Synthetic HI Spectra for Spiral Galaxies¶

By Juan Cabanela (Minnesota State University Moorhead)¶

This program is designed to allow you to model the neutral hydrogen line spectrum (the so-called 21-cm line) of a model spiral galaxy as viewed from outside the galaxy. In other words, the model radio spectrum of spiral galaxies. We do this for

1. Unresolved single-dish spectra where we assume the entire galaxy falls within the radio beam (assuming a 145 arcsecond beam)with a 5 km/s velocity resolution
2. Resolved aperture synthesis spectra (as might be produced by the VLA) in which we can resolve the galaxy, essentially getting the spectrum for every point within the galaxy.

This code generates spectra for model spiral galaxies with the HI gas density profile (the density versus radius) and rotation curve initially assumed to be similar to the Milky Way. However, you can sketch any rotation curve or HI gas density profile on those plots and the modelled unresolved "single-dish" spectrum and the resolved "aperture synthesis" velocity map are updated. You can also modify the redshift $cz$ or gas velocity dispersion by sliding the respective sliders.