33 research outputs found
Galactic properties that favour star cluster formation: a statistical view
The presence or absence of star clusters in galaxies, and the properties of
star cluster populations compared to their host galaxy properties, are
important observables for validating models of cluster formation, galaxy
formation, and galaxy assembly. In this work, we apply a Bayesian approach to
fit two models to data from surveys of young clusters in star forming galaxies.
The first model is a logistic regression, which allows us to include galaxies
which do not have any young clusters. The second model is a hurdle model, which
includes galaxies with zero clusters and also incorporates information about
the total mass in the cluster system. We investigate two predictors (star
formation rate and total stellar mass in the galaxy) and look at clusters
younger than 10 or 100 Myr. We find that in all cases, star formation rate is
the better predictor for both the probability of hosting clusters and the total
mass in the cluster system. We compare our results to similar models for old
globular clusters, and conclude that star cluster formation was more abundant
and more efficient at higher redshifts, likely because of the high gas content
of galaxies at that time.Comment: 10 pages, 5 figures, accepted by MNRA
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
Light from the Darkness: Detecting Ultra-diffuse Galaxies in the Perseus Cluster through Over-densities of Globular Clusters with a Log-Gaussian Cox Process
We introduce a new method for detecting ultra-diffuse galaxies by searching for over-densities in intergalactic globular cluster populations. Our approach is based on an application of the log-Gaussian Cox process, which is a commonly used model in the spatial statistics literature but rarely used in astronomy. This method is applied to the globular cluster data obtained from the PIPER survey, a Hubble Space Telescope imaging program targeting the Perseus cluster. We successfully detect all confirmed ultra-diffuse galaxies with known globular cluster populations in the survey. We also identify a potential galaxy that has no detected diffuse stellar content. Preliminary analysis shows that it is unlikely to be merely an accidental clump of globular clusters or other objects. If confirmed, this system would be the first of its kind. Simulations are used to assess how the physical parameters of the globular cluster systems within ultra-diffuse galaxies affect their detectability using our method. We quantify the correlation of the detection probability with the total number of globular clusters in the galaxy and the anticorrelation with increasing half-number radius of the globular cluster system. The Sérsic index of the globular cluster distribution has little impact on detectability