The inner Galactic bar traced by the VVV survey

TL;DR

This study uses VVV survey data to map the Galactic bulge's bar structure, revealing an inner component with a different orientation, possibly a secondary inner bar, distinct from the large-scale Galactic bar.

Contribution

It provides new observational evidence for an inner structure with a different orientation in the Galactic bar, based on near-infrared reddening and luminosity function analysis.

Findings

Detected variation in red clump magnitude indicating bar orientation change

Confirmed the presence of an inner structure with a different angle

Suggested the inner structure is a secondary bar approximately 500 pc in size

Abstract

We use the VVV survey observations in bulge regions close to the Galactic plane to trace the bar inclination at the Galactic latitude b\sim\pm1{\deg} and to investigate a distinct structure in the inner regions of the bar that was previously detected at positive latitude (b=+1{\deg}). We use the (J-Ks) colors of the red clump stars to obtain reddening values on 6 x 6 arcmin scale, minimizing the problems arising from differential extinction. Dereddened magnitudes are then used to build the luminosity function of the bulge in regions of ~0.4 sq deg to obtain the mean red clump magnitudes. These are used as distance indicators to trace the bar structure. The luminosity function clearly shows the red clump mean magnitude variation with longitude, as expected from a large scale bar oriented towards us at positive Galactic longitude, with a dereddened magnitude varying from Ks_0=13.4 at l=-10{\deg} to Ks_0=12.4 at l=+10{\deg}. We detect a change in the orientation of the bar in the central regions with |l|<4{\deg} at b=\pm1{\deg}, in agreement with results obtained at positive latitudes by other authors. Our results are based on a different dataset and at different latitude, which shows that this change in the bar orientation is real. This suggests that there is an inner structure distinct to the large-scale Galactic bar, with a different orientation angle. This inner structure could be a secondary, inner bar, with a semi-major axis of ~500 pc that is symmetric with respect to the Galactic plane.