Reconciling the Results of the z~2 MOSDEF and KBSS-MOSFIRE Surveys

Jordan N. Runco, Naveen A. Reddy, Alice E. Shapley, Charles C. Steidel, Ryan L. Sanders, Allison L. Strom, Alison L. Coil, Mariska Kriek, Bahram Mobasher, Max Pettini, Gwen C. Rudie, Brian Siana, Michael W. Topping, Ryan F. Trainor, William R. Freeman, Irene Shivaei, Mojegan Azadi, Sedona H. Price, Gene C. K. Leung, Tara Fetherolf, Laura de Groot, Tom Zick, Francesca M. Fornasini, Guillermo Barro

Published 2021-12-17, updated 2022-06-09Version 2

The combination of the MOSDEF and KBSS-MOSFIRE surveys represents the largest joint investment of Keck/MOSFIRE time to date, with ~3000 galaxies at 1.4<=z<=3.8, roughly half of which are at z~2. MOSDEF is photometric- and spectroscopic-redshift selected with a rest-optical magnitude limit, while KBSS-MOSFIRE is primarily selected based on rest-UV colors and a rest-UV magnitude limit. Analyzing both surveys in a uniform manner with consistent spectral-energy-distribution (SED) models, we find that the MOSDEF z~2 targeted sample has a higher median M_* and redder rest U-V color than the KBSS-MOSFIRE z~2 targeted sample, and a smaller median SED-based SFR and sSFR (SFR(SED) and sSFR(SED)). Specifically, MOSDEF targeted a larger population of red galaxies with U-V and V-J >=1.25, while KBSS-MOSFIRE contains more young galaxies with intense star formation. Despite these differences in the z~2 targeted samples, the subsets of the surveys with multiple emission lines detected and analyzed in previously published work are much more similar. All median host-galaxy properties with the exception of stellar population age -- i.e., M_*, SFR(SED), sSFR(SED), A_V, and UVJ colors -- agree within the uncertainties. Additionally, when uniform emission-line fitting and stellar Balmer absorption correction techniques are applied, there is no significant offset between the two samples in the [OIII]$\lambda$5008/H$\beta$ vs. [NII]$\lambda$6585/H$\alpha$ diagnostic diagram, in contrast to previously-reported discrepancies. We can now combine the MOSDEF and KBSS-MOSFIRE surveys to form the largest z~2 sample with moderate-resolution rest-optical spectra and construct the fundamental scaling relations of star-forming galaxies during this important epoch.