Discovery of Extraplanar H i Clouds and a H i Tail in the M101 Galaxy Group with FAST

Abstract

We present a new high-sensitivity H i observation toward nearby spiral galaxy M101 and its adjacent 2° × 2° region using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). From the observation, we detect a more extended and asymmetric H i disk around M101. While the H i velocity field within the M101's optical disk region is regular, indicating that the relatively strong disturbance occurs in its outer disk. Moreover, we identify three new H i clouds located on the southern edge of the M101's H i disk. The masses of the three H i clouds are 1.3 × 107 M ⊙, 2.4 × 107 M ⊙, and 2.0 × 107 M ⊙, respectively. The H i clouds similar to dwarf companion NGC 5477 rotate with the H i disk of M101. Unlike NGC 5477, they have no optical counterparts. Furthermore, we detect a new H i tail in the extended H i disk of M101. The H i tail detected gives reliable evidence for M101 interaction with the dwarf companion NGC 5474. We argue that the extraplanar gas (three H i clouds) and the H i tail detected in the M101's disk may originate from a minor interaction with NGC 5474.

Discovery of an Isolated Dark Dwarf Galaxy in the Nearby Universe

“…The FAST H I observations of FAST J0139+4328 in the new survey were carried out on 2021 August 2 (region ID: DEC+433059-6). The detailed data reduction is similar to Xu et al (2021). According to Zhang et al (2022), we flag radio frequency interferences (RFIs).…”

A Dynamical Model of the M101/NGC 5474 Encounter

“…Nonetheless, some broad inferences are possible. Deep 21 cm mapping of the system (Huchtmeier & Witzel 1979;Mihos et al 2012;Xu et al 2021) has revealed H I between the two galaxies at intermediate velocities. Our model shows no similar stellar tidal bridge linking the galaxies, which suggests the observed H I stream may be a result of ram pressure effects rather than simple tidal stripping.…”

“…Meanwhile, Hubble imaging of the stellar populations in M101's NE Plume has revealed ∼ 300 Myr old post-starburst population (Mihos et al 2018), likely marking the time since M101's most recent interaction. These observations, coupled with deep HI mapping of the M101 system (Walter et al 2008;Mihos et al 2012;Xu et al 2021) and new imaging and spectroscopy of NGC 5474 (Bellazzini et al 2020) provide updated constraints on a potential interaction between M101 and NGC 5474. We use these new constraints to develop the first self-consistent N-body simulation of the M101/NGC 5474 encounter, explaining a wide variety of the observed properties while also giving insight into the subsequent evolution of M101's disk.…”

Probing galaxy evolution through Hi 21-cm emission and absorption: current status and prospects with square kilometre array

“…Cold mode accretion is predominant in low-mass (halo mass M h 10 11 M ) galaxies residing in lowdensity and high-redshift environments, while hot mode accretion dominates in high-mass (M h 10 11 M ) galaxies evolving in high-density environments. While direct kinematic evidence of gas accretion is rare, there are potential indirect signatures of gas accretion onto galaxies (Putman 2017), including observations of Hi filaments and tails around galaxies, extra-planar Hi gas clouds, and extended and warped or lopsided Hi spiral discs (e.g., Sancisi et al 2008;de Blok et al 2014;Leisman et al 2016;Xu et al 2021).…”