Open Access[C II ] emission and star formation in late‐type galaxies
Author(s) -
Pierini D.,
Leech K. J.,
Tuffs R. J.,
Völk H. J.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02401.x
Subject(s) - physics , astrophysics , galaxy , spiral galaxy , star formation , interstellar medium , virgo cluster , luminous infrared galaxy , astronomy , line (geometry) , elliptical galaxy , geometry , mathematics
We demonstrate the existence of a reasonably tight linear correlation between the ratio of the [C II ( 2 P 3/2 ‐‐ 2 P 1/2 )] (λ 158 μ m) fine‐structure cooling line intensity to the [ 12 CO (J=1 → 0)] (λ 2.6 mm) line emission, I C II /I CO , and the H α (λ 6563 Å ) equivalent width (EW), over the range 2‐‐71 Å in H α EW, for a sample of 21 late‐type galaxies. The latter is composed of an optically selected sample of 12 normal Virgo cluster spiral galaxies with [C II ] detections obtained by us with LWS on board ISO, supplemented by nine galaxies with higher star formation rates (SFRs), for which [C II ] data and, in particular, H α EW data are available in the literature. We infer I C II /I CO to be a reliable tracer of the current normalized, global SFR for non‐starburst spiral galaxies. Moreover, we find that the ratio of the [C II ] line to the total far‐infrared (FIR) continuum intensity, I C II /I FIR , decreases from ∼ 0.5 to ∼ 0.1 per cent with decreasing SFR, which we propose is due to a `[C II ]‐quiet' component of I FIR from dust heated by the general interstellar radiation field. The more `quiescent' galaxies in the sample have I C II /I CO different from those observed in `compact' Galactic interstellar regions. Therefore their [C II ] emission is interpreted to be dominated by diffuse regions of the interstellar medium. For normal `star‐forming' galaxies the diffuse component of the [C II ] emission is estimated to account for at least 50 per cent of the total.