Spatial Correlation Between Dust and H$\alpha$ Emission in Dwarf Irregular Galaxies

TL;DR

This study reveals a positive correlation between Hα emission and dust optical depth in dwarf irregular galaxies, consistent across small spatial scales and similar to larger galaxies, supporting the dusty birth-cloud model.

Contribution

It demonstrates that the correlation between Hα luminosity and dust optical depth exists at spatial scales as small as 30 pc in dwarf irregular galaxies, extending previous findings to lower-mass systems.

Findings

Positive correlation between Hα surface density and optical depth in most galaxies.

Correlation persists down to 30 pc spatial scales.

Relationship is similar to that observed in larger spiral galaxies.

Abstract

Using a sample of dwarf irregular galaxies selected from the ALFALFA blind HI-survey and observed using the VIMOS IFU, we investigate the relationship between H$\alpha$ emission and Balmer optical depth ($\tau_{\text{b}}$). We find a positive correlation between H$\alpha$ luminosity surface density and Balmer optical depth in 8 of 11 at $\geq$ 0.8$\sigma$ significance (6 of 11 at $\geq$ 1.0$\sigma$) galaxies. Our spaxels have physical scales ranging from 30 to 80 pc, demonstrating that the correlation between these two variables continues to hold down to spatial scales as low as 30 pc. Using the Spearman's rank correlation coefficient to test for correlation between $\Sigma_{\text{H}\alpha}$ and $\tau_{\text{b}}$ in all the galaxies combined, we find $\rho = 0.39$, indicating a positive correlation at 4$\sigma$ significance. Our low stellar-mass galaxy results are in agreement with observations of emission line regions in larger spiral galaxies, indicating that this relationship is independent of the size of the galaxy hosting the emission line region. The positive correlation between H$\alpha$ luminosity and Balmer optical depth within spaxels is consistent with the hypothesis that young star-forming regions are surrounded by dusty birth-clouds.