The Dual Role of Starbursts and Active Galactic Nuclei in Driving Extreme Molecular Outflows

Gowardhan, Avani; Spoon, H. W. W.; Riechers, Dominik A.; González-Alfonso, E.; Farrah, D.; Fischer, J.; Darling, Jeremy; Fergulio, Chiara; Afonso, J.; Bizzocchi, L.

doi:10.3847/1538-4357/aabccc

Cited by 33 publications

(28 citation statements)

References 142 publications

(201 reference statements)

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“…Moreover, grain growth in the interstellar medium can also contribute to the increase of the dust mass at later times (Michałowski 2015), while turbulence may further accelerate the growth of dust grains (Mattsson 2020). The associated dust-to-gas ratios can be quite high, with values up to ∼1/30 in dust-reddened quasars (Banerji et al 2017), and potentially up to ∼1/20 to 1/10 in heavily dust-obscured ULIRG nuclei (Gowardhan et al 2018). The combination of high column densities and substantial dust content should lead to large IR optical depths, forming particularly favourable conditions for AGN radiative feedback.…”

Section: Discussionmentioning

confidence: 99%

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AGN-driven galactic outflows: comparing models to observations

Ishibashi

Fabian

Arakawa

2021

Monthly Notices of the Royal Astronomical Society

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The actual mechanism(s) powering galactic outflows in active galactic nuclei (AGN) is still a matter of debate. At least two physical models have been considered in the literature: wind shocks and radiation pressure on dust. Here we provide a first quantitative comparison of the AGN radiative feedback scenario with observations of galactic outflows. We directly compare our radiation pressure-driven shell models with the observational data from the most recent compilation of molecular outflows on galactic scales. We show that the observed dynamics and energetics of galactic outflows can be reproduced by AGN radiative feedback, with the inclusion of radiation trapping and/or luminosity evolution. The predicted scalings of the outflow energetics with AGN luminosity can also quantitatively account for the observational scaling relations. Furthermore, sources with both ultra-fast and molecular outflow detections are found to be located in the ‘forbidden’ region of the NH − λ plane. Overall, an encouraging agreement is obtained over a wide range of AGN and host galaxy parameters. We discuss our results in the context of recent observational findings and numerical simulations. In conclusion, AGN radiative feedback is a promising mechanism for driving galactic outflows that should be considered, alongside wind feedback, in the interpretation of future observational data.

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Section: Discussionmentioning

confidence: 99%

“…Moreover, large amounts of dust are likely expected in the nuclei of ULIRGlike systems, yielding high dust-to-gas ratios (e.g. Gowardhan et al 2018). These peculiar environments should form favourable conditions for AGN radiative feedback.…”

Section: Individual Comparisonmentioning

confidence: 99%

AGN-driven galactic outflows: comparing models to observations

Ishibashi

Fabian

Arakawa

2021

Monthly Notices of the Royal Astronomical Society

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“…Given that molecular gas is the main fuel for star formation, these massive molecular outflows are expected to affect significantly the evolution of star formation in galaxies. In some of the AGNdriven outflows the ejection rate is so high (significantly higher than the star formation rate) that, if maintained, it can potentially clean the galaxy of its molecular gas content within only a few tens million years, hence potentially be effective in totally quenching star formation on short timescales (Sturm et al 2011;Cicone et al 2014;Fiore et al 2017;Gowardhan et al 2018;Fluetsch et al 2019). However, these depletion times assume that there is no significant accretion on similar timescales (assumption which may be appropriate locally but not necessarily in the distant universe) and that the observed outflow is not an isolated ejection event but a continuous process (which is not really the case in the blast wave scenario and also in the case of AGN flickering).…”

Section: Molecular Gas Componentmentioning

confidence: 99%

Cool outflows in galaxies and their implications

Veilleux

Maiolino

Bolatto

et al. 2020

Astron Astrophys Rev

396

310

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Neutral-atomic and molecular outflows are a common occurrence in galaxies, near and far. They operate over the full extent of their galaxy hosts, from the innermost regions of galactic nuclei to the outermost reaches of galaxy halos. They carry a substantial amount of material that would otherwise have been used to form new stars. These cool outflows may have a profound impact on the evolution of their host galaxies and environments. This article provides an overview of the basic physics of cool outflows, a comprehensive assessment of the observational techniques and diagnostic tools used to characterize them, a detailed description of the best-studied cases, and a more general discussion of the statistical properties of these outflows in the local and distant universe. The remaining outstanding issues that have not yet been resolved are summarized at the end of the review to inspire new research directions.

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“…Such outflows have long been observed around starbursts and active galactic nuclei with atomic tracers (see the review by Veilleux et al 2005). More recently, these kinematic signatures have been increasingly observed in molecular emission, including H 2 (Rupke & Veilleux 2013;Petric et al 2018), CO (Gowardhan et al 2018;Fluetsch et al 2019), OH (González-Alfonso et al 2017), HCN, HNC, and HCO + (Aalto et al 2012;Lindberg et al 2016), and CH + (Falgarone et al 2017;Vidal-García et al 2021), revealing the multi-phase nature of these flows. These molecular observations are challenging to explain given that molecules cannot survive in the hot gas (T > 10 6 K) generated by shock waves at these velocities.…”

Section: Introductionmentioning

confidence: 95%

Self-generated ultraviolet radiation in molecular shock waves

Lehmann

Godard

Forêts

et al. 2022

A&A

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Context. The energetics and physical conditions of the interstellar medium and feedback processes remain challenging to probe. Aims. Shocks, modelled over a broad range of parameters, are used to construct a new tool to deduce the mechanical energy and physical conditions from observed atomic or molecular emission lines. Methods. We compute magnetised, molecular shock models with velocities Vs = 5–80 km s−1, pre-shock proton densities nH = 102–106 cm−3, weak or moderate magnetic field strengths, and in the absence or presence of an external UV radiation field. These parameters represent the broadest published range of physical conditions for molecular shocks. As a key shock tracer, we focus on the production of CH+ and post-process the radiative transfer of its rovibrational lines. We develop a simple emission model of an ensemble of shocks for connecting any observed emission lines to the mechanical energy and physical conditions of the system. Results. For this range of parameters, we find the full diversity (C-, C*-, CJ-, and J-type) of magnetohydrodynamic shocks. H2 and H are dominant coolants, with up to 30% of the shock kinetic flux escaping in Lyα photons. The reformation of molecules in the cooling tail means H2 is even a good tracer of dissociative shocks and shocks that were initially fully atomic. The known shock tracer CH+ can also be a significant coolant, reprocessing up to 1% of the kinetic flux. Its production and excitation is intimately linked to the presence of H2 and C+. For each shock model we provide integrated intensities of rovibrational lines of H2, CO, and CH+, and atomic H lines, and atomic fine-structure and metastable lines. We demonstrate how to use these shock models to deduce the mechanical energy and physical conditions of extragalactic environments. As a template example, we interpret the CH+(1−0) emission from the Eyelash starburst galaxy. A mechanical energy injection rate of at least 1011 L⊙ into molecular shocks is required to reproduce the observed line. We find that shocks with velocities as low as 5 km s−1 irradiated by a strong UV field are compatible with the available energy budget. The low-velocity, externally irradiated shocks are at least an order magnitude more efficient than the most efficient shocks with no external irradiation in terms of the total mechanical energy required. We predict differences of more than two orders of magnitude in the intensities of the pure rotational lines of CO, Lyα, and the metastable lines of O, S+, and N between representative models of low-velocity (Vs ~ 10 km s−1) externally irradiated shocks and higher-velocity shocks (Vs ≥ 50 km s−1) with no external irradiation. Conclusions. Shock modelling over an extensive range of physical conditions allows for the interpretation of challenging observations of broad line emission from distant galaxies. Our new method opens up a promising avenue to quantitatively probe the physical conditions and mechanical energy of galaxy-scale gas flows.

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The Dual Role of Starbursts and Active Galactic Nuclei in Driving Extreme Molecular Outflows

Cited by 33 publications

References 142 publications

AGN-driven galactic outflows: comparing models to observations

AGN-driven galactic outflows: comparing models to observations

Cool outflows in galaxies and their implications

Self-generated ultraviolet radiation in molecular shock waves

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