When Is a Bulge Not a Bulge? Revealing the Satellite Nature of NGC 5474's Bulge
Figure 5 of Garner et al. (subm.). From left to right: the stellar velocities, gas velocities, and velocity differences across NGC 5474. The top row of panels shows the velocities, while the bottom row shows their associated uncertainties. The 20 arcsec red circle outlines the position of the putative bulge in each map centered at the origin. North is up and east is to the left.Abstract
A satellite galaxy of the nearby spiral M101, NGC 5474 has a prominent bulge offset from the kinematic center of the underlying star-forming disk that has gained attention in recent years. Recent studies have proposed that this putative offset bulge is not a classical bulge within the plane of the disk but instead a dwarf companion galaxy along the line-of-sight. Using integral field spectroscopy data taken as part of the PPak IFS Nearby Galaxies Survey (PINGS), we perform the first analysis of the stellar and gas kinematics of this putative bulge and portions of the disk. We find a radial velocity offset of ~24 km/s between the emission lines produced by the disk HII regions and the absorption lines produced by the putative bulge stellar component. We interpret this velocity offset as evidence that the putative bulge and disk are two separate objects, the former orbiting around the latter, supporting simulations and obserations of this peculiar system. We attempt to place this external companion into the context of the M101 Group and the M101-NGC 5474 interaction.
Ray Garner
TAMU Astronomy Postdoctoral Researcher
I’m a scientist, Star Wars fan, and amateur photographer raised in Georgia. My research interests include galaxy evolution, star formation, satellite galaxies, and nebular diagnostics.