Wednesday 29th May 2013

A search for CII-158$μ$m line emission in HCM\,6A, a Lyman-$α$ emitter at $z=6.56$

Nissim Kanekar (1), Jeff Wagg (2,3), Ranga Ram Chary (4), Chris Carilli (5)

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 $3\sigma$ 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$^2$)$^{-1}$.

arXiv:1305.6469 [astro-ph.CO]

Water vapor in nearby infrared galaxies as probed by Herschel

Chentao Yang, Yu Gao, A. Omont, Daizhong Liu, K. G. Isaak, D. Downes, P. P. van der Werf, Nanyao Lu

We report the first systematic study of the submillimeter water vapor rotational emission lines in infrared (IR) galaxies based on the Fourier Transform Spectrometer (FTS) data of {\it Herschel} SPIRE. Among the 176 galaxies with publicly available FTS data, 45 have at least one H$_2$O emission line detected. The H$_2$O line luminosities range from $\sim 1 \times 10^5$ L$_{\odot}$ to $\sim 5 \times 10^7$ L$_{\odot}$ while the total IR luminosities (L$_\mathrm{IR}$) have a similar spread ($\sim$1-300 $\times 10^{10}$ L$_{\odot}$). In addition, emission lines of H$_2$O$^+$ and H$_2^{18}$O are also detected. H$_2$O is found, for most galaxies, to be the strongest molecular emitter after CO in FTS spectra. The luminosity of the five most important H$_2$O lines is near-linearly correlated with L$_\mathrm{IR}$ no matter strong AGN signature is present or not. However, the luminosity of H$_2$O(2$_{11}-2_{02}$) and H$_2$O(2$_{20}-2_{11}$) appears to increase slightly faster than linear with L$_\mathrm{IR}$. Although the slope turns out to be slightly steeper when z$\sim$2-4 ULIRGs are included, the correlation is still closely linear. We find that L$_\mathrm{H_2O}/\mathrm{L}_\mathrm{IR}$ decreases with increasing f$_{25}$/f$_{60}$, but see no dependence on f$_{60}$/f$_{100}$, possibly indicating that very warm dust contributes little to the excitation of the submillimeter H$_2$O lines. The average spectral line energy distribution (SLED) of entire sample is consistent with individual SLEDs and the IR pumping plus collisional excitation model, showing that the strongest lines are H$_2$O(2$_{02}-1_{11}$) and H$_2$O(3$_{21}-3_{12}$).

arXiv:1305.6351 [astro-ph.GA]
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