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  • 标题:The ALFALFA Almost Dark Galaxy AGC 229101: A 2 Billion Solar Mass H i Cloud with a Very Low Surface Brightness Optical Counterpart
  • 本地全文:下载
  • 作者:Lukas Leisman ; Katherine L.Rhode ; Catherine Ball
  • 期刊名称:The Astronomical journal
  • 印刷版ISSN:0004-6256
  • 电子版ISSN:1538-3881
  • 出版年度:2021
  • 卷号:162
  • 期号:6
  • 页码:1-14
  • DOI:10.3847/1538-3881/ac2a38
  • 语种:English
  • 出版社:American Institute of Physics
  • 摘要:We present results from deep H i and optical imaging of AGC 229101, an unusual H i source detected at vhelio =7116 km s−1 in the Arecibo Legacy Fast ALFA (ALFALFA) blind H i survey. Initially classified as a candidate "dark" source because it lacks a clear optical counterpart in Sloan Digital Sky Survey (SDSS) or Digitized Sky Survey 2 (DSS2) imaging, AGC 229101 has 109.31±0.05 M⊙ of H i, but an H i line width of only 43 ± 9 km s−1. Low-resolution Westerbork Synthesis Radio Telescope (WSRT) imaging and higher-resolution Very Large Array (VLA) B-array imaging show that the source is significantly elongated, stretching over a projected length of ∼80 kpc. The H i imaging resolves the source into two parts of roughly equal mass. WIYN partially populated One Degree Imager (pODI) optical imaging reveals a faint, blue optical counterpart coincident with the northern portion of the H i. The peak surface brightness of the optical source is only μg ∼ 26.6 mag arcsec−2, well below the typical cutoff that defines the isophotal edge of a galaxy, and its estimated stellar mass is only 107.32±0.33 M⊙, yielding an overall neutral gas-to-stellar mass ratio of M/M* = . We demonstrate the extreme nature of this object by comparing its properties with those of other H i-rich sources in ALFALFA and the literature. We also explore potential scenarios that might explain the existence of AGC 229101, including a tidal encounter with neighboring objects and a merger of two dark H i clouds.
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