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CONSTRAINING THE ISM PROPERTIES OF THE CLOVERLEAF QUASAR HOST GALAXY WITH HERSCHEL SPECTROSCOPY

2016; IOP Publishing; Volume: 832; Issue: 2 Linguagem: Inglês

10.3847/0004-637x/832/2/209

1538-4357

Bade Uzgil, C. M. Bradford, S. Hailey-Dunsheath, Philip R. Maloney, James E. Aguirre,

Stellar, planetary, and galactic studies

ABSTRACT We present Herschel observations of the far-infrared (FIR) fine-structure (FS) lines [C ii ]158 μ m, [O i ]63 μ m, [O iii ]52 μ m, and [Si ii ]35 μ m in the z = 2.56 Cloverleaf quasar, and combine them with published data in an analysis of the dense interstellar medium (ISM) in this system. Observed [C ii ]158 μ m, [O i ]63 μ m, and FIR continuum flux ratios are reproduced with photodissociation region (PDR) models characterized by moderate far-ultraviolet (FUV) radiation fields with <?CDATA ${G}_{0}\,=$?> 0.3–1 × 10 3 and atomic gas densities <?CDATA ${n}_{{\rm{H}}}\,=$?> 3–5 × 10 3 cm −3 , depending on contributions to [C ii ]158 μ m from ionized gas. We assess the contribution to the [C ii ]158 μ m flux from an active galactic nucleus (AGN) narrow line region (NLR) using ground-based measurements of the [N ii ]122 μ m transition, finding that the NLR can contribute at most 20%–30% of the observed [C ii ]158 μ m flux. The PDR density and far-UV radiation fields inferred from the atomic lines are not consistent with the CO emission, indicating that the molecular gas excitation is not solely provided via UV heating from local star formation (SF), but requires an additional heating source. X-ray heating from the AGN is explored, and we find that X-ray-dominated region (XDR) models, in combination with PDR models, can match the CO cooling without overproducing the observed FS line emission. While this XDR/PDR solution is favored given the evidence for both X-rays and SF in the Cloverleaf, we also investigate alternatives for the warm molecular gas, finding that either mechanical heating via low-velocity shocks or an enhanced cosmic-ray ionization rate may also contribute. Finally, we include upper limits on two other measurements attempted in the Herschel program: [C ii ]158 μ m in FSC 10214 and [O i ]63 μ m in APM 08279+5255.