The Vertical X-shaped Structure in the Milky Way: Evidence from a Simple Boxy Bulge Model

Abstract

A vertical X-shaped structure was recently reported in the Galactic bulge. Here we present evidence of a similar X-shaped structure in the Shen et al. (2010) bar/boxy bulge model that simultaneously matches the stellar kinematics successfully. The X-shaped structure is found in the central region of our bar/boxy bulge model, and is qualitatively consistent with the observed one in many aspects. End-to-end separations of the X-shaped structure in the radial and vertical directions are roughly 3 kpc and 1.8 kpc, respectively. The X-shaped structure contains about 7% of light in the boxy bulge region, but it is significant enough to be identified in observations. An X-shaped structure naturally arises in the formation of bar/boxy bulges, and is mainly associated with orbits trapped around the vertically-extended x_1 family. Like the bar in our model, the X-shaped structure tilts away from the Sun--Galactic center line by 20 degrees. The X-shaped structure becomes increasingly symmetric about the disk plane, so the observed symmetry may indicate that it formed at least a few billion years ago. The existence of the vertical X-shaped structure suggests that the formation of the Milky Way bulge is shaped mainly by internal disk dynamical instabilities.

Accepted for publication in ApJL; minor changes after the referee's report; 6 pages; emulateapj format

References in corpus (11)

• Dynamics of Barred Galaxies
• A Near-Infrared Study of 2MASS Bars in Local Galaxies: An Anchor for High Redshift Studies
• The population of barred galaxies in the local universe I. Detection and characterisation of bars
• The origin of the split red clump in the Galactic bulge of the Milky Way
• Modelling the Galactic bar using OGLE-II Red Clump Giant Stars
• K-Band Observations of Boxy Bulges. I. Morphology and Surface Brightness Profiles
• The Bulge Radial Velocity Assay (BRAVA): I. Techniques and a Rotation Curve
• Tracing the long bar with red-clump giants
• Kinematics at the Edge of the Galactic Bulge: Evidence for Cylindrical Rotation
• The Bulge Radial Velocity Assay (BRAVA): I. Sample Selection and a Rotation Curve
• Proper Motions in the Galactic Bulge: Plaut's Window

Cited by in corpus (55)

• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• Reddening and Extinction Toward the Galactic Bulge from OGLE-III: The Inner Milky Way's Rv ~ 2.5 Extinction Curve
• Secular Evolution in Disk Galaxies
• Chemodynamical history of the Galactic Bulge
• Made-to-Measure models of the Galactic Box/Peanut bulge: stellar and total mass in the bulge region
• Separation of Stellar Populations by an Evolving Bar: Implications for the Bulge of the Milky Way
• A New Photometric Model of the Galactic Bar using Red Clump Giants
• The Milky Way bar and bulge revealed by APOGEE DR16 and Gaia EDR3
• The Fermi-LAT GeV Excess Traces Stellar Mass in the Galactic Bulge
• Constraining the structure and formation of the Galactic bulge from a field in its outskirts. FLAMES-GIRAFFE spectra of about 400 red giants around (l,b)=(0°,-10°)
• Peanuts, brezels and bananas: food for thought on the orbital structure of the Galactic bulge
• Metal-poor stars towards the Galactic bulge - a population potpourri
• A Vertical Resonance Heating Model for X- or Peanut-Shaped Galactic Bulges
• A parametric description of the 3D structure of the Galactic Bar/Bulge using the VVV survey
• The Giraffe Inner Bulge Survey (GIBS) II. Metallicity distributions and alpha element abundances at fixed Galactic latitude
• Young stars in an old bulge: a natural outcome of internal evolution in the Milky Way
• Metallicity gradients through disk Instability: A simple model for the Milky Way's boxy bulge
• The Bar and Spiral Arms in the Milky Way: Structure and Kinematics
• The Milky Way without X: An alternative interpretation of the double red clump in the Galactic bulge
• Stars behind bars I: The Milky Way's central stellar populations
• N-body simulation insights into the X-shaped bulge of the Milky Way: Kinematics and distance to the Galactic Centre
• The phase-space of boxy-peanut and X-shaped bulges in galaxies I. Properties of non-periodic orbits
• Observed properties of boxy/peanut/barlens bulges
• The X-Shaped Milky Way Bulge in OGLE-III Photometry and in N-Body Models
• The Carnegie-Irvine Galaxy Survey. V. Statistical study of bars and buckled bars
• On the orbits that generate the X-shape in the Milky Way bulge
• Box/peanut-shaped bulges in action space
• New insight on the origin of the double red clump in the Milky Way bulge
• Central Engine and Host Galaxy of RXJ 1301.9+2747: A Multiwavelength View of a Low-mass Black Hole Active Galactic Nuclei with Ultra-soft X-ray Emission
• Kinematics of RR Lyrae stars in the Galactic bulge with OGLE-IV and Gaia DR2
• Was the Milky Way Bulge Formed From The Buckling Disk Instability, Hierarchical Collapse, Accretion of Clumps, or All of the Above?
• Resonant Orbits and the High Velocity Peaks Towards the Bulge
• On the Correlation Between Metallicity and the X-Shaped Morphology of the Milky Way Bulge
• Uncertainties in the Deprojection of the Observed Bar Properties
• Mapping the Three-Dimensional "X-Shaped Structure" in Models of the Galactic Bulge
• Kinematics of the X-shaped Milky Way Bulge: Expectations from a Self-consistent N-body Model
• Orbit-Superposition Dynamical Modeling of Barred Galaxies
• What to expect from dynamical modelling of galactic haloes
• Assembling the Milky Way bulge from globular clusters: Evidence from the double red clump
• Are high velocity peaks in the Milky Way bulge due to the bar?
• The Globular Cluster Origin of the Milky Way Outer Bulge: Evidence from Sodium Bimodality
• Asymmetric streaming motion in the Galactic bulge X-shaped structure revealed by the OGLE-III proper motions
• Theoretical Models of the Galactic Bulge
• GalMod: a Galactic synthesis population model
• Difference in chemical composition between the bright and faint red clump stars in the Milky Way bulge
• Mapping the tilt of the Milky Way bulge velocity ellipsoids with ARGOS and $Gaia$ DR2
• Galactic resonance rings. Modelling of motions in the wide solar neighborhood
• Influence of the Galactic bar on the kinematics of the disc stars with Gaia EDR3 data
• A new look at the kinematics of the bulge from an N-body model
• Metallicity Properties of the Galactic Bulge Stars Near and Far: Expectations from the Auriga Simulation
• The Impact of Classical Bulges on Stellar Bars and Box-Peanut-X-Features in Disk Galaxies
• The disc origin of the Milky Way bulge: On the high velocity dispersion of metal-rich stars at low latitude
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data III. Panoramic view of the bulge
• Deprojection of external barred galaxies from photometry
• Blanco DECam Bulge Survey (BDBS) IV: Metallicity Distributions and Bulge Structure from 2.6 Million Red Clump Stars