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Articles 1 - 8 of 8
Full-Text Articles in Physical Sciences and Mathematics
The Bar-Halo Interaction - I. From Fundamental Dynamics To Revised N-Body Requirements, Md Weinberg, N Katz
The Bar-Halo Interaction - I. From Fundamental Dynamics To Revised N-Body Requirements, Md Weinberg, N Katz
Astronomy Department Faculty Publication Series
A galaxy remains near equilibrium for most of its history. Only through resonances can non-axisymmetric features, such as spiral arms and bars, exert torques over large scales and change the overall structure of the galaxy. In this paper, we describe the resonant interaction mechanism in detail, derive explicit criteria for the particle number required to simulate these dynamical processes accurately using N-body simulations, and illustrate them with numerical experiments. To do this, we perform a direct numerical solution of perturbation theory, in short, by solving for each orbit in an ensemble and make detailed comparisons with N-body simulations. The criteria …
A Magellanic Origin For The Warp Of The Galaxy, Md Weinberg, L Blitz
A Magellanic Origin For The Warp Of The Galaxy, Md Weinberg, L Blitz
Astronomy Department Faculty Publication Series
We show that a Magellanic Cloud origin for the warp of the Milky Way can explain most quantitative features of the outer H I layer recently identified by Levine et al. We construct a model, similar to that presented by Weinberg in 1998, that produces distortions in the dark matter halo, and we calculate the combined effect of these dark halo distortions and the direct tidal forcing by the Magellanic Clouds on the disk warp in the linear regime. The interaction of the dark matter halo with the disk and resonances between the orbit of the Clouds and the disk …
A Two Micron All Sky Survey View Of The Sagittarius Dwarf Galaxy. Ii. Swope Telescope Spectroscopy Of M Giant Stars In The Dynamically Cold Sagittarius Tidal Stream, Sr Majewski, We Kunkel, Dr Law, Rj Patterson, Aa Polak, Hj Rocha-Pinto, Jd Crane, Pm Frinchaboy, Cb Hummels, Kv Johnston, J Rhee, Mf Skrutskie, M Weinberg
A Two Micron All Sky Survey View Of The Sagittarius Dwarf Galaxy. Ii. Swope Telescope Spectroscopy Of M Giant Stars In The Dynamically Cold Sagittarius Tidal Stream, Sr Majewski, We Kunkel, Dr Law, Rj Patterson, Aa Polak, Hj Rocha-Pinto, Jd Crane, Pm Frinchaboy, Cb Hummels, Kv Johnston, J Rhee, Mf Skrutskie, M Weinberg
Astronomy Department Faculty Publication Series
We have obtained moderate resolution (~6 km s-1) spectroscopy of several hundred M giant candidates selected from Two Micron All Sky Survey photometry. Radial velocities are presented for stars mainly in the southern Galactic hemisphere, and the primary targets have Galactic positions consistent with association to the tidal tail system of the Sagittarius (Sgr) dwarf galaxy. M giant stars selected from the apparent trailing debris arm of Sgr have velocities showing a clear trend with orbital longitude, as expected from models of the orbit and destruction of Sgr. A minimum 8 kpc width of the trailing stream about the Sgr …
A Two Micron All Sky Survey View Of The Sagittarius Dwarf Galaxy. I. Morphology Of The Sagittarius Core And Tidal Arms, Sr Majewski, Mf Skrutskie, Md Weinberg, Jc Ostheimer
A Two Micron All Sky Survey View Of The Sagittarius Dwarf Galaxy. I. Morphology Of The Sagittarius Core And Tidal Arms, Sr Majewski, Mf Skrutskie, Md Weinberg, Jc Ostheimer
Astronomy Department Faculty Publication Series
We present the first all-sky view of the Sagittarius (Sgr) dwarf galaxy mapped by M-giant star tracers detected in the complete Two Micron All Sky Survey (2MASS). Near-infrared photometry of Sgr's prominent M-giant population permits an unprecedentedly clear view of the center of Sgr. The main body is fitted with a King profile of limiting major-axis radius 30°—substantially larger than previously found or assumed—beyond which is a prominent break in the density profile from stars in the Sgr tidal tails; thus the Sgr radial profile resembles that of Galactic dwarf speroidal (dSph) satellites. Adopting traditional methods for analyzing dSph light …
An Upper Limit To The Age Of The Galactic Bar, Aa Cole, Md Weinberg
An Upper Limit To The Age Of The Galactic Bar, Aa Cole, Md Weinberg
Astronomy Department Faculty Publication Series
Using data from the Two Micron All Sky Survey, we identify a population of infrared carbon stars with J-KS ≥ 2 in the Milky Way. These stars are shown to trace the stellar bar previously identified in IR and optical surveys. The properties of C stars strongly suggest that they are of intermediate age. We conclude that the bar is likely to have formed more recently than 3 Gyr ago and must be younger than 6 Gyr. Implications and further tests of this conclusion are briefly discussed.
The Equilibrium State Of Molecular Regions In The Outer Galaxy, Mh Heyer, Jm Carpenter, Ronald L. Snell
The Equilibrium State Of Molecular Regions In The Outer Galaxy, Mh Heyer, Jm Carpenter, Ronald L. Snell
Astronomy Department Faculty Publication Series
A summary of global properties and an evaluation of the equilibrium state of molecular regions in the outer Galaxy are presented from the decomposition of the FCRAO Outer Galaxy Survey and targeted 12CO and 13CO observations of four giant molecular cloud complexes. The ensemble of identified objects includes both small, isolated clouds and clumps within larger cloud complexes. The 12CO luminosity function and size distribution of a subsample of objects with well-defined distances are determined such that ΔN/ΔLCO = L and ΔN/Δre = r. 12CO velocity dispersions …
An Adaptive Algorithm For N-Body Field Expansions, Md Weinberg
An Adaptive Algorithm For N-Body Field Expansions, Md Weinberg
Astronomy Department Faculty Publication Series
An expansion of a density field or particle distribution in basis functions that solve the Poisson equation both provides an easily parallelized N-body force algorithm and simplifies perturbation theories. The expansion converges quickly and provides the highest computational advantage if the lowest order potential-density pair in the basis looks like the unperturbed galaxy or stellar system. Unfortunately, there are only a handful of such bases in the literature that limit this advantage. This paper presents an algorithm for deriving these bases to match a wide variety of galaxy models. The method is based on efficient numerical solution of the Sturm-Liouville …
Dynamics Of An Interacting Luminous Disc, Dark Halo And Satellite Companion, Md Weinberg
Dynamics Of An Interacting Luminous Disc, Dark Halo And Satellite Companion, Md Weinberg
Astronomy Department Faculty Publication Series
This paper describes a method, based on linear perturbation theory, to determine the dynamical interaction between extended halo and spheroid components and an environmental disturbance. One finds that resonant interaction between a galaxy and passing interlopers or satellite companions can carry the disturbance inward, deep inside the halo, where it can perturb the disc. Applied to the Milky Way for example, the LMC and SMC appear to be sufficient to cause the observed Galactic warp and possibly seed other asymmetries. This is a multi-scale interaction in which the halo wake has a feature at roughly half the satellite orbital radius …