310 research outputs found
The Age of Ellipticals and the Color-Magnitude Relation
Using new narrowband color observations of early-type galaxies in clusters,
we reconstruct the color-magnitude relation (CMR) with a higher degree of
accuracy than previous work. We then use the spectroscopically determined ages
and metallicities from three samples (Trager et al 2008, Thomas et al 2005,
Gallazzi et al 2006), combined with multi-metallicity SED models, to compare
predicted colors for galaxies with young ages (less than 8 Gyr) with the known
CMR. We find that the CMR cannot by reproduced by the spectroscopically
determined ages and metallicities in any of the samples despite the high
internal accuracies to the spectroscopic indices. In contrast, using only the
index to determine [Fe/H], and assuming a mean age of 12 Gyr for a
galaxy's stellar population, we derive colors that exactly match not only the
color zeropoint of the CMR but also its slope. We consider the source of young
age estimates, the H index, and examine the conflict between red
continuum colors and large H values in galaxy spectra. We conclude that
our current understanding of stellar populations is insufficient to correctly
interpret H values and that the sum of our galaxy observations supports
an old and monolithic scenario of galaxy formation. This result has a
devastating impact on every study that has used the H index to calculate
galaxy age, as the use of the H versus MgFe diagram will result in
incorrectly deduced young ages.Comment: 29 pages, 9 figures. This version deviates from the version accepted
by Ap
The Atmospheric Pressure at the Surface of Mars
Photoelectric observation of atmospheric pressure on Mars surfac
The atmospheric pressure at the surface of Mars, volume 6, number 12
Atmospheric pressure at surface of Mars estimated from photoelectric measurements of eclipses of Phobo
Age and Metallicity Estimations in Old Stellar Populations from Stromgren Photometry
We present a new technique to determine age and metallicity of old stellar
populations (globular clusters and elliptical galaxies) using an iterative
principal component analysis on narrow band (Str\"omgren) colors. Our technique
is capable of reproducing globular cluster [Fe/H] values to 0.02 dex and CMD
ages to 1.0 Gyrs. We also present preliminary results on the application of our
technique to a sample of high mass, field ellipticals and low mass, cluster
dwarf ellipticals. We confirm the results of earlier studies which find that
globular clusters increase in metallicity with age and that age and metallicity
increase with galaxy mass. However, we find that dwarf ellipticals deviate from
the elliptical sequence by having little to no correlation between age and
metallicity.Comment: 8 pages IAU LaTeX, 5 figures, contributing talk IAU #198 Near-Field
Cosmology with Dwarf Elliptical Galaxie
Cluster Populations in A115 and A2283
This paper presents four color narrow-band photometry of clusters A115
() and A2283 () in order to follow the star formation history
of various galaxy types. Although located at similar redshifts, the two
clusters display very different fractions of blue galaxies (i.e. the
Butcher-Oemler effect, for A115, for A2283). A system
of photometric classification is applied to the cluster members that divides
the cluster population into four classes based on their recent levels of star
formation. It is shown that the blue population of each cluster is primarily
composed of normal starforming (SFR < 1 M_{\sun} yrs) galaxies at the
high luminosity end, but with an increasing contribution from a dwarf starburst
population below . This dwarf starburst population appears to be
the same population of low mass galaxies identified in recent HST imaging (Koo
et al 1997), possible progenitors to present-day cluster dwarf ellipticals,
irregulars and BCD's. Deviations in the color-magnitude relationship for the
red galaxies in each cluster suggest that a population of blue S0's is evolving
into present-day S0 colors at this epoch. The radial distribution of the blue
population supports the prediction of galaxy harassment mechanisms for tidally
induced star formation operating on an infalling set of gas-rich galaxies.Comment: 28 pages including 2 tables and 9 figures, AASTeX v4.0. Accepted by
Ap.J. Data, referee report and response are avaliable from
http://zebu.uoregon.edu/~j
Hysteresis in one-dimensional reaction-diffusion systems
We introduce a simple nonequilibrium model for a driven diffusive system with
nonconservative reaction kinetics which exhibits ergodicity breaking and
hysteresis in one dimension. These phenomena can be understood through a
description of the dominant stochastic many-body dynamics in terms of an
equilibrium single-particle problem, viz. the random motion of a shock in an
effective potential. This picture also leads to the exact phase diagram of the
system and suggests a new generic mechanism for "freezing by heating".Comment: 4 Pages, 5 figure
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