5,573 research outputs found
Consumption inequality and income uncertainty
This paper places the debate over using consumption or income in studies of inequality growth in a formal intertemporal setting. It highlights the importance of permanent and transitory income uncertainty in the evaluation of growth in consumption inequality. We derive conditions under which the growth of variances and covariances of income and consumption can be used to separately identify the growth in the variance of permanent and transitory income shocks. Household data from Britain for the period 1968-1992 are used to show a strong growth in transitory inequality toward the end of this period, while younger cohorts are shown to face significantly higher levels of permanent inequality
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UNCOVER: The Growth of the First Massive Black Holes from JWST/NIRSpec—Spectroscopic Redshift Confirmation of an X-Ray Luminous AGN at z = 10.1
The James Webb Space Telescope is now detecting early black holes (BHs) as they transition from seeds to supermassive BHs. Recently, Bogdan et al. reported the detection of an X-ray luminous supermassive BH, UHZ-1, with a photometric redshift at z \u3e 10. Such an extreme source at this very high redshift provides new insights on seeding and growth models for BHs given the short time available for formation and growth. Harnessing the exquisite sensitivity of JWST/NIRSpec, here we report the spectroscopic confirmation of UHZ-1 at z = 10.073 ± 0.002. We find that the NIRSpec/Prism spectrum is typical of recently discovered z ≈ 10 galaxies, characterized primarily by star formation features. We see no clear evidence of the powerful X-ray source in the rest-frame UV/optical spectrum, which may suggest heavy obscuration of the central BH, in line with the Compton-thick column density measured in the X-rays. We perform a stellar population fit simultaneously to the new NIRSpec spectroscopy and previously available photometry. The fit yields a stellar-mass estimate for the host galaxy that is significantly better constrained than prior photometric estimates (�⋆∼1.4−0.4+0.3×108M⊙). Given the predicted BH mass (MBH ∼ 107–108M⊙), the resulting ratio of MBH/M⋆ remains 2 to 3 orders of magnitude higher than local values, thus lending support to the heavy seeding channel for the formation of supermassive BHs within the first billion years of cosmic evolution
Gravitational waves from inspiraling compact binaries: Second post-Newtonian waveforms as search templates
We ascertain the effectiveness of the second post-Newtonian approximation to
the gravitational waves emitted during the adiabatic inspiral of a compact
binary system as templates for signal searches with kilometer-scale
interferometric detectors. The reference signal is obtained by solving the
Teukolsky equation for a small mass moving on a circular orbit around a large
nonrotating black hole. Fitting factors computed from this signal and these
templates, for various types of binary systems, are all above the 90% mark.
According to Apostolatos' criterion, second post-Newtonian waveforms should
make acceptably effective search templates.Comment: LaTeX, one eps figure. Hires and color versions are available from
http://jovian.physics.uoguelph.ca/~droz/uni/papers/search.htm
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UNCOVER: Illuminating the Early Universe—JWST/NIRSpec Confirmation of z \u3e 12 Galaxies
Observations of high-redshift galaxies provide a critical direct test to the theories of early galaxy formation, yet to date, only three have been spectroscopically confirmed at z \u3e 12. Due to strong gravitational lensing over a wide area, the galaxy cluster field A2744 is ideal for searching for the earliest galaxies. Here we present JWST/NIRSpec observations of two galaxies: a robust detection at zspec 12.393 0.001 0.004 = - + , and a plausible candidate at zspec 13.079 0.001 0.013 = - + . The galaxies are discovered in JWST/NIRCam imaging and their distances are inferred with JWST/NIRSpec spectroscopy, all from the JWST Cycle 1 UNCOVER Treasury survey. Detailed stellar population modeling using JWST NIRCam and NIRSpec data corroborates the primeval characteristics of these galaxies: low mass (∼108 Me), young, rapidly assembling, metal-poor, and star-forming. Interestingly, both galaxies are spatially resolved, having lensing-corrected rest-UV effective radii on the order of 300–400 pc, which are notably larger than other spectroscopically confirmed systems at similar redshifts. The observed dynamic range of z 10 sizes spans over 1 order of magnitude, implying a significant scatter in the size–mass relation at early times. Deep into the epoch of reionization, these discoveries elucidate the emergence of the first galaxies
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UNCOVER Spectroscopy Confirms the Surprising Ubiquity of Active Galactic Nuclei in Red Sources at z \u3e 5
The James Webb Space Telescope is revealing a new population of dust-reddened broad-line active galactic nuclei (AGN) at redshifts z ≳ 5. Here we present deep NIRSpec/Prism spectroscopy from the Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) of 15 AGN candidates selected to be compact, with red continua in the rest-frame optical but with blue slopes in the UV. From NIRCam photometry alone, they could have been dominated by dusty star formation or an AGN. Here we show that the majority of the compact red sources in UNCOVER are dust-reddened AGN: 60% show definitive evidence for broad-line Hα with a FWHM \u3e 2000 km s −1, 20% of the current data are inconclusive, and 20% are brown dwarf stars. We propose an updated photometric criterion to select red z \u3e 5 AGN that excludes brown dwarfs and is expected to yield \u3e80% AGN. Remarkably, among all zphot \u3e 5 galaxies with F277W – F444W \u3e 1 in UNCOVER at least 33% are AGN regardless of compactness, climbing to at least 80% AGN for sources with F277W – F444W \u3e 1.6. The confirmed AGN have black hole masses of 107–109M⊙. While their UV luminosities (−16 \u3e MUV \u3e −20 AB mag) are low compared to UV-selected AGN at these epochs, consistent with percent-level scattered AGN light or low levels of unobscured star formation, the inferred bolometric luminosities are typical of 107–109M⊙ black holes radiating at ∼10%–40% the Eddington limit. The number densities are surprisingly high at ∼10−5 Mpc−3 mag−1, 100 times more common than the faintest UV-selected quasars, while accounting for ∼1% of the UV-selected galaxies. While their UV faintness suggests they may not contribute strongly to reionization, their ubiquity poses challenges to models of black hole growth
Design and implementation of a compliant robot with force feedback and strategy planning software
Force-feedback robotics techniques are being developed for automated precision assembly and servicing of NASA space flight equipment. Design and implementation of a prototype robot which provides compliance and monitors forces is in progress. Computer software to specify assembly steps and makes force feedback adjustments during assembly are coded and tested for three generically different precision mating problems. A model program demonstrates that a suitably autonomous robot can plan its own strategy
Detection of high energy X-rays from the galactic center region
Observations of the galactic center region made with the high energy X-ray detector on OSO-8 are discussed. A strong hard X-ray which was detected during these observations from the vicinity of the galactic center are examined. The counting rate spectrum and the photon number spectrum of the flux are determined. Comparisons with the high energy X-ray fluxes observed from sources in the region by others are discussed
Recovering the stationary phase condition for accurately obtaining scattering and tunneling times
The stationary phase method is often employed for computing tunneling {\em
phase} times of analytically-continuous {\em gaussian} or infinite-bandwidth
step pulses which collide with a potential barrier. The indiscriminate
utilization of this method without considering the barrier boundary effects
leads to some misconceptions in the interpretation of the phase times. After
reexamining the above barrier diffusion problem where we notice the wave packet
collision necessarily leads to the possibility of multiple reflected and
transmitted wave packets, we study the phase times for tunneling/reflecting
particles in a framework where an idea of multiple wave packet decomposition is
recovered. To partially overcome the analytical incongruities which rise up
when tunneling phase time expressions are obtained, we present a theoretical
exercise involving a symmetrical collision between two identical wave packets
and a one dimensional squared potential barrier where the scattered wave
packets can be recomposed by summing the amplitudes of simultaneously reflected
and transmitted waves.Comment: 32 pages, 5 figures, 1 tabl
Improved filters for gravitational waves from inspiralling compact binaries
The order of the post-Newtonian expansion needed, to extract in a reliable
and accurate manner the fully general relativistic gravitational wave signal
from inspiralling compact binaries, is explored. A class of approximate wave
forms, called P-approximants, is constructed based on the following two inputs:
(a) The introduction of two new energy-type and flux-type functions e(v) and
f(v), respectively, (b) the systematic use of Pade approximation for
constructing successive approximants of e(v) and f(v). The new P-approximants
are not only more effectual (larger overlaps) and more faithful (smaller
biases) than the standard Taylor approximants, but also converge faster and
monotonically. The presently available O(v/c)^5-accurate post-Newtonian results
can be used to construct P-approximate wave forms that provide overlaps with
the exact wave form larger than 96.5% implying that more than 90% of potential
events can be detected with the aid of P-approximants as opposed to a mere
10-15 % that would be detectable using standard post-Newtonian approximants.Comment: Latex ([prd,aps,eqsecnum,epsf]{revtex}), 40 pages including 12
encapsulated figures. (The paper, together with all the figures and tables is
available from ftp://carina.astro.cf.ac.uk/pub/incoming/sathya/dis97.uu
Time-frequency detection of Gravitational Waves
We present a time-frequency method to detect gravitational wave signals in
interferometric data. This robust method can detect signals from poorly modeled
and unmodeled sources. We evaluate the method on simulated data containing
noise and signal components. The noise component approximates initial LIGO
interferometer noise. The signal components have the time and frequency
characteristics postulated by Flanagan and Hughes for binary black hole
coalescence. The signals correspond to binaries with total masses between to and with (optimal filter) signal-to-noise ratios of 7
to 12. The method is implementable in real time, and achieves a coincident
false alarm rate for two detectors 1 per 475 years. At this false
alarm rate, the single detector false dismissal rate for our signal model is as
low as 5.3% at an SNR of 10. We expect to obtain similar or better detection
rates with this method for any signal of similar power that satisfies certain
adiabaticity criteria. Because optimal filtering requires knowledge of the
signal waveform to high precision, we argue that this method is likely to
detect signals that are undetectable by optimal filtering, which is at present
the best developed detection method for transient sources of gravitational
waves.Comment: 24 pages, 5 figures, uses REVTE
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