14 research outputs found
Constraining the Tilt of the Milky Way's Dark Matter Halo with the Sagittarius Stream
Recent studies have suggested that the Milky Way (MW)'s Dark Matter (DM) halo
may be significantly tilted with respect to its central stellar disk, a feature
that might be linked to its formation history. In this work, we demonstrate a
method of constraining the orientation of the minor axis of the DM halo using
the angle and frequency variables. This method is complementary to other
traditional techniques, such as orbit fitting. We first test the method using a
simulated tidal stream evolving in a realistic environment inside an MW-mass
host from the FIRE cosmological simulation, showing that the theoretical
description of a stream in the action-angle-frequency formalism still holds for
a realistic dwarf galaxy stream in a cosmological potential. Utilizing the
slopes of the line in angle and frequency space, we show that the correct
rotation frame yields a minimal slope difference, allowing us to put a
constraint on the minor axis location. Finally, we apply this method to the
Sagittarius stream's leading arm. We report that the MW's DM halo is oblate
with the flattening parameter in the potential and the minor
axis pointing toward . Our constraint on the minor
axis location is weak and disagrees with the estimates from other works; we
argue that the inconsistency can be attributed in part to the observational
uncertainties and in part to the influence of the Large Magellanic Cloud.Comment: 16 pages, 12 figure
Synthetic Gaia DR3 surveys from the FIRE cosmological simulations of Milky-Way-mass galaxies
The third data release (DR3) of Gaia has provided a five-fold increase in the
number of radial velocity measurements of stars, as well as a stark improvement
in parallax and proper motion measurements. To help with studies that seek to
test models and interpret Gaia DR3, we present nine Gaia synthetic surveys,
based on three solar positions in three Milky-Way-mass galaxies of the Latte
suite of the Fire-2 cosmological simulations. These synthetic surveys match the
selection function, radial velocity measurements, and photometry of Gaia DR3,
adapting the code base Ananke, previously used to match the Gaia DR2 release in
Sanderson et al. 2020. The synthetic surveys are publicly available and can be
found at http://ananke.hub.yt/. Similarly to the previous release of Ananke,
these surveys are based on cosmological simulations and thus able to model
non-equilibrium dynamical effects, making them a useful tool in testing and
interpreting Gaia DR3.Comment: 17 pages, 7 tables, 6 figure
On the stability of tidal streams in action space
In the Gaia era it is increasingly apparent that traditional static,
parameterized models are insufficient to describe the mass distribution of our
complex, dynamically evolving Milky Way (MW). In this work, we compare
different time-evolving and time-independent representations of the
gravitational potentials of simulated MW-mass galaxies from the FIRE-2 suite of
cosmological baryonic simulations. Using these potentials, we calculate actions
for star particles in tidal streams around three galaxies with varying merger
histories at each snapshot from 7 Gyr ago to the present day. We determine the
action-space coherence preserved by each model using the Kullback-Leibler
Divergence to gauge the degree of clustering in actions and the relative
stability of the clusters over time. We find that all models produce a
clustered action space for simulations with no significant mergers. However, a
massive (mass ratio prior to infall more similar than 1:8) interacting galaxy
not present in the model will result in mischaracterized orbits for stars most
affected by the interaction. The locations of the action space clusters (i.e.
the orbits of the stream stars) are only preserved by the time-evolving model,
while the time-independent models can lose significant amounts of information
as soon as 0.5--1 Gyr ago, even if the system does not undergo a significant
merger. Our results imply that reverse-integration of stream orbits in the MW
using a fixed potential is likely to give incorrect results if integrated
longer than 0.5 Gyr into the past
LMC-driven anisotropic boosts in stream--subhalo interactions
Dark Matter (DM) subhalos are predicted to perturb stellar streams; stream
morphologies and dynamics can constrain the mass distribution of subhalos.
Using FIRE-2 simulations of Milky Way-mass galaxies, we show that presence of a
Large Magellanic Cloud (LMC)--analog significantly changes stream-subhalo
encounter rates. Three key factors drive these changes. First, the LMC--analog
brings in many subhalos, increasing encounter rates for streams near the
massive satellite by up to 20--40%. Second, the LMC--analog displaces the host
from its center-of-mass (inducing reflex motion), causing a north-south
asymmetry in the density and radial velocity distribution of subhalos. This
asymmetry results in encounter rates varying by 50--70% across the sky at the
same distance. Finally, the LMC--mass satellite induces a density wake in the
host's DM halo, further boosting the encounter rates near the LMC--analog. We
also explore the influence of stream orbital properties, finding a 50% increase
in encounters for streams moving retrograde to the LMC--analog's orbit in the
opposite hemisphere. The dependence of encounter rates on stream location and
orbit has important implications for where to search for new streams with spurs
and gaps in the Milky Way.Comment: 26 pages, 15 figures, submitted to AP
The observable properties of galaxy accretion events in Milky Way-like galaxies in the FIRE-2 cosmological simulations
In the -Cold Dark Matter model of the Universe, galaxies form in
part through accreting satellite systems. Previous work have built an
understanding of the signatures of these processes contained within galactic
stellar halos. This work revisits that picture using seven Milky Way-like
galaxies in the \textit{Latte} suite of FIRE-2 cosmological simulations. The
resolution of these simulations allows a comparison of contributions from
satellites above M10M, enabling the
analysis of observable properties for disrupted satellites in a fully
self-consistent and cosmological context. Our results show that, the time of
accretion and the stellar mass of an accreted satellite are fundamental
parameters that in partnership dictate the resulting spatial distribution,
orbital energy, and [/Fe]-[Fe/H] compositions of the stellar debris of
such mergers . These parameters also govern the resulting
dynamical state of an accreted galaxy at , leading to the expectation that
the inner regions of the stellar halo (R 30 kpc)
should contain fully phase-mixed debris from both lower and higher mass
satellites. In addition, we find that a significant fraction of the lower mass
satellites accreted at early times deposit debris in the outer halo
(R 50 kpc) that are fully phased-mixed, indicating
that they could be identified in kinematic surveys. Our results suggest that,
as future surveys become increasingly able to map the outer halo of our Galaxy,
they may reveal the remnants of long-dead dwarf galaxies whose counterparts are
too faint to be seen in higher redshift surveys.Comment: Submitted for publication in Ap
Cross-correlation Analysis of the SPIDER Experiment
The B-mode polarization in the cosmic microwave background (CMB) radiation has
been actively searched for in recent CMB experiments. Since the signal, if exists, is
expected to be very faint, the studies of polarized forgrounds have become necessary.
We use data from SPIDER and Planck to characterize polarized dust emission and
Galactic synchrotron radiation. Using two frequency channels from SPIDER (90,
150 GHz) and four from Planck (100, 143, 217, 353 GHz), we generate all possible
EE and BB cross-power spectra. Within each multipole bin, we fit two frequencies
models to the data, with and without contribution from synchrotron. We present
the fitted parameters. We find that the mean dust spectral indices for EE and BB
are statistically different. Without synchrotron contribution, we estimate that β
EE
d =
1.45+0.06
−0.06 and β
BB
d = 1.62+0.10
−0.09. With synchotron contribution, we find β
EE
d = 1.37+0.06
−0.07
and β
BB
d = 1.56+0.09
−0.08. However, if we truncate our analysis up to the multipole l ∼
145, the differences between the two shrink. β
EE
d
and β
BB
d
are within uncertainties,
and the estimated values approach what reported in Planck Collaboration Int. LIV.
This suggests that the physical properties of dust depend on angular scale. We
also investigate the impacts of using actual band centers estimated by flat spectrum
source, instead of using the nominal band centers. We find that the values of the
fitted parameters are 6% differences for the CMB amplitude and the dust spectral
index and are 18% differences for the dust amplitude
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Using Action Space Clustering to Constrain the Accretion History of Milky Way like Galaxies
In the currently favored cosmological paradigm galaxies form hierarchically
through the accretion of numerous satellite galaxies. Since the satellites are
much less massive than the host halo, they occupy a small fraction of the
volume in action space defined by the potential of the host halo. Since actions
are conserved when the potential of the host halo changes adiabatically, stars
from an accreted satellite are expected to remain clustered in action space as
the host halo evolves. In this paper, we identify accreted satellites in three
Milky Way like disk galaxies from the cosmological baryonic FIRE-2 simulations
by tracking satellite galaxies through simulation snapshots. We then try to
recover these satellites by applying the cluster analysis algorithm Enlink to
the orbital actions of accreted star particles in the present-day snapshot. We
define several metrics to quantify the success of the clustering algorithm and
use these metrics to identify well-recovered and poorly-recovered satellites.
We plot these satellites in the infall time-progenitor mass (or stellar mass)
space, and determine the boundaries between the well-recovered and
poorly-recovered satellites in these two spaces with classification tree
method. The groups found by Enlink are more likely to correspond to a real
satellite if they have high significance, a quantity assigned by Enlink. Since
cosmological simulations predict that most stellar halos have a population of
insitu stars, we test the ability of Enlink to recover satellites when the
sample is contaminated by 10-50% of insitu star particles, and show that most
of the satellites well-recovered by Enlink in the absence of insitu stars, stay
well-recovered even with 50% contamination. We thus expect that, in the future,
cluster analysis in action space will be useful in upcoming data sets (e.g.
Gaia) for identifying accreted satellites in the Milky Way
Using Action Space Clustering to Constrain the Accretion History of Milky Way like Galaxies
In the currently favored cosmological paradigm galaxies form hierarchically
through the accretion of numerous satellite galaxies. Since the satellites are
much less massive than the host halo, they occupy a small fraction of the
volume in action space defined by the potential of the host halo. Since actions
are conserved when the potential of the host halo changes adiabatically, stars
from an accreted satellite are expected to remain clustered in action space as
the host halo evolves. In this paper, we identify accreted satellites in three
Milky Way like disk galaxies from the cosmological baryonic FIRE-2 simulations
by tracking satellite galaxies through simulation snapshots. We then try to
recover these satellites by applying the cluster analysis algorithm Enlink to
the orbital actions of accreted star particles in the present-day snapshot. We
define several metrics to quantify the success of the clustering algorithm and
use these metrics to identify well-recovered and poorly-recovered satellites.
We plot these satellites in the infall time-progenitor mass (or stellar mass)
space, and determine the boundaries between the well-recovered and
poorly-recovered satellites in these two spaces with classification tree
method. The groups found by Enlink are more likely to correspond to a real
satellite if they have high significance, a quantity assigned by Enlink. Since
cosmological simulations predict that most stellar halos have a population of
insitu stars, we test the ability of Enlink to recover satellites when the
sample is contaminated by 10-50% of insitu star particles, and show that most
of the satellites well-recovered by Enlink in the absence of insitu stars, stay
well-recovered even with 50% contamination. We thus expect that, in the future,
cluster analysis in action space will be useful in upcoming data sets (e.g.
Gaia) for identifying accreted satellites in the Milky Way
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The Galaxy Progenitors of Stellar Streams around Milky Way-mass Galaxies in the FIRE Cosmological Simulations
Stellar streams record the accretion history of their host galaxy. We present
a set of simulated streams from disrupted dwarf galaxies in 13 cosmological
simulations of Milky Way (MW)-mass galaxies from the FIRE-2 suite at ,
including 7 isolated Milky Way-mass systems and 6 hosts resembling the MW-M31
pair (full dataset at: https://flathub.flatironinstitute.org/sapfire). In
total, we identify 106 simulated stellar streams, with no significant
differences in the number of streams and masses of their progenitors between
the isolated and paired environments. We resolve simulated streams with stellar
masses ranging from up to , similar to
the mass range between the Orphan and Sagittarius streams in the MW. We confirm
that present-day simulated satellite galaxies are good proxies for stellar
stream progenitors, with similar properties including their stellar mass
function, velocity dispersion, [Fe/H] and [/H] evolution tracks, and
orbital distribution with respect to the galactic disk plane. Each progenitor's
lifetime is marked by several important timescales: its infall, star-formation
quenching, and stream-formation times. We show that the ordering of these
timescales is different between progenitors with stellar masses higher and
lower than . Finally, we show that the main factor
controlling the rate of phase-mixing, and therefore fading, of tidal streams
from satellite galaxies in MW-mass hosts is non-adiabatic evolution of the host
potential. Other factors commonly used to predict phase-mixing timescales, such
as progenitor mass and orbital circularity, show virtually no correlation with
the number of dynamical times required for a stream to become phase-mixed