Asymptotic giant branch-stars in the GLIMPSE database

II. Distribution in the inner Milky Way

¹ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
² Paltzerweg 38, 3722 JG Bilthoven, The Netherlands

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Received: 29 December 2025
Accepted: 28 May 2026

Abstract

Aims. In the preceding paper (paper I) we showed that the GLIMPSE database contains millions of asymptotic giant branch (AGB) stars. Their nature follows from two properties: the objects have the same color after correction for interstellar extinction (see paper I, Fig. 7), and the number of objects grows exponentially with the apparent magnitude at 8 μm and always at the same rate; the growth in luminosity follows from the predicted exponential increase in luminosity of AGB stars (see paper I, Fig. 14).

Methods. We analyzed the interstellar extinction of the stars and the variation in their numbers as a function of longitude to derive their Galactic distribution and their association with interstellar dust.

Results. We find that the stars are spread out in a flat disk with a radius of about 7 kpc embedded in a presumably larger, flat, thick layer of dust. The counts of the stars led to the distinction of three populations of AGB stars: (i) an outer disk for R > 1.5 kpc with a density that rises slowly toward the Galactic Center (GC), (ii) an inner disk for R < 1.5 kpc with a stellar density that rises rapidly toward the GC (≈R⁻⁴) and (iii) inside R = 300 pc the GC Area that contains the Inner Galactic Bulge (IGB) and the Nuclear Stellar Disk (NSD). We present complete 2D images of both objects. Inside the NSD the dust density is significantly enhanced and the luminosity of the AGB stars is higher than elsewhere in the Milky Way. The NSD is the true center of the Milky Way.

Conclusions. The GLIMPSE database contains a full description of the AGB stars in the inner Milky Way.