4,439 research outputs found
Central Star Formation in Pseudobulges and Classical Bulges
I use Spitzer 3.6-8.0 \mu m color profiles to compare the radial structure of
star formation in pseudobulges and classical bulges. Pseudobulges are
``bulges'' which form through secular evolution, rather than mergers. In this
study, pseudobulges are identified using the presence of disk-like structure in
the center of the galaxy (nuclear spiral, nuclear bar, and/or high ellipticity
in bulge); classical bulges are those galaxy bulges with smooth isophotes which
are round compared to the outer disk, and show no disky structure in their
bulge. I show that galaxies structurally identified as having pseudobulges have
higher central star formation rates than those of classical bulges. Further, I
also show that galaxies identified as having classical bulges have remarkably
regular star formation profiles. The color profiles of galaxies with classical
bulges show a star forming outer disk with a sharp change, consistent with a
decline in star formation rates, toward the center of the galaxy. Classical
bulges have a nearly constant inner profile (r < 1.5 kpc) that is similar to
elliptical galaxies. Pseudobulges in general show no such transition in star
formation properties from the outer disk to the central pseudobulge. Thus I
conclude that pseudobulges and classical bulges do in fact form their stars via
different mechanisms. Further, this adds to the evidence that classical bulges
form most of their stars in fast episodic bursts, in a similar fashion to
elliptical galaxies; whereas, pseudobulges form stars from longer lasting
secular processes.Comment: accepted to ApJ Letter
A global magnetic anomaly map
A subset of POGO satellite magnetometer data has been formed that is suitable for analysis of crustal magnetic anomalies. Using a thirteenth order field model, fit to these data, magnetic residuals have been calculated over the world to latitude limits of plus 50 deg. These residuals averaged over one degree latitude-longitude blocks represent a detailed global magnetic anomaly map derived solely from satellite data. Preliminary analysis of the map indicates that the anomalies are real and of geological origin
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Intrinsic chess rating
This paper develops and tests formulas for representing playing strength at chess by the quality of moves played, rather than by the results of games. Intrinsic quality is estimated via evaluations given by computer chess programs run to high depth, ideally so that their playing strength is sufficiently far ahead of the best human players as to be a `relatively omniscient' guide. Several formulas, each having intrinsic skill parameters s for `sensitivity' and c for `consistency', are argued theoretically and tested by regression on large sets of tournament games played by humans of varying strength as measured by the internationally standard Elo rating system. This establishes a correspondence between Elo rating and the parameters. A smooth correspondence is shown between statistical results and the century points on the Elo scale, and ratings are shown to have stayed quite constant over time. That is, there has been little or no `rating inflation'. The theory and empirical results are transferable to other rational-choice settings in which the alternatives have well-defined utilities, but in which complexity and bounded information constrain the perception of the utility values
Rations for dairy cows
"May, 1939""Revised April 1942""The average annual production for Missouri dairy cows, 160 pounds of butterfat, can be raised to approximately 300 pounds through proper feeding."--First paragraph.M. J. Regan and W. H. Cloninge
How Barred is the NIR Nearby Universe? An analysis using 2MASS
We determine a firm lower limit to the bar fraction of 0.58 in the nearby
universe using J+H+Ks-band images for 134 spirals from 2MASS. With a mean
deprojected semi-major axis of 5.1 kpc, and a mean deprojected ellipticity of
0.45 this local bar sample lays the ground work for studies on bar formation
and evolution at high redshift.Comment: In the proceedings "Penetrating Bars through Masks of Cosmic Dust:
The Hubble Tuning Fork strikes a New Note
Improved definition of crustal magnetic anomalies for MAGSAT data
The routine correction of MAGSAT vector magnetometer data for external field effects such as the ring current and the daily variation by filtering long wavelength harmonics from the data is described. Separation of fields due to low altitude sources from those caused by high altitude sources is affected by means of dual harmonic expansions in the solution of Dirichlet's problem. This regression/harmonic filter procedure is applied on an orbit by orbit basis, and initial tests on MAGSAT data from orbit 1176 show reduction in external field residuals by 24.33 nT RMS in the horizontal component, and 10.95 nT RMS in the radial component
Microscopic Surface Structure of Liquid Alkali Metals
We report an x-ray scattering study of the microscopic structure of the
surface of a liquid alkali metal. The bulk liquid structure factor of the
eutectic K67Na33 alloy is characteristic of an ideal mixture, and so shares the
properties of an elemental liquid alkali metal. Analysis of off-specular
diffuse scattering and specular x-ray reflectivity shows that the surface
roughness of the K-Na alloy follows simple capillary wave behavior with a
surface structure factor indicative of surface induced layering. Comparison of
thelow-angle tail of the K67Na33 surface structure factor with the one measured
for liquid Ga and In previously suggests that layering is less pronounced in
alkali metals. Controlled exposure of the liquid to H2 and O2 gas does not
affect the surface structure, indicating that oxide and hydride are not stable
at the liquid surface under these experimental conditions.Comment: 12 pages, 3 figures, published in Phys. Rev.
Inner Molecular Rings in Barred Galaxies: BIMA SONG CO Observations
Although inner star-forming rings are common in optical images of barred
spiral galaxies, observational evidence for the accompanying molecular gas has
been scarce. In this paper we present images of molecular inner rings, traced
using the CO (1-0) emission line, from the
Berkeley-Illinois-Maryland-Association Survey of Nearby Galaxies (BIMA SONG).
We detect inner ring CO emission from all five SONG barred galaxies classified
as inner ring (type (r)). We also examine the seven SONG barred galaxies
classified as inner spiral (type (s)); in one of these, NGC 3627, we find
morphological and kinematic evidence for a molecular inner ring. Inner ring
galaxies have been classified as such based on optical images, which emphasize
recent star formation. We consider the possibility that there may exist inner
rings in which star formation efficiency is not enhanced. However, we find that
in NGC 3627 the inner ring star formation efficiency is enhanced relative to
most other regions in that galaxy. We note that the SONG (r) galaxies have a
paucity of CO and H alpha emission interior to the inner ring (except near the
nucleus), while NGC 3627 has relatively bright bar CO and H alpha emission; we
suggest that galaxies with inner rings such as NGC 3627 may be misclassified if
there are significant amounts of gas and star formation in the bar.Comment: To be published in the Astrophysical Journal, July 2002 A version of
the paper with full resolution figures is available at:
http://www.astro.umd.edu/~mregan/ms.ps.g
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