Work

The Survey of Lines in M31 (slim): Investigating the Origins of [c Ii] Emission

Year: 2014

Type: article

Abstract: The [C ii ] 158 μm line is one of the strongest emission lines observed in star-forming galaxies and has been empirically measured to correlate with the star-formation rate (SFR) globally and on kiloparsec scales. However, because of the multiphase origins of [C ii ], one might expect this relation to break down at small scales. We investigate the origins of [C ii ] emission by examining high spatial resolution observations of [C ii ] in M31 with the Survey of Lines in M31. We present five ∼700 × 700 pc (3' × 3') fields mapping the [C ii ] emission, Hα emission, and the ancillary infrared (IR) data. We spatially separate star-forming regions from diffuse gas and dust emission on ∼50 pc scales. We find that the [C ii ]–SFR correlation holds even at these scales, although the relation typically has a flatter slope than found at larger (kiloparsec) scales. While the Hα emission in M31 is concentrated in the SFR regions, we find that a significant amount (∼20%–90%) of the [C ii ] emission comes from outside star-forming regions and that the total IR emission (TIR) has the highest diffuse fraction of all SFR tracers. We find a weak correlation of the [C ii ]/TIR to dust color in each field and find a large-scale trend of increasing [C ii ]/TIR with galactocentric radius. The differences in the relative diffuse fractions of [C ii ], Hα, and IR tracers are likely caused by a combination of energetic photon leakage from H ii regions and heating by the diffuse radiation field arising from older (B-star) stellar populations. However, we find that by averaging our measurements over kiloparsec scales, these effects are minimized, and the relation between [C ii ] and SFR found in other nearby galaxy studies is retrieved.

Source: The Astrophysical Journal

DOI: 10.1088/0004-637x/798/1/24