Sumo Puff: Tidal Debris or Disturbed Ultra-Diffuse Galaxy?
Sumo Puff: Tidal Debris or Disturbed Ultra-Diffuse Galaxy?
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DOI：
10.1093/pasj/psx051
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发表时间：
2017-04
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我们报告了一个角度为$\gtrsim30^{\prime\prime}$的漫射恒星云的发现，我们称之为“相扑扑”，数据来自超prime- cam斯巴鲁战略计划（HSC-SSP）。虽然我们没有这个天体的红移，但它在角上接近合并后的星系，红移$z=0.0431$，并且预计在另外两个${\sim}L_\star$星系的几个虚拟半径（假设类似的红移）内，我们用它来表示潜在的红移范围$0.0055 < z < 0.0431$。物体的光分布是平坦的，其特点是低Sersic指数（$n\sim0.3$）。它具有较低的中央$g$波段表面亮度${\sim}26.4$ magarcsec $^{-2}$，较大的有效半径${\sim}13^{\prime\prime}$ （${\sim}11$ kpc在$z=0.0431$和${\sim}1.5$ kpc在$z=0.0055$）和细长的形貌（$b/a\sim0.4$）。它的红色（$g-i\sim1$）与被动演化的恒星群一致，与附近合并后的星系相似，我们可能会看到将相扑扑与这个星系连接起来的潮汐物质。我们对这个天体的性质提供了两种可能的解释：(1)它是一个极端的、星系大小的潮汐特征，与最近的合并事件有关；或者(2)它是一个前景矮星系，具有与一个淬灭的、扰动的超漫射星系一致的特性。我们提出了一个定性的比较与模拟，证明了可行性形成一个结构类似于这个对象在合并事件。后续的光谱和/或更深入的成像来确认潮汐物质桥的存在，将是揭示这个物体真实性质的必要条件。
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.