Browsing by Subject "galactic bulge"

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The Bulge Radial Velocity Assay (BRAVA). II. Complete Sample And Data Release
(2012-03) Kunder, Andrea; Koch, Andreas; Rich, R. Michael; de Propris, Roberto; Howard, Christian D.; Stubbs, Scott A.; Johnson, Christian I.; Shen, Juntai T.; Wang, Yougang G.; Robin, Annie C.; Kormendy, John; Soto, Mario; Frinchaboy, Peter; Reitzel, David B.; Zhao, HongSheng; Origlia, Livia; Kormendy, John
We present new radial velocity measurements from the Bulge Radial Velocity Assay, a large-scale spectroscopic survey of M-type giants in the Galactic bulge/bar region. The sample of similar to 4500 new radial velocities, mostly in the region -10 degrees < l < +10 degrees and b approximate to -6 degrees, more than doubles the existent published data set. Our new data extend our rotation curve and velocity dispersion profile to +20 degrees, which is similar to 2.8 kpc from the Galactic center. The new data confirm the cylindrical rotation observed at -6 degrees and -8 degrees and are an excellent fit to the Shen et al. N-body bar model. We measure the strength of the TiO epsilon molecular band as a first step toward a metallicity ranking of the stellar sample, from which we confirm the presence of a vertical abundance gradient. Our survey finds no strong evidence of previously unknown kinematic streams. We also publish our complete catalog of radial velocities, photometry, TiO band strengths, and spectra, which is available at the Infrared Science Archive as well as at UCLA.
Manganese Abundances In The Globular Cluster Omega Centauri
(2010-07) Cunha, Katia; Smith, Verne V.; Bergemann, Maria; Suntzeff, Nicholas B.; Lambert, David L.; Lambert, David L.
We present manganese abundances in 10 red giant members of the globular cluster omega Centauri; eight stars are from the most metal-poor population (RGB MP and RGB MInt1) while two targets are members of the more metal-rich groups (RGB MInt2 and MInt3). This is the first time Mn abundances have been studied in this peculiar stellar system. The LTE values of [Mn/Fe] in omega Cen overlap those of Milky Way stars in the metal-poor. Cen populations ([Fe/H] similar to -1.5 to -1.8), however unlike what is observed in Milky Way halo and disk stars, [Mn/Fe] declines in the two more metal-rich RGB MInt2 and MInt3 targets. Non-LTE calculations were carried out in order to derive corrections to the LTE Mn abundances. The non-LTE results for omega Cen in comparison with the non-LTE [Mn/Fe] versus [Fe/H] trend obtained for the Milky Way confirm and strengthen the conclusion that the manganese behavior in omega Cen is distinct. These results suggest that low-metallicity supernovae (with metallicities <= -2) of either Type II or Type Ia dominated the enrichment of the more metal-rich stars in omega Cen. The dominance of low-metallicity stars in the chemical evolution of omega Cen has been noted previously in the s-process elements where enrichment from metal-poor asymptotic giant branch stars is indicated. In addition, copper, which also has metallicity-dependent yields, exhibits lower values of [Cu/Fe] in the RGB MInt2 and MInt3 omega Cen populations.
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.