Analysing the structure of the bulge with Mira variables

Abstract

The Galactic bulge at latitude $4<|b|$(deg.)$<10$ was claimed to show an X-shape, which means that stellar density distributions along the line of sight have a double peak. However, this double peak is only observed with the red-clump population, and doubt has been cast on its use as a perfect standard candle.\ As such, a boxy bulge without an X-shape is not discarded. 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, OGLE-IV, with an average age of 9 Gyr. We analysed an area of the bulge far from the plane, where we fitted the density of the Miras with boxy bulge and X-shaped bulge models and calculated the probability of each model. We find that the probability of a boxy bulge fitting the data is $p=0.19$, whereas the probability for the X-shaped bulge is only $p=2.85\cdot 10^{-6}$ (equivalent to a tension of the model with the data of a 4.7$\sigma$ 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.

arXiv comment5 pages, 3 figures, accepted for publication in A&A Letters

References in corpus (21)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Mapping the Three-Dimensional Density of the Galactic Bulge with VVV Red Clump Stars
• Two Red Clumps and the X-Shaped Milky Way Bulge
• AGB Variables and the Mira Period-Luminosity Relation
• Microlensing optical depth towards the Galactic bulge from MOA observations during 2000 with Difference Image Analysis
• Deciphering the 3D structure of the old Galactic bulge from the OGLE RR Lyrae stars
• The Gaia-ESO Survey: metallicity and kinematic trends in the Milky Way bulge
• VVV Survey Near-Infrared Photometry of Known Bulge RR Lyrae stars: the Distance to the Galactic Center and Absence of a Barred Distribution of the Metal-Poor Population
• The X-shaped Bulge of the Milky Way revealed by WISE
• A boxy bulge in the Milky Way. Inversion of the stellar statistics equation with 2MASS data
• The Age and Structure of the Galactic Bulge from Mira Variables
• Revised Geometric Estimates of the North Galactic Pole and the Sun's Height Above the Galactic Midplane
• Young stars in an old bulge: a natural outcome of internal evolution in the Milky Way
• The Milky Way without X: An alternative interpretation of the double red clump in the Galactic bulge
• 3D kinematics through the X-shaped Milky Way bulge
• Orbital dynamics of three-dimensional bars: IV. Boxy isophotes in face-on views
• The X-Shaped Milky Way Bulge in OGLE-III Photometry and in N-Body Models
• Reinforcing the link between the double red clump and the X-shaped bulge of the Milky Way
• Absence of an X-shaped Structure in the Milky Way Bulge Using Mira Variable Stars
• A case against an X-shaped structure in the Milky Way young bulge
• Distribution of red clump stars does not support the X-shaped Galactic bulge

Cited by in corpus (1)

• A three-dimensional map of the Milky Way using 66,000 Mira variable stars