497 research outputs found
Integral field spectroscopy in the near infrared of NGC 3125-A and SBS 0335-052
We present integral field spectroscopy in the near infrared of the nearby
dwarf starburst galaxies NGC 3125-A and of the low metallicity dwarf galaxy SBS
0335-052. The use of adaptive optics in the observations produces sub-arcsecond
angular resolution. We pinpoint the star forming cores of both galaxies,
identify relevant ISM components such as dust, photo ionized gas, shock excited
gas and molecular gas. We relate these components to the large scale star
formation process of the galaxies. In particular we find the emission of the
near infrared lines of H2 and especially [FeII] does not coincide with the HII
region in NGC 3125. We have the first clear detection of [FeII] in SBS
0335-052
Identifying the lights position in photometric stereo under unknown lighting
Reconstructing the 3D shape of an object from a set of images is a classical
problem in Computer Vision. Photometric stereo is one of the possible
approaches. It stands on the assumption that the object is observed from a
fixed point of view under different lighting conditions. The traditional
approach requires that the position of the light sources is accurately known.
It has been proved that the lights position can be estimated directly from the
data, when at least 6 images of the observed object are available. In this
paper, we give a Matlab implementation of the algorithm for solving the
photometric stereo problem under unknown lighting, and propose a simple
shooting technique to solve the bas-relief ambiguity.Comment: new versio
Delayed Photoionization Feedback in a Super Star Cluster in SBS0335-052E
SBS0335-052 is a well studied Blue Compact Dwarf galaxy with one of the
lowest metallicities of any known galaxy. It also contains 6 previously
identified Super Star Clusters. We combine archival HST NICMOS images in the Pa
alpha line and the 1.6 micron continuum of the eastern component, SBS0335-052E,
with other space and ground based data to perform a multi-wavelength analysis
of the super star clusters. We concentrate on the southern most clusters,
designated S1 and S2, which appear to be the youngest clusters and are the
strongest emitters of Pa alpha, radio, and x-ray flux. Our analysis leads to a
possible model for S1 and perhaps S2 as a cluster of very young, massive stars
with strong stellar winds. The wind density can be high enough to absorb the
majority of ionizing photons within less than 1000 AU of the stars, creating
very compact HII regions that emit optically thick radiation at radio
wavelengths. These winds would then effectively quench the photoionizing flux
very close to the stars. This can delay the onset of negative feedback by
photoionization and photodissociation on star formation in the clusters. This
is significant since SBS0335-052E resembles the conditions that were probably
common for high redshift star formation in galaxies near the epoch of
reionization.Comment: Accepted for publication in the Astrophysical Journa
Integral-field near-infrared spectroscopy of two blue dwarf galaxies: NGC 5253 and He 2-10
We present integral field spectroscopy in the near infrared (NIR) of He 2-10
and NGC 5253, two well known nearby dwarf irregular galaxies showing high
star-formation rates. Our data provide an unprecedented detailed view of the
interstellar medium and star formation in these galaxies, allowing us to obtain
spatially resolved information from the NIR emission and absorption line
tracers. We study the spatial distribution and kinematics of different
components of the interstellar medium (ISM) mostly through the Bracket series
lines, the molecular hydrogen spectrum, [FeII] emission, and CO absorptions.
Although the ISM is mostly photo-excited, as derived by the [FeII]/Bry and H2
line ratios, some regions corresponding to non-thermal radio sources show a
[FeII]/Bry excess due to a significant contribution of SN driven shocks. In He
2-10 we find that the molecular gas clouds, as traced by CO(2-1) and H2
infrared line, show consistent morphologies and velocities when studied with
the two different tracers. Moreover, there is a clear association with the
youngest super star clusters as traced by the ionized gas. In the same galaxy
we observe a cavity depleted of gas, which is surrounded by some of the most
active regions of star formation, that we interpret as a signature of
feedback-induced star formation from older episodes of star formation. Finally,
we measured high turbulence in the ISM of both galaxies, sigma~30-80 km/s,
driven by the high star-formation activity.Comment: 12 pages, 10 figures, accepted for publication in A&
Bessel beam illumination reduces random and systematic errors in quantitative functional studies using light-sheet microscopy
Light-sheet microscopy (LSM), in combination with intrinsically transparent zebrafish larvae, is a choice method to observe brain function with high frame rates at cellular resolution. Inherently to LSM, however, residual opaque objects cause stripe artifacts, which obscure features of interest and, during functional imaging, modulate fluorescence variations related to neuronal activity. Here, we report how Bessel beams reduce streaking artifacts and produce high-fidelity quantitative data demonstrating a fivefold increase in sensitivity to calcium transients and a 20 fold increase in accuracy in the detection of activity correlations in functional imaging. Furthermore, using principal component analysis, we show that measurements obtained with Bessel beams are clean enough to reveal in one-shot experiments correlations that can not be averaged over trials after stimuli as is the case when studying spontaneous activity. Our results not only demonstrate the contamination of data by systematic and random errors through conventional Gaussian illumination and but,furthermore, quantify the increase in fidelity of such data when using Bessel beams
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