643 research outputs found
Observation of the Ettingshausen effect in quantum Hall systems
Evidence of the Ettingshausen effect in the breakdown regime of the integer
quantum Hall effect has been observed in a GaAs/AlGaAs two-dimensional electron
system. Resistance of micro Hall bars attached to both edges of a current
channel shows remarkable asymmetric behaviors which indicate an electron
temperature difference between the edges. The sign of the difference depends on
the direction of the electric current and the polarity of the magnetic field.
The results are consistent with the recent theory of Akera.Comment: 4 pages, 6 figures, submitted to Phys. Rev.
Rigid Limit in N=2 Supergravity and Weak-Gravity Conjecture
We analyze the coupled N=2 supergravity and Yang-Mills system using
holomorphy, near the rigid limit where the former decouples from the latter. We
find that there appears generically a new mass scale around g M_{pl} where g is
the gauge coupling constant and M_{pl} is the Planck scale. This is in accord
with the weak-gravity conjecture proposed recently. We also study the scale
dependence of the gauge theory prepotential from its embedding into
supergravity.Comment: 17 pages, minor correction
Superconformal Algebras and Mock Theta Functions
It is known that characters of BPS representations of extended superconformal
algebras do not have good modular properties due to extra singular vectors
coming from the BPS condition. In order to improve their modular properties we
apply the method of Zwegers which has recently been developed to analyze
modular properties of mock theta functions. We consider the case of N=4
superconformal algebra at general levels and obtain the decomposition of
characters of BPS representations into a sum of simple Jacobi forms and an
infinite series of non-BPS representations.
We apply our method to study elliptic genera of hyper-Kahler manifolds in
higher dimensions. In particular we determine the elliptic genera in the case
of complex 4 dimensions of the Hilbert scheme of points on K3 surfaces K^{[2]}
and complex tori A^{[[3]]}.Comment: 28 page
The Halpha Luminosity Function of the Galaxy Cluster Abell 521 at z = 0.25
We present an optical multicolor-imaging study of the galaxy cluster Abell
521 at , using Suprime-Cam on the Subaru Telescope, covering an area
of arcmin ( Mpc at ). Our imaging data taken with both a narrow-band filter,
(\AA and \AA), and broad-band filters,
, and allow us to find 165 H
emitters. We obtain the H luminosity function (LF) for the cluster
galaxies within 2 Mpc; the Schechter parameters are ,
Mpc, and erg s. Although the faint end slope, , is consistent with
that of the local cluster H LFs, the characteristic luminosity,
, is about 6 times (or mag) brighter. This strong
evolution implies that Abell 521 contains more active star-forming galaxies
than the local clusters, being consistent with the observed Butcher-Oemler
effect. However, the bright of Abell 521 may be, at least in part,
due to the dynamical condition of this cluster.Comment: 21 pages, 7 figures, ApJ, Part 1, in pres
The HI content of star-forming galaxies at z = 0.24
We use observations from the Giant Metrewave Radio Telescope (GMRT) to
measure the atomic hydrogen gas content of star-forming galaxies at z = 0.24
(i.e. a look-backtime of ~3 Gyr). The sample of galaxies studied were selected
from Halpha-emitting field galaxies detected in a narrow-band imaging survey
with the Subaru Telescope. The Anglo-Australian Telescope was used to obtain
precise optical redshifts for these galaxies. We then coadded the HI 21 cm
emission signal for all the galaxies within the GMRT spectral line data cube.
From the coadded signal of 121 galaxies, we measure an average atomic
hydrogen gas mass of (2.26 +- 0.90)*10^9 solar masses. We translate this HI
signal into a cosmic density of neutral gas at z = 0.24 of Omega_gas = (0.91 +-
0.42)*10^-3. This is the current highest redshift at which Omega_gas has been
constrained from 21 cm emission and our value is consistent with that estimated
from damped Lyman-alpha systems around this redshift. We also find that the
correlations between the Halpha luminosity and the radio continuum luminosity
and between the star formation rate and the HI gas content in star-forming
galaxies at z = 0.24 are consistent with the correlations found at z = 0. These
two results suggest that the star formation mechanisms in field galaxies ~3 Gyr
ago were not substantially different from the present, even though the star
formation rate is 3 times higher.Comment: 11 pages, contains 9 figures and 1 table. Accepted for publishing in
MNRAS 2007 January 22. Received 2007 January 22; in original form 2006
November 3
Anti-correlation between the mass of a supermassive black hole and the mass accretion rate in type I ultraluminous infrared galaxies and nearby QSOs
We discovered a significant anti-correlation between the mass of a
supermassive black hole (SMBH), , and the luminosity ratio of
infrared to active galactic nuclei (AGN) Eddington luminosity, , over four orders of magnitude for ultraluminous infrared
galaxies with type I Seyfert nuclei (type I ULIRGs) and nearby QSOs. This
anti-correlation ( vs. ) can be interpreted
as the anti-correlation between the mass of a SMBH and the rate of mass
accretion onto a SMBH normalized by the AGN Eddington rate, . In other words, the mass accretion rate is not proportional to that of the central BH mass. Thus, this
anti-correlation indicates that BH growth is determined by the external mass
supply process, and not the AGN Eddington-limited mechanism. Moreover, we found
an interesting tendency for type I ULIRGs to favor a super-Eddington accretion
flow, whereas QSOs tended to show a sub-Eddington flow. On the basis of our
findings, we suggest that a central SMBH grows by changing its mass accretion
rate from super-Eddington to sub-Eddington. According to a coevolution scenario
of ULIRGs and QSOs based on the radiation drag process, it has been predicted
that a self-gravitating massive torus, whose mass is larger than a central BH,
exists in the early phase of BH growth (type I ULIRG phase) but not in the
final phase of BH growth (QSO phase). At the same time, if one considers the
mass accretion rate onto a central SMBH via a turbulent viscosity, the
anti-correlation ( vs. ) is well explained
by the positive correlation between the mass accretion rate
and the mass ratio of a massive torus to a SMBH.Comment: 29 pages, 4 figures, accepted for publication in Ap
Gas Metallicity of Narrow-Line Regions in Narrow-Line Seyfert 1 Galaxies and Broad-Line Seyfert 1 Galaxies
We investigate gas metallicity of narrow-line regions in narrow-line Seyfert
1 galaxies (NLS1s) and broad-line ones (BLS1s) in order to examine whether or
not there is a difference in the gas metallicity between the two populations of
Seyfert 1 galaxies. We apply two methods to study this issue. One is to use the
emission-line flux ratio of [N II]6583/H_alpha in combination with some other
optical emission-line flux ratios. This method, which has been often applied to
Seyfert 2 galaxies, suggests that the gas metallicity of narrow-line regions is
indistinguishable or possibly higher in BLS1s than in NLS1s. On the contrary,
the other method in which only forbidden emission-line fluxes are used results
in that NLS1s tend to possess metal-richer gas in the narrow-line regions than
BLS1s. We point out that this inconsistency may be owing to the contamination
of the broad component of permitted lines into the narrow component of ones in
the first method. Since the results derived by using only forbidden
emission-line fluxes do not suffer from any uncertainty of the fitting function
for the broad component of Balmer lines, the results from this method are more
reliable than those derived by using permitted lines. We thus conclude that the
gas metallicity of narrow-line regions tends to be higher in NLS1s than in
BLS1s.Comment: 12 pages including 10 figures, to appear in The Astrophysical Journa
Static black holes with a negative cosmological constant: Deformed horizon and anti-de Sitter boundaries
Using perturbative techniques, we investigate the existence and properties of
a new static solution for the Einstein equation with a negative cosmological
constant, which we call the deformed black hole. We derive a solution for a
static and axisymmetric perturbation of the Schwarzschild-anti-de Sitter black
hole that is regular in the range from the horizon to spacelike infinity. The
key result is that this perturbation simultaneously deforms the two boundary
surfaces--i.e., both the horizon and spacelike two-surface at infinity. Then we
discuss the Abbott-Deser mass and the Ashtekar-Magnon one for the deformed
black hole, and according to the Ashtekar-Magnon definition, we construct the
thermodynamic first law of the deformed black hole. The first law has a
correction term which can be interpreted as the work term that is necessary for
the deformation of the boundary surfaces. Because the work term is negative,
the horizon area of the deformed black hole becomes larger than that of the
Schwarzschild-anti-de Sitter black hole, if compared under the same mass,
indicating that the quasistatic deformation of the Schwarzschild-anti-de Sitter
black hole may be compatible with the thermodynamic second law (i.e., the area
theorem).Comment: 31 pages, 5 figures, one reference added, to be published in PR
Extended High-Ionization Nuclear Emission-Line Region in the Seyfert Galaxy NGC 4051
We present an optical spectroscopic analysis of the well-known Seyfert galaxy
NGC 4051. The high-ionization nuclear emission-line region (HINER) traced by
[Fe X]6374 is found to be spatially extended to a radius of 3a rcseconds (150
pc) west and southwest from the nucleus; NGC 4051 is the third example which
has an extended HINER.
The nuclear spectrum shows that the flux of [Fe X]6374 is stronger than that
of [Fe VII] 6087 in our observation. This property cannot be interpreted in
terms of a simple one-zone photoionization model.
In order to understand what happens in the nuclear region in NGC 4051, we
investigate the physical condition of the nuclear emission-line region in
detail using new photoionization models in which the following three
emission-line components are taken into account; (1) optically thick,
ionization-bounded clouds; (2) optically thin, matter-bounded clouds; and (3) a
contamination component which emits H and H lines. Here the
observed extended HINER is considered to be associated with the low-density,
matter-bounded clouds. Candidates of the contamination component are either the
broad-line region (BLR) or nuclear star forming regions or both. The complexity
of the excitation condition found in NGC 4051 can be consistently understood if
we take account of these contamination components.Comment: 16 pages, including figures. To Appear in the Astronomical Journal
February 2000 Issu
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