4,425 research outputs found
Spectral decomposition of the stellar kinematics in the polar disk galaxy NGC 4650A
Context. The prototype of Polar Ring Galaxies NGC 4650A contains two main
structural components, a central spheroid, which is the host galaxy, and an
extended polar disk. Both photometric and kinematic studies revealed that these
two components co-exist on two different planes within the central regions of
the galaxy. Aims. The aim of this work is to study the spectroscopic and
kinematic properties of the host galaxy and the polar disk in the central
regions of NGC 4650A by disentangling their contributions to the observed
galaxy spectrum.
Methods. We applied the spectral decomposition technique introduced in
previous works to long-slit spectroscopic observations in the CaII triplet
region. We focused the analysis along the PA = 152 that corresponds to the
photometric minor axis of the host galaxy, where the superimposition of the two
components is more relevant and the spectral decomposition is necessary. We aim
to disentangle the stars that move in the equatorial plane of the host galaxy
from those that move in the meridan plane, which is along the polar disk.
Results. We successfully disentangled the spectra of the two structural
components of NGC 4650A and measured their line-of-sight velocity and velocity
dispersion profiles, and the stellar content along PA = 152. The host galaxy
shows significant rotation along its photometric minor axis, indicating that
the gravitational potential is not axisymmetric. The polar disk shows a
kinematic decoupling: the inner regions counter-rotating with respect the
outer-regions and the host spheroid. This suggests a complex formation history
for the polar disk, characterised by mass accretion with decoupled angular
momenta.Comment: Accepted for publication in Astronomy and Astrophysics. 7 pages, 5
figure
A kinematically decoupled component in NGC4778
We present a kinematical and photometrical study of a member, NGC4778, of the
nearest (z=0.0137) compact group: Hickson 62. Our analysis reveals that Hickson
62a, also known as NGC4778, is an S0 galaxy with kinematical and morphological
peculiarities, both in its central regions (r < 5'') and in the outer halo. In
the central regions, the rotation curve shows the existence of a kinematically
decoupled stellar component, offset with respect to the photometric center. In
the outer halo we find an asymmetric rotation curve and a velocity dispersion
profile showing a rise on the SW side, in direction of the galaxy NGC4776.Comment: Proceedings of the first workshop of astronomy and astrophysics for
student
Status of the ATLAS Experiment and Early Physics Measurements
The ATLAS experiment has collected several hundred million cosmic ray events during 2008 and 2009 providing the primary source for commissioning the detectors, trigger, data acquisition and event reconstruction programs. The data allowed studying the performance of all detector components. Results on performance and readiness of the sub-detectors will be reported. We will also outline the potential for early physics measurements during the first year of operation
Photometric structure of the peculiar galaxy ESO 235-G58
We present the near-infrared and optical properties of the peculiar galaxy
ESO 235-G58, which resembles a late-type ringed barred spiral seen close to
face-on. However, the apparent bar of ESO 235-G58 is in reality an edge-on disk
galaxy of relatively low luminosity. We have analyzed the light and color
distributions of ESO 235-G58 in the NIR and optical bands and compared them
with the typical properties observed for other morphological galaxy types,
including polar ring galaxies. Similar properties are observed for ESO 235-G58,
polar ring galaxies, and spiral galaxies, which leads us to conclude that this
peculiar system is a polar-ring-related galaxy, characterized by a low inclined
ring/disk structure, as pointed out by Buta & Crocker in an earlier study,
rather than a barred galaxy.Comment: 16 pages, 15 figures, accepted for publication in Astronomy &
Astrophysic
Metallicity of the polar disk in NGC4650A: constraints for cold accretion scenario
We used high resolution spectra in the optical and near-infrared wavelength
range to study the abundance ratios and metallicities of the HII regions
associated with the polar disk in NGC4650A, in order to put constraints on the
formation of the polar disk through cold gas accretion along a filament; this
might be the most realistic way by which galaxies get their gas. We have
compared the measured metallicities for the polar structure in NGC4650A with
those of different morphological types and we have found that they are similar
to those of late-type galaxies: such results is consistent with a polar disk
formed by accretion from cosmic web filaments of external cold gas.Comment: Proceeding of the conference "Hunting for the Dark: The Hidden Side
of Galaxy Formation", Malta, 19-23 Oct. 200
The NIR structure of the barred galaxy NGC253 from VISTA
[abridged] We used J and Ks band images acquired with the VISTA telescope as
part of the science verification to quantify the structures in the stellar disk
of the barred Sc galaxy NGC253. Moving outward from the galaxy center, we find
a nuclear ring within the bright 1 kpc diameter nucleus, then a bar, a ring
with 2.9 kpc radius. From the Ks image we obtain a new measure of the
deprojected length of the bar of 2.5 kpc. The bar's strength, as derived from
the curvature of the dust lanes in the J-Ks image, is typical of weak bars.
From the deprojected length of the bar, we establish the corotation radius
(R_CR=3 kpc) and bar pattern speed (Omega_b = 61.3 km /s kpc), which provides
the connection between the high-frequency structures in the disk and the
orbital resonances induced by the bar. The nuclear ring is located at the inner
Lindblad resonance. The second ring does not have a resonant origin, but it
could be a merger remnant or a transient structure formed during an
intermediate stage of the bar formation. The inferred bar pattern speed places
the outer Lindblad resonance within the optical disk at 4.9 kpc, in the same
radial range as the peak in the HI surface density. The disk of NGC253 has a
down-bending profile with a break at R~9.3 kpc, which corresponds to about 3
times the scale length of the inner disk. We discuss the evidence for a
threshold in star formation efficiency as a possible explanation of the steep
gradient in the surface brightness profile at large radii. The NIR photometry
unveils the dynamical response of the NGC253 stellar disk to its central bar.
The formation of the bar may be related to the merger event that determined the
truncation of stars and gas at large radii and the perturbation of the disk's
outer edge.Comment: Accepted for publication in Astronomy & Astrphysics. High resolution
pdf file is available at the following link:
https://www.dropbox.com/s/4o4cofs1lyjrtpv/NGC253.pd
Structure of Early-Type Galaxies: 2D Fit of the Light Distribution for a Complete Volume-Limited Sample
We outline the results of a two-dimensional (2D) fit of the light
distribution of early-type galaxies belonging to a complete volume-limited
sample, and briefly discuss the significant correlations among the structural
parameters. In particular we reconfirm that the lack of structural homology is
likely a characteristic of hot stellar systems.Comment: 8 pages and 4 figures. To appear in the proceedings of the
Euroconference "the Evolution of Galaxies on Cosmological Timescales" Nov
30th - Dec 5th 1998 Puerto de la Cruz Tenerife, Spai
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