Parametrized Asymmetric Neutral hydrogen Disk Integrated Spectrum Characterization (PANDISC) I: Introduction to A Physically Motivated H I Model

TL;DR

The paper introduces PANDISC, a physically motivated model for galaxy H I spectra that accurately reproduces diverse profiles and enables robust analysis of galaxy dynamics and properties.

Contribution

We develop PANDISC, a flexible, physically motivated model for integrated H I spectra, and demonstrate its effectiveness with MCMC fitting and applications to galaxy dynamics.

Findings

Model accurately reproduces diverse H I profiles.

Fitted results agree with catalogued velocity widths even at low S/N.

Uncovers relationships between H I width and rotation curve structure.

Abstract

Modelling the integrated H I spectra of galaxies has been a difficult task due to their diverse shapes, but more dynamical information is waiting to be explored in Hi line profiles. Based on simple assumptions, we construct a physically motivated model for the integrated Hi spectra: Parametrized Asymmetric Neutral hydrogen Disk Integrated Spectrum Characterization (PANDISC). The model shows great flexibility in reproducing the diverse Hi profiles. We use Monte-Carlo Markov Chain (MCMC) for fitting the model to global H I profiles, producing statistically robust quantitative results. Comparing with several samples of H I data available in the literature , we find the model-fitted results agree with catalogued velocity widths (e.g., W50) down to the lowest S/N. The model is also shown to be useful for applications like the baryonic Tully-Fisher relation (BTFR) and profile-based sample control. By comparing v_r to v_flat , we uncover how the H I width is affected by the structure of the rotation curve, following a trend consistent with the difference in the BTFR slope. We also select a sample of spectra with broad wing-like features suggestive of a population of galaxies with unusual gas dynamics. The PANDISC model bears both promise and limitations for potential use beyond H I lines. Further application on the whole ALFALFA sample will enable us to perform large scale ensemble studies of the H I properties and dynamics in nearby galaxies.