27 research outputs found
The Answer is Blowing in the Wind
A 'News & Views' article -- no abstract
The Carina Flare: What can fragments in the wall tell us?
CO(J=2--1) and CO(J=2--1) observations of the molecular cloud
G285.90+4.53 (Cloud~16) in the Carina Flare supershell (GSH287+04-17) with the
APEX telescope are presented. With an algorithm DENDROFIND we identify 51
fragments and compute their sizes and masses. We discuss their mass spectrum
and interpret it as being the result of the shell fragmentation process
described by the pressure assisted gravitational instability - PAGI. We
conclude that the explanation of the clump mass function needs a combination of
gravity with pressure external to the shell.Comment: 19 pages, 14 figures, accepted by A&
How to create Sgr A East: Where did the supernova explode?
Sgr A East is the supernova remnant closest to the centre of the Milky Way.
Its age has been estimated to be either very young, around 1-2 kyr, or about 10
kyr, and its exact origin remains unclear. We aspire to create a simple model
of a supernova explosion that reproduces the shape, size, and location of Sgr A
East. Using a simplified hydrodynamical code, we simulated the evolution of a
supernova remnant in the medium around the Galactic centre. The latter consists
of a nearby massive molecular cloud with which Sgr A East is known to be
interacting and a wind from the nuclear star cluster. Our preferred models of
the Sgr A East remnant are compatible with an age of around 10 kyr. We also
find suitable solutions for older ages, but not for ages younger than 5 kyr.
Our simulations predict that the supernova exploded at a distance of about 3.5
pc from the Galactic centre, below the Galactic plane, slightly eastwards from
the centre and 3 pc behind it.Comment: 13 pages, 15 figures, accepted by A&
Ionized regions in the central arcsecond of NGC 1068. YJHK spatially resolved spectroscopy
Context. Several bright emission line regions have been observed in the
central 100 parsecs of the active galaxy NGC 1068. Aims. We aim to determine
the properties and ionization mechanism of three regions of NGC 1068: the
nucleus (B) and two clouds located at 0.3" and 0.7" north of it (C and D).
Methods. We combined SPHERE (0.95 - 1.65 um) and SINFONI (1.5 - 2.45 um)
spectra for the three regions B, C, and D. We compared these spectra to several
CLOUDY photoionization models and to the MAPPINGS III Library of Fast Radiative
Shock Models. Results. The emission line spectra of the three regions are
almost identical to each other and contribute to most of the emission line flux
in the nuclear region. The emitting media contain multiple phases, the most
luminous of which have temperatures ranging from 104.8 K to 106 K. Central
photoionization models can reproduce some features of the spectra, but the fast
radiative shock model provides the best fit to the data. Conclusions. The
similarity between the three regions indicates that they belong to the same
class of objects. Based on our comparisons, we conclude that they are shock
regions located where the jet of the active galactic nucleus impacts massive
molecular clouds.Comment: A&A, Forthcoming article, accepted for publicatio
A 3D model for the stellar populations in the nuclei of NGC 1433,NGC 1566, and NGC 1808
Aims. We aim to characterize the properties of the stellar populations in the
central few hundred parsecs of nearby galactic nuclei; specifically their age,
mass, and 3D geometry. Methods. We use spatially resolved spectroscopic
observations of NGC 1433, NGC 1566, and NGC 1808 obtained with SINFONI to
constrain a 3D model composed of a spherically symmetric nuclear star cluster
(NSC) and an extended thick stellar disk. We computed UV to mid-infrared single
stellar population (UMISSP) spectra to determine the age of the stellar
populations and construct synthetic observations for our model. To overcome
degeneracies between key parameters, we simultaneously fit the spatially
resolved line-of-sight velocity, line-of-sight-velocity-dispersion,
low-spectral-resolution NIR continuum, and high-spectral-resolution CO
absorption features for each pixel. Results. For the three objects, we derive
the age and mass of the young and old stellar populations in the NSC and
surrounding disk, as well as their 3D geometry: radius for the NSC; thickness,
inclination, and position angle for the disk. These results are consistent with
published independent measurements when available. Conclusions. The proposed
method allows us to derive a consistent 3D model of the stellar populations in
nearby galactic centers solely based on a near-infrared IFU observation
GS100-02-41: a new large HI shell in the outer part of the Galaxy
Massive stars have a profound effect on the surrounding interstellar medium.
They ionize and heat the neutral gas, and due to their strong winds, they swept
the gas up forming large HI shells. In this way, they generate a dense shell
where the physical conditions for the formation of new stars are given. The aim
of this study is to analyze the origin and evolution of the large HI shell
GS100-02-41 and its role in triggering star forming processes.To characterize
the shell and its environs, we carry out a multi-wavelength study. We analyze
he HI 21 cm line, the radio continuum, and infrared emission distributions. The
analysis of the HI data shows an expanding shell structure centred at (l, b) =
(100.6 deg, -2.04 deg) in the velocity range from -29 to -51.7 km/s.
We infer for GS100-02-41, a kinematical distance of 2.8 +/- 0.6 kpc. Several
massive stars belonging to Cep OB1 are located in projection within the large
HI, shell boundaries. The analysis of the radio continuum and infrared data
reveal that there is no continuum counterpart of the HI shell. On the other
hand, three slightly extended radio continuum sources are observed in
projection onto the dense HI shell. From their flux density determinations we
infer that they are thermal in nature. An analysis of the HI emission
distribution in the environs of these sources shows, for each of them, a region
of low emissivity having a good morphological correlation with the ionized gas
in a velocity range similar to the one where GS100-02-41 is detected. The
origin of GS100-02-41 could have been mainly due to the action of the Cep OB1
massive stars located inside the HI shell. The obtained age difference between
the HI shell and the HII regions, together with their relative location, led us
to conclude that the ionizing stars could have been created as a consequence of
the shell evolution.Comment: Accepted for publication in A&
Spitzer/IRAC view of Sh 2-284: Searching for evidence of triggered star formation in an isolated region in the outer Milky Way
Using Spitzer/IRAC observations of a region to be observed by the CoRoT
satellite, we have unraveled a new complex star-forming region at low
metallicity in the outer Galaxy. We perform a study of S284 in order to outline
the chain of events in this star-forming region. We used four-band Spitzer/IRAC
photometry as well as Halpha imaging obtained with INT/WFC. Combining these
data with the optical photometry obtained in the frame of CoRoTs preparation
and the 2MASS catalog we analysed the properties and distribution of young
stellar objects (YSOs) associated with point-like sources. We also studied the
SEDs of regions of extended emission, complementing our dataset with IRAS and
MSX data. We find that S284 is unique in several ways: it is very isolated at
the end of a spiral arm and both the diffuse dust and ionized emission are
remarkably symmetric. We have partially resolved the central clusters of the
three bubbles present in this region. Despite the different scales present in
its multiple-bubble morphology, our study points to a very narrow spread of
ages among the powering high-mass clusters. In contrast, the particular
sawtooth structure of the extended emission at the rim of each ionized bubble
harbours either small lower-mass clusters with a younger stellar population or
individual young reddened protostars. In particular, triggered star formation
is considered to be at work in these regions.Comment: Accepted by A&A. 13 pages, 10 figures, 2 Table
Continuous star formation in IZw18
We study the dynamical and chemical evolution of a galaxy similar to IZw18
under the assumption of a continuous star formation during bursts. We adopt a
2-D hydrocode coupled with detailed chemical yields originating from SNeII,
SNeIa and from single intermediate-mass stars. Different nucleosynthetic yields
and different IMF slopes are tested. In most of the explored cases, a galactic
wind develops, mostly carrying out of the galaxy the metal-enriched gas
produced by the burst itself. The chemical species with the largest escape
probabilities are Fe and N. Consequently, we predict that the [/Fe] and
[/N] ratios outside the galaxy are lower than inside. In order to
reproduce the chemical composition of IZw18, the best choice seems to be the
adoption of the yields of Meynet & Maeder (2002) which take into account
stellar rotation, although these authors do not follow the whole evolution of
all the stars. Models with a flat IMF (x=0.5) seem to be able to better
reproduce the chemical properties of IZw18, but they inject in the gas a much
larger amount of energy and the resulting galactic wind is very strong, at
variance with observations. We also predict the evolution of the abundances in
the \hi medium and compare them with recent {\sl FUSE} observations.Comment: 17 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic