1,406 research outputs found
Near-infrared integral-field spectroscopy of violent starburst environments
Near-infrared (NIR) integral-field spectroscopy (IFS) of violent starburst
environments at high spatial (and spectral) resolution has the potential to
revolutionise our ideas regarding the local interactions between the
newly-formed massive stars and the interstellar medium (ISM) of their host
galaxies. To illustrate this point, I present NIR IFS analysis of the central
starburst region of NGC 1140, obtained with CIRPASS on Gemini-South. While
strong [FeII] emission is found throughout the galaxy, higher-order Brackett
emission is predominantly associated with the northern starburst region. Based
on the spatial distributions of the [FeII] versus Brackett line emission, I
conclude that a galaxy-wide starburst was induced several x 10^7 yr ago, with
more recent starburst activity concentrated around the northern starburst
region. I look forward and discuss the exciting prospects that IFS at higher
spatial (and spectral) resolution will allow us trace (i) the massive outflows
("superwinds") expected to originate in the dense, young massive star clusters
commonly found in intense starburst environments, and (ii) their impact on the
galaxy's ISM.Comment: Submitted to "Adaptive Optics-Assisted Integral-Field Spectroscopy",
Rutten R.G.M., Benn C.R., Mendez J., eds., May 2005, La Palma (Spain), New
Astr. Re
Probing discs around massive young stellar objects with CO first overtone emission
We present high resolution (R~50,000) spectroastrometry over the CO 1st
overtone bandhead of a sample of seven intermediate/massive young stellar
objects. These are primarily drawn from the red MSX source (RMS) survey, a
systematic search for young massive stars which has returned a large, well
selected sample of such objects. The mean luminosity of the sample is
approximately 5 times 10^4 L_\odot, indicating the objects typically have a
mass of ~15 solar masses. We fit the observed bandhead profiles with a model of
a circumstellar disc, and find good agreement between the models and
observations for all but one object. We compare the high angular precision
(0.2-0.8 mas) spectroastrometric data to the spatial distribution of the
emitting material in the best-fitting models. No spatial signatures of discs
are detected, which is entirely consistent with the properties of the
best-fitting models. Therefore, the observations suggest that the CO bandhead
emission of massive young stellar objects originates in small-scale disks, in
agreement with previous work. This provides further evidence that massive stars
form via disc accretion, as suggested by recent simulations.Comment: Accepted for publication in MNRA
Spin-Phonon Coupling in Iron Pnictide Superconductors
The magnetic moment in the parent phase of the iron-pnictide superconductors
varies with composition even when the nominal charge of iron is unchanged. We
propose the spin-lattice coupling due to the magneto-volume effect as the
primary origin of this effect, and formulate a Landau theory to describe the
dependence of the moment to the Fe-As layer separation. We then compare the
superconductive critical temperature of doped iron pnictides to the local
moment predicted by the theory, and suggest that the spin-phonon coupling may
play a role in the superconductivity of this compound
The RMS Survey: Mid-Infrared Observations of Candidate Massive YSOs in the Southern Hemisphere
Abridged abstract: The Red MSX Source (RMS) survey is an ongoing effort to
return a large, well-selected sample of massive young stellar objects (MYSOs)
within our Galaxy. A series of ground-based follow-up observations are being
undertaken in order to remove contaminant objects from our list of 2000
candidates, and to begin characterising these MYSOs. As a part of these
follow-up observations, high resolution (~1") mid-IR imaging aids the
identification of contaminant objects which are resolved (UCHII regions, PN) as
opposed to those which are unresolved (YSOs, evolved stars) as well as
identifying YSOs near UCHII regions and other multiple sources. We present 10.4
micron imaging observations for 346 candidate MYSOs in the RMS survey in the
Southern Hemisphere, primarily outside the region covered by the GLIMPSE
Spitzer Legacy Survey. These were obtained using TIMMI2 on the ESO 3.6m
telescope in La Silla, Chile. Our photometric accuracy is of order 0.05Jy, and
our astrometric accuracy is 0.8", which is an improvement over the nominal 2"
accuracy of the MSX PSC.Comment: 9 page paper accepted to A&A. Online data for table 2 and figure 1
will be available in the published online version of this paper via A&A. The
paper contains 7 figures and 3 table
The RNA-binding protein ELAV regulates Hox RNA processing, expression and function within the Drosophila nervous system
The regulated head-to-tail expression of Hox genes provides a coordinate system for the activation of specific programmes of cell differentiation according to axial level. Recent work indicates that Hox expression can be regulated via RNA processing but the underlying mechanisms and biological significance of this form of regulation remain poorly understood. Here we explore these issues within the developing Drosophila central nervous system (CNS). We show that the pan-neural RNA-binding protein (RBP) ELAV (Hu antigen) regulates the RNA processing patterns of the Hox gene Ultrabithorax (Ubx) within the embryonic CNS. Using a combination of biochemical, genetic and imaging approaches we demonstrate that ELAV binds to discrete elements within Ubx RNAs and that its genetic removal reduces Ubx protein expression in the CNS leading to the respecification of cellular subroutines under Ubx control, thus defining for the first time a specific cellular role of ELAV within the developing CNS. Artificial provision of ELAV in glial cells (a cell type that lacks ELAV) promotes Ubx expression, suggesting that ELAVdependent regulation might contribute to cell type-specific Hox expression patterns within the CNS. Finally, we note that expression of abdominal A and Abdominal B is reduced in elav mutant embryos, whereas other Hox genes (Antennapedia) are not affected. Based on these results and the evolutionary conservation of ELAV and Hox genes we propose that the modulation of Hox RNA processing by ELAV serves to adapt the morphogenesis of the CNS to axial level by regulating Hox expression and consequently activating local programmes of neural differentiation
Probing the envelopes of massive young stellar objects with diffraction limited mid-infrared imaging
Massive stars form whilst they are still embedded in dense envelopes. As a
result, the roles of rotation, mass loss and accretion in massive star
formation are not well understood. This study evaluates the source of the
Q-band, lambda=19.5 microns, emission of massive young stellar objects (MYSOs).
This allows us to determine the relative importance of rotation and outflow
activity in shaping the circumstellar environments of MYSOs on 1000 AU scales.
We obtained diffraction limited mid-infrared images of a sample of 20 MYSOs
using the VLT/VISIR and Subaru/COMICS instruments. For these 8 m class
telescopes and the sample selected, the diffraction limit, ~0.6", corresponds
to approximately 1000 AU. We compare the images and the spectral energy
distributions (SEDs) observed to a 2D, axis-symmetric dust radiative transfer
model that reproduces VLTI/MIDI observations of the MYSO W33A. We vary the
inclination, mass infall rate, and outflow opening angle to simultaneously
recreate the behaviour of the sample of MYSOs in the spatial and spectral
domains. The mid-IR emission of 70 percent of the MYSOs is spatially resolved.
In the majority of cases, the spatial extent of their emission and their SEDs
can be reproduced by the W33A model featuring an in-falling, rotating dusty
envelope with outflow cavities. There is independent evidence that most of the
sources which are not fit by the model are associated with ultracompact HII
regions and are thus more evolved. We find that, in general, the diverse 20
micron morphology of MYSOs can be attributed to warm dust in the walls of
outflow cavities seen at different inclinations. This implies that the warm
dust in the outflow cavity walls dominates the Q-band emission of MYSOs. In
turn, this emphasises that outflows are an ubiquitous feature of massive star
formation.Comment: Accepted for publication in A&A. The images in this version have been
compressed. A high resolution version is available on reques
The circumstellar disk, envelope, and bi-polar outflow of the Massive Young Stellar Object W33A
The Young Stellar Object (YSO) W33A is one of the best known examples of a
massive star still in the process of forming. Here we present Gemini North
ALTAIR/NIFS laser-guide star adaptive-optics assisted K-band integral-field
spectroscopy of W33A and its inner reflection nebula. In our data we make the
first detections of a rotationally-flattened outer envelope and fast bi-polar
jet of a massive YSO at near-infrared wavelengths. The predominant spectral
features observed are Br-gamma, H_2, and a combination of emission and
absorption from CO gas. We perform a 3-D spectro-astrometric analysis of the
line emission, the first study of its kind. We find that the object's Br-gamma
emission reveals evidence for a fast bi-polar jet on sub-milliarcsecond scales,
which is aligned with the larger-scale outflow. The hybrid CO features can be
explained as a combination of hot CO emission arising in a disk close to the
central star, while cold CO absorption originates in the cooler outer envelope.
Kinematic analysis of these features reveals that both structures are rotating,
and consistent with being aligned perpendicularly to both the ionised jet and
the large-scale outflow. Assuming Keplerian rotation, we find that the
circumstellar disk orbits a central mass of >10Msun, while the outer envelope
encloses a mass of ~15Msun. Our results suggest a scenario of a central star
accreting material from a circumstellar disk at the centre of a cool extended
rotating torus, while driving a fast bi-polar wind. These results therefore
provide strong supporting evidence for the hypothesis that the formation
mechanism for high-mass stars is qualitatively similar to that of low-mass
stars.Comment: 13 pages, 18 figs. Accepted for publication in MNRA
VISIR/VLT mid-infrared imaging of Seyfert nuclei: Nuclear dust emission and the Seyfert-2 dichotomy
Half of the Seyfert-2 galaxies escaped detection of broad lines in their
polarised spectra observed so far. Some authors have suspected that these
non-HBLRs contain real Sy2 nuclei without intrinsic broad line region hidden
behind a dust torus. If this were true, then their nuclear structure would
fundamentally differ from that of Sy2s with polarised broad lines: in
particular, they would not be explained by orientation-based AGN unification.
Further arguments for two physically different Sy2 populations have been
derived from the warm and cool IRAS F25/F60 ratios. These ratios, however,
refer to the entire host galaxies and are unsuitable to conclusively establish
the absence of a nuclear dust torus. Instead, a study of the Seyfert-2
dichotomy should be performed on the basis of nuclear properties only. Here we
present the first comparison between [OIII] 5007A and mid-infrared imaging at
matching spatial resolution. Exploring the Seyfert-2 dichotomy we find that the
distributions of nuclear mid-infrared/[OIII] luminosity ratios are
indistinguishable for Sy1s and Sy2s with and without detected polarised broad
lines and irrespective of having warm or cool IRAS F25/F60 ratios. We find no
evidence for the existence of a population of real Sy2s with a deficit of
nuclear dust emission. Our results suggest 1) that all Seyfert nuclei possess
the same physical structure including the putative dust torus and 2) that the
cool IRAS colours are caused by a low contrast of AGN to host galaxy. Then the
Seyfert-2 dichotomy is explained in part by unification of non-HBLRs with
narrow-line Sy1s and to a larger rate by observational biases caused by a low
AGN/host contrast and/or an unfavourable scattering geometry.Comment: 11 pages, 6 figures, accepted by A&
Integral field near-infrared spectroscopy of II Zw 40
We present integral field spectroscopy in the near-infrared of the nearby
starburst galaxy IIZw40. Our new observations provide an unprecedented detailed
view of the interstellar medium and star formation of this galaxy. The
radiation emitted by the galaxy is dominated by a giant HII region, which
extends over an area of more than 400 pc in size. A few clusters are present in
this area, however one in particular appears to be the main source of ionizing
photons. We derive the properties of this object and compare them with those of
the 30 Doradus cluster in the Large magellanic cloud (LMC). We study the
spatial distribution and velocity field of different components of the
inetrstellar medium (ISM), mostly through the Bracket series lines, the
molecular hydrogen spectrum, and [FeII]. We find that [FeII] and H2 are mostly
photon excited, but while the region emitting [FeII] is almost coincident with
the giant HII region observed in the lines of atomic H and He, the H2 has a
quite different distribution in space and velocity. The age of the stellar
population in the main cluster is such that no supernova (SN) should be present
yet so that the gas kinematics must be dominated by the young stars. We do not
see, in the starbursting region, any geometrical or dynamical structure that
can be related to the large scale morphology of the galaxy.Comment: Accepted for publication on A&
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