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Dark Memories of the Past: Discovery of Ultra-Diffuse Objects around NGC 1068

Published online by Cambridge University Press:  30 October 2019

Ichi Tanaka ,
Masafumi Yagi  and
Yoshiaki Taniguchi
Ichi Tanaka
Affiliation:
Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, Hawaii, 96720, U.S.A. email: ichi@naoj.org
Masafumi Yagi
Affiliation:
National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo, 181-8588, Japan email: YAGI.Masafumi@nao.ac.jp
Yoshiaki Taniguchi
Affiliation:
The Open University of Japan, 2-11 Wakaba, Mihama-ku, Chiba 261-8586, Japan email: yoshiaki-taniguchi@ouj.ac.jp
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Abstract

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We have searched for a sign of the past dynamical disturbance events on NGC 1068, an archetypical Type-2 Seyfert galaxy, using deep and wide optical imaging data by the Subaru telescope. The data taken by Hyper Suprime-Cam (HSC) as well as the archived data by Suprime-Cam reveal several faint outer structures of the galaxy, most of which were never reported before. We discover three large (re = 3 -5.5 kpc), extremely diffuse objects (UDOs) within 45 kpc from the center of NGC 1068. We suggest that two of these UDOs are actually a part of a large loop-like structure surrounding NGC 1068. Such an extremely faint loop or stream is the direct evidence for a past minor merger event. The third UDO has a distorted morphology, suggesting that it is under the influence of strong tidal field. Furthermore, we have identified another ultra-diffuse but compact (μ0,r > 25 mag arcsec-2, re ~ 0.8kpc) dwarf galaxy within ~140 kpc from NGC 1068. We speculate that this ultra-diffuse dwarf could be the object related to the ancient tidal disruption event (tidal dwarf) during the early mass assembly period of NGC 1068. We also detect an asymmetric outer one-arm structure emanated from the western edge of the outermost disk of NGC 1068 together with a ripple-like structure at the opposite side. These structures are also expected to arise in a late phase (up to several billion years ago) of a minor merger, according to numerical simulations. Our findings are consistent with the idea that the AGN activity in NGC 1068 is caused by a past minor merger.

Keywords

galaxies: dwarfgalaxies: interactiongalaxies: individual (NGC 1068)
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 14 , Symposium S344: Dwarf Galaxies: From the Deep Universe to the Present , August 2018 , pp. 349 - 352
Copyright
© International Astronomical Union 2019 

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