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Published November 2012 | Published + Submitted
Journal Article Open

Investigation of Dual Active Nuclei, Outflows, Shock-heated Gas, and Young Star Clusters in Markarian 266

Abstract

Results of observations with the Spitzer, Hubble, GALEX, Chandra, and XMM-Newton space telescopes are presented for the luminous infrared galaxy (LIRG) merger Markarian 266. The SW (Seyfert 2) and NE (LINER) nuclei reside in galaxies with Hubble types SBb (pec) and S0/a (pec), respectively. Both companions are more luminous than L^* galaxies and they are inferred to each contain a ≈2.5 × 10^8 M_☉ black hole. Although the nuclei have an observed hard X-ray flux ratio of fX (NE)/fX (SW) = 6.4, Mrk 266 SW is likely the primary source of a bright Fe Kα line detected from the system, consistent with the reflection-dominated X-ray spectrum of a heavily obscured active galactic nucleus (AGN). Optical knots embedded in an arc with aligned radio continuum radiation, combined with luminous H_2 line emission, provide evidence for a radiative bow shock in an AGN-driven outflow surrounding the NE nucleus. A soft X-ray emission feature modeled as shock-heated plasma with T ~ 10^7 K is cospatial with radio continuum emission between the galaxies. Mid-infrared diagnostics provide mixed results, but overall suggest a composite system with roughly equal contributions of AGN and starburst radiation powering the bolometric luminosity. Approximately 120 star clusters have been detected, with most having estimated ages less than 50 Myr. Detection of 24 μm emission aligned with soft X-rays, radio continuum, and ionized gas emission extending ~34" (20 kpc) north of the galaxies is interpreted as ~2 × 10^7 M_☉ of dust entrained in an outflowing superwind. At optical wavelengths this Northern Loop region is resolved into a fragmented morphology indicative of Rayleigh-Taylor instabilities in an expanding shell of ionized gas. Mrk 266 demonstrates that the dust "blow-out" phase can begin in a LIRG well before the galaxies fully coalesce during a subsequent ultraluminous infrared galaxy (ULIRG) phase, and rapid gas consumption in luminous dual AGNs with kiloparsec-scale separations early in the merger process may explain the paucity of detected binary QSOs (with parsec-scale orbital separations) in spectroscopic surveys. An evolutionary sequence is proposed representing a progression from dual to binary AGNs, accompanied by an increase in observed L_x /L_(ir) ratios by over two orders of magnitude.

Additional Information

© 2012 American Astronomical Society. Received 2010 November 13; accepted 2012 July 29; published 2012 September 24. This work is based on observations with the following facilities: the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA, the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555, the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060, and the Galaxy Evolution Explorer (GALEX), which is operated for NASA by the California Institute of Technology under NASA contract NAS5-98034. The Aladin (CDS, Strasbourg) and SAOImage DS9 tools were used for image analysis. Support for this work was provided by the following NASA grants: an award issued by JPL/Caltech (Spitzer PID 3672, PI: J. Mazzarella); HST-GO10592.01-A (ACS imaging, PI: A. Evans) and program 11235 (NICMOS imaging, PI: J. Surace) issued by the STScI. K. Iwasawa acknowledges support from Spanish grant MICINN (AYA2010-21782-C03-01). This research made use of the NASA/IPAC Extragalactic Database (NED) and the Infrared Science Archive (IRSA), which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.We thank Masa Imanishi for providing FITS files for the Nobeyama Millimeter Array observations and Tsuyoshi Ishigaki for supplying optical emission-line images. We thank Chris Mihos for helpful discussions regarding merger timescales. Finally, we thank the anonymous referee for very helpful comments that led to improvements to the manuscript. Facilities: CXO (ACIS-S), XMM (EPIC pn, OM), GALEX (FUV, NUV), HST (ACS, NICMOS), UH:2.2m, Spitzer (IRAC, MIPS, IRS) Objects: Mrk 266, Mrk 266 SW, Mrk 266 NE

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