Fitting spectral energy distributions of FMOS-COSMOS emission-line galaxies atz∼ 1.6: Star formation rates, dust attenuation, and [OIII]λ5007 emission-line luminosities

Abstract

We perform a spectral energy distribution fitting analysis on a COSMOS photometric sample covering the ultra-violet up to the farinfrared wavelengths and including emission lines from the Fiber Multi-Object Spectrograph (FMOS) survey. The sample consists of 182 objects with Hα and [OIII]λ5007 emission line measurements lying in a redshift range of 1.40 < z < 1.68. We obtain robust estimates of the stellar mass and star-formation rate spanning over a range of 10 9.5 −10 11.5 M and 10 1 −10 3 M yr −1 from the Bayesian analysis performed with CIGALE and using continuum photometry and Hα fluxes. Combining photometry and spectroscopy gives secure estimations of the amount of dust attenuation for both continuum and line emissions. We obtain a median attenuation of A Hα = 1.16 ± 0.19 mag and A [OIII] = 1.41 ± 0.22 mag. Hα and [OIII]λ5007 attenuations are found to increase with stellar mass, confirming previous findings with Hα. A difference of 57% in the attenuation experienced by emission lines and continuum is found to be in agreement with the emission lines being more attenuated than the continuum emission. Implementation of new CLOUDY HII-region models in CIGALE enables good fits of the Hα, Hβ, [OIII]λ5007 emission lines with discrepancies smaller than 0.2 dex in the predicted fluxes. Fitting the [NII]λ6584 line is found challenging due to well-known discrepancies in the locus of galaxies in the [NII]-BPT diagram at intermediate and high redshifts. We find a positive correlation between SFR and L [OIII]λ5007 after correcting for dust attenuation and we derive the linear relation log 10 (SFR/M yr −1 ) = log 10 (L [OIII] /ergs s −1 ) − (41.20 ± 0.02). Leaving the slope as a free parameter leads to log 10 (SFR/M yr −1 ) = (0.83 ± 0.06) log 10 (L [OIII] /ergs s −1 ) − (34.01 ± 2.63). The spread in the relation is driven by differences in the gas-phase metallicity and ionization parameter accounting for a 0.24 dex and 1.1 dex of the dispersion, respectively. We report an average value of log U ≈ −2.85 for this sample of galaxies. Including HII-region models to fit simultaneously photometric data and emission line fluxes is paramount to analyses of upcoming data sets from large spectroscopic surveys of the future, such as MOONS and PFS.

The Physical Properties of Star-Forming Galaxies with Strong [O III] Lines at z=3.25

“…Such a correlation has been reported before (e.g. Straughn et al 2009;Villa-Vélez et al 2021). It is also clear that most of our [O III] ELGs have dust-corrected luminosities in range of 10 42.6−43.6 .…”

“…This SFH can fit the high-z SFGs well since they usually have a relatively strong star formation activity. It also avoids the systematic biases caused by the degeneracy between the slope of dust attenuation curve, effective dust attenuation and the intrinsic UV slope of model templates (Yuan et al 2019;Villa-Vélez et al 2021;Qin et al 2022). The degeneracy is indeed smaller for blue SFGs.…”

The Physical Properties of Star-forming Galaxies with Strong [O iii] Lines at z = 3.25

“…A strong correlation is seen. Such a correlation has been reported before (e.g., Straughn et al 2009;Villa-Vélez et al 2021). It is also clear that most of our [O III] ELGs have dust-corrected luminosities in the range of 10 42.6 −10 43.6 .…”

“…This SFH can fit the high-z SFGs well since they usually have a relatively strong star formation activity. It also avoids the systematic biases caused by the degeneracy between the slope of the dust attenuation curve, effective dust attenuation, and intrinsic UV slope of model templates (Yuan et al 2019;Villa-Vélez et al 2021;Qin et al 2022). The degeneracy is indeed smaller for blue SFGs.…”

Spectral Energy Distributions in Three Deep-drilling Fields of the Vera C. Rubin Observatory Legacy Survey of Space and Time: Source Classification and Galaxy Properties

“…30 Stellar templates are from Bruzual & Charlot (2003), and a Chabrier initial mass function (Chabrier 2003) is adopted. Nebular emission is also included in a self-consistent manner using CLOUDY photoionization calculations (Ferland et al 2017), as described and implemented in Villa-Vélez et al (2021). Dust attenuation is assumed to follow Calzetti et al (2000), and dust emission in the IR is assumed to follow templates in Dale et al (2014) for simplicity.…”