Analysing the structure of the bulge with Mira variables
Abstract
Context. The Galactic bulge at latitude 4 < b(deg) < 10 was claimed to show an Xshape, which means that stellar density distributions along the line of sight have a double peak. However, this double peak is only observed with the redclump population, and doubt has been cast on its use as a perfect standard candle. As such, a boxy bulge without an Xshape is not discarded.
Aims: We aim to constrain the shape of the bulge making use of a different population: Mira variables from the new Optical Gravitational Lensing Experiment data release, OGLEIV, with an average age of 9 Gyr.
Methods: We analysed an area of the bulge far from the plane, where we fitted the density of the Miras with boxy bulge and Xshaped bulge models and calculated the probability of each model.
Results: We find that the probability of a boxy bulge fitting the data is p = 0.19, whereas the probability for the Xshaped bulge is only p = 2.85 × 10^{−6} (equivalent to a tension of the model with the data of a 4.7σ level). Therefore, the boxy bulge model seems to be more appropriate for describing the Galactic bulge, although we cannot exclude any model with complete certainty.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 October 2022
 DOI:
 10.1051/00046361/202244810
 arXiv:
 arXiv:2210.03643
 Bibcode:
 2022A&A...666L..13C
 Keywords:

 Galaxy: bulge;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 5 pages, 3 figures, accepted for publication in A&