OutLines: Modeling Spectral Lines from Winds, Bubbles, and Outflows
Sophia R. Flury
TL;DR
OutLines delivers a physically driven framework for modeling emission and absorption lines from winds, bubbles, and outflows, addressing limitations of empirical and multi-Gaussian approaches. By employing the Sobolev approximation, multiple velocity-field choices (including CAK β-law, AccPlaw, and VelPlaw), and diverse radial density profiles across spherical, filled-cone, and hollow-cone geometries (with disks and cavities), the code links spectral features to wind physics and geometry. The authors validate the method on four astrophysical cases—an H II region knot, a Green Pea-like super star cluster, a starburst galaxy, and an AGN—deriving physically meaningful outflow properties and insights into feedback and LyC escape. As an openly available tool, OutLines enables robust, physics-based inference from large spectroscopic surveys, with potential to inform studies of baryon cycling, galaxy evolution, and AGN-driven feedback in the era of WEAVE-LOFAR and 4MOST/WAVES.
Abstract
Common methods for studying the kinematics and geometry of outflowing gas rely on modeling emission and absorption lines in integrated spectra using methods that are not physically motivated, including empirical quantiles or fitting multiple Gaussian or Voigt profiles. Such methods are not always consistent with the interpretation of these features and, as a result, miss key underlying physics and can even lead to inaccurate interpretations of observations. To address this problem, we present the publicly available python code OutLines, which provides astrophysical models of spectral emission and absorption line profiles produced by outflows in a variety of environments. The OutLines code accounts for differences in parameterization of the velocity field and density profile while allowing for different outflow geometries, making OutLines versatile and useful for a wide variety of astrophysical phenomena. We demonstrate the wide applicability of OutLines by using the code to model line profiles in an H II region knot, super star clusters, a starburst galaxy, and an AGN. In each of these contexts, we illustrate how OutLines can illuminate key underlying physics in ways that improve our scientific understanding and address important open questions in astronomy, including the key mechanisms in the baryon cycle, the evolution of H II regions and galaxies, and even Lyman continuum escape. OutLines will be a critical resource as massively multiplexed spectroscopic surveys like WEAVE-LOFAR and 4MOST/WAVES come online, providing the means to probe feedback kinematics with deeper, higher resolution spectroscopy for unprecedented large samples of galaxies.