2021/04/27 by Elizabeth Tarantino, Alberto D. Bolatto, Rodrigo Herrera-Camus +11
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Ionization #Line (geometry) #Molecular cloud #Phase (matter) #Spectroscopy #Thermal emission #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/abfcc6
23 pages, 11 figures, 4 tables, accepted to The Astrophysical Journal
arxiv created 2021/04/27 · openalex created_date 2021/05/10 · openalex publication_date 2021/07/01 · arxiv updated 2021/08/18 · openalex updated_date 2026/08/06
Abstract The [C ii ] fine-structure transition at 158 μ m is frequently the brightest far-infrared line in galaxies. Due to its low ionization potential, C + can trace the ionized, atomic, and molecular phases of the ISM. We present velocity-resolved [C ii ] and [N ii ] pointed observations from SOFIA/GREAT on ∼500 pc scales in the nearby galaxies M101 and NGC 6946 and investigate the multiphase origin of [C ii ] emission over a range of environments. We show that ionized gas makes a negligible contribution to the [C ii ] emission in these positions using [N ii ] observations. We spectrally decompose the [C ii ] emission into components associated with the molecular and atomic phases using existing CO (2–1) and H i data and show that a peak signal-to-noise ratio of 10–15 is necessary for a reliable decomposition. In general, we find that in our pointings ≳50% of the [C ii ] emission arises from the atomic phase, with no strong dependence on star formation rate, metallicity, or galactocentric radius. We do find a difference between pointings in these two galaxies, where locations in NGC 6946 tend to have larger fractions of [C ii ] emission associated with the molecular phase than in M101. We also find a weak but consistent trend for fainter [C ii ] emission to exhibit a larger contribution from the atomic medium. We compute the thermal pressure of the cold neutral medium through the [C ii ] cooling function and find <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>th</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi>k</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>3.8</mml:mn> <mml:mo>–</mml:mo> <mml:mn>4.6</mml:mn> <mml:mspace width="0.25em"/> <mml:mspace width="0.50em"/> <mml:mo stretchy="false">[</mml:mo> <mml:mi mathvariant="normal">K</mml:mi> <mml:mspace width="0.33em"/> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">]</mml:mo> </mml:math> , a value slightly higher than similar determinations, likely because our observations are biased toward star-forming regions.