38 research outputs found
The ISO 170um Luminosity Function of Galaxies
We constructed a local luminosity function (LF) of galaxies using a
flux-limited sample (S_170 > 0.195Jy) of 55 galaxies at z < 0.3 taken from the
ISO FIRBACK survey at 170um. The overall shape of the 170-um LF is found to be
different from that of the total 60-um LF (Takeuchi et al. 2003): the bright
end of the LF declines more steeply than that of the 60-um LF. This behavior is
quantitatively similar to the LF of the cool subsample of the IRAS PSCz
galaxies. We also estimated the strength of the evolution of the LF by assuming
the pure luminosity evolution (PLE): L(z) \propto (1+z)^Q. We obtained
Q=5.0^{+2.5}_{-0.5} which is similar to the value obtained by recent Spitzer
observations, in spite of the limited sample size. Then, integrating over the
170-um LF, we obtained the local luminosity density at 170um, \rho_L(170um). A
direct integration of the LF gives \rho_L(170um) = 1.1 \times 10^8 h Lsun
Mpc^{-3}, whilst if we assume a strong PLE with Q=5, the value is 5.2 \times
10^7 h Lsun Mpc^{-3}. This is a considerable contribution to the local FIR
luminosity density. By summing up with other available infrared data, we
obtained the total dust luminosity density in the Local Universe,
\rho_L(dust)=1.1 \times 10^8 h Lsun Mpc^{-3}. Using this value, we estimated
the cosmic star formation rate (SFR) density hidden by dust in the Local
Universe. We obtained \rho_SFR(dust) \simeq 1.1-1.2 h \times 10^{-2} Msun
yr^{-1} Mpc^{-3}$, which means that 58.5% of the star formation is obscured by
dust in the Local Universe.Comment: A&A in pres
The evolution of clusters in the CLEF cosmological simulation: X-ray structural and scaling properties
We present results from a study of the X-ray cluster population that forms
within the CLEF cosmological hydrodynamics simulation, a large N-body/SPH
simulation of the Lambda CDM cosmology with radiative cooling, star formation
and feedback. The scaled projected temperature and entropy profiles at z=0 are
in good agreement with recent high-quality observations of cool core clusters,
suggesting that the simulation grossly follows the processes that structure the
intracluster medium (ICM) in these objects. Cool cores are a ubiquitous
phenomenon in the simulation at low and high redshift, regardless of a
cluster's dynamical state. This is at odds with the observations and so
suggests there is still a heating mechanism missing from the simulation. Using
a simple, observable measure of the concentration of the ICM, which correlates
with the apparent mass deposition rate in the cluster core, we find a large
dispersion within regular clusters at low redshift, but this diminishes at
higher redshift, where strong "cooling-flow" systems are absent in our
simulation. Consequently, our results predict that the normalisation and
scatter of the luminosity-temperature relation should decrease with redshift;
if such behaviour turns out to be a correct representation of X-ray cluster
evolution, it will have significant consequences for the number of clusters
found at high redshift in X-ray flux-limited surveys.Comment: 20 pages, 21 figures, MNRAS, accepted with minor modifications to
original manuscrip
Cosmological Magnetogenesis driven by Radiation Pressure
The origin of large scale cosmological magnetic fields remains a mystery,
despite the continuous efforts devoted to that problem. We present a new model
of magnetic field generation, based on local charge separation provided by an
anisotropic and inhomogeneous radiation pressure. In the cosmological context,
the processes we explore take place at the epoch of the reionisation of the
Universe. Under simple assumptions, we obtain results (i) in terms of the order
of magnitude of the field generated at large scales and (ii) in terms of its
power spectrum. The amplitudes obtained (B ~ 8.10^(-6) micro-Gauss) are
considerably higher than those obtained in usual magnetogenesis models and
provide suitable seeds for amplification by adiabatic collapse and/or dynamo
during structure formation.Comment: 9 pages, 2 figure
Dusty Infrared Galaxies: Sources of the Cosmic Infrared Background
The discovery of the Cosmic Infrared Background (CIB) in 1996, together with
recent cosmological surveys from the mid-infrared to the millimeter have
revolutionized our view of star formation at high redshifts. It has become
clear, in the last decade, that a population of galaxies that radiate most of
their power in the far-infrared (the so-called ``infrared galaxies'')
contributes an important part of the whole galaxy build-up in the Universe.
Since 1996, detailed (and often painful) investigations of the high-redshift
infrared galaxies have resulted in the spectacular progress covered in this
review. We outline the nature of the sources of the CIB including their
star-formation rate, stellar and total mass, morphology, metallicity and
clustering properties. We discuss their contribution to the stellar content of
the Universe and their origin in the framework of the hierarchical growth of
structures. We finally discuss open questions for a scenario of their evolution
up to the present-day galaxies.Comment: To appear in Annual Reviews of Astronomy and Astrophysics, 2005, vol
43. 31 pages, 12 color figure