1,498 research outputs found
Detectability of High Redshift Ellipticals in the Hubble Deep Field
Relatively few intensively star-forming galaxies at redshifts z>2.5 have been
found in the Hubble Deep Field (HDF). This has been interpreted to imply a low
space density of elliptical galaxies at high z, possibly due to a late (z<2.5)
epoch of formation, or to dust obscuration of the ellipticals that are forming
at z~3. I use HST UV (2300 Ang) images of 25 local early-type galaxies to
investigate a third option, that ellipticals formed at z>4.5, and were fading
passively by 2<z<4.5. Present-day early-types are faint and centrally
concentrated in the UV. If ellipticals formed their stars in a short burst at
z>4.5, and have faded passively to their present brightnesses at UV
wavelengths, they would generally be below the HDF detection limits in any of
its bands at z>2.5. Quiescent z ~ 3 ellipticals, if they exist, should turn up
in sufficiently deep IR images.Comment: AAS LaTex, 11 pages, 1 table, 1 figure, some corrections and
clarifications, accepted for publication in ApJ
A revised Cepheid distance to NGC 4258 and a test of the distance scale
In a previous paper (Maoz et al. 1999), we reported a Hubble Space Telescope
(HST) Cepheid distance to the galaxy NGC 4258 obtained using the calibrations
and methods then standard for the Key Project on the Extragalactic Distance
Scale. Here, we reevaluate the Cepheid distance using the revised Key Project
procedures described in Freedman et al. (2001). These revisions alter the zero
points and slopes of the Cepheid Period-Luminosity (P-L) relations derived at
the Large Magellanic Cloud (LMC), the calibration of the HST WFPC2 camera, and
the treatment of metallicity differences. We also provide herein full
information on the Cepheids described in Maoz et al. 1999. Using the refined
Key Project techniques and calibrations, we determine the distance modulus of
NGC 4258 to be 29.47 +/- 0.09 mag (unique to this determination) +/- 0.15 mag
(systematic uncertainties in Key Project distances), corresponding to a metric
distance of 7.8 +/- 0.3 +/- 0.5 Mpc and 1.2 sigma from the maser distance of
7.2 +/- 0.5 Mpc. We also test the alternative Cepheid P-L relations of Feast
(1999), which yield more discrepant results. Additionally, we place weak limits
upon the distance to the LMC and upon the effect of metallicity in Cepheid
distance determinations.Comment: 26 pages in emulateapj5 format, including 6 figures and 5 tables.
Accepted for publication in the Astrophysical Journa
Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
We present improved black hole masses for 35 active galactic nuclei (AGNs)
based on a complete and consistent reanalysis of broad emission-line
reverberation-mapping data. From objects with multiple line measurements, we
find that the highest precision measure of the virial product is obtained by
using the cross-correlation function centroid (as opposed to the
cross-correlation function peak) for the time delay and the line dispersion (as
opposed to full width half maximum) for the line width and by measuring the
line width in the variable part of the spectrum. Accurate line-width
measurement depends critically on avoiding contaminating features, in
particular the narrow components of the emission lines. We find that the
precision (or random component of the error) of reverberation-based black hole
mass measurements is typically around 30%, comparable to the precision attained
in measurement of black hole masses in quiescent galaxies by gas or stellar
dynamical methods. Based on results presented in a companion paper by Onken et
al., we provide a zero-point calibration for the reverberation-based black hole
mass scale by using the relationship between black hole mass and host-galaxy
bulge velocity dispersion. The scatter around this relationship implies that
the typical systematic uncertainties in reverberation-based black hole masses
are smaller than a factor of three. We present a preliminary version of a
mass-luminosity relationship that is much better defined than any previous
attempt. Scatter about the mass-luminosity relationship for these AGNs appears
to be real and could be correlated with either Eddington ratio or object
inclination.Comment: 61 pages, including 8 Tables and 16 Figures. Accepted for publication
in The Astrophysical Journa
Reverberation Mapping and the Physics of Active Galactic Nuclei
Reverberation-mapping campaigns have revolutionized our understanding of AGN.
They have allowed the direct determination of the broad-line region size,
enabled mapping of the gas distribution around the central black hole, and are
starting to resolve the continuum source structure. This review describes the
recent and successful campaigns of the International AGN Watch consortium,
outlines the theoretical background of reverberation mapping and the
calculation of transfer functions, and addresses the fundamental difficulties
of such experiments. It shows that such large-scale experiments have resulted
in a ``new BLR'' which is considerably different from the one we knew just ten
years ago. We discuss in some detail the more important new results, including
the luminosity-size-mass relationship for AGN, and suggest ways to proceed in
the near future.Comment: Review article to appear in Astronomical Time Series, Proceedings of
the Wise Observatory 25th Ann. Symposium. 24 pages including 7 figure
Does It Matter Whether You or Your Brain Did It? An Empirical Investigation of the Influence of the Double Subject Fallacy on Moral Responsibility Judgments
Despite progress in cognitive neuroscience, we are still far from understanding the relations between the brain and the conscious self. We previously suggested that some neuroscientific texts that attempt to clarify these relations may in fact make them more difficult to understand. Such textsâranging from popular science to high-impact scientific publicationsâposition the brain and the conscious self as two independent, interacting subjects, capable of possessing opposite psychological states. We termed such writing âDouble Subject Fallacyâ (DSF). We further suggested that such DSF language, besides being conceptually confusing and reflecting dualistic intuitions, might affect peopleâs conceptions of moral responsibility, lessening the perception of guilt over actions. Here, we empirically investigated this proposition with a series of three experiments (pilot and two preregistered replications). Subjects were presented with moral scenarios where the defendant was either (1) clearly guilty, (2) ambiguous, or (3) clearly innocent while the accompanying neuroscientific evidence about the defendant was presented using DSF or non-DSF language. Subjects were instructed to rate the defendantâs guilt in all experiments. Subjects rated the defendant in the clearly guilty scenario as guiltier than in the two other scenarios and the defendant in the ambiguously described scenario as guiltier than in the innocent scenario, as expected. In Experiment 1 (N = 609), an effect was further found for DSF language in the expected direction: subjects rated the defendant less guilty when the neuroscientific evidence was described using DSF language, across all levels of culpability. However, this effect did not replicate in Experiment 2 (N = 1794), which focused on different moral scenario, nor in Experiment 3 (N = 1810), which was an exact replication of Experiment 1. Bayesian analyses yielded strong evidence against the existence of an effect of DSF language on the perception of guilt. Our results thus challenge the claim that DSF language affects subjectsâ moral judgments. They further demonstrate the importance of good scientific practice, including preregistration andâmost criticallyâreplication, to avoid reaching erroneous conclusions based on false-positive results
Minisuperspace Quantization of "Bubbling AdS" and Free Fermion Droplets
We quantize the space of 1/2 BPS configurations of Type IIB SUGRA found by
Lin, Lunin and Maldacena (hep-th/0409174), directly in supergravity. We use the
Crnkovic-Witten-Zuckerman covariant quantization method to write down the
expression for the symplectic structure on this entire space of solutions. We
find the symplectic form explicitly around AdS_5 x S^5 and obtain a U(1)
Kac-Moody algebra, in precise agreement with the quantization of a system of N
free fermions in a harmonic oscillator potential, as expected from AdS/CFT. As
a cross check, we also perform the quantization around AdS_5 x S^5 by another
method, using the known spectrum of physical perturbations around this
background and find precise agreement with our previous calculation.Comment: 22 Pages + 2 Appendices, JHEP3; v3: explanation of factor 2 mismatch
added, references reordered, published versio
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