4,372 research outputs found
The Faint End of the Quasar Luminosity Function at z ~ 4: Implications for Ionization of the Intergalactic Medium and Cosmic Downsizing
We present an updated determination of the z ~ 4 QSO luminosity function (QLF), improving the quality of the determination of the faint end of the QLF presented by Glikman et al. (2010). We have observed an additional 43 candidates from our survey sample, yielding one additional QSO at z = 4.23 and increasing the completeness of our spectroscopic follow-up to 48% for candidates brighter than R = 24 over our survey area of 3.76 deg^2. We study the effect of using K-corrections to compute the rest-frame absolute magnitude at 1450 Å compared with measuring M_(1450) directly from the object spectra. We find a luminosity-dependent bias: template-based K-corrections overestimate the luminosity of low-luminosity QSOs, likely due to their reliance on templates derived from higher luminosity QSOs. Combining our sample with bright quasars from the Sloan Digital Sky Survey and using spectrum-based M 1450 for all the quasars, we fit a double power law to the binned QLF. Our best fit has a bright-end slope, α = 3.3 ± 0.2, and faint-end slope, β = 1.6^(+0.8)_(–0.6). Our new data revise the faint-end slope of the QLF down to flatter values similar to those measured at z ~ 3. The break luminosity, though poorly constrained, is at M* = –24.1^(+0.7)_(–1.9), approximately 1-1.5 mag fainter than at z ~ 3. This QLF implies that QSOs account for about half the radiation needed to ionize the intergalactic medium at these redshifts
Is Pregnancy-Associated Melanoma Associated with Adverse Outcomes?
BACKGROUND: Melanoma is the most common malignancy encountered during pregnancy. Conflicting data have led to ongoing confusion regarding pregnancy-associated melanoma (PAM) in the media and among the public. The objective of this study was to better characterize both the clinical presentation of PAM and its prognostic implications.
STUDY DESIGN: Female patients of reproductive age, with stage 0 to IV cutaneous melanoma, were identified from our prospectively maintained database. Clinical and histopathologic factors were analyzed with appropriate statistical methods. Univariable and then multivariable analysis were used on matched data to compare disease-free survival (DFS), overall survival (OS), and melanoma-specific survival (MSS) for stage 0-III PAMs vs non-PAMs. Kaplan-Meier survival curves were then plotted for OS and MSS and compared using the log-rank test.
RESULTS: The clinical presentation of melanoma was similar for PAM and non-PAM patients. There was no significant difference in recurrence between the 2 groups; for PAM patients, 38.5% of patients had recurrence, as compared with 36.6% of non-PAM patients (p = 0.641). For PAM patients, median follow-up was 14.6 years (range 0 to 42.6 years) and 11.1 years (0 to 48.5 years) for the non-PAM patients. No significant differences in DFS, MSS, or OS were identified on univariable or multivariable analysis for PAM vs non-PAM patients in stage 0/I/II and stage III cutaneous melanoma, respectively (p = 0.880 DFS, p = 0.219 OS, and p = 0.670 MSS).
CONCLUSIONS: We observed no difference in DFS, OS, or MSS between the 2 groups. Pregnant patients should be screened for melanoma in a similar manner to nonpregnant patients and should be counseled that their survival is not adversely affected by their pregnancy
Dust in the 55 Cancri planetary system
The presence of debris disks around 1-Gyr-old main sequence stars
suggests that an appreciable amount of dust may persist even in mature
planetary systems. Here we report the detection of dust emission from 55
Cancri, a star with one, or possibly two, planetary companions detected through
radial velocity measurements. Our observations at 850m and 450m imply
a dust mass of 0.0008-0.005 Earth masses, somewhat higher than that in the the
Kuiper Belt of our solar system. The estimated temperature of the dust grains
and a simple model fit both indicate a central disk hole of at least 10 AU in
radius. Thus, the region where the planets are detected is likely to be
significantly depleted of dust. Our results suggest that far-infrared and
sub-millimeter observations are powerful tools for probing the outer regions of
extrasolar planetary systems.Comment: 8 pages and 2 figures, to appear in the Astrophysical Journa
Galaxy Cluster Correlation Function to z ~ 1.5 in the IRAC Shallow Cluster Survey
We present the galaxy cluster autocorrelation function of 277 galaxy cluster
candidates with 0.25 \le z \le 1.5 in a 7 deg^2 area of the IRAC Shallow
Cluster Survey. We find strong clustering throughout our galaxy cluster sample,
as expected for these massive structures. Specifically, at = 0.5 we find a
correlation length of r_0 = 17.40^{+3.98}_{-3.10} h^-1 Mpc, in excellent
agreement with the Las Campanas Distant Cluster Survey, the only other
non-local measurement. At higher redshift, = 1, we find that strong
clustering persists, with a correlation length of r_0=19.14^{+5.65}_{-4.56}
h^-1 Mpc. A comparison with high resolution cosmological simulations indicates
these are clusters with halo masses of \sim 10^{14} Msun, a result supported by
estimates of dynamical mass for a subset of the sample. In a stable clustering
picture, these clusters will evolve into massive (10^{15} Msun) clusters by the
present day.Comment: 4 pages, 4 figures, 1 table. ApJ Letters, in pres
Perturbative matching of staggered four-fermion operators with hypercubic fat links
We calculate the one-loop matching coefficients between continuum and lattice
four-fermion operators for lattice operators constructed using staggered
fermions and improved by the use of fattened links. In particular, we consider
hypercubic fat links and SU(3) projected Fat-7 links, and their mean-field
improved versions. We calculate only current-current diagrams, so that our
results apply for operators whose flavor structure does not allow
``eye-diagrams''. We present general formulae, based on two independent
approaches, and give numerical results for the cases in which the operators
have the taste (staggered flavor) of the pseudo-Goldstone pion. We find that
the one-loop corrections are reduced down to the 10-20% level, resolving the
problem of large perturbative corrections for staggered fermion calculations of
matrix elements.Comment: 37 pages, no figure, 20 table
CO J=2-1 line emission in cluster galaxies at z~1: fueling star formation in dense environments
We present observations of CO J=2-1 line emission in infrared-luminous
cluster galaxies at z~1 using the IRAM Plateau de Bure Interferometer. Our two
primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie
within 2 Mpc of the centers of two massive (>10^14 Msun) galaxy clusters. CO
line emission is not detected in either DOG. We calculate 3-sigma upper limits
to the CO J=2-1 line luminosities, L'_CO < 6.08x10^9 and < 6.63x10^9 K km/s
pc^2. Assuming a CO-to-H_2 conversion factor derived for ultraluminous infrared
galaxies in the local Universe, this translates to limits on the cold molecular
gas mass of M_H_2 < 4.86x10^9 Msun and M_H_2 < 5.30x10^9 Msun. Both DOGs
exhibit mid-infrared continuum emission that follows a power-law, suggesting
that an AGN contributes to the dust heating. As such, estimates of the star
formation efficiencies in these DOGs are uncertain. A third cluster member with
an infrared luminosity, L_IR < 7.4x10^11 Lsun, is serendipitously detected in
CO J=2-1 line emission in the field of one of the DOGs located roughly two
virial radii away from the cluster center. The optical spectrum of this object
suggests that it is likely an obscured AGN, and the measured CO line luminosity
is L'_CO = (1.94 +/- 0.35)x10^10 K km/s pc^2, which leads to an estimated cold
molecular gas mass M_H_2 = (1.55+/-0.28)x10^10 Msun. A significant reservoir of
molecular gas in a z~1 galaxy located away from the cluster center demonstrates
that the fuel can exist to drive an increase in star-formation and AGN activity
at the outskirts of high-redshift clusters.Comment: 22 pages, 4 figures; accepted for publication in Ap
The half-filled Landau level - composite fermions and dipoles
The composite-fermion approach as formulated in the fermion Chern-Simons
theory has been very successful in describing the physics of the lowest Landau
level near Landau level filling factor 1/2. Recent work has emphasized the fact
that the true quasiparticles at these filling factors are electrically neutral
and carry an electric dipole moment. In a previous work, we discussed at length
two formulations in terms of dipolar quasiparticles. Here we briefly review one
approach - termed electron-centered quasiparticles - and show how it can be
extended from 1/2 to nearby filling factors where the quasiparticles carry both
an electric dipole moment and an overall charge.Comment: 10 pages, minor improvements of notation and referencin
DLCQ of Fivebranes, Large N Screening, and L^2 Harmonic Forms on Calabi Manifolds
We find one explicit L^2 harmonic form for every Calabi manifold. Calabi
manifolds are known to arise in low energy dynamics of solitons in Yang-Mills
theories, and the L^2 harmonic form corresponds to the supersymmetric ground
state. As the normalizable ground state of a single U(N) instanton, it is
related to the bound state of a single D0 to multiple coincident D4's in the
non-commutative setting, or equivalently a unit Kaluza-Klein mode in DLCQ of
fivebrane worldvolume theory. As the ground state of nonabelian massless
monopoles realized around a monopole-``anti''-monopole pair, it shows how the
long range force between the pair is screened in a manner reminiscent of large
N behavior of quark-anti-quark potential found in AdS/CFT correspondence.Comment: LaTeX, 23 page
One-loop matching coefficients for improved staggered bilinears
We calculate one-loop matching factors for bilinear operators composed of
improved staggered fermions. We compare the results for different improvement
schemes used in the recent literature, all of which involve the use of smeared
links. These schemes aim to reduce, though not completely eliminate, O(a^2)
discretization errors. We find that all these improvement schemes substantially
reduce the size of matching factors compared to unimproved staggered fermions.
The resulting corrections are comparable to, or smaller than, those found with
Wilson and domain-wall fermions. In the best case (``Fat-7'' and mean-field
improved HYP links) the corrections are 10 % or smaller at 1/a = 2 GeV.Comment: 13 pages, 1 figure (misleading sentence in sec. II removed; version
to appear in Physical Review D
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