523 research outputs found
Galactic fountains and outflows in star forming dwarf galaxies: ISM expulsion and chemical enrichment
We investigated the impact of supernova feedback in gas-rich dwarf galaxies
experiencing a low-to-moderate star formation rate, typical of relatively
quiescent phases between starbursts. We calculated the long term evolution of
the ISM and the metal-rich SN ejecta using 3D hydrodynamic simulations, in
which the feedback energy is deposited by SNeII exploding in distinct OB
associations. We found that a circulation flow similar to galactic fountains is
generally established, with some ISM lifted at heights of one to few kpc above
the galactic plane. This gas forms an extra-planar layer, which falls back to
the plane in about yr, once the star formation stops. Very little or no
ISM is expelled outside the galaxy system for the considered SFRs, even though
in the most powerful model the SN energy is comparable to the gas binding
energy. The metal-rich SN ejecta is instead more vulnerable to the feedback and
we found that a significant fraction (25-80\%) is vented in the intergalactic
medium, even for low SN rate ( - yr).
About half of the metals retained by the galaxy are located far ( 500 pc)
from the galactic plane. Moreover, our models indicate that the circulation of
the metal-rich gas out from and back to the galactic disk is not able to erase
the chemical gradients imprinted by the (centrally concentrated) SN explosions.Comment: 19 pages, MNRAS accepte
AsmetaF: A Flattener for the ASMETA Framework
Abstract State Machines (ASMs) have shown to be a suitable high-level
specification method for complex, even industrial, systems; the ASMETA
framework, supporting several validation and verification activities on ASM
models, is an example of a formal integrated development environment. Although
ASMs allow modeling complex systems in a rather concise way -and this is
advantageous for specification purposes-, such concise notation is in general a
problem for verification activities as model checking and theorem proving that
rely on tools accepting simpler notations.
In this paper, we propose a flattener tool integrated in the ASMETA framework
that transforms a general ASM model in a flattened model constituted only of
update, parallel, and conditional rules; such model is easier to map to
notations of verification tools. Experiments show the effect of applying the
tool to some representative case studies of the ASMETA repository.Comment: In Proceedings F-IDE 2018, arXiv:1811.09014. The first two authors
are supported by ERATO HASUO Metamathematics for Systems Design Project (No.
JPMJER1603), JST. Funding Reference number: 10.13039/501100009024 ERAT
Evolution of the ISM of Starburst galaxies: the SN heating efficiency
The interstellar medium heated by SN explosions may acquire an expansion
velocity larger than the escape velocity and leave the galaxy through a
supersonic wind. SN ejecta are transported out of the galaxies by such winds
which thus affect the chemical evolution of the galaxies. The effectiveness of
the processes mentioned above depends on the heating efficiency (HE) of the
SNe, that is a matter of debate. We have constructed a simple semi-analytic
model, considering the essential ingredients of a SB environment which is able
to qualitatively trace the thermalisation history of the ISM in a SB region and
determine the HE evolution. We find that, as long as the mass-loss rate of the
clouds remains larger than the rate at which the SNRs interact one with each
other, the SN heating efficiency remains very small, as radiative cooling of
the gas dominates. We conclude that the HE value has a time-dependent trend
that is sensitive to the initial conditions of the system.Comment: 17 pages, 18 figures, A&A accepte
Multidimensional Hydrodynamical Simulations of radiative cooling SNRs-clouds interactions: an application to Starburst Environments
In this work we are interested to study the by-products of SNR-clouds in a
starburst (SB) system. These interactions can have an important role in the
recycling of matter from the clouds to the ISM and vice-versa. In the present
work, we have focused our attention on the global effects of the interactions
between clouds and SN shock waves in the ISM of SB environments, and performed
3-D radiative cooling hydrodynamical simulations with the adaptive YGUAZU grid
code. We have also considered the effects of the photo-evaporation due to the
presence of a high number of UV photons from hot stars and supernovae (SNe).
The results have shown that, in the presence of radiative cooling, instead of
an efficient gas mixing with the diffuse ISM, the interactions cause the
fragmentation of the clouds into smaller ones. The results have also revealed
that the SNR-clouds interactions are less efficient at producing substantial
mass loss from the clouds to the diffuse ISM than mechanisms such as the
photo-evaporation caused by the UV flux from the hot stars.Comment: 15 pages, 25 figures. Figures with higher resolution at the page:
http://www.astro.iag.usp.br/~dalpino/ Astronomy & Astrophysics accepte
MHD turbulence-Star Formation Connection: from pc to kpc scales
The transport of magnetic flux to outside of collapsing molecular clouds is a
required step to allow the formation of stars. Although ambipolar diffusion is
often regarded as a key mechanism for that, it has been recently argued that it
may not be efficient enough. In this review, we discuss the role that MHD
turbulence plays in the transport of magnetic flux in star forming flows. In
particular, based on recent advances in the theory of fast magnetic
reconnection in turbulent flows, we will show results of three-dimensional
numerical simulations that indicate that the diffusion of magnetic field
induced by turbulent reconnection can be a very efficient mechanism, especially
in the early stages of cloud collapse and star formation. To conclude, we will
also briefly discuss the turbulence-star formation connection and feedback in
different astrophysical environments: from galactic to cluster of galaxy
scales.Comment: 6 pages, 5 figures, 274 IAU Symposium: Advances in Plasma
Astrophysic
Star formation triggered by SN explosions: an application to the stellar association of Pictoris
In the present study, considering the physical conditions that are relevant
in interactions between supernova remnants (SNRs) and dense molecular clouds
for triggering star formation we have built a diagram of SNR radius versus
cloud density in which the constraints above delineate a shaded zone where star
formation is allowed. We have also performed fully 3-D radiatively cooling
numerical simulations of the impact between SNRs and clouds under different
initial conditions in order to follow the initial steps of these interactions.
We determine the conditions that may lead either to cloud collapse and star
formation or to complete cloud destruction and find that the numerical results
are consistent with those of the SNR-cloud density diagram. Finally, we have
applied the results above to the Pictoris stellar association which is
composed of low mass Post-T Tauri stars with an age of 11 Myr. It has been
recently suggested that its formation could have been triggered by the shock
wave produced by a SN explosion localized at a distance of about 62 pc that may
have occurred either in the Lower Centaurus Crux (LCC) or in the Upper
Centaurus Lupus (UCL) which are both nearby older subgroups of that association
(Ortega and co-workers). Using the results of the analysis above we have shown
that the suggested origin for the young association at the proposed distance is
plausible only for a very restricted range of initial conditions for the parent
molecular cloud, i.e., a cloud with a radius of the order of 10 pc and density
of the order of 20 cm and a temperature of the order of 50100 K.Comment: 9 pages, 10 figures, to appear in MNRA
Galactic Outflows and the pollution of the Galactic Environment by Supernovae
We here explore the effects of the SN explosions into the environment of
star-forming galaxies like the Milky Way. Successive randomly distributed and
clustered SNe explosions cause the formation of hot superbubbles that drive
either fountains or galactic winds above the galactic disk, depending on the
amount and concentration of energy that is injected by the SNe. In a galactic
fountain, the ejected gas is re-captured by the gravitational potential and
falls back onto the disk. From 3D nonequilibrium radiative cooling
hydrodynamical simulations of these fountains, we find that they may reach
altitudes up to about 5 kpc in the halo and thus allow for the formation of the
so called intermediate-velocity-clouds (IVCs) which are often observed in the
halos of disk galaxies. The high-velocity-clouds that are also observed but at
higher altitudes (of up to 12 kpc) require another mechanism to explain their
production. We argue that they could be formed either by the capture of gas
from the intergalactic medium and/or by the action of magnetic fields that are
carried to the halo with the gas in the fountains. Due to angular momentum
losses to the halo, we find that the fountain material falls back to smaller
radii and is not largely spread over the galactic disk. Instead, the SNe ejecta
fall nearby the region where the fountain was produced, a result which is
consistent with recent chemical models of the galaxy. The fall back material
leads to the formation of new generations of molecular clouds and to supersonic
turbulence feedback in the disk.Comment: 10 pages, 5 figures; paper of invited talk for the Procs. of the 2007
WISER Workshop (World Space Environment Forum), Alexandria, Egypt, October
2007, Spa. Sci. Rev
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