Hot Molecular Gas in the Circumnuclear Disk

Mills, Elisabeth A. C.; Togi, Aditya; Kaufman, Michael J.

doi:10.3847/1538-4357/aa951f

Cited by 16 publications

(16 citation statements)

References 81 publications

(184 reference statements)

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“…This star formation might be associated with star formation occurring near Sgr A * (R ≤ 10 pc). This would be consistent with claims of observational evidence for ongoing star formation in this region (Yusef-Zadeh et al 2008), although we note that these claims are controversial at the moment (Mills, Togi & Kaufman 2017). Such star formation might also be related to the formation of the nuclear stellar cluster (NSC; see e.g.…”

Section: Spatial Distribution Of Star Formationsupporting

confidence: 89%

Simulations of the Milky Way’s Central Molecular Zone – II. Star formation

Sormani

Treß

Glover

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Abstract The Milky Way’s central molecular zone (CMZ) has emerged in recent years as a unique laboratory for the study of star formation. Here we use the simulations presented in Tress et al. 2020 to investigate star formation in the CMZ. These simulations resolve the structure of the interstellar medium at sub-parsec resolution while also including the large-scale flow in which the CMZ is embedded. Our main findings are as follows. (1) While most of the star formation happens in the CMZ ring at R ≳ 100 pc, a significant amount also occurs closer to SgrA* at R ≲ 10 pc. (2) Most of the star formation in the CMZ happens downstream of the apocentres, consistent with the “pearls-on-a-string” scenario, and in contrast to the notion that an absolute evolutionary timeline of star formation is triggered by pericentre passage. (3) Within the timescale of our simulations (∼100 Myr), the depletion time of the CMZ is constant within a factor of ∼2. This suggests that variations in the star formation rate are primarily driven by variations in the mass of the CMZ, caused for example by AGN feedback or externally-induced changes in the bar-driven inflow rate, and not by variations in the depletion time. (4) We study the trajectories of newly born stars in our simulations. We find several examples that have age and 3D velocity compatible with those of the Arches and Quintuplet clusters. Our simulations suggest that these prominent clusters originated near the collision sites where the bar-driven inflow accretes onto the CMZ, at symmetrical locations with respect to the Galactic centre, and that they have already decoupled from the gas in which they were born.

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Section: Spatial Distribution Of Star Formationsupporting

confidence: 89%

Simulations of the Milky Way’s Central Molecular Zone – II. Star formation

Sormani

Treß

Glover

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…For these densities, our non-LTE excitation models shown in Figure A.1 imply temperatures ranging from T k ≃400 to 2000 K. Both the elevated T k and low n H (compared to the local Roche density) are compatible with the non-thermal H 2 level populations inferred from IR observations with the VLT (Ciurlo et al 2016). These T k and n H also agree with H 2 multi-line detections ( T ex (H 2 )~1100 K, Mills et al 2017) with ISO . Infrared observations provide lower spectral resolution, thus it is difficult to extract the different velocity components independently.…”

Section: Physical Conditions Of High-velocity Co Gassupporting

confidence: 84%

“…From the CO J =3-2 maps, we determine an interferometer-alone to single-dish line flux ratio of ≃0.2 (HPVW range). As we expect the unresolved cloudlets to be hot (Goicoechea et al 2013; Mills et al 2017) the contrast between emission from the extended background and these cloudlets is likely to increase for the more excited CO lines, leading to larger flux ratios. In the following we attribute the origin of the mid- J 12 CO HPVW emission to the same cloudlets.…”

Section: Results: Detected Lines and Wing Emissionmentioning

confidence: 97%

“…Owing to hostile conditions inside the cavity of the CND, the presence of molecular gas was originally not expected. Recent studies, however, point toward its existence (e.g., Herrnstein & Ho 2002; Goicoechea et al 2013; Ciurlo et al 2016; Moser et al 2017; Mills et al 2017; Yusef-Zadeh et al 2017). Indeed, obtaining high-resolution spectral images of the molecular gas emission close to Sgr A* is currently feasible with radio interferometers such as ALMA (e.g., Moser et al 2017; Yusef-Zadeh et al 2017).…”

Section: Introductionmentioning

confidence: 99%

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High-velocity hot CO emission close to Sgr A*

Goicoechea

Santa-Maria

Teyssier

et al. 2018

A&A

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The properties of molecular gas, the fuel that forms stars, inside the cavity of the circumnuclear disk (CND) are not well constrained. We present results of a velocity-resolved submillimeter scan (~480 to 1250 GHz) and [C ii] 158 μm line observations carried out with Herschel/HIFI toward Sgr A*; these results are complemented by a ~2′×2′ 12CO (J=3-2) map taken with the IRAM 30 m telescope at ~7″ resolution. We report the presence of high positive-velocity emission (up to about +300 km s−1) detected in the wings of 12CO J=5-4 to 10-9 lines. This wing component is also seen in H2O (11,0-10,1), a tracer of hot molecular gas; in [C ii]158 μm, an unambiguous tracer of UV radiation; but not in [C i] 492, 806 GHz. This first measurement of the high-velocity 12CO rotational ladder toward Sgr A* adds more evidence that hot molecular gas exists inside the cavity of the CND, relatively close to the supermassive black hole (< 1 pc). Observed by ALMA, this velocity range appears as a collection of 12CO (J=3-2) cloudlets lying in a very harsh environment that is pervaded by intense UV radiation fields, shocks, and affected by strong gravitational shears. We constrain the physical conditions of the high positive-velocity CO gas component by comparing with non-LTE excitation and radiative transfer models. We infer Tk≃400 K to 2000 K for nH≃(0.2-1.0)·105 cm−3. These results point toward the important role of stellar UV radiation, but we show that radiative heating alone cannot explain the excitation of this ~10-60 M⊙ component of hot molecular gas inside the central cavity. Instead, strongly irradiated shocks are promising candidates.

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“…The existence of molecular material in such a hostile environment: affected by enhanced UV fields, X-rays, cosmic-rays particles, stellar winds, shocks, turbulence and strong gravity effects, was initially not expected. However, it has been more or less convincingly demonstrated recently (e.g., Yusef-Zadeh et al 2001; Herrnstein & Ho 2002; Goicoechea et al 2013, 2018; Goto et al 2014; Feldmeier-Krause et al 2015; Moultaka et al 2015; Ciurlo et al 2016; Moser et al 2017; Mills et al 2017; Yusef-Zadeh et al 2017b). Still, controversy prevails because it is not easy to assign unprojected distances from the observed molecular features to Sgr A*.…”

Section: Introductionmentioning

confidence: 99%

High-speed molecular cloudlets around the Galactic center’s supermassive black hole

Goicoechea

Pety

Chapillon

et al. 2018

A&A

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We present 1″-resolution ALMA observations of the circumnuclear disk (CND) and the interstellar environment around Sgr A*. The images unveil the presence of small spatial scale 12CO (J=3-2) molecular “cloudlets” (≲20,000 AU size) within the central parsec of the Milky Way, in other words, inside the cavity of the CND, and moving at high speeds, up to 300 km s−1 along the line-of-sight. The 12CO-emitting structures show intricate morphologies: extended and filamentary at high negative-velocities (vLSR ≲−150 km s−1), more localized and clumpy at extreme positive-velocities (vLSR ≳+200 km s−1). Based on the pencil-beam 12CO absorption spectrum toward Sgr A* synchrotron emission, we also present evidence for a diffuse molecular gas component producing absorption features at more extreme negative-velocities (vLSR <−200 km s−1). The CND shows a clumpy spatial distribution traced by the optically thin H13CN (J=4-3) emission. Its motion requires a bundle of non-uniformly rotating streams of slightly different inclinations. The inferred gas density peaks, molecular cores of a few 105 cm−3, are lower than the local Roche limit. This supports that CND cores are transient. We apply the two standard orbit models, spirals vs. ellipses, invoked to explain the kinematics of the ionized gas streamers around Sgr A*. The location and velocities of the 12CO cloudlets inside the cavity are inconsistent with the spiral model, and only two of them are consistent with the Keplerian ellipse model. Most cloudlets, however, show similar velocities that are incompatible with the motions of the ionized streamers or with gas bounded to the central gravity. We speculate that they are leftovers of more massive molecular clouds that fall into the cavity and are tidally disrupted, or that they originate from instabilities in the inner rim of the CND that lead to fragmentation and infall from there. In either case, we show that molecular cloudlets, all together with a mass of several 10 M⊙, exist around Sgr A*. Most of them must be short-lived, ≲104 yr: photoevaporated by the intense stellar radiation field, G0≃105.3 to 104.3, blown away by winds from massive stars in the central cluster, or disrupted by strong gravitational shears.

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Hot Molecular Gas in the Circumnuclear Disk

Cited by 16 publications

References 81 publications

Simulations of the Milky Way’s Central Molecular Zone – II. Star formation

Simulations of the Milky Way’s Central Molecular Zone – II. Star formation

High-velocity hot CO emission close to Sgr A*

High-speed molecular cloudlets around the Galactic center’s supermassive black hole

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