The ALPINE-ALMA [C II] survey: Investigation of 10 galaxies at z ∼ 4.5 with [O II] and [C II] line emission − ISM properties and [O II]−SFR relation

Year: 2022 DOI: 10.1093/mnras/stac071 We present 10 main-sequence ALPINE galaxies (log (M/M_⊙) = 9.2−11.1 and SFR = 23−190 M_⊙ yr⁻¹) at z ∼ 4.5 with optical [O II] measurements from Keck/MOSFIRE spectroscopy and Subaru/MOIRCS narrow-band imaging. This is the largest such multiwavelength sample at these redshifts, combining various measurements in the ultraviolet, optical, and far-infrared including [C II]_(158 μm) line emission and dust continuum from ALMA and H α emission from Spitzer photometry. For the first time, this unique sample allows us to analyse the relation between [O II] and total star-formation rate (SFR) and the interstellar medium (ISM) properties via [O II]/[C II] and [O II]/H α luminosity ratios at z ∼ 4.5. The [O II]−SFR relation at z ∼ 4.5 cannot be described using standard local descriptions, but is consistent with a metal-dependent relation assuming metallicities around 50 per cent solar. To explain the measured dust-corrected luminosity ratios of log(L_[OII]/L_[CII]) ∼ 0.98^(+0.21)_(−0.22) and log(L_[OII]/L_(Hα)) ∼ −0.22^(+0.13)_(−0.15) for our sample, ionization parameters log (U) < −2 and electron densities log(nₑ/[cm⁻³]) ∼ 2.5−3 are required. The former is consistent with galaxies at z ∼ 2−3, however lower than at z > 6. The latter may be slightly higher than expected given the galaxies' specific SFR. The analysis of this pilot sample suggests that typical log (M/M_⊙) > 9 galaxies at z ∼ 4.5 to have broadly similar ISM properties as their descendants at z ∼ 2 and suggest a strong evolution of ISM properties since the epoch of reionization at z > 6.