APOGEE Kinematics I: Overview of the Kinematics of the Galactic Bulge as Mapped by APOGEE

TL;DR

This paper maps the stellar kinematics of the Galactic bulge using APOGEE data, revealing cylindrical rotation, a central kinematic peak, and a connection between the bulge and disk chemodynamics, aligning with models of barred galaxy structures.

Contribution

It provides the first extensive kinematic maps of the bulge and inner disk from APOGEE, demonstrating the bulge's cylindrical rotation and linking chemodynamics to galaxy formation models.

Findings

Bulge exhibits cylindrical rotation across all latitudes.

Kinematic and chemical gradients are smallest at the bulge center.

Inner disk stars with [Fe/H] > -1.0 likely originate from the disk.

Abstract

We present the stellar kinematics across the Galactic bulge and into the disk at positive longitudes from the SDSS-III APOGEE spectroscopic survey of the Milky Way. APOGEE includes extensive coverage of the stellar populations of the bulge along the mid-plane and near-plane regions. From these data, we have produced kinematic maps of 10,000 stars across longitudes 0 deg < l < 65 deg, and primarily across latitudes of |b| < 5 deg in the bulge region. The APOGEE data reveal that the bulge is cylindrically rotating across all latitudes and is kinematically hottest at the very centre of the bulge, with the smallest gradients in both kinematic and chemical space inside the inner-most region (l,|b|) < (5,5) deg. The results from APOGEE show good agreement with data from other surveys at higher latitudes and a remarkable similarity to the rotation and dispersion maps of barred galaxies viewed edge on. The thin bar that is reported to be present in the inner disk within a narrow latitude range of |b| < 2 deg appears to have a corresponding signature in [Fe/H] and [alpha/Fe]. Stars with [Fe/H] > -0.5 have dispersion and rotation profiles that are similar to that of N-body models of boxy/peanut bulges. There is a smooth kinematic transition from the thin bar and boxy bulge (l,|b|) < (15,12) deg out into the disk for stars with [Fe/H] > -1.0, and the chemodynamics across (l,b) suggests the stars in the inner Galaxy with [Fe/H] > -1.0 have an origin in the disk.