744 research outputs found
Spectral gradients in central cluster galaxies: further evidence of star formation in cooling flows
We have obtained radial gradients in the spectral features D4000 and Mg2 for
a sample of 11 central cluster galaxies (CCGs). The new data strongly confirm
the correlations between line-strength indices and the cooling flow phenomenon
found in our earlier study. We find that such correlations depend on the
presence and characteristics of emission lines in the inner regions of the
CCGs. CCGs in cooling flow clusters exhibit a clear sequence in the D4000-Mg2
plane, with a neat segregation depending on emission-line types and blue
morphology. This sequence can be modelled, using stellar population models with
a normal IMF, by a recent burst of star formation. In CCGs with emission lines,
the gradients in the spectral indices are flat or positive inside the
emission-line regions, suggesting the presence of young stars. Outside the
emission-line regions, and in cooling flow galaxies without emission lines,
gradients are negative and consistent with those measured in CCGs in clusters
without cooling flows and giant elliptical galaxies. Index gradients measured
exclusively in the emission-line region correlate with mass deposition rate. We
have also estimated the radial profiles of the mass transformed into new stars
which are remarkably parallel to the radial behaviour of the mass deposition
rate. A large fraction (probably most) of the cooling flow gas accreted into
the emission-line region is converted into stars. We discuss the evolutionary
sequence suggested by McNamara (1997), in which radio triggered star formation
bursts take place several times during the lifetime of the cooling flow. This
scenario is consistent with the available observations.Comment: 19 pages, 18 PostScript figures, accepted for publication in MNRA
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
The Tully-Fisher relation of intermediate redshift field and cluster galaxies from Subaru spectroscopy
We have carried out spectroscopic observations in 4 cluster fields using
Subaru's FOCAS multi-slit spectrograph and obtained spectra for 103 bright disk
field and cluster galaxies at . Seventy-seven of these
show emission lines, and 33 provide reasonably-secure determinations of the
galaxies' rotation velocity. The rotation velocities, luminosities, colours and
emission-line properties of these galaxies are used to study the possible
effects of the cluster environment on the star-formation history of the
galaxies. Comparing the Tully-Fisher relations of cluster and field galaxies at
similar reshifts we find no measurable difference in rest-frame -band
luminosity at a given rotation velocity (the formal difference is mag). The colours of the cluster emission line galaxies are only marginally
redder in rest-frame (by mag) than the field galaxies in
our sample. Taken at face value, these results seem to indicate that bright
star-forming cluster spirals are similar to their field counterparts in their
star-formation properties. However, we find that the fraction of disk galaxies
with absorption-line spectra (i.e., with no current star formation) is larger
in clusters than in the field by a factor of --5. This suggests that the
cluster environment has the overall effect of switching off star formation in
(at least) some spiral galaxies. To interpret these observational results, we
carry out simulations of the possible effects of the cluster environment on the
star-formation history of disk galaxies and thus their photometric and
spectroscopic properties. Finally, we evaluate the evolution of the rest-frame
absolute -band magnitude per unit redshift at fixed rotation velocity.Comment: 21 pages, 13 figures, accepted for publication in MNRA
Spectral Indices in Cooling Flow Galaxies: Evidence for Star Formation
Through the study of two absorption spectral features in the optical range
(Mg2 and the 4000 A break), we find evidence for star formation in the inner
regions of cooling-flow galaxies. The application of simple stellar population
models reveals that the measured indices are explained if a relatively small
fraction of the total mass flow (5-17%) is forming new stars with a normal IMF.
However, we argue that this is only a lower limit, and conclude that a large
fraction of the gas accreted inside the galaxy could be forming stars. In
addition, the analysis of line-strength gradients in the inner galaxy regions
reveals that, in the mean, they are lower than those of normal ellipticals, and
exhibit a hint of correlation with the mass accretion rate. Simultaneously, the
spectral indices in the outer regions of some galaxies, with and without
cooling flow, attain extremely low values, suggesting that they could be
hosting star formation with an origin not related to the cooling flows.Comment: PostScript file (compressed and encoded) containing 21 page
Evidence for power-law frequency dependence of intrinsic dielectric response in the CaCuTiO
We investigated the dielectric response of CaCuTiO (CCTO) thin
films grown epitaxially on LaAlO (001) substrates by Pulsed Laser
Deposition (PLD). The dielectric response of the films was found to be strongly
dominated by a power-law in frequency, typical of materials with localized
hopping charge carriers, in contrast to the Debye-like response of the bulk
material. The film conductivity decreases with annealing in oxygen, and it
suggests that oxygen deficit is a cause of the relatively high film
conductivity. With increase of the oxygen content, the room temperature
frequency response of the CCTO thin films changes from the response indicating
the presence of some relatively low conducting capacitive layers to purely
power law, and then towards frequency independent response with a relative
dielectric constant . The film conductance and dielectric
response decrease upon decrease of the temperature with dielectric response
being dominated by the power law frequency dependence. Below 80 K, the
dielectric response of the films is frequency independent with
close to . The results provide another piece of evidence for an
extrinsic, Maxwell-Wagner type, origin of the colossal dielectric response of
the bulk CCTO material, connected with electrical inhomogeneity of the bulk
material.Comment: v4: RevTeX, two-column, 9 pages, 7 figures; title modified, minor
content change in p.7, reference adde
The host galaxy of GRB010222: The strongest damped Lyman-alpha system known
Analysis of the absorption lines in the afterglow spectrum of the gamma-ray
burst GRB010222 indicates that its host galaxy (at a redshift of z=1.476) is
the strongest damped Lyman-alpha (DLA) system known, having a very low
metallicity and modest dust content. This conclusion is based on the detection
of the red wing of Lyman-alpha plus a comparison of the equivalent widths of
ultraviolet Mg I, Mg II, and Fe II lines with those in other DLAs. The column
density of H I, deduced from a fit to the wing of Lyman-alpha, is (5 +/- 2)
10^22 cm^-2. The ratio of the column densities of Zn and Cr lines suggests that
the dust content in our line of sight through the galaxy is low. This could be
due to either dust destruction by the ultraviolet emission of the afterglow or
to an initial dust composition different to that of the diffuse interstellar
material, or a combination of both.Comment: Submitted to MNRAS 12 page
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