427 research outputs found
HAZMAT VI: The Evolution of Extreme Ultraviolet Radiation Emitted from Early M Star
Quantifying the evolution of stellar extreme ultraviolet (EUV, 100 -- 1000
) emission is critical for assessing the evolution of
planetary atmospheres and the habitability of M dwarf systems. Previous studies
from the HAbitable Zones and M dwarf Activity across Time (HAZMAT) program
showed the far- and near-UV (FUV, NUV) emission from M stars at various stages
of a stellar lifetime through photometric measurements from the Galaxy
Evolution Explorer (GALEX). The results revealed increased levels of
short-wavelength emission that remain elevated for hundreds of millions of
years. The trend for EUV flux as a function of age could not be determined
empirically because absorption by the interstellar medium prevents access to
the EUV wavelengths for the vast majority of stars. In this paper, we model the
evolution of EUV flux from early M stars to address this observational gap. We
present synthetic spectra spanning EUV to infrared wavelengths of 0.4
0.05 M stars at five distinct ages between 10 and 5000 Myr, computed
with the PHOENIX atmosphere code and guided by the GALEX photometry. We model a
range of EUV fluxes spanning two orders of magnitude, consistent with the
observed spread in X-ray, FUV, and NUV flux at each epoch. Our results show
that the stellar EUV emission from young M stars is 100 times stronger than
field age M stars, and decreases as t after remaining constant for a few
hundred million years. This decline stems from changes in the chromospheric
temperature structure, which steadily shifts outward with time. Our models
reconstruct the full spectrally and temporally resolved history of an M star's
UV radiation, including the unobservable EUV radiation, which drives planetary
atmospheric escape, directly impacting a planet's potential for habitability.Comment: 23 pages, 15 figures, accepted to Ap
Gravitational Lensing as Signal and Noise in Lyman-alpha Forest Measurements
In Lyman-alpha forest measurements it is generally assumed that quasars are
mere background light sources which are uncorrelated with the forest.
Gravitational lensing of the quasars violates this assumption. This effect
leads to a measurement bias, but more interestingly it provides a valuable
signal. The lensing signal can be extracted by correlating quasar magnitudes
with the flux power spectrum and with the flux decrement. These correlations
will be challenging to measure but their detection provides a direct measure of
how features in the Lyman-alpha forest trace the underlying mass density field.
Observing them will test the fundamental hypothesis that fluctuations in the
forest are predominantly driven by fluctuations in mass, rather than in the
ionizing background, helium reionization or winds. We discuss ways to
disentangle the lensing signal from other sources of such correlations,
including dust, continuum and background residuals. The lensing-induced
measurement bias arises from sample selection: one preferentially collects
spectra of magnified quasars which are behind overdense regions. This
measurement bias is ~0.1-1% for the flux power spectrum, optical depth and the
flux probability distribution. Since the effect is systematic, quantities such
as the amplitude of the flux power spectrum averaged across scales should be
interpreted with care.Comment: 22 pages, 8 figures; v2: references added, discussion expanded,
matches PRD accepted versio
Optimal capture of non-Gaussianity in weak lensing surveys: power spectrum, bispectrum and halo counts
We compare the efficiency of weak lensing-selected galaxy clusters counts and
of the weak lensing bispectrum at capturing non-Gaussian features in the dark
matter distribution. We use the halo model to compute the weak lensing power
spectrum, the bispectrum and the expected number of detected clusters, and
derive constraints on cosmological parameters for a large, low systematic weak
lensing survey, by focusing on the - plane and on the dark
energy equation of state. We separate the power spectrum into the resolved and
the unresolved parts of the data, the resolved part being defined as detected
clusters, and the unresolved part as the rest of the field. We consider four
kinds of clusters counts, taking into account different amount of information :
signal-to-noise ratio peak counts; counts as a function of clusters' mass;
counts as a function of clusters' redshift; and counts as a function of
clusters' mass and redshift. We show that when combined with the power
spectrum, those four kinds of counts provide similar constraints, thus allowing
one to perform the most direct counts, signal-to-noise peaks counts, and get
percent level constraints on cosmological parameters. We show that the weak
lensing bispectrum gives constraints comparable to those given by the power
spectrum and captures non-Gaussian features as well as clusters counts, its
combination with the power spectrum giving errors on cosmological parameters
that are similar to, if not marginally smaller than, those obtained when
combining the power spectrum with cluster counts. We finally note that in order
to reach its potential, the weak lensing bispectrum must be computed using all
triangle configurations, as equilateral triangles alone do not provide useful
information.Comment: Matches ApJ-accepted versio
Clustering Analyses of 300,000 Photometrically Classified Quasars--I. Luminosity and Redshift Evolution in Quasar Bias
Using ~300,000 photometrically classified quasars, by far the largest quasar
sample ever used for such analyses, we study the redshift and luminosity
evolution of quasar clustering on scales of ~50 kpc/h to ~20 Mpc/h from
redshifts of z~0.75 to z~2.28. We parameterize our clustering amplitudes using
realistic dark matter models, and find that a LCDM power spectrum provides a
superb fit to our data with a redshift-averaged quasar bias of b_Q =
2.41+/-0.08 () for . This represents a better
fit than the best-fit power-law model (; ). We find b_Q increases with redshift.
This evolution is significant at >99.6% using our data set alone, increasing to
>99.9999% if stellar contamination is not explicitly parameterized. We measure
the quasar classification efficiency across our full sample as a = 95.6 +/-
^{4.4}_{1.9}%, a star-quasar separation comparable with the star-galaxy
separation in many photometric studies of galaxy clustering. We derive the mean
mass of the dark matter halos hosting quasars as MDMH=(5.2+/-0.6)x10^{12}
M_solar/h. At z~1.9 we find a deviation from luminosity-independent
quasar clustering; this suggests that increasing our sample size by a factor of
1.8 could begin to constrain any luminosity dependence in quasar bias at z~2.
Our results agree with recent studies of quasar environments at z < 0.4, which
detected little luminosity dependence to quasar clustering on proper scales >50
kpc/h. At z < 1.6, our analysis suggests that b_Q is constant with luminosity
to within ~0.6, and that, for g < 21, angular quasar autocorrelation
measurements are unlikely to have sufficient statistical power at z < 1.6 to
detect any luminosity dependence in quasars' clustering.Comment: 13 pages, 9 figures, 2 tables; uses amulateapj; accepted to Ap
The Impact of Temperature Fluctuations on the Lyman-alpha Forest Power Spectrum
We explore the impact of spatial fluctuations in the intergalactic medium
temperature on the Lyman-alpha forest flux power spectrum near z ~ 3. We
develop a semianalytic model to examine temperature fluctuations resulting from
inhomogeneous HI and incomplete HeII reionizations. Detection of these
fluctuations might provide insight into the reionization histories of hydrogen
and helium. Furthermore, these fluctuations, neglected in previous analyses,
could bias constraints on cosmological parameters from the Lyman-alpha forest.
We find that the temperature fluctuations resulting from inhomogeneous HI
reionization are likely to be very small, with an rms amplitude of < 5%,
. More important are the temperature fluctuations
that arise from incomplete HeII reionization, which might plausibly be as large
as 50%, . In practice, however, these temperature
fluctuations have only a small effect on flux power spectrum predictions. The
smallness of the effect is possibly due to density fluctuations dominating over
temperature fluctuations on the scales probed by current measurements. On the
largest scales currently probed, k ~ 0.001 s/km (~0.1 h/Mpc), the effect on the
flux power spectrum may be as large as ~10% in extreme models. The effect is
larger on small scales, up to ~20% at k = 0.1 s/km, due to thermal broadening.
Our results suggest that the omission of temperature fluctuations effects from
previous analyses does not significantly bias constraints on cosmological
parameters.Comment: 11 pages, 5 figures, ApJ accepte
Orange emission in Pr3+-doped fluoroindate glasses
We synthesize and study the properties of praseodymium doped fluoroindate glasses. Glass compositions with praseodymium molar concentrations up to 5% were obtained with good optical quality. Thermal, optical, and luminescence properties are investigated. Judd–Ofelt analysis is used to determine radiative lifetime and emission cross-section of the orange transition originating from the 3P0 level. We find that these glasses are good candidates for the realization of blue diode laser pumped orange lasers for quantum information processing applications
Optimal Surveys for Weak Lensing Tomography
Weak lensing surveys provide a powerful probe of dark energy through the
measurement of the mass distribution of the local Universe. A number of
ground-based and space-based surveys are being planned for this purpose. Here,
we study the optimal strategy for these future surveys using the joint
constraints on the equation of state parameter wn and its evolution wa as a
figure of merit by considering power spectrum tomography. For this purpose, we
first consider an `ideal' survey which is both wide and deep and exempt from
systematics. We find that such a survey has great potential for dark energy
studies, reaching one sigma precisions of 1% and 10% on the two parameters
respectively. We then study the relative impact of various limitations by
degrading this ideal survey. In particular, we consider the effect of sky
coverage, survey depth, shape measurements systematics, photometric redshifts
systematics and uncertainties in the non-linear power spectrum predictions. We
find that, for a given observing time, it is always advantageous to choose a
wide rather than a deep survey geometry. We also find that the dark energy
constraints from power spectrum tomography are robust to photometric redshift
errors and catastrophic failures, if a spectroscopic calibration sample of
10^4-10^5 galaxies is available. The impact of these systematics is small
compared to the limitations that come from potential uncertainties in the power
spectrum, due to shear measurement and theoretical errors. To help the planning
of future surveys, we summarize our results with comprehensive scaling
relations which avoid the need for full Fisher matrix calculations.Comment: Submitted to MNRAS. 10 pages, including 13 figures and 2 table
Consumer Perceptions of Blended Hydrogen in the Home: Learning from HyDeploy
This report presents the results of research into consumer perceptions and the subsequent degree of acceptance of blended hydrogen in domestic properties. Evidence from two trial sites of the HyDeploy programme: i) a private site trial at Keele University, North Staffordshire; ii) and a public site trial at Winlaton, Gateshead are discussed
Quasars at intermediate redshift are not special; but they are often satellites
Understanding the links between the activity of supermassive black holes
(SMBH) at the centres of galaxies and their host dark matter haloes is a key
question in modern astrophysics. The final data release of the SDSS-IV eBOSS
provides the largest contemporary spectroscopic sample of galaxies and QSOs.
Using this sample and covering the redshift interval , we have
measured the clustering properties of the eBOSS QSOs, Emission Line Galaxies
(ELGs) and Luminous Red Galaxies (LRGs). We have also measured the fraction of
QSOs as a function of the overdensity defined by the galaxy population. Using
these measurements, we investigate how QSOs populate and sample the galaxy
population, and how the host dark-matter haloes of QSOs sample the underlying
halo distribution. We find that the probability of a galaxy hosting a QSO is
independent of the host dark matter halo mass of the galaxy. We also find that
about 60\% of eBOSS QSOs are hosted by LRGs and about 20-40\% of QSOs are
hosted by satellite galaxies. We find a slight preference for QSOs to populate
satellite galaxies over central galaxies. This is connected to the host halo
mass distribution of different types of galaxies. Based on our analysis, QSOs
should be hosted by a very broad distribution of haloes, and their occurrence
should be modulated only by the efficiency of galaxy formation processes.Comment: 15 pages, 6 Figures, Data and code from this analysis is available at
https://www.roe.ac.uk/~salam/GQOD/ , submitted to MNRAS, comments and
suggestions are welcom
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