# CHANG-ES XVII: H-alpha Imaging of Nearby Edge-on Galaxies, New SFRs, and an Extreme Star Formation Region -- Data Release 2

## TL;DR

This paper presents new H-alpha imaging data for 24 edge-on galaxies, updates star formation rate estimates using combined IR and H-alpha data, and discovers new correlations between star formation and radio properties, including a novel SFR-radio scale height relation.

## Contribution

It introduces improved SFR estimates combining H-alpha and IR data, and uncovers new correlations between star formation rates and radio continuum properties in edge-on galaxies.

## Key findings

- Discovered a correlation between SFR and radio scale height.
- Identified a star formation region far from the disk in NGC 4157.
- Showed the importance of dust extinction correction in SFR calibrations.

## Abstract

We present new narrow-band H-alpha imaging for 24 nearby edge-on galaxies in the CHANG-ES survey. We use the images in conjunction with WISE 22 micron imaging of the sample to estimate improved star formation rates (SFRs) using the updated recipe from Vargas et al. (2018). We explore correlations between the updated star formation properties and radio continuum scale heights, scale lengths, and diameters, measured in Krause et al. (2018). We find a newly discovered correlation between SFR and radio scale height that did not exist using mid-IR only SFR calibrations. This implies that a mid-IR extinction correction should be applied to SFR calibrations when used in edge-on galaxies, due to attenuation by dust. The updated SFR values also show newly discovered correlations with radio scale length and radio diameter, implying that the previously-measured relationship between radio scale height and radio diameter originates from star formation within the disk. We also identify a region of star formation located at extreme distance from the disk of NGC 4157, possibly ionized by a single O5.5 V star. This region is spatially coincident with an XUV disk feature, as traced by GALEX NUV imaging. We theorize that the star formation feature arose due to gravitational instability within gas from an accretion event. New H-alpha images from this work can be found at the CHANG-ES data release web site, https://www.queensu.ca/changes.