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The reliability of [C II] as an indicator of the star formation rate

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Abstract
The [C II] 157.74 mu m line is an important coolant for the neutral interstellar gas. Since [C II] is the brightest spectral line for most galaxies, it is a potentially powerful tracer of star formation activity. In this paper, we present a calibration of the star formation rate (SFR) as a function of the [C II] luminosity for a sample of 24 star-forming galaxies in the nearby Universe. This sample includes objects classified as H II regions or low-ionization nuclear emission-line regions, but omits all Seyfert galaxies with a significant contribution from the active galactic nucleus to the mid-infrared photometry. In order to calibrate the SFR against the line luminosity, we rely on both Galaxy Evolution Explorer far-ultraviolet data, which is an ideal tracer of the unobscured star formation, and MIPS 24 mu m, to probe the dust-enshrouded fraction of star formation. In the case of normal star-forming galaxies, the [C II] luminosity correlates well with the SFR. However, the extension of this relation to more quiescent (H alpha EW <= 10 angstrom) or ultraluminous galaxies should be handled with caution, since these objects show a non-linearity in the L-[C II]-to-L-FIR ratio as a function of L-FIR (and thus, their star formation activity). We provide two possible explanations for the origin of the tight correlation between the [C II] emission and the star formation activity on a global galaxy-scale. A first interpretation could be that the [C II] emission from photodissociation regions (PDRs) arises from the immediate surroundings of star-forming regions. Since PDRs are neutral regions of warm dense gas at the boundaries between H II regions and molecular clouds and they provide the bulk of [C II] emission in most galaxies, we believe that a more or less constant contribution from these outer layers of photon-dominated molecular clumps to the [C II] emission provides a straightforward explanation for this close link between the [C II] luminosity and SFR. Alternatively, we consider the possibility that the [C II] emission is associated with the cold interstellar medium, which advocates an indirect link with the star formation activity in a galaxy through the Schmidt law.
Keywords
ISM: lines and bands, galaxies: star formation, infrared: galaxies, ultraviolet: galaxies, LATE-TYPE GALAXIES, 158 MU-M, MULTIBAND IMAGING PHOTOMETER, ULTRALUMINOUS INFRARED GALAXIES, SPACE-OBSERVATORY MEASUREMENTS, INITIAL MASS FUNCTION, MICRON LINE DEFICIT, PHOTODISSOCIATION REGIONS, INTERSTELLAR-MEDIUM, H-ALPHA

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Citation

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Chicago
De Looze, Ilse, Maarten Baes, George J Bendo, Luca Cortese, and Jacopo Fritz. 2011. “The Reliability of [C II] as an Indicator of the Star Formation Rate.” Monthly Notices of the Royal Astronomical Society 416 (4): 2712–2724.
APA
De Looze, Ilse, Baes, M., Bendo, G. J., Cortese, L., & Fritz, J. (2011). The reliability of [C II] as an indicator of the star formation rate. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 416(4), 2712–2724.
Vancouver
1.
De Looze I, Baes M, Bendo GJ, Cortese L, Fritz J. The reliability of [C II] as an indicator of the star formation rate. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. 2011;416(4):2712–24.
MLA
De Looze, Ilse, Maarten Baes, George J Bendo, et al. “The Reliability of [C II] as an Indicator of the Star Formation Rate.” MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 416.4 (2011): 2712–2724. Print.
@article{2113908,
  abstract     = {The [C II] 157.74 mu m line is an important coolant for the neutral interstellar gas. Since [C II] is the brightest spectral line for most galaxies, it is a potentially powerful tracer of star formation activity. In this paper, we present a calibration of the star formation rate (SFR) as a function of the [C II] luminosity for a sample of 24 star-forming galaxies in the nearby Universe. This sample includes objects classified as H II regions or low-ionization nuclear emission-line regions, but omits all Seyfert galaxies with a significant contribution from the active galactic nucleus to the mid-infrared photometry. In order to calibrate the SFR against the line luminosity, we rely on both Galaxy Evolution Explorer far-ultraviolet data, which is an ideal tracer of the unobscured star formation, and MIPS 24 mu m, to probe the dust-enshrouded fraction of star formation. In the case of normal star-forming galaxies, the [C II] luminosity correlates well with the SFR. However, the extension of this relation to more quiescent (H alpha EW {\textlangle}= 10 angstrom) or ultraluminous galaxies should be handled with caution, since these objects show a non-linearity in the L-[C II]-to-L-FIR ratio as a function of L-FIR (and thus, their star formation activity). 
We provide two possible explanations for the origin of the tight correlation between the [C II] emission and the star formation activity on a global galaxy-scale. A first interpretation could be that the [C II] emission from photodissociation regions (PDRs) arises from the immediate surroundings of star-forming regions. Since PDRs are neutral regions of warm dense gas at the boundaries between H II regions and molecular clouds and they provide the bulk of [C II] emission in most galaxies, we believe that a more or less constant contribution from these outer layers of photon-dominated molecular clumps to the [C II] emission provides a straightforward explanation for this close link between the [C II] luminosity and SFR. Alternatively, we consider the possibility that the [C II] emission is associated with the cold interstellar medium, which advocates an indirect link with the star formation activity in a galaxy through the Schmidt law.},
  author       = {De Looze, Ilse and Baes, Maarten and Bendo, George J and Cortese, Luca and Fritz, Jacopo},
  issn         = {0035-8711},
  journal      = {MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY},
  keyword      = {ISM: lines and bands,galaxies: star formation,infrared: galaxies,ultraviolet: galaxies,LATE-TYPE GALAXIES,158 MU-M,MULTIBAND IMAGING PHOTOMETER,ULTRALUMINOUS INFRARED GALAXIES,SPACE-OBSERVATORY MEASUREMENTS,INITIAL MASS FUNCTION,MICRON LINE DEFICIT,PHOTODISSOCIATION REGIONS,INTERSTELLAR-MEDIUM,H-ALPHA},
  language     = {eng},
  number       = {4},
  pages        = {2712--2724},
  title        = {The reliability of [C II] as an indicator of the star formation rate},
  url          = {http://dx.doi.org/10.1111/j.1365-2966.2011.19223.x},
  volume       = {416},
  year         = {2011},
}

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