Structure of the Galactic Bulge: Is the Milky Way a Double-barred Galaxy?

Abstract

Using the data of the IRSF/SIRIUS infrared survey along the Galactic plane (| l | ≤ 10.°5 at b = +1°), we find a distinct structure, which is probably a secondary bar, inside the primary bar of our Galaxy. The apparent magnitude peak of Bulge red clump stars changes continuously from KS ∼ 13.5 (l = −10°) to KS ∼ 12.3 (l = +10°), and this can be explained by the bar structure of the Galactic Bulge. However, the apparent magnitude changes by only ∼ 0.1 mag over the central 8°, and this indicates that there is a distinct structure inside the primary bar. In the process of the distance derivation, we have used the infrared extinction law in the J, H, and KS bands toward the Galactic center newly determined from our survey.