138 research outputs found
Super star clusters and Supernovae in interacting LIRGs unmasked by NIR adaptive optics
We report on an on-going near-IR adaptive optics survey targeting interacting
luminous IR galaxies. High-spatial resolution NIR data are crucial to enable
interpretation of kinematic, dynamical and star formation (SF) properties of
these very dusty objects. Whole progenitor nuclei in the interactions can be
missed if only optical HST imaging is used. Here we specifically present the
latest results regarding core-collapse supernovae found within the highly
extincted nuclear regions of these galaxies. Direct detection and study of such
highly obscured CCSNe is crucial for revising the optically-derived SN rates
used for providing an independent measurement of the SF history of the
Universe. We also present thus-far the first NIR luminosity functions of super
star cluster (SSC) candidates. The LFs can then be used to constrain the
formation and evolution of SSCs via constraints based on initial mass functions
and cluster disruption models.Comment: 6 pages. To appear in proceedings of 'Galaxies and their Masks'
(Namibia, April 2010), published by Springer, New York, eds. D.L. Block, K.C.
Freeman, I. Puerar
FIRST-based survey of Compact Steep Spectrum sources, II. MERLIN and VLA observations of Medium-sized Symmetric Objects
A new sample of candidate Compact Steep Spectrum (CSS) sources that are much
weaker than the CSS source prototypes has been selected from the VLA FIRST
catalogue. MERLIN `snapshot' observations of the sources at 5 GHz indicate that
six of them have an FR II-like morphology, but are not edge-brightened as is
normal for Medium-sized Symmetric Objects (MSOs) and FR IIs. Further
observations of these six sources with the VLA at 4.9 GHz and MERLIN at 1.7
GHz, as well as subsequent full-track observations with MERLIN at 5 GHz of what
appeared to be the two sources of greatest interest are presented. The results
are discussed with reference to the established evolutionary model of CSS
sources being young but in which not all of them evolve to become old objects
with extended radio structures. A lack of stable fuelling in some of them may
result in an early transition to a so-called coasting phase so that they fade
away instead of growing to become large-scale objects. It is possible that one
of the six sources (1542+323) could be labelled as a prematurely `dying' MSO or
a `fader'.Comment: 13 pages, matches the version printed in Astronomy & Astrophysic
The M81 Group Dwarf Irregular Galaxy DDO 165. II. Connecting Recent Star Formation with ISM Structures and Kinematics
We compare the stellar populations and complex neutral gas dynamics of the
M81 group dIrr galaxy DDO 165 using data from the HST and the VLA. Paper I
identified two kinematically distinct HI components, multiple localized high
velocity gas features, and eight HI holes and shells (the largest of which
spans ~2.2x1.1 kpc). Using the spatial and temporal information from the
stellar populations in DDO 165, we compare the patterns of star formation over
the past 500 Myr with the HI dynamics. We extract localized star formation
histories within 6 of the 8 HI holes identified in Paper I, as well as 23 other
regions that sample a range of stellar densities and neutral gas properties.
From population synthesis modeling, we derive the energy outputs (from stellar
winds and supernovae) of the stellar populations within these regions over the
last 100 Myr, and compare with refined estimates of the energies required to
create the HI holes. In all cases, we find that "feedback" is energetically
capable of creating the observed structures in the ISM. Numerous regions with
significant energy inputs from feedback lack coherent HI structures but show
prominent localized high velocity gas features; this feedback signature is a
natural product of temporally and spatially distributed star formation. In DDO
165, the extended period of heightened star formation activity (lasting more
than 1 Gyr) is energetically capable of creating the observed holes and high
velocity gas features in the neutral ISM.Comment: The Astrophysical Journal, in press. Full-resolution version
available on request from the first autho
The isolated interacting galaxy pair NGC 5426/27 (Arp 271)
We present H alpha observations of the isolated interacting galaxy pair NGC
5426/27 using the scanning Fabry-Perot interferometer PUMA. The velocity field,
various kinematical parameters and rotation curve for each galaxy were derived.
The FWHM map and the residual velocities map were also computed to study the
role of non-circular motions of the gas. Most of these motions can be
associated with the presence of spiral arms and structure such as central bars.
We found a small bar-like structure in NGC 5426, a distorted velocity field for
NGC 5427 and a bridge-like feature between both galaxies which seems to be
associated with NGC 5426. Using the observed rotation curves, a range of
possible masses was computed for each galaxy. These were compared with the
orbital mass of the pair derived from the relative motion of the participants.
The rotation curve of each galaxy was also used to fit different mass
distribution models considering the most common theoretical dark halo models.
An analysis of the interaction process is presented and a possible 3D scenario
for this encounter is also suggested.Comment: 27 pages, 15 figures, to be published in Astronomy & Astrophysic
Unravelling the mystery of the M31 bar
The inclination of M31 is too close to edge-on for a bar component to be
easily recognised and is not sufficiently edge-on for a boxy/peanut bulge to
protrude clearly out of the equatorial plane. Nevertheless, a sufficient number
of clues allow us to argue that this galaxy is barred. We use fully
self-consistent N-body simulations of barred galaxies and compare them with
both photometric and kinematic observational data for M31. In particular, we
rely on the near infrared photometry presented in a companion paper. We compare
isodensity contours to isophotal contours and the light profile along cuts
parallel to the galaxy major axis and offset towards the North, or the South,
to mass profiles along similar cuts on the model. All these comparisons, as
well as position velocity diagrams for the gaseous component, give us strong
arguments that M31 is barred. We compare four fiducial N-body models to the
data and thus set constraints on the parameters of the M31 bar, as its
strength, length and orientation. Our `best' models, although not meant to be
exact models of M31, reproduce in a very satisfactory way the main relevant
observations. We present arguments that M31 has both a classical and a
boxy/peanut bulge. Its pseudo-ring-like structure at roughly 50' is near the
outer Lindblad resonance of the bar and could thus be an outer ring, as often
observed in barred galaxies. The shape of the isophotes also argues that the
vertically thin part of the M31 bar extends considerably further out than its
boxy bulge, i.e. that the boxy bulge is only part of the bar, thus confirming
predictions from orbital structure studies and from previous N-body
simulations.Comment: 14 pages, 12 figures, minor corrections, accepted by MNRAS. Version
with high resolution figures at http://www.oamp.fr/dynamique/pap/M31_th.pd
Ramond-Ramond Fields, Fractional Branes and Orbifold Differential K-Theory
We study D-branes and Ramond-Ramond fields on global orbifolds of Type II
string theory with vanishing H-flux using methods of equivariant K-theory and
K-homology. We illustrate how Bredon equivariant cohomology naturally realizes
stringy orbifold cohomology. We emphasize its role as the correct cohomological
tool which captures known features of the low-energy effective field theory,
and which provides new consistency conditions for fractional D-branes and
Ramond-Ramond fields on orbifolds. We use an equivariant Chern character from
equivariant K-theory to Bredon cohomology to define new Ramond-Ramond couplings
of D-branes which generalize previous examples. We propose a definition for
groups of differential characters associated to equivariant K-theory. We derive
a Dirac quantization rule for Ramond-Ramond fluxes, and study flat
Ramond-Ramond potentials on orbifolds.Comment: 46 pages; v2: typos correcte
Outline of a Theory of Scientific Aesthetics
I offer a theory of art that is based on science. I maintain that, as any other human activity, art can be studied with the tools of science. This does not mean that art is scientific, but aesthetics, the theory of art, can be formulated in accord with our scientific knowledge. I present elucidations of the concepts of aesthetic experience, art, work of art, artistic movement, and I discuss the ontological status of artworks from the point of view of scientific philosophy.Fil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentin
Super-heavy fermion material as metallic refrigerant for adiabatic demagnetization cooling
Low-temperature refrigeration is of crucial importance in fundamental
research of condensed matter physics, as the investigations of fascinating
quantum phenomena, such as superconductivity, superfluidity and quantum
criticality, often require refrigeration down to very low temperatures.
Currently, cryogenic refrigerators with He gas are widely used for cooling
below 1 Kelvin. However, usage of the gas is being increasingly difficult due
to the current world-wide shortage. Therefore, it is important to consider
alternative methods of refrigeration. Here, we show that a new type of
refrigerant, super-heavy electron metal, YbCoZn, can be used for
adiabatic demagnetization refrigeration, which does not require 3He gas. A
number of advantages includes much better metallic thermal conductivity
compared to the conventional insulating refrigerants. We also demonstrate that
the cooling performance is optimized in YbScCoZn by
partial Sc substitution with 0.19. The substitution induces chemical
pressure which drives the materials close to a zero-field quantum critical
point. This leads to an additional enhancement of the magnetocaloric effect in
low fields and low temperatures enabling final temperatures well below 100 mK.
Such performance has up to now been restricted to insulators. Since nearly a
century the same principle of using local magnetic moments has been applied for
adiabatic demagnetization cooling. This study opens new possibilities of using
itinerant magnetic moments for the cryogen-free refrigeration
- …