401 research outputs found
Statistics of galaxy warps in the HDF North and South
We present a statistical study of the presence of galaxy warps in the Hubble
deep fields. Among a complete sample of 45 edge-on galaxies above a diameter of
1.''3, we find 5 galaxies to be certainly warped and 6 galaxies as good
candidates. In addition, 4 galaxies reveal a characteristic U-warp. Compared to
statistical studies of local warps, and taking into account the strong bias
against observing the outer parts of galaxies at high redshift, these numbers
point towards a very high frequency of warps at z \sim 1: almost all galaxy
discs might be warped. Furthermore, the amplitude of warps are stronger than
for local warps. This is easily interpreted in terms of higher galaxy
interactions and matter accretion in the past. This result supports these two
mechanisms as the best candidates for the origin of early warps. The mean
observed axis ratio of our sample of edge-on galaxies is significantly larger
in the high-z sample than is found for samples of local spiral galaxies. This
might be due to disk thickening due to more frequent galaxy interactions.Comment: 9 pages, 7 figures, accepted in A and
Effect of the Environment on the Fundamental Plane of Elliptical Galaxies
We present an analysis of interacting E/S0 galaxies location on the
Fundamental Plane. Using the NEMO package, we performed N-body simulations of
close encounters and mergers between two spherical galaxies. We followed how
structural and dynamical parameters (central density, half-mass radius and
velocity dispersion)of galaxies are changed during the encounter. We analysed
the dependence of these changes on initial mass concentration and presence of
dark halo. The results of our simulations are used to discuss the Fundamental
Plane for interacting early-type galaxies.Comment: Poster presented at JENAM-2000 (Joint European and National
Astronomical meeting - S02. Morphology and dynamics of stellar systems: star
clusters, galactic arms and rings
Galaxy transmutations: The double ringed galaxy ESO 474-G26
Surface photometry and a 21cm HI line spectrum of the giant double-ringed
galaxy ESO 474-G26 are presented. The morphology of this system is unique among
the 30,000 galaxies with >B15. Two almost orthogonal optical rings with
diameters of 60 and 40 kpc surround the central body (assuming H0=70 km/s/Mpc).
The outer one is an equatorial ring, while the inner ring lies in a nearly
polar plane. The rings have blue optical colors typical of late-type spirals.
Both appear to be rotating around the central galaxy, so that this system can
be considered as a kinematically confirmed polar ring galaxy. Its observational
characteristics are typical of galaxy merger remnants. Although the central
object has a surface brightness distribution typical of elliptical galaxies, it
has a higher surface brightness for its effective radius than ordinary
ellipticals. Possible origins of this galaxy are discussed and numerical
simulations are presented that illustrate the formation of the two rings in the
merging process of two spiral galaxies, in which the observed appearance of ESO
474-G26 appears to be a transient stage.Comment: Accepted for publication in A&
The origin of polar ring galaxies: evidence for galaxy formation by cold accretion
Polar ring galaxies are flattened stellar systems with an extended ring of
gas and stars rotating in a plane almost perpendicular to the central galaxy.
We show that their formation can occur naturally in a hierarchical universe
where most low mass galaxies are assembled through the accretion of cold gas
infalling along megaparsec scale filamentary structures. Within a large
cosmological hydrodynamical simulation we find a system that closely resembles
the classic polar ring galaxy NGC 4650A. How galaxies acquire their gas is a
major uncertainty in models of galaxy formation and recent theoretical work has
argued that cold accretion plays a major role. This idea is supported by our
numerical simulations and the fact that polar ring galaxies are typically low
mass systems.Comment: 4 pages, 5 figures, stability of the ring discussed, minor changes to
match the accepted version by ApJL. A preprint with high-resolution figures
is available at http://krone.physik.unizh.ch/~andrea/PolarRing/PolarRing.p
Genes of tumor necrosis factors and their receptors and the primary open angle glaucoma in the population of Central Russia
To examine the association of genetic polymorphisms (-308)G/A TNFα, (+250)A/G Ltα, (+36)A/G TNFR1, (+1663) A/G TNFR2 with the development of primary open angle glaucoma (POAG) among people in Central Russi
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
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
Near-infrared and optical observations of galactic warps: A common, unexplained feature of most discs
Context: Warps occurring in galactic discs have been studied extensively in
HI and in the optical, but rarely in the near-infrared (NIR) bands that trace
the older stellar populations.
Aims: We provide NIR data of nearby edge-on galaxies, combined with optical
observations, for direct comparison of the properties of galactic warps as a
function of wavelength, and calculate warp curves for each galaxy and obtain
the characteristic warp parameters. We discuss these properties as possible
constraints to the different mechanisms that have been proposed for the
development and persistence of galactic warps.
Methods: We observed 20 galaxies that were selected from a statistically
complete diameter-limited subsample of edge-on disc galaxies. We used the Cerro
Tololo Infrared Imager (CIRIM) at the CTIO 1.5m Ritchey-Chretien telescope to
acquire the NIR data. We used the 1.54m Danish and 0.92m Dutch telescopes at
the European Southern Observatory's La Silla site for our optical observations.
Results: Our results show that 13 of our 20 sample galaxies are warped, with
the warp more pronounced in the optical than at NIR wavelengths. In the
remaining seven galaxies, no warp is apparent within the limitations of our
automated detection method. The transition between the unperturbed inner disc
and the outer, warped region is rather abrupt. S0 galaxies exhibit very small
or no warps. The magnetic model remains one of a number of interesting
formation scenarios.Comment: 16 page
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
New photometric investigation of the double ringed galaxy ESO474-G26. Unveiling the formation scenario
We present a detailed photometric study of the peculiar double ringed galaxy
ESO474-G26. Near-Infrared (NIR) and optical data have been used, with the main
goal to constrain the formation history of ESO474-G26. NIR photometry is
fundamental in this kind of study, because gives better constraints on the
Spectral Energy Distribution (SED) and well traces the older stellar population
of the galaxy. This galaxy presents a very complex structure, with two almost
orthogonal rings, one in the equatorial and another in the polar plane, around
an elliptical-like object. Due to the peculiar morphology of ESO474-G26, we
used both NIR images (J and K bands) to derive accurate analysis of the stellar
light distribution, and optical images (in the B, V and R bands) to derive
color profiles and color maps to study the structure of the rings. The
observational characteristic of ESO474-G26 are typical of galaxies which have
experienced some kind of interactions during their evolution. We investigated
two alternatives: a merging process and an accretion event.Comment: 19 pages, 20 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Society (MNRAS
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