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arXiv · 1704.06681

Sumo Puff: Tidal Debris or Disturbed Ultra-Diffuse Galaxy?

Johnny P. Greco·Jenny E. Greene·Adrian M. Price-Whelan·Alexie Leauthaud·Song Huang·Andy D. Goulding·Michael A. Strauss·Yutaka Komiyama·Robert H. Lupton·Satoshi Miyazaki·Masahiro Takada·Masayuki Tanaka·Tomonori Usuda
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Abstract

We report the discovery of a diffuse stellar cloud with an angular extent $\gtrsim30^{\prime\prime}$, which we term "Sumo Puff", in data from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). While we do not have a redshift for this object, it is in close angular proximity to a post-merger galaxy at redshift $z=0.0431$ and is projected within a few virial radii (assuming similar redshifts) of two other ${\sim}L_\star$ galaxies, which we use to bracket a potential redshift range of $0.0055 < z < 0.0431$. The object's light distribution is flat, as characterized by a low Sersic index ($n\sim0.3$). It has a low central $g$-band surface brightness of ${\sim}26.4$ mag arcsec$^{-2}$, large effective radius of ${\sim}13^{\prime\prime}$ (${\sim}11$ kpc at $z=0.0431$ and ${\sim}1.5$ kpc at $z=0.0055$), and an elongated morphology ($b/a\sim0.4$). Its red color ($g-i\sim1$) is consistent with a passively evolving stellar population and similar to the nearby post-merger galaxy, and we may see tidal material connecting Sumo Puff with this galaxy. We offer two possible interpretations for the nature of this object: (1) it is an extreme, galaxy-size tidal feature associated with a recent merger event, or (2) it is a foreground dwarf galaxy with properties consistent with a quenched, disturbed ultra-diffuse galaxy. We present a qualitative comparison with simulations that demonstrates the feasibility of forming a structure similar to this object in a merger event. Follow-up spectroscopy and/or deeper imaging to confirm the presence of the bridge of tidal material will be necessary to reveal the true nature of this object.

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Johnny P. Greco, Jenny E. Greene, Adrian M. Price-Whelan, Alexie Leauthaud, Song Huang, Andy D. Goulding, Michael A. Strauss, Yutaka Komiyama, Robert H. Lupton, Satoshi Miyazaki, Masahiro Takada, Masayuki Tanaka, Tomonori Usuda. 2017-04-21. Sumo Puff: Tidal Debris or Disturbed Ultra-Diffuse Galaxy?. https://doi.org/10.1093/pasj%2Fpsx051

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