Feedback from OB stars on their parent cloud: gas exhaustion rather than gas ejection

Abstract

Context. Stellar feedback from high-mass stars shapes the interstellar medium, and thereby impacts gas that will form future generations of stars. However, due to our inability to track the time evolution of individual molecular clouds, quantifying the exact role of stellar feedback on their star formation history is an observationally challenging task. Aims. In the present study, we take advantage of the unique properties of the G316.75-00.00 massive-star forming ridge to determine how stellar feedback from O-stars impacts the dynamical stability of massive filaments. The G316.75 ridge is 13.6 pc long ridge and contains 18,900 M of H 2 gas, half of which is infrared dark and half of which infrared bright. The infrared bright part has already formed four O-type stars over the past 2 Myr, while the infrared dark part is still quiescent. Therefore, by assuming the star forming properties of the infrared dark part represent the earlier evolutionary stage of the infrared bright part, we can quantify how feedback impacts these properties by contrasting the two. Methods. We used publicly available Herschel/HiGAL and molecular line data to measure the ratio of kinetic to gravitational energy per-unit-length, α line vir , across the entire ridge. By using both dense (i.e.N 2 H + and NH 3 ) and more diffuse (i.e. 13 CO) gas tracers, we were able to compute α line vir for a range of gas volume densities (∼1×10 2 -1×10 5 cm −3 ). Results. This study shows that despite the presence of four embedded O-stars, the ridge remains gravitationally bound (i.e. α line vir ≤ 2) nearly everywhere, except for some small gas pockets near the high-mass stars. In fact, α line vir is almost indistinguishable for both parts of the ridge. These results are at odds with most hydrodynamical simulations in which O-star-forming clouds are completely dispersed by stellar feedback within a few cloud free-fall times. However, from simple theoretical calculations, we show that such feedback inefficiency is expected in the case of high-gas-density filamentary clouds. Conclusions. We conclude that the discrepancy between numerical simulations and the observations presented here originates from different cloud morphologies and average densities at the time when the first O-stars form. In the case of G316.75, we speculate that the ridge could arise from the aftermath of a cloud-cloud collision, and that such filamentary configuration promotes the inefficiency of stellar feedback. This does very little to the dense gas already present, but potentially prevents further gas accretion onto the ridge. These results have important implications regarding, for instance, how stellar feedback is implemented in cosmological and galaxy scale simulations.

The Origin of Massive Stars: The Inertial-inflow Model

“…For example, the accretion rates in our simulation may maintain our stars bloated until they reach the main sequence as an intermediate-mass star and ionization feedback would not play a role in that initial phase, as also confirmed observationally by the high luminosity of young, massive protostars (Ginsburg et al 2017). There is also tentative observational evidence that stellar radiation cannot strongly affect the mass inflow when this occurs through dense filaments (Watkins et al 2019). Radiative feedback mechanisms may also assist the formation of massive stars, by suppressing fragmentation in the neighborhood of a massive star, which increases the mass reservoir available for its growth, while preventing the formation of lower-mass stars (Krumholz et al 2007).…”

Synthetic line and continuum observations of simulated turbulent clouds: the apparent widths of filaments

“…In the present context, the radial velocity difference across a filament may be a discriminating signature of filament formation by turbulence (as here). The data presented in Ragan et al (2012) and Watkins et al (2019) show some indication for velocity gradients perpendicular to the filament long axes, but on larger scales than those simulated here, and rotation would produce a similar effect. Arzoumanian et al (2018) find evidence for redand blue-shifted 13 CO emission on alternate sides of a ∼1 pc-long filament identified in C 18 O, which they attributed to interaction between the filament and an extended sheet-like structure.…”

Edge collapse and subsequent longitudinal accretion in filament S242

“…where G is the gravitational constant; M line is the line mass estimated as M line = µm H N H 2 d, where the N H 2 is the H 2 column density along the skeleton and d is defined as half of the S242 filament width (∼0.4 pc). Furthermore, for a filament the virial parameters could be calculated as (Ostriker 1964;Watkins et al 2019)…”