557 research outputs found
Dust properties and distribution in dwarf galaxies
We present a study of the extinction, traced by the Balmer decrement, in HII
regions in the dwarf galaxies NGC 1569 and NGC 4214. We find that the
large-scale extinction around the most prominent HII regions in both galaxies
forms a shell in which locally the intrinsic extinction can adopt relatively
high values ( mag) despite the low metallicity and thus the
low overall dust content. The small-scale extinction (spatial resolution
0.3'') shows fluctuations that are most likely due to variations in the
dust distribution. We compare the distribution of the extinction to that of the
dust emission, traced by Spitzer emission at 8 and 24 \mi, and to the emission
of cold dust at 850 \mi. We find in general a good agreement between all
tracers, expect for the 850 \mi emission in NGC 4214 which is more extended
than the extinction and the other emissions. Whereas in NGC 1569 the dust
emission at all wavelengths is very similar, NGC 4214 shows spatial variations
in the 24-to-850 \mi ratio. We furthermore compared the 24 \mi and the
extinction-corrected Halpha emission from HII regions in a sample of galaxies
with a wide range of metallicities and found a good correlation between both
emissions, independent of metallicity. We suggest that this lack of dependence
on metallicity might be due to the formation of dust shells with a relatively
constant opacity, like the ones observed here, around ionizing stars.Comment: 5 pages, to appear in proceeding of IAU Symposition 255
"Low-metallicity star formation", ed. L. Hunt, S. Madden, & R. Schneider
(Cambridge: CUP
Towards understanding two-level-systems in amorphous solids -- Insights from quantum circuits
Amorphous solids show surprisingly universal behaviour at low temperatures.
The prevailing wisdom is that this can be explained by the existence of
two-state defects within the material. The so-called standard tunneling model
has become the established framework to explain these results, yet it still
leaves the central question essentially unanswered -- what are these two-level
defects? This question has recently taken on a new urgency with the rise of
superconducting circuits in quantum computing, circuit quantum electrodynamics,
magnetometry, electrometry and metrology. Superconducting circuits made from
aluminium or niobium are fundamentally limited by losses due to two-level
defects within the amorphous oxide layers encasing them. On the other hand,
these circuits also provide a novel and effective method for studying the very
defects which limit their operation. We can now go beyond ensemble measurements
and probe individual defects -- observing the quantum nature of their dynamics
and studying their formation, their behaviour as a function of applied field,
strain, temperature and other properties. This article reviews the plethora of
recent experimental results in this area and discusses the various theoretical
models which have been used to describe the observations. In doing so, it
summarises the current approaches to solving this fundamentally important
problem in solid-state physics.Comment: 34 pages, 7 figures, 1 tabl
A Herschel and CARMA view of CO and [C II] in Hickson Compact groups
Understanding the evolution of galaxies from the starforming blue cloud to
the quiescent red sequence has been revolutionized by observations taken with
Herschel Space Observatory, and the onset of the era of sensitive millimeter
interferometers, allowing astronomers to probe both cold dust as well as the
cool interstellar medium in a large set of galaxies with unprecedented
sensitivity. Recent Herschel observations of of H2-bright Hickson Compact
Groups of galaxies (HCGs) has shown that [CII] may be boosted in diffuse
shocked gas. CARMA CO(1-0) observations of these [CII]-bright HCGs has shown
that these turbulent systems also can show suppression of SF. Here we present
preliminary results from observations of HCGs with Herschel and CARMA, and
their [CII] and CO(1-0) properties to discuss how shocks influence galaxy
transitions and star formation.Comment: 4 pages, 3 figures, Proceedings for IAU Symposium 309, Galaxies in 3D
across the Univers
Optimal fast single pulse readout of qubits
The computer simulations of the process of single pulse readout from the
flux-biased phase qubit is performed in the frame of one-dimensional
Schroedinger equation. It has been demonstrated that the readout error can be
minimized by choosing the optimal pulse duration and the depth of a potential
well, leading to the fidelity of 0.94 for 2ns and 0.965 for 12ns sinusoidal
pulses.Comment: 4 pages, 6 figure
Formation of Molecular Gas in the debris of violent Galaxy Interactions
In many gravitational interactions between galaxies, gas and stars that have
been torn from either or both of the precursor galaxies can collect in 'tidal
tails'. Star formation begins anew in these regions to produce 'tidal dwarf
galaxies', giving insight into the process of galaxy formation through the
well-defined timescale of the interaction. But tracking the star formation
process has proved to be difficult: the tidal dwarf galaxies with young stars
showed no evidence of the molecular gas out of which new stars form. Here we
report the discovery of molecular gas (carbon monoxide emission) in two tidal
dwarf galaxies. In both cases, the molecular gas peaks at the same location as
the maximum in atomic-hydrogen density, unlike most gas-rich galaxies. We infer
from this that the molecular gas formed from the HI, rather than being torn in
molecular form from the interacting galaxies. Star formation in the tidal
dwarfs appears to mimic that process in normal spiral galaxies like our own.Comment: 8 pages, 3 figures, Nature in pres
The dust SED in the dwarf galaxy NGC 1569: Indications for an altered dust composition?
We discuss the interpretation of the dust SED from the mid-infrared to the
millimeter range of NGC 1569. The model developed by D\'esert et al. (1990)
including three dust components (Polyaromatic Hydrocarbons, Very Small Grains
and big grains) can explain the data using a realistic interstellar radiation
field and adopting an enhanced abundance of VSGs. A simple three-temperature
model is also able to reproduce the data but requires a very low dust
temperature which is considered to be unlikely in this low-metallicity
starburst galaxy. The high abundance of Very Small Grains might be due to large
grain destruction in supernova shocks. This possibility is supported by ISO
data showing that the emission at 14.3 m, tracing VSGs, is enhanced with
respect to the emission at 6.7 m and 850 m in regions of high star
formation.Comment: 4 pages, conference proceedings paper, "The Spectral Energy
Distribution of Gas-Rich Galaxies: Confronting Models with Data", Heidelberg,
4-8 Oct. 2004, eds. C.C. Popescu & R.J. Tuffs, AIP Conf. Ser., in pres
- …