169 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
Reliable random error estimation in the measurement of line-strength indices
We present a new set of accurate formulae for the computation of random
errors in the measurement of atomic and molecular indices. The new expressions
are in excellent agreement with numerical simulations. We have found that, in
some cases, the use of approximated equations can give misleading line-strength
index errors. It is important to note that accurate errors can only be achieved
after a full control of the error propagation throughout the data reduction
with a parallel processing of data and error frames. Finally, simple recipes
for the estimation of the required signal-to-noise ratio to achieve a fixed
index error are presented.Comment: 9 pages, LaTeX file + 5 PostScript figures, psfig.sty and laa-s.sty
required, to be published in Astronomy & Astrophysics Supplement Serie
Near-IR line-strengths in elliptical galaxies: evidence for IMF variations?
We present new relations between recently defined line-strength indices in
the near-IR (CaT*, CaT, PaT, MgI, and sTiO) and central velocity dispersion
(sigma_0) for a sample of 35 early-type galaxies, showing evidence for
significant anti-correlations between CaII triplet indices (CaT* and CaT) and
log(sigma_0). These relations are interpreted in the light of our recent
evolutionary synthesis model predictions, suggesting the existence of important
Ca underabundances with respect to Fe and/or an increase of the dwarf to giant
stars ratio along the mass sequence of elliptical galaxies.Comment: 5 pages, 3 figures, LaTeX. Accepted for publication in MNRAS Pink
Pages. See related information in
http://www.ucm.es/info/Astrof/ellipt/CATRIPLET.htm
Empirical calibration of the near-IR Ca II triplet - I. The stellar library and index definition
A new stellar library at the near-IR spectral region developed for the
empirical calibration of the Ca II triplet and stellar population synthesis
modeling is presented. The library covers the range 8348-9020 Angstrom at 1.5
Angstrom (FWHM) spectral resolution, and consists of 706 stars spanning a wide
range in atmospheric parameters. We have defined a new set of near-IR indices,
CaT*, CaT and PaT, which mostly overcome the limitations of previous
definitions, the former being specially suited for the measurement of the Ca II
triplet strength corrected for the contamination from Paschen lines. We also
present a comparative study of the new and the previous calcium indices, as
well as the corresponding transformations between the different systems. A
thorough analysis of the sources of index errors and the procedure to calculate
them is given. Finally, index and error measurements for the whole stellar
library are provided together with the final spectra.Comment: 24 pages, 10 figures, LaTeX. For associated spectra, tables and
software, see http://www.ucm.es/info/Astrof/ellipt/CATRIPLET.html or
http://www.nottingham.ac.uk/~ppzrfp/CATRIPLET.htm
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
Early-type galaxies in the Coma cluster: a new piece in the calcium puzzle
We present measurements of the CaII triplet and the Ca4227 Lick-index for a
sample of early-type galaxies in the Coma cluster, deriving, for the first
time, their corresponding relationships with velocity dispersion. Compared with
a similar subsample of ellipticals in the field, Coma galaxies with velocity
dispersions in the range ~ 180-270 km/s exhibit significant differences in the
strengths of the Ca features, suggesting an influence of the environment on the
star formation histories of these galaxies. We argue that the main scenarios
previously proposed to explain the relatively low CaII triplet of galaxies are
not able by themselves to simultaneously reconcile the strengths of the two Ca
indices in both environments.Comment: 6 pages including 2 figures. Accepted for publication in ApJL. For
associated data tables see
http://www.ucm.es/info/Astrof/ellipt/CATRIPLET.htm
Empirical calibration of the near-IR CaII triplet - IV. The stellar population synthesis models
We present a new stellar population synthesis model, which predicts SEDs for
single-age single-metallicity stellar populations, SSPs, at resolution 1.5A
(FWHM) in the spectral region of the near-IR CaII triplet feature. The main
ingredient of the model is a new extensive empirical stellar spectral library
presented in Cenarro et al., which is composed of more than 600 stars. Two main
products of interest for stellar population analysis are presented. The first
is a library of SEDs for SSPs covering a large range of ages, metallicities and
different IMF types. They are well suited to model galaxy data, since the SSP
spectra, with flux-calibrated response curves, can be smoothed to match the
resolution of galaxy data, taking into account the internal velocity dispersion
of the galaxy, allowing the user to analyze the observed spectrum in its own
system. We also produce integrated absorption line indices for the same SSPs in
the form of equivalent widths. We find the following behaviour for the CaII
feature in old-aged SSPs: i) the CaII triplet feature does not change much with
time for all metallicities for ages larger than ~3 Gyr, ii) this index shows a
strong dependence with metallicity for values below [M/H] ~-0.5 and iii) for
larger metallicities this feature does not show a significant dependence either
on age or on the metallicity, being more sensitive to changes in the slope of
power-like IMF shapes. The SSP spectra have been calibrated with measurements
for globular clusters. Fitting the models to two early-type galaxies of
different luminosities, we find that the CaII measurements cannot be fitted
unless a very dwarf-dominated IMF is imposed, or if the Ca abundance is even
lower than the Fe abundance.Comment: 32 pages, 20 postscript figures, LaTeX. MNRAS, in press. Model
predictions can be found at http://www.iac.es/galeria/vazdekis/ or
http://www.ucm.es/info/Astrof/ellipt/CATRIPLET.htm
The Relationship between Brachycephalic Head Features in Modern Persian Cats and Dysmorphologies of the Skull and Internal Hydrocephalus
Background: Cat breeders observed a frequent occurrence of internal hydrocephalus in Persian cats with extreme brachycephalic head morphology. Objective: To investigate a possible relationship among the grade of brachycephaly, ventricular dilatation, and skull dysmorphologies in Persian cats. Animals: 92 Persian-, 10 Domestic shorthair cats. Methods: The grade of brachycephaly was determined on skull models based on CT datasets. Cranial measurements were examined with regard to a possible correlation with relative ventricular volume, and cranial capacity. Persians with high (peke-face Persians) and lower grades of brachycephaly (doll-face Persians) were investigated for the presence of skull dysmorphologies.
Results: The mean cranial index of the peke-face Persians (0.97 ± 0.14) was significantly higher than the mean cranial index of doll-face Persians (0.66 ± 0.04; P < 0.001). Peke-face Persians had a lower relative nasal bone length (0.15 ± 0.04) compared to doll-face (0.29 ± 0.08; P < 0.001). The endocranial volume was significantly lower in doll-face than peke-face Persians (89.6 ± 1.27% versus 91.76 ± 2.07%; P < 0.001). The cranial index was significantly correlated with this variable (Spearman´s r: 0.7; P < 0.0001).
Mean ventricle: Brain ratio of the peke-face group (0.159 ± 0.14) was significantly higher compared to doll-face Persians (0.015 ± 0.01; P < 0.001). Conclusion and Clinical Relevance: High grades of brachycephaly are also associated with malformations of the calvarial and facial bones as well as dental malformations. As these dysmorphologies can affect animal welfare, the selection for extreme forms of brachycephaly in Persian cats should be reconsidered
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