47 research outputs found
A thin diffuse component of the Galactic Ridge X-ray emission and heating of the interstellar medium contributed by the radiation of Galactic X-ray binaries
We predict a thin (scale height 80 pc) diffuse component of the
Galactic Ridge X-ray emission (GRXE) arising from the scattering of the
radiation of bright X-ray binaries (XBs) by the interstellar medium (ISM). The
morphology of this scattered component is expected to trace the clumpy
molecular and HI clouds. We calculate this contribution to the GRXE from known
Galactic XBs assuming that they are all persistent. The known XBs sample is
incomplete, however, because it is flux limited and spans the lifetime of X-ray
astronomy ( years). We therefore also use a simulated sample of
sources, to estimate the diffuse emission we should expect in an optimistic
case assuming that the X-ray luminosity of our Galaxy is on average similar to
that of other galaxies. In the calculations we also take into account the
enhancement of the total scattering cross-section due to coherence effects in
the elastic scattering from multi-electron atoms and molecules. This scattered
emission can be distinguished from the contribution of low X-ray luminosity
stars by the presence of narrow fluorescent K- lines of Fe, Si, and
other abundant elements present in the ISM and by directly resolving the
contribution of low X-ray luminosity stars. We find that within
latitude of the Galactic plane the scattered emission contributes on average
of the GRXE flux in the case of known sources and over in the
case of simulated sources. In the latter case, the scattered component is found
to even dominate the stellar emission in certain parts of the Galactic plane.
X-rays with energies keV from XBs should also penetrate deep inside
the HI and molecular clouds, where they are absorbed and heat the ISM. We find
that this heating rate dominates the heating by cosmic rays (assuming a solar
neighborhood energy density) in a considerable part of the Galaxy. [abridged]Comment: Minor changes; additional references; matches published versio
Artist: Fast radiative transfer for large-scale simulations of the epoch of reionization
We introduce the ‘Asymmetric Radiative Transfer In Shells Technique’ (ARTIST), a new method for photon propagation on large scales that explicitly conserves photons, propagates photons at the speed of light, approximately accounts for photon directionality, and closely reproduces results of more detailed radiative transfer (RT) methods. Crucially, it is computationally fast enough to evolve the large cosmological volumes required to predict the 21cm power spectrum on scales that will be probed by future experiments targeting the epoch of reionization (EoR). Most seminumerical models aimed at predicting the EoR 21cm signal on these scales use an excursion set formalism (ESF) to model the gas ionization, which achieves computational viability by making a number of approximation
ARTIST:Fast radiative transfer for large-scale simulations of the epoch of reionisation
We introduce the "Asymmetric Radiative Transfer In Shells Technique"
(ARTIST), a new method for photon propagation on large scales that explicitly
conserves photons, propagates photons at the speed of light, approximately
accounts for photon directionality, and closely reproduces results of more
detailed radiative transfer (RT) codes. Crucially, it is computationally fast
enough to evolve the large cosmological volumes required to predict the 21cm
power spectrum on scales that will be probed by future experiments targeting
the Epoch of Reionisation (EoR). Most semi-numerical models aimed at predicting
the EoR 21cm signal make use of an excursion set formalism (ESF) approach,
which achieves computational viability by compromising on photon conservation,
constraining ionised regions to be spherical by construction, and not
accounting for light-travel time. By implementing our RT method within the
semi-numerical code SimFast21, we show that ARTIST predicts a significantly
different evolution for the EoR ionisation field compared to the code's native
ESF. In particular, ARTIST predicts a more gradual evolution of the
volume-averaged ionisation fraction, and up to an order-of-magnitude difference
in the ionisation power, depending on the physical parameters assumed. Its
application to large-scale EoR simulations will therefore allow more
physically-motivated constraints to be obtained for key EoR parameters, such as
the escape fraction.Comment: 18 pages, 16 figures, published by MNRAS (14 August 2019
Probing quasar lifetimes with proximate -centimetre absorption in the diffuse intergalactic medium at redshifts
Enhanced ionizing radiation in close proximity to redshift
quasars creates short windows of intergalactic Ly transmission blueward
of the quasar Ly emission lines. The majority of these Ly
near-zones are consistent with quasars that have optically/UV bright lifetimes
of . However, lifetimes as short as appear to be required by the smallest Ly
near-zones. These short lifetimes present an apparent challenge for the growth
of black holes at . Accretion over
longer timescales is only possible if black holes grow primarily in an obscured
phase, or if the quasars are variable on timescales comparable to the
equilibriation time for ionized hydrogen. Distinguishing between very young
quasars and older quasars that have experienced episodic accretion with
Ly absorption alone is challenging, however. We therefore predict the
signature of proximate 21-cm absorption around radio-loud quasars.
For modest pre-heating of intergalactic hydrogen by the X-ray background, where
the spin temperature prior to any quasar
heating, we find proximate 21-cm absorption should be observable in the spectra
of radio-loud quasars. The extent of the proximate 21-cm absorption is
sensitive to the integrated lifetime of the quasar. Evidence for proximate
21-cm absorption from the diffuse intergalactic medium within of
a (radio-loud) quasar would be consistent with a short quasar lifetime, , and would provide a complementary constraint on
models for high redshift black hole growth.Comment: 19 pages, 12 figures, 2 tables. Accepted for publication in MNRA
Possible evidence for a large-scale enhancement in the Lyman- forest power spectrum at redshift
Inhomogeneous reionization enhances the 1D Lyman- forest power
spectrum on large scales at redshifts . This is due to coherent
fluctuations in the ionized hydrogen fraction that arise from large-scale
variations in the post-reionization gas temperature, which fade as the gas
cools. It is therefore possible to use these relic fluctuations to constrain
inhomogeneous reionization with the power spectrum at wavenumbers
. We use the Sherwood-Relics suite
of hybrid radiation hydrodynamical simulations to perform a first analysis of
new Lyman- forest power spectrum measurements at .
These data extend to wavenumbers , with
a relative uncertainty of -- per cent in each wavenumber bin. Our
analysis returns a preference for an enhancement in the
Lyman- forest power spectrum at large scales, in excess of that
expected for a spatially uniform ultraviolet background. This large-scale
enhancement could be a signature of inhomogeneous reionization, although the
statistical precision of these data is not yet sufficient for obtaining a
robust detection of the relic post-reionization fluctuations. We show that
future power spectrum measurements with relative uncertainties of per cent should provide unambiguous evidence for an enhancement in the
power spectrum on large scales.Comment: Accepted by MNRAS, 13 pages, 8 figure
Unveiling Dark Matter free-streaming at the smallest scales with high redshift Lyman-alpha forest
This study introduces novel constraints on the free-streaming of thermal
relic warm dark matter (WDM) from Lyman- forest flux power spectra. Our
analysis utilises a high-resolution, high-redshift sample of quasar spectra
observed using the HIRES and UVES spectrographs (). We employ a
Bayesian inference framework and a simulation-based likelihood that encompasses
various parameters including the free-streaming of dark matter, cosmological
parameters, the thermal history of the intergalactic medium, and inhomogeneous
reionization, to establish lower limits on the mass of a thermal relic WDM
particle of (at 95\% C.L.). This result surpasses previous
limits from the Lyman- forest through reduction of the measured
uncertainties due to a larger statistical sample and by measuring clustering to
smaller scales (). The approximately
two-fold improvement due to the expanded statistical sample suggests that the
effectiveness of Lyman- forest constraints on WDM models at high
redshifts are limited by the availability of high-quality quasar spectra.
Restricting the analysis to comparable scales and thermal history priors as in
prior studies () lowers the bound on the
WDM mass to . As the precision of the measurements
increases, it becomes crucial to examine the instrumental and modelling
systematics. On the modelling front, we argue that the impact of the thermal
history uncertainty on the WDM particle mass constraint has diminished due to
improved independent observations. At the smallest scales, the primary source
of modeling systematic arises from the structure in the peculiar velocity of
the intergalactic medium and inhomogeneous reionization.Comment: 22 pages, 14 figures, 2 tables; submitte
Possible evidence for a large-scale enhancement in the Lyman-α forest power spectrum at redshift z ≥ 4
Inhomogeneous reionization enhances the 1D Lyα forest power spectrum on large scales at redshifts z ≥ 4. This is due to coherent fluctuations in the ionized hydrogen fraction that arise from large-scale variations in the post-reionization gas temperature, which fade as the gas cools. It is therefore possible to use these relic fluctuations to constrain inhomogeneous reionization with the power spectrum at wavenumbers log10(k/km−1 s) ≲ −1.5. We use the Sherwood-Relics suite of hybrid radiation hydrodynamical simulations to perform a first analysis of new Lyα forest power spectrum measurements at 4.0 ≤ z ≤ 4.6. These data extend to wavenumbers log10(k/km−1 s) ≃ −3, with a relative uncertainty of 10–20 per cent in each wavenumber bin. Our analysis returns a 2.7σ preference for an enhancement in the Lyα forest power spectrum at large scales, in excess of that expected for a spatially uniform ultraviolet background. This large-scale enhancement could be a signature of inhomogeneous reionization, although the statistical precision of these data is not yet sufficient for obtaining a robust detection of the relic post-reionization fluctuations. We show that future power spectrum measurements with relative uncertainties of ≲ 2.5 per cent should provide unambiguous evidence for an enhancement in the power spectrum on large scales
The effect of inhomogeneous reionisation on the Lyman-alpha forest power spectrum at redshift z > 4: implications for thermal parameter recovery
We use the Sherwood–Relics suite of hybrid hydrodynamical and radiative transfer simulations to model the effect of inhomogeneous reionization on the 1D power spectrum of the Lyman α (Lyα) forest transmitted flux at redshifts 4.2 ≤ z ≤ 5. Relative to models that assume a homogeneous ultraviolet background, reionization suppresses the power spectrum at small scales, k ∼ 0.1 km−1 s, by ∼10 per cent because of spatial variations in the thermal broadening kernel and the divergent peculiar velocity field associated with overpressurized intergalactic gas. On larger scales, k 4, 0.006≤k≤0.2km−1s, we find inhomogeneous reionization does not introduce any significant bias in thermal parameter recovery for the current measurement uncertainties of ∼10 per cent. However, for 5 per cent uncertainties, ∼1σ shifts between the estimated and true parameters occur