237 research outputs found
First Interferometric Observations of Molecular Gas in a Polar Ring: The Helix Galaxy NGC 2685
We have detected four Giant Molecular cloud Associations (GMAs) (sizes <
6.6'' ~ 430 pc) in the western and eastern region of the polar ring in NGC2685
(the Helix galaxy) using the Owens Valley Radio Observatory (OVRO) millimeter
interferometer. Emission from molecular gas is found close to the brightest
Halpha and HI peaks in the polar ring and is confirmed by new IRAM 30m single
dish observations. The CO and HI line velocities are very similar, providing
additional kinematic confirmation that the CO emission emerges from the polar
ring. For the first time, the total molecular mass within a polar ring is
determined (M_H2~(8-11)x10^6 M_sol, using the standard Galactic conversion
factor). We detect about M_H2~4.4x10^6 M_sol in the nuclear region with the
single dish. Our upper limit derived from the interferometric data is lower
(M_H2<0.7x10^6 M_sol) suggesting that the molecular gas is distributed in an
extended (< 1.3 kpc) diffuse disk. These new values are an order of magnitude
lower than in previous reports. The total amount of molecular gas and the
atomic gas content of the polar ring are consistent with formation due to
accretion of a small gas-rich object, such as a dwarf irregular. The properties
of the NGC2685 system suggest that the polar ring and the host galaxy have been
in a stable configuration for a considerable time (few Gyr). The second (outer)
HI ring within the disk of NGC2685 is very likely at the outer Lindblad
resonance (OLR) of the ~ 11 kpc long stellar bar.Comment: 8 pages, 4 figures, accepted by ApJ Letter
Polar Ring Galaxies and the Tully Fisher relation: implications for the dark halo shape
We have investigated the Tully-Fisher relation for Polar Ring Galaxies
(PRGs), based on near infrared, optical and HI data available for a sample of
these peculiar objects. The total K-band luminosity, which mainly comes from
the central host galaxy, and the measured HI linewidth at 20% of the peak line
flux density, which traces the potential in the polar plane, place most polar
rings of the sample far from the Tully-Fisher relation defined for spiral
galaxies, with many PRGs showing larger HI linewidths than expected for the
observed K band luminosity. This result is confirmed by a larger sample of
objects, based on B-band data. This observational evidence may be related to
the dark halo shape and orientation in these systems, which we study by
numerical modeling of PRG formation and dynamics: the larger rotation
velocities observed in PRGs can be explained by a flattened polar halo, aligned
with the polar ring.Comment: 22 pages, 8 postscript figures, accepted for publication in
Astrophysical Journa
Evidence for coupling between the Sagittarius dwarf galaxy and the Milky Way warp
Using recent determinations of the mass and orbit of Sagittarius, I calculate
its orbital angular momentum. From the latest observational data, I also
calculate the angular momentum of the Milky Way's warp. I find that both
angular momenta are directed toward l=270, b=0, and have magnitude 2-8x10^12
M_Sun kpc km s^-1, where the range in both cases reflects uncertainty in the
mass. The coincidence of the angular momenta is suggestive of a coupling
between these systems. Direct gravitational torque of Sgr on the disk is ruled
out as the coupling mechanism. Gravitational torque due to a wake in the halo
and the impulsive deposition of momentum by a passage of Sgr through the disk
are still both viable mechanisms pending better simulations to test their
predictions on the observed Sgr-MW system.Comment: 11 pages, to appear in the February 1 issue of ApJ
A catalog of warps in spiral and lenticular galaxies in the Southern hemisphere
A catalog of optical warps of galaxies is presented. This can be considered
complementary to that reported by
Sanchez-Saavedra et al., with 42 galaxies in the northern hemisphere, and to
that by Reshetnikov & Combes, with 60 optical warps.
The limits of the present catalog are: logr25 > 0.60, B_{t} < 14.5,
delta(2000) < 0, -2.5 < t < 7. Therefore, lenticular galaxies have also been
considered. This catalog lists 150 warped galaxies out of a sample of 276
edge-on galaxies and covers the whole southern hemisphere, except the Avoidance
Zone.
It is therefore very suitable for statistical studies of warps. It also
provides a source guide for detailed particular observations. We confirm the
large frequency of warped spirals: nearly all galaxies are warped. The
frequency and warp angle do not present important differences for the different
types of spirals. However, no lenticular warped galaxy has been found within
the specified limits. This finding constitutes an important restriction for
theoretical models.Comment: 12 pages, 6 figures, to be published in Astronomy and Astrophysic
A neutral hydrogen survey of polar ring galaxies IV. Parkes observations
A total of 33 polar ring galaxies and polar ring galaxy candidates were
observed in the 21-cm HI line with the 64-m Parkes radio telescope. The
objects, selected by their optical morphology, are all south of declination -39
degrees and in only 5 of them HI had been reported previously. HI line emission
was detected towards 18 objects, though in 3 cases the detection may be
confused by another galaxy in the telescope beam, and one is a marginal
detection. Eight objects were detected for the first time in HI, of which 5 did
not have previously known redshifts.Comment: Accepted by Astronomy and Astrophysics, 12/2/2002; new references
added on 20/2/200
Candidate genes and clinical-laboratory parameters in pregnant women with preeclampsia
They studied the associations of genetic polymorphisms with clinico-laboratory indicators among pregnant women with preeclampsia depending on hereditary complicatio
Near-Infrared photometry in the J, H and Kn bands for Polar Ring Galaxies: II. Global Properties
We discuss the properties of the host galaxy and ring light distributions in
the optical and near infrared bands for a sample of Polar Ring Galaxies (PRGs),
presented in Paper I (Iodice et al. 2002, Paper I). The goal of this work is to
test different formation scenarios for PRGs, proposed by different authors in
the last decades, by comparing their predictions with these new data. The
strategy is twofold: i) the integrated colors of the main components in these
systems are compared with those of standard morphological galaxy types, to
investigate whether differences in colors are caused by dust absorption or
difference in stellar populations. We then derived an estimate of the stellar
population ages in PRGs, which can be used to set constrains on the dynamical
modeling and the time evolution of these systems; ii) we analyse the structural
parameters of the host galaxy in order to understand whether this component is
a standard early-type system as its morphology suggests, and the light
distribution in the polar ring to measure its radial extension. These
observational results indicate that the global properties of PRGs are better
explained by dissipative merging of disks with un-equal masses as proposed by
Bekki (1998), rather than the accretion-or stripping-of gas by a pre-existing
early-type galaxy.Comment: 11 pages, 7 postscript figures, accepted for publication in A&
Radio Continuum Emission in Polar-Ring Galaxies
We have used the Very Large Array aperture synthesis telescope to conduct a
radio continuum survey of polar-ring galaxies, at 20cm and 6cm. Forty objects
were observed at 20cm with 5" resolution. Twenty (50%) of the program sources
were detected at 20cm, down to our 5-sigma limit of 0.5 mJy/beam. This
detection rate is similar to those in surveys with comparable sensitivity for
early-type galaxies without polar rings. Sixteen of the objects we detected at
20cm were also observed at 6cm. We show radio continuum maps for the five
objects in our sample that have noticeably extended emission. Our spatial
resolution was sufficient to distinguish between emission originating in the
host galaxy from that in the polar ring. The radio morphology of the extended
sources, as well as the radio to far-infrared flux ratio and the radio spectral
indices of our detected sources, indicate that star formation, not nuclear
activity, is the dominant source of the radio continuum emission in polar-ring
galaxies. However, the implied star-formation rates are modest, and only one of
our sample galaxies will consume its supply of cool gas within 500 Myr.Comment: 21 pages, 7 figures. Produced with AASTeX 5.2 To appear in November
2004 Astronomical Journa
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