662 research outputs found
Testing Reionization with Gamma Ray Burst Absorption Spectra
We propose to study cosmic reionization using absorption line spectra of
high-redshift Gamma Ray Burst (GRB) afterglows. We show that the statistics of
the dark portions (gaps) in GRB absorption spectra represent exquisite tools to
discriminate among different reionization models. We then compute the
probability to find the largest gap in a given width range [Wmax, Wmax + dW] at
a flux threshold Fth for burst afterglows at redshifts 6.3 < z < 6.7. We show
that different reionization scenarios populate the (Wmax, Fth) plane in a very
different way, allowing to distinguish among different reionization histories.
We provide here useful plots that allow a very simple and direct comparison
between observations and model results. Finally, we apply our methods to GRB
050904 detected at z = 6.29. We show that the observation of this burst
strongly favors reionization models which predict a highly ionized
intergalactic medium at z~6, with an estimated mean neutral hydrogen fraction
xHI = 6.4 \pm 0.3 \times 10^-5 along the line of sight towards GRB 050904.Comment: 5 pages, 3 figures, revised to match the accepted version; major
change: gap statistics is now studied in terms of the flux threshold Fth,
instead of the observed J-band flux FJ; MNRAS in pres
Mapping metals at high redshift with far-infrared lines
Cosmic metal enrichment is one of the key physical processes regulating
galaxy formation and the evolution of the intergalactic medium (IGM). However,
determining the metal content of the most distant galaxies has proven so far
almost impossible; also, absorption line experiments at become
increasingly difficult because of instrumental limitations and the paucity of
background quasars. With the advent of ALMA, far-infrared emission lines
provide a novel tool to study early metal enrichment. Among these, the [CII]
line at 157.74 m is the most luminous line emitted by the interstellar
medium of galaxies. It can also resonant scatter CMB photons inducing
characteristic intensity fluctuations () near the peak of the
CMB spectrum, thus allowing to probe the low-density IGM. We compute both [CII]
galaxy emission and metal-induced CMB fluctuations at by using
Adaptive Mesh Refinement cosmological hydrodynamical simulations and produce
mock observations to be directly compared with ALMA BAND6 data ( GHz). The [CII] line flux is correlated with as
. Such
relation is in very good agreement with recent ALMA observations (e.g. Maiolino
et al. 2015; Capak et al. 2015) of galaxies. We predict that a
() galaxy can be detected at in
(2000) hours, respectively. CMB resonant scattering can produce Jy/beam emission/absorptions features that are very challenging to be
detected with current facilities. The best strategy to detect these signals
consists in the stacking of deep ALMA observations pointing fields with known
galaxies. This would allow to simultaneously detect both
[CII] emission from galactic reionization sources and CMB fluctuations produced
by metals.Comment: 13 pages, 6 figure
Dust from AGBs: relevant factors and modelling uncertainties
The dust formation process in the winds of Asymptotic Giant Branch stars is
discussed, based on full evolutionary models of stars with mass in the range
MMM, and metallicities .
Dust grains are assumed to form in an isotropically expanding wind, by growth
of pre--existing seed nuclei. Convection, for what concerns the treatment of
convective borders and the efficiency of the schematization adopted, turns out
to be the physical ingredient used to calculate the evolutionary sequences with
the highest impact on the results obtained. Low--mass stars with MM produce carbon type dust with also traces of silicon carbide. The
mass of solid carbon formed, fairly independently of metallicity, ranges from a
few M, for stars of initial mass M, to
M for MM; the size of dust
particles is in the range mm. On the contrary,
the production of silicon carbide (SiC) depends on metallicity. For the size of SiC grains varies in the range m, while the mass of SiC formed is
. Models of
higher mass experience Hot Bottom Burning, which prevents the formation of
carbon stars, and favours the formation of silicates and corundum. In this case
the results scale with metallicity, owing to the larger silicon and aluminium
contained in higher--Z models. At Z= we find that the most
massive stars produce dust masses M, whereas models of
smaller mass produce a dust mass ten times smaller. The main component of dust
are silicates, although corundum is also formed, in not negligible quantities
().Comment: Paper accepted for publication in Monthly Notices of the Royal
Astronomical Society Main Journal (2014 January 4
A genome walking strategy for the identification of eukaryotic nucleotide sequences adjacent to known regions
Determination of nucleotide sequences adjacent to a known region is a recurring need in many genome scale studies. Various methods have been developed based on PCR techniques in order to fulfill th..
Very extended cold gas, star formation and outflows in the halo of a bright QSO at z>6
Past observations of QSO host galaxies at z >6 have found cold gas and star
formation on compact scales of a few kiloparsecs. We present new high
sensitivity IRAM PdBI follow-up observations of the [CII] 158micron emission
line and FIR continuum in the host galaxy of SDSS J1148+5152, a luminous QSO at
redshift 6.4189. We find that a large fraction of the gas traced by [CII] is at
high velocities, up to ~1400 km/s relative to the systemic velocity, confirming
the presence of a major quasar-driven outflow indicated by previous
observations. The outflow has a complex morphology and reaches a maximum
projected radius of ~30 kpc. The extreme spatial extent of the outflow allows
us, for the first time in an external galaxy, to estimate mass-loss rate,
kinetic power and momentum rate of the outflow as a function of the projected
distance from the nucleus and the dynamical time-scale. These trends reveal
multiple outflow events during the past 100 Myr, although the bulk of the mass,
energy and momentum appear to have been released more recently, within the past
~20 Myr. Surprisingly, we discover that also the quiescent gas at systemic
velocity is extremely extended. More specifically, we find that, while 30% of
the [CII] within v\in(-200, 200) km/s traces a compact component that is not
resolved by our observations, 70% of the [CII] emission in this velocity range
is extended, with a projected FWHM size of 17.4+-1.4 kpc. We detect FIR
continuum emission associated with both the compact and the extended [CII]
components, although the extended FIR emission has a FWHM of 11+-3 kpc, thus
smaller than the extended [CII] source. Overall, our results indicate that the
cold gas traced by [CII] is distributed up to r~30 kpc. A large fraction of
extended [CII] is likely associated with star formation on large scales, but
the [CII] source extends well beyond the FIR continuum.Comment: Accepted for publication in A&A, 21 pages, 18 figures, 3 tables (v2:
accepted version, discussion expanded in Sect. 3, 4 and in the Appendices,
minor changes elsewhere
Physical Properties of the First Quasars
Since the beginning of the new millennium, more than 100 quasars
have been discovered through several surveys and followed-up with
multi-wavelength observations. These data provided a large amount of
information on the growth of supermassive black holes at the early epochs, the
properties of quasar host galaxies and the joint formation and evolution of
these massive systems. We review the properties of the highest- quasars
known so far, especially focusing on some of the most recent results obtained
in (sub-)millimeter bands. We discuss key observational challenges and open
issues in theoretical models and highlight possible new strategies to improve
our understanding of the galaxy-black hole formation and evolution in the early
Universe
The Brightest Ly Emitter: Pop III or Black Hole?
CR7 is the brightest emitter (LAE) known to date,
and spectroscopic follow-up by Sobral et al. (2015) suggests that CR7 might
host Population (Pop) III stars. We examine this interpretation using
cosmological hydrodynamical simulations. Several simulated galaxies show the
same "Pop III wave" pattern observed in CR7. However, to reproduce the extreme
CR7 /HeII1640 line luminosities () a
top-heavy IMF and a massive () PopIII burst with age
Myr are required. Assuming that the observed properties of and HeII emission are typical for Pop III, we predict that in the
COSMOS/UDS/SA22 fields, 14 out of the 30 LAEs at with should also host Pop III stars producing an
observable . As an alternate
explanation, we explore the possibility that CR7 is instead powered by
accretion onto a Direct Collapse Black Hole (DCBH). Our model predicts
, , and X-ray luminosities that are in agreement
with the observations. In any case, the observed properties of CR7 indicate
that this galaxy is most likely powered by sources formed from pristine gas. We
propose that further X-ray observations can distinguish between the two above
scenarios.Comment: 6 pages, 4 figure
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