1,022 research outputs found
A New Star-Formation Rate Calibration from Polycyclic Aromatic Hydrocarbon Emission Features and Application to High Redshift Galaxies
We calibrate the integrated luminosity from the polycyclic aromatic
hydrocarbon (PAH) features at 6.2\micron, 7.7\micron\ and 11.3\micron\ in
galaxies as a measure of the star-formation rate (SFR). These features are
strong (containing as much as 5-10\% of the total infrared luminosity) and
suffer minimal extinction. Our calibration uses \spitzer\ Infrared Spectrograph
(IRS) measurements of 105 galaxies at , infrared (IR) luminosities
of 10^9 - 10^{12} \lsol, combined with other well-calibrated SFR indicators.
The PAH luminosity correlates linearly with the SFR as measured by the
extinction-corrected \ha\ luminosity over the range of luminosities in our
calibration sample. The scatter is 0.14 dex comparable to that between SFRs
derived from the \paa\ and extinction-corrected \ha\ emission lines, implying
the PAH features may be as accurate a SFR indicator as hydrogen recombination
lines. The PAH SFR relation depends on gas-phase metallicity, for which we
supply an empirical correction for galaxies with 0.2 < \mathrm{Z} \lsim
0.7~\zsol. We present a case study in advance of the \textit{James Webb Space
Telescope} (\jwst), which will be capable of measuring SFRs from PAHs in
distant galaxies at the peak of the SFR density in the universe () with
SFRs as low as ~10~\sfrunits. We use \spitzer/IRS observations of the PAH
features and \paa\ emission plus \ha\ measurements in lensed star-forming
galaxies at to demonstrate the ability of the PAHs to derive
accurate SFRs. We also demonstrate that because the PAH features dominate the
mid-IR fluxes, broad-band mid-IR photometric measurements from \jwst\ will
trace both the SFR and provide a way to exclude galaxies dominated by an AGN.Comment: Accepted for publication in Ap
A More Fundamental Plane
We combine strong-lensing masses with SDSS stellar velocity dispersions and
HST-ACS effective (half-light) radii for 36 lens galaxies from the Sloan Lens
ACS (SLACS) Survey to study the mass dependence of mass-dynamical structure in
early-type galaxies. We find that over a 180--390 km/s range in velocity
dispersion, structure is independent of lensing mass to within 5%. This result
suggests a systematic variation in the total (i.e., luminous plus dark matter)
mass-to-light ratio as the origin of the tilt of the fundamental plane (FP)
scaling relationship between galaxy size, velocity dispersion, and surface
brightness. We construct the FP of the lens sample, which we find to be
consistent with the FP of the parent SDSS early-type galaxy population, and
present the first observational correlation between mass-to-light ratio and
residuals about the FP. Finally, we re-formulate the FP in terms of surface
mass density rather than surface brightness. By removing the complexities of
stellar-population effects, this mass-plane formulation will facilitate
comparison to numerical simulations and possible use as a cosmological distance
indicator.Comment: 4+epsilon pages, 1 figure, emulateapj. Revised version accepted for
publication in the ApJ Letter
Grazing Animal Production Systems and Grazing Land Characteristics in a Semi-Arid Region of Greece
Rough grazing in Greece cover about 40% of the total land area, is publicly owned and managed extensively (Hadjigeorgiou et al., 2002). The Prefecture of Larisa is in the centre of Greece, and has 212,000 ha of rough grazing land, with a variable topography ranging from sea level up to 3,000 m a.s.l. This area is utilized by a total population of 135,000 LU (mainly sheep, goats and some suckler cows), which consumes annually an appreciable fraction of their total nutrient requirements from rough grazing
The Sloan-Lens ACS Survey II: stellar populations and internal structure of early-type lens galaxies
We derive Fundamental Plane parameters of 15 early-type lens galaxies
identified by the Sloan Lens ACS (SLACS) Survey. The size of the sample allows
us to investigate for the first time the distribution of lens galaxies in the
FP space. After correcting for evolution, we find that lens galaxies occupy a
subset of the local FP. The edge-on projection (approximately M vs M/L) is
indistinguishable from that of normal early-type galaxies. However -- within
the fundamental plane -- the lens galaxies appear to concentrate at the edge of
the region populated by normal early-type galaxies. We show that this is a
result of our selection procedure (approximately velocity dispersion
sigma>240km/s). We conclude that SLACS lenses are a fair sample of high
velocity dispersion early-type galaxies. By comparing the central stellar
velocity dispersion that of the best fit lens model, we find
== =1.01+-0.02 with 0.065 rms scatter. We conclude that
within the Einstein radii the SLACS lenses are very well approximated by
isothermal ellipsoids, requiring a fine tuning of the stellar and dark matter
distribution (bulge-halo ``conspiracy''). Interpreting the offset from the
local FP in terms of evolution of the stellar mass-to-light ratio, we find for
the SLACS lenses d log M/L_B/dz=-0.69+-0.08 (rms 0.11) consistent with the rate
found for field early-type galaxies and with a scenario where most of the stars
were formed at high redshift (>2) with secondary episodes of star formation
providing less than ~10% of the stellar mass below z=1. We discuss star
formation history and structural homogeneity in the context of formation
mechanisms such as collisionless (``dry'') mergers. [Abridged]Comment: 2006, ApJ, 604, 622; 13 pages, 7 figures, 2 tables. Replaced Table 2,
since the previous version was incorrectly sorted. Updated references. No
changes in plots or content. More info available at SLACS website
www.slacs.or
Two-Channel Kondo Physics from Tunnelling Impurities with Triangular Symmetry
Tunnelling impurities in metals have been known for some time to have the
potential for exhibiting Kondo-like physics. However previous models based on
an impurity hopping between two equivalent positions have run into trouble due
to the existence of relevant operators that drive the system away from the
non-Fermi-liquid Kondo fixed point. In the case of an impurity hopping among
positions with higher symmetry, such as triangular symmetry, it is shown here
that the non-Fermi-liquid behavior at low temperatures can be generic. Using
various bosonization techniques, the fixed point is shown to be {\em stable}.
However, unlike the conventional two-channel Kondo (2CK) model, it has {\em
four} leading irrelevant operators, implying that while the form of the
singular temperature dependence of physical quantities is similar to the 2CK
model, there will not be simple universal amplitude ratios. The phase diagram
of this system is analyzed and a critical manifold is found to separate the
non-Fermi-liquid from a conventional Fermi liquid fixed point. Generalization
to higher symmetries, such as cubic, and the possibility of physical
realizations with dynamic Jahn-Teller impurities is discussed.Comment: 20 pages, 4 figures, RevTex format, submitted to Phys. Rev.
``X-Ray Edge'' Singularities in Nanotubes and Quantum Wires with Multiple Subbands
Band theory predicts an inverse square root van Hove singularity in the
tunneling density of states at the minimum energy of an unoccupied subband in a
one-dimensional quantum wire. With interactions, an orthogonality catastrophe
analogous to the x-ray edge effect for core levels in a metal strongly reduces
this singularity by a power B of the energy above threshold, with B
approximately 0.3 for typical carbon nanotubes. Despite the anomalous tunneling
characteristic, good quasiparticles corresponding to the unoccupied subband
states do exist.Comment: 4 page
Solution of two channel spin-flavor Kondo model
We investigate a model where an impurity couples to both the spin and the
flavor currents of the two channel conduction electrons. This model can be used
as a prototype model of a magnetic impurity tunneling between two sites in a
metal and of some heavy fermion systems where the ground state of the impurity
has a fourfold degeneracy. The system is shown to flow to a doubly degenerate
non fermi-liquid(NFL) fixed point; the thermodynamic quantities show NFL
behaviors, but the transport quantities show fermi liquid (FL) behaviors . A
spin-flavor coupling double tensor term is shown to drive the system to one of
the two singlet FL fixed points. The relation with SU(4) Coqblin-Schrieffer
model is studied. The implications on the possible experiments are given.Comment: 11 pages, REVTEX, no figures. To appear in Phys. Rev. B (Rapid Comm.)
July 1, 199
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