132 research outputs found
The Formation and Evolution of S0 Galaxies
This thesis studies the origin of local S0 galaxies and their possible links
to other morphological types. To address these issues, two different approaches
have been adopted: a detailed study of the stellar populations of S0s in the
Fornax Cluster and a study of the Tully-Fisher Relation (TFR) of local S0s in
different environments.Comment: Ph.D. Thesis submitted to The University of Nottingham, U.K. Please
download the complete version at
http://www.nottingham.ac.uk/~ppxapgg/phdthesis.pd
Central Stellar Populations of S0 Galaxies in The Fornax Cluster
Based on FORS2-VLT long-slit spectroscopy, the analysis of the central
absorption line indices of 9 S0 galaxies in the Fornax Cluster is presented.
Central indices correlate with central velocity dispersions as observed in
ellipticals. However, the stellar population properties of these S0s indicates
that the observed trends are produced by relative differences in age and
alpha-element abundances and not in metallicity ([Fe/H]) as previous studies
have found in elliptical galaxies. The observed scatter in the line indices vs.
velocity dispersion relations can be partially explained by the
rotationally-supported nature of many of these systems. The presence of tighter
line indices vs. maximum (circular) rotational velocity relations confirms this
statement. It was also confirmed that the dynamical mass is the driving
physical property of all these correlations and in our Fornax S0s it has to be
estimated assuming rotational support.Comment: To appear in the Proceedings of IAU Symposium 241: "Stellar
Populations as Building Blocks of Galaxies", 10-16 December, 2006 at La
Palma, Canary Islands, Spai
Spectroscopic bulge-disc decomposition: a new method to study the evolution of lenticular galaxies
A new method for spectroscopic bulge-disc decomposition is presented, in
which the spatial light profile in a two-dimensional spectrum is decomposed
wavelength-by-wavelength into bulge and disc components, allowing separate
one-dimensional spectra for each component to be constructed. This method has
been applied to observations of a sample of nine S0s in the Fornax Cluster in
order to obtain clean high-quality spectra of their individual bulge and disc
components. So far this decomposition has only been fully successful when
applied to galaxies with clean light profiles, consequently limiting the number
of galaxies that could be separated into bulge and disc components. Lick index
stellar population analysis of the component spectra reveals that in those
galaxies where the bulge and disc could be distinguished, the bulges have
systematically higher metallicities and younger stellar populations than the
discs. This correlation is consistent with a picture in which S0 formation
comprises the shutting down of star formation in the disc accompanied by a
final burst of star formation in the bulge. The variation in spatial-fit
parameters with wavelength also allows us to measure approximate colour
gradients in the individual components. Such gradients were detected separately
in both bulges and discs, in the sense that redder light is systematically more
centrally concentrated in all components. However, a search for radial
variations in the absorption line strengths determined for the individual
components revealed that they are absent from the vast majority of S0 discs and
bulges. The absence of gradients in line indices for most galaxies implies that
the colour gradient cannot be attributed to age or metallicity variations, and
is therefore most likely associated with varying degrees of obscuration by
dust.Comment: 10 pages, 10 figures, 1 table, accepted for publication in MNRA
Stellar population gradients in Fornax Cluster S0 galaxies: connecting bulge and disk evolution
We present absorption-line index gradients for a sample of S0 galaxies in the
Fornax Cluster. The sample has been selected to span a wide range in galaxy
mass, and the deep VLT-FORS2 spectroscopy allows us to explore the stellar
populations all the way to the outer disk-dominated regions of these galaxies.
We find that globally, in both bulges and disks, star formation ceased earliest
in the most massive systems, as a further manifestation of downsizing. However,
within many galaxies, we find an age gradient which indicates that star
formation ended first in the outermost regions. Metallicity gradients, when
detected, are always negative such that the galaxy centres are more metal-rich.
This finding fits with a picture in which star formation continued in the
central regions, with enriched material, after it had stopped in the outskirts.
Age and metallicity gradients are correlated, suggesting that large differences
in star formation history between the inner and outer parts of S0 galaxies
yield large differences in their chemical enrichment. In agreement with
previous results, we conclude that the radial variations in the stellar
populations of S0 galaxies are compatible with the hypothesis that these
galaxies are the descendants of spiral galaxies whose star formation has
ceased. With the addition of radial gradient information, we are able to show
that this shutdown of star formation occurred from the outside inward, with the
later star formation in the central regions offering a plausible mechanism for
enhancing the bulge light in these systems, as the transformation to more
bulge-dominated S0 galaxies requires.Comment: 9 pages, 4 figures and Appendix, accepted for publication in MNRA
Exploring Disk Galaxy Dynamics Using IFU Data
In order to test the basic equations believed to dictate the dynamics of disk
galaxies, we present and analyze deep two-dimensional spectral data obtained
using the PPAK integral field unit for the early-type spiral systems NGC 2273,
NGC 2985, NGC 3898 and NGC 5533. We describe the care needed to obtain and
process such data to a point where reliable kinematic measurements can be
obtained from these observations, and a new more optimal method for deriving
the rotational motion and velocity dispersions in such disk systems. The data
from NGC 2273 and NGC 2985 show systematic variations in velocity dispersion
with azimuth, as one would expect if the shapes of their velocity ellipsoids
are significantly anisotropic, while the hotter disks in NGC 3898 and NGC 5533
appear to have fairly isotropic velocity dispersions. Correcting the rotational
motion for asymmetric drift using the derived velocity dispersions reproduces
the rotation curves inferred from emission lines reasonably well, implying that
this correction is quite robust, and that the use of the asymmetric drift
equation is valid. NGC 2985 is sufficiently close to face on for the data,
combined with the asymmetric drift equation, to determine all three components
of the velocity ellipsoid. The principal axes of this velocity ellipsoid are
found to be in the ratio sigma_z:sigma_phi:sigma_R ~ 0.7:0.7:1, which shows
unequivocally that this disk distribution function respects a third integral of
motion. The ratio is also consistent with the predictions of epicyclic theory,
giving some confidence in the application of this approximation to even fairly
early-type disk galaxies.Comment: 15 pages, 7 figures, accepted for publication in MNRA
Spatially Resolved [FeII] 1.64 \mu m Emission in NGC 5135. Clues for Understanding the Origin of the Hard X-rays in Luminous Infrared Galaxies
Spatially resolved near-IR and X-ray imaging of the central region of the
Luminous Infrared Galaxy NGC 5135 is presented. The kinematical signatures of
strong outflows are detected in the [FeII]1.64 \mu m emission line in a compact
region at 0.9 kpc from the nucleus. The derived mechanical energy release is
consistent with a supernova rate of 0.05-0.1 yr. The apex of the
outflowing gas spatially coincides with the strongest [FeII] emission peak and
with the dominant component of the extranuclear hard X-ray emission. All these
features provide evidence for a plausible direct physical link between
supernova-driven outflows and the hard X-ray emitting gas in a LIRG. This
result is consistent with model predictions of starbursts concentrated in small
volumes and with high thermalization efficiencies. A single high-mass X-ray
binary (HMXB) as the major source of the hard X-ray emission although not
favoured, cannot be ruled out. Outside the AGN, the hard X-ray emission in NGC
5135 appears to be dominated by the hot ISM produced by supernova explosions in
a compact star-forming region, and not by the emission due to HMXB. If this
scenario is common to U/LIRGs, the hard X-rays would only trace the most
compact (< 100 pc) regions with high supernova and star formation densities,
therefore a lower limit to their integrated star formation. The SFR derived in
NGC 5135 based on its hard X-ray luminosity is a factor of two and four lower
than the values obtained from the 24 \mu m and soft X-ray luminosities,
respectively.Comment: Accepted for Publication in ApJ, 18 pages, 2 figure
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