68 research outputs found
A Highly Consistent Framework for the Evolution of the Star-Forming "Main Sequence" from z~0-6
Using a compilation of 25 studies from the literature, we investigate the
evolution of the star-forming galaxy (SFG) Main Sequence (MS) in stellar mass
and star formation rate (SFR) out to . After converting all
observations to a common set of calibrations, we find a remarkable consensus
among MS observations ( dex 1 interpublication scatter). By
fitting for time evolution of the MS in bins of constant mass, we deconvolve
the observed scatter about the MS within each observed redshift bins. After
accounting for observed scatter between different SFR indicators, we find the
width of the MS distribution is dex and remains constant over cosmic
time. Our best fits indicate the slope of the MS is likely time-dependent, with
our best fit , with the age of the Universe in Gyr. We use our fits to create
empirical evolutionary tracks in order to constrain MS galaxy star formation
histories (SFHs), finding that (1) the most accurate representations of MS SFHs
are given by delayed- models, (2) the decline in fractional stellar mass
growth for a "typical" MS galaxy today is approximately linear for most of its
lifetime, and (3) scatter about the MS can be generated by galaxies evolving
along identical evolutionary tracks assuming an initial spread in
formation times of Gyr.Comment: 59 pages, 10 tables, 12 figures, accepted to ApJS; v2, slight changes
to text, added new figure and fit
A Novel Application of Conditional Normalizing Flows: Stellar Age Inference with Gyrochronology
Stellar ages are critical building blocks of evolutionary models, but
challenging to measure for low mass main sequence stars. An unexplored solution
in this regime is the application of probabilistic machine learning methods to
gyrochronology, a stellar dating technique that is uniquely well suited for
these stars. While accurate analytical gyrochronological models have proven
challenging to develop, here we apply conditional normalizing flows to
photometric data from open star clusters, and demonstrate that a data-driven
approach can constrain gyrochronological ages with a precision comparable to
other standard techniques. We evaluate the flow results in the context of a
Bayesian framework, and show that our inferred ages recover literature values
well. This work demonstrates the potential of a probabilistic data-driven
solution to widen the applicability of gyrochronological stellar dating.Comment: Accepted at the ICML 2023 Workshop on Machine Learning for
Astrophysics. 10 pages, 3 figures (+1 in appendices
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
Monte Carlo Techniques for Addressing Large Errors and Missing Data in Simulation-based Inference
Upcoming astronomical surveys will observe billions of galaxies across cosmic
time, providing a unique opportunity to map the many pathways of galaxy
assembly to an incredibly high resolution. However, the huge amount of data
also poses an immediate computational challenge: current tools for inferring
parameters from the light of galaxies take hours per fit. This is
prohibitively expensive. Simulation-based Inference (SBI) is a promising
solution. However, it requires simulated data with identical characteristics to
the observed data, whereas real astronomical surveys are often highly
heterogeneous, with missing observations and variable uncertainties determined
by sky and telescope conditions. Here we present a Monte Carlo technique for
treating out-of-distribution measurement errors and missing data using standard
SBI tools. We show that out-of-distribution measurement errors can be
approximated by using standard SBI evaluations, and that missing data can be
marginalized over using SBI evaluations over nearby data realizations in the
training set. While these techniques slow the inference process from
sec to min per object, this is still significantly faster than
standard approaches while also dramatically expanding the applicability of SBI.
This expanded regime has broad implications for future applications to
astronomical surveys.Comment: 8 pages, 2 figures, accepted to the Machine Learning and the Physical
Sciences workshop at NeurIPS 202
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