radiation fields are ubiquitous in high-z DSFGs, even more so than typical mass or UV-selected high-z galaxies. We also confirm the extreme level of dust obscuration in DSFGs, measuring very high Balmer decrements and very high ratios of IR to UV and IR to Hα luminosities. This work demonstrates the need to broaden the use of wide bandwidth technology in the millimeter to spectroscopically confirm larger samples of high-z DSFGs, as the difficulty in confirming such sources at optical/near-infrared wavelengths is exceedingly challenging given their obscuration.

A simultaneous search for high-z LAEs and LBGs in the SHARDS survey

“…The SFRs, corrected for extinction following the above prescription, are given in Table 1, where we show the SFR based on L(L yα) and/or L 1500 depending on whether the galaxy presents emission line or continuum emission. As expected for these early galaxies, the SFRs are fairly high (e.g., Bouwens et al 2007Bouwens et al , 2015Mashian et al 2016;Casey et al 2017), with those calculated with L 1500 being ∼ 58 M yr −1 on average. The complete LBGs SFR distribution can be seen in Fig.…”

“…7, where there are 7 objects forming stars at a rate above 10 3 M yr −1 . These galaxies are very dusty starforming galaxies (see Casey et al 2017) whose SEDs show a very red UV slope. An example is given in Fig.…”

Three Dusty Star-forming Galaxies at z ∼ 1.5: Mergers and Disks on the Main Sequence

“…The galaxies in the present paper were selected from their parent sample based on their high signal to noise (SNR) and spatially resolved Hα and [NII] emission. The three galaxies presented in this paper are the only ones that have sufficiently resolved emission to allow for a kinematic analysis from the original 114 targets in the Casey et al (2017) sample. One galaxy, named 850.95, is also published in Drew et al (2018, hereafter D18) as an observational counter example to the hypothesis that galaxies at intermediate redshifts may have declining rotation curves.…”

“…Apertures of extraction were placed on each pixel with an aperture radius of half the average seeing. Adjusting the aperture size does not significantly change the radial velocity and velocity dispersion measurements presented in the Casey et al (2017) because they are estimated using a range of SFHs from a continuous star formation history to an instantaneous burst, following the procedure of Hainline et al (2011). The errors on LIR and, as a direct result, SFR are estimated following the procedure of Casey (2012).…”

The Strong Gravitationally Lensed Herschel Galaxy HLock01: Optical Spectroscopy Reveals a Close Galaxy Merger with Evidence of Inflowing Gas

“…However, such studies are limited by the faintness of these galaxies at short wavelengths, with the massive stars giving rise to the UV continuum being embedded in large quantities of dust. Considerable spectroscopic efforts have been successfully used to obtain accurate spectroscopic redshifts, probe for signs of active galactic nucleus (AGN) activity, and investigate properties of the ionized gas in SMGs, mainly by using rest-frame optical nebular emission lines (e.g., Chapman et al 2004Chapman et al , 2005Swinbank et al 2004Swinbank et al , 2005Swinbank et al , 2006Alaghband-Zadeh et al 2012;Olivares et al 2016;Casey et al 2017;Danielson et al 2017). However, the typical faintness of high-z galaxies and the dust obscuration of SMGs make it almost impossible with current facilities to obtain high signal-to-noise ratio (S/N) spectra, a requirement for properly studying the properties of the young stars, and to look for signatures of outflowing/inflowing gas.…”