447 research outputs found
Alien Registration- Humphrey, Eva R. (Bath, Sagadahoc County)
https://digitalmaine.com/alien_docs/9272/thumbnail.jp
Alternative funding : looking beyond the nation state
"Article for a special issue of Futures, UK, prepared to coincide with the 1995 UN Social Summit
The Relation between Dynamical Mass-to-light Ratio and Color for Massive Quiescent Galaxies out to z ~ 2 and Comparison with Stellar Population Synthesis Models
Article / Letter to editorSterrewach
The international symposia on career development and public policy: retrospect and prospect
Between 1999 and 2011, seven international symposia on career development and public policy were held at various venues across the world, and an International Centre was established to support and maintain continuity between these events. These developments were closely intertwined with a number of other significant international developments. The origins of the symposia are described; their core design features are defined; their evolution is outlined and reviewed; and their impact is assessed. This article concludes with a discussion of the prospects for future symposia and for the International Centre
Large-Scale Distributed Bayesian Matrix Factorization using Stochastic Gradient MCMC
Despite having various attractive qualities such as high prediction accuracy
and the ability to quantify uncertainty and avoid over-fitting, Bayesian Matrix
Factorization has not been widely adopted because of the prohibitive cost of
inference. In this paper, we propose a scalable distributed Bayesian matrix
factorization algorithm using stochastic gradient MCMC. Our algorithm, based on
Distributed Stochastic Gradient Langevin Dynamics, can not only match the
prediction accuracy of standard MCMC methods like Gibbs sampling, but at the
same time is as fast and simple as stochastic gradient descent. In our
experiments, we show that our algorithm can achieve the same level of
prediction accuracy as Gibbs sampling an order of magnitude faster. We also
show that our method reduces the prediction error as fast as distributed
stochastic gradient descent, achieving a 4.1% improvement in RMSE for the
Netflix dataset and an 1.8% for the Yahoo music dataset
Stellar Kinematics of z ~ 2 Galaxies and the Inside-out Growth of Quiescent Galaxies
Using stellar kinematics measurements, we investigate the growth of massive, quiescent galaxies from z ~{} 2 to today. We present X-Shooter spectra from the UV to NIR and dynamical mass measurements of five quiescent massive ({gt}10 M ) galaxies at z ~{} 2. This triples the sample of z {gt} 1.5 galaxies with well-constrained ({}{} {lt} 100 km s) velocity dispersion measurements. From spectral population synthesis modeling we find that these galaxies have stellar ages that range from 0.5 to 2 Gyr, with no signs of ongoing star formation. We measure velocity dispersions (290-450 km s) from stellar absorption lines and find that they are 1.6-2.1 times higher than those of galaxies in the Sloan Digital Sky Survey at the same mass. Sizes are measured using GALFIT from Hubble Space Telescope Wide Field Camera 3 H and UDS K-band images. The dynamical masses correspond well to the spectral energy distribution based stellar masses, with dynamical masses that are ~{}15% higher. We find that M /M may decrease slightly with time, which could reflect the increase of the dark matter fraction within an increasing effective radius. We combine different stellar kinematic studies from the literature and examine the structural evolution from z ~{} 2 to z ~{} 0: we confirm that at fixed dynamical mass, the effective radius increases by a factor of ~{}2.8, and the velocity dispersion decreases by a factor of ~{}1.7. The mass density within one effective radius decreases by a factor of ~{}20, while within a fixed physical radius (1 kpc) it decreases only mildly (factor of ~{}2). When we allow for an evolving mass limit by selecting a population of galaxies at fixed number density, a stronger size growth with time is found (factor of ~{}4), velocity dispersion decreases by a factor of ~{}1.4, and interestingly, the mass density within 1 kpc is consistent with no evolution. This finding suggests that massive quiescent galaxies at z ~{} 2 grow inside out, consistent with the expectations from minor mergers
Stellar Kinematics of z ~ 2 Galaxies and the Inside-out Growth of Quiescent Galaxies
Using stellar kinematics measurements, we investigate the growth of massive, quiescent galaxies from z ~{} 2 to today. We present X-Shooter spectra from the UV to NIR and dynamical mass measurements of five quiescent massive ({gt}10 M ) galaxies at z ~{} 2. This triples the sample of z {gt} 1.5 galaxies with well-constrained ({}{} {lt} 100 km s) velocity dispersion measurements. From spectral population synthesis modeling we find that these galaxies have stellar ages that range from 0.5 to 2 Gyr, with no signs of ongoing star formation. We measure velocity dispersions (290-450 km s) from stellar absorption lines and find that they are 1.6-2.1 times higher than those of galaxies in the Sloan Digital Sky Survey at the same mass. Sizes are measured using GALFIT from Hubble Space Telescope Wide Field Camera 3 H and UDS K-band images. The dynamical masses correspond well to the spectral energy distribution based stellar masses, with dynamical masses that are ~{}15% higher. We find that M /M may decrease slightly with time, which could reflect the increase of the dark matter fraction within an increasing effective radius. We combine different stellar kinematic studies from the literature and examine the structural evolution from z ~{} 2 to z ~{} 0: we confirm that at fixed dynamical mass, the effective radius increases by a factor of ~{}2.8, and the velocity dispersion decreases by a factor of ~{}1.7. The mass density within one effective radius decreases by a factor of ~{}20, while within a fixed physical radius (1 kpc) it decreases only mildly (factor of ~{}2). When we allow for an evolving mass limit by selecting a population of galaxies at fixed number density, a stronger size growth with time is found (factor of ~{}4), velocity dispersion decreases by a factor of ~{}1.4, and interestingly, the mass density within 1 kpc is consistent with no evolution. This finding suggests that massive quiescent galaxies at z ~{} 2 grow inside out, consistent with the expectations from minor mergers
Inferring More from Less: Prospector as a Photometric Redshift Engine in the Era of JWST
The advent of the James Webb Space Telescope (JWST) signals a new era in
exploring galaxies in the high- universe. Current and upcoming JWST imaging
will potentially detect galaxies out to , creating a new urgency in
the quest to infer accurate photometric redshifts (photo-) for individual
galaxies from their spectral energy distributions, as well as masses, ages and
star formation rates. Here we illustrate the utility of informed priors
encoding previous observations of galaxies across cosmic time in achieving
these goals. We construct three joint priors encoding empirical constraints of
redshifts, masses, and star formation histories in the galaxy population within
the \prospector\ Bayesian inference framework. In contrast with uniform priors,
our model breaks an age-mass-redshift degeneracy, and thus reduces the mean
bias error in masses from 0.3 to 0.1 dex, and in ages from 0.6 to 0.2 dex in
tests done on mock JWST observations. Notably, our model recovers redshifts at
least as accurately as the state-of-the-art photo- code \eazy\ in deep JWST
fields, but with two advantages: tailoring a model based on a particular survey
renders mostly unnecessary given well-motivated priors; obtaining joint
posteriors describing stellar, active galactic nuclei, gas, and dust
contributions becomes possible. We can now confidently use the joint
distribution to propagate full non-Gaussian redshift uncertainties into
inferred properties of the galaxy population. This model,
``\prospector-'', is intended for fitting galaxy photometry where the
redshift is unknown, and will be instrumental in ensuring the maximum science
return from forthcoming photometric surveys with JWST. The code is made
publicly available online as a part of \prospector.Comment: Accepted for publication in ApJL. 13 pages, 6 figures, 2 tables. The
code is made publicly available online as a part of Prospector; the version
used in this work corresponds to the state of the Git repository at commit
820ad7
- …