342,931 research outputs found
Comment on Universal Reduced Potential Function for Diatomic Systems
First principles prove why a recent claim by R.H. Xie and P.S. Hsu (Phys.
Rev. Lett. 96, 243201 (2006)) on the scaling power of a covalent Sutherland
parameter to expose a universal function cannot be validated.Comment: 1 page, at the UGent archive, 11 references, revised for publication
in PR
Low Star Formation Rates for z=1 Early-Type Galaxies in the Very Deep GOODS-MIPS Imaging: Implications for their Optical/Near-Infrared Spectral Energy Distributions
We measure the obscured star formation in z~1 early-type galaxies. This
constrains the influence of star formation on their optical/near-IR colors,
which, we found, are redder than predicted by the model by Bruzual & Charlot
(2003). From deep ACS imaging we construct a sample of 95 morphologically
selected early-type galaxies in the HDF-N and CDF-S with spectroscopic
redshifts in the range 0.85<z<1.15. We measure their 24 micron fluxes from the
deep GOODS-MIPS imaging and derive the IR luminosities and star formation
rates. The fraction of galaxies with >2 sigma detections (~25 muJy} is
17(-4,+9)%. Of the 15 galaxies with significant detections at least six have an
AGN. Stacking the MIPS images of the galaxies without significant detections
and adding the detected galaxies without AGN we find an upper limit on the mean
star formation rate (SFR) of 5.2+/-3.0 Msol yr^-1, and on the mean specific SFR
of 4.6+/-2.2 * 10^-11 yr^-1. Under the assumption that the average SFR will
decline at the same rate as the cosmic average, the in situ growth in stellar
mass of the early-type galaxy population is less than 14+/-7% between z=1 and
the present. We show that the typically low IR luminosity and SFR imply that
the effect of obscured star formation (or AGN) on their rest-frame
optical/near-IR SEDs is negligible for ~90% of the galaxies in our sample.
Hence, their optical/near-IR colors are most likely dominated by evolved
stellar populations. This implies that the colors predicted by the Bruzual &
Charlot (2003) model for stellar populations with ages similar to those of z~1
early-type galaxies (~1-3 Gyr) are most likely too blue, and that stellar
masses of evolved, high-redshift galaxies can be overestimated by up to a
factor of ~2.Comment: Accepted for publication in ApJ, 8 pages, 4 figures, 1 tabl
Mass-to-Light Ratios of Field Early-Type Galaxies at z~1 from Ultra-Deep Spectroscopy: Evidence for Mass-dependent Evolution
We present an analysis of the Fundamental Plane for a sample of 27 field
early-type galaxies in the redshift range 0.6<z<1.15. The galaxies in this
sample have high S/N spectra obtained at the VLT and high resolution imaging
from the ACS. We find that the mean evolution in M/L of our sample is , with a large galaxy-to-galaxy scatter. This value can
be too low by 0.3 due to selection effects, resulting in . The strong correlation between M/L and rest-frame color
indicates that the observed scatter is not due to measurement errors, but due
to intrinsic differences between the stellar populations of the galaxies. This
pace of evolution is much faster than the evolution of cluster galaxies.
However, we find that the measured M/L evolution strongly depends on galaxy
mass. For galaxies with masses , we find no significant
difference between the evolution of field and cluster galaxies: Delta ln (M/L_B) =
-1.12+/-0.06z$ for cluster galaxies. The relation between the measured M/L
evolution and mass is partially due to selection effects. However, even when
taking selection effects into account, we still find a relation between M/L
evolution and mass, which is most likely caused by a lower mean age and a
larger intrinsic scatter for low mass galaxies. Results from lensing early-type
galaxies, which are mass-selected, show a very similar trend with mass. This,
combined with our findings, provides evidence for down-sizing. Previous studies
of the rate of evolution of field early-type galaxies found a large range of
mutually exclusive values. We show that these differences are largely caused by
the differences between fitting methods. (Abridged)Comment: figures 3 and 4 available at
http://www.strw.leidenuniv.nl/~vdwel/private/FPpaper
Superstrings and WZNW Models
We give a brief review of our approach to the quantization of superstrings.
New is a covariant derivation of the measure at tree level and a path integral
formula for this measure.Comment: 12 pp, LaTeX, Contribution to the QTS3 Conference Proceeding
New Entropy Formula with Fluctuating Reservoir
Finite heat reservoir capacity and temperature fluctuations lead to
modification of the well known canonical exponential weight factor. Requiring
that the corrections least depend on the one-particle energy, we derive a
deformed entropy, K(S). The resulting formula contains the Boltzmann-Gibbs, the
Renyi and the Tsallis formulas as particular cases. For extreme large
fluctuations (compared to the Gaussian case) a new, parameter-free entropy -
probability relation emerges. This formula and the corresponding canonical
equilibrium distribution are nearly Boltzmannian for high probability, but
deviate from the classical result for low probability. In the extreme large
fluctuation limit the canonical distribution resembles for low probability the
cumulative Gompertz distribution
Dynamical Models of Elliptical Galaxies in z=0.5 Clusters: II. Mass-to-Light Ratio Evolution without Fundamental Plane Assumptions
We study M/L evolution of early-type galaxies using dynamical modeling of
resolved internal kinematics. This makes fewer assumptions than Fundamental
Plane (FP) studies and provides a powerful new approach for studying galaxy
evolution. We focus on the sample of 25 galaxies in clusters at z=0.5 modeled
in Paper I. For comparison we compile and homogenize M/L literature data for 60
nearby galaxies that were modeled in comparable detail. The nearby sample obeys
log(M/L)_B = Z + S log(sigma_eff/[200 km/s]), with Z = 0.896 +/- 0.010, S =
0.992 +/- 0.054, and sigma_eff the effective velocity dispersion. The z=0.5
sample follows a similar relation but with lower zeropoint. The implied M/L
evolution is Delta log(M/L) / Delta z = -0.457 +/- 0.046(random) +/-
0.078(systematic), consistent with passive evolution following high-redshift
formation. This agrees with the FP results for this sample by van Dokkum & van
der Marel. This confirms that FP evolution tracks M/L evolution, which is an
important verification of the assumptions that underly FP studies. However,
while we find more FP evolution for galaxies of low sigma_eff (or low mass),
the dynamical M/L evolution instead shows little trend with sigma_eff. We argue
that this difference can be plausibly attributed to a combination of two
effects: (a) evolution in structural galaxy properties other than M/L; and (b)
the neglect of rotational support in studies of FP evolution. The results leave
the question open whether the low-mass galaxies in the sample have younger
population ages than the high-mass galaxies. This highlights the general
importance in the study of population ages for complementing dynamical
measurements with broad-band colors or spectroscopic population diagnostics.Comment: ApJ, submitted; 17 pages formatted with emulateap
Photo-ionization modelling of planetary nebulae -- II. Galactic bulge nebulae, a comparison with literature results
We have constructed photo-ionization models of five galactic bulge planetary
nebulae using our automatic method which enables a fully self-consistent
determination of the physical parameters of a planetary nebula. The models are
constrained using the spectrum, the IRAS and radio fluxes and the angular
diameter of the nebula. We also conducted a literature search for physical
parameters determined with classical methods for these nebulae. Comparison of
the distance independent physical parameters with published data shows that the
stellar temperatures generally are in good agreement and can be considered
reliable. The literature data for the electron temperature, electron density
and also for the abundances show a large spread, indicating that the use of
line diagnostics is not reliable and that the accuracy of these methods needs
to be improved. Comparison of the various abundance determinations indicates
that the uncertainty in the electron temperature is the main source of
uncertainty in the abundance determination. The stellar magnitudes predicted by
the photo-ionization models are in good agreement with observed values.Comment: Accepted for publication in MNRA
The Evolution of Rest-Frame K-band Properties of Early-Type Galaxies from z=1 to the Present
We measure the evolution of the rest-frame K-band Fundamental Plane from z=1
to the present by using IRAC imaging of a sample of early-type galaxies in the
Chandra Deep Field-South at z~1 with accurately measured dynamical masses. We
find that evolves as , which is
slower than in the B-band (). In the B-band
the evolution has been demonstrated to be strongly mass dependent. In the
K-band we find a weaker trend: galaxies more massive than
evolve as ;
less massive galaxies evolve as . As
expected from stellar population models the evolution in is slower than
the evolution in . However, when we make a quantitative comparison, we
find that the single burst Bruzual-Charlot models do not fit the results well,
unless large dust opacities are allowed at z=1. Models with a flat IMF fit
better, Maraston models with a different treatment of AGB stars fit best. These
results show that the interpretation of rest-frame near-IR photometry is
severely hampered by model uncertainties and therefore that the determination
of galaxy masses from rest-frame near-IR photometry may be harder than was
thought before.Comment: 5 pages, 3 figures, Accepted for publication in ApJ
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