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

TL;DR

This study reports a tentative detection of molecular gas in a highly magnified galaxy at redshift 4.9, illustrating the challenges of observing gas in typical early-universe galaxies without gravitational lensing.

Contribution

First detection of molecular gas in a z=4.9 galaxy using gravitational lensing, providing insights into gas content and observational challenges at high redshift.

Findings

Gas mass ~ 1 x 10^9 M_sun

Gas fraction ~ 0.59

Detection difficulty without lensing

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.