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

We report the detection of 158 μm [C ii] fine-structure line emission from MIPS J142824.0+352619, a hyperluminous (LIR ∼ 1013 L☉) starburst galaxy at z = 1.3. The line is bright, corresponding to a fraction L[C ii]/LFIR ≈ 2 × 10−3 of the far-IR (FIR) continuum. The [C ii], 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 L[C ii]/LFIR ratio is higher than observed in local ultraluminous infrared galaxies or in the few high-redshift QSOs detected in [C ii], but the L[C ii]/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.