The spatial distribution and internal structure of astronomical systems contain vast amount of information about the underlying physics that governs the formation, evolution, and fate of these systems. While astronomical data collected by large-, medium-, and small-size surveys are becoming more abundant, precise and accurate modeling is becoming more challenging. The scale and complexity of these multi-wavelength surveys are exceeding the capabilities of traditional data analysis models, hence the need for novel inference models.
One of the key challenges of modeling the empirical data is how to account for the measurement errors of varying magnitudes. The low signal-to-noise ratio (SNR) regime hinders the ability to infer the spatial structure of a population from abundant but noisy measurements, diluting the spatial signals. Typical measurements with SNR below the detection limit are often discarded or stacked to boost the signal above the detection limit. Binning and stacking can introduce selection bias, information loss, and smearing out the signal component. While stacking amplifies the SNR of the population average properties, it suppresses intrinsic scatter of the population under study. In practice, performing a statistical inference on large astronomical datasets has become a bottleneck of traditional population- and likelihood-based approaches.
To address some of the above challenges, we developed Population Profile Estimator (PoPE), a population-based,
Bayesian inference model to analyze a class of problems that are concerned with the spatial distribution or internal
spatial structure of a sample of astronomical systems. Our method uses the conditional statistics of spatial
profile of multiple observables assuming the individual observations are measured with errors of varying magnitude.
Assuming the conditional statistics of our observables can be described with a multivariate normal distribution,
the model reduces to the conditional average profile and conditional covariance between all observables.
The method consists of two steps: (1) reconstructing the average profile using non-parametric regression with Gaussian
Processes and (2) estimating the the property profiles covariance given a set of independent variable. Our
population-based method is computationally efficient and capable of inferring average profiles of a population from
noisy measurements, without stacking and binning nor parameterizing the shape of the average profile. This code is an
implementation of Population Profile Estimator (PoPE) method that performs a regression analysis described in
Farahi, Nagai & Cheng (2020).
If you use PoPE or derivates based on it, please cite the following paper (Farahi et al. 2020) which introduced the tool.
numpy, scipy, matplotlib, pandas, sklearn, pymc3, KLLR.
[1]. A. Farahi, D. Nagai, Y. Cheng, "PoPE: A population-based approach to model spatial structure of astronomical systems", AJ 161 30 (2021). arXiv link. Journal link.
Run the following to install:
pip install pope
To start using PoPE, simply use from PoPE import estimate_mean_property_profile to
access the primary functions and class. The exact requirements for the inputs are
listed in the docstring of the estimate_mean_property_profile() class further below.
An example for using PoPE looks like this:
from PoPE import estimate_mean_property_profile
# load data and add measurement noise
# Xs, Ys1, Ys2, Ys1err, Ys2err = load_data()
# compute the average profile
mp, gp, model = estimate_mean_property_profile(Xs, Ys1, Ys2, Ys1err, Ys2err,
Xu_shapes=[15, 7], kernel_scales=[2.0, 2.0])
See examples "./examples/simulated_example.py" and "./examples/TNG_example.py" for more information. To replicate
plots presented in the paper, you can run python3 TNG_profile_example.py and python3 fake_simulated_example.py
If you have any questions or want to modify the code for your own purpose, please do not hesitate to email arya.farahi@austin.utexas.edu for help.