arXiv:1309.0093v1 [astro-ph.CO] 31 Aug 2013 eso ftehs ug teso–called (the bulge di host velocity the stellar the of with correlate persion that tightly indicates heart evidence masses the Dynamical their at galaxies. found nearby are most of (SMBHs) holes black Supermassive INTRODUCTION 1 o.Nt .Ato.Soc. Astron. R. Not. Mon. r n a crto,eovn notepplto fbrigh ( of redshifts population lower the at into observed evolving AGN accretion, gas and ers remnants en- merger to 2011). into the al. and infall et in AGN Ellison its activity the (e.g. trigger star-formation fuel and to the galaxy, regions hance interstel central host the innermost the of the interac- within motion and radial gas Mergers large-scale lar 2008). induce can al. SMBHs) et tions active Hopkins Multiple (i.e. (e.g. AGN related 2008). evolution and galaxy closely morphology, Heinz linking formation, mechanism & are star physical Merloni potential galaxies a 2005; offer of Mergers al. build–up et Matteo growth fundamental and (Di evolution: a SMBHs galaxy and revealing of SMBHs 2000) between Merritt connection & Ferrarese tion; coe 2018 October 8 ⋆ tfn Bianchi Stefano the companion of dwarf view a panchromatic in a nucleus merger: galactic active minor 3341 NGC The arzoFiore Fabrizio c 5 4 3 2 1 etrfrCsooyadAtoPril hsc,TeOi S Ohio The Physics, Astro-Particle Columb and University, Cosmology State for Ohio Center Sp The Granada, Astronomy, 33, 18008 Frascati of Astronom´ıa s/n, di Department la Via de INAF, Glorieta - IAA-CSIC, Roma Stu di Universit`a Astronomico degli Fisica, Osservatorio e Matematica di Dipartimento -al [email protected](SB) bianchi@fis.uniroma3.it E-mail: 00RAS 0000 Se”SBswudke ngoigb ute merg- further by growing on keep would SMBHs “Seed” 2 ai aFranca La Fabio , 1 000 ⋆ nioPiconcelli Enrico , 0–0 00)Pitd8Otbr21 M L (MN 2018 October 8 Printed (0000) 000–000 , e words: ons the galaxies. Key on massive mergers of minor evolution of the role in the potentially understand and and to 3341 order NGC in su st on ho needed of of efforts growth to existence hierarchical theoretical a of The unlikely and models of system. observational very the example minor-merging in are a exceptional implications 3341C important of an have NGC galaxy is satellite st and 3341 the compa a year, NGC in dwarf with that per secondary consistent suggest masses galaxy, the therefore solar We primary of few the one a of 3341B, of nucleus NGC the in hand, AGN confir other 2 analysis Seyfert panchromatic a Our 3341. of NGC in system triple-merging aais interaction galaxies: epeetXry( X-ray present We ABSTRACT z ∼ –)ad nly into finally, and, 2–4) M BH aais cie-glxe:Syet-Xry:idvda:NC31- NGC3341 individual: X-rays: - Seyfert galaxies: - active galaxies: 1 – σ mt Mathur Smita , ∗ Chandra 2 rela- iRm r,vadlaVsaNvl 4 04 oa Italy Roma, 00146 84, Navale Vasca della via Tre, Roma di Miguel , s- t - aeUiest,Clmu,O 43210 OH Columbus, University, tate s ho420 USA 43210, Ohio us, ain 04,MnePri aoe M Italy RM, Catone, Porzio Monte 00040, ,rdo( radio ), ytmi hc w cience omagravitation- a of form separation orbital nuclei where at active a pair object two indicates linked ideal AGN” which ally “binary the in term are system The clearly SMBH. they discovering therefore, and, waves. gravitational of sources host powerful the most expected of the are axes be SMBHs to binary rotational coalescing the Finally, to disk. galaxy narrow respect bi-conical with and regions the jets and line radio jets, the radio of in Unified orientations bendings radio-quiet random the the and and of distortions radio-loud ingredient the between AGN, (key phe- forma- difference torus the the AGN i.e. molecular models), the review), the a of of for aspects tion 2003, important Komossa (e.g. many nomenon to been has linked SMBHs binary also Quataert of presence & the (Haiman Interestingly, 2004). inevitable therefore binary/multiple be of should formation SMBHs the ga SMBHs, all contain the and bulges in hierarchically tic merge galaxies galaxies massive If among Universe. local relics SMBH ubiquitous the uini ersne yapaeweetence r at can- are objects nuclei such the Unfortunately, evo- where pc. binary phase 0.1–1 the of a called of separation by is timescale a represented nuclei longest is active The lution AGN”. separated “dual widely a two with galaxy ne P´erez-TorresAngel G rc h cie aiyosral hs fSMBH of phase easily-observable active, the trace AGN ´ EVLA 4 , 5 iri Matt Giorgio , and A T E tl l v2.2) file style X EVN ,adacia pia aao the of data optical archival and ), 3 , 1 to G activity, AGN of et iia ore are sources similar rfrigregion ar-forming utrs Further ructures. triggered AGN n hasse can system a ch stepresence the ms 6 in.O the On nions. 0p hl a while pc 10 ta AGN. an st lac- - 2 Stefano Bianchi, et al. not be spatially resolved with the present telescopes (e.g. Ωm = 0.27 (i.e. the default ones in xspec 12.7.1: Arnaud Merritt & Milosavljevi´c2005) for a review). On the other 1996). hand, any observational evidence even for dual AGN is so far very rare. Most of the known candidates have large separa- tions (tens of kpc), and were found thanks to the SDSS (e.g. 2.1 Chandra Djorgovski et al. 1987; Kochanek et al. 1999; Hennawi et al. NGC 3341 was observed by Chandra on 2012, Novem- 2006; Myers et al. 2008; Green et al. 2010). On the other ber 9, for a total exposure time of 50 ks (ObsID 13871), hand, the high penetrative power of hard X–ray observa- with the Advanced CCD Imaging Spectrometer (ACIS; tions provides a unique and often ultimate tool in the hunt Garmire et al. 2003). Data were reduced with the Chandra for multiple active nuclei in a galaxy. The first clear-cut Interactive Analysis of Observations (CIAO; Fruscione et al. example in the X-rays was found in the Ultra-luminous In- 2006) 4.5 and the Chandra Calibration Data Base (CALDB) frared Galaxy (ULIRG) NGC 6240 (Komossa et al. 2003), 4.5.5 software, adopting standard procedures. Spectra and followed by a handful of other confirmed cases (Ballo et al. count-rates were extracted from circular regions of 2 arcsec 2004; Guainazzi et al. 2005; Bianchi et al. 2008; Evans et al. of radius, apart from NGC 3341B (2.5 arcsec), the back- 2008; Piconcelli et al. 2010), including the very close pair ground evaluated from circular regions of 5 arcsec of radius. (only 150 pc) found recently in NGC 3393 (Fabbiano et al. No source has enough counts for a rebinning which allows 2011). A common property of these dual AGN is that they us to use the χ2 statistics. We therefore opted for the Cash are heavily dust-enshrouded nuclei. In addition some mem- (1976) statistics in the following fits to X-ray data. bers of these systems show no (or very weak) explicit AGN evidence in their optical/near-IR spectra. NGC 3341 is a nearby (z=0.027) disturbed system 2.2 SDSS consisting of a minor merger between a giant disk galaxy The Sloan Digital Sky Survey (SDSS-III) Data Release 9 (MB=−20.3 mag) and two low-mass dwarf companions within the galaxy disk (see left panel of Fig. 1), with a stel- (DR9) provided us with images in different filters (u: 3551 ˚ ˚ ˚ ˚ ˚ lar mass ratio of 50:2:1 (primary:B:C, Barth et al. 2008, A, g: 4686 A, r: 6166 A, i: 7480 A, z: 8932 A) of the NGC3341 B08 hereafter). The two offset companions are at projected field, and an optical spectrum of NGC3341B (Plate: 0578, MJD: 52339, Fiber: 0495), with a wavelength coverage of distance of 5.1 kpc (9.5 arcsec) (NGC 3341B; MB=−17 − 3800-9200 A,˚ and a resolution of 1500 at 3800 A.˚ Further mag) and 8.4 kpc (15.6 arcsec) (NGC 3341C; MB= 16.6 1 mag) from the nucleus and may be dwarf ellipticals or the details can be found at the SDSS-III website . spheroidal merger remnant of low-mass spirals. The separa- tion between B and C is ∼12 arcsec i.e. d=6.4 kpc. On the 2.3 VLA basis of Sloan Digital Sky Survey observations and follow-up Keck II spectroscopy, B08 confirmed the physical association We used publicly available, unpublished radio observations between the three objects (based on the common radial ve- of N