The CO Emission in the Taffy Galaxies (UGC 12914/15) at 60 pc Resolution. I. The Battle for Star Formation in the Turbulent Taffy Bridge

Creators: Appleton, P. N.; Emonts, B.; Lisenfeld, U.; Falgarone, E.; Guillard, P.; Boulanger, F.; Braine, J.; Ogle, P.; Struck, C.; Vollmer, B.; Yeager, T.

Abstract

We present Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of 0.″2 (60 pc) of CO emission from the Taffy galaxies (UGC 12914/5). The observations are compared with narrowband Paα, mid-IR, radio continuum and X-ray imaging, plus optical spectroscopy. The galaxies have undergone a recent head-on collision, creating a massive gaseous bridge that is known to be highly turbulent. The bridge contains a complex web of narrow molecular filaments and clumps. The majority of the filaments are devoid of star formation, and fall significantly below the Kennicutt–Schmidt relationship for normal galaxies, especially for the numerous regions undetected in Paα emission. Within the loosely connected filaments and clumps of gas we find regions of high velocity dispersion that appear gravitationally unbound for a wide range of likely values of X_(CO). Like the "Firecracker" region in the Antennae system, they would require extremely high external dynamical or thermal pressure to stop them dissipating rapidly on short crossing timescales of 2–5 Myr. We suggest that the clouds may be transient structures within a highly turbulent multiphase medium that is strongly suppressing star formation. Despite the overall turbulence in the system, stars seem to have formed in compact hotspots within a kiloparsec-sized extragalactic H ii region, where the molecular gas has a lower velocity dispersion than elsewhere, and shows evidence for a collision with an ionized gas cloud. Like the shocked gas in the Stephan's Quintet group, the conditions in the Taffy bridge shows how difficult it is to form stars within a turbulent, multiphase, gas.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 November 4; revised 2022 March 29; accepted 2022 March 29; published 2022 June 1. This paper made use of data from the following observatories/instruments: the Atacama Large Millimeter/submillimeter Array (ALMA), the Hubble Space Telescope (HST; NICMOS), the Chandra X-ray telescope S3 Advanced CCD Imaging Spectrometer, the Very Large Array (VLA), the Spitzer Space telescope, as well as IRAC and MIPS and the Double Beam Spectrograph on the 5 m Hale telescope at the Palomar Observatory. The paper made use of the following software: Community Astronomy Software Applications (CASA; NRAO), IDL (L3Harris Geospatial Solutions), Python 3 open source software, PypeIt (Prochaska et al. 2020), and SAOImage DS9 (Chandra X-ray Science Center, HEASARC and JWST Mission office at STSCI.) This paper makes use of the following ALMA data: ADS/JAO.ALMA.2016.1.01037.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The DBSP spectra are based on observations obtained at the Hale Telescope, Palomar Observatory as part of a continuing collaboration between California Institute of Technology, NASA/JPL, Yale University, and the National Astronomical Observatories of China. This work also contains archival data obtained with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. P.A. would like to acknowledge the NRAO visitor support during a visit to NRAO-Charlottesville early in this project. P.A. would also like to thank the Institut d'Astrophysique de Paris for support as a Visiting Scientist in 2019 October in connection with this work. U.L. acknowledges support from project PID2020-114414GB-100, financed by MCIN/AEI/10.13039/501100011033, from projects P20_00334 and FQM108, financed by the Junta de Andalucia and from FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades/Proyecto A-FQM-510-UGR20. The authors wish to thank the anonymous referee for many important suggestions that improved this paper.

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