85 research outputs found
Tidal distortions in pairs of early-type galaxies
The authors are conducting an imaging survey of pairs of elliptical galaxies which has already produced interesting results. Some pairs present a common pattern of distortion interpreted in terms of tidal effects (Davoust and Prugniel, 1988; Prugniel et al., 1989). Other examples drawn from the literature (Borne and Hoessel, 1988; Colina and Perez-Fournon, 1990) share the same morphology. New cases and lists of the characteristics of 24 such systems. The authors' pairs are drawn from a sample of binary and multiple galaxies which has in turn been extracted from the CGCG, UGC (Nilson, 1973) and VV (Vorontsov-Velyaminov, 1959) catalogues. This sample includes that of Karachentsev (1972). It contains 1800 pairs, among which 700 are S - S or mixed morphology pairs. The authors are working on the remainder to produce a sample of close physical pairs of elliptical galaxies (they also include bulge dominated SO's since the morphological discrimination from ellipticals is often ambiguous, in particular for interacting galaxies). One of the interests of this work is to provide a sample selected on purely optical criteria, at variance with other works (e.g., Valentijn and Casertano, 1988). This will allow statistical studies of non-optical properties of these pairs (in particular radio emission). The authors have so far obtained charge-coupled device (CCD) images of 125 pairs with a 2m telescope and velocities' differences of 78 pairs were obtained using the 1.93 meter telescope of Observatoire de Haute Provence and from the literature. One is an optical pair (VV 190). Eighteen of our pairs present the morphological effect described in Davoust and Prugniel (1988): the external parts of each member are stretched in opposite senses in a direction rougly perpendicular to the pair axis. The proportion of 15 plus or minus 4 percent distorted pairs confirms previous estimates. Except for a few cases involving flattened galaxies with nearly aligned major axes which deserve careful detailed analysis (Prugniel, 1989), the apparent distortions do correspond to physical distortions. We have searched the literature for isophote maps showing this effect. In the survey of radio galaxies by Colina and Perez-Fournon (1990), 7 out of 20 pairs show this characteristic distortion
New atmospheric parameters and spectral interpolator for the MILES cool stars
Context: The full spectrum fitting of stellar spectra against a library of
empirical spectra is a well-established approach to measure the atmospheric
parameters of FGK stars with a high internal consistency. Extending it towards
cooler stars still remains a challenge. Aims: We address this question by
improving the interpolator of the MILES (Medium-resolution INT Library of
Empirical Spectra) library in the low effective temperature regime (Tefff <
4800 K), and we refine the determination of the parameters of the cool MILES
stars. Methods: We use the ULySS package to determine the atmospheric
parameters (Teff, logg and [Fe/H]), and measure the biases of the results with
respect to our updated compilation of parameters calibrated against theoretical
spectra. After correcting some systematic effects, we compute a new
interpolator that we finally use to redetermine the atmospheric parameters
homogeneously and assess the biases. Results: Based on an updated literature
compilation, we determine Teff in a more accurate and unbiased manner compared
to those determined with the original interpolator. The validity range is
extended downwards to about Teff = 2900 K compared to 3500 K previously. The
mean residual biases on Teff, logg, and [Fe/H], with respect to the literature
compilation for the coolest stars (Teff <= 3800 K) computed using the new
interpolator, are -15 K, -0.02 dex, and 0.02 dex respectively. The
corresponding estimations of the external precision are 63 K, 0.23 dex, and
0.15 dex respectively. For the stars with Teff in the range 3800 - 4200 K, the
determinations of Teff and [Fe/H] have been slightly improved. At higher
temperatures, the new interpolator is comparable to the original one. The new
version of the interpolator is publicly available.Comment: A&A Accepted, 30 pages, 10 figure
Kinematics and stellar populations of the dwarf elliptical galaxy IC 3653
We present the first 3D observations of a diffuse elliptical galaxy (dE). The
good quality data (S/N up to 40) reveal the kinematical signature of an
embedded stellar disc, reminiscent of what is commonly observed in elliptical
galaxies, though similarity of their origins is questionable. Colour map built
from HST ACS images confirms the presence of this disc. Its characteristic
scale (about 3 arcsec = 250 pc) is about a half of galaxy's effective radius,
and its metallicity is 0.1-0.2 dex larger than the underlying population.
Fitting the spectra with synthetic single stellar populations (SSP) we found an
SSP-equivalent age of 5 Gyr and nearly solar metallicity [Fe/H]=-0.06 dex. We
checked that these determinations are consistent with those based on Lick
indices, but have smaller error bars. The kinematical discovery of a stellar
disc in dE gives additional support to an evolutionary link from dwarf
irregular galaxies due to stripping of the gas against the intra-cluster
medium.Comment: 15 pages, 10 figures, accepted to MNRA
Internal kinematics and stellar populations of dE galaxies: Clues to their formation/evolution
What is the origin of the numerous population of diffuse elliptical galaxies
(dE) in clusters? These galaxies formed their stars several billion years ago
and lost their gas. Though the stellar winds resulting from star formation and
the interactions with the environment undoubedtly play a role, their respective
role and details of the mechanism of this evolution is still debated.
In this presentation we will review the first 3D spectroscopic observations
of a handful of dE galaxies. These data reveal complex kinematical structures,
with embedded discs and counter rotating cores, and they open extremely
promising perspectives for studying the history of the stellar population
throughout these various features.
The presence of disks, which was already known from detailed image analysis,
and of complex kinematics and the new constraints on the stellar population
enforce the hypothesis of the evolutionary connection between dEs and disk
galaxies.Comment: To be published in the proceedings of IAU Colloquium 198 on a
"near-field cosmology with dwarf elliptical galaxies
NBursts: Simultaneous Extraction of Internal Kinematics and Parametrized SFH from Integrated Light Spectra
We present a novel approach for simultaneous extraction of stellar population
parameters and internal kinematics from the spectra integrated along a line of
sight. We fit a template spectrum into an observed one in a pixel space using a
non-linear minimization in the multidimensional parameter space,
including characteristics of the line-of-sight velocity distribution (LOSVD)
and parametrized star formation history (SFH). Our technique has been applied
to IFU and multi-object spectroscopy of low-luminosity early type galaxies.Comment: 2 pages, to appear in the proceedings of IAU Symposium 241 (Stellar
Populations as Building Blocks of Galaxies
HyperLEDA. III. The catalogue of extragalactic distances
We present the compilation catalogue of redshift-independent distances
included in the HyperLEDA database. It is actively maintained to be up-to-date,
and the current version counts 6640 distance measurements for 2335 galaxies
compiled from 430 published articles. Each individual series is recalibrated
onto a common distance scale based on a carefully selected set of high-quality
measurements. This information together with data on HI line-width, central
velocity dispersion, magnitudes, diameters, and redshift is used to derive a
homogeneous distance estimate and physical properties of galaxies, such as
their absolute magnitudes and intrinsic size.Comment: accepted to A&
The transmutation of dwarf galaxies : stellar populations
Transition-type dwarf (TTD) galaxies share characteristics of early-and late-type dwarfs. Thus, they are suspected to be the thread that connects them. We selected 19 TTD galaxies in the nearby Universe (cz < 2900 km s(-1)) from the Sloan Digital Sky Survey. They span the luminosity range from similar to-14.5 to -19.0 mag in the B band, and are located in different environments.
We derive their single stellar population parameters and star formation histories, using the full spectrum fitting technique with two independent population synthesis models. Irrespective of the synthesis models, we find that these dwarfs have a relatively young mean age (around 1-2 Gyr) and low metallicities (similar to-0.7 dex). Moreover, they had approximately constant star formation rates until a few Gyr ago, associated with strong metal enrichment during the first few Gyr of their evolution. We compare these results with the results from Koleva et al., who studied dwarf elliptical (dE) galaxies in the same luminosity range. We find that (1) both samples occupy the same region in the luminosity-metallicity relation, (2) the build-up of the stellar mass in both types of galaxies is very similar, with most of the stars already formed 5 Gyr ago and (3) contrary to the dEs, TTDs are forming stars at present, but after 1 Gyr of passive evolution, their star formation histories would appear identical to that of dEs.
As far as the stellar population is concerned, the transformation of TTDs into dEs is definitely possible. A star-forming dwarf galaxy can be stripped of at least a fraction of its gas, and its star formation rate can be reduced to that of the TTDs of the present sample. Continued gas removal may drive a galaxy to the state of a gas-depleted bona fide dE. However, we cannot exclude a scenario where a star-forming galaxy is rapidly transformed into an early type without passing through a noticeable 'transition' phase, as suggested by the relatively small fraction of observed dEs with an interstellar medium. We cannot exclude swinging back and forth between a late-type dwarf and a TTD (in the case of episodic star formation) or an early-type dwarf and a TTD (in the case of gas infall)
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