تچان ِ فربال ِ سرد
tacân-e farbâl-e sard
Fr.: écoulement d'accrétion froid
1) A type of → accretion flow by a
→ compact object
such as a → black hole
that consists of cool → optically thick
gas and has a relatively high mass → accretion rate,
in contrast to → hot accretion flows.
2) Gas accreting from the → intergalactic medium (IGM)
onto → galactic haloes with sufficiently low velocities so
that it will not be shocked to the → virial temperature
of the halo, but will instead flow at a relatively low temperature
(T ~ 104 K).
Galaxies grow by accreting gas from → cosmic filaments.
Feedback from star formation
and → active galactic nuclei
returns a significant fraction of the
→ interstellar medium
(ISM) to the halo and may even blow it out of the halo into the IGM.
This "cold accretion" will happen if the cooling time of → virialized
gas is too
short to maintain a hot, → hydrostatic halo.
The existence of such a cold accretion
mode has been confirmed by simulations, which have furthermore demonstrated
that cold mode accretion can also be important for halos sufficiently massive
to contain hot, hydrostatic gas. Because gas accretes preferentially along the
filaments of the cosmic web, the streams of infalling gas have relatively high gas
densities and correspondingly low cooling times. This allows the cold streams to
penetrate the hot, hydrostatic halos surrounding massive galaxies, particularly
at → high redshifts
(F. van de Voort et al., 2012, MNRAS 421, 2809).
→ cold; → accretion;