HI Observations of two New Dwarf Galaxies: Pisces A & B with the SKA Pathfinder KAT-7

TL;DR

This study uses KAT-7 observations to analyze the HI content and kinematics of the dwarf galaxies Pisces A and B, revealing their irregular nature and non-equilibrium state, and discussing their potential as a large population of faint, isolated dwarfs.

Contribution

First detailed HI kinematic analysis of Pisces A and B using KAT-7, demonstrating their irregular, non-equilibrium state and providing insights into faint dwarf galaxy populations.

Findings

Pisces A and B are dwarf irregular galaxies with small rotation velocities.

Random motions dominate gravitational support in these galaxies.

They are likely isolated, gas-rich dwarfs outside the virial radius of larger galaxies.

Abstract

Context. Pisces A & Pisces B are the only two galaxies found via optical imaging and spectroscopy out of 22 HI clouds identified in the GALFAHI survey as dwarf galaxy candidates. Aims. Derive the HI content and kinematics of Pisces A & B. Methods. Aperture synthesis HI observations using the seven dish Karoo Array Telescope (KAT-7), which is a pathfinder instrument for MeerKAT, the South African precursor to the mid-frequency Square Kilometre Array (SKA-MID). Results. The small rotation velocities detected of ~5 km/sec and ~10 km/sec in Pisces A & B respectively, and their HI content show that they are really dwarf irregular galaxies (dIrr). Despite that small rotation component, it is more the random motions ~9-11 km/sec that provide most of the gravitational support, especially in the outer parts. The study of their kinematics, especially the strong gradients of random motions, suggest that those two dwarf galaxies are not yet in equilibrium. Conclusions. These HI rich galaxies may be indicative of a large population of dwarfs at the limit of detectability. However, such gas-rich dwarf galaxies will most likely never be within the virial radius of MW-type galaxies and become sub-halo candidates. Systems such as Pisces A & B are more likely to be found at a few Mpc.s from MW-type galaxies.