X-Ray Emission from the Taffy (VV254) Galaxies and Bridge

Creators: Appleton, P. N.; Lanz, L.; Bitsakis, T.; Wang, J.; Peterson, B. W.; Lisenfeld, U.; Alatalo, K.; Guillard, P.; Boulanger, F.; Cluver, M.; Gao, Y.; Helou, G.; Ogle, P.; Struck, C.

Abstract

We present the first X-ray observations of the Taffy galaxies (UGC 12914/5) with the Chandra observatory and detect soft X-ray emission in the region of the gas-rich, radio-continuum-emitting Taffy bridge. The results are compared to Herschel observations of dust and diffuse [C ii] line-emitting gas. The diffuse component of the Taffy bridge has an X-ray luminosity of L_(X(0.5-8 keV) = 5.4 × 10^(39) erg s^(−1), which accounts for 19% of the luminosity of the sum for the two galaxies. The total mass in hot gas is (0.8–1.3) × 10^8 M_⊙, which is approximately 1% of the total (H i + H_2) gas mass in the bridge, and ~11% of the mass of warm molecular hydrogen discovered by Spitzer. The soft X-ray and dense CO-emitting gas in the bridge have offset distributions, with the X-rays peaking along the northwestern side of the bridge in the region where stronger far-IR dust and diffuse [C ii] gas is observed by Herschel. We detect nine Ultra Luminous X-ray sources in the system, the brightest of which is found in the bridge, associated with an extragalactic H ii region. We suggest that the X-ray-emitting gas has been shocked—heated to high temperatures and "splashed" into the bridge by the collision. The large amount of gas stripped from the galaxies into the bridge and its very long gas depletion timescale (>10 Gyr) may explain why this system, unlike most major mergers, is not a powerful IR emitter.

Additional Information

© 2015. The American Astronomical Society. Received 2015 July 16; accepted 2015 September 15; published 2015 October 14. We thank an anonymous referee for very helpful comments that improved the manuscript. The scientific results reported in this article are based on observations made by the Chandra X-ray Observatory. Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number GO3-14087X, issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. The work is also based, in part, on observations made with Herschel, a European Space Agency Cornerstone Mission with significant participation by NASA. Partial support for LL, PA & KA was also provided for Herschel observations, through a contract issued by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Partial support for K.A. was also provided by NASA through Hubble Fellowship grant #HST-HF2-51352.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. J.W. acknowledges support from NSFC grants 11443003 and 11473021.

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