614 research outputs found
Identifying rent pressures [on housing market] in your neighbourhood: a new model of Irish regional rent indicators. ESRI WP567, June 2017
Since 2013, researchers in the Economic and Social Research Institute (ESRI)
have compiled a hedonic rental index for the Residential Tenancies Board (RTB). The
indicator estimates a standardised rental index on a national, Dublin and outside of Dublin
basis based on the 950,000 rental properties registered with the RTB. The provision in late
2016 of detailed geographical identifiers has enabled an alternative series of indicators to
be estimated. In particular, hedonic rental indicators for 137 local electoral areas (LEAs)
are now available on a quarterly basis from 2007 quarter 3 to 2016 quarter 4. By providing
a more accurate assessment of regional trends in rental supply and demand, the indicators
should enable a more precise implementation of policies in the rental market. They should
also serve as a proxy for measuring underlying economic activity in these regions on an
ongoing basis
Large Fluctuations in the High-Redshift Metagalactic Ionizing Background
Recent observations have shown that the scatter in opacities among coeval
segments of the Lyman-alpha forest increases rapidly at z > 5. In this paper,
we assess whether the large scatter can be explained by fluctuations in the
ionizing background in the post-reionization intergalactic medium. We find that
matching the observed scatter at z ~ 5.5 requires a short spatially averaged
mean free path of 3 shorter than direct
measurements at z ~ 5.2. We argue that such rapid evolution in the mean free
path is difficult to reconcile with our measurements of the global H I
photoionization rate, which stay approximately constant over the interval z ~
4.8 - 5.5. However, we also show that measurements of the mean free path at z >
5 are likely biased towards higher values by the quasar proximity effect. This
bias can reconcile the short values of the mean free path that are required to
explain the large scatter in opacities. We discuss the implications of this
scenario for cosmological reionization. Finally, we investigate whether other
statistics applied to the z > 5 Lyman-alpha forest can shed light on the origin
of the scatter. Compared to a model with a uniform ionizing background, models
that successfully account for the scatter lead to enhanced power in the
line-of-sight flux power spectrum on scales k < 0.1 h/Mpc. We find tentative
evidence for this enhancement in observations of the high-redshift Lyman-alpha
forest.Comment: Matches version published by MNRAS with clarifications and expanded
discussio
Lyman-alpha Damping Wing Constraints on Inhomogeneous Reionization
One well-known way to constrain the hydrogen neutral fraction, x_H, of the
high-redshift intergalactic medium (IGM) is through the shape of the red
damping wing of the Lya absorption line. We examine this method's effectiveness
in light of recent models showing that the IGM neutral fraction is highly
inhomogeneous on large scales during reionization. Using both analytic models
and "semi-numeric" simulations, we show that the "picket-fence" absorption
typical in reionization models introduces both scatter and a systematic bias to
the measurement of x_H. In particular, we show that simple fits to the damping
wing tend to overestimate the true neutral fraction in a partially ionized
universe, with a fractional error of ~ 30% near the middle of reionization.
This bias is generic to any inhomogeneous model. However, the bias is reduced
and can even underestimate x_H if the observational sample only probes a subset
of the entire halo population, such as quasars with large HII regions. We also
find that the damping wing absorption profile is generally steeper than one
would naively expect in a homogeneously ionized universe. The profile steepens
and the sightline-to-sightline scatter increases as reionization progresses. Of
course, the bias and scatter also depend on x_H and so can, at least in
principle, be used to constrain it. Damping wing constraints must therefore be
interpreted by comparison to theoretical models of inhomogeneous reionization.Comment: 11 pages, 10 figures; submitted to MNRA
The HeI 584 A Forest as a Diagnostic of Helium Reionization
We discuss the potential of using the HeI 584 A forest to detect and study
HeII reionization. Significant 584 A absorption is expected from intergalactic
HeII regions, whereas there should be no detectable absorption from low density
gas in HeIII regions. Unlike HeII Ly-alpha absorption (the subject of much
recent study), the difficulty with using this transition to study HeII
reionization is not saturation but rather that the absorption is weak. The
Gunn-Peterson optical depth for this transition is tau ~ 0.1 x_{HeII} Delta^2
[(1+z)/5]^{9/2}, where x_{HeII} is the fraction of helium in HeII and Delta is
the density in units of the cosmic mean. In addition, HeI 584 A absorption is
contaminated by lower redshift HI Ly-alpha absorption with a comparable flux
decrement. We estimate the requirements for a definitive detection of
redshifted HeI absorption from low density gas (Delta ~ 1), which would
indicate that HeII reionization was occurring. We find that this objective can
be accomplished (using coeval HI Ly-alpha absorption to mask dense regions and
in cross correlation) with a spectral resolution of 10^4 and a signal-to-noise
ratio per resolution element of ~ 10. Such specifications may be achievable on
a few known z ~ 3.5 quasar sightlines with the Cosmic Origins Spectrograph on
the Hubble Space Telescope. We also discuss how HeI absorption can be used to
measure the hardness of the ionizing background above 13.6 eV.Comment: 12 pages, 5 figures, updated to match published versio
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