A SOFIA Survey of [C ii] in the galaxy M51 I. [C ii] as a tracer of Star Formation

Jorge Pineda, Christian Fischer, Maria Kapala, Jurgen Stutzki, Christof Buchbender, Paul Goldsmith, Monika Ziebart, Simon C.O. Glover, Ralf S. Klessen, Jin Koda, Carsten Kramer, Bhaswati Mookerjea, Karin Sandstrom, Nick Scoville, Rowan Smith

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    We present a [C ii] 158 μm map of the entire M51 (including M51b) grand design spiral galaxy observed with the Far Infrared Field-Imaging Line Spectrometer (FIFI-LS) instrument on board the Stratospheric Observatory For Infrared Astronomy (SOFIA). We compare the [C ii] emission with the total far-infrared (TIR) intensity and star formation rate (SFR) surface density maps (derived using Hα and 24 μm emission) to study the relationship between [C ii] and the star formation activity in a variety of environments within M51 on scales of 16'' corresponding to ~660 pc. We find that [C ii] and the SFR surface density are well correlated in the central, spiral arm, and inter-arm regions. The correlation is in good agreement with that found for a larger sample of nearby galaxies at kpc scales. We find that the SFR, and [C ii] and TIR luminosities in M51, are dominated by the extended emission in M51's disk. The companion galaxy M51b, however, shows a deficit of [C ii] emission compared with the TIR emission and SFR surface density, with [C ii] emission detected only in the SW part of this galaxy. The [C ii] deficit is associated with an enhanced dust temperature in this galaxy. We interpret the faint [C ii] emission in M51b to be a result of suppressed star formation in this galaxy, while the bright mid- and far-infrared emission, which drive the TIR and SFR values, are powered by other mechanisms. A similar but less-pronounced effect is seen at the location of the black hole in M51's center. The observed [C ii] deficit in M51b suggests that this galaxy is a valuable laboratory to study the origin of the apparent [C ii] deficit observed in ultra-luminous galaxies.
    Original languageEnglish
    JournalThe Astrophysical Journal Letters
    Early online date17 Dec 2018
    Publication statusPublished - 2018


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