A Search for C II 158 μm Line Emission in HCM 6A, a Lyα Emitter at z = 6.56

July 2013 • 2013ApJ...771L..20K

Authors • Kanekar, Nissim • Wagg, Jeff • Chary, Ranga Ram • Carilli, Christopher L.

Abstract • We report a Plateau de Bure Interferometer search for C II 158 μm emission from HCM 6A, a lensed Lyα emitter (LAE) at z = 6.56. Our non-detections of C II 158 μm line emission and 1.2 mm radio continuum emission yield 3σ limits of L_C\,\scriptsize{II} < 6.4 \times 10^7 \times (\Delta V/100\ km\ s^{-1})^{1/2} L for the C II 158 μm line luminosity and S 1.2 mm < 0.68 mJy for the 1.2 mm flux density. The local conversion factor between L C II and the star formation rate (SFR) yields an SFR < 4.7 M yr-1, ≈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 1.2 mm continuum emission yields a total SFR < 28 M yr-1 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 HCM 6A yields a stellar mass of 1.3 × 109 M and an SFR of ≈10 M yr-1, with negligible dust obscuration. We fortuitously detect CO J = 3-2 emission from a z = 0.375 galaxy in the foreground cluster A370, and obtain a CO line luminosity of L'(CO) > (8.95 ± 0.79) × 108 K km s-1 pc2 and a molecular gas mass of M(H2) > (4.12 ± 0.36) × 109 M , for a CO-to-H2 conversion factor of 4.6 M (K km s-1 pc2)-1.


IPAC Authors

Ranga-Ram Chary

Senior Scientist