302 research outputs found
Effective Radii and Color Gradients in Radio Galaxies
We present de Vaucouleurs' effective radii in B and R bands for a sample of
Molonglo Reference Catalogue radio galaxies and a control sample of normal
galaxies. We use the ratio of the scale lengths in the two bands as an
indicator to show that the radio galaxies tend to have excess of blue color in
their inner region much more frequently than the control galaxies. We show that
the scale length ratio is a useful indicator of radial color variation even
when the conventional color gradient is too noisy to serve the purpose.Comment: 11 pages, 4 figures, (LaTeX: aaspp4, epsfig), to appear in ApJL 199
Initial correlations in nonequilibrium Falicov-Kimball model
The Keldysh boundary problem in a nonequilibrium Falicov-Kimball model in
infinite dimensions is studied within the truncated and self-consistent
perturbation theories, and the dynamical mean-field theory. Within the model
the system is started in equilibrium, and later a uniform electric field is
turned on. The Kadanoff-Baym-Wagner equations for the nonequilibrium Green
functions are derived, and numerically solved. The contributions of initial
correlations are studied by monitoring the system evolution. It is found that
the initial correlations are essential for establishing full electron
correlations of the system and independent on the starting time of preparing
the system in equilibrium. By examining the contributions of the initial
correlations to the electric current and the double occupation, we find that
the contributions are small in relation to the total value of those physical
quantities when the interaction is weak, and significantly increase when the
interaction is strong. The neglect of initial correlations may cause artifacts
in the nonequilibrium properties of the system, especially in the strong
interaction case
Hubble Space Telescope faint object camera instrument handbook (Post-COSTAR), version 5.0
The faint object camera (FOC) is a long-focal-ratio, photon-counting device capable of taking high-resolution two-dimensional images of the sky up to 14 by 14 arc seconds squared in size with pixel dimensions as small as 0.014 by 0.014 arc seconds squared in the 1150 to 6500 A wavelength range. Its performance approaches that of an ideal imaging system at low light levels. The FOC is the only instrument on board the Hubble Space Telescope (HST) to fully use the spatial resolution capabilities of the optical telescope assembly (OTA) and is one of the European Space Agency's contributions to the HST program
Calibrating Type Ia Supernovae using the Planetary Nebula Luminosity Function I. Initial Results
We report the results of an [O III] lambda 5007 survey for planetary nebulae
(PN) in five galaxies that were hosts of well-observed Type Ia supernovae: NGC
524, NGC 1316, NGC 1380, NGC 1448 and NGC 4526. The goals of this survey are to
better quantify the zero-point of the maximum magnitude versus decline rate
relation for supernovae Type Ia and to validate the insensitivity of Type Ia
luminosity to parent stellar population using the host galaxy Hubble type as a
surrogate. We detected a total of 45 planetary nebulae candidates in NGC 1316,
44 candidates in NGC 1380, and 94 candidates in NGC 4526. From these data, and
the empirical planetary nebula luminosity function (PNLF), we derive distances
of 17.9 +0.8/-0.9 Mpc, 16.1 +0.8/-1.1 Mpc, and 13.6 +1.3/-1.2 Mpc respectively.
Our derived distance to NGC 4526 has a lower precision due to the likely
presence of Virgo intracluster planetary nebulae in the foreground of this
galaxy. In NGC 524 and NGC 1448 we detected no planetary nebulae candidates
down to the limiting magnitudes of our observations. We present a formalism for
setting realistic distance limits in these two cases, and derive robust lower
limits of 20.9 Mpc and 15.8 Mpc, respectively.
After combining these results with other distances from the PNLF, Cepheid,
and Surface Brightness Fluctuations distance indicators, we calibrate the
optical and near-infrared relations for supernovae Type Ia and we find that the
Hubble constants derived from each of the three methods are broadly consistent,
implying that the properties of supernovae Type Ia do not vary drastically as a
function of stellar population. We determine a preliminary Hubble constant of
H_0 = 77 +/- 3 (random) +/- 5 (systematic) km/s/Mpc for the PNLF, though more
nearby galaxies with high-quality observations are clearly needed.Comment: 25 pages, 12 figures. Accepted for publication by the Astrophysical
Journal. Figures degraded to comply with limit. Full paper is available at:
http://www.as.ysu.edu/~jjfeldme/pnlf_Ia.pd
Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: II. Rotating Versus Non-Rotating Dwarfs
We present spatially-resolved internal kinematics and stellar chemical
abundances for a sample of dwarf elliptical (dE) galaxies in the Virgo Cluster
observed with Keck/ESI. We find that 4 out of 17 dEs have major axis rotation
velocities consistent with rotational flattening, while the remaining dEs have
no detectable major axis rotation. Despite this difference in internal
kinematics, rotating and non-rotating dEs are remarkably similar in terms of
their position in the Fundamental Plane, morphological structure, stellar
populations, and local environment. We present evidence for faint underlying
disks and/or weak substructure in a fraction of both rotating and non-rotating
dEs, but a comparable number of counter-examples exist for both types which
show no evidence of such structure. Absorption-line strengths were determined
based on the Lick/IDS system (Hbeta, Mgb, Fe5270, Fe5335) for the central
region of each galaxy. We find no difference in the line-strength indices, and
hence stellar populations, between rotating and non-rotating dE galaxies. The
best-fitting mean age and metallicity for our 17 dE sample are 5 Gyr and Fe/H =
-0.3 dex, respectively, with rms spreads of 3 Gyr and 0.1 dex. The majority of
dEs are consistent with solar alpha/Fe abundance ratios. By contrast, the
stellar populations of classical elliptical galaxies are, on average, older,
more metal rich, and alpha-enhanced relative to our dE sample. The local
environments of both dEs types appear to be diverse in terms of their proximity
to larger galaxies in real or velocity space within the Virgo Cluster. Thus,
rotating and non-rotating dEs are remarkably similar in terms of their
structure, stellar content, and local environments, presenting a significant
challenge to theoretical models of their formation. (abridged)Comment: 33 pages, 12 figures. To appear in the October 2003 Astronomical
Journal. See http://www.ucolick.org/~mgeha/geha_dE.ps.gz for version with
high resolution figure
NGC 770: A Counter-Rotating Core in a Low-Luminosity Elliptical Galaxy
We present evidence for a counter-rotating core in the low-luminosity (M_B =
-18.2) elliptical galaxy NGC 770 based on internal stellar kinematic data. This
counter-rotating core is unusual as NGC 770 is not the primary galaxy in the
region and it lies in an environment with evidence of on-going tidal
interactions. We discovered the counter-rotating core via single-slit Keck/ESI
echelle spectroscopy; subsequent integral field spectroscopy was obtained with
the Gemini/GMOS IFU. The counter-rotating region has a peak rotation velocity
of 21 km/s as compared to the main galaxy's rotation speed of greater than 45
km/s in the opposite direction. The counter-rotating region extends to a radius
of 4'' (0.6 kpc), slightly smaller than the half-light radius of the galaxy
which is 5.3'' (0.8 kpc) and is confined to a disk whose scale height is less
than 0.8'' (0.1 kpc). We compute an age and metallicity of the inner
counter-rotating region of 3 +/- 0.5 Gyr and [Fe/H] = 0.2 +/- 0.2 dex, based on
Lick absorption-line indices. The lack of other large galaxies in this region
limits possible scenarios for the formation of the counter-rotating core. We
discuss several scenarios and favor one in which NGC 770 accreted a small
gas-rich dwarf galaxy during a very minor merging event. If this scenario is
correct, it represents one of the few known examples of merging between two
dwarf-sized galaxies.Comment: 26 pages, 9 figures. Accepted to AJ. See this
http://www.ociw.edu/~mgeha/geha.ps.gz for version with high resolution
figure
Extented ionized gas emission and kinematics of the compact group galaxies in HCG 16: Signatures of mergers
We report on kinematic observations of Ha emission line from four late-type
galaxies of Hickson Compact Group 16 (H16a,b,c and d) obtained with a scanning
Fabry-Perot interferometer and samplings of 16 km/s and 1". The velocity fields
show kinematic peculiarities for three of the four galaxies: H16b, c and d.
Misalignments between the kinematic and photometric axes of gas and stellar
components (H16b,c,d), double gas systems (H16c) and severe warping of the
kinematic major axis (H16b and c) were some of the peculiarities detected. We
conclude that major merger events have taken place in at least two of the
galaxies group. H16c and d, based on their significant kinematic peculiarities,
their double nuclei and high infrared luminosities. Their Ha gas content is
strongly spatially concentred - H16d contains a peculiar bar-like structure
confined to the inner 1 h^-1 kpc region. These observations are in
agreement with predictions of simulations, namely that the gas flows towards
the galaxy nucleus during mergers, forms bars and fuel the central activity.
Galaxy H16b, and Sb galaxy, also presents some of the kinematic evidences for
past accretion events. Its gas content, however, is very spare, limiting our
ability to find other kinematic merging indicators, if they are present. We
find that isolated mergers, i.e., they show an anormorphous morphology and no
signs of tidal tails. Tidal arms and tails formed during the mergers may have
been stripped by the group potential (Barnes & Hernquist 1992) ar alternatively
they may have never been formed. Our observations suggest that HCG 16 may be a
young compact group in formation throught the merging of close-by objects in a
dense environment.Comment: Accepted for publication in ApJ. 35 pages, 13 figures. tar file
gzipped and uuencode
Stellar Kinematics of the Double Nucleus of M31
We report observations of the double nucleus of M31 with the f/48 long-slit
spectrograph of the HST Faint Object Camera. We obtain a total exposure of
19,000 sec. over 7 orbits, with the 0.063-arcsec-wide slit along the line
between the two brightness peaks (PA 42). A spectrum of Jupiter is used as a
spectral template. The rotation curve is resolved, and reaches a maximum
amplitude of ~250 km/s roughly 0.3 arcsec either side of a rotation center
lying between P1 and P2, 0.16 +/- 0.05 arcsec from the optically fainter P2. We
find the velocity dispersion to be < 250 km/s everywhere except for a narrow
``dispersion spike'', centered 0.06 +/- 0.03 arcsec on the anti-P1 side of P2,
in which sigma peaks at 440 +/- 70 km/s. At much lower confidence, we see local
disturbances to the rotation curve at P1 and P2, and an elevation in sigma at
P1. At very low significance we detect a weak asymmetry in the line-of-sight
velocity distribution opposite to the sense usually encountered. Convolving our
V and sigma profiles to CFHT resolution, we find good agreement with the
results of Kormendy & Bender (1998, preprint), though there is a 20%
discrepancy in the dispersion that cannot be attributed to the dispersion
spike. Our results are not consistent with the location of the maximum
dispersion as found by Bacon et al. We find that the sinking star cluster model
of Emsellem & Combes (1997) does not reproduce either the rotation curve or the
dispersion profile. The eccentric disk model of Tremaine (1995) fares better,
and can be improved somewhat by adjusting the original parameters. However,
detailed modeling will require dynamical models of significantly greater
realism.Comment: 29 pages, Latex, AASTeX v4.0, with 7 eps figures. To appear in The
Astronomical Journal, February 199
Dynamical Models of Elliptical Galaxies in z=0.5 Clusters: I. Data-Model Comparison and Evolution of Galaxy Rotation
We present spatially resolved stellar rotation velocity and velocity
dispersion profiles form Keck/LRIS absorption-line spectra for 25 galaxies,
mostly visually classified ellipticals, in three clusters at z=0.5. We
interpret the kinematical data and HST photometry using oblate axisymmetric
two-integral f(E,Lz) dynamical models based on the Jeans equations. This yields
good fits, provided that the seeing and observational characteristics are
carefully modeled. The fits yield for each galaxy the dynamical M/L and a
measure of the galaxy rotation rate. Paper II addresses the implied M/L
evolution. Here we study the rotation-rate evolution by comparison to a sample
of local elliptical galaxies of similar present-day luminosity. The brightest
galaxies in the sample all rotate too slowly to account for their flattening,
as is also observed at z=0. But the average rotation rate is higher at z=0.5
than locally. This may be due to a higher fraction of misclassified S0 galaxies
(although this effect is insufficient to explain the observed strong evolution
of the cluster S0 fraction with redshift). Alternatively, dry mergers between
early-type galaxies may have decreased the average rotation rate over time. It
is unclear whether such mergers are numerous enough in clusters to explain the
observed trend quantitatively. Disk-disk mergers may affect the comparison
through the so-called progenitor bias, but this cannot explain the direction of
the observed rotation-rate evolution. Additional samples are needed to
constrain possible environmental dependencies and cosmic variance in galaxy
rotation rates. Either way, studies of the internal stellar dynamics of distant
galaxies provide a valuable new approach for exploring galaxy evolution.Comment: ApJ, submitted; 17 pages formatted with emulateap
The Luminosity Profiles of Brightest Cluster Galaxies
(Abridged) We have derived detailed R band luminosity profiles and structural
parameters for a total of 430 brightest cluster galaxies (BCGs), down to a
limiting surface brightness of 24.5 mag/arcsec^2. Light profiles were initially
fitted with a Sersic's R^(1/n) model, but we found that 205 (~48) BCGs require
a double component model to accurately match their light profiles. The best fit
for these 205 galaxies is an inner Sersic model, with indices n~1-7, plus an
outer exponential component.
Thus, we establish the existence of two categories of the BCGs luminosity
profiles: single and double component profiles. We found that double profile
BCGs are brighter ~0.2 mag than single profile BCG. In fact, the
Kolmogorov-Smirnov test applied to these subsamples indicates that they have
different total magnitude distributions, with mean values M_R=-23.8 +/- 0.6 mag
for single profile BCGs and M_R=-24.0 +/- 0.5 mag for double profile BCGs. We
find that partial luminosities for both subsamples are indistinguishable up to
r = 15 kpc, while for r > 20 kpc the luminosities we obtain are on average 0.2
mag brighter for double profile BCGs. This result indicates that extra-light
for double profile BCGs does not come from the inner region but from the outer
regions of these galaxies.
The best fit slope of the Kormendy relation for the whole sample is a = 3.13
+/- 0.04$. However, when fitted separately, single and double profile BCGs show
different slopes: a_(single) = 3.29 +/- 0.06 and a_(double)= 2.79 +/- 0.08.
On the other hand, we did not find differences between these two BCGs
categories when we compared global cluster properties such as the BCG-projected
position relative to the cluster X-ray center emission, X-ray luminosity, or
BCG orientation with respect to the cluster position angle.Comment: August 2011 issue of ApJS, volume 195, 15
http://iopscience.iop.org/0067-0049/195/2/1
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