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

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 ∼ kpc scales. However, due to the multi-phase 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 M 31, with the Survey of Lines in M 31 (SLIM). We present five ∼ 700×700 pc (3 ×3 ) Fields mapping the [C ii] emission, Hα emission, combined with 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 (∼ kpc) scales. While the Hα emission in M 31 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 (TIR) emission 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 ∼ kpc scales, these effects are minimized, and the relation between [C ii] and SFR found in other nearby galaxy studies is retrieved.

SÍGAME Simulations of the , , and Line Emission from Star-forming Galaxies at

“…Since the ionization potential of O + is 35.1 eV, [O III] is seen in hot diffuse ionized gas (e.g., Hii regions or the hot ionized medium), where the transition is easily excited (n cr ∼ 5.1 × 10 2 cm −3 and E u /k B ∼ 163 K). Although they trace different ISM phases, all three fine-structure lines have been proposed as tracers of the star formation rate (SFR) of galaxies (Kapala et al 2015;Herrera-Camus et al 2015). For example, De Looze et al (2014) found the line emissions to correlate with the SFRs for a sample of local and high-z starburst galaxies.…”

The Spatially Resolved Cooling Line Deficit in Galaxies

“…Maps of luminous infrared galaxies resolved at 24 μm from GOALS (Armus et al 2009) were convolved to match the 160 μm resolution using the convolution kernel methodology of Aniano et al (2011). To minimize any possible effects of starlight contamination at shorter wavelengths (see, e.g., Kapala et al 2015), the calibration of total infrared (TIR, 3-1100 μm) luminosity was performed utilizing 70, 100, and 160 μm photometry, which closely tracks full-SED integrated TIR luminosity (Galametz et al 2013). …”

Attenuation Modified by DIG and Dust as Seen in M31

“…The fields and data are also used by Kapala et al (2015) to trace the origin of [CII] line emission, as part of the Survey of Lines in M31 (SLIM, PI Sandstrom K.). The positions of the five fields are shown in Fig.…”