HI Galaxy Signatures in the SARAO MeerKAT Galactic Plane Survey - II. The Local Void and its substructure

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 Hi 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 under-dense for the longitude range 350○ < ℓ < 35○ up to redshift z < 4500 $\rm km \, s^{-1}$. The galaxies in the Void tend to have Hi 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.