601 research outputs found
Disk Heating, Galactoseismology, and the Formation of Stellar Halos
Deep photometric surveys of the Milky Way have revealed diffuse structures
encircling our Galaxy far beyond the "classical" limits of the stellar disk.
This paper reviews results from our own and other observational programs, which
together suggest that, despite their extreme positions, the stars in these
structures were formed in our Galactic disk. Mounting evidence from recent
observations and simulations implies kinematic connections between several of
these distinct structures. This suggests the existence of collective disk
oscillations that can plausibly be traced all the way to asymmetries seen in
the stellar velocity distribution around the Sun. There are multiple
interesting implications of these findings: they promise new perspectives on
the process of disk heating, they provide direct evidence for a stellar halo
formation mechanism in addition to the accretion and disruption of satellite
galaxies, and, they motivate searches of current and near-future surveys to
trace these oscillations across the Galaxy. Such maps could be used as
dynamical diagnostics in the emerging field of "Galactoseismology", which
promises to model the history of interactions between the Milky Way and its
entourage of satellites, as well examine the density of our dark matter halo.
As sensitivity to very low surface brightness features around external galaxies
increases, many more examples of such disk oscillations will likely be
identified. Statistical samples of such features not only encode detailed
information about interaction rates and mergers, but also about long
sought-after dark matter halo densities and shapes. Models for the Milky Way's
own Galactoseismic history will therefore serve as a critical foundation for
studying the weak dynamical interactions of galaxies across the universe.Comment: 20 pages, 5 figures, accepted in for publication in a special edition
of the journal "Galaxies", reporting the proceedings of the conference "On
the Origin (and Evolution) of Baryonic Galaxy Halos", Puerto Ayora, Ecuador,
March 13-17 2017, Eds. Duncan A. Forbes and Ericson D. Lope
ELVES III: Environmental Quenching by Milky Way-Mass Hosts
Isolated dwarf galaxies usually exhibit robust star formation but satellite
dwarf galaxies are often devoid of young stars, even in Milky Way-mass groups.
Dwarf galaxies thus offer an important laboratory of the environmental
processes that cease star formation. We explore the balance of quiescent and
star-forming galaxies (quenched fractions) for a sample of ~400 satellite
galaxies around 30 Local Volume hosts from the Exploration of Local VolumE
Satellites (ELVES) Survey. We present quenched fractions as a function of
satellite stellar mass, projected radius, and host halo mass, to conclude that
overall, the quenched fractions are similar to the Milky Way, dropping below
50% at satellite M* ~ 10^8 M_sun. We may see hints that quenching is less
efficient at larger radius. Through comparison with the semi-analytic modeling
code satgen, we are also able to infer average quenching times as a function of
satellite mass in host halo-mass bins. There is a gradual increase in quenching
time with satellite stellar mass rather than the abrupt change from rapid to
slow quenching that has been inferred for the Milky Way. We also generally
infer longer average quenching times than recent hydrodynamical simulations.
Our results are consistent with models that suggest a wide range of quenching
times are possible via ram-pressure stripping, depending on the clumpiness of
the circumgalactic medium, the orbits of the satellites, and the degree of
earlier preprocessing.Comment: 18 pages, 12 figures, replaced post-refereeing, no major change
Exploring Halo Substructure with Giant Stars. XV. Discovery of a Connection between the Monoceros Ring and the Triangulum-Andromeda Overdensity?
Thanks to modern sky surveys, over twenty stellar streams and overdensity
structures have been discovered in the halo of the Milky Way. In this paper, we
present an analysis of spectroscopic observations of individual stars from one
such structure, "A13", first identified as an overdensity using the M giant
catalog from the Two Micron All-Sky Survey. Our spectroscopic observations show
that stars identified with A13 have a velocity dispersion of 40
, implying that it is a genuine coherent structure rather
than a chance super-position of random halo stars. From its position on the
sky, distance (15~kpc heliocentric), and kinematical properties, A13 is
likely to be an extension of another low Galactic latitude substructure -- the
Galactic Anticenter Stellar Structure (also known as the Monoceros Ring) --
towards smaller Galactic longitude and farther distance. Furthermore, the
kinematics of A13 also connect it with another structure in the southern
Galactic hemisphere -- the Triangulum-Andromeda overdensity. We discuss these
three connected structures within the context of a previously proposed scenario
that one or all of these features originate from the disk of the Milky Way.Comment: 12 pages, 9 figures. Accepted for publication in Ap
Origin of rotational kinematics in the globular cluster system of M31: A new clue to the bulge formation
We propose that the rotational kinematics of the globular cluster system
(GCS) in M31 can result from a past major merger event that could have formed
its bulge component. We numerically investigate kinematical properties of
globular clusters (GCs) in remnants of galaxy mergers between two disks with
GCs in both their disk and halo components. We find that the GCS formed during
major merging can show strongly rotational kinematics with the maximum
rotational velocities of 140 - 170 km/s for a certain range of orbital
parameters of merging. We also find that a rotating stellar bar, which can be
morphologically identified as a boxy bulge if seen edge-on, can be formed in
models for which the GCSs show strongly rotational kinematics. We thus suggest
that the observed rotational kinematics of GCs with different metallicities in
M31 can be closely associated with the ancient major merger event. We discuss
whether the formation of the rotating bulge/bar in M31 can be due to the
ancient merger.Comment: 5 pages, 5 figures, accepted in MNRAS Letter
The effect of septorhinoplasty on quality of life and nasal function in asians
This is the first study that aimed to assess the effects of septorhinoplasty on quality of life (QOL) in an Asian population. The study consisted of 2 parts. First, the Derriford Appearance Scale 59 (DAS-59) was translated into Korean, and the reliability and validity were assessed by administering the Korean version of Derriford Appearance Scale 59 (DAS-59K) and 36-item short-form health survey to 88 inpatients scheduled for operations. Then, a prospective study was conducted which included 31 patients who underwent primary septorhinoplasty from October 2008 through May 2009. The changes in QOL and nasal symptoms were evaluated by comparing the preoperative and postoperative 3 month DAS-59K and nasal obstruction symptom evaluation scales. Principal component analysis of the DAS-59K showed an optimum 5-factor and the Cronbach α for each factor was greater than 0.7. Significant correlation was found between the DAS-59K and 36-item short-form health survey. Objective evaluation showed at least an improvement in every patient. After septorhinoplasty, there was improvement at scores related to general self-consciousness, negative self-concept, and physical stress (P < 0.05). The pattern of improvement differed by sex, age, and the presence of external nose deviation. Mean nasal obstruction symptom evaluation scores decreased significantly after surgery. The DAS-59K is a reliable and valid test, which can be a useful tool to assess individual response to living with problems of appearance. Septorhinoplasty improves both QOL and nasal function which should be taken into consideration in future counseling of individual patients expecting septorhinoplasty. Copyright © 2013 by Lippincott Williams & Wilkins
Standardized Luminosity of the Tip of the Red Giant Branch utilizing Multiple Fields in NGC 4258 and the CATs Algorithm
The Tip of the Red Giant Branch provides a luminous standard candle for
calibrating distance ladders that reach Type Ia supernova (SN Ia) hosts.
However, recent work reveals that tip measurements vary at the 0.1 mag
level for different stellar populations and locations within a host, which may
lead to inconsistencies along the distance ladder. We pursue a calibration of
the tip using 11 Hubble Space Telescope fields around the maser host, NGC 4258,
that is consistent with SN Ia hosts by standardizing tip measurements via their
contrast ratios. We find -band tips that exhibit a full 0.3 mag range
and 0.1 mag dispersion. We do not find any correlation between HI column
density and the apparent tip to 0.04 0.03 mag/cm. We search for a
tip-contrast relation (TCR) and measure the TCR within the fields of NGC 4258
of mag/, where is the contrast ratio. This value is
consistent with the TCR originally discovered in the GHOSTS sample (Wu et al.
2022) of mag/R. Combining these measurements, we find a global
TCR of mag/R and a calibration of mag. We also use stellar models to simulate single
age and metallicity stellar populations with [Fe/H] from to and
ages from 3 Gyr to 12 Gyr and reconstruct the global TCR found here to a factor
of 2. This work is combined in a companion analysis with tip
measurements of nearby SN Ia hosts to measure .Comment: 20 pages, 12 figures, 3 tables. Submitted to Ap
CATS: The Hubble Constant from Standardized TRGB and Type Ia Supernova Measurements
The Tip of the Red Giant Branch (TRGB) provides a luminous standard candle
for constructing distance ladders to measure the Hubble constant. In practice
its measurements via edge-detection response (EDR) are complicated by the
apparent fuzziness of the tip and the multi-peak landscape of the EDR. As a
result, it can be difficult to replicate due to a case-by-case measurement
process. Previously we optimized an unsupervised algorithm, Comparative
Analysis of TRGBs (CATs), to minimize the variance among multiple halo fields
per host without reliance on individualized choices, achieving state-of-the-art
0.05 mag distance measures for optimal data. Further, we found an
empirical correlation at 5 confidence in the GHOSTS halo survey between
our measurements of the tip and their contrast ratios (ratio of stars 0.5 mag
just below and above the tip), useful for standardizing the apparent tips at
different host locations. Here, we apply this algorithm to an expanded sample
of SN Ia hosts to standardize these to multiple fields in the geometric anchor,
NGC 4258. In concert with the Pantheon SN Ia sample, this analysis produces
a (baseline) result of km/s/Mpc. The largest difference
in between this and similar studies employing the TRGB derives from
corrections for SN survey differences and local flows used in most recent SN Ia
compilations but which were absent in earlier studies. SN-related differences
total 2.0 km/s/Mpc. A smaller share, 1.4 km/s/Mpc, results from
the inhomogeneity of the TRGB calibration across the distance ladder. We employ
a grid of 108 variants around the optimal TRGB algorithm and find the median of
variants is km/s/Mpc with an additional uncertainty due to
algorithm choices of 0.83 km/s/Mpc. None of these TRGB variants result in
less than 71.6 km/s/Mpc.Comment: Submitted to ApJL, comments welcom
Molecular gas in the inner 0.7kpc-radius ring of M31
The study of the gas kinematic in the central 1.5kpc x 1.5kpc region of M31
has revealed several surprises. The starting point of this investigation was
the detection at the IRAM-30m telescope of molecular gas with very large line
splittings up to 260km/s within the beam (40 pc). In this region, which is
known for its low gas content, we also detect an ionised gas outflow in the
circumnuclear region (within 75pc from the centre) extending to the whole area
in X-ray. Relying on atomic, ionised, and molecular gas, we account for most
observables with a scenario that assumes that a few hundreds Myr ago, M31
underwent a frontal collision with M32, which triggered some star-formation
activity in the centre, and this collision explains the special configuration
of M31 with two rings observed at 0.7kpc and 10kpc. The inner disc (whose
rotation is detected in HI and ionised gas ([NII])) has thus been tilted
(inclination: 43deg, PA: 70deg) with respect to the main disc (inclination:
77deg, PA: 35deg). One of the CO velocity components is compatible with this
inner disc, while the second one comes from a tilted ring-like material with
40deg inclination and PA=-35deg. The relic star formation estimated by previous
works to have occurred more than 100Myr ago could have been triggered by the
collision and could be linked to the outflow detected in the ionised gas. Last,
we demonstrate that the amplitude of the line splittings detected in CO centred
on the systemic velocity with a relatively high spatial resolution (40pc)
cannot be accounted for by a possible weak bar that is roughly aligned along
the minor axis. Although M31 has a triaxial bulge, there are no bar indicators
in the gas component (photometry, no strong skewness of the isovelocities,
etc.).Comment: 20 pages, 20 figures, Astronomy and Astrophysics, accepte
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