233 research outputs found
Exploring Photometric Redshifts as an Optimization Problem: An Ensemble MCMC and Simulated Annealing-Driven Template-Fitting Approach
Using a grid of million elements () adapted from
COSMOS photometric redshift (photo-z) searches, we investigate the general
properties of template-based photo-z likelihood surfaces. We find these
surfaces are filled with numerous local minima and large degeneracies that
generally confound rapid but "greedy" optimization schemes, even with
additional stochastic sampling methods. In order to robustly and efficiently
explore these surfaces, we develop BAD-Z [Brisk Annealing-Driven Redshifts
(Z)], which combines ensemble Markov Chain Monte Carlo (MCMC) sampling with
simulated annealing to sample arbitrarily large, pre-generated grids in
approximately constant time. Using a mock catalog of 384,662 objects, we show
BAD-Z samples times more efficiently compared to a brute-force
counterpart while maintaining similar levels of accuracy. Our results represent
first steps toward designing template-fitting photo-z approaches limited mainly
by memory constraints rather than computation time.Comment: 14 pages, 8 figures; submitted to MNRAS; comments welcom
Hierarchical Bayesian Inference of Globular Cluster Properties
We present a hierarchical Bayesian inference approach to estimating the
structural properties and the phase space center of a globular cluster (GC)
given the spatial and kinematic information of its stars based on lowered
isothermal cluster models. As a first step towards more realistic modelling of
GCs, we built a differentiable, accurate emulator of the lowered isothermal
distribution function using interpolation. The reliable gradient information
provided by the emulator allows the use of Hamiltonian Monte Carlo methods to
sample large Bayesian models with hundreds of parameters, thereby enabling
inference on hierarchical models. We explore the use of hierarchical Bayesian
modelling to address several issues encountered in observations of GC including
an unknown GC center, incomplete data, and measurement errors. Our approach not
only avoids the common technique of radial binning but also incorporates the
aforementioned uncertainties in a robust and statistically consistent way.
Through demonstrating the reliability of our hierarchical Bayesian model on
simulations, our work lays out the foundation for more realistic and complex
modelling of real GC data.Comment: 16 pages, 12 figures, and 2 table
Improving Power Spectral Estimation using Multitapering: Precise asteroseismic modeling of stars, exoplanets, and beyond
Asteroseismic time-series data have imprints of stellar oscillation modes,
whose detection and characterization through time-series analysis allows us to
probe stellar interiors physics. Such analyses usually occur in the Fourier
domain by computing the Lomb-Scargle (LS) periodogram, an estimator of the
\textit{power spectrum} underlying unevenly-sampled time-series data. However,
the LS periodogram suffers from the statistical problems of (1) inconsistency
(or noise) and (2) bias due to high spectral leakage. In addition, it is
designed to detect strictly periodic signals but is unsuitable for
non-sinusoidal periodic or quasi-periodic signals. Here, we develop a
multitaper spectral estimation method that tackles the inconsistency and bias
problems of the LS periodogram. We combine this multitaper method with the
Non-Uniform Fast Fourier Transform (\texttt{mtNUFFT}) to more precisely
estimate the frequencies of asteroseismic signals that are non-sinusoidal
periodic (e.g., exoplanet transits) or quasi-periodic (e.g., pressure modes).
We illustrate this using a simulated and the Kepler-91 red giant light curve.
Particularly, we detect the Kepler-91b exoplanet and precisely estimate its
period, days, in the frequency domain using the multitaper
F-test alone. We also integrate \texttt{mtNUFFT} into the \texttt{PBjam}
package to obtain a Kepler-91 age estimate of Gyr. This \%
improvement in age precision relative to the Gyr APOKASC-2
(uncorrected) estimate illustrates that \texttt{mtNUFFT} has promising
implications for Galactic archaeology, in addition to stellar interiors and
exoplanet studies. Our frequency analysis method generally applies to
time-domain astronomy and is implemented in the public Python package
\texttt{tapify}, available at \url{https://github.com/aaryapatil/tapify}.Comment: 32 pages (3 pages in the Appendix), 14 figures, 2 tables, Submitted
to A
Searching for the extra-tidal stars of globular clusters using high-dimensional analysis and a core particle spray code
Three-body interactions can eject stars from the core of a globular cluster,
causing them to enter the Galactic halo as extra-tidal stars. While finding
extra-tidal stars is imperative for understanding cluster evolution, connecting
isolated extra-tidal field stars back to their birth cluster is extremely
difficult. In this work, we present a new methodology consisting of
high-dimensional data analysis and a particle spray code to identify
extra-tidal stars of any Galactic globular cluster using M3 as a case study.
Using the t-Stochastic Neighbour Embedding (t-SNE) and Uniform Manifold
Approximation and Projection (UMAP) machine learning dimensionality reduction
algorithms, we first identify a set of 103 extra-tidal candidates in the APOGEE
DR17 data catalogue with chemical abundances similar to M3 stars. To confirm
each candidate's extra-tidal nature, we introduce Corespray; a new Python-based
three-body particle spray code that simulates extra-tidal stars for any
Galactic globular cluster. Using Gaia EDR3 proper motions and APOGEE DR17
radial velocities, we apply multivariate Gaussian modelling and an extreme
deconvolution to identify the extra-tidal candidates that are more likely to be
associated with a distribution of Corespray-simulated M3 extra-tidal stars than
the field. Through these methods, we identify 13 new high-probability
extra-tidal stars of M3. Future applications of Corespray will yield better
understandings of core dynamics, star formation histories and binary fractions
in globular clusters.Comment: 15 pages, 8 figures, 2 tables. Submitted to Monthly Notices of the
Royal Astronomical Societ
Source Selection for Cluster Weak Lensing Measurements in the Hyper Suprime-Cam Survey
We present optimized source galaxy selection schemes for measuring cluster
weak lensing (WL) mass profiles unaffected by cluster member dilution from the
Subaru Hyper Suprime-Cam Strategic Survey Program (HSC-SSP). The ongoing
HSC-SSP survey will uncover thousands of galaxy clusters to . In
deriving cluster masses via WL, a critical source of systematics is
contamination and dilution of the lensing signal by cluster {members, and by
foreground galaxies whose photometric redshifts are biased}. Using the
first-year CAMIRA catalog of 900 clusters with richness larger than 20
found in 140 deg of HSC-SSP data, we devise and compare several
source selection methods, including selection in color-color space (CC-cut),
and selection of robust photometric redshifts by applying constraints on their
cumulative probability distribution function (PDF; P-cut). We examine the
dependence of the contamination on the chosen limits adopted for each method.
Using the proper limits, these methods give mass profiles with minimal dilution
in agreement with one another. We find that not adopting either the CC-cut or
P-cut methods results in an underestimation of the total cluster mass
() and the concentration of the profile (). The level of
cluster contamination can reach as high as at
Mpc/ for low-z clusters without cuts, while employing either the P-cut or
CC-cut results in cluster contamination consistent with zero to within the 0.5%
uncertainties. Our robust methods yield a detection of the
stacked CAMIRA surface mass density profile, with a mean mass of
.Comment: 19 pages, 4 tables, 12 figures, accepted to PASJ special issu
Star Formation at From the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH)
Using the first 50% of data collected for the Spitzer Large Area Survey with
Hyper-Suprime-Cam (SPLASH) observations on the 1.8 deg Cosmological
Evolution Survey (COSMOS) we estimate the masses and star formation rates of
3398 star-forming galaxies at with a
substantial population up to . We find that the
strong correlation between stellar mass and star formation rate seen at lower
redshift (the "main sequence" of star-forming galaxies) extends to .
The observed relation and scatter is consistent with a continued increase in
star formation rate at fixed mass in line with extrapolations from
lower-redshift observations. It is difficult to explain this continued
correlation, especially for the most massive systems, unless the most massive
galaxies are forming stars near their Eddington-limited rate from their first
collapse. Furthermore, we find no evidence for moderate quenching at higher
masses, indicating quenching either has not occurred prior to or
else occurs rapidly, so that few galaxies are visible in transition between
star-forming and quenched.Comment: ApJL, accepte
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