1,508 research outputs found
Big fish, small fish: Two New Ultra-Faint Satellites of the Milky Way
We report the discovery of two new Milky Way satellites in the neighboring
constellations of Pisces and Pegasus identified in data from the Sloan Digital
Sky Survey. Pisces II, an ultra-faint dwarf galaxy lies at the distance of ~180
kpc, some 15 degrees away from the recently detected Pisces I. Segue 3, an
ultra-faint star cluster lies at the distance of 16 kpc. We use deep follow-up
imaging obtained with the 4-m Mayall telescope at Kitt Peak National
Observatory to derive their structural parameters. Pisces II has a half-light
radius of ~60 pc, while Segue 3 is twenty times smaller at only 3pc.Comment: Accepted for publication in ApJ
How to make an ultra-faint dwarf spheroidal galaxy: tidal stirring of disky dwarfs with shallow dark matter density profiles
In recent years the Sloan Digital Sky Survey has unraveled a new population
of ultra-faint dwarf galaxies (UFDs) in the vicinity of the Milky Way (MW)
whose origin remains a puzzle. Using a suite of collisionless N-body
simulations, we investigate the formation of UFDs in the context of the tidal
stirring model for the formation of dwarf spheroidal galaxies in the Local
Group (LG). Our simulations are designed to reproduce the tidal interactions
between MW-sized host galaxies and rotationally supported dwarfs embedded in
10^9 M_sun dark matter (DM) halos. We explore a variety of inner density slopes
\rho \propto r^{-\alpha} for the dwarf DM halos, ranging from core-like (\alpha
= 0.2) to cuspy (\alpha = 1), and different dwarf orbital configurations. Our
experiments demonstrate that UFDs can be produced via tidal stirring of disky
dwarfs on relatively tight orbits, consistent with a redshift of accretion by
the host galaxy of z \sim 1, and with intermediate values for the halo inner
density slopes (\rho \propto r^{-0.6}). The inferred slopes are in excellent
agreement with those resulting from both the modeling of the rotation curves of
dwarf galaxies and recent cosmological simulations of dwarf galaxy formation.
Comparing the properties of observed UFDs with those of their simulated
counterparts, we find remarkable similarities in terms of basic observational
parameters. We conclude that tidal stirring of rotationally supported dwarfs
represents a viable mechanism for the formation of UFDs in the LG environment.Comment: 6 pages, 4 figures, revised version accepted for publication in ApJ
Letter
Limit on the LMC mass from a census of its satellites
We study the orbits of ultra-faint dwarf galaxies in the combined presence of
the Milky Way and LMC and we find 6 dwarfs which were likely accreted with the
LMC (Car 2, Car 3, Hor 1, Hyi 1, Phe 2, Ret 2), in addition to the SMC,
representing strong evidence of dwarf galaxy group infall. This procedure
depends on the gravitational pull of the LMC, thus allowing us to place a lower
bound on the Cloud's mass of . This
mass estimate is validated by applying the technique to a cosmological zoom-in
simulation of a Milky Way-like galaxy with an LMC analogue where we find that
while this lower bound may be overestimated, it will improve in the future with
smaller observational errors. We apply this technique to dwarf galaxies lacking
radial velocities and find that Eri 3 has a broad range of radial velocities
for which it has a significant chance () of having being bound to the
Cloud. We study the non-Magellanic classical satellites and find that Fornax
has an appreciable probability of being an LMC satellite if the LMC is
sufficiently massive. In addition, we explore how the orbits of the Milky Way
satellites change in the presence of the LMC and find a significant change for
several objects. Finally, we find that the LMC satellites are slightly smaller
than the Milky Way satellites at a fixed luminosity, possibly due to the
different tidal environments they have experienced.Comment: 9 pages, 7 figures. Submitted to MNRAS. Comments welcom
RIP: The Macho Era (1974-2004)
This article reviews the life and death of a scientific theory.Comment: 10 pages, 3 figures, invited review for "The Fifth International
Workshop on the Identification of Dark Matter", eds N. Spooner, V.
Kudryavtsev (World Scientific, Singapore
Fitting orbits to tidal streams with proper motions
The Galaxy's stellar halo seems to be a tangle of disrupted systems that have
been tidally stretched out into streams. Each stream approximately delineates
an orbit in the Galactic force-field. In the first paper in this series we
showed that all six phase-space coordinates of each point on an orbit can be
reconstructed from the orbit's path across the sky and measurements of the
line-of-sight velocity along the orbit. In this paper we complement this
finding by showing that the orbit can also be reconstructed if we know proper
motions along the orbit rather than the radial velocities. We also show that
accurate proper motions of stream stars would enable distances to be determined
to points on the stream that are independent of any assumption about the
Galaxy's gravitational potential. Such "Galactic parallaxes" would be as
fundamental as conventional trigonometric parallaxes, but measureable to
distances ~70 times further.Comment: 5 pages, 2 figures, submitted to MNRAS Letter
- …