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Register a new user[CII] $158,mumathrm{m}$ line emission from Orion A. I. A template for extragalactic studies?
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The [CII] $158,mumathrm{m}$ fine-structure line is one of the dominant coolants of the neutral interstellar medium. It is hence one of the brightest far-infrared emission lines and can be observed not only in star-forming regions throughout the Galaxy, but also in the diffuse interstellar medium and in distant galaxies. [CII] line emission has been suggested to be a powerful tracer of star-formation. We aim to understand the origin of [CII] emission and its relation to other tracers of interstellar gas and dust. This includes a study of the heating efficiency of interstellar gas as traced by the [CII] line to test models of gas heating. We make use of a one-square-degree map of velocity-resolved [CII] line emission towards the Orion Nebula complex, including M43 and NGC 1977. The [CII] intensity is tightly correlated with PAH emission in the IRAC $8,mumathrm{m}$ band and far-infrared emission from warm dust. The correlation between [CII] and CO(2-1) is affected by the detailed geometry of the region. We find particularly low [CII]-over-FIR intensity ratios towards large columns of (warm and cold) dust, which suggest the interpretation of the [CII] deficit in terms of a FIR excess. A slight decrease in the FIR line-over-continuum intensity ratio can be attributed to a decreased heating efficiency of the gas. We find that, at the mapped spatial scales, predictions of the star-formation rate from [CII] emission underestimate the star-formation rate calculated from YSO counts in the Orion Nebula complex by an order of magnitude. [CII] emission from the Orion Nebula complex arises dominantly in the cloud surfaces, many viewed in edge-on geometry. [CII] emission from extended faint cloud surfaces may contribute significantly to the total [CII] emission on galactic scales.
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We present the first results of an observational programme undertaken to map the fine structure line emission of singly ionized carbon ([CII] 157.7409 micron) over extended regions using a Fabry Perot spectrometer newly installed at the focal plane of a 100cm balloon-borne far-infrared telescope. This new combination of instruments has a velocity resolution of ~200 km/s and an angular resolution of 1.5. During the first flight, an area of 30x15 in Orion A was mapped. The observed [CII] intensity distribution has been compared with the velocity-integrated intensity distributions of 13CO(1-0), CI(1-0) and CO(3-2) from the literature. The observed line intensities and ratios have been analyzed using the PDR models by Kaufman et al. 1999 to derive the incident UV flux and volume density at a few selected positions.
The [CII] 157.74 $mu$m transition is the dominant coolant of the neutral interstellar gas, and has great potential as a star formation rate (SFR) tracer. Using the Herschel KINGFISH sample of 46 nearby galaxies, we investigate the relation of [CII] surface brightness and luminosity with SFR. We conclude that [CII] can be used for measurements of SFR on both global and kiloparsec scales in normal star-forming galaxies in the absence of strong active galactic nuclei (AGN). The uncertainty of the $Sigma_{rm [CII]}-Sigma_{rm SFR}$ calibration is $pm$0.21 dex. The main source of scatter in the correlation is associated with regions that exhibit warm IR colors, and we provide an adjustment based on IR color that reduces the scatter. We show that the color-adjusted $Sigma_{rm[CII]}-Sigma_{rm SFR}$ correlation is valid over almost 5 orders of magnitude in $Sigma_{rm SFR}$, holding for both normal star-forming galaxies and non-AGN luminous infrared galaxies. Using [CII] luminosity instead of surface brightness to estimate SFR suffers from worse systematics, frequently underpredicting SFR in luminous infrared galaxies even after IR color adjustment (although this depends on the SFR measure employed). We suspect that surface brightness relations are better behaved than the luminosity relations because the former are more closely related to the local far-UV field strength, most likely the main parameter controlling the efficiency of the conversion of far-UV radiation into gas heating. A simple model based on Starburst99 population-synthesis code to connect SFR to [CII] finds that heating efficiencies are $1%-3%$ in normal galaxies.
The [CII] fine structure transition at 158 microns is the dominant cooling line of cool interstellar gas, and is the brightest of emission lines from star forming galaxies from FIR through meter wavelengths. With the advent of ALMA and NOEMA, capable of detecting [CII]-line emission in high-redshift galaxies, there has been a growing interest in using the [CII] line as a probe of the physical conditions of the gas in galaxies, and as a SFR indicator at z>4. In this paper, we use a semi-analytical model of galaxy evolution (G.A.S.) combined with the code CLOUDY to predict the [CII] luminosity of a large number of galaxies at 4< z<8. At such high redshift, the CMB represents a strong background and we discuss its effects on the luminosity of the [CII] line. We study the LCII-SFR and LCII-Zg relations and show that they do not strongly evolve with redshift from z=4 and to z=8. Galaxies with higher [CII] luminosities tend to have higher metallicities and higher star formation rates but the correlations are very broad, with a scatter of about 0.5 dex for LCII-SFR. Our model reproduces the LCII-SFR relations observed in high-redshift star-forming galaxies, with [CII] luminosities lower than expected from local LCII-SFR relations. Accordingly, the local observed LCII-SFR relation does not apply at high-z. Our model naturally produces the [CII] deficit, which appears to be strongly correlated with the intensity of the radiation field in our simulated galaxies. We then predict the [CII] luminosity function, and show that it has a power law form in the range of LCII probed by the model with a slope alpha=1. The slope is not evolving from z=4 to z=8 but the number density of [CII]-emitters decreases by a factor of 20x. We discuss our predictions in the context of current observational estimates on both the differential and cumulative luminosity functions.
A tight relation between the [CII]158$mu$m line luminosity and star formation rate is measured in local galaxies. At high redshift ($z>5$), though, a much larger scatter is observed, with a considerable (15-20%) fraction of the outliers being [CII]-deficient. Moreover, the [CII] surface brightness ($Sigma_{rm CII}$) of these sources is systematically lower than expected from the local relation. To clarify the origin of such [CII]-deficiency we have developed an analytical model that fits local [CII] data, and has been validated against radiative transfer simulations performed with CLOUDY. The model predicts an overall increase of $Sigma_{rm CII}$ with the surface star formation rate ($Sigma_*$). However, for $Sigma_* > 1 M_odot~{rm yr}^{-1}~{rm kpc}^{-2}$, $Sigma_{rm CII}$ saturates. We conclude that underluminous [CII] systems can result from a combination of three factors: (a) large upward deviations from the Kennicutt-Schmidt relation ($kappa_s gg 1$), parameterized by the burstiness parameter $kappa_s$; (b) low metallicity; (c) low gas density, at least for the most extreme sources (e.g. CR7). Observations of [CII] emission alone cannot break the degeneracy among the above three parameters; this requires additional information coming from other emission lines (e.g. [OIII]88$mu$m, CIII]1909A, CO lines). Simple formulae are given to interpret available data for low and high-$z$ galaxies.
We report a Plateau de Bure interferometer search for CII-158$mu$m emission from HCM6A, a lensed Lyman-$alpha$ emitter (LAE) at $z = 6.56$. Our non-detections of CII-158$mu$m line emission and 1.2mm radio continuum emission yield $3sigma$ limits of L$_{rm CII} < 6.4 times 10^7 times (Delta V/100 km s^{-1})^{1/2}$ L$_odot$ on the CII-158$mu$m line luminosity and S$_{rm 1.2mm} < 0.68$ mJy on the 1.2mm flux density. The local conversion factor between L$_{rm CII}$ and star formation rate (SFR) yields an SFR $< 4.7$ M$_odot$ yr$^{-1}$, $approx 2$ times lower than that inferred from the ultraviolet (UV) continuum, suggesting that the local factor may not be applicable in high-$z$ LAEs. The non-detection of 1.2mm continuum emission yields a total SFR $< 28$ M$_odot$/yr; any obscured star formation is thus within a factor of two of the visible star formation. Our best-fit model to the rest-frame UV/optical spectral energy distribution of HCM6A yields a stellar mass of $1.3 times 10^9$ M$_odot$ and an SFR of ~10 M$_odot$/yr, with negligible dust obscuration. We fortuitously detect CO J=3-2 emission from a $z=0.375$ galaxy in the foreground cluster Abell370, obtaining a CO line luminosity of L$^prime ({rm CO}) > (8.95 pm 0.79) times 10^8$ K km s$^{-1}$ pc$^2$, and a molecular gas mass of M$({rm H_2}) > (4.12 pm 0.36) times 10^9$ M$_odot$, for a CO-to-H$_2$ conversion factor of 4.6 M$_odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$.
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