156 research outputs found
Galaxy evolution in nearby galaxy groups. III. A GALEX view of NGC 5846, the largest group in the local universe
We explore the co-evolution of galaxies in nearby groups (V < 3000 km/s) with
a multi-wavelength approach. We analyze GALEX far-UV (FUV) and near-UV (NUV)
imaging and SDSS u,g,r,i,z data of groups spanning a large range of dynamical
phases. We characterize the photometric properties of
spectroscopically-confirmed galaxy members and investigate the global
properties of the groups through a dynamical analysis. Here we focus on NGC
5846, the third most massive association of Early-Type Galaxies (ETG) after the
Virgo and Fornax clusters. The group, composed of 90 members, is dominated by
ETGs (about 80 per cent), and among ETGs about 40\% are dwarfs. Results are
compared with those obtained for three groups in the LeoII cloud, which are
radically different both in member-galaxy population and dynamical properties.
The FUV-NUV cumulative colour distribution and the normalized UV luminosity
function (LF) significantly differ due to the different fraction of late-type
galaxy population. The UV LF of NGC 5846 resembles that of the Virgo cluster,
however our analysis suggests that star-formation episodes are still occurring
in most of the group galaxies, including ETGs. The NUV-i colour distribution,
the optical-UV colour-colour diagram, and NUV-r vs. Mr colour-magnitude
relation suggest that the gas contribution cannot be neglected in the evolution
of ETG-type group members. Our analysis highlights that NGC~5846 is still in an
active phase of its evolution, notwithstanding the dominance of dwarf and
bright ETGs and its virialized configuration.Comment: 26 pages, 13 figures, accepted for publication in MNRA
A New Fluid Dynamic Model for the CFD Simulations of Fluidized Beds
A new Eulerian-Eulerian multidimensional model is proposed for the study of the dynamics of dense fluidized suspensions. The main distinctive feature of this new formulation of the equations of motion resides in the closure relationships adopted to express the fluid-particle interaction force. The force accounts for three contributions: buoyant force, drag force and elastic force. The buoyant force is related to the weight of the fluid displaced by the particles. The drag force is expressed as the product of the drag exerted on an unhindered particle, subject to the same volumetric flux of fluid, and a âcorrective functionâ dependent on both bed voidage and particle Reynolds number. The elastic force is related to spatial gradients in the bed voidage and is parallel to the drag force; the force can be regarded as the component of the drag which arises when the homogeneity of the suspension is lost at the macroscopic length scale. The model is used to study the fluidization dynamics of liquid-solid homogeneous beds and gas-solid bubbling beds with particles belonging to the Group B of the Geldartâs classification (1). The results of the simulations are compared with experimental data mainly in terms of average bed height, average bed voidage and diameter of the rising bubbles
Dust in high-z radio-loud AGN
We present continuum observations of a small sample of high-redshift,
radio-loud AGN (radio galaxies and quasars) aimed at the detection of thermal
emission from dust. Seven AGN were observed with IRAM and SEST at 1.25mm; two
of them, the radio galaxies 1243+036 () and MG1019+0535 () were also observed at 0.8mm with the JCMT submillimetre telescope.
Additional VLA observations were obtained in order to derive the spectral shape
of the synchrotron radiation of MG1019+0535 at high radio frequencies.
MG1019+0535 and TX0211122 were expected to contain a large amount of dust
based on their depleted Ly emission. The observations suggest a clear
1.25-mm flux density excess over the synchrotron radiation spectrum of
MG1019+0535, suggesting the presence of thermal emission from dust in this
radio galaxy, whereas the observations of TX0211122 were not sensitive
enough to meaningfully constrain its dust content. On the other hand, our
observations of 1243+036 provide a stringent upper limit on the total dust mass
of M. Finally, we find that the spectra of the radio-loud
quasars in our sample () steepen between rest-frame radio and the
far-infrared. We discuss the main implications of our results, concentrating on
the dusty radio galaxy, MG1019+0535.Comment: 11 pages, A&A LaTeX, 4 figure
Dust in High Redshift Radio Galaxies and the Early Evolution of Spheroidal Galaxies
Several lines of evidence suggest that early-type galaxies might have been
very dusty during their initial evolutionary stages, characterized by intense
star formation activity. The radio selection has provided, by far, the richest
samples of high- galaxies, most likely of early type, which may therefore
yield crucial direct information on the period when the bulk of stars were
born. In order to investigate the role of dust in these phases, we have
analyzed recent observations of a number of high- radio galaxies in the
framework of a self-consistent scenario for the evolution of early type
galaxies. The available data can be fully accounted for by ``opaque'' models
similar to that already used by Mazzei and De Zotti (1994a) to fit the spectrum
of the hyperluminous galaxy IRAS~F. However, there is still
considerable latitude for models. Good fits can be obtained with galactic ages
ranging from 0.05 to 2 Gyr. Crucial constraints may be provided by ground-based
sub-mm measurements and by observations with the forthcoming Infrared Space
Observatory (ISO).Comment: MNRAS accepted; latex file, 10 pages, 7 figures available upon
reques
Galaxy evolution in groups. NGC 3447/NGC 3447A: the odd couple in LGG 225
Local Group Analogs (LGA) are galaxy associations dominated by few bright
Spirals, reminiscent of the LG. The NGC3447/NGC3447A system, member of the LGG
225 group, a nearby LGA, is considered a physical pair: an intermediate
luminosity late type spiral, NGC3447, and an irregular companion, NGC3447A,
linked by a faint filament of matter. A ring-like structure in the NGC3447
outskirts is emphasised by UV observations. This work aims to contribute to the
understanding of galaxy evolution in low density environments, favourable
habitat to highly effective encounters. We performed a multi-wavelength
analysis of the surface photometry of this system to derive spectral energy
distribution and structural properties using UV and optical images. We also
characterised the velocity field of the pair using new kinematic observations.
All these data are used to constrain smooth particle hydrodynamic simulations
with chemo-photometric implementation to shed light on the evolution of this
system. Luminosity profiles are all consistent with the presence of a disc
extending and including NGC3447A. The overall velocity field does not emphasise
any significant rotation pattern, rather a small velocity gradient between
NGC3447 and NGC3447A. Our simulation, detached from a large grid explored to
best-fit the global properties of the system, suggests that this arises from an
encounter between two halos of equal mass. NGC3447 and NGC3447A belong to the
same halo, NGC3447A being a substructure of the same disk as NGC3447. The halo
gravitational instability, enhanced by the encounter, fuels a long lived
instability in this dark matter dominated disk, driving its morphology. This
system may warn about a new class of "false pairs" and the potential danger of
a misunderstanding of such objects in pair surveys that could produce a severe
underestimate of the total mass of the system. (abridged)Comment: 14 pages, 10 figures, A&A accepte
Self-Consistent Evolution of Ring Galaxies
Ring galaxies are commonly known as objects where a burst of star formation
was triggered by a close encounter with an intruder, maybe a satellite galaxy.
BVRI CCD observations of five ring galaxies have been performed. Here we
present the results of a self-consistent approach to reproduce their observed
morphology and spectral energy distribution using updated --body simulations
and evolutionary population synthesis models extending from UV to far--IR
wavelengths. Some suggestions about the evolutionary properties of these
starburst galaxies are then derived.Comment: MNRAS accepted; latex file, 20 pages, 3 tables and 11 figures
available upon reques
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