2,313 research outputs found
Possible evidence for an inverted temperature-density relation in the intergalactic medium from the flux distribution of the Lyman-alpha forest
We compare the improved measurement of the Lya forest flux probability
distribution at 1.7<z<3.2 presented by Kim et al. (2007) to a large set of
hydrodynamical simulations of the Lya forest with different cosmological
parameters and thermal histories. The simulations are in good agreement with
the observational data if the temperature-density relation for the low density
intergalactic medium (IGM), T=T_0 Delta^{gamma-1}, is either close to
isothermal or inverted (gamma<1). Our results suggest that the voids in the IGM
may be significantly hotter and the thermal state of the low density IGM may be
substantially more complex than is usually assumed at these redshifts. We
discuss radiative transfer effects which alter the spectral shape of ionising
radiation during the epoch of HeII reionisation as a possible physical
mechanism for achieving an inverted temperature-density relation at z~3.Comment: 16 pages, 6 figures, accepted for publication in MNRAS following
minor revision. The accepted version includes an expanded discussion of the
flux power spectru
Probing 3-D matter distribution at z~2 with QSO multiple lines of sight
We investigate the 3-D matter distribution at z~2 with high resolution (R ~
40000) spectra of QSO pairs and groups obtained with the UVES spectrograph at
ESO VLT. Our sample is unique for the number density of objects and the variety
of separations, between 0.5 and 7 proper Mpc. We compute the real space
cross-correlation function of the Lyman-alpha forest transmitted fluxes. There
is a significant clustering signal up to ~2 proper Mpc, which is still present
when absorption lines with high column density (log N > 13.8) are excluded.Comment: Poster paper presented at the IAU Colloquium #199 on "Probing
Galaxies through Quasar Absorption Lines" held in Shanghai, China from March
14th to 18th, 200
Tomography of the intergalactic medium with Ly-alpha forests in close QSO pairs
We study the three-dimensional distribution of non virialised matter at z~2
using high resolution spectra of QSO pairs and simulated spectra drawn from
cosmological hydrodynamical simulations. We have collected the largest sample
of QSO pairs ever observed with UVES at the ESO-VLT, with angular separations
between ~1 and 14 arcmin. The observed correlation functions of the transmitted
flux in the HI Lyman alpha forest along and transverse to the lines of sight
are in good agreement implying that the distortions in redshift space due to
peculiar velocities are small. The clustering signal is significant up to
velocity separations of ~200 km/s, or about 3 h^{-1} comoving Mpc. The regions
at lower overdensity (rho/ < 6.5) are still clustered but on smaller
scales (Delta v < 100 km/s). The observed and simulated correlation functions
are compatible at the 3 sigma level. A better concordance is obtained when only
the low overdensity regions are selected for the analysis or when the effective
optical depth of the simulated spectra is increased artificially, suggesting a
deficiency of strong lines in the simulated spectra. We found that also a lower
value of the power-law index of the temperature-density relation for the Lyman
alpha forest gas improves the agreement between observed and simulated results.
If confirmed, this would be consistent with other observations favouring a late
HeII reionization epoch (at z~3). We remark the detection of a significant
clustering signal in the cross correlation coefficient at a transverse velocity
separation Delta v_{\perp} ~500 km/s whose origin needs further investigation.Comment: Accepted for publication in MNRAS, revised version matching the
accepted on
Studying the Warm Hot Intergalactic Medium in emission: a reprise
The Warm-Hot Intergalactic Medium (WHIM) is believed to host a significant
fraction of the ``missing baryons'' in the nearby Universe. Its signature has
been detected in the X-ray absorption spectra of distant quasars. However, its
detection in emission, that would allow us to study the WHIM in a systematic
way, is still lacking. Motivated by the possibility to perform these studies
with next generation integral field spectrometers, and thanks to the
availability of a large suite of state-of-the-art hydrodynamic simulations --
the CAMELS suite -- we study here in detail the emission properties of the WHIM
and the possibility to infer its physical properties with upcoming X-ray
missions like Athena. We focused on the two most prominent WHIM emission lines,
the OVII triplet and the OVIII singlet, and build line surface brightness maps
in a lightcone, mimicking a data cube generated through integral field
spectroscopy. We confirm that detectable WHIM emission, even with next
generation instruments, is largely associated to galaxy-size dark matter halos
and that the WHIM properties evolve little from to now. Some
characteristics of the WHIM, like the line number counts as a function of their
brightness, depend on the specific hydrodynamic simulation used, while others,
like the WHIM clustering properties, are robust to this aspect. The large
number of simulations available in the CAMELS datasets allows us to assess the
sensitivity of the WHIM properties to the background cosmology and to the
energy feedback mechanisms regulated by AGN and stellar activity. [ABRIDGED]Comment: 23 pages, 17 figures, 3 table
Studying the WHIM with Gamma Ray Bursts
We assess the possibility to detect and characterize the physical state of
the missing baryons at low redshift by analyzing the X-ray absorption spectra
of the Gamma Ray Burst [GRB] afterglows, measured by a micro calorimeters-based
detector with 3 eV resolution and 1000 cm2 effective area and capable of fast
re-pointing, similar to that on board of the recently proposed X-ray satellites
EDGE and XENIA. For this purpose we have analyzed mock absorption spectra
extracted from different hydrodynamical simulations used to model the
properties of the Warm Hot Intergalactic Medium [WHIM]. These models predict
the correct abundance of OVI absorption lines observed in UV and satisfy
current X-ray constraints. According to these models space missions like EDGE
and XENIA should be able to detect about 60 WHIM absorbers per year through the
OVII line. About 45 % of these have at least two more detectable lines in
addition to OVII that can be used to determine the density and the temperature
of the gas. Systematic errors in the estimates of the gas density and
temperature can be corrected for in a robust, largely model-independent
fashion. The analysis of the GRB absorption spectra collected in three years
would also allow to measure the cosmic mass density of the WHIM with about 15 %
accuracy, although this estimate depends on the WHIM model. Our results suggest
that GRBs represent a valid, if not preferable, alternative to Active Galactic
Nuclei to study the WHIM in absorption. The analysis of the absorption spectra
nicely complements the study of the WHIM in emission that the spectrometer
proposed for EDGE and XENIA would be able to carry out thanks to its high
sensitivity and large field of view.Comment: 16 pages, 16 figures, accepted for publication by Ap
An improved measurement of the flux distribution of the Ly\u3b1 forest in QSO absorption spectra: the effect of continuum fitting, metal contamination and noise properties
We have performed an extensive Voigt profile analysis of the neutral hydrogen (HI) and metal absorption present in a sample of 18 high resolution, high signal-to-noise QSO spectra observed with VLT/UVES. We use this analysis to separate the metal contribution from the HI absorption and present an improved measurement of the flux probability distribution function (PDF) due to HI absorption alone at = 2.07, 2.52, and 2.94. The flux PDF is sensitive to the continuum fit in the normalised flux range 0.8 < F < 1.0 and to metal absorption at 0.2 < F < 0.8. Our new measurements of the flux PDF due to HI absorption alone are systematically lower at 0.2 < F < 0.8 by up to 30% compared to the widely used measurement of McDonald et al. (2000), based on a significantly smaller sample of Keck/HIRES data. This discrepancy is probably due to a combination of our improved removal of the metal absorption and cosmic variance, since variations in the flux PDF between different lines-of-sight are large. The HI effective optical depth at 1.7 < z < 4 is best fit with a single power law, (0.0023 +-0.0007) (1+z)^(3.65 +- 0.21), in good agreement with previous measurements from comparable data. As also found previously, the effect of noise on the flux distribution is not significant in high resolution, high signal-to-noise data
Neutrino Halos in Clusters of Galaxies and their Weak Lensing Signature
We study whether non-linear gravitational effects of relic neutrinos on the
development of clustering and large-scale structure may be observable by weak
gravitational lensing. We compute the density profile of relic massive
neutrinos in a spherical model of a cluster of galaxies, for several neutrino
mass schemes and cluster masses. Relic neutrinos add a small perturbation to
the mass profile, making it more extended in the outer parts. In principle,
this non-linear neutrino perturbation is detectable in an all-sky weak lensing
survey such as EUCLID by averaging the shear profile of a large fraction of the
visible massive clusters in the universe, or from its signature in the general
weak lensing power spectrum or its cross-spectrum with galaxies. However,
correctly modeling the distribution of mass in baryons and cold dark matter and
suppressing any systematic errors to the accuracy required for detecting this
neutrino perturbation is severely challenging.Comment: 13 pages, 11 figures. Submitted to JCA
TTF-Podants and TTF-Calixarene assemblies : original striuctural solutions towards redoxresponsive ligands
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