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Lyman-alpha photons through rotating outflows

10 Nov 2018 . category: academic . Comments
#astrophysics #galaxy #montecarlo #simulations #article

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. It evolved into a research article that we published on the journal Monthly Notices of the Royal Astronomical Society (Volume 482, Issue 4, February 2019, Pages 4553–4561) with DOI: 10.1093/mnras/sty3009.

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.


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Maria Camila loves learning, traveling, living new experiences and meeting new friends. She doesn't like trying new food tho, but she compensates it in ice-cream eating!