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H$_2$ mass-velocity relationship from 3D numerical simulations of jet-driven molecular outflows

Abstract : Previous numerical studies have shown that in protostellar outflows, the mass-velocity distribution $m(v)$ can be well described by a broken power law $\propto v^{- \gamma}$. On the other hand, recent observations of a sample of outflows show that the CO intensity-velocity distribution, closely related to $m(v)$, follows an exponential law $\propto \exp(-v/v_0)$. In the present work, we revisit the physical origin of the mass-velocity relationship $m(v)$ in jet-driven protostellar outflows. We investigate the respective contributions of the different regions of the outflow, from the swept-up ambient gas to the jet. We performed 3D numerical simulations of a protostellar jet propagating into a molecular cloud using the hydrodynamical code Yguazu-a. The code takes into account atomic and ionic species and was modified to include the H$_2$ gas. We find that by excluding the jet contribution, $m(v)$ is satisfyingly fitted with a single exponential law, with $v_0$ well in the range of observational values. The jet contribution results in additional components in the mass-velocity relationship. This empirical mass-velocity relationship is found to be valid locally in the outflow. The exponent $v_0$ is almost constant in time and for a given level of mixing between the ambient medium and the jet material. In general, $v_0$ displays only a weak spatial dependence. A simple modeling of the L1157 outflow successfully reproduces the various components of the observed CO intensity-velocity relationship. Our simulations indicate that these components trace the outflow cavity of swept-up gas and the material entrained along the jet, respectively. The CO intensity-velocity exponential law is naturally explained by the jet-driven outflow model. The entrained material plays an important role in shaping the mass-velocity profile.
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Preprints, Working Papers, ...
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https://hal-cnrs.archives-ouvertes.fr/hal-03079580
Contributor : Bertrand Le Floch <>
Submitted on : Thursday, December 17, 2020 - 11:53:26 AM
Last modification on : Saturday, December 19, 2020 - 3:25:42 AM

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  • HAL Id : hal-03079580, version 1
  • ARXIV : 2012.06525

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Adriano Cerqueira, Bertrand Lefloch, Alejandro Esquivel, Pedro Rivera-Ortiz, Claudio Codella, et al.. H$_2$ mass-velocity relationship from 3D numerical simulations of jet-driven molecular outflows. 2020. ⟨hal-03079580⟩

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