Lyman-alpha photons through rotating outflows

This work began as my Physics undergraduate thesis at Universidad de los Andes in Bogotá, Colombia. It was developed under the supervising of the AstroAndes professor Dr. Jaime Forero-Romero. We continued the research until the publication of our results.

Abstract:

Outflows and rotation are two ubiquitous kinematic features in the gas kinematics of galaxies. Here we introduce a semi-analytic model to quantify how rotating outflows impact the morphology of the Lyman-alpha emission line. The model is contrasted against Monte Carlo radiative transfer simulations of outflowing gas with additional solid body rotation. We explore a range of neutral Hydrogen optical depth of 10^5 <= tau_H <= 10^7, rotational velocity 0 <= v_rot / (km/s) <= 100 and outflow velocity 0 <= v_out / (ks/s) <= 50. We find three consequences of rotation. First, it introduces a dependency with viewing angle; second it broadens the line and third it increases the flux at the line’s center. For all viewing angles, the semi-analytic model reproduces the radiative transfer results for the line width and flux change at the line’s center within a 7% and 50% precision for an optical depth of tau_H=10^5, respectively, and within 2% and 1% for an optical depth of tau_H=10^7. Using this model we also show that the peaks of integrated spectra taken from opposite sides of an edge-on rotating gas distribution should have a separation of v_rot/2. The semi-analytic model presented here is a convenient tool to introduce rotational kinematics as a post-processing step of idealized Monte Carlo simulations; it provides a framework to interpret Lyman-alpha spectra in systems where rotation is expected or directly measured through kinematic maps.

Publication:

Our research article was published on the journal Monthly Notices of the Royal Astronomical Society (MNRAS) Volume 482, Issue 4, February 2019, Pages 4553–4561, DOI: 10.1093/mnras/sty3009. It is publicly available in the arXiv.