The Baryonic Tully-Fisher Relation in the Local Group and the Equivalent Circular Velocity of Pressure Supported Dwarfs

TL;DR

This paper investigates the Baryonic Tully-Fisher Relation in the Local Group, establishing a scaling factor that links velocity dispersions of pressure supported dwarfs to the circular velocities of rotationally supported galaxies, revealing a unified kinematic scale.

Contribution

It introduces a scaling factor relating velocity dispersions to circular velocities, providing a unified kinematic framework for different dwarf galaxy types.

Findings

Rotationally supported Local Group galaxies follow the Tully-Fisher relation.

A scaling factor $eta_c=2$ relates velocity dispersion to circular velocity for pressure supported dwarfs.

The relation $eta_c$ depends on the mass-to-light ratio $Upsilon_*$.

Abstract

We explore the Baryonic Tully-Fisher Relation in the Local Group. Rotationally supported Local Group galaxies adhere precisely to the relation defined by more distant galaxies. For pressure supported dwarf galaxies, we determine the scaling factor $\beta_c$ that relates their observed velocity dispersion to the equivalent circular velocity of rotationally supported galaxies of the same mass such that $V_o = \beta_c \sigma_*$. For a typical mass-to-light ratio $\Upsilon_* = 2\;\mathrm{M}_{\odot}/\mathrm{L}_{\odot}$ in the $V$-band, we find that $\beta_c = 2$. More generally, $\log \beta_c = 0.25 \log \Upsilon_* +0.226$. This provides a common kinematic scale relating pressure and rotationally supported dwarf galaxies.