H i galaxy signatures in the SARAO MeerKAT galactic plane survey – II. The Local Void and its substructure

Abstract

ABSTRACT The Local Void is one of the nearest large voids, located at a distance of 23 Mpc. It lies largely behind the Galactic Bulge and is therefore extremely difficult to observe. We use H i 21 cm emission observations from the SARAO MeerKAT Galactic Plane Survey (SMGPS) to study the Local Void and its surroundings over the Galactic longitude range 329° < ℓ < 55°, Galactic latitude |b| < 1.5°, and redshift cz < 7500 $\rm km \, s^{-1}$. We have detected 291 galaxies to median rms sensitivity of 0.44 mJy per beam per 44 $\rm km \, s^{-1}$ channel. We find 17 galaxies deep inside the Void, 96 at the border of the Void, while the remaining 178 galaxies are in average density environments. The extent of the Void is ∼58 Mpc. It is severely underdense for the longitude range 350° < ℓ < 35° up to redshift z < 4500 $\rm km \, s^{-1}$. The galaxies in the Void tend to have H i masses that are lower (by approximately 0.25 dex) than their average density counterparts. We find several potential candidates for small groups of galaxies, of which two groups (with 3 members and 5 members) in the Void show signs of filamentary substructure within the Void.