7,025 research outputs found
The infrared luminosity function of galaxies at redshifts z=1 and z~2 in the GOODS fields
We present the rest-frame 8 micron luminosity function (LF) at redshifts z=1
and ~2, computed from Spitzer 24 micron-selected galaxies in the GOODS fields
over an area of 291 sq. arcmin. Using classification criteria based on X-ray
data and IRAC colours, we identify the AGN in our sample. The rest-frame 8
micron LF for star-forming galaxies at redshifts z=1 and ~2 have the same shape
as at z~0, but with a strong positive luminosity evolution. The number density
of star-forming galaxies with log_{10}(nu L_nu(8 micron))>11 increases by a
factor >250 from redshift z~0 to 1, and is basically the same at z=1 and ~2.
The resulting rest-frame 8 micron luminosity densities associated with star
formation at z=1 and ~2 are more than four and two times larger than at z~0,
respectively. We also compute the total rest-frame 8 micron LF for star-forming
galaxies and AGN at z~2 and show that AGN dominate its bright end, which is
well-described by a power-law. Using a new calibration based on Spitzer
star-forming galaxies at 0<z<0.6 and validated at higher redshifts through
stacking analysis, we compute the bolometric infrared (IR) LF for star-forming
galaxies at z=1 and ~2. We find that the respective bolometric IR luminosity
densities are (1.2+/-0.2) x 10^9 and (6.6^{+1.2}_{-1.0}) x 10^8 L_sun Mpc^{-3},
in agreement with previous studies within the error bars. At z~2, around 90% of
the IR luminosity density associated with star formation is produced by
luminous and ultraluminous IR galaxies (LIRG and ULIRG), with the two
populations contributing in roughly similar amounts. Finally, we discuss the
consistency of our findings with other existing observational results on galaxy
evolution.Comment: Accepted for publication in the ApJ. 33 pages, 15 figures. Uses
emulateap
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The TAMORA algorithm: satellite rainfall estimates over West Africa using multi-spectral SEVIRI data
A multi-spectral rainfall estimation algorithm has been developed for the Sahel region of West Africa with the purpose of producing accumulated rainfall estimates for drought monitoring and food security. Radar data were used to calibrate multi-channel SEVIRI data from MSG, and a probability of rainfall at several different rain-rates was established for each combination of SEVIRI radiances. Radar calibrations from both Europe (the SatPrecip algorithm) and Niger (TAMORA algorithm) were used. 10 day estimates were accumulated from SatPrecip and TAMORA and compared with kriged gauge data and TAMSAT satellite rainfall estimates over West Africa. SatPrecip was found to produce large overestimates for the region, probably because of its non-local calibration. TAMORA was negatively biased for areas of West Africa with relatively high rainfall, but its skill was comparable to TAMSAT for the low-rainfall region climatologically similar to its calibration area around Niamey. These results confirm the high importance of local calibration for satellite-derived rainfall estimates. As TAMORA shows no improvement in skill over TAMSAT for dekadal estimates, the extra cloud-microphysical information provided by multi-spectral data may not be useful in determining rainfall accumulations at a ten day timescale. Work is ongoing to determine whether it shows improved accuracy at shorter timescales
Mid-Infrared Emission from E+A Galaxies in the Coma Cluster
We have used ISO to observe at 12m seven E+A galaxies plus an additional
emission line galaxy, all in the Coma cluster. E+A galaxies lacking narrow
emission lines have 2.2m to 12m flux density ratios or limits similar
to old stellar populations (typical of early-type galaxies). Only galaxies with
emission lines have enhanced 12m flux density. Excess 12m emission is
therefore correlated with the presence of on-going star formation or an active
galactic nucleus (AGN).
By comparing the current star formation rates with previous rates estimated
from the Balmer absorption features, we divide the galaxies into two groups:
those for which star formation has declined significantly following a dramatic
peak 1 Gyr ago; and those with a significant level of ongoing star
formation or/and an AGN. There is no strong difference in the spatial
distribution on the sky between these two groups. However, the first group has
systemic velocities above the mean cluster value and the second group below
that value. This suggests that the two groups differ kinematically.
Based on surveys of the Coma cluster in the radio, the IRAS sources, and
galaxies detected in H emission, we sum the far infrared luminosity
function of galaxies in the cluster. We find that star formation in late type
galaxies is probably the dominant component of the Coma cluster far infrared
luminosity. The presence of significant emission from intracluster dust is not
yet firmly established. The member galaxies also account for most of the far
infrared output from nearby rich clusters in general.Comment: AAS Latex, accepted for publication in Ap
Measuring the Angular Correlation Function for Faint Galaxies in High Galactic Latitude Fields
A photometric survey of faint galaxies in three high Galactic latitude fields
(each ) with sub-arcsecond seeing is used to study the
clustering properties of the faint galaxy population. Multi-color photometry of
the galaxies has been obtained to magnitude limits of , and
. Angular correlation analysis is applied to magnitude-limited and
color-selected samples of galaxies from the three fields for angular
separations ranging from . General agreement is obtained with other
recent studies which show that the amplitude of the angular correlation
function, , is smoothly decreasing as a function of limiting
magnitude. The observed decline of rules out the viability of
``maximal merger'' galaxy evolution models. Using redshift distributions
extrapolated to faint magnitude limits, models of galaxy clustering evolution
are calculated and compared to the observed I-band . Faint
galaxies are determined to have correlation lengths and clustering evolution
parameters of either and ;
and ; or and
, assuming and with . The latter case is for clustering fixed in co-moving
coordinates and is probably unrealistic since most local galaxies are observed
to be more strongly clustered. No significant variations in the clustering
amplitude as a function of color are detected, for all the color-selected
galaxy samples considered. (Abridged)Comment: LaTeX (aaspp4.sty), 54 pages including 15 postscript figures; 3
additional uuencoded, gzipped postscript files (~300 kb each) of Figs. 1, 2
and 3 available at ftp://ftp.astro.ubc.ca/pub/woods ; To be published in the
Nov. 20, 1997 issue of The Astrophysical Journa
Molecular cloning of a human homologue of Drosophila heterochromatin protein HP1 using anti-centromere autoantibodies with anti-chromo specificity
We have identified a novel autoantibody specificity in scleroderma that we term anti-chromo. These antibodies recognize several chromosomal antigens with apparent molecular mass of between 23 and 25 kDa, as determined by immunoblots. Anti-chromo autoantibodies occur in 10-15% of sera from patients with anti-centromere antibodies (ACA). We used anti-chromo antibodies to screen a human expression library and obtained cDNA clones encoding a 25 kDa chromosomal autoantigen. DNA sequence analysis reveals this protein to be a human homologue of HP1, a heterochromatin protein of Drosophila melanogaster. We designate our cloned protein HP1Hs alpha. Epitope mapping experiments using both human and Drosophila HP1 reveal that anti-chromo antibodies target a region at the amino terminus of the protein. This region contains a conserved motif, the chromo domain (or HP1/Pc box), first recognized by comparison of Drosophila HP1 with the Polycomb gene product. Both proteins are thought to play a role in creating chromatin structures in which gene expression is suppressed. Anti-chromo thus defines a novel type of autoantibody that recognizes a conserved structural motif found on a number of chromosomal proteins
VO: A Strongly Correlated Metal Close to a Mott- Hubbard Transition
Here we present experimental and computational evidences to support that
rock-salt cubic VO is a strongly correlated metal with Non-Fermi-Liquid
thermodynamics and an unusually strong spin-lattice coupling. An unexpected
change of sign of metallic thermopower with composition is tentatively ascribed
to the presence of a pseudogap in the density of states. These properties are
discussed as signatures of the proximity to a magnetic quantum phase
transition. The results are summarized in a new electronic phase diagram for
the 3d monoxides, which resembles that of other strongly correlated systems.
The structural and electronic simplicity of 3d monoxides make them ideal
candidates to progress in the understanding of highly correlated electron
systems.Comment: Submitted to Phys. Rev.
Non-standard connections in classical mechanics
In the jet-bundle description of first-order classical field theories there
are some elements, such as the lagrangian energy and the construction of the
hamiltonian formalism, which require the prior choice of a connection. Bearing
these facts in mind, we analyze the situation in the jet-bundle description of
time-dependent classical mechanics. So we prove that this connection-dependence
also occurs in this case, although it is usually hidden by the use of the
``natural'' connection given by the trivial bundle structure of the phase
spaces in consideration. However, we also prove that this dependence is
dynamically irrelevant, except where the dynamical variation of the energy is
concerned. In addition, the relationship between first integrals and
connections is shown for a large enough class of lagrangians.Comment: 17 pages, Latex fil
The Influence of the effect of solute on the thermodynamic driving force on grain refinement of Al alloys
Grain refinement is known to be strongly affected by the solute in cast alloys. Addition of some solute can reduce grain size considerably while others have a limited effect. This is usually attributed to the constitutional supercooling which is quantified by the growth restriction factor, Q. However, one factor that has not been considered is whether different solutes have differing effects on the thermodynamic driving force for solidification. This paper reveals that addition of solute reduces the driving force for solidification for a given undercooling, and that for a particular Q value, it is reduced more substantially when adding eutectic-forming solutes than peritectic-forming elements. Therefore, compared with the eutectic-forming solutes, addition of peritectic-forming solutes into Al alloys not only possesses a higher initial nucleation rate resulted from the larger thermodynamic driving force for solidification, but also promotes nucleation within the constitutionally supercooled zone during growth. As subsequent nucleation can occur at smaller constitutional supercoolings for peritectic-forming elements, a smaller grain size is thus produced. The very small constitutional supercooling required to trigger subsequent nucleation in alloys containing Ti is considered as a major contributor to its extraordinary grain refining efficiency in cast Al alloys even without the deliberate addition of inoculants.The Australian Research Council (ARC DP10955737)
High resolution mid-infrared spectroscopy of ultraluminous infrared galaxies
(Abridged) We present R~600, 10-37um spectra of 53 ULIRGs at z<0.32, taken
using the IRS on board Spitzer. All of the spectra show fine structure emission
lines of Ne, O, S, Si and Ar, as well as molecular Hydrogen lines. Some ULIRGs
also show emission lines of Cl, Fe, P, and atomic Hydrogen, and/or absorption
features from C_2H_2, HCN, and OH. We employ diagnostics based on the
fine-structure lines, as well as the EWs and luminosities of PAH features and
the strength of the 9.7um silicate absorption feature (S_sil), to explore the
power source behind the infrared emission in ULIRGs. We show that the IR
emission from the majority of ULIRGs is powered mostly by star formation, with
only ~20% of ULIRGs hosting an AGN with a comparable or greater IR luminosity
than the starburst. The detection of the 14.32um [NeV] line in just under half
the sample however implies that an AGN contributes significantly to the mid-IR
flux in ~42% of ULIRGs. The emission line ratios, luminosities and PAH EWs are
consistent with the starbursts and AGN in ULIRGs being more extincted, and for
the starbursts more compact, versions of those in lower luminosity systems. The
excitations and electron densities in the NLRs of ULIRGs appear comparable to
those of lower luminosity starbursts, though there is evidence that the NLR gas
in ULIRGs is more dense. We show that the combined luminosity of the 12.81um
[NeII] and 15.56um [NeIII] lines correlates with both IR luminosity and the
luminosity of the 6.2 micron and 11.2 micron PAH features in ULIRGs, and use
this to derive a calibration between PAH luminosity and star formation rate.
Finally, we show that ULIRGs with 0.8 < S_sil < 2.4 are likely to be powered
mainly by star formation, but that ULIRGs with S_sil < 0.8, and possibly those
with S_sil > 2.4, contain an IR-luminous AGN.Comment: 62 pages in preprint format, 4 tables, 23 figures. ApJ accepte
Fibre bundle formulation of relativistic quantum mechanics. I. Time-dependent approach
We propose a new fibre bundle formulation of the mathematical base of
relativistic quantum mechanics. At the present stage the bundle form of the
theory is equivalent to its conventional one, but it admits new types of
generalizations in different directions.
In the present first part of our investigation we consider the time-dependent
or Hamiltonian approach to bundle description of relativistic quantum
mechanics. In it the wavefunctions are replaced by (state) liftings of paths or
sections along paths of a suitably chosen vector bundle over space-time whose
(standard) fibre is the space of the wavefunctions. Now the quantum evolution
is described as a linear transportation (by means of the evolution transport
along paths in the space-time) of the state liftings/sections in the (total)
bundle space. The equations of these transportations turn to be the bundle
versions of the corresponding relativistic wave equations.Comment: 16 standard LaTeX pages. The packages AMS-LaTeX and amsfonts are
required. The paper continuous the application of fibre bundle formalism to
quantum physics began in the series of works quant-ph/9803083,
quant-ph/9803084, quant-ph/9804062, quant-ph/9806046, quant-ph/9901039,
quant-ph/9902068, and quant-ph/0004041. For related papers, view
http://theo.inrne.bas.bg/~bozho
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