Since 2014, a science team led by researchers of NAOJ and the University
of Edinburgh has conducted a deep contiguous photometric survey of the
M81 Group using HSC on the Subaru Telescope (Figure 1 left).
Lying at 12 million light-years, the M81 Group is one of the nearest
galaxy groups. Its proximity and resemblance to the Local Group have
fueled much astronomical research over several decades. It contains more
than 40 member galaxies, including the large spiral galaxy M81, the
peculiar galaxies M82 and NGC3077, 9 late-type galaxies, at least 20
low-luminosity early-type dwarfs, and a variety of stellar debris
features, some of which are tidal dwarf galaxy candidates. Strong tidal
interactions between M81, M82 and NGC 3077 had been revealed through the
neutral hydrogen gas studies. In 2015, the same science team showed,
for the first time, that the signatures of these interactions are also
present in the low surface brightness stellar distribution (Note 1).
The F8D1 stream was revealed through analyzing the spatial distribution of
individual stars with
properties which place them at the distance of the M81 Group. Since F8D1
lies at the edge of the survey footprint (Figure 1), only one tidal arm
can be seen, extending approximately 200,000 light-years to the
northeast.
The team has recently been awarded further observing time to search for a
counterpart stream to the southwest.
The discovery of a huge tidal tail from F8D1 is compelling
evidence that the galaxy’s present day properties have been strongly
shaped by events which have occurred in the past billion years. The team
estimates that more than one-third of F8D1’s luminosity is contained in
the tidal tail and they suggest that the source of the disruption has
been a recent close passage to the massive spiral M81.
Rokas
Žemaitis, a Ph.D. student at the University of Edinburgh who led the
work, comments that, "The discovery that F8D1 is tidally disrupting is
very exciting and it will be important to establish how many other UDGs
also show faint tidal tails."
These results appeared as Žemaitis et al. "A tale of a tail: a tidally disrupting ultra-diffuse galaxy in the M81 group" in the Monthly Notices of the Royal Astronomical Society on November 2, 2022.
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