12,894 research outputs found
Dynamical analysis for a scalar-tensor model with Gauss-Bonnet and non-minimal couplings
We study the autonomous system for a scalar-tensor model of dark energy with
Gauss-Bonnet and non-minimal couplings. The critical points describe important
stable asymptotic scenarios including quintessence, phantom and de Sitter
attractor solutions. Two functional forms for the coupling functions and the
scalar potential were considered: power-law and exponential functions of the
scalar field. For the exponential functions the existence of stable
quintessence, phantom or de Sitter solutions, allows an asymptotic behavior
where the effective Newtonian coupling becomes constant. The phantom solutions
could be realized without appealing to ghost degrees of freedom. Transient
inflationary and radiation dominated phases can also be described.Comment: 31 pages, 3 figures, to appear in EPJ
Gas Kinematics and Excitation in the Filamentary IRDC G035.39-00.33
Some theories of dense molecular cloud formation involve dynamical
environments driven by converging atomic flows or collisions between
preexisting molecular clouds. The determination of the dynamics and physical
conditions of the gas in clouds at the early stages of their evolution is
essential to establish the dynamical imprints of such collisions, and to infer
the processes involved in their formation. We present multi-transition 13CO and
C18O maps toward the IRDC G035.39-00.33, believed to be at the earliest stages
of evolution. The 13CO and C18O gas is distributed in three filaments
(Filaments 1, 2 and 3), where the most massive cores are preferentially found
at the intersecting regions between them. The filaments have a similar
kinematic structure with smooth velocity gradients of ~0.4-0.8 km s-1 pc-1.
Several scenarios are proposed to explain these gradients, including cloud
rotation, gas accretion along the filaments, global gravitational collapse, and
unresolved sub-filament structures. These results are complemented by HCO+,
HNC, H13CO+ and HN13C single-pointing data to search for gas infall signatures.
The 13CO and C18O gas motions are supersonic across G035.39-00.33, with the
emission showing broader linewidths toward the edges of the IRDC. This could be
due to energy dissipation at the densest regions in the cloud. The average H2
densities are ~5000-7000 cm-3, with Filaments 2 and 3 being denser and more
massive than Filament 1. The C18O data unveils three regions with high CO
depletion factors (f_D~5-12), similar to those found in massive starless cores.Comment: 20 pages, 14 figures, 6 tables, accepted for publication in MNRA
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