Infrared Space Observatory measurements of [C II] line variations in galaxies

S. Malhotra, G. Helou, G. Stacey, D. Hollenbach, S. Lord, C. A. Beichman, H. Dinerstein, D. A. Hunter, K. Y. Lo, N. Y. Lu, R. H. Rubin, N. Silbermann, H. A. Thronson, M. W. Werner

Research output: Contribution to journalArticle

129 Citations (Scopus)

Abstract

We report measurements of the [C II] fine-structure line at 157.714 μm in 30 normal star-forming galaxies with the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). The ratio of the line to total far-infrared (FIR) luminosity, L[C II]/LFIR, measures the ratio of the cooling of gas to that of dust, and thus the efficiency of the grain photoelectric heating process. This ratio varies by more than a factor of 40 in the current sample. About two-thirds of the galaxies have L[C II]/LFIR ratios in the narrow range of (2-7) × 10-3. The other one-third show trends of decreasing L[C II]/LFIR with increasing dust temperature, as measured by the flux ratio of infrared emission at 60 and 100 μm, Fv(60 μm)/Fv(100 μm), and with increasing star formation activity, measured by the ratio of FIR and blue-band luminosity, LFIR/LB. We also find three FIR-bright galaxies that are deficient in the [C II] line, which is undetected with 3 a upper limits of L[C II]/LFIR < (0.5-2) × 10-4. The trend in the L[C II]/LFIR ratio with the temperature of dust and with star formation activity may be due to decreased efficiency of photoelectric heating of gas at high UV radiation intensity as dust grains become positively charged, decreasing the yield and the energy of the photoelectrons. The three galaxies with no observed photodissociation region lines have among the highest LFIR/LB and Fv(60 μm)/Fv(100 μm) ratios. Their lack of [C II] lines may be due to a continuing trend of decreasing L[C II]/LFIR with increasing star formation activity and dust temperature seen in one-third of the sample with warm IRAS colors. In that case, the upper limits on L[C II]/LFIR imply a ratio of UV flux to gas density of G0/n > 10 cm3 (where G0 is in units of the local average interstellar field). The low L[C II]/LFIR ratio could also be due to either weak [C II], owing to self-absorption, or a strong FIR continuum from regions weak in [C II], such as dense H II regions or plasma ionized by hard radiation of active galactic nuclei. The mid-infrared and radio images of these galaxies show that most of the emission comes from a compact nucleus. CO and H I are detected in these galaxies, with H I seen in absorption toward the nucleus.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume491
Issue number1 PART II
StatePublished - 1997
Externally publishedYes

Fingerprint

Infrared Space Observatory (ISO)
observatory
galaxies
dust
spectrometer
radio
heating
cooling
wavelength
plasma
luminosity
gas
nuclei
self absorption
H II regions
active galactic nuclei
temperature
star formation
fine structure
spectrometers

Keywords

  • Galaxies: ISM
  • Infrared: ISM: lines and bands
  • ISM: atoms
  • Radiation mechanisms: thermal

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Malhotra, S., Helou, G., Stacey, G., Hollenbach, D., Lord, S., Beichman, C. A., ... Werner, M. W. (1997). Infrared Space Observatory measurements of [C II] line variations in galaxies. Astrophysical Journal, 491(1 PART II).

Infrared Space Observatory measurements of [C II] line variations in galaxies. / Malhotra, S.; Helou, G.; Stacey, G.; Hollenbach, D.; Lord, S.; Beichman, C. A.; Dinerstein, H.; Hunter, D. A.; Lo, K. Y.; Lu, N. Y.; Rubin, R. H.; Silbermann, N.; Thronson, H. A.; Werner, M. W.

In: Astrophysical Journal, Vol. 491, No. 1 PART II, 1997.

Research output: Contribution to journalArticle

Malhotra, S, Helou, G, Stacey, G, Hollenbach, D, Lord, S, Beichman, CA, Dinerstein, H, Hunter, DA, Lo, KY, Lu, NY, Rubin, RH, Silbermann, N, Thronson, HA & Werner, MW 1997, 'Infrared Space Observatory measurements of [C II] line variations in galaxies', Astrophysical Journal, vol. 491, no. 1 PART II.
Malhotra S, Helou G, Stacey G, Hollenbach D, Lord S, Beichman CA et al. Infrared Space Observatory measurements of [C II] line variations in galaxies. Astrophysical Journal. 1997;491(1 PART II).
Malhotra, S. ; Helou, G. ; Stacey, G. ; Hollenbach, D. ; Lord, S. ; Beichman, C. A. ; Dinerstein, H. ; Hunter, D. A. ; Lo, K. Y. ; Lu, N. Y. ; Rubin, R. H. ; Silbermann, N. ; Thronson, H. A. ; Werner, M. W. / Infrared Space Observatory measurements of [C II] line variations in galaxies. In: Astrophysical Journal. 1997 ; Vol. 491, No. 1 PART II.
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abstract = "We report measurements of the [C II] fine-structure line at 157.714 μm in 30 normal star-forming galaxies with the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). The ratio of the line to total far-infrared (FIR) luminosity, L[C II]/LFIR, measures the ratio of the cooling of gas to that of dust, and thus the efficiency of the grain photoelectric heating process. This ratio varies by more than a factor of 40 in the current sample. About two-thirds of the galaxies have L[C II]/LFIR ratios in the narrow range of (2-7) × 10-3. The other one-third show trends of decreasing L[C II]/LFIR with increasing dust temperature, as measured by the flux ratio of infrared emission at 60 and 100 μm, Fv(60 μm)/Fv(100 μm), and with increasing star formation activity, measured by the ratio of FIR and blue-band luminosity, LFIR/LB. We also find three FIR-bright galaxies that are deficient in the [C II] line, which is undetected with 3 a upper limits of L[C II]/LFIR < (0.5-2) × 10-4. The trend in the L[C II]/LFIR ratio with the temperature of dust and with star formation activity may be due to decreased efficiency of photoelectric heating of gas at high UV radiation intensity as dust grains become positively charged, decreasing the yield and the energy of the photoelectrons. The three galaxies with no observed photodissociation region lines have among the highest LFIR/LB and Fv(60 μm)/Fv(100 μm) ratios. Their lack of [C II] lines may be due to a continuing trend of decreasing L[C II]/LFIR with increasing star formation activity and dust temperature seen in one-third of the sample with warm IRAS colors. In that case, the upper limits on L[C II]/LFIR imply a ratio of UV flux to gas density of G0/n > 10 cm3 (where G0 is in units of the local average interstellar field). The low L[C II]/LFIR ratio could also be due to either weak [C II], owing to self-absorption, or a strong FIR continuum from regions weak in [C II], such as dense H II regions or plasma ionized by hard radiation of active galactic nuclei. The mid-infrared and radio images of these galaxies show that most of the emission comes from a compact nucleus. CO and H I are detected in these galaxies, with H I seen in absorption toward the nucleus.",
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T1 - Infrared Space Observatory measurements of [C II] line variations in galaxies

AU - Malhotra, S.

AU - Helou, G.

AU - Stacey, G.

AU - Hollenbach, D.

AU - Lord, S.

AU - Beichman, C. A.

AU - Dinerstein, H.

AU - Hunter, D. A.

AU - Lo, K. Y.

AU - Lu, N. Y.

AU - Rubin, R. H.

AU - Silbermann, N.

AU - Thronson, H. A.

AU - Werner, M. W.

PY - 1997

Y1 - 1997

N2 - We report measurements of the [C II] fine-structure line at 157.714 μm in 30 normal star-forming galaxies with the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). The ratio of the line to total far-infrared (FIR) luminosity, L[C II]/LFIR, measures the ratio of the cooling of gas to that of dust, and thus the efficiency of the grain photoelectric heating process. This ratio varies by more than a factor of 40 in the current sample. About two-thirds of the galaxies have L[C II]/LFIR ratios in the narrow range of (2-7) × 10-3. The other one-third show trends of decreasing L[C II]/LFIR with increasing dust temperature, as measured by the flux ratio of infrared emission at 60 and 100 μm, Fv(60 μm)/Fv(100 μm), and with increasing star formation activity, measured by the ratio of FIR and blue-band luminosity, LFIR/LB. We also find three FIR-bright galaxies that are deficient in the [C II] line, which is undetected with 3 a upper limits of L[C II]/LFIR < (0.5-2) × 10-4. The trend in the L[C II]/LFIR ratio with the temperature of dust and with star formation activity may be due to decreased efficiency of photoelectric heating of gas at high UV radiation intensity as dust grains become positively charged, decreasing the yield and the energy of the photoelectrons. The three galaxies with no observed photodissociation region lines have among the highest LFIR/LB and Fv(60 μm)/Fv(100 μm) ratios. Their lack of [C II] lines may be due to a continuing trend of decreasing L[C II]/LFIR with increasing star formation activity and dust temperature seen in one-third of the sample with warm IRAS colors. In that case, the upper limits on L[C II]/LFIR imply a ratio of UV flux to gas density of G0/n > 10 cm3 (where G0 is in units of the local average interstellar field). The low L[C II]/LFIR ratio could also be due to either weak [C II], owing to self-absorption, or a strong FIR continuum from regions weak in [C II], such as dense H II regions or plasma ionized by hard radiation of active galactic nuclei. The mid-infrared and radio images of these galaxies show that most of the emission comes from a compact nucleus. CO and H I are detected in these galaxies, with H I seen in absorption toward the nucleus.

AB - We report measurements of the [C II] fine-structure line at 157.714 μm in 30 normal star-forming galaxies with the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). The ratio of the line to total far-infrared (FIR) luminosity, L[C II]/LFIR, measures the ratio of the cooling of gas to that of dust, and thus the efficiency of the grain photoelectric heating process. This ratio varies by more than a factor of 40 in the current sample. About two-thirds of the galaxies have L[C II]/LFIR ratios in the narrow range of (2-7) × 10-3. The other one-third show trends of decreasing L[C II]/LFIR with increasing dust temperature, as measured by the flux ratio of infrared emission at 60 and 100 μm, Fv(60 μm)/Fv(100 μm), and with increasing star formation activity, measured by the ratio of FIR and blue-band luminosity, LFIR/LB. We also find three FIR-bright galaxies that are deficient in the [C II] line, which is undetected with 3 a upper limits of L[C II]/LFIR < (0.5-2) × 10-4. The trend in the L[C II]/LFIR ratio with the temperature of dust and with star formation activity may be due to decreased efficiency of photoelectric heating of gas at high UV radiation intensity as dust grains become positively charged, decreasing the yield and the energy of the photoelectrons. The three galaxies with no observed photodissociation region lines have among the highest LFIR/LB and Fv(60 μm)/Fv(100 μm) ratios. Their lack of [C II] lines may be due to a continuing trend of decreasing L[C II]/LFIR with increasing star formation activity and dust temperature seen in one-third of the sample with warm IRAS colors. In that case, the upper limits on L[C II]/LFIR imply a ratio of UV flux to gas density of G0/n > 10 cm3 (where G0 is in units of the local average interstellar field). The low L[C II]/LFIR ratio could also be due to either weak [C II], owing to self-absorption, or a strong FIR continuum from regions weak in [C II], such as dense H II regions or plasma ionized by hard radiation of active galactic nuclei. The mid-infrared and radio images of these galaxies show that most of the emission comes from a compact nucleus. CO and H I are detected in these galaxies, with H I seen in absorption toward the nucleus.

KW - Galaxies: ISM

KW - Infrared: ISM: lines and bands

KW - ISM: atoms

KW - Radiation mechanisms: thermal

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M3 - Article

VL - 491

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

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