THE MOSDEF SURVEY: THE STRONG AGREEMENT BETWEEN Hα AND UV-TO-FIR STAR FORMATION RATES FOR z ∼ 2 STAR-FORMING GALAXIES*

Abstract

We present the first direct comparison between Balmer line and panchromatic SED-based SFRs for z ∼ 2 galaxies. For this comparison we used 17 star-forming galaxies selected from the MOSFIRE Deep Evolution Field (MOSDEF) survey, with 3σ detections for Hα and at least two IR bands (Spitzer/MIPS 24 µm and Herschel/PACS 100 and 160 µm, and in some cases Herschel/SPIRE 250, 350, and 500 µm). The galaxies have total IR (8 − 1000 µm) luminosities of ∼ 10 11.4 − 10 12.4 L and star-formation rates (SFRs) of ∼ 30 − 250 M yr −1 . We fit the UV-to-far-IR SEDs with flexible stellar population synthesis (FSPS) models -which include both stellar and dust emission -and compare the inferred SFRs with the SFR(Hα,Hβ) values corrected for dust attenuation using Balmer decrements. The two SFRs agree with a scatter of 0.17 dex. Our results imply that the Balmer decrement accurately predicts the obscuration of the nebular lines and can be used to robustly calculate SFRs for star-forming galaxies at z ∼ 2 with SFRs up to ∼ 200 M yr −1 . We also use our data to assess SFR indicators based on modeling the UV-to-mid-IR SEDs or by adding SFR(UV) and SFR(IR), for which the latter is based on the mid-IR only or on the full IR SED. All these SFRs show a poorer agreement with SFR(Hα,Hβ) and in some cases large systematic biases are observed. Finally, we show that the SFR and dust attenuation derived from the UV-to-near-IR SED alone are unbiased when assuming a delayed exponentially declining star-formation history.

THE BURSTY STAR FORMATION HISTORIES OF LOW-MASS GALAXIES AT 0.4 < z < 1 REVEALED BY STAR FORMATION RATES MEASURED FROM Hβ AND FUV

“…In this case, the Hβ-to-FUV ratio is almost constant around −0.2 for all masses and seems to match the prediction of the IGIMF Minimal1 model (the purple dotted line in the left panel of Figure 5). However, as shown by other studies, the SFRs measured from FUV and nebular emission line are usually in very good agreement for massive galaxies (see W12 for z = 0 galaxies and Shivaei et al (2015Shivaei et al ( , 2016 for z ∼ 2 galaxies). Therefore, we suspect that the SMC curve "over-corrects" the dust extinction for massive galaxies to push their Hβ-to-FUV ratios to being significantly smaller than unity (i.e., negative in logarithmic scale).…”

Nebular Emission Line Ratios in z ≃ 2–3 Star-forming Galaxies with KBSS-MOSFIRE: Exploring the Impact of Ionization, Excitation, and Nitrogen-to-Oxygen Ratio∗

“…Shivaei et al (2016) reported that for z ∼ 2 galaxies from the MOSFIRE Deep Evolution Field survey (MOSDEF, Kriek et al 2015), Hα-based estimates of SFR are consistent with those estimated from the full panchromatic SED (including UV and far-IR photometry). Dust extinction toward star-forming regions is estimated by comparing the Balmer decrement (Hα/Hβ) with the expected Case B value of 2.86 (Osterbrock 1989).…”

A Radio-to-mm Census of Star-forming Galaxies in Protocluster 4C23.56 at Z = 2.5: Gas Mass and Its Fraction Revealed with ALMA

“…Tanaka et al 2017, in preparation). While the SFRs might be overestimated for the less massive galaxies (e.g., see Figure 8 in Shivaei et al 2016), further investigation is beyond the scope of this paper. Since thegalaxies detected in Suzuki et al 2017, in preparation).…”