145 research outputs found
The highest-speed local dark matter particles come from the Large Magellanic Cloud
Using N-body simulations of the Large Magellanic Cloud (LMC's) passage through the Milky Way (MW), tailored to reproduce observed kinematic properties of both galaxies, we show that the high-speed tail of the Solar Neighborhood dark matter distribution is overwhelmingly of LMC origin. Two populations contribute at high speeds: 1) Particles that were once bound to the LMC, and 2) MW halo particles that have been accelerated owing to the response of the halo to the recent passage of the LMC. These particles reach speeds of 700-900 km/s with respect to the Earth, near or somewhat higher that the local escape speed of the MW. The high-speed particles follow trajectories similar to the Solar reflex motion, with peak velocities reached in June. For low-mass dark matter, these high-speed particles can dominate the signal in direct-detection experiments, extending the reach of the experiments to lower mass and elastic scattering cross sections even with existing data sets. Our study shows that even non-disrupted MW satellite galaxies can leave a significant dark matter footprint in the Solar Neighborhood.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
A Widespread, Clumpy Starburst in the Isolated Ongoing Dwarf Galaxy Merger dm1647+21
Interactions between pairs of isolated dwarf galaxies provide a critical
window into low-mass hierarchical, gas-dominated galaxy assembly and the
buildup of stellar mass in low-metallicity systems. We present the first
VLT/MUSE optical IFU observations of the interacting dwarf pair dm1647+21,
selected from the TiNy Titans survey. The H emission is widespread and
corresponds to a total unobscured star formation rate (SFR) of 0.44 M
yr, 2.7 times higher than the SFR inferred from SDSS data. The implied
specific SFR (sSFR) for the system is elevated by more than an order of
magnitude above non-interacting dwarfs in the same mass range. This increase is
dominated by the lower-mass galaxy, which has a sSFR enhancement of 50.
Examining the spatially-resolved maps of classic optical line diagnostics, we
find the ISM excitation can be fully explained by star formation. The velocity
field of the ionized gas is not consistent with simple rotation. Dynamical
simulations indicate that the irregular velocity field and the stellar
structure is consistent with the identification of this system as an ongoing
interaction between two dwarf galaxies. The widespread, clumpy enhancements in
star formation in this system point to important differences in the effect of
mergers on dwarf galaxies, compared to massive galaxies: rather than the
funneling of gas to the nucleus and giving rise to a nuclear starburst,
starbursts in low-mass galaxy mergers may be triggered by large-scale ISM
compression, and thus be more distributed.Comment: Accepted for publication in ApJ. 11 pages, 5 figures, 1 table.
Figures slightly degraded to meet arXiv size restrictions. For more
information about TiNy Titans see https://lavinia.as.arizona.edu/~tinytitans
Resolved Kinematics of Runaway and Field OB Stars in the Small Magellanic Cloud
We use GAIA DR2 proper motions of the RIOTS4 field OB stars in the Small
Magellanic Cloud (SMC) to study the kinematics of runaway stars. The data
reveal that the SMC Wing has a systemic peculiar motion relative to the SMC Bar
of (v_RA, v_Dec) = (62 +/-7, -18+/-5) km/s and relative radial velocity +4.5
+/- 5.0 km/s. This unambiguously demonstrates that these two regions are
kinematically distinct: the Wing is moving away from the Bar, and towards the
Large Magellanic Cloud with a 3-D velocity of 64 +/- 10 km/s. This is
consistent with models for a recent, direct collision between the Clouds. We
present transverse velocity distributions for our field OB stars, confirming
that unbound runaways comprise on the order of half our sample, possibly more.
Using eclipsing binaries and double-lined spectroscopic binaries as tracers of
dynamically ejected runaways, and high-mass X-ray binaries (HMXBs) as tracers
of runaways accelerated by supernova kicks, we find significant contributions
from both populations. The data suggest that HMXBs have lower velocity
dispersion relative to dynamically ejected binaries, consistent with the former
corresponding to less energetic supernova kicks that failed to unbind the
components. Evidence suggests that our fast runaways are dominated by
dynamical, rather than supernova, ejections.Comment: Accepted to ApJ Letters. 10 pages, 4 figure
Space Motions of the Dwarf Spheroidal Galaxies Draco and Sculptor based on HST Proper Motions with ~10-year Time Baseline
We present new proper motion (PM) measurements of the dwarf spheroidal
galaxies (dSphs) Draco and Sculptor using multi-epoch images obtained with the
Hubble Space Telescope ACS/WFC. Our PM results have uncertainties far lower
than previous measurements, even made with the same instrument. The PM results
for Draco and Sculptor are (mu_W,mu_N)_Dra =
(-0.0562+/-0.0099,-0.1765+/-0.0100) mas/yr and (mu_W,mu_N)_Scl =
(-0.0296+/-0.0209,-0.1358 +/-0.0214) mas/yr. The implied Galactocentric
velocity vectors for Draco and Sculptor have radial and tangential components:
(V_rad,V_tan)_Dra = (-88.6,161.4) +/- (4.4,5.6) km/s; and (V_rad,V_tan)_Scl =
(72.6,200.2) +/- (1.3,10.8) km/s. We study the detailed orbital history of both
Draco and Sculptor via numerical orbit integrations. Orbital periods of Draco
and Sculptor are found to be 1-2 and 2-5 Gyrs, respectively, accounting for
uncertainties in the MW mass. We also study the influence of the Large
Magellanic Cloud (LMC) on the orbits of Draco and Sculptor. Overall, the
inclusion of the LMC increases the scatter in the orbital results. Based on our
calculations, Draco shows a rather wide range of orbital parameters depending
on the MW mass and inclusion/exclusion of the LMC, but Sculptor's orbit is very
well constrained with its most recent pericentric approach to the MW being
0.3-0.4 Gyr ago. Our new PMs imply that the orbital trajectories of both Draco
and Sculptor are confined within the Disk of Satellites (DoS), better so than
implied by earlier PM measurements, and likely rule out the possibility that
these two galaxies were accreted together as part of a tightly bound group.Comment: 17 pages, 8 figures, 6 tables. Accepted for publication in Ap
Gaia DR2 Proper Motions of Dwarf Galaxies within 420 kpc: Orbits, Milky Way Mass, Tidal Influences, Planar Alignments, and Group Infall
A proper understanding of the Milky Way (MW) dwarf galaxies in a cosmological
context requires knowledge of their 3D velocities and orbits. However, proper
motion (PM) measurements have generally been of limited accuracy and available
only for more massive dwarfs. We therefore present a new study of the
kinematics of the MW dwarf galaxies. We use the Gaia DR2 for those dwarfs that
have been spectroscopically observed in the literature. We derive systemic PMs
for 39 galaxies and galaxy candidates out to 420 kpc, and generally find good
consistency for the subset with measurements available from other studies. We
derive the implied Galactocentric velocities, and calculate orbits in canonical
MW halo potentials of "low" () and "high" mass
(). Comparison of the distributions of orbital
apocenters and 3D velocities to the halo virial radius and escape velocity,
respectively, suggests that the satellite kinematics are best explained in the
high-mass halo. Tuc III, Crater II, and additional candidates have orbital
pericenters small enough to imply significant tidal influences. Relevant to the
missing satellite problem, the fact that fewer galaxies are observed to be near
apocenter than near pericenter implies that there must be a population of
distant dwarf galaxies yet to be discovered. Of the 39 dwarfs: 12 have orbital
poles that do not align with the MW plane of satellites (given reasonable
assumptions about its intrinsic thickness); 10 have insufficient PM accuracy to
establish whether they align; and 17 satellites align, of which 11 are
co-orbiting and (somewhat surprisingly, in view of prior knowledge) 6 are
counter-orbiting. Group infall might have contributed to this, but no
definitive association is found for the members of the Crater-Leo group.Comment: 18 pages, 7 figures, 4 tables, accepted for publication in A&
Physical Properties of Complex C Halo Clouds
Observations from the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) Survey
of the tail of Complex C are presented and the halo clouds associated with this
complex cataloged. The properties of the Complex C clouds are compared to
clouds cataloged at the tail of the Magellanic Stream to provide insight into
the origin and destruction mechanism of Complex C. Magellanic Stream and
Complex C clouds show similarities in their mass distributions (slope = -0.7
and -0.6, respectively) and have a common linewidth of 20 - 30 km/s (indicative
of a warm component), which may indicate a common origin and/or physical
process breaking down the clouds. The clouds cataloged at the tail of Complex C
extend over a mass range of 10^1.1 to 10^4.8 solar masses, sizes of 10^1.2 to
10^2.6 pc, and have a median volume density of 0.065 cm^(-3) and median
pressure of (P/k) = 580 K cm^{-3}. We do not see a prominent two-phase
structure in Complex C, possibly due to its low metallicity and inefficient
cooling compared to other halo clouds. From assuming the Complex C clouds are
in pressure equilibrium with a hot halo medium, we find a median halo density
of 5.8 x 10^(-4) cm^(-3), which given a constant distance of 10 kpc, is at a
z-height of ~3 kpc. Using the same argument for the Stream results in a median
halo density of 8.4 x 10^(-5) x (60kpc/d) cm^(-3). These densities are
consistent with previous observational constraints and cosmological
simulations. We also assess the derived cloud and halo properties with three
dimensional grid simulations of halo HI clouds and find the temperature is
generally consistent within a factor of 1.5 and the volume densities, pressures
and halo densities are consistent within a factor of 3.Comment: Accepted for publication in AJ. 54 pages, including 6 tables and 16
figure
Gas and Star Formation in Satellites of Milky Way Analogs
We have imaged the entirety of eight (plus one partial) Milky Way (MW)âlike satellite systems, a total of 42 (45) satellites, from the Satellites Around Galactic Analogs II catalog in both Hα and H i with the CanadaâFranceâHawaii Telescope and the Jansky Very Large Array. In these eight systems we have identified four cases where a satellite appears to be currently undergoing ram pressure stripping (RPS) as its H i gas collides with the circumgalactic medium (CGM) of its host. We also see a clear suppression of gas fraction (M HI/M *) with decreasing (projected) satelliteâhost separationâto our knowledge, the first time this has been observed in a sample of MW-like systems. Comparisons to the Auriga, A Project Of Simulating The Local Environment, and TNG50 cosmological zoom-in simulations show consistent global behavior, but they systematically underpredict gas fractions across all satellites by roughly 0.5 dex. Using a simplistic RPS model, we estimate the average peak CGM density that satellites in these systems have encountered to be logÏcgm/gcmâ3ââ27.3 . Furthermore, we see tentative evidence that these satellites are following a specific star formation rate to gas fraction relation that is distinct from field galaxies. Finally, we detect one new gas-rich satellite in the UGC 903 system with an optical size and surface brightness meeting the standard criteria to be considered an ultra-diffuse galaxy
A Population of Accreted SMC Stars in the LMC
We present an analysis of the stellar kinematics of the Large Magellanic
Cloud based on ~5900 new and existing velocities of massive red supergiants,
oxygen-rich and carbon-rich AGB stars, and other giants. After correcting the
line-of-sight velocities for the LMC's space motion and accounting for
asymmetric drift in the AGB population, we derive a rotation curve that is
consistent with all of the tracers used, as well as that of published HI data.
The amplitude of the rotation curve is v_0=87+/-5 km s^-1 beyond a radius
R_0=2.4+/-0.1 kpc, and has a position angle of the kinematic line of nodes of
theta=142 degrees +/-5 degrees. By examining the outliers from our fits, we
identify a population of 376 stars, or >~5% of our sample, that have
line-of-sight velocities that apparently oppose the sense of rotation of the
LMC disk. We find that these kinematically distinct stars are either
counter-rotating in a plane closely aligned with the LMC disk, or rotating in
the same sense as the LMC disk, but in a plane that is inclined by 54 degrees
+/- 2 degrees to the LMC. Their kinematics clearly link them to two known HI
arms, which have previously been interpreted as being pulled out from the LMC.
We measure metallicities from the Ca triplet lines of ~1000 LMC field stars and
30 stars in the kinematically distinct population. For the LMC field, we find a
median [Fe/H]=-0.56 +/- 0.02 with dispersion of 0.5 dex, while for the
kinematically distinct stars the median [Fe/H] is -1.25 +/- 0.13 with a
dispersion of 0.7 dex. The metallicity differences provide strong evidence that
the kinematically distinct population originated in the SMC. This
interpretation has the consequence that the HI arms kinematically associated
with the stars are likely falling into the LMC, instead of being pulled out.Comment: 12 pages, 8 color figures, accepted for publication in the
Astrophysical Journa
AN ULTRA-FAINT GALAXY CANDIDATE DISCOVERED in EARLY DATA from the MAGELLANIC SATELLITES SURVEY
We report a new ultra-faint stellar system found in Dark Energy Camera data from the first observing run of the Magellanic Satellites Survey (MagLiteS). MagLiteS J0644-5953 (Pictor II or Pic II) is a low surface brightness (Ό = 28.5+1 -1 mag arcsec-2 within its half-light radius) resolved overdensity of old and metal-poor stars located at a heliocentric distance of 45+5 -4 kpc. The physical size (r1/2 = 46+15 -11) and low luminosity (Mv = -3.2+0.4 -0.5 mag) of this satellite are consistent with the locus of spectroscopically confirmed ultra-faint galaxies. MagLiteS J0644-5953 (Pic II) is located 11.3+3.1 -0.9 kpc from the Large Magellanic Cloud (LMC), and comparisons with simulation results in the literature suggest that this satellite was likely accreted with the LMC. The close proximity of MagLiteS J0644-5953 (Pic II) to the LMC also makes it the most likely ultra-faint galaxy candidate to still be gravitationally bound to the LMC.Peer reviewe
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