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We study the effects of a metallicity variation on the thermal balance and [CII] fine-structure line strengths in interstellar photon dominated regions (PDRs). We find that a reduction in the dust-to-gas ratio and the abundance of heavy elements in the gas phase changes the heat balance of the gas in PDRs. The surface temperature of PDRs decreases as the metallicity decreases except for high density ($n>10^6$ cm$^{-3}$) clouds exposed to weak ($chi< 100$) FUV fields where vibrational H$_2$-deexcitation heating dominates over photoelectric heating of the gas. We incorporate the metallicity dependence in our KOSMA-$tau$ PDR model to study the metallicity dependence of [CII]/CO line ratios in low metallicity galaxies. We find that the main trend in the variation of the observed CII/CO ratio with metallicity is well reproduced by a single spherical clump, and does not necessarily require an ensemble of clumps as in the semi-analytical model presented by Bolatto et al. (1999).
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] s
The scatter in the relationship between the strength of [CII] 158$mu$m emission and the star formation rate at high-redshift has been the source of much recent interest. Although the relationship is well-established locally, several intensely star-fo
We consider the capabilities of ALMA and the ngVLA to detect and image the[CII] 158,$mu$m line from galaxies into the cosmic `dark ages ($z sim 10$ to 20). The [CII] line may prove to be a powerful tool in determining spectroscopic redshifts, and gal
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
We present new ALMA observations and physical properties of a Lyman Break Galaxy at z=7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, $M_{rm UV}approx-22.4$, and has been spectroscopically identified in Ly$alpha$ with