10,505 research outputs found
Spatially resolved spectroscopy of Coma cluster early-type galaxies IV. Completing the dataset
The long-slit spectra obtained along the minor axis, offset major axis and
diagonal axis are presented for 12 E and S0 galaxies of the Coma cluster drawn
from a magnitude-limited sample studied before. The rotation curves, velocity
dispersion profiles and the H_3 and H_4 coefficients of the Hermite
decomposition of the line of sight velocity distribution are derived. The
radial profiles of the Hbeta, Mg, and Fe line strength indices are measured
too. In addition, the surface photometry of the central regions of a subsample
of 4 galaxies recently obtained with Hubble Space Telescope is presented. The
data will be used to construct dynamical models of the galaxies and study their
stellar populations.Comment: 40 pages, 7 figures, 6 tables. Accepted for publication in ApJ
Homogeneity of Stellar Populations in Early-Type Galaxies with Different X-ray Properties
We have found the stellar populations of early-type galaxies are homogeneous
with no significant difference in color or Mg2 index, despite the dichotomy
between X-ray extended early-type galaxies and X-ray compact ones. Since the
X-ray properties reflect the potential gravitational structure and hence the
process of galaxy formation, the homogeneity of the stellar populations implies
that the formation of stars in early-type galaxies predat es the epoch when the
dichotomy of the potential structure was established.Comment: 6 pages, 5 figures, accepted for publication in Ap
HI Detection in two Dwarf S0 Galaxies in Nearby Groups: ESO384-016 and NGC 59
An \hi survey of 10 dE/dS0 galaxies in the nearby Sculptor and Centaurus A
groups was made using the Australia Telescope Compact Array (ATCA). The
observed galaxies have accurate distances derived by Jerjen et al (1998; 2000b)
using the surface brightness fluctuation technique. Their absolute magnitudes
are in the range . Only two of the ten galaxies were
detected at our detection limit ( \msol for the Centaurus
group and \msol for the Sculptor group), the two dS0
galaxies ESO384-016 in the Centaurus A Group and NGC 59 in the Sculptor Group,
with \hi masses of \msol and \msol respectively. Those two detections were confirmed using the Green
Bank Telescope. These small \hi reservoirs could fuel future generations of low
level star formation and could explain the bluer colors seen at the center of
the detected galaxies. Similarly to what is seen with the Virgo dEs, the two
objects with \hi appear to be on the outskirt of the groups.Comment: 25 pages (11 figures), accepted by A
On the eigenproblems of PT-symmetric oscillators
We consider the non-Hermitian Hamiltonian H=
-\frac{d^2}{dx^2}+P(x^2)-(ix)^{2n+1} on the real line, where P(x) is a
polynomial of degree at most n \geq 1 with all nonnegative real coefficients
(possibly P\equiv 0). It is proved that the eigenvalues \lambda must be in the
sector | arg \lambda | \leq \frac{\pi}{2n+3}. Also for the case
H=-\frac{d^2}{dx^2}-(ix)^3, we establish a zero-free region of the
eigenfunction u and its derivative u^\prime and we find some other interesting
properties of eigenfunctions.Comment: 21pages, 9 figure
Green's function formalism for spin transport in metal-insulator-metal heterostructures
We develop a Green's function formalism for spin transport through
heterostructures that contain metallic leads and insulating ferromagnets. While
this formalism in principle allows for the inclusion of various magnonic
interactions, we focus on Gilbert damping. As an application, we consider
ballistic spin transport by exchange magnons in a metal-insulator-metal
heterostructure with and without disorder. For the former case, we show that
the interplay between disorder and Gilbert damping leads to spin current
fluctuations. For the case without disorder, we obtain the dependence of the
transmitted spin current on the thickness of the ferromagnet. Moreover, we show
that the results of the Green's function formalism agree in the clean and
continuum limit with those obtained from the linearized stochastic
Landau-Lifshitz-Gilbert equation. The developed Green's function formalism is a
natural starting point for numerical studies of magnon transport in
heterostructures that contain normal metals and magnetic insulators.Comment: 13 pages, 8 figure
Harmonic oscillator well with a screened Coulombic core is quasi-exactly solvable
In the quantization scheme which weakens the hermiticity of a Hamiltonian to
its mere PT invariance the superposition V(x) = x^2+ Ze^2/x of the harmonic and
Coulomb potentials is defined at the purely imaginary effective charges
(Ze^2=if) and regularized by a purely imaginary shift of x. This model is
quasi-exactly solvable: We show that at each excited, (N+1)-st
harmonic-oscillator energy E=2N+3 there exists not only the well known harmonic
oscillator bound state (at the vanishing charge f=0) but also a normalizable
(N+1)-plet of the further elementary Sturmian eigenstates \psi_n(x) at
eigencharges f=f_n > 0, n = 0, 1, ..., N. Beyond the first few smallest
multiplicities N we recommend their perturbative construction.Comment: 13 pages, Latex file, to appear in J. Phys. A: Math. Ge
Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 from the Nuclear Stellar Dynamics
We analyze the nuclear stellar dynamics of the SB0 galaxy NGC 1023, utilizing
observational data both from the Space Telescope Imaging Spectrograph aboard
the Hubble Space Telescope and from the ground. The stellar kinematics measured
from these long-slit spectra show rapid rotation (V = 70 km/s at a distance of
0.1 arcsec = 4.9 pc from the nucleus) and increasing velocity dispersion toward
the nucleus (where sigma = 295 +/- 30 km/s). We model the observed stellar
kinematics assuming an axisymmetric mass distribution with both two and three
integrals of motion. Both modeling techniques point to the presence of a
central dark compact mass (which presumably is a supermassive black hole) with
confidence > 99%. The isotropic two-integral models yield a best-fitting black
hole mass of (6.0 +/- 1.4) x 10^7 M_sun and mass-to-light ratio (M/L_V) of 5.38
+/- 0.08, and the goodness-of-fit (chi^2) is insensitive to reasonable values
for the galaxy's inclination. The three-integral models, which
non-parametrically fit the observed line-of-sight velocity distribution as a
function of position in the galaxy, suggest a black hole mass of (3.9 +/- 0.4)
x 10^7 M_sun and M/L_V of 5.56 +/- 0.02 (internal errors), and the edge-on
models are vastly superior fits over models at other inclinations. The internal
dynamics in NGC 1023 as suggested by our best-fit three-integral model shows
that the velocity distribution function at the nucleus is tangentially
anisotropic, suggesting the presence of a nuclear stellar disk. The nuclear
line of sight velocity distribution has enhanced wings at velocities >= 600
km/s from systemic, suggesting that perhaps we have detected a group of stars
very close to the central dark mass.Comment: 21 pages, 12 figures, accepted in the Astrophysical Journa
Kinematic Structure of Merger Remnants
We use numerical simulations to study the kinematic structure of remnants
formed from mergers of equal-mass disk galaxies. In particular, we show that
remnants of dissipational mergers, which include the radiative cooling of gas,
star formation, feedback from supernovae, and the growth of supermassive black
holes, are smaller, rounder, have, on average, a larger central velocity
dispersion, and show significant rotation compared to remnants of
dissipationless mergers. The increased rotation speed of dissipational remnants
owes its origin to star formation that occurs in the central regions during the
galaxy merger. We have further quantified the anisotropy, three-dimensional
shape, minor axis rotation, and isophotal shape of each merger remnant, finding
that dissipational remnants are more isotropic, closer to oblate, have the
majority of their rotation along their major axis, and are more disky than
dissipationless remnants. Individual remnants display a wide variety of
kinematic properties. A large fraction of the dissipational remnants are oblate
isotropic rotators. Many dissipational, and all of the dissipationless, are
slowly rotating and anisotropic. The remnants of gas-rich major mergers can
well-reproduce the observed distribution of projected ellipticities, rotation
parameter (V/\sigma)*, kinematic misalignments, Psi, and isophotal shapes. The
dissipationless remnants are a poor match to this data. Our results support the
merger hypothesis for the origin of low-luminosity elliptical galaxies provided
that the progenitor disks are sufficiently gas-rich, however our remnants are a
poor match to the bright ellipticals that are slowly rotating and uniformly
boxy.Comment: 22 pages, 17 figures, accepted to Ap
Ellipticals with Kinematically-Distinct Cores: (V-I) Color Images with WFPC2
We have analysed HST/WFPC2 F555W and F814W images for fifteen elliptical
galaxies with kinematically-distinct cores. For each of them we have derived
surface brightness and isophotal parameter profiles in the two bands, color
maps, and radial profiles in (V-I). We have detected photometric evidence for
faint stellar disks, on scales of a few tens to a few arcseconds, in seven
galaxies, namely NGC 1427, 1439, 1700, 4365, 4406, 4494 and 5322. In NGC 1700,
the isophotes are slightly boxy at the scale of the counter-rotating component,
and disky at larger radii. We find no difference in (V-I) color greater than
0.02 mag between these disks and the surrounding galactic regions. Hence the
stellar populations in the kinematically distinct cores are not strongly
deviant from the population of the main body. For one galaxy, NGC 4365, the
innermost region is bluer than the surrounding regions. This area extends to
about 15pc, and contains a luminosity of 2.5x10^6 L. If interpreted as
a stellar population effect, an age difference of 3-4 Gyrs, or an
variation of about 0.2 dex, is derived. The nuclear intensity profiles
show a large variety: some galaxies have steep cusp profiles, others have
shallow cusps and a ``break radius''. The nuclear cusps of galaxies with
kinematically-distinct cores follow the same trends as the nuclei of normal
galaxies. We have not been able to identify a unique, qualifying feature in the
WFPC2 images which distinguish the galaxies with kinematically distinct cores
from the kinematically normal cores. [shortened]Comment: 56 pages, latex, 17 figures; figure 1 available upon request; ApJ,
481 in pres
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