94 research outputs found
The baryon mass function for galaxy clusters
Context: The evolution of the cluster abundance with redshift is known to be
a powerful cosmological constraint when applied to X-ray clusters. Recently,
the evolution of the baryon mass function has been proposed as a new variant
that is free of the uncertainties present in the temperature-mass relation. A
flat model with Omega_matter ~ 0.3 was shown to be preferred in the case of a
standard cold dark matter scenario.
Aims: We compared the high redshift predictions of the baryon mass in
clusters with data for a more general class of spectra with a varying shape
factor Gamma without any restriction to the standard cold dark matter scenario
in models normalized to reproduce the local baryon mass function.
Methods: Using various halo mass functions existing in the literature we
evaluated the corresponding baryon mass functions for the case of the
non-standard power spectra mentioned previously.
Results: We found that models with Omega_matter ~ 1 and Gamma ~ 0.12
reproduce high redshift cluster data just as well as the concordance model
does.
Conclusions: Finally, we conclude that the baryon mass function evolution
alone does not efficiently discriminate between the more general family of flat
cosmological models with non-standard power spectra.Comment: Typos corrected. Replaced to match published version. 5 pages, 2
figures, aa.cl
Measuring cosmic magnetic fields by rotation measure-galaxy cross-correlations in cosmological simulations
Using cosmological MHD simulations of the magnetic field in galaxy clusters
and filaments we evaluate the possibility to infer the magnetic field strength
in filaments by measuring cross-correlation functions between Faraday Rotation
Measures (RM) and the galaxy density field. We also test the reliability of
recent estimates considering the problem of data quality and Galactic
foreground (GF) removal in current datasets. Besides the two self-consistent
simulations of cosmological magnetic fields based on primordial seed fields and
galactic outflows analyzed here, we also explore a larger range of models
scaling up the resulting magnetic fields of one of the simulations. We find
that, if an unnormalized estimator for the cross-correlation functions and a GF
removal procedure is used, the detectability of the cosmological signal is only
possible for future instruments (e.g. SKA and ASKAP). However, mapping of the
observed RM signal to the underlying magnetization of the Universe (both in
space and time) is an extremely challenging task which is limited by the
ambiguities of our model parameters, as well as to the weak response of the RM
signal in low density environments. Therefore, we conclude that current data
cannot constrain the amplitude and distribution of magnetic fields within the
large scale structure and a detailed theoretical understanding of the build up
and distribution of magnetic fields within the Universe will be needed for the
interpretation of future observations.Comment: 11 pages, 11 figures, comparation between RM data and simulations in
fig. 8, submited to MNRAS
The host galaxies of long-duration GRBs in a cosmological hierarchical scenario
We developed a Monte Carlo code to generate long-duration gamma ray burst
(LGRB) events within cosmological hydrodynamical simulations consistent with
the concordance model. As structure is assembled, LGRBs are generated in the
substructure that formed galaxies today. We adopted the collapsar model so that
LGRBs are produced by single, massive stars at the final stage of their
evolution. We found that the observed properties of the LGRB host galaxies
(HGs) are reproduced if LGRBs are also required to be generated by low
metallicity stars. The low metallicity condition imposed on the progenitor
stars of LGRBs selects a sample of HGs with mean gas abundances of 12 + log O/H
\~ 8.6. For z<1 the simulated HGs of low metallicity LGRB progenitors tend to
be faint, slow rotators with high star formation efficiency, compared with the
general galaxy population, in agreement with observations. At higher redshift,
our results suggest that larger systems with high star formation activity could
also contribute to the generation of LGRBs from low metallicity progenitors
since the fraction of low metallicity gas available for star formation
increases for all systems with look-back time. Under the hypothesis of our LGRB
model, our results support the claim that LGRBs could be unbiased tracers of
star formation at high redshifts.Comment: Final revised version with minor changes. 9 pages, 9 figures,
mn2e.cls. To appear in MNRA
An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way's circumgalactic medium and the Local Group
To characterize the absorption properties of this circumgalactic medium (CGM)
and its relation to the LG we present the so-far largest survey of metal
absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet
(UV) spectra of extragalactic background sources. The UV data are obtained with
the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST)
and are supplemented by 21 cm radio observations of neutral hydrogen. Along 270
sightlines we measure metal absorption in the lines of SiII, SiIII, CII, and
CIV and associated HI 21 cm emission in HVCs in the velocity range
|v_LSR|=100-500 km s^-1. With this unprecedented large HVC sample we were able
to improve the statistics on HVC covering fractions, ionization conditions,
small-scale structure, CGM mass, and inflow rate. For the first time, we
determine robustly the angular two point correlation function of the
high-velocity absorbers, systematically analyze antipodal sightlines on the
celestial sphere, and compare the absorption characteristics with that of
Damped Lyman alpha absorbers (DLAs) and constrained cosmological simulations of
the LG. Our study demonstrates that the Milky Way CGM contains sufficient
gaseous material to maintain the Galactic star-formation rate at its current
level. We show that the CGM is composed of discrete gaseous structures that
exhibit a large-scale kinematics together with small-scale variations in
physical conditions. The Magellanic Stream clearly dominates both the cross
section and mass flow of high-velocity gas in the Milky Way's CGM. The possible
presence of high-velocity LG gas underlines the important role of the local
cosmological environment in the large-scale gas-circulation processes in and
around the Milky Way (abridged).Comment: 37 pages, 25 figures, 8 tables, accepted for publication in A&
Radio continuum observations of new radio halos and relics from the NVSS and WENSS surveys
Radio halos and relics are diffuse radio sources found in galaxy clusters
showing significant substructure at X-ray wavelengths. These sources provide
important information about non-thermal processes taking place in the ICM.
Until now only a few dozen relics and halos are known, while models predict
that a much larger number of these sources exist. In this paper we present the
results of an extensive observing campaign to search for new diffuse radio
sources in galaxy clusters. We discovered 6 new radio relics, including a
probable double relic system, and 2 radio halos. In addition, we confirm the
presence of diffuse radio emission in four galaxy clusters. By constructing a
sample of 35 radio relics we find that relics are mostly found along the major
axis of the X-ray emission from the ICM, while their orientation is
perpendicular to this axis. This is consistent with the scenario that relics
trace merger shock waves. The major and minor axis ratio distribution of the
ICM for clusters with relics is also broader than that of the NORAS-REFLEX
sample. We compared the X-ray luminosity and redshift distributions of clusters
with relics to an X-ray selected sample from the NORAS and REFLEX surveys. We
find tentative evidence for an increase of the cluster's relic fraction with
X-ray luminosity and redshift. [abridged]Comment: 20 pages, 26 figures, accepted for publication in A\&A on July 14,
201
Study of the relationship between the gamma ray bursts and their host galaxies
Gamma ray bursts (GRBs) belong to the most energetic events in the Universe.
Recently, the extragalactic nature of these sources has been confirmed with the
discovery of several host galaxies (HGs) and the measurement of their
redshifts. To explain the origin of GRBs various models have been proposed,
among which the coalescence of compact objects and the "collapsar" scenarios
are the most representative, being the collapsar model one of the most accepted
to explain the long duration GRBs. A natural consequence of this model is that
the GRBs would trace the star formation rate (SFR) of their HGs. In this
contributed paper we present preliminary results of the development of a
Montecarlo-based code for collapsar event formation which is coupled to
chemical-cosmological simulations aiming at studying the properties of HGs in a
hierarchical scenario.Comment: Minor changes after referee report. To appear in the 48th Bulletin of
the Argentine Astronomical Society (BAAA 48, 2005). 4 pages, baaa-eng.st
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