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Cosmic clocks: a tight radius–velocity relationship for H i-selected galaxies

Meurer, Gerhardt R. and Obreschkow, Danail and Wong, O. Ivy and Zheng, Zheng and Audcent-Ross, Fiona M. and Hanish, D. J. (2018) Cosmic clocks: a tight radius–velocity relationship for H i-selected galaxies. Monthly Notices of the Royal Astronomical Society, 476 (2). pp. 1624-1636. ISSN 0035-8711.

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H I-selected galaxies obey a linear relationship between their maximum detected radius Rmax and rotational velocity. This result covers measurements in the optical, ultraviolet, and H I emission in galaxies spanning a factor of 30 in size and velocity, from small dwarf irregulars to the largest spirals. Hence, galaxies behave as clocks, rotating once a Gyr at the very outskirts of their discs. Observations of a large optically selected sample are consistent, implying this relationship is generic to disc galaxies in the low redshift Universe. A linear radius–velocity relationship is expected from simple models of galaxy formation and evolution. The total mass within R_(max) has collapsed by a factor of 37 compared to the present mean density of the Universe. Adopting standard assumptions, we find a mean halo spin parameter λ in the range 0.020–0.035. The dispersion in λ, 0.16 dex, is smaller than expected from simulations. This may be due to the biases in our selection of disc galaxies rather than all haloes. The estimated mass densities of stars and atomic gas at R_(max) are similar (∼0.5 M⊙ pc^(−2)), indicating outer discs are highly evolved. The gas consumption and stellar population build time-scales are hundreds of Gyr, hence star formation is not driving the current evolution of outer discs. The estimated ratio between R_(max) and disc scalelength is consistent with long-standing predictions from monolithic collapse models. Hence, it remains unclear whether disc extent results from continual accretion, a rapid initial collapse, secular evolution, or a combination thereof.

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Meurer, Gerhardt R.0000-0002-0163-2507
Additional Information:© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2018 January 29. Received 2018 January 14; in original form 2017 May 22. Published: 09 March 2018. GRM acknowledges useful discussions with Tim Heckman, Brent Tully, Ken Freeman, Joss Bland-Hawthorn, Emma Ryan-Weber, and Martin Zwaan. GRM also thanks the Center for Astrophysical Sciences of the Johns Hopkins University, and the National Astronomical Observatories of the Chinese Academy of Sciences for their hospitality during visits while this paper was being developed. ZZ is supported by the National Natural Science Foundation of China Grant No. 11703036. Partial funding for the SINGG and SUNGG surveys came from National Aeronautics and Space Administration (NASA) grants NAG5-13083 (Long-Term Space Astrophysics program), GALEX GI04-0105-0009 (NASA GALEX Guest Investigator grant), and NNX09AF85G (GALEX archival grant) to GRM. The SINGG observations were made possible by a generous allocation of time from the Survey Program of the National Optical Astronomy Observatory (NOAO), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation. GALEX is a NASA Small Explorer, launched in 2003 April. We gratefully acknowledge NASA's support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d'Etudes Spatiales of France and the Korean Ministry of Science and Technology. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
National Natural Science Foundation of China11703036
Subject Keywords:galaxies: dwarf – galaxies: fundamental parameters – galaxies: kinematics and dynamics – galaxies: spiral – galaxies: structure
Issue or Number:2
Record Number:CaltechAUTHORS:20180509-144242455
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Official Citation:Gerhardt R Meurer, Danail Obreschkow, O Ivy Wong, Zheng Zheng, Fiona M Audcent-Ross, D J Hanish; Cosmic clocks: a tight radius–velocity relationship for H I-selected galaxies, Monthly Notices of the Royal Astronomical Society, Volume 476, Issue 2, 11 May 2018, Pages 1624–1636,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86321
Deposited By: Tony Diaz
Deposited On:10 May 2018 17:32
Last Modified:09 Mar 2020 13:19

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