492 research outputs found
A GPU-Enabled, High-Resolution Cosmological Microlensing Parameter Survey
In the era of synoptic surveys, the number of known gravitationally lensed
quasars is set to increase by over an order of magnitude. These new discoveries
will enable a move from single-quasar studies to investigations of statistical
samples, presenting new opportunities to test theoretical models for the
structure of quasar accretion discs and broad emission line regions (BELRs). As
one crucial step in preparing for this influx of new lensed systems, a
large-scale exploration of microlensing convergence-shear parameter space is
warranted, requiring the computation of O(10^5) high resolution magnification
maps. Based on properties of known lensed quasars, and expectations from
accretion disc/BELR modelling, we identify regions of convergence-shear
parameter space, map sizes, smooth matter fractions, and pixel resolutions that
should be covered. We describe how the computationally time-consuming task of
producing ~290000 magnification maps with sufficient resolution (10000^2
pixel/map) to probe scales from the inner edge of the accretion disc to the
BELR can be achieved in ~400 days on a 100 teraflop/s high performance
computing facility, where the processing performance is achieved with graphics
processing units. We illustrate a use-case for the parameter survey by
investigating the effects of varying the lens macro-model on accretion disc
constraints in the lensed quasar Q2237+0305. We find that although all
constraints are consistent within their current error bars, models with more
densely packed microlenses tend to predict shallower accretion disc radial
temperature profiles. With a large parameter survey such as the one described
here, such systematics on microlensing measurements could be fully explored.Comment: 30 pages, 3 figures, accepted for publication in Ap
A detailed two-dimensional stellar population study of M32
We present Two-Dimensional Spectroscopy of the 9x12 arcsec^2 central region
of M32 obtained with the 2D_FIS fibre spectrograph installed at the William
Herschel Telescope. From these spectra line strength maps have been
reconstructed for about 20 absorption lines, mostly belonging to the Lick
system. We find good agreement with long-slit line strength profiles in the
literature. In contrast with previous studies, indices were azimuthally
averaged along continuum isophotes of M32. A remarkable result is that no
gradients are presented in the spectral indices. So, we have fitted the mean
values of each spectral index and central colours to the models of Vazdekis et
al. (1996) and Worthey (1994), finding that an intermediate age (~4 Gyr) and
metallicity similar to solar (Z=0.02) are the best fitted values for the
innermost region of M32.Comment: accepted in MNRA
Two-Dimensional Line Strength Maps in Three Well-studied Early-Type Galaxies
Integral field spectroscopy has been obtained for the nuclear regions of 3
large, well-studied, early-type galaxies. From these spectra we have obtained
line strength maps for about 20 absorption lines, mostly belonging to the Lick
system. An extensive comparison with multi-lenslet spectroscopy shows that
accurate kinematic maps can be obtained, and also reproducible line strength
maps. Comparison with long-slit spectroscopy also produces good agreement. We
show that Mg is enhanced with respect to Fe in the inner disk of one of the
three galaxies studied, the Sombrero. [Mg/Fe] there is larger than in the rest
of the bulge. The large values of Mg/Fe in the central disk are consistent with
the centres of other early-type galaxies, and not with large disks, like the
disk of our Galaxy, where [Mg/Fe] is approximately 0. We confirm with this
observation a recent result of Worthey (1998) that Mg/Fe is determined by the
central kinetic energy, or escape velocity, of the stars, only, and not by the
formation time scale of the stars. A stellar population analysis using the
models of Vazdekis et al. (1996) shows that our observed H gamma agrees well
with what is predicted based on the other lines. Using the line strength of the
Ca II IR triplet as an indicator of the abundance of Ca, we find that Ca
follows Fe, and not Mg, in these galaxies. This is peculiar, given the fact
that Ca is an alpha-element. Finally, by combining the results of this paper
with those of Vazdekis et al. (1997) we find that the line strength gradients
in the three galaxies are primarily caused by variations in metallicity.Comment: 23 pages, Latex, includes mn.sty, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Recurrence of the blue wing enhancements in the high ionization lines of SDSS 1004+4112 A
We present integral field spectroscopic observations of the quadruple-lensed
QSO SDSS 1004+4112 taken with the fiber system INTEGRAL at the William Herschel
Telescope on 2004 January 19. In May 2003 a blueward enhancement in the high
ionization lines of SDSS 1004+4112A was detected and then faded. Our
observations are the first to note a second event of similar characteristics
less than one year after. Although initially attributed to microlensing, the
resemblance among the spectra of both events and the absence of
microlensing-induced changes in the continuum of component A are puzzling. The
lack of a convincing explanation under the microlensing or intrinsic
variability hypotheses makes the observed enhancements particularly relevant,
calling for close monitoring of this object.Comment: 4 pages, 5 figure
Spectroscopy of the Lens Galaxy of Q0957+561A,B. Implications of a possible central massive dark object
We present new long-slit William Herschel Telescope spectroscopic
observations of the lens galaxy G1 associated with the double-imaged QSO
0957+561A,B. The obtained central stellar velocity dispersion, sigma_l = 310
+/- 20 km/s, is in reasonable agreement with other measurements of this
dynamical parameter. Using all updated measurements of the stellar velocity
dispersion in the internal region of the galaxy (at angular separations < 1".5)
and a simple isotropic model, we discuss the mass of a possible central massive
dark object. It is found that the data of Falco et al. (1997) suggest the
existence of an extremely massive object of (0.5-2.1) x 10E10/h M_\odot (80%
confidence level), whereas the inclusion of very recent data (Tonry & Franx
1998, and this paper) substantially changes the results: the compact central
mass must be 6 x10E9/h M_\odot at the 90% confidence level. We note that,
taking into account all the available dynamical data, a compact nucleus with a
mass of 10E9/h M_\odot (best fit) cannot be ruled out.Comment: 20 pages, 10 figures ApJ, in pres
"Dos ortografías frente a frente en la obra de Malón de Chaide"
Pedro Malón de Chaide quiso que su obra saliera impresa según
su propio criterio ortográfico, en buena medida contrario al que se usaba en las
imprentas. En el Prólogo de La conversión de la Magdalena se queja de que, habiendo
él descuidado la supervisión del trabajo editorial, advirtió, cuando ya se
había impreso buena parte del libro, que se había hecho cambiando sus grafías
por las acostumbradas. Lo restante del libro se quiso realizar obedeciendo al
autor, pero los primeros pliegos de esta última parte salieron impresos con una
mezcla de las dos ortografías contradictorias. En el presente trabajo se intenta
explicar cómo pudo suceder tal cosa, recurriendo a los conocimientos de que
se dispone sobre el proceso de fabricación de un libro en el Siglo de Oro, y a
la legislación que le afectaba en los distintos reinos de España
Chasma Boreale, Mars: A Sapping and Outflow Channel with a Tectono-thermal Origin
A detailed geomorphological study of Chasma Boreale, a widely known feature of Mars’ north polar cap, has been carried out for the first time, along with a quantitative paleohydro logical model. It is concluded that the chasma was eroded by a flow whose discharge was on the order of magnitude of 109 m sec21. This catastrophic flow is thought to have been preceded
by a powerful sapping process, caused by a tectonic control in the distribution and present aspect of most of the polar troughs. This tectonic forcing probably played a major role in the inception of not only Chasma Boreale but also
other polar reentrants as wel
Integrated spectra extraction based on signal-to-noise optimization using Integral Field Spectroscopy
We propose and explore the potential of a method to extract high
signal-to-noise (S/N) integrated spectra related to physical and/or
morphological regions on a 2-dimensional field using Integral Field
Spectroscopy (IFS) observations by employing an optimization procedure based on
either continuum (stellar) or line (nebular) emission features. The
optimization method is applied to a set of IFS VLT-VIMOS observations of
(U)LIRG galaxies, describing the advantages of the optimization by comparing
the results with a fixed-aperture, single spectrum case, and by implementing
some statistical tests. We demonstrate that the S/N of the IFS optimized
integrated spectra is significantly enhanced when compared with the single
aperture unprocessed case. We provide an iterative user-friendly and versatile
IDL algorithm that allows the user to spatially integrate spectra following
more standard procedures. This is made available to the community as part of
the PINGSoft IFS software package.Comment: Accepted for publication in Astronomy & Astrophysics, 12 pages, 7
figure
Clean optical spectrum of the radio jet of 3C 120
We present integral field spectroscopy (IFS) of the central region of 3C 120.
We have modeled the nuclear and host galaxy 3D spectra using techniques
normally applied to imaging, decoupling both components, and obtained a
residual datacube. Using this residual datacube, we detected the extended
emission line region associated with the radio jet. We obtained, for the first
time, a clean spectrum of this region and found compelling evidences of a
jet-cloud interaction. The jet compresses and splits the gas cloud which is
ionized by the AGN and/or by the strong local UV photon field generated by a
shock process. We cannot confirm the detection of an extended emission line
region associated with the counter-jet reported by Axon (1989).Comment: 13 pages, 3 figures, accepted for publishing in Ap
Dynamic behaviour of AA 2024 under blast loading : experiments and simulations
The dynamic behaviour of AA2024-T3 is investigated. Dynamic tensile tests using a servo-hydraulic and a light weight shock testing machine (LSM) have been performed. The servo-hydraulic test machine proves to be more reliable and reaches higher strain rates. Neither test revealed any strain rate effect of AA2024-T3. Two types of fracture tests were carried out to determine the dynamic crack propagation behaviour of this alloy, using prestressed plates and pressurized barrels, both with the help of explosives. The prestressed plates proved to be not suitable, whereas the barrel tests were quite reliable, allowing to measure the crack speeds. Computer simulations with a user defined, rate dependent cohesive zone model were in agreement with experiments, capturing the rate toughening effect
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