1,085 research outputs found
A galaxy overdensity at z=0.401 associated with an X-ray emitting structure of Warm-Hot Intergalactic Medium
We present the results of spectroscopic observations of galaxies associated
with the diffuse X-ray emitting structure discovered by Zappacosta et al.
(2002). After measuring the redshifts of 161 galaxies, we confirm an
overdensity of galaxies with projected dimensions of at least 2 Mpc, determine
its spectroscopic redshift in z=0.401+/-0.002, and show that it is spatially
coincident with the diffuse X-ray emission. This confirms the original claim
that this X-ray emission has an extragalactic nature and is due to the Warm-Hot
Intergalactic Medium (WHIM). We used this value of the redshift to compute the
temperature of the emitting gas. The resulting value depends on the metallicity
that is assumed for the IGM, and is constrained to be between 0.3 and 0.6 keV
for metallicities between 0.05 and 0.3 solar, in good agreement with the
expectations from the WHIM.Comment: 9 pages, A&A, in press, minor language change
Chasing the observational signatures of seed black holes at z > 7: candidate statistics
Supermassive black holes (SMBHs) of 10^9-10^10 Msun were already in place ~13
Gyr ago, at z>6. Super-Eddington growth of low-mass BH seeds (~100 Msun) or
less extreme accretion onto ~10^5 Msun seeds have been recently considered as
the main viable routes to these SMBHs. Here we study the statistics of these
SMBH progenitors at z~6. The growth of low- and high-mass seeds and their host
galaxies are consistently followed using the cosmological data constrained
model GAMETE/QSOdust, which reproduces the observed properties of high-z
quasars, like SDSS J1148+5251. We show that both seed formation channels can be
in action over a similar redshift range, 15 < z < 18 and are found in dark
matter halos with comparable mass, ~5x10^7 Msun. However, as long as the
systems evolve in isolation (i.e. no mergers occur), noticeable differences in
their properties emerge: at z>= 10 galaxies hosting high-mass seeds have
smaller stellar mass and metallicity, the BHs accrete gas at higher rates and
star formation proceeds less efficiently than in low-mass seeds hosts. At z<10
these differences are progressively erased, as the systems experience minor or
major mergers and every trace of the BH origin gets lost.Comment: accepted for publication in MNRA
Constraining the thermal history of the Warm-Hot Intergalactic Medium
We have identified a large-scale structure traced by galaxies at z=0.8,
within the Lockman Hole, by means of multi-object spectroscopic observations.
By using deep XMM images we have investigated the soft X-ray emission from the
Warm-Hot Intergalactic Medium (WHIM) expected to be associated with this
large-scale structure and we set a tight upper limit to its flux in the very
soft 0.2-0.4 keV band. The non-detection requires the WHIM at these redshifts
to be cooler than 0.1 keV. Combined with the WHIM emission detections at lower
redshift, our result indicates that the WHIM temperature is rapidly decreasing
with redshift, as expected in popular cosmological models.Comment: 10 pages, 5 figures, 1 appendix. A&A accepte
Studying the WHIM Content of the Galaxy Large-Scale Structures along the Line of Sight to H 2356-309
We make use of a 500ks Chandra HRC-S/LETG spectrum of the blazar H2356-309,
combined with a lower S/N spectrum of the same target, to search for the
presence of warm-hot absorbing gas associated with two Large-Scale Structures
(LSSs) crossed by this sightline at z=0.062 (the Pisces-Cetus Supercluster,
PCS) and at z=0.128 ("Farther Sculptor Wall", FSW). No statistically
significant (>=3sigma) individual absorption is detected from any of the strong
He- or H-like transitions of C, O and Ne at the redshifts of the structures.
However we are still able to constrain the physical and geometrical parameters
of the associated putative absorbing gas, by performing joint spectral fit of
marginal detections and upper limits of the strongest expected lines with our
self-consistent hybrid ionization WHIM spectral model. At the redshift of the
PCS we identify a warm phase with logT=5.35_-0.13^+0.07 K and log N_H
=19.1+/-0.2 cm^-2 possibly coexisting with a hotter and less significant phase
with logT=6.9^+0.1_-0.8 K and log N_H=20.1^+0.3_-1.7 cm^-2 (1sigma errors). For
the FSW we estimate logT=6.6_-0.2^+0.1 K and log N_H=19.8_-0.8^+0.4 cm^-2. Our
constraints allow us to estimate the cumulative number density per unit
redshifts of OVII WHIM absorbers. We also estimate the cosmological mass
density obtaining Omega_b(WHIM)=(0.021^+0.031_-0.018) (Z/Z_sun)^-1, consistent
with the mass density of the intergalactic 'missing baryons' for high
metallicities.Comment: 29 pages, 8 figures, 4 tables. Accepted for publication in Ap
Chasing the observational signatures of seed black holes at z > 7: candidate observability
Observing the light emitted by the first accreting black holes (BHs) would
dramatically improve our understanding of the formation of quasars at z > 6,
possibly unveiling the nature of their supermassive black hole (SMBH) seeds. In
previous works we explored the relative role of the two main competing BH seed
formation channels, Population III remnants (low-mass seeds) and direct
collapse BHs (high-mass seeds), investigating the properties of their host
galaxies in a cosmological context. Building on this analysis, we predict here
the spectral energy distribution and observational features of low- and
high-mass BH seeds selected among the progenitors of a z~6 SMBH. We derive the
processed emission from both accreting BHs and stars by using the
photo-ionization code Cloudy, accounting for the evolution of metallicity and
dust-to-gas mass ratio in the interstellar medium of the host galaxies, as
predicted by the cosmological data- constrained model GAMETE/QSOdust. We show
how future missions like JWST and ATHENA will be able to detect the light
coming from SMBH progenitors already at z~16. We build upon previous
complementary studies and propose a method based on the combined analysis of
near infrared (NIR) colors, IR excess (IRX) and UV continuum slopes (i.e.
color-color and IRX-Beta diagrams) to distinguish growing seed BH host galaxies
from starburst-dominated systems in JWST surveys. Sources selected through this
criterion would be the best target for follow-up X-ray observations.Comment: accepted for publicaztion in MNRA
An X-ray WHIM metal absorber from a Mpc-scale empty region of space
We report a detection of an absorption line at ~44.8 {\AA} in a > 500 ks
Chandra HRC-S/LETG X-ray grating spectrum of the blazar H 2356-309. This line
can be identified as intervening CV-K{\alpha} absorption, at z\approx0.112,
produced by a warm (log T = 5.1 K) intergalactic absorber. The feature is
significant at a 2.9{\sigma} level (accounting for the number of independent
redshift trials). We estimate an equivalent hydrogen column density of log
N_H=19.05 (Z/Zsun)^-1 cm^-2. Unlike other previously reported FUV/X-ray metal
detections of warm-hot intergalactic medium (WHIM), this CV absorber lies in a
region with locally low galaxy density, at ~2.2 Mpc from the closest galaxy at
that redshift, and therefore is unlikely to be associated with an extended
galactic halo. We instead tentatively identify this absorber with an
intervening Warm-Hot Intergalactic Medium filament possibly permeating a
large-scale, 30 Mpc extended, structure of galaxies whose redshift centroid,
within a cylinder of 7.5 Mpc radius centered on the line of sight to H
2356-309, is marginally consistent (at a 1.8{\sigma} level) with the redshift
of the absorber.Comment: ApJ accepted, 6 pages, 3 figure
Cervical cancer screening: from molecular basis to diagnostic practice, going through new technologies.
In the era of Human Papillomavirus (HPV) vaccination, a lot of misunderstanding still exists among healthcare professionals and patients regarding HPV infection. The purpose of this review is to synthesize the clinical molecular mechanisms that contribute to HPV-mediated cervical carcinogenesis, as well as to appraise the current status of new biomarkers and technologies in terms of available data on clinical applications and future promises
Il contributo dei giochi matematici all'innovazione didattica
The contribution intends to illustrate the possible role of the mathematics games as stimulus to didactics, in order to make the students interested in non standard “mathematical” situations, with the aim to facilitate the approach through problems to the learning of the subject
Chasing the observational signatures of seed black holes at z > 7: Candidate statistics
Supermassive black holes (SMBHs) of 109–1010M were already in place ∼13 Gyr ago, at
z > 6. Super-Eddington growth of low-mass BH seeds (∼100M) or less extreme accretion
on to∼105M seeds have been recently considered as the main viable routes to these SMBHs.
Here, we study the statistics of these SMBH progenitors at z ∼ 6. The growth of low- and
high-mass seeds and their host galaxies are consistently followed using the cosmological data
constrained model GAMETE/QSODUST, which reproduces the observed properties of high-z
quasars, like SDSS J1148+5251.We show that both seed formation channels can be in action
over a similar redshift range 15 < z < 18 and are found in dark matter haloes with comparable
mass, ∼5 × 107M. However, as long as the systems evolve in isolation (i.e. no mergers
occur), noticeable differences in their properties emerge: At z ≥ 10 galaxies hosting high-mass
seeds have smaller stellar mass and metallicity, the BHs accrete gas at higher rates and star
formation proceeds less efficiently than in low-mass seeds hosts. At z < 10 these differences
are progressively erased, as the systems experience minor or major mergers and every trace of
the BH origin gets lost
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