12,082 research outputs found
Luminosity functions of Lyman-alpha emitters at z=6.5, and z=5.7: evidence against reionization at z=6
Lyman-alpha emission from galaxies should be suppressed completely or
partially at redshifts beyond reionization. Without knowing the instrinsic
properties of galaxies at z = 6.5, this attenuation is hard to infer in any one
source, but can be infered from a comparison of luminosity functions of
lyman-alpha emitters at redshifts just before and after reionization. We
combine published surveys of widely varying depths and areas to construct
luminosity functions at z=6.5 and 5.7, where the characteristic luminosity
L_star and density phi_star are well constrained while the faint-end slope of
the luminosity function is essentially unconstrained. Excellent consistency is
seen in all but one published result. We then calculate the likelihood of
obtaining the z=6.5 observations given the z=5.7 luminosity function with (A)
no evolution and (B) an attenuation of a factor of three. Hypothesis (A) gives
an acceptable likelihood while (B) does not. This indicates that the z=6.5
lyman-alpha lines are not strongly suppressed by a neutral intergalactic medium
and that reionization was largely complete at z = 6.5.Comment: Submitted to Astrophysical Journal Letter
Infrared Counterpart of the Gravitational Lens 1938+66.6
We report the detection of a very red source coincident with the
gravitational lens 1938+66.6 (Patnaik et al. 1992) in K' (2.12 micron), H (1.6
micron), J (1.25 micron), and Thuan-Gunn r (0.65 micron) bands. 1938+66.6 has
previously been detected as a partial radio ring indicating lensing. We find
K'=17.1 +- 0.1 and r = 23.9 +- 0.2, making it a very red source with (r-K')=6.8
+- 0.25. We also observed in Thuan-Gunn g band (0.49 micron) and found g>24.5
at the 90% confidence level. We interpret our observations as a reddened
gravitational lens on the basis of its optical-IR color and positional
coincidence with the radio source.Comment: 8 pages, one PostScript figure; uses AAS LaTeX macros. Accepted for
publication in The Astronomical Journa
The Volume Fraction of Ionized Intergalactic Gas at Redshift z=6.5
The observed number density of Lyman-alpha sources implies a minimum volume
of the inter-galactic medium that must be ionized, in order to allow the
Lyman-alpha photons to escape attenuation. We estimate this volume by assigning
to each Lyman-alpha emitter the minimum Stromgren sphere that would allow half
its Lyman-alpha photons to escape. This implies a lower limit to ionized gas
volume fraction of 20-50% at redshift z=6.5. This is a lower limit in two ways:
First, we conservatively assume that the Lyman-alpha sources seen (at a
relatively bright flux limit) are the only ones present; and second, we assume
the smallest Stromgren sphere volume that will allow the photons to escape.
This limit is completely independent of what ionizing photon sources produced
the bubbles. Deeper Lyman-alpha surveys are possible with present technology,
and can strengthen these limits by detecting a higher density of Lyman-alpha
galaxies.Comment: Submitted to ApJ Letter
Starburst Intensity Limit of Galaxies at z~5-6
The peak star formation intensity in starburst galaxies does not vary
significantly from the local universe to redshift z~6. We arrive at this
conclusion through new surface brightness measurements of 47 starburst galaxies
at z~5-6, doubling the redshift range for such observations. These galaxies are
spectroscopically confirmed in the Hubble Ultra Deep Field (HUDF) through the
GRism ACS program for Extragalactic Science (GRAPES) project. The starburst
intensity limit for galaxies at z~5-6 agree with those at z~3-4 and z~0 to
within a factor of a few, after correcting for cosmological surface brightness
dimming and for dust. The most natural interpretation of this constancy over
cosmic time is that the same physical mechanisms limit starburst intensity at
all redshifts up to z~6 (be they galactic winds, gravitational instability, or
something else). We do see two trends with redshift: First, the UV spectral
slope of galaxies at z~5-6 is bluer than that of z~3 galaxies, suggesting an
increase in dust content over time. Second, the galaxy sizes from z~3 to z~6
scale approximately as the Hubble parameter 1/H(z). Thus, galaxies at z~6 are
high redshift starbursts, much like their local analogs except for slightly
bluer colors, smaller physical sizes, and correspondingly lower overall
luminosities. If we now assume a constant maximum star formation intensity, the
differences in observed surface brightness between z~0 and z~6 are consistent
with standard expanding cosmology and strongly inconsistent with tired light
model.Comment: Accepted for publication in ApJ (23 pages, 5 figures). Minor changes
to tex
JPL's Real-Time Weather Processor project (RWP) metrics and observations at system completion
As an integral part of the overall upgraded National Airspace System (NAS), the objective of the Real-Time Weather Processor (RWP) project is to improve the quality of weather information and the timeliness of its dissemination to system users. To accomplish this, an RWP will be installed in each of the Center Weather Service Units (CWSUs), located in 21 of the 23 Air Route Traffic Control Centers (ARTCCs). The RWP System is a prototype system. It is planned that the software will be GFE and that production hardware will be acquired via industry competitive procurement. The ARTCC is a facility established to provide air traffic control service to aircraft operating on Instrument Flight Rules (IFR) flight plans within controlled airspace, principally during the en route phase of the flight. Covered here are requirement metrics, Software Problem Failure Reports (SPFRs), and Ada portability metrics and observations
Ly-alpha emitting galaxies at redshift z~4.5 in the LALA Cetus field
We present a large sample of Ly-alpha emitting galaxies spectroscopically
confirmed at z~4.5, based on IMACS spectroscopic observations of candidate LAEs
in the LALA Cetus field. We identify 110 z~4.5 LAEs based on single line
detections with no continuum emission blueward of the line. The Ly-alpha
confirmation rate varies from <50% to 76% for candidates selected in different
narrowband filters at slightly different redshifts. We find a drop in the LAE
density at redshift 4.50+-0.03 from redshift 4.39-4.47 by a factor of 66%,
which could be a large scale void in the distribution of star-forming galaxies
(~18Mpc along the line of sight and ~80Mpc across). The sample includes many
objects with equivalent widths >200A. These large EW candidates are
spectroscopically confirmed at the same rate as candidates with more modest
EWs. A composite spectrum of all 110 confirmed LAEs shows the characteristic
asymmetry of the Ly-alpha line. It also places new and stringent upper limits
on the CIV 1549/Ly-alpha and HeII 1640/Ly-alpha line ratios, providing a new
upper limit on the fraction of active galactic nuclei in Ly-alpha selected
galaxy samples, and on the contribution of Pop III populations. Finally, we
calculate the Ly-alpha luminosity function for our z~4.5 sample, which is
consistent with those at other redshifts, showing that there is no evolution in
Ly-alpha luminosity function from z~3.1-6.6.Comment: 30 pages, 10 figures, ApJ submitte
Evolution of Lyman Alpha Galaxies: Stellar Populations at z ~ 0.3
We present the results of a stellar population analysis of 30 Lyman alpha
emitting galaxies (LAEs) at z ~ 0.3, previously discovered with the Galaxy
Evolution Explorer (GALEX). With a few exceptions, we can accurately fit model
spectral energy distributions to these objects, representing the first time
this has been done for a large sample of LAEs at z < 3, a gap of ~ 8 Gyr in the
history of the Universe. From the 26/30 LAEs which we can fit, we find an age
and stellar mass range of 200 Myr - 10 Gyr and 10^9 - 10^11 Msol, respectively.
These objects thus appear to be significantly older and more massive than LAEs
at high-redshift. We also find that these LAEs show a mild trend towards higher
metallicity than those at high redshift, as well as a tighter range of dust
attenuation and interstellar medium geometry. These results suggest that
low-redshift LAEs have evolved significantly from those at high redshift.Comment: Accepted for publication in the Astrophysical Journal. Replaced with
accepted version. Eight pages, four figures, in emulateapj forma
The impact of private sector provision on equitable provision of coronary revascularisation
Objective: To investigate the impact of including private sector data on assessments of equity of coronary revascularisation provision using NHS data only.
Design: Analyses of Hospital Episodes Statistics and private sector data by age, sex, and PCT of residence. For each PCT, the share of London's total population and revascularisations (all admissions, NHS-funded, and privately-funded admissions) were calculated. GINI coefficients were derived to provide an index of inequality across sub-populations, with parametric bootstrapping to estimate confidence intervals.
Setting: London Participants London residents undergoing coronary revascularisation April 2001 - December 2003. Intervention Coronary artery bypass graft or angioplasty
Main outcome measures: Directly-standardised revascularisation rates, GINI coefficients.
Results: NHS-funded age-standardised revascularisation rates varied from 95.2 to 193.9 per 100,000 and privately funded procedures from 7.6 to 57.6. Although the age distribution did not vary by funding, the proportion of revascularisations among women that were privately funded (11.0%) was lower than among men (17.0%). Privately funded rates were highest in PCTs with the lowest death rates (p=0.053). NHS-funded admission rates were not related to deprivation nor age-standardised deaths rates from coronary heart disease. Privately-funded admission rates were lower in more deprived PCTs. NHS provision was significantly more egalitarian (Gini coefficient 0.12) than the private sector (0.35). Including all procedures was significantly less equal (0.13) than NHS funded care alone.
Conclusion: Private provision exacerbates geographical inequalities. Those responsible for commissioning care for defined populations must have access to consistent data on provision of treatment wherever it takes place
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