1,153 research outputs found
The Rewards of Patience: An 822 Day Time Delay in the Gravitational Lens SDSS J1004+4112
We present 107 new epochs of optical monitoring data for the four brightest
images of the gravitational lens SDSS J1004+4112 observed between October 2006
and June 2007. Combining this data with the previously obtained light curves,
we determine the time delays between images A, B and C. We confirm our previous
measurement finding that A leads B by dt_BA=40.6+-1.8 days, and find that image
C leads image A by dt_CA=821.6+-2.1 days. The lower limit on the remaining
delay is that image D lags image A by dt_AD>1250 days. Based on the
microlensing of images A and B we estimate that the accretion disk size at a
rest wavelength of 2300 angstrom is 10^{14.8+-0.3} cm for a disk inclination of
cos{i}=1/2, which is consistent with the microlensing disk size-black hole mass
correlation function given our estimate of the black hole mass from the MgII
line width of logM_BH/M_sun=8.44+-0.14. The long delays allow us to fill in the
seasonal gaps and assemble a continuous, densely sampled light curve spanning
5.7 years whose variability implies a structure function with a logarithmic
slope of gamma = 0.35+-0.02. As C is the leading image, sharp features in the C
light curve can be intensively studied 2.3 years later in the A/B pair,
potentially allowing detailed reverberation mapping studies of a quasar at
minimal cost.Comment: Submitted to ApJ, 12 pages, 3 figure
Alignment of galaxies relative to their local environment in SDSS-DR8
We study the alignment of galaxies relative to their local environment in
SDSS-DR8 and, using these data, we discuss evolution scenarios for different
types of galaxies. We defined a vector field of the direction of anisotropy of
the local environment of galaxies. We summed the unit direction vectors of all
close neighbours of a given galaxy in a particular way to estimate this field.
We found the alignment angles between the spin axes of disc galaxies, or the
minor axes of elliptical galaxies, and the direction of anisotropy. The
distributions of cosines of these angles are compared to the random
distributions to analyse the alignment of galaxies. Sab galaxies show
perpendicular alignment relative to the direction of anisotropy in a sparse
environment, for single galaxies and galaxies of low luminosity. Most of the
parallel alignment of Scd galaxies comes from dense regions, from 2...3 member
groups and from galaxies with low luminosity. The perpendicular alignment of S0
galaxies does not depend strongly on environmental density nor luminosity; it
is detected for single and 2...3 member group galaxies, and for main galaxies
of 4...10 member groups. The perpendicular alignment of elliptical galaxies is
clearly detected for single galaxies and for members of < 11 member groups; the
alignment increases with environmental density and luminosity. We confirm the
existence of fossil tidally induced alignment of Sab galaxies at low z. The
alignment of Scd galaxies can be explained via the infall of matter to
filaments. S0 galaxies may have encountered relatively massive mergers along
the direction of anisotropy. Major mergers along this direction can explain the
alignment of elliptical galaxies. Less massive, but repeated mergers are
possibly responsible for the formation of elliptical galaxies in sparser areas
and for less luminous elliptical galaxies.Comment: 15 pages, 15 figures, accepted for publication in A&
Galaxy filaments as pearl necklaces
Context. Galaxies in the Universe form chains (filaments) that connect groups
and clusters of galaxies. The filamentary network includes nearly half of the
galaxies and is visually the most striking feature in cosmological maps.
Aims. We study the distribution of galaxies along the filamentary network,
trying to find specific patterns and regularities.
Methods. Galaxy filaments are defined by the Bisous model, a marked point
process with interactions. We use the two-point correlation function and the
Rayleigh Z-squared statistic to study how galaxies and galaxy groups are
distributed along the filaments.
Results. We show that galaxies and groups are not uniformly distributed along
filaments, but tend to form a regular pattern. The characteristic length of the
pattern is around 7 Mpc/h. A slightly smaller characteristic length 4 Mpc/h can
also be found, using the Z-squared statistic.
Conclusions. We find that galaxy filaments in the Universe are like pearl
necklaces, where the pearls are galaxy groups distributed more or less
regularly along the filaments. We propose that this well defined characteristic
scale could be used to test various cosmological models and to probe
environmental effects on the formation and evolution of galaxies.Comment: 8 pages, 9 figures, 1 table, accepted for publication in A&
Hourly Variability in Q0957+561
We have continued our effort to re-reduce archival Q0957+561 brightness
monitoring data and present results for 1629 R-band images using the methods
for galaxy subtraction and seeing correction reported previously. The new
dataset comes from 4 observing runs, several nights apiece, with sampling of
typically 5 minutes, which allows the first measurement of the structure
function for variations in the R-band from timescales of hours to years.
Comparison of our reductions to previous reductions of the same data, and to
r-band photometry produced at Apache Point Observatory shows good overall
agreement. Two of the data runs, separated by 417 days, permit a sharpened
value for the time delay of 417.4 days, valid only if the time delay is close
to the now-fashionable 417-day value; our data do not constrain a delay if it
is more than three days from this 417-day estimate. Our present results show no
unambiguous signature of the daily microlensing, though a suggestive feature is
found in the data. Both time delay measurement and microlensing searches suffer
from from the lack of sampling at half-day offsets, inevitable at a single
observatory, hence the need for round-the-clock monitoring with participation
by multiple observatories.Comment: AASTeX 4.0 preprint style, 21 pages, 8 EPS figure
Characterizing neuromorphologic alterations with additive shape functionals
The complexity of a neuronal cell shape is known to be related to its
function. Specifically, among other indicators, a decreased complexity in the
dendritic trees of cortical pyramidal neurons has been associated with mental
retardation. In this paper we develop a procedure to address the
characterization of morphological changes induced in cultured neurons by
over-expressing a gene involved in mental retardation. Measures associated with
the multiscale connectivity, an additive image functional, are found to give a
reasonable separation criterion between two categories of cells. One category
consists of a control group and two transfected groups of neurons, and the
other, a class of cat ganglionary cells. The reported framework also identified
a trend towards lower complexity in one of the transfected groups. Such results
establish the suggested measures as an effective descriptors of cell shape
The use of a modular titanium baseplate with a press-fit keel implanted with a surface cementing technique for primary total knee arthroplasty
pre-printLittle data exists regarding outcomes following TKA performed with surface-cementation for the fixation of modular tibial baseplates with press-fit keels.Thus, we retrospectively reviewed the clinical and radiographic outcomes of 439 consecutive primary TKAs performed with surface cemented tibial components. There were 290 female patients and 149 male patients with average age of 62 years (range 30-84). Two tibial components were revised for aseptic loosening (0.5%) and four tibial components (0.9%) were removed to improve instability ( = 2) or malalignment ( = 2). Complications included 13 deep infections treated with 2-stage revision (12) and fusion (1). These results support the surface cement technique with a modular grit-blasted titanium surface and cruciform stem during primary TKA
A Two-Year Time Delay for the Lensed Quasar SDSS J1029+2623
We present 279 epochs of optical monitoring data spanning 5.4 years from 2007
January to 2012 June for the largest image separation (22.6 arcsec)
gravitationally lensed quasar, SDSS J1029+2623. We find that image A leads the
images B and C by dt_AB = (744+-10) days (90% confidence); the uncertainty
includes both statistical uncertainties and systematic differences due to the
choice of models. With only a ~1% fractional error, the interpretation of the
delay is limited primarily by cosmic variance due to fluctuations in the mean
line-of-sight density. We cannot separate the fainter image C from image B, but
since image C trails image B by only 2-3 days in all models, the estimate of
the time delay between image A and B is little affected by combining the fluxes
of images B and C. There is weak evidence for a low level of microlensing,
perhaps created by the small galaxy responsible for the flux ratio anomaly in
this system. Interpreting the delay depends on better constraining the shape of
the gravitational potential using the lensed host galaxy, other lensed arcs and
the structure of the X-ray emission.Comment: Accepted for publication in The Astrophysical Journal. Changes in
response to referee's comment
Long-term variation in distribution of sunspot groups
We studied the relation between the distribution of sunspot groups and the
Gleissberg cycle. As the magnetic field is related to the area of the sunspot
groups, we used area-weighted sunspot group data. On the one hand, we confirm
the previously reported long-term cyclic behaviour of the sum of the northern
and southern sunspot group mean latitudes, although we found a somewhat longer
period (P~104 years). We introduced the difference between the ensemble average
area of sunspot groups for the two hemispheres, which turns out to show similar
behaviour. We also investigated a further aspect of the Gleissberg cycle where
while in the 19th century the consecutive Schwabe cycles are sharply separated
from each other, one century later the cycles overlap each other more and more.Comment: 4 page
The white dwarf in dwarf nova SDSS J080434.20+510349.2: Entering the instability strip?
SDSS J080434.20+510349.2 is the WZ type binary that displayed rare outburst
in 2006 (Pavlenko et al., 2007). During the long-lasting tail of the late stage
of the outburst binary shown the two-humped or four-humped profile of the
orbital light modulation. The amplitude of orbital light curve decreased while
the mean brightness decreased, more over that occurred 10 times faster
during the fast outburst decline in respect to the late quiet state of slow
outburst fading. There were no white dwarf pulsations detected neither 1 - 1.5
months prior to the outburst nor in 1.5 - 2 months after the 2006 outburst in
this system. However the strong non-radial pulsations with period 12.6 minutes
and mean amplitude of 0.05^m were first detected in V band with 2.6-m Shajn
mirror telescope of the Crimean astrophysical observatory in ~ 8 months after
the outburst. The evolution of pulsations over two years in 2006 - 2008 is
considered. It is supposed that pulsations first appeared when the cooling
white dwarf (after the outburst) entered the instability strip although the
possibility of temporary lack of pulsations at some occasions also could not be
excluded.Comment: Submitted to Proceedings of 16th European White Dwarf Workshop
(EUROWD08
A Determination of H_0 with the CLASS Gravitational Lens B1608+656: III. A Significant Improvement in the Precision of the Time Delay Measurements
The gravitational lens CLASS B1608+656 is the only four-image lens system for
which all three independent time delays have been measured. This makes the
system an excellent candidate for a high-quality determination of H_0 at
cosmological distances. However, the original measurements of the time delays
had large (12-20%) uncertainties, due to the low level of variability of the
background source during the monitoring campaign. In this paper, we present
results from two additional VLA monitoring campaigns. In contrast to the ~5%
variations seen during the first season of monitoring, the source flux density
changed by 25-30% in each of the subsequent two seasons. We analyzed the
combined data set from all three seasons of monitoring to improve significantly
the precision of the time delay measurements; the delays are consistent with
those found in the original measurements, but the uncertainties have decreased
by factors of two to three. We combined the delays with revised isothermal mass
models to derive a measurement of H_0. Depending on the positions of the galaxy
centroids, which vary by up to 0.1 arcsec in HST images obtained with different
filters, we obtain H_0 = 61-65 km/s/Mpc, for (Omega_M,Omega_L) = (0.3,0.7). The
value of H_0 decreases by 6% if (Omega_M,Omega_L) = (1.0,0.0). The formal
uncertainties on H_0 due to the time delay measurements are +/- 1 (+/- 2)
km/s/Mpc for the 1-sigma (2-sigma) confidence limits. Thus, the systematic
uncertainties due to the lens model, which are on the order of +/- 15 km/s/Mpc,
now dominate the error budget for this system. In order to improve the
measurement of H_0 with this lens, new models that incorporate the constraints
provided by stellar dynamics and the optical/infrared Einstein ring seen in HST
images must be developed.Comment: Accepted for publication in ApJ. 32 pages, 8 figures (3 in color
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