637 research outputs found
On the hydrodynamics of the matter reinserted within superstellar clusters
We present semi-analytical and numerical models, accounting for the impact of
radiative cooling on the hydrodynamics of the matter reinserted as strong
stellar winds and supernovae within the volume occupied by young, massive and
compact superstellar clusters. First of all we corroborate the location of the
threshold line in the mechanical energy input rate vs the cluster size plane,
found by Silich et al. (2004). Such a line separates clusters able to drive a
quasi-adiabatic or a strongly radiative wind from clusters in which
catastrophic cooling occurs within the star cluster volume. Then we show that
the latter, clusters above the threshold line, undergo a bimodal behavior in
which the central densest zones cool rapidly and accumulate the injected matter
to eventually feed further generations of star formation, while the outer zones
are still able to drive a stationary wind. The results are presented into a
series of universal dimensionless diagrams from which one can infer: the size
of the two zones, the fraction of the deposited mass that goes into each of
them and the luminosity of the resultant winds, for clusters of all sizes and
energy input rates, regardless the assumed adiabatic terminal speed V_A.Comment: 18 pages, 6 figures, accepted for publication in Ap
Exploring GLIMPSE Bubble N107: Multiwavelength Observations and Simulations
Context. Bubble N107 was discovered in the infrared emission of dust in the
Galactic Plane observed by the Spitzer Space Telescope (GLIMPSE survey: l ~
51.0 deg, b ~ 0.1 deg). The bubble represents an example of shell-like
structures found all over the Milky Way Galaxy.
Aims. We aim to analyse the atomic and molecular components of N107, as well
as its radio continuum emission. With the help of numerical simulations, we aim
to estimate the bubble age and other parameters which cannot be derived
directly from observations.
Methods. From the observations of the HI (I-GALFA) and 13CO (GRS) lines we
derive the bubble's kinematical distance and masses of the atomic and molecular
components. With the algorithm DENDROFIND, we decompose molecular material into
individual clumps. From the continuum observations at 1420 MHz (VGPS) and 327
MHz (WSRT), we derive the radio flux density and the spectral index. With the
numerical code ring, we simulate the evolution of stellar-blown bubbles similar
to N107.
Results. The total HI mass associated with N107 is 5.4E3 Msun. The total mass
of the molecular component (a mixture of cold gasses of H2, CO, He and heavier
elements) is 1.3E5 Msun, from which 4.0E4 Msun is found along the bubble
border. We identified 49 molecular clumps distributed along the bubble border,
with the slope of the clump mass function of -1.1. The spectral index of -0.30
of a strong radio source located apparently within the bubble indicates
nonthermal emission, hence part of the flux likely originates in a supernova
remnant, not yet catalogued. The numerical simulations suggest N107 is likely
less than 2.25 Myr old. Since first supernovae explode only after 3 Myr or
later, no supernova remnant should be present within the bubble. It may be
explained if there is a supernova remnant in the direction towards the bubble,
however not associated with it.Comment: 15 pages, 11 figure
The fragmentation of expanding shells III: Oligarchic accretion and the mass spectrum of fragments
We use SPH simulations to investigate the gravitational fragmentation of
expanding shells through the linear and non--linear regimes. The results are
analysed using spherical harmonic decomposition to capture the initiation of
structure during the linear regime; the potential-based method of Smith et al.
(2009) to follow the development of clumps in the mildly non-linear regime; and
sink particles to capture the properties of the final bound objects during the
highly non-linear regime. In the early, mildly non--linear phase of
fragmentation, we find that the clump mass function still agrees quite well
with the mass function predicted by the analytic model. However, the sink mass
function is quite different, in the sense of being skewed towards high-mass
objects. This is because, once the growth of a condensation becomes non-linear,
it tends to be growing non-competitively from its own essentially separate
reservoir; we call this Oligarchic Accretion.Comment: 14 pages, accepted for publication in MNRA
- …