58 research outputs found
Large Scale Morphological Segregation in Optically Selected Galaxy Redshift Catalogs
We present the results of an exhaustive analysis of the morphological
segregation of galaxies in the CfA and SSRS catalogs through the scaling
formalism. Morphological segregation between ellipticals and spirals has been
detected at scales up to 15-20 h Mpc in the CfA catalog, and up to 20-30
h Mpc in the SSRS catalog. Moreover, it is present not only in the
densest areas of the galaxy distribution, but also in zones of moderate
density.Comment: 9 pages, (1 figure included), uuencode compressed Postscript,
(accepted for publication in ApJ Letters), FTUAM-93-2
Shape and kinematics of elliptical galaxies: evolution due to merging at z < 1.5
[EN]Aims. We investigate the evolution in the shape and kinematics of elliptical galaxies in a cosmological framework.
Methods. We identified relaxed, elliptical-like objects (ELOs) at redshifts z = 0, z = 0.5, z = 1 and z = 1.5 within a set of hydrodynamic, self-consistent simulations completed for a concordance cosmological model.
Results. The population of elliptical systems that we analysed evolve systematically with time becoming rounder in general by z = 0 and also more velocity dispersion supported. We found that this is due primarily to major dry mergers where only a modest amount of angular momentum is involved in the merger event. Despite the general trend, in a significant number of cases the merger event involves a relatively high amount of specific angular momentum, which causes the system in general to acquire higher rotational support and/or a more oblate shape. These evolutionary patterns persist when we study our systems in projection, in simulating true observations, and thus should be evident in future observations.Peer reviewe
Is the Fast Evolution Scenario for Virialized Compact Groups Really Compelling? The Role of a Dark Massive Group Halo
We report on results of N-body simulations aimed at testing the hypothesis
that galaxies in X-ray emitting (i.e., virialized) Compact Groups are not
tidally stripped when they are embedded in a common, massive, quiescent dark
matter halo. To disentangle the effects of interactions from spurious effects
due to an incorrect choice of the initial galaxy model configurations, these
have been chosen to be tidally-limited King spheres, representing systems in
quasi-equilibrium within the tidal field of the halo. The potential of the halo
has been assumed to be frozen and the braking due to dynamical friction
neglected. Our results confirm the hypothesis of low rates of tidal stripping
and suggest a scenario for virialized Compact Group evolution in their
quiescent phases with only very moderate tidally induced galaxy evolution can
be generally expected. This implies the group stability, provided that the
dynamical friction timescales in these systems are not much shorter than the
Hubble time. We discuss briefly this possibility, in particular taking account
of the similarity between the velocity dispersions of a typical virialized
Compact Groups and the internal velocity dispersion of typical member galaxies.
A number of puzzling observational data on Compact Groups can be easily
explained in this framework. Other observations would be better understood as
the result of enhanced merging activity in the proto-group environment, leading
to virialized Compact Group formation through mergers of lower mass halos, as
predicted by hierarchical scenarios of structure formation.Comment: 18 pages, 1 postscript file, 2 tables, to be published in ApJLet
A tidal extension in the Ursa Minor dwarf spheroidal galaxy
We report the detection of main-sequence and blue horizontal-branch stars of
the Ursa Minor dwarf spheroidal galaxy beyond its tidal radius, indicating the
existence of a possible tidal extension in this satellite of the Milky Way.
This tidal extension could spread out well beyond the area covered in our
survey (R>80 arcmin),as suggested by the presence of a ``break'' to a shallower
slope observed in its density profile. The V-band surface brightness for this
possible tidal extension range from 29.8 to 31.5 mag arcsec^-2. The area
covered in our survey (~1.65 deg^2) is not enough to discriminate if this
extra-tidalpopulation is part of a tidal tail or an extended halo around the
galaxy.
The existence of this tidal extension in Ursa Minor indicates that this
satellite is currently undergoing a tidal disruption process by the Milky Way.
We discuss the possibility of a tidal origin for the high mass-to-light ratio
observed in this galaxy on the basis on our result and recent theoretical
simulations of the tidal disruption of dwarf satellites in the Galactic halo.Comment: 13 pages, 3 figures, accepted for publication in Astrophysical
Journal Letter
The Origin of Kinematically Persistent Planes of Satellites as Driven by the Early Evolution of the Cosmic Web in ÎCDM
Kinematically persistent planes (KPPs) of satellites are fixed sets of satellites co-orbiting around their host galaxy, whose orbital poles are conserved and clustered across long cosmic time intervals. They play the role of âskeletons,â ensuring the long-term durability of positional planes. We explore the physical processes behind their formation in terms of the dynamics of the local cosmic web (CW), characterized via the so-called Lagrangian volumes (LVs) built up around two zoom-in, cosmological hydro-simulations of Milky Wayâmass disk galaxy + satellites systems, where three KPPs have been identified. By analyzing the LV deformations in terms of the reduced tensor of inertia (TOI), we find an outstanding alignment between the LV principal directions and the KPP satellitesâ orbital poles. The most compressive local mass flows (along the eË3 eigenvector) are strong at early times, feeding the so-called eË3 -structure, while the smallest TOI axis rapidly decreases. The eË3 -structure collapse marks the end of this regime and is the timescale for the establishment of satellite orbital pole clustering when the Universe is âČ4 Gyr old. KPP protosatellites aligned with eË3 are those whose orbital poles are either aligned from early times or have been successfully bent at eË3 -structure collapse. KPP satellites associated with eË1 tend to have early trajectories already parallel to eË3 . We show that KPPs can arise as a result of the ÎCDM-predicted large-scale dynamics acting on particular sets of protosatellites, the same dynamics that shape the local CW environment
Confidence limits of evolutionary synthesis models III. On time-integrated quantities
Evolutionary synthesis models are a fundamental tool to interpret the
properties of observed stellar systems. In order to achieve a meaningful
comparison between models and real data, it is necessary to calibrate the
models themselves, i.e. to evaluate the dispersion due to the discreteness of
star formation as well as the possible model errors. In this paper we show that
linear interpolations in the log M - log t_k plane, that are customary in the
evaluation of isochrones in evolutionary synthesis codes, produce unphysical
results. We also show that some of the methods used in the calculation of
time-integrated quantities (kinetic energy, and total ejected masses of
different elements) may produce unrealistic results. We propose alternative
solutions to solve both problems. Moreover, we have quantified the expected
dispersion of these quantities due to stochastic effects in stellar
populations. As a particular result, we show that the dispersion in the 14N/12C
ratio increases with time.Comment: 11 pages, 8 figures, accepted by A&
LVGPy: Diseño, desarrollo y puesta en marcha de un âLaboratorio Virtual de GeomatemĂĄtica en lenguaje Pythonâ
Se describen los objetivos, metodologĂa y resultados del Proyecto de InnovaciĂłn con NÂș de proyecto 211, Convocatoria 2017/2017. El proyecto fue desarrollado por profesores de las Facultades de BiologĂa y GeologĂa
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