Astrophys. J., 742, 11 (2011/November-3)
The interstellar medium in distant star-forming galaxies: turbulent pressure, fragmentation, and cloud scaling relations in a dense gas disk at z = 2.3.
SWINBANK A.M., PAPADOPOULOS P.P., COX P., KRIPS M., IVISON R.J., SMAIL I., THOMSON A.P., NERI R., RICHARD J. and EBELING H.
Abstract (from CDS):
We have used the Institut de Radioastronomie Millimétrique (IRAM) Plateau de Bure Interferometer and the Expanded Very Large Array to obtain a high-resolution map of the CO(6-5) and CO(1-0) emission in the lensed, star-forming galaxy SMM J2135-0102 at z = 2.32. The kinematics of the gas are well described by a model of a rotationally supported disk with an inclination-corrected rotation speed, vrot= 320±25 km/s, a ratio of rotational-to-dispersion support of v/σ = 3.5±0.2, and a dynamical mass of (6.0±0.5)x1010 M☉ within a radius of 2.5 kpc. The disk has a Toomre parameter, Q = 0.50±0.15, suggesting that the gas will rapidly fragment into massive clumps on scales of LJ∼ 400 pc. We identify star-forming regions on these scales and show that they are ∼10xdenser than those in quiescent environments in local galaxies, and significantly offset from the local molecular cloud scaling relations (Larson's relations). The large offset compared to local molecular cloud line-width-size scaling relations implies that supersonic turbulence should remain dominant on scales ∼100x smaller than in the kinematically quiescent interstellar medium (ISM) of the Milky Way, while the molecular gas in SMM J2135 is expected to be ∼50x denser than that in the Milky Way on all scales. This is most likely due to the high external hydrostatic pressure we measure for the ISM, Ptot/kB∼ (2±1)x107 K/cm3. In such highly turbulent ISM, the subsonic regions of gravitational collapse (and star formation) will be characterized by much higher critical densities, ncrit> = 108/cm3, a factor ≳ 1000x more than the quiescent ISM of the Milky Way.
galaxies: evolution - galaxies: high-redshift - galaxies: individual: SMM J2135-0102 - galaxies: ISM - galaxies: starburst - galaxies: star formation
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