1,379 research outputs found
On Semiclassical Limits of String States
We explore the relation between classical and quantum states in both open and
closed (super)strings discussing the relevance of coherent states as a
semiclassical approximation. For the closed string sector a gauge-fixing of the
residual world-sheet rigid translation symmetry of the light-cone gauge is
needed for the construction to be possible. The circular target-space loop
example is worked out explicitly.Comment: 12 page
A multi-wavelength study of the evolution of Early-Type Galaxies in Groups: the ultraviolet view
ABRIDGED- The UV-optical color magnitude diagram (CMD) of rich galaxy groups
is characterised by a well developed Red Sequence (RS), a Blue Cloud (BC) and
the so-called Green Valley (GV). Loose, less evolved groups of galaxies likely
not virialized yet may lack a well defined RS. This is actually explained in
the framework of galaxy evolution. We are focussing on understanding galaxy
migration towards the RS, checking for signatures of such a transition in their
photometric and morphological properties. We report on the UV properties of a
sample of ETGs galaxies inhabiting the RS. The analysis of their structures, as
derived by fitting a Sersic law to their UV luminosity profiles, suggests the
presence of an underlying disk. This is the hallmark of dissipation processes
that still must have a role in the evolution of this class of galaxies. SPH
simulations with chemo-photometric implementations able to match the global
properties of our targets are used to derive their evolutionary paths through
UV-optical CDM, providing some fundamental information such as the crossing
time through the GV, which depends on their luminosity. The transition from the
BC to the RS takes several Gyrs, being about 3-5 Gyr for the the brightest
galaxies and more long for fainter ones, if it occurs. The photometric study of
nearby galaxy structures in UV is seriously hampered by either the limited FoV
of the cameras (e.g in HST) or by the low spatial resolution of the images (e.g
in the GALEX). Current missions equipped with telescopes and cameras sensitive
to UV wavelengths, such as Swift-UVOT and Astrosat-UVIT, provide a relatively
large FoV and better resolution than the GALEX. More powerful UV instruments
(size, resolution and FoV) are obviously bound to yield fundamental advances in
the accuracy and depth of the surface photometry and in the characterisation of
the galaxy environment.Comment: 12 pages, 6 figures: accepted for publication in Astrophysics & Space
Science as contributions to the workshop: "UV astronomy, the needs and the
means
Detection of replicative Kashmir Bee Virus and Black Queen Cell Virus in Asian hornet Vespa velutina (Lepelieter 1836) in Italy
Information concerning the pathogenic role of honey bee viruses in invasive species are still scarce. The aim of this investigation was to assess the presence of several honey bee viruses, such as Black Queen Cell Virus (BQCV), Kashmir Bee Virus (KBV), Slow Paralysis Virus (SPV), Sac Brood Virus (SBV), Israeli Acute Paralysis Virus (IAPV), Acute Bee Paralysis Virus (ABPV), Chronic Bee Paralysis Virus (CBPV), in Vespa velutina specimens collected in Italy during 2017. Results of this investigation indicate that among pathogens, replicative form of KBV and BQCV were detected, assessing the spillover effect of both these viruses from managed honey bees to hornets
Gas-Rich Dwarf Galaxies from the PSS-II --- II. Optical Properties
We describe the optical properties of a sample of 101 gas-rich field dwarf
galaxies found on PSS-II (Second Palomar Sky Survey) plates, most newly
discovered as part of a survey to investigate the clustering properties of
dwarf galaxies relative to giants. These galaxies have low surface brightnesses
and are relatively distant, with recession velocities ranging up to 10,000
km/s. They have bluer V-I colors (median value of 0.75) than either actively
star-forming giant galaxies or low metallicity globular clusters, implying that
these dwarfs have both low metallicities and little past star formation. These
galaxies are also extremely gas rich, with a median HI mass to V luminosity
ratio of approximately 2 in solar units. We divide the sample into two groups:
true dwarfs with diameters (at 25 I mag arcsec^-2) less than 7.5 kpc and
Magellanic dwarfs with diameters greater than that value. The true dwarfs have
greater HI mass to V luminosity ratios and slightly bluer V-I colors than the
Magellanic dwarfs. Overall, the optical properties of our sample of dwarf
galaxies point towards their being quiescent objects that have undergone little
star formation over the age of the universe. They are not faded objects, but
instead may be going through one of their first periods of weak star formation.Comment: 27 pages, to appear in 20 May 1997 ApJ, paper also available at
http://www.astro.nwu.edu/astro/pildis/dwarfphot.html and
http://zebu.uoregon.edu/~js/dwarf.htm
VEGAS: a VST Early-type GAlaxy Survey. IV. NGC 1533, IC 2038 and IC 2039: an interacting triplet in the Dorado group
This paper focuses on NGC 1533 and the pair IC 2038 and IC 2039 in Dorado a
nearby, clumpy, still un-virialized group. We obtained their surface photometry
from deep OmegaCAM@ESO-VST images in g and r bands. For NGC 1533, we map the
surface brightness down to mag/arcsec and mag/arcsec and out to about . At such faint levels
the structure of NGC 1533 appear amazingly disturbed with clear structural
asymmetry between inner and outer isophotes in the North-East direction. We
detect new spiral arm-like tails in the outskirts, which might likely be the
signature of a past interaction/merging event. Similarly, IC 2038 and IC 2039
show tails and distortions indicative of their ongoing interaction. Taking
advantages of deep images, we are able to detect the optical counterpart to the
HI gas. The analysis of the new deep data suggests that NGC 1533 had a complex
history made of several interactions with low-mass satellites that generated
the star-forming spiral-like structure in the inner regions and are shaping the
stellar envelope. In addition, the VST observations show that also the two less
luminous galaxies, IC 2038 and IC 2039, are probably interacting each-other
and, in the past, IC 2038 could have also interacted with NGC 1533, which
stripped away gas and stars from its outskirts. The new picture emerging from
this study is of an interacting triplet, where the brightest galaxy NGC 1533
has ongoing mass assembly in the outskirts.Comment: Accepted for publication in The Astronomical Journal. High-resolution
version of paper is available at the following link:
https://www.dropbox.com/preview/VEGAS_IV.pdf?role=persona
Formation and evolution of dusty starburst galaxies I. A new method for deriving spectral energy distribution
We present a new numerical code which is designed to derive a spectral energy
distribution (SED) for an arbitrary spatial distribution of stellar and gaseous
components in a dusty starburst galaxy. We apply a ray tracing method to
numerical simulations and thereby estimate extinction and reemission of stellar
light by dusty gas in an explicitly self-consistent manner. By using this code,
we can investigate simultaneously dynamical and photometric evolution of a
dusty galaxy based on stellar and gaseous dynamical simulations. As an example,
we demonstrate when and how a major galaxy merger with dusty starburst becomes
an ultra-luminous infrared galaxy owing to strong internal dust extinction. We
furthermore discuss advantages and disadvantages of the present new code in
clarifying the nature and the origin of low and high redshift dusty starburst
galaxies.Comment: 44 pages 19 figures (11 color), accepted by Ap
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