413 research outputs found
A SINFONI view of Galaxy Centers: Morphology and Kinematics of five Nuclear Star Formation Rings
We present near-infrared (H- and K-band) integral-field observations of the
circumnuclear star formation rings in five nearby spiral galaxies. The data,
obtained at the Very Large Telescope with the SINFONI spectrograph, are used to
construct maps of various emission lines that reveal the individual star
forming regions ("hot spots") delineating the rings. We derive the
morphological parameters of the rings, and construct velocity fields of the
stars and the emission line gas. We propose a qualitative, but robust,
diagnostic for relative hot spot ages based on the intensity ratios of the
emission lines Brackett gamma, HeI, and [FeII]. Application of this diagnostic
to the data presented here provides tentative support for a scenario in which
star formation in the rings is triggered predominantly at two well-defined
regions close to, and downstream from, the intersection of dust lanes along the
bar with the inner Lindblad resonance.Comment: 45 pages incl. 4 tables and 12 (mostly color) figures. Accepted for
publication in AJ. A version with full resolution figures can be obtained at
ftp://ftp.rssd.esa.int/pub/tboeker/SINFONI/ms.pd
2335 Evaluation of anterior chamber angle: Gonioscopy, ultrasound biomicroscopy and scheimpflug photography
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Molecular gas in the central regions of the latest-type spiral galaxies
Using the IRAM 30m telescope, we have surveyed an unbiased sample of 47
nearby spiral galaxies of very late (Scd-Sm) Hubble-type for emission in the
CO(1-0) and CO(2-1) lines. The sensitivity of our data (a few mK) allows
detection of about 60% of our sample in at least one of the CO lines. The
median detected H2 mass is 1.4\times 10^7 \msun within the central few kpc,
assuming a standard conversion factor. We use the measured line intensities to
complement existing studies of the molecular gas content of spiral galaxies as
a function of Hubble-type and to significantly improve the statistical
significance of such studies at the late end of the spiral sequence. We find
that the latest-type spirals closely follow the correlation between molecular
gas content and galaxy luminosity established for earlier Hubble types. The
molecular gas in late-type galaxies seems to be less centrally concentrated
than in earlier types. We use Hubble Space Telescope optical images to
correlate the molecular gas mass to the properties of the central galaxy disk
and the compact star cluster that occupies the nucleus of most late-type
spirals. There is no clear correlation between the luminosity of the nuclear
star cluster and the molecular gas mass, although the CO detection rate is
highest for the brightest clusters. It appears that the central surface
brightness of the stellar disk is an important parameter for the amount of
molecular gas at the galaxy center. Whether stellar bars play a critical role
for the gas dynamics remains unclear, in part because of uncertainties in the
morphological classifications of our sample.Comment: 27 pages, 15 figures, accepted by A&
Bar-Driven Mass Build-Up within the Central 50pc of NGC6946
We have used the new extended A configuration of the IRAM Plateau de Bure
interferometer to study the dense molecular gas in the nucleus of the nearby
spiral galaxy NGC6946 at unprecedented spatial resolution in the HCN(1-0) and
CO(2-1) lines. The gas distribution in the central 50pc has been resolved and
is consistent with a gas ring or spiral driven by the inner 400pc long stellar
bar. For the first time, it is possible to directly compare the location of
(dense) giant molecular clouds with that of (optically) visible HII regions in
space-based images. We use the 3mm continuum and the HCN emission to estimate
in the central 50pc the star formation rates in young clusters that are still
embedded in their parent clouds and hence are missed in optical and near-IR
surveys of star formation. The amount of embedded star formation is about 1.6
times as high as that measured from HII regions alone, and appears roughly
evenly split between ongoing dust-obscured star formation and very young giant
molecular cloud cores that are just beginning to form stars. The build-up of
central mass seems to have continued over the past > 10 Myrs, to have occurred
in an extended (albeit small) volume around the nucleus, and to be closely
related to the presence of an inner bar.Comment: 4 pages, 4 figures, accepted for A&A Letters (PdBI special issue
Nuclear Star Clusters across the Hubble Sequence
Over the last decade, HST imaging studies have revealed that the centers of
most galaxies are occupied by compact, barely resolved sources. Based on their
structural properties, position in the fundamental plane, and spectra, these
sources clearly have a stellar origin. They are therefore called ``nuclear star
clusters'' (NCs) or ``stellar nuclei''. NCs are found in galaxies of all Hubble
types, suggesting that their formation is intricately linked to galaxy
evolution. In this contribution, I briefly review the results from recent
studies of NCs, touch on some ideas for their formation, and mention some open
issues related to the possible connection between NCs and supermassive black
holes.Comment: 6 page conference proceedings, to appear in "The impact of HST on
European Astronomy" (41st ESLAB Symposium), pdflatex file, uses svmult.cls
(included
Evolution in the Dust Lane Fraction of Edge-on L* Spiral Galaxies since z=0.8
The presence of a well-defined and narrow dust lane in an edge-on spiral
galaxy is the observational signature of a thin and dense molecular disk, in
which gravitational collapse has overcome turbulence. Using a sample of
galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction
of massive disks that display a dust lane. Our goal is to explore the evolution
in the stability of the molecular ISM disks in spiral galaxies over a cosmic
timescale. We check the reliability of our morphological classifications
against changes in restframe wavelength, resolution, and cosmic dimming with
(artificially redshifted) images of local galaxies from SDSS. We find that the
fraction of L* disks with dust lanes in COSMOS is consistent with the local
fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly
lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively
supports the notion that a high specific star formation rate can efficiently
destroy or inhibit a dense molecular disk. A small subsample of higher redshift
COSMOS galaxies display low internal reddening (E[B-V]), as well as a low
incidence of dust lanes. These may be disks in which the growth of the dusty
ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most
massive galaxies display a lower dust lane fraction than lower mass galaxies. A
small contribution of recent mergers or starbursts to this most massive
population may be responsible. The fact that the fraction of galaxies with dust
lanes in COSMOS is consistent with little or no evolution implies that models
to explain the Spectral Energy Distribution or the host galaxy dust extinction
of supernovae based on local galaxies are still applicable to higher redshift
spirals. It also suggests that dust lanes are long lived phenomena or can be
reformed over very short time-scales.Comment: 14 pages, 9 figures, 2 tables, accepted for publication by Ap
Herschel/SPIRE observations of the dusty disk of NGC 4244
We present Herschel/SPIRE images at 250, 350, and 500 mu m of NGC 4244, a typical low-mass, disk-only and edge-on spiral galaxy. The dust disk is clumpy and shows signs of truncation at the break radius of the stellar disk. This disk coincides with the densest part of the Hi disk. We compare the spectral energy distribution (SED), including the new SPIRE fluxes, to 3D radiative transfer models; a smooth model disk and a clumpy model with embedded heating. Each model requires a very high value for the dust scale-length (h(d) = 2-5 h(*)), higher dust masses than previous models of NGC 4244 (M-d = 0.47-1.39 x 10(7) M-circle dot) and a face-on optical depth of tau(f.o.)(V) = 0.4-1.12, in agreement with previous disk opacity studies. The vertical scales of stars and dust are similar. The clumpy model much better mimics the general morphology in the sub-mm images and the general SED. The inferred gas-to-dust mass ratio is compatible with those of similar low-mass disks. The relatively large radial scale-length of the dust disk points to radial mixing of the dusty ISM within the stellar disk. The large vertical dust scale and the clumpy dust distribution of our SED model are both consistent with a scenario in which the vertical structure of the ISM is dictated by the balance of turbulence and self-gravity
Polarized Proton Beams from Laser-induced Plasmas
We report on the concept of an innovative source to produce polarized
proton/deuteron beams of a kinetic energy up to several GeV from a laser-driven
plasma accelerator. Spin effects have been implemented into the PIC simulation
code VLPL to make theoretical predictions about the behavior of proton spins in
laser-induced plasmas. Simulations of spin-polarized targets show that the
polarization is conserved during the acceleration process. For the experimental
realization, a polarized HCl gas-jet target is under construction using the
fundamental wavelength of a Nd:YAG laser system to align the HCl bonds and
simultaneously circular polarized light of the fifth harmonic to
photo-dissociate, yielding nuclear polarized H atoms. Subsequently, their
degree of polarization is measured with a Lamb-shift polarimeter. The final
experiments, aiming at the first observation of a polarized particle beam from
laser-generated plasmas, will be carried out at the 10 PW laser system SULF at
SIOM/Shanghai.Comment: 7 pages, 7 figure
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