FAST reveals new evidence for M94 as a merger

Abstract

We report the first high-sensitivity HI observation toward the spiral galaxy M94 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). From these observations, we discovered that M94 has a very extended HI disk, twice larger than that observed by THINGS, which is accompanied by an HI filament and seven HVCs (high velocity clouds) at different distances. The projected distances of these clouds and filament are less than 50 kpc from the galactic center. We measured a total integrated flux (including all clouds/filament) of 127.3 ($\pm$1) Jy km s${}^{-1}$, corresponding to a H I mass of (6.51$\pm$0.06)$\times$10${}^8$M${}_{\odot }$, which is 63.0% more than that observed by THINGS. By comparing numerical simulations with the HI maps and the optical morphology of M94, we suggest that M94 is likely a remnant of a major merger of two galaxies, and the HVCs and HI filament could be the tidal features originated from the first collision of the merger happened about 5 Gyr ago. Furthermore, we found a seemingly isolated HI cloud at a projection distance of 109 kpc without any optical counterpart detected. We discussed the possibilities of the origin of this cloud, such as dark dwarf galaxy and RELHIC (REionization-Limited HI Cloud). Our results demonstrate that high-sensitivity and wide-field HI imaging is important in revealing the diffuse cold gas structures and tidal debris which is crucial to understanding the dynamical evolution of galaxies.

14 pages, 8 figures

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Cited by in corpus (9)

• HiFAST: an HI data calibration and imaging pipeline for FAST
• Addition of the Local Volume sample of galaxies from the FAST HI survey
• The FAST Ursa Major supergroup HI survey (FUMaS): catalog and HI mass function
• Not so-dark: High resolution HI imaging of J0139+4328 and identification of an optical counterpart
• HI-bearing dark galaxies predictions from constrained Local Group simulations: how many and where to find them
• HI Content of Group Galaxies from the FAST All Sky HI Survey
• Dynamical Preconditions for Ice Formation in Supernova Remnant and Cloud Interactions: A 2D MHD Study
• Recent Developments on the HI Gas of Low-Redshift Galaxies Seen by the 21cm Emission Lines
• The FAST Hundred-Deg${}^2$ HI Deep (HD${}^2$) Survey: Early Results from the Pilot Survey