212 research outputs found
Models of Distorted and Evolving Dark Matter Halos
We investigate the ability of basis function expansions to reproduce the
evolution of a Milky Way-like dark matter halo, extracted from a cosmological
zoom-in simulation. For each snapshot, the density of the halo is reduced to a
basis function expansion, with interpolation used to recreate the evolution
between snapshots. The angular variation of the halo density is described by
spherical harmonics, and the radial variation either by biorthonormal basis
functions adapted to handle truncated haloes or by splines. High fidelity orbit
reconstructions are attainable using either method with similar computational
expense. We quantify how the error in the reconstructed orbits varies with
expansion order and snapshot spacing. Despite the many possible biorthonormal
expansions, it is hard to beat a conventional Hernquist-Ostriker expansion with
a moderate number of terms ( radial and angular). As two
applications of the developed machinery, we assess the impact of the
time-dependence of the potential on (i) the orbits of Milky Way satellites, and
(ii) planes of satellites as observed in the Milky Way and other nearby
galaxies. Time evolution over the last 5 Gyr introduces an uncertainty in the
Milky Way satellites' orbital parameters of per cent, comparable to
that induced by the observational errors or the uncertainty in the present-day
Milky Way potential. On average, planes of satellites grow at similar rates in
evolving and time-independent potentials. There can be more, or less, growth in
the plane's thickness, if the plane becomes less, or more, aligned with the
major or minor axis of the evolving halo.Comment: MNRAS, submitte
Novel constraints on the particle nature of dark matter from stellar streams
Tidal streams are highly sensitive to perturbations from passing dark matter
(DM) subhalos and thus provide a means of measuring their abundance. In a
recent paper, we analyzed the distribution of stars along the GD-1 stream with
a combination of data from the Gaia satellite and the Pan-STARRS survey, and we
demonstrated that the population of DM subhalos predicted by the cold dark
matter (CDM) paradigm are necessary and sufficient to explain the perturbations
observed in the linear density of stars. In this paper, we use the measurements
of the subhalo mass function (SHMF) from the GD-1 data combined with a similar
analysis of the Pal 5 stream to provide novel constraints on alternative DM
scenarios that predict a suppression of the SHMF on scales smaller than the
mass of dwarf galaxies, marginalizing over uncertainties in the slope and
normalization of the unsuppressed SHMF and the susceptibility of DM subhalos in
the inner Milky Way to tidal disruption. In particular, we derive a 95% lower
limit on the mass of warm dark matter (WDM) thermal relics from streams alone that strengthens to when adding dwarf satellite counts. Similarly, we
constrain the axion mass in ultra-light ("fuzzy") dark matter (FDM) models to
be from streams alone or when adding dwarf satellite counts.
Because we make use of simple approximate forms of the streams' SHMF
measurement, our analysis is easy to replicate with other alternative DM models
that lead to a suppression of the SHMF.Comment: JCAP, in press. Code available to fully replicate the analysis at
https://github.com/jobovy/dark-matter-constraints-from-stellar-stream
A deeper look at the GD1 stream::density variations and wiggles
Using deep photometric data from CFHT/Megacam, we study the morphology and
density of the GD-1 stream, one of the longest and coldest stellar streams in
the Milky Way. Our deep data recovers the lower main sequence of the stream
with unprecedented quality, clearly separating it from Milky Way foreground and
background stars. An analysis of the distance to different parts of the stream
shows that GD-1 lies at a heliocentric distance between 8 and 10 kpc, with only
a shallow gradient across 45 deg on the sky. Matched filter maps of the stream
density show clear density variations, such as deviations from a single orbital
track and tentative evidence for stream fanning. We also detect a clear
under-density in the middle of the stream track at =-45 deg
surrounded by overdense stream segments on either side. This location is a
promising candidate for the elusive missing progenitor of the GD-1 stream. We
conclude that the GD-1 stream has clearly been disturbed by interactions with
the Milky Way disk or other sub-halos.Comment: submitted to MNRAS, comments welcom
The near-UV: the true window on jet rotation
High resolution observations of jet rotation in newly forming stars have the potential to support theories of magneto-centrifugal jet launching. We report a detection of a radial velocity difference across the blue-shifted jet from RY Tau, the direction of which matches the CO disk rotation sense. Now, in 3 of 3 cases, the sense of the near-UV jet gradient matches the disk rotation sense, implying that we are indeed observing jet rotation. It seems the jet core, probed at near-UV wavelengths, is protected by the outer jet layers from kinematic contaminations, and thus represents the only true window on jet rotation
Clouds, Streams and Bridges: Redrawing the blueprint of the Magellanic System with Gaia DR1
We present the discovery of stellar tidal tails around the Large and the
Small Magellanic Clouds in the Gaia DR1 data. In between the Clouds, their
tidal arms are stretched towards each other to form an almost continuous
stellar bridge. Our analysis relies on the exquisite quality of the Gaia's
photometric catalogue to build detailed star-count maps of the Clouds. We
demonstrate that the Gaia DR1 data can be used to detect variable stars across
the whole sky, and in particular, RR Lyrae stars in and around the LMC and the
SMC. Additionally, we use a combination of Gaia and Gale to follow the
distribution of Young Main Sequence stars in the Magellanic System. Viewed by
Gaia, the Clouds show unmistakable signs of interaction. Around the LMC, clumps
of RR Lyrae are observable as far as ~20 degrees, in agreement with the most
recent map of Mira-like stars reported in Deason et al (2016). The SMC's outer
stellar density contours show a characteristic S-shape, symptomatic of the
on-set of tidal stripping. Beyond several degrees from the center of the dwarf,
the Gaia RR Lyrae stars trace the Cloud's trailing arm, extending towards the
LMC. This stellar tidal tail mapped with RR Lyrae is not aligned with the
gaseous Magellanic Bridge, and is shifted by some ~5 degrees from the Young
Main Sequence bridge. We use the offset between the bridges to put constraints
on the density of the hot gaseous corona of the Milky Way.Comment: Submitted to MNRA
Effects of Symmetry Breaking on the Strong and Electroweak Interactions of the Vector Nonet
Starting from a chiral invariant and quark line rule conserving Lagrangian of
pseudoscalar and vector nonets we introduce first and second order symmetry
breaking as well as quark line rule violating terms and fit the parameters, at
tree level, to many strong and electroweak processes. A number of predictions
are made. The electroweak interactions are included in a manifestly gauge
invariant manner. The resulting symmetry breaking pattern is discussed in
detail. Specifically, for the ``strong'' interactions, we study all the vector
meson masses and V -> \phi \phi decays, including isotopic spin violations. In
the electroweak sector we study the { rho^0 , omega , phi } -> e^+e^- decays, {
pi^+ , K^+ , K^0 } ``charge radii'', K_{l3} ``slope factor'' and the overall
e^+e^- -> pi^+ pi^- process. It is hoped that the resulting model may be useful
as a reasonable description of low energy physics in the range up to about 1
GeV.Comment: 43 pages (LaTeX), 5 PostScript figures are included as
uuencoded-compressed-tar file at the en
The Pisces Plume and the Magellanic wake
Using RR Lyrae stars in the Gaia Data Release 2 and Pan-STARRS1 we study the properties of the Pisces overdensity, a diffuse substructure in the outer halo of the Milky Way. We show that along the line of sight, Pisces appears as a broad and long plume of stars stretching from 40 to 110 kpc with a steep distance gradient. On the sky Pisces’s elongated shape is aligned with the Magellanic Stream. Using follow-up VLT FORS2 spectroscopy, we have measured the velocity distribution of the Pisces candidate member stars and have shown it to be as broad as that of the Galactic halo but offset to negative velocities. Using a suite of numerical simulations, we demonstrate that the structure has many properties in common with the predicted behaviour of the Magellanic wake, i.e. the Galactic halo overdensity induced by the infall of the Magellanic Clouds
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