ALMA resolves turbulent, rotating [CII] emission in a young starburst galaxy at z=4.8
Abstract
We present spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) [CII] observations of the z=4.7555 submillimetre galaxy, ALESS 73.1. Our 0.5" FWHM map resolves the [CII] emitting gas which is centred close to the active galactic nucleus (AGN). The gas kinematics are dominated by rotation but with high turbulence, vrot/sigmaint~3.1, and a Toomre Q parameter <1 throughout the disk. By fitting three independent thin rotating disk models to our data, we derive a total dynamical mass of 3+-2x1010 Msol. This is close to the molecular gas mass derived from previous CO(2-1) observations, and implies a CO to H2 conversion factor alphaCO<2.3Msol(K km/s/pc2)-1. The mass budget also constrains the stellar mass to <3.1x1010 Msol, and entails a gas fraction of fgas>~0.4. The diameter of the dust continuum emission is <2 kpc, while the star-formation rate is as high as 1000 Msol/yr. Combined with our stellar mass constraint, this implies an extreme specific star formation rate >80 Gyr-1, especially since there are no clear indications of recent merger activity. Finally, our high signal-to-noise [CII] measurement revises the observed [NII]/[CII] ratio, which suggests a close to solar metallicity, unless the [CII] flux contains significant contributions from HII regions. Our observations suggest that ALESS73.1 is a nascent galaxy undergoing its first major burst of star formation, embedded within an unstable but metal-rich gas disk.
Turn this paper into a lesson
ArcXiv compiles a structured reading guide from this paper's metadata: plain-English importance, contributions, prerequisite concepts, which sections to read first, flashcards, and a quiz. Grounded in the abstract, never invented.