The Effect of Bars on the Ionized ISM: Optical Emission Lines from Milky Way Analogs

Dhanesh Krishnarao, Christy Tremonti, Amelia Fraser-McKelvie, Katarina Kraljic, Nicholas Fraser Boardman, Karen L. Masters, Robert A. Benjamin, L. Matthew Haffner, Amy Jones, Zachary J. Pace, Gail Zasowski, Matthew Bershady, Dmitry Bizyaev, Jonathan Brinkmann, Joel R. Brownstein, Niv Drory, Kaike Pan, Kai Zhang

Published 2020-07-03Version 1

Gas interior to the bar of the Milky Way has recently been shown as the closest example of a Low Ionization (Nuclear) Emission Region--LI(N)ER--in the universe. To better understand the nature of this gas, a sample of face-on galaxies with integral field spectroscopy are used to study the ionized gas conditions of 240 barred and 250 nonbarred galaxies, focusing on those that are most similar to the Milky Way. Strong optical line emission of $[NII]$ $\lambda 6584$, H$\alpha$, $[OIII]$ $\lambda 5007$, and H$\beta$ are used to diagnose the dominant ionization mechanisms of gas across galaxies and the Galaxy via Baldwin-Phillips-Terlevich (BPT) Diagrams. Barred galaxies show a strong suppression of star formation and an increase in composite and LI(N)ER like spectra in their inner regions when compared with similar nonbarred counterparts. This effect is lessened in galaxies of very low ($\log_{10}(M_\star/M_\odot) \lesssim 10.4$) or very high ($\log_{10}(M_\star/M_\odot) \gtrsim 11.1$) total stellar mass. Bar masks from Galaxy Zoo:3D show the bar's non-axisymmetric effect on the ionized gas and help predict the face-on distribution of ionized gas conditions near the bar of the Milky Way.