Abstract
Accurate parametrization of galaxies detected in the 21-cm H I emission is of fundamental importance to the measurement of commonly used indicators of galaxy evolution, including the Tully-Fisher relation and the H I mass function. Here, we propose a new analytic function, named the `busy function’, that can be used to accurately describe the characteristic double-horn H I profile of many galaxies. The busy function is a continuous, differentiable function that consists of only two basic functions, the error function, erf(x), and a polynomial, |x|n, of degree n ≥ 2. We present the basic properties of the busy function and illustrate its great flexibility in fitting a wide range of H I profiles from the Gaussian profiles of dwarf galaxies to the broad, asymmetric double-horn profiles of spiral galaxies. Applications of the busy function include the accurate and efficient parametrization of observed H I spectra of galaxies and the construction of spectral templates for simulations and matched-filtering algorithms. We demonstrate the busy function’s power by automatically fitting it to the H I spectra of 1000 galaxies from the HI Parkes All-Sky Survey (HIPASS) Bright Galaxy Catalog, using our own C/C++ implementation, and comparing the resulting parameters with the catalogued ones. We also present two methods for determining the uncertainties of observational parameters derived from the fit.
Author
Westmeier, T.; Jurek, R.; Obreschkow, D.; Koribalski, B. S.; Staveley-Smith, L.
Journal
Monthly Notices of the Royal Astronomical Society
Paper Publication Date
December 2013
Paper Type
Astrostatistics