Concurrent Starbursts in Molecular Gas Disks within a Pair of Colliding Galaxies at z = 1.52

Silverman, J. D. and Daddi, E. and Rujopakarn, W. and Renzini, A. and Mancini, C. and Bournaud, F. and Puglisi, A. and Rodighiero, G. and Liu, D. and Sargent, M. and Arimoto, N. and Bethermin, M. and Fensch, J. and Hayward, C. C. and Kartaltepe, J. and Kashino, D. and Koekemoer, A. and Magdis, G. and McCracken, H. J. and Nagao, T. and Sheth, K. and Smolčić, Vernesa and Valentino, F. (2018) Concurrent Starbursts in Molecular Gas Disks within a Pair of Colliding Galaxies at z = 1.52. Astrophysical Journal, 868. pp. 75-17. ISSN 0004-637X

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We report on the discovery of a merger-driven starburst at z = 1.52, PACS-787, based on high signal-to-noise ALMA observations. CO(5–4) and continuum emission (850 μm) at a spatial resolution of 0 3 reveal two compact (r_1/2 ∼ 1 kpc) and interacting molecular gas disks at a separation of 8.6 kpc, indicative of an early stage in a merger. With an SFR of 991 Me_⊙ yr^−1 , this starburst event should occur closer to final coalescence, as is usually seen in hydrodynamical simulations. From the CO size, inclination, and velocity profile for both disks, the dynamical mass is calculated through a novel method that incorporates a calibration using simulations of galaxy mergers. Based on the dynamical mass, we measure (1) the molecular gas mass, independent from the CO luminosity, (2) the ratio of the total gas mass and the CO(1–0) luminosity (α_CO ≡ M_gas/ L’CO 1-0 ), and (3) the gas-to-dust ratio, with the latter two being lower than typically assumed. We find that the high star formation triggered in both galaxies is caused by a set of optimal conditions: a high gas mass/fraction, a short depletion time (τ_depl = 85 and 67 Myr) to convert gas into stars, and the interaction of likely counter-rotating molecular disks that may accelerate the loss of angular momentum. The state of interaction is further established by the detection of diffuse CO and continuum emission, tidal debris that bridges the two nuclei and is associated with stellar emission seen by HST/WFC3. This observation demonstrates the power of ALMA to study the dynamics of galaxy mergers at high redshift.

Item Type: Article
Keywords: galaxies: high-redshift, galaxies: ISM, galaxies: starburst, galaxies: star formation
Date: 2018
Subjects: NATURAL SCIENCES > Physics > Astronomy and Astrophysics
Additional Information: © 2018. The American Astronomical Society. Received 2018 July 6; Revised 2018 September 19; Accepted 2018 October 1; Published 2018 November 21.
Divisions: Faculty of Science > Department of Physics
Publisher: IOP Publishing
Depositing User: Vernesa Smolčić
Date Deposited: 29 Mar 2019 12:46
Last Modified: 29 Mar 2019 12:58

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