59 research outputs found
Stellar occultation lightcurve modeling for elliptical occulting bodies
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001.Includes bibliographical references (leaf 41).We present a new method of calculating model lightcurves for stellar occultations by the Jovian planets. We model the occulting planet as a three-dimensional body of non-zero ellipticity, and define two ellipses of intersection with the body which dictate the appearance of the lightcurve. These include the visible-limb plane ellipse, which is the observed figure of the body as seen in the sky, and the line-of-sight ellipse, which contains the line of sight to the occulted star, and is the plane in which the starlight is refracted. The observed stellar flux during the occultation is primarily dictated by the ellipticity and subsequent radius of curvature of the instantaneous ellipse in the line-of-sight plane. This new method is applied to several test cases, as well as to the Jovian occultation of HIP9369 on 10 October 1999. Lightcurves generated by this model are compared to identical situations using the method published in Hubbard et al. (1997), showing that the Hubbard model works well for low-latitude occultations, but fails at higher latitudes. In the case of the high-latitude Jovian occultation, the best-fit lightcurve, produced from this new method, yielded a half-light equatorial radius of 71,343±1.2 km with a scale height of 19.25±0.5km, and an isothermal temperature of 139K. The same data, fit using a lightcurve generated by the method described in Hubbard et al. (1997), resulted in a half-light equatorial radius of 71,819km with a scale height of 17.9km with errors comparable to the previous fit, resulting in an isothermal temperature of 129K. Lightcurves are numerically generated for an ellipsoidal planet and, for comparison, an approximation to the ellipsoidal case consisting of a sphere with radius equal to the radius of curvature of the ellipsoid at the half-light point. We find that in the case of an occultation where the line-of-sight ellipticity does not vary, that the radius of curvature approximation matches the ellipsoidal planet lightcurve to within 0.007%. For an oblique occultation however, the line-of-sight ellipticity varies, and the approximation, using only a single radius of curvature sphere, is only good to about 1%. As a result, we find that using a model such as that presented in Baum and Code (1953) to fit the lightcurve of an ellipsoidal planet can return values for half-light radius (after accounting for the distance between the center of curvature and the center of the body) which may match the local distance to the center of the ellipsoid to a fraction of a percent, while returning values of scale height which may be in error by several percent. Test cases are also then put through numerical inversions, to obtain temperature versus pressure profiles. Test cases with spherical planets return temperature profiles that match those used to create the lightcurves, while test cases with ellipsoidal planets return temperature profiles which can differ from the input temperatures by tens of degrees, assuming a constant local gravity over the course of the occultation.by Bryan Hilbert.S.M
A Deeper Look at Faint Hα Emission in Nearby Dwarf Galaxies
We present deep Hα imaging of three nearby dwarf galaxies, carefully selected to optimize observations with the Maryland-Magellan Tunable Filter (MMTF) on the Magellan 6.5 m telescope. An effective bandpass of ~13 Å is used, and the images reach 3σ flux limits of ~8 × 10^(−18) erg s^(−1) cm^(−2), which is about an order of magnitude lower than standard narrowband observations obtained by the most recent generation of local Hα galaxy surveys. The observations were originally motivated by the finding that the Hα/FUV flux ratio of galaxies systematically declines as global galactic properties such as the star formation rate (SFR) and stellar mass decrease. The three dwarf galaxies selected for study have SFRs that, when calculated from their Hα luminosities using standard conversion recipes, are ~50% of those based on the FUV. Follow-up studies of many of the potential causes for the trends in the Hα/FUV flux ratio have been performed, but the possibility that previous observations have missed a non-negligible fraction of faint ionized emission in dwarf galaxies has not been investigated. The MMTF observations reveal both diffuse and structured Hα emission (filaments, shells, possible single-star H ii regions) spanning extents up to 2.5 times larger relative to previous observations. However, only up to an additional ~5% of Hα flux is captured, which does not account for the trends in the Hα/FUV ratio. Beyond investigation of the Hα/FUV ratio, the impact of the newly detected extended flux on our understanding of star formation, the properties of H ii regions, and the propagation of ionizing photons warrant further investigation
Medication adherence in patients with myotonic dystrophy and facioscapulohumeral muscular dystrophy
Myotonic dystrophy (DM) and facioscapulohumeral muscular dystrophy (FSHD) are the two most common adult muscular dystrophies and have progressive and often disabling manifestations. Higher levels of medication adherence lead to better health outcomes, especially important to patients with DM and FSHD because of their multisystem manifestations and complexity of care. However, medication adherence has not previously been studied in a large cohort of DM type 1 (DM1), DM type 2 (DM2), and FSHD patients. The purpose of our study was to survey medication adherence and disease manifestations in patients enrolled in the NIH-supported National DM and FSHD Registry. The study was completed by 110 DM1, 49 DM2, and 193 FSHD patients. Notable comorbidities were hypertension in FSHD (44 %) and DM2 (37 %), gastroesophageal reflux disease in DM1 (24 %) and DM2 (31 %) and arrhythmias (29 %) and thyroid disease (20 %) in DM1. Each group reported high levels of adherence based on regimen complexity, medication costs, health literacy, side effect profile, and their beliefs about treatment. Only dysphagia in DM1 was reported to significantly impact medication adherence. Approximately 35 % of study patients reported polypharmacy (taking 6 or more medications). Of the patients with polypharmacy, the DM1 cohort was significantly younger (mean 55.0 years) compared to DM2 (59.0 years) and FSHD (63.2 years), and had shorter disease duration (mean 26 years) compared to FSHD (26.8 years) and DM2 (34.8 years). Future research is needed to assess techniques to ease pill swallowing in DM1 and to monitor polypharmacy and potential drug interactions in DM and FSHD
Effects of large-scale structure on the accuracy of weak lensing mass measurements
Weak gravitational lensing has become an important method to determine the
masses of galaxy clusters. The intrinsic shapes of the galaxies are a dominant
source of uncertainty, but there are other limitations to the precision that
can be achieved. In this paper we revisit a typically ignored source of
uncertainty: structure along the line-of sight. Using results from the
Millennium Simulation we confirm the validity of analytical calculations that
have shown that such random projections are particularly important for studies
of the cluster density profile. In general the contribution of large-scale
structure to the total error budget is comparable to the statistical errors. We
find that the precision of the mass measurement can be improved only slightly
by modelling the large-scale structure using readily available data.Comment: submitted to MNRAS; 10 pages, 8 figure
Lensing Magnification: Implications for Counts of Submillimeter Galaxies and SZ Clusters
We study lensing magnification of source galaxies by intervening galaxy
groups and clusters using a halo model. Halos are modeled with truncated NFW
profiles with ellipticity added to their lensing potential and propagated to
observable lensing statistics. We present the formalism to calculate observable
effects due to a distribution of halos of different masses at different
redshifts along the l ine of sight. We calculate the effects of magnification
on the number counts of high-redshift galaxies. Using BLAST survey data for
submillimeter galaxies (SMGs), we find that magnification affects the steep,
high flux par t of the counts by about 60%. The effect becomes much stronger if
the intrinsic distribution is signi ficantly steeper than observed. We also
consider the effect of this high-redshift galaxy population on contaminating
the Sunyaev-Zel'dovich (SZ) signal of massive clusters using the halo model
approach. We find that for the majority of clusters expected to be detected
with ongoing SZ surveys, there is significant contamination from the Poisson
noise due to background SMGs. This contr ibution can be comparable to the SZ
increment for typical clusters and can also contaminate the SZ decrement of low
mass clusters. Thus SZ observations, especially for the increment part of the
SZ spectrum, need to include careful modeling of this irreducible contamination
for mass estimation. Lensing further enhances the contamination, especially
close to the cores of massive clusters and for very disturbed clusters with
large magnification cross-section.Comment: 21 pages, 14 figures, Submitted to MNRA
Powerful Radio-Loud Quasars are Triggered by Galaxy Mergers in the Cosmic Bright Ages
While supermassive black holes are ubiquitous features of galactic nuclei,
only a small minority are observed during episodes of luminous accretion. The
physical mechanism(s) driving the onset of fueling and ignition in these active
galactic nuclei (AGN) are still largely unknown for many galaxies and
AGN-selection criteria. Attention has focused on AGN triggering by means of
major galaxy mergers gravitationally funneling gas towards the galactic center,
with evidence both for and against this scenario. However, several recent
studies have found that radio-loud AGN overwhelmingly reside in ongoing or
recent major galaxy mergers. In this study, we test the hypothesis that major
galaxy mergers are important triggers for radio-loud AGN activity in powerful
quasars during cosmic noon (1 < z < 2). To this end, we compare Hubble Space
Telescope WFC3/IR observations of the z > 1 3CR radio-loud broad-lined quasars
to three matched radio-quiet quasar control samples. We find strong evidence
for major-merger activity in nearly all radio-loud AGN, in contrast to the much
lower merger fraction in the radio-quiet AGN. These results suggest major
galaxy mergers are key ingredients to launching powerful radio jets. Given many
of our radio-loud quasars are blue, our results present a possible challenge to
the "blow-out" paradigm of galaxy evolution models in which blue quasars are
the quiescent end result following a period of red quasar feedback initiated by
a galaxy merger. Finally, we find a tight correlation between black hole mass
and host galaxy luminosity for these different high-redshift AGN samples
inconsistent with those observed for local elliptical galaxies.Comment: Published by Ap
Strong lensing in the MareNostrum Universe: biases in the cluster lens population
Strong lensing is one of the most direct probes of the mass distribution in
the inner regions of galaxy clusters. It can be used to constrain the density
profiles and to measure the mass of the lenses. Moreover, the abundance of
strong lensing events can be used to constrain the structure formation and the
cosmological parameters through the so-called "arc-statistics" approach.
However, several issues related to the usage of strong lensing clusters in
cosmological applications are still controversial, leading to the suspect that
several biases may affect this very peculiar class of objects. With this study
we aim at better understanding the properties of galaxy clusters which can
potentially act as strong lenses. We do so by investigating the properties of a
large sample of galaxy clusters extracted from the N-body/hydrodynamical
simulation MareNostrum Universe. We explore the correlation between the cross
section for lensing and many properties of clusters, like the mass, the
three-dimensional and projected shapes, their concentrations, the X-ray
luminosity and the dynamical activity. We find that the probability of strong
alignments between the major axes of the lenses and the line of sight is a
growing function of the lensing cross section. In projection, the strong lenses
appear rounder within R200, but we find that their cores tend to be more
elliptical as the lensing cross section increases. We also find that the
cluster concentrations estimated from the projected density profiles tend to be
biased high. The X-ray luminosity of strong lensing clusters is higher than
that of normal lenses of similar mass and redshift. This is particular
significant for the least massive lenses. Finally, we find that the strongest
lenses generally exhibit an excess of kinetic energy within the virial radius,
indicating that they are more dynamically active than usual clusters.Comment: 22 pages, 18 figures, accepted for publication on A&
CFHTLenS: the environmental dependence of galaxy halo masses from weak lensing
We use weak gravitational lensing to analyse the dark matter haloes around satellite galaxies in galaxy groups in the Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS) data set. This data set is derived from the Canada–France–Hawaii Telescope Legacy Survey Wide survey, and encompasses 154 deg^2 of high-quality shape data. Using the photometric redshifts, we divide the sample of lens galaxies with stellar masses in the range 10^(9)–10^(10.5) M_⊙ into those likely to lie in high-density environments (HDE) and those likely to lie in low-density environments (LDE). Through comparison with galaxy catalogues extracted from the Millennium Simulation, we show that the sample of HDE galaxies should primarily (∼61 per cent) consist of satellite galaxies in groups, while the sample of LDE galaxies should consist of mostly (∼87 per cent) non-satellite (field and central) galaxies. Comparing the lensing signals around samples of HDE and LDE galaxies matched in stellar mass, the lensing signal around HDE galaxies clearly shows a positive contribution from their host groups on their lensing signals at radii of ∼500–1000 kpc, the typical separation between satellites and group centres. More importantly, the subhaloes of HDE galaxies are less massive than those around LDE galaxies by a factor of 0.65 ± 0.12, significant at the 2.9σ level. A natural explanation is that the haloes of satellite galaxies are stripped through tidal effects in the group environment. Our results are consistent with a typical tidal truncation radius of ∼40 kpc
Constraining primordial non-Gaussianity with future galaxy surveys
We study the constraining power on primordial non-Gaussianity of future
surveys of the large-scale structure of the Universe for both near-term surveys
(such as the Dark Energy Survey - DES) as well as longer term projects such as
Euclid and WFIRST. Specifically we perform a Fisher matrix analysis forecast
for such surveys, using DES-like and Euclid-like configurations as examples,
and take account of any expected photometric and spectroscopic data. We focus
on two-point statistics and we consider three observables: the 3D galaxy power
spectrum in redshift space, the angular galaxy power spectrum, and the
projected weak-lensing shear power spectrum. We study the effects of adding a
few extra parameters to the basic LCDM set. We include the two standard
parameters to model the current value for the dark energy equation of state and
its time derivative, w_0, w_a, and we account for the possibility of primordial
non-Gaussianity of the local, equilateral and orthogonal types, of parameter
fNL and, optionally, of spectral index n_fNL. We present forecasted constraints
on these parameters using the different observational probes. We show that
accounting for models that include primordial non-Gaussianity does not degrade
the constraint on the standard LCDM set nor on the dark-energy equation of
state. By combining the weak lensing data and the information on projected
galaxy clustering, consistently including all two-point functions and their
covariance, we find forecasted marginalised errors sigma (fNL) ~ 3, sigma
(n_fNL) ~ 0.12 from a Euclid-like survey for the local shape of primordial
non-Gaussianity, while the orthogonal and equilateral constraints are weakened
for the galaxy clustering case, due to the weaker scale-dependence of the bias.
In the lensing case, the constraints remain instead similar in all
configurations.Comment: 20 pages, 10 Figures. Minor modifications; accepted by MNRA
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