Molecular gas in distant galaxies from ALMA studies

TL;DR

ALMA has revolutionized the study of distant galaxies by detecting high-redshift objects, revealing their gas content, star formation, and structures during the epoch of reionization, with findings on gas fractions and galaxy properties.

Contribution

This paper summarizes recent ALMA observations of high-redshift galaxies, highlighting new insights into their gas content, star formation, and early universe structures.

Findings

Gas fraction increases steeply with redshift as (1+z)^2

Star formation efficiency increases with redshift as (1+z)^{0.6} to (1+z)^{1}

Detection of galaxies at z=8-9 in continuum and emission lines

Abstract

ALMA is now fully operational, and has been observing in early science mode since 2011. The millimetric (mm) and sub-mm domain is ideal to tackle galaxies at high redshift, since the emission peak of the dust at 100$\mu$m is shifted in the ALMA bands (0.3mm to 1mm) for z=2 to 9, and the CO lines, stronger at the high-J levels of the ladder, are found all over the 0.3-3mm range. Pointed surveys and blind deep fields have been observed, and the wealth of data collected reveal a drop at high redshifts (z $>$ 6) of dusty massive objects, although surprisingly active and gas-rich objects have been unveiled through gravitational lensing. The window of the reionization epoch is now wide open, and ALMA has detected galaxies at z=8-9 mainly in continuum, [CII] and [OIII] lines. Galaxies have a gas fraction increasing steeply with redshift, as (1+z)$^2$, while their star formation efficiency increases also but more slightly, as (1+z)$^{0.6}$ to (1+z)$^1$. Individual object studies have revealed luminous quasars, with black hole masses much higher than expected, clumpy galaxies with resolved star formation rate compatible with the Kennicutt-Schmidt relation, extended cold and dense gas in a circumgalactic medium, corresponding to Lyman-$\alpha$ blobs, and proto-clusters, traced by their brightest central galaxies.