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Published June 10, 2015 | Published
Journal Article Open

ALMA Resolves the Properties of Star-forming Regions in a Dense Gas Disk at z ~ 3


We exploit long baseline ALMA submillimeter observations of the lensed star-forming galaxy SDP 81 at z = 3.042 to investigate the properties of the interstellar medium (ISM) on scales of 50–100 pc. The kinematics of the ^(12)CO gas within this system are well described by a rotationally supported disk with an inclination-corrected rotation speed, v_(rot) = 320 ± 20 km s^(−1), and a dynamical mass of M_(dyn) = (3.5 ± 1.0)× 10^(10) M_☉ within a radius of 1.5 kpc. The disk is gas-rich and unstable, with a Toomre parameter, Q = 0.30 ± 0.10, and so into star-forming regions with Jeans length L_J ~ 130 pc. We identify five star-forming regions within the ISM on these scales and show that their scaling relations between luminosity, line widths, and sizes are significantly offset from those typical of molecular clouds in local galaxies (Larson's relations). These offsets are likely to be caused by the high external hydrostatic pressure for the ISM, P_(tot)/k_B ~ 40_(-20^(+30) × 10^7 K cm^(−3), which is ~10^4× higher than the typical ISM pressure in the Milky Way. The physical conditions of the star-forming ISM and giant molecular clouds appear to be similar to those found in the densest environments in the local universe, such as those in the Galactic center.

Additional Information

© 2015 American Astronomical Society. Received 2015 May 1; accepted 2015 May 18; published 2015 June 9. We would like to thank the anonymous referee for a constructive report on this paper. A.M.S. acknowledges an STFC Advanced Fellowship (ST/H005234/1) and the Leverhume foundation. I.R.S. acknowledges STFC (ST/I001573/1), the ERC Advanced Grant DUSTYGAL 321334, and a Royal Society/Wolfson Merit Award. C.F. acknowledges CAPES funding (proc. 12203-1). We also thank Padelis Papadopoulos for useful discussions. This paper uses data from ALMA program ADS/JAO.ALMA#2011.0.00016.SV. ALMA is a partnership of ESO, NSF (USA), NINS (Japan), NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea) and the Republic of Chile. The JAO is operated by ESO, AUI/NRAO and NAOJ.

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August 22, 2023
August 22, 2023