1,611 research outputs found
HI aperture synthesis and optical observations of the pair of galaxies NGC 6907 and 6908
NGC 6908, a S0 galaxy situated in direction of NGC 6907, was only recently
recognized as a distinct galaxy, instead of only a part of NGC 6907. We present
21 cm radio synthesis observations obtained with the GMRT and optical images
and spectroscopy obtained with the Gemini North telescope of this pair of
interacting galaxies. From the radio observations we obtained the velocity
field and the HI column density map of the whole region containing the NGC
6907/8 pair, and by means of the Gemini multi-object spectroscopy we obtained
high quality photometric images and resolution spectra sampling the
two galaxies. By comparing the rotation curve of NGC 6907 obtained from the two
opposite sides around the main kinematic axis, we were able to distinguish the
normal rotational velocity field from the velocity components produced by the
interaction between the two galaxies. Taking into account the rotational
velocity of NGC 6907 and the velocity derived from the absorption lines for NGC
6908, we verified that the relative velocity between these systems is lower
than 60 km s. The emission lines observed in the direction of NGC 6908,
not typical of S0 galaxies, have the same velocity expected for the NGC 6907
rotation curve. Some of them, superimposed on the absorption profiles, which
reinforces the idea that they were not formed in NGC 6908. Finally, the HI
profile exhibits details of the interaction, showing three components: one for
NGC 6908, another for the excited gas in the NGC 6907 disk and a last one for
the gas with higher relative velocities left behind NGC 6908 by dynamical
friction, used to estimate the time when the interaction started in years ago.Comment: 11 pages, 5 tables, 13 figures. Corrected typos. Accepted for
publication in MNRAS. The definitive version will be available at
http://www.blackwell-synergy.co
The Kinematically Measured Pattern Speeds of NGC 2523 and NGC 4245
We have applied the Tremaine-Weinberg continuity equation method to derive
the bar pattern speed in the SB(r)b galaxy NGC 2523 and the SB(r)0/a galaxy NGC
4245 using the Calcium Triplet absorption lines. These galaxies were selected
because they have strong inner rings which can be used as independent tracers
of the pattern speed. The pattern speed of NGC 2523 is 26.4 6.1 km
s kpc, assuming an inclination of 49.7 and a distance
of 51.0 Mpc. The pattern speed of NGC 4245 is 75.5 31.3 km s
kpc, assuming an inclination of 35.4 and a distance of 12.6
Mpc. The ratio of the corotation radius to the bar radius of NGC 2523 and NGC
4245 is 1.4 0.3 and 1.1 0.5, respectively. These values place the
bright inner rings near and slightly inside the corotation radius, as predicted
by barred galaxy theory. Within the uncertainties, both galaxies are found to
have fast bars that likely indicate dark halos of low central concentration.
The photometric properties, bar strengths, and disk stabilities of both
galaxies are also discussed.Comment: Accepted for publication in The Astronomical Journal, 11 figures, 2
table
An integrated cryogenic optical modulator
Integrated electrical and photonic circuits (PIC) operating at cryogenic
temperatures are fundamental building blocks required to achieve scalable
quantum computing, and cryogenic computing technologies. Optical interconnects
offer better performance and thermal insulation than electrical wires and are
imperative for true quantum communication. Silicon PICs have matured for room
temperature applications but their cryogenic performance is limited by the
absence of efficient low temperature electro-optic (EO) modulation. While
detectors and lasers perform better at low temperature, cryogenic optical
switching remains an unsolved challenge. Here we demonstrate EO switching and
modulation from room temperature down to 4 K by using the Pockels effect in
integrated barium titanate (BaTiO3)-based devices. We report the nonlinear
optical (NLO) properties of BaTiO3 in a temperature range which has previously
not been explored, showing an effective Pockels coefficient of 200 pm/V at 4 K.
We demonstrate the largest EO bandwidth (30 GHz) of any cryogenic switch to
date, ultra-low-power tuning which is 10^9 times more efficient than thermal
tuning, and high-speed data modulation at 20 Gbps. Our results demonstrate a
missing component for cryogenic PICs. It removes major roadblocks for the
realisation of novel cryogenic-compatible systems in the field of quantum
computing and supercomputing, and for interfacing those systems with the real
world at room-temperature
Atributos químicos das fases sólida e aquosa do solo de sítios de restinga sob diferentes coberturas vegetais no estado de Sergipe.
bitstream/CPATC/19773/1/f_11_2007.pd
Microwave and Millimeter Wave Techniques
Contains reports on two research project.Joint Services Electronics Program (Contract DAABO7-76-C-1400
The Remarkable Central Structure of the Barred Galaxy NGC 1415
A remarkable structure is observed in the innermost regions of the barred
galaxy NGC 1415 : a small stellar bar, bright circumnuclear ionized gas seen in
Halpha, two bright ionized gas sources, seen in Halpha, just beyond the ends of
the small bar and a boxy distribution of optical continuum. We have developed a
mass distribution model consisting in disk, a bulge, and a bar to approximate t
he observed central morphology and its surface brightness. In order to
reproduce the observed optical brightness distribution a two-component bar was
used, with one component to model the elongated isophotes of the bar and the
second component to model the boxy-shaped isophotes. We interpret the
circumnuclear ionized gas as forming a circumnuclear ring and the two bright
sources as a nuclear and/or circumnuclear outflow slightly out of the plane of
the disk.Comment: 19 pages, 29 figures. To be published in February 2000, ApJ, 52
The detection of non-thermal radio continuum spokes and the study of star formation in the Cartwheel
New sensitive Very Large Array 20 cm continuum observations of the Cartwheel,
the prototypical collisional ring galaxy, were carried out with the principal
aim of tracing supernova remnants that are expected to lie in the wake of the
expanding ring and in the ring itself. We detect predominantly non-thermal
radio continuum emission from regions associated with 13 ring HII complexes.
The emission interior to the ring is confined to structures that resemble
spokes of the wheel. The spokes start near bright HII complexes, and extend to
around 6 arcsec (4 kpc) inward in the direction of the geometrical center of
the ring. There is no apparent positional coincidence between the radio
continuum and optical spokes. Radial distribution of intensity along the spokes
suggests that the past star formation rate (SFR) in the Cartwheel was much
lower than the current SFR. New Halpha observations were used to revise the
current SFR in the Cartwheel. The revised value is 18 Msun/yr, which is a
factor of 4 lower than the value reported previously, but is in good agreement
with the SFR estimated from far infrared luminosity. About 30% of the observed
20 cm continuum non-thermal emission seems to originate in processes that are
not related to star formation. Revised SFR in the Cartwheel is comparable to
that in the rest of the ring galaxies.Comment: 6 pages, uses emulateapj.cls. Scheduled to appear in ApJL February
10, 200
Central Activity in the Barred Galaxy NGC 3367
We report the radio continuum structure of the barred galaxy NGC 3367 with an
angular resolution of 4''.5. The radio structure indicates emission from the
disk and from a triple source consisting of the nucleus straddled by extended
sources (the lobes). The triple source shows an excess of radio continuum
emission compared to the emission expected from the total radio - Halpha
correlation, suggesting a non-thermal origin probably related to AGN activity
and no to star formation processes. The triple source is about 12 kpc in
diameter at a P.A. 40, close (but not aligned) to that of the stellar bar P.A.
65. Only the southwest lobe is polarized. The polarizatrion asymmetry between
the two lobes suggests that the triple source axis is slightly out of the
plane.Comment: 13 latex pages, 8 figures. To appear in Astronomical Journal, July
199
An Imaging Survey of Early-Type Barred Galaxies
This paper presents the results of a high-resolution imaging survey, using
both ground-based and Hubble Space Telescope images, of a complete sample of
nearby barred S0--Sa galaxies in the field, with a particular emphasis on
identifying and measuring central structures within the bars: secondary bars,
inner disks, nuclear rings and spirals, and off-plane dust. A discussion of the
frequency and statistical properties of the various types of inner structures
has already been published. Here, we present the data for the individual
galaxies and measurements of their bars and inner structures. We set out the
methods we use to find and measure these structures, and how we discriminate
between them. In particular, we discuss some of the deficiencies of ellipse
fitting of the isophotes, which by itself cannot always distinguish between
bars, rings, spirals, and dust, and which can produce erroneous measurements of
bar sizes and orientations.Comment: LaTeX, 66 pages (including 42 figures, 36 in color). To appear in The
Astrophysical Journal Supplement. Full-resolution and text-only versions
available at http://www.iac.es/galeria/erwin/research
Ultraviolet-Optical observations of the Seyfert 2 Galaxies NGC 7130, NGC 5135 and IC 3639: Implications for the Starburst-AGN Connection
We present and discuss HST (WFPC2 and FOC) images and UV GHRS spectra plus
ground-based near UV through to near IR spectra of three Seyfert 2 nuclei (NGC
7130, NGC 5135 and IC 3639). These galaxies, together to Mrk 477, were selected
from a bigger sample that comprises the 20 brightest Seyfert 2 nuclei, with the
goal to study the origin of the UV-optical-near IR featureless continuum in
Seyfert 2 nuclei. These four galaxies have bolometric luminosities, as computed
with the four IRAS bands, of 10^11 Lsol. They are close enough to be resolved
with HST the nuclear zone. This makes these Seyfert 2 galaxies benchmarks to
study the Starburst-AGN connection in more distant galaxies.
The data provide direct evidence of the existence of a central nuclear
starburst that dominates the UV light, and that seem to be responsible for the
origin of the so called featureless continuum. These starbursts are dusty and
compact. They have sizes (from less than 100 pc to a few hundred pc) much
smaller and closer to the nucleus than that seen in the prototype Seyfert 2
galaxy NGC 1068. The bolometric luminosity of these starbursts is similar to
the estimated bolometric luminosities of their obscured Seyfert 1 nuclei, and
thus they contribute in the same amount to the overall energetics of these
galaxies.Comment: to be published in ApJ 505, September issue. The figures are in a tar
files at: http://www.iaa.es/~rosa/Seyfert
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