179 research outputs found
Deconstructing double-barred galaxies in 2D and 3D. II. Two distinct groups of inner bars
The intrinsic photometric properties of inner and outer stellar bars within
17 double-barred galaxies are thoroughly studied through a photometric analysis
consisting of: i) two-dimensional multi-component photometric decompositions,
and ii) three-dimensional statistical deprojections for measuring the
thickening of bars, thus retrieving their 3D shape. The results are compared
with previous measurements obtained with the widely used analysis of integrated
light. Large-scale bars in single- and double-barred systems show similar
sizes, and inner bars may be longer than outer bars in different galaxies. We
find two distinct groups of inner bars attending to their in-plane length and
ellipticity, resulting in a bimodal behaviour for the inner/outer bar length
ratio. Such bimodality is related neither to the properties of the host galaxy
nor the dominant bulge, and it does not show a counterpart in the dimension off
the disc plane. The group of long inner bars lays at the lower end of the outer
bar length vs. ellipticity correlation, whereas the short inner bars are out of
that relation. We suggest that this behaviour could be due to either a
different nature of the inner discs from which the inner bars are dynamically
formed, or a different assembly stage for the inner bars. This last possibility
would imply that the dynamical assembly of inner bars is a slow process taking
several Gyr to happen. We have also explored whether all large-scale bars are
prone to develop an inner bar at some stage of their lives, possibility we
cannot fully confirm or discard.Comment: 14 pages, 8 figures, 1 table. Accepted for publication in MNRA
Stellar kinematics in double-barred galaxies: the sigma-hollows
We present SAURON integral-field stellar velocity and velocity dispersion
maps for four double-barred early-type galaxies: NGC2859, NGC3941, NGC4725 and
NGC5850. The presence of the inner bar does not produce major changes in the
line-of-sight velocity, but it appears to have an important effect in the
stellar velocity dispersion maps: we find two sigma-hollows of amplitudes
between 10 and 40 km/s on either side of the center, at the ends of the inner
bars. We have performed numerical simulations to explain these features. Ruling
out other possibilities, we conclude that the sigma-hollows are an effect of
the contrast between two kinematically different components: the high velocity
dispersion of the bulge and the more ordered motion (low velocity dispersion)
of the inner bar.Comment: 5 pages, 2 figures. Accepted for publication in ApJ Letter
CATÁLOGO DE LAS PLANTAS VASCULARES ESPONTÁNEAS Y CULTIVADAS DE LA REGIÓN DE MURCIA. II. MAGNOLIACEAE-PAPAVERACEAE
This publication is the second issue of a check list of wild and relevant cultivate plants in the Region of Murcia (South-eastern Spain). The model of exposition and all the data about the format of the presented catalogue come explained in a precedent paper (ALCARAZ et al. 1993). The present paper includes a catalogue of 69 taxa of vascular plants.Esta publicación constituye la segunda entrega de una serie sobre el catálogo provisional de las plantas vasculares silvestres, así como las más destacadas de las ornamentales y agrícolas de la Región de Murcia. El modelo de exposición y todos los datos concernientes al formato del catálogo se presentaron en la entrega anterior (ALCARAZ et al., 1993). En total se incluyen en este trabajo 69 táxones de Angiospermae
Superdense massive galaxies in the Nearby Universe
Superdense massive galaxies (r_e~1 kpc; M~10^{11} Msun) were common in the
early universe (z>1.5). Within some hierarchical merging scenarios, a
non-negligible fraction (1-10%) of these galaxies is expected to survive since
that epoch retaining their compactness and presenting old stellar populations
in the present universe. Using the NYU Value-Added Galaxy Catalog from the SDSS
Data Release 6 we find only a tiny fraction of galaxies (~0.03%) with r_e<1.5
kpc and M_*>8x10^{10} Msun in the local Universe (z<0.2). Surprinsingly, they
are relatively young (~2 Gyr) and metal-rich ([Z/H]~0.2). The consequences of
these findings within the current two competing size evolution scenarios for
the most massive galaxies ("dry" mergers vs "puffing up" due to quasar
activity) are discussed.Comment: Accepted for publication in ApJ Letters; 3 figure
Smooth kinematic and metallicity gradients between the Milky Way's nuclear star cluster and nuclear stellar disc. Different components of the same structure?
The innermost regions of most galaxies are characterised by the presence of
extremely dense nuclear star clusters. Nevertheless, these clusters are not the
only stellar component present in galactic nuclei, where larger stellar
structures known as nuclear stellar discs, have also been found. Understanding
the relation between nuclear star clusters and nuclear stellar discs is
challenging due to the large distance towards other galaxies which limits their
analysis to integrated light. The Milky Way's centre, at only 8 kpc, hosts a
nuclear star cluster and a nuclear stellar disc, constituting a unique template
to understand their relation and formation scenario. We aim to study the
kinematics and stellar metallicity of stars from the Milky Way's nuclear star
cluster and disc to shed light on the relation between these two Galactic
centre components. We used publicly available photometric, proper motions, and
spectroscopic catalogues to analyse a region of centred on
the Milky Way's nuclear star cluster. We built colour magnitude diagrams, and
applied colour cuts to analyse the kinematic and metallicity distributions of
Milky Way's nuclear star cluster and disc stars with different extinction along
the line of sight. We detect kinematics and metallicity gradients for the
analysed stars along the line of sight towards the Milky Way's nuclear star
cluster, suggesting a smooth transition between the nuclear stellar disc and
cluster. We also find a bi-modal metallicity distribution for all the analysed
colour bins, which is compatible with previous work on the bulk population of
the nuclear stellar disc and cluster. Our results suggest that these two
Galactic centre components might be part of the same structure with the Milky
Way's nuclear stellar disc being the grown edge of the nuclear star cluster.Comment: Submitted to A&A. 13 pages, 9 figure
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