Reconciling the results of the z ∼2 MOSDEF and KBSS-MOSFIRE Surveys

Abstract

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 colours and a rest-UV magnitude limit. Analysing both surveys in a uniform manner with consistent spectral-energy- distribution (SED) models, we find that the MOSDEF z ∼2 targeted sample has higher median M ∗and redder rest U −V colour than the KBSS-MOSFIRE z ∼2 targeted sample, and smaller median SED-based SFR and sSFR (SFR(SED) and sSFR(SED)). Specifically, MOSDEF tar geted 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 analysed in previous 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 colours -agree within the uncertainties. Additionally, when uniform emission-line fitting and stellar Balmer absorption correction techniques are applied, there is no significant offset between both samples in the [O III ] λ5008/H βversus [N II ] λ6585/H αdiagnostic diagram, in contrast to previously reported discrepancies. We can now combine the MOSDEF and KBSS-MOSFIRE surv e ys 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.