DETECTION OF THE 158 μm C II TRANSITION AT z = 1.3: EVIDENCE FOR A GALAXY-WIDE STARBURST

We report the detection of 158 micron CII fine-structure line emission from MIPS J142824. 0+352619, a hyperluminous (LIR ~ 10¹3 Lₛun) starburst galaxy at z=1. 3. The line is bright, and corresponds to a fraction LCII/LFIR = 2 x 10^-3 of the far-IR (FIR) continuum. The CII, CO, and FIR continuum emission may be modeled as arising from photodissociation regions (PDRs) that have a characteristic gas density of n ~ 10⁴. 2 cm^-3, and that are illuminated by a far-UV radiation field ~10³. 2 times more intense than the local interstellar radiation field. The mass in these PDRs accounts for approximately half of the molecular gas mass in this galaxy. The LCII/LFIR ratio is higher than observed in local ULIRGs or in the few high-redshift QSOs detected in CII, but the LCII/LFIR and LCO/LFIR ratios are similar to the values seen in nearby starburst galaxies. This suggests that MIPS J142824. 0+352619 is a scaled-up version of a starburst nucleus, with the burst extended over several kiloparsecs.