310 research outputs found
Rapid Environmental Quenching of Satellite Dwarf Galaxies in the Local Group
In the Local Group, nearly all of the dwarf galaxies (M_star < 10^9 M_sun)
that are satellites within 300 kpc (the virial radius) of the Milky Way (MW)
and Andromeda (M31) have quiescent star formation and little-to-no cold gas.
This contrasts strongly with comparatively isolated dwarf galaxies, which are
almost all actively star-forming and gas-rich. This near dichotomy implies a
rapid transformation of satellite dwarf galaxies after falling into the halos
of the MW or M31. We combine the observed quiescent fractions for satellites of
the MW and M31 with the infall times of satellites from the Exploring the Local
Volume in Simulations (ELVIS) suite of cosmological zoom-in simulations to
determine the typical timescales over which environmental processes within the
MW/M31 halos remove gas and quench star formation in low-mass satellite
galaxies. The quenching timescales for satellites with M_star < 10^8 M_sun are
short, < 2 Gyr, and quenching is more rapid at lower M_star. These satellite
quenching timescales can be 1 - 2 Gyr longer if one includes the time that
satellites were environmentally preprocessed by low-mass groups prior to MW/M31
infall. We compare with quenching timescales for more massive satellites from
previous works to synthesize the nature of satellite galaxy quenching across
the observable range of M_star = 10^{3-11} M_sun. The satellite quenching
timescale increases rapidly with satellite M_star, peaking at ~9.5 Gyr for
M_star ~ 10^9 M_sun, and the timescale rapidly decreases at higher M_star to <
5 Gyr at M_star > 5 x 10^9 M_sun. Overall, galaxies with M_star ~ 10^9 M_sun,
similar to the Magellanic Clouds, exhibit the longest quenching timescales,
regardless of environmental or internal mechanisms.Comment: 6 pages, 3 figures. Accepted in ApJ Letters. Matches published
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The Local Group: The Ultimate Deep Field
Near-field cosmology -- using detailed observations of the Local Group and
its environs to study wide-ranging questions in galaxy formation and dark
matter physics -- has become a mature and rich field over the past decade.
There are lingering concerns, however, that the relatively small size of the
present-day Local Group ( Mpc diameter) imposes insurmountable
sample-variance uncertainties, limiting its broader utility. We consider the
region spanned by the Local Group's progenitors at earlier times and show that
it reaches co-moving Mpc in linear size (a volume of ) at . This size at early cosmic epochs is large enough
to be representative in terms of the matter density and counts of dark matter
halos with . The Local
Group's stellar fossil record traces the cosmic evolution of galaxies with
(reaching
at ) over a region that is comparable to or larger than
the Hubble Ultra-Deep Field (HUDF) for the entire history of the Universe. It
is highly complementary to the HUDF, as it probes much fainter galaxies but
does not contain the intrinsically rarer, brighter sources that are detectable
in the HUDF. Archaeological studies in the Local Group also provide the ability
to trace the evolution of individual galaxies across time as opposed to
evaluating statistical connections between temporally distinct populations. In
the JWST era, resolved stellar populations will probe regions larger than the
HUDF and any deep JWST fields, further enhancing the value of near-field
cosmology.Comment: 6 pages, 5 figures; MNRAS Letters, in pres
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