Browsing by Subject "radial-velocity assay"

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Kinematics At the Edge of the Galactic Bulge: Evidence for Cylindrical Rotation
(2009-09) Howard, Christian D.; Rich, R. Michael; Clarkson, Will; Mallery, Ryan; Kormendy, John; De Propris, Roberto; Robin, Anne C.; Fux, Roger; Reitzel, David B.; Zhao, HongSheng; Kuijken, Konrad; Koch, Andreas; Kormendy, John
We present new results from BRAVA, a large-scale radial velocity survey of the Galactic bulge, using M giant stars selected from the Two Micron All Sky Survey catalog as targets for the Cerro Tololo Inter-American Observatory 4 m Hydra multi-object spectrograph. The purpose of this survey is to construct a new generation of self-consistent bar models that conform to these observations. We report the dynamics for fields at the edge of the Galactic bulge at latitudes b = -8 degrees and compare to the dynamics at b = -4 degrees. We find that the rotation curve V (r) is the same at b = -8 degrees as at b = -4 degrees. That is, the Galactic boxy bulge rotates cylindrically, as do boxy bulges of other galaxies. The summed line-of-sight velocity distribution at b = -8 degrees is Gaussian, and the binned longitude-velocity plot shows no evidence for either a (disk) population with cold dynamics or for a (classical bulge) population with hot dynamics. The observed kinematics are well modeled by an edge-on N-body bar, in agreement with published structural evidence. Our kinematic observations indicate that the Galactic bulge is a prototypical product of secular evolution in galaxy disks, in contrast with stellar population results that are most easily understood if major mergers were the dominant Formation process.
Our Milky Way As A Pure-Disk Galaxy-A Challenge for Galaxy Formation
(2010-09) Shen, Juntai T.; Rich, R. Michael; Kormendy, John; Howard, Christian D.; De Propris, Roberto; Kunder, Andrea; Shen, Juntai T.; Kormendy, John
Bulges are commonly believed to form in the dynamical violence of galaxy collisions and mergers. Here, we model the stellar kinematics of the Bulge Radial Velocity Assay ( BRAVA) and find no sign that the Milky Way contains a classical bulge formed by scrambling pre-existing disks of stars in major mergers. Rather, the bulge appears to be a bar seen somewhat end-on, as hinted from its asymmetric boxy shape. We construct a simple but realistic N-body model of the Galaxy that self-consistently develops a bar. The bar immediately buckles and thickens in the vertical direction. As seen from the Sun, the result resembles the boxy bulge of our Galaxy. The model fits the BRAVA stellar kinematic data covering the whole bulge strikingly well with no need for a merger-made classical bulge. The bar in our best-fit model has a half-length of similar to 4 kpc and extends 20 degrees from the Sun-Galactic center line. We use the new kinematic constraints to show that any classical bulge contribution cannot be larger than similar to 8% of the disk mass. Thus, the Galactic bulge is a part of the disk and not a separate component made in a prior merger. Giant, pure-disk galaxies like our own present a major challenge to the standard picture in which galaxy Formation is dominated by hierarchical clustering and galaxy mergers.