98 research outputs found
Measuring the temperature and profiles of Ly α absorbers
The distribution of the absorption line broadening observed in the Lyα forest carries information about the temperature, T, and widths, λF, of the filaments in the intergalactic medium (IGM), and the background hydrogen photo-ionization rate, ΓHI. In this work, we present and test a new method for inferring T and λF and ΓHI from combining the distribution of the absorption line broadening and the median flux. The method accounts for any underlying degeneracies. We apply our method to mock spectra from the reference model of the EAGLE cosmological simulation, and we demonstrate that we are able to reconstruct the IGM properties
How to constrain warm dark matter with the Lyman forest
The flux power spectrum of the high resolution Lyman- forest data
exhibits suppression at small scales. The origin of this suppression can be due
to long-sought warm dark matter (WDM) or to thermal effects, related to the
largely unknown reionization history of the Universe. Previous works explored a
specific class of reionization histories that exhibit sufficiently strong
thermal supression and leave little room for warm dark matter interpretation.
In this work we choose a different class of reionization histories, fully
compatible with available data on evolution of reionization, but much colder
then the reionization histories used by previous authors in determining the
nature of dark matter, thus leaving the broadest room for the WDM
interpretation of the suppression in the flux power spectrum. We find that WDM
thermal relics with masses below 1.9 keV (95% CL) would produce a suppression
at scales that are larger than observed maximum of the flux power spectrum,
independently of assumptions about thermal effects. This WDM mass is
significantly lower than previously claimed bounds, demonstrating the level of
systematic uncertainty of the Lyman- forest method, due to the previous
modelling. We also discuss how this uncertainty may affect also data at large
scales measured by eBOSS.Comment: 8 pages, 6 figure
Re-design Geography of spaces. Widen the edges
Landscape project always works with nature: something perpetually transforming, expanding and retracting, without any rigid limits; it gives thickness to the edges, and looks at the "uncertainty" as one of the conditions in which the future scenarios can be prefigured. The contemporary territory has been described by features of complexity and uncertainty; a place where edges and internal limits are undefined, dynamic, and porous. Therefore, assuming the way of thinking of a landscape architect, it can be useful to understand and design that kind of places (Corner, 2006). The main characteristic of contemporary city is to be fragmented, that means lack of relations among places, and presence of many "other spaces" (Foucault, 2001): heterotopics, utopian and empty ones. Therefore, this kind of situation has led to disorientation, and it causes deprivation of the landscape. A paradigm shift is required (Ricci, 2012): new ecological continuity and public uses must to be implemented among fragments
No observational constraints from hypothetical collisions of hypothetical dark halo primordial black holes with galactic objects
It was suggested by several authors that hypothetical primordial black holes
(PBHs) may contribute to the dark matter in our Galaxy. There are strong
constraints based on the Hawking evaporation that practically exclude PBHs with
masses m~1e15-1e16g and smaller as significant contributors to the Galactic
dark matter. Similarly, PBHs with masses greater than about 1e26g are
practically excluded by the gravitational lensing observation. The mass range
between 10e16g<m<10e26g is unconstrained. In this paper, we examine possible
observational signatures in the unexplored mass range, investigating
hypothetical collisions of PBHs with main sequence stars, red giants, white
dwarfs, and neutron stars in our Galaxy. This has previously been discussed as
possibly leading to an observable photon eruption due to shock production
during the encounter. We find that such collisions are either too rare to be
observed (if the PBH masses are typically larger than about 1e20g), or produce
too little power to be detected (if the masses are smaller than about 1e20g).Comment: Accepted for publication in The Astrophysical Journa
The intergalactic medium thermal history at redshift z=1.7--3.2 from the Lyman alpha forest: a comparison of measurements using wavelets and the flux distribution
We investigate the thermal history of the intergalactic medium (IGM) in the
redshift interval z=1.7--3.2 by studying the small-scale fluctuations in the
Lyman alpha forest transmitted flux. We apply a wavelet filtering technique to
eighteen high resolution quasar spectra obtained with the Ultraviolet and
Visual Echelle Spectrograph (UVES), and compare these data to synthetic spectra
drawn from a suite of hydrodynamical simulations in which the IGM thermal state
and cosmological parameters are varied. From the wavelet analysis we obtain
estimates of the IGM thermal state that are in good agreement with other
recent, independent wavelet-based measurements. We also perform a reanalysis of
the same data set using the Lyman alpha forest flux probability distribution
function (PDF), which has previously been used to measure the IGM
temperature-density relation. This provides an important consistency test for
measurements of the IGM thermal state, as it enables a direct comparison of the
constraints obtained using these two different methodologies. We find the
constraints obtained from wavelets and the flux PDF are formally consistent
with each other, although in agreement with previous studies, the flux PDF
constraints favour an isothermal or inverted IGM temperature-density relation.
We also perform a joint analysis by combining our wavelet and flux PDF
measurements, constraining the IGM thermal state at z=2.1 to have a temperature
at mean density of T0/[10^3 K]=17.3 +/- 1.9 and a power-law temperature-density
relation exponent gamma=1.1 +/- 0.1 (1 sigma). Our results are consistent with
previous observations that indicate there may be additional sources of heating
in the IGM at z<4.Comment: 15 pages, 14 figures, matches version accepted for publication on
MNRA
Involvement of gut microbiota in schizophrenia and treatment resistance to antipsychotics
The gut microbiota is constituted by more than 40, 000 bacterial species involved in key processes including high order brain functions. Altered composition of gut microbiota has been implicated in psychiatric disorders and in modulating the efficacy and safety of psychotropic medications. In this work we characterized the composition of the gut microbiota in 38 patients with schizophrenia (SCZ) and 20 healthy controls (HC), and tested if SCZ patients with different response to antipsychotics (18 patients with treatment resistant schizophrenia (TRS), and 20 responders (R)) had specific patterns of gut microbiota composition associated with different response to antipsychotics. Moreover, we also tested if patients treated with typical antipsychotics (n=20) presented significant differences when compared to patients treated with atypical antipsychotics (n=31). Our findings showed the presence of distinct composition of gut microbiota in SCZ versus HC, with several bacteria at the different taxonomic levels only present in either one group or the other. Similar findings were observed also depending on treatment response and exposure to diverse classes of antipsychotics. Our results suggest that composition of gut microbiota could constitute a biosignatures of SCZ and TRS
The impact of feedback from galaxy formation on the Lyman-alpha transmitted flux
The forest of Lyman-alpha absorption lines seen in the spectra of distant
quasars has become an important probe of the distribution of matter in the
Universe. We use large, hydrodynamical simulations from the OWLS project to
investigate the effect of feedback from galaxy formation on the probability
distribution function and the power spectrum of the Lyman-alpha transmitted
flux. While metal-line cooling is unimportant, both galactic outflows from
massive galaxies driven by active galactic nuclei and winds from low-mass
galaxies driven by supernovae have a substantial impact on the flux statistics.
At redshift z=2.25, the effects on the flux statistics are of a similar
magnitude as the statistical uncertainties of published data sets. The changes
in the flux statistics are not due to differences in the temperature-density
relation of the photo-ionised gas. Instead, they are caused by changes in the
density distribution and in the fraction of hot, collisionally ionised gas. It
may be possible to disentangle astrophysical and cosmological effects by taking
advantage of the fact that they induce different redshift dependencies. In
particular, the magnitude of the feedback effects appears to decrease rapidly
with increasing redshift. Analyses of Lyman-alpha forest data from surveys that
are currently in process, such as BOSS/SDSS-III and X-Shooter/VLT, must take
galactic winds into account.Comment: 15 pages, 11 figures. MNRAS in pres
- …