Observational limits on the gas mass of a z=4.9 galaxy

Abstract

We present the results of a search for molecular gas emission from a star-forming galaxy at z = 4.9. The galaxy benefits from magnification of 22 +/- 5x due to strong gravitational lensing by the foreground cluster MS1358+62. We target the CO(5-4) emission at a known position and redshift from existing Hubble Space Telescope/ACS imaging and Gemini/NIFS [OII]3727 imaging spectroscopy, and obtain a tentative detection at the 4.3sigma level with a flux of 0.104 +/- 0.024Jkm/s. From the CO line luminosity and assuming a CO-to-H2 conversion factor alpha=2, we derive a gas mass M_gas ~ 1^{+1}_{-0.6} x 10^9 M_sun. Combined with the existing data, we derive a gas fraction Mgas/(Mgas + M*) = 0.59^{+0.11}_{-0.06}. The faint line flux of this galaxy highlights the difficulty of observing molecular gas in representative galaxies at this epoch, and suggests that routine detections of similar galaxies in the absence of gravitational lensing will remain challenging even with ALMA in full science operations.

14 pages, 4 figures, published in ApJL

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• CO line emission from galaxies in the Epoch of Reionization
• Molecular gas properties of a lensed star-forming galaxy at z~3.6: a case study
• Search for [CII] emission in z=6.5-11 star-forming galaxies
• Lyα emission from galaxies in the Epoch of Reionization
• A deep search for molecular gas in two massive Lyman break galaxies at z=3 and 4: vanishing CO-emission due to low metallicity?
• The detection of FIR emission from high redshift star-forming galaxies in the ECDF-S
• Measuring the average molecular gas content of star-forming galaxies at $z=3-4$
• Molecular gas budget and characterization of intermediate-mass star-forming galaxies at $z\approx 2-3$