Aperture synthesis observations of the circumnuclear ring in the Galactic center

Guêsten, R.; Genzel, R.; Wright, M. C. H.; Jaffe, D. T.; Stützki, J.; Harris, A. I.

doi:10.1086/165355

Cited by 239 publications

(292 citation statements)

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“…Previous studies proposed that the CNR formed through the collision of two molecular clouds (e.g. Guesten et al 1987) or through the assembly of multiple dynamically different streamers (e.g. Jackson et al 1993).…”

Section: Introductionmentioning

confidence: 99%

Modelling the formation of the circumnuclear ring in the Galactic centre

Mapelli

Trani

2016

A&A

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Several thousand solar masses of molecular, atomic and ionized gas lie in the innermost ∼ 10 pc of our Galaxy. The most relevant structure of molecular gas is the circumnuclear ring (CNR), a dense and clumpy ring surrounding the supermassive black hole (SMBH), with a radius of ∼ 2 pc. We propose that the CNR formed through the tidal disruption of a molecular cloud, and we investigate this scenario by means of N-body smoothed-particle hydrodynamics simulations. We ran a grid of simulations with different cloud mass (4 × 10 4 , 1.3 × 10 5 M⊙), different initial orbital velocity (vin = 0.2 − 0.5 vesc, where vesc is the escape velocity from the SMBH), and different impact parameter (b = 8, 26 pc). The disruption of the molecular cloud leads to the formation of very dense and clumpy gas rings, containing most of the initial cloud mass. If the initial orbital velocity of the cloud is sufficiently low (vin < 0.4 vesc, for b = 26 pc) or the impact parameter is sufficiently small (b < ∼ 10 pc, for vin > 0.5 vesc), at least two rings form around the SMBH: an inner ring (with radius ∼ 0.4 pc) and an outer ring (with radius ∼ 2 − 4 pc). The inner ring forms from low-angular momentum material that engulfs the SMBH during the first periapsis passage, while the outer ring forms later, during the subsequent periapsis passages of the disrupted cloud. The inner and outer rings are misaligned by ∼ 24 degrees, because they form from different gas streamers, which are affected by the SMBH gravitational focusing in different ways. The outer ring matches several properties (mass, rotation velocity, temperature, clumpiness) of the CNR in our Galactic centre. We speculate that the inner ring might account for the neutral gas observed in the central cavity.

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Section: Introductionmentioning

confidence: 99%

Modelling the formation of the circumnuclear ring in the Galactic centre

Mapelli

Trani

2016

A&A

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“…Converging to Sgr A * , there are arc-shaped ionized gas streamers with a minispiral morphology (Sgr A West) that seem to be feeding the nucleus (Lo & Claussen 1983;Roberts & Goss 1993). Both the black hole and Sgr A West are surrounded by a ring of molecular gas and dust (the CND; Becklin et al 1982;Güsten et al 1987), whose inner edge suffers UV-photoionization (Roberts & Goss 1993) due to a dense stellar population of massive stars in the Central cluster (Krabbe et al 1995;Figer 2008). …”

Section: Introductionmentioning

confidence: 99%

“…These studies have characterized the CND as dense (∼10 5−6 cm −3 ; Marr et al 1993;Marshall et al 1995), clumpy, and very turbulent (with large linewidths). It extends from its inner edge, 1.6 pc from Sgr A * , to > ∼ 2 pc, according to interferometric studies (Wright et al 2001;Christopher et al 2005), and it has an inclination (rotation axis from the line of sight; LOS) of about 60 • −70 • , with the major axis aligned approximately along the Galactic plane (position angle of ∼30 • east of north; Güsten et al 1987;Jackson et al 1993;A&A 526, A54 (2011) Gatley et al (1986) Yusef Telesco et al (1996) Atomic species Liszt et al (1985) (H i, [O Genzel et al (1985) Lugten et al ) Jackson et al (1993) Serabyn et al (1994 Marshall et al 1995). The gas is moving in circular orbits, rotating around the nucleus with a velocity of 110 km s −1 (Liszt et al 1985;Marr et al 1993), but it also presents noncircular motions (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Mapping photodissociation and shocks in the vicinity of Sagittarius A^∗

Amo-Baladrón

Martı́n-Pintado

Martín

2010

A&A

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Aims. We study the chemistry in the harsh environments of galactic nuclei using the nearest one, the Galactic center (GC). Methods. We have obtained maps of the molecular emission within the central five arcminutes (12 pc) of the GC in selected molecular tracers: SiO(2-1), HNCO(5 0,5 -4 0,4 ), and the J = 1 → 0 transition of H 13 CO + , HN 13 C, and C 18 O at an angular resolution of 30 (1.2 pc). The mapped region includes the circumnuclear disk (CND) and the two surrounding giant molecular clouds (GMCs) of the Sgr A complex, known as the 20 and 50 km s −1 molecular clouds. Additionally, we simultaneously observed the J = 2 → 1 and J = 3 → 2 transitions of SiO toward selected positions to estimate the physical conditions of the molecular gas using the large velocity gradient approximation. Results. The SiO(2-1) emission shows all the molecular features identified in previous studies, covering the same velocity range as the H 13 CO + (1-0) emission, which also presents a similar distribution. In contrast, HNCO(5-4) emission appears in a narrow velocity range mostly concentrated in the 20 and 50 km s −1 GMCs. A similar trend follows the HN 13 C(1-0) emission. The HNCO column densities and fractional abundances present the highest contrast, with difference factors of ≥60 and 28, respectively. Their highest values are found toward the cores of the GMCs, whereas the lowest ones are measured at the CND. SiO abundances do not follow this trend, with high values found toward the CND, as well as the GMCs. By comparing our abundances with those of prototypical Galactic sources we conclude that HNCO, similar to SiO, is ejected from grain mantles into gas-phase by nondissociative C-shocks. This results in the high abundances measured toward the CND and the GMCs. However, the strong UV radiation from the Central cluster utterly photodissociates HNCO as we get closer to the center, whereas SiO seems to be more resistant against UV-photons or it is produced more efficiently by the strong shocks in the CND. This UV field could be also responsible for the trend found in the HN 13 C abundance. Conclusions. We discuss the possible connections between the molecular gas at the CND and the GMCs using the HNCO/SiO, SiO/CS, and HNCO/CS intensity ratios as probes of distance to the Central cluster. In particular, the HNCO/SiO intensity ratio is proved to be an excellent tool for evaluating the distance to the center of the different gas components.

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“…The CND is assumed to be an association of clouds/filaments of dense (10 4 -10 7 cm −3 ) and warm (several 100 K) molecular gas (∼10 5 M of dust and gas, (Christopher et al 2005)), which orbits the nucleus in a circular rotation pattern, with a sharp inner edge at 1.5 pc that extends no further than 7 pc from the centre (Guesten et al 1987;Christopher et al 2005;Montero-Castaño et al 2009). The region inside this cavity contains atomic and ionized gas.…”

Section: Introductionmentioning

confidence: 99%

The Galactic centre mini-spiral in the mm-regime

Kunneriath

Eckart

Vogel

et al. 2012

A&A

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Context. The mini-spiral is a feature of the interstellar medium in the central ∼2 pc of the Galactic center. It is composed of several streamers of dust and ionised and atomic gas with temperatures between a few 100 K to 10 4 K. There is evidence that these streamers are related to the so-called circumnuclear disk of molecular gas and are ionized by photons from massive, hot stars in the central parsec.Aims. We attempt to constrain the emission mechanisms and physical properties of the ionized gas and dust of the mini-spiral region with the help of our multiwavelength data sets. Results. We present high resolution maps of the mini-spiral, and obtain a spectral index of 0.5±0.25 for Sgr A*, indicating an inverted synchrotron spectrum. We find electron densities within the range 0.8-1.5×10 4 cm −3 for the mini-spiral from the radio continuum maps, along with a dust mass contribution of ∼0.25 M from the MIR dust continuum, and extinctions ranging from 1.8-3 at 2.16 µm in the Brγ line. Conclusions. We observe a mixture of negative and positive spectral indices in our 1.3 mm and 3 mm observations of the extended emission of the mini-spiral, which we interpret as evidence that there are a range of contributions to the thermal free-free emission by the ionized gas emission and by dust at 1.3 mm.

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Aperture synthesis observations of the circumnuclear ring in the Galactic center

Cited by 239 publications

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Modelling the formation of the circumnuclear ring in the Galactic centre

Modelling the formation of the circumnuclear ring in the Galactic centre

Mapping photodissociation and shocks in the vicinity of Sagittarius A^∗

The Galactic centre mini-spiral in the mm-regime

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Aperture synthesis observations of the circumnuclear ring in the Galactic center

Cited by 239 publications

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Modelling the formation of the circumnuclear ring in the Galactic centre

Modelling the formation of the circumnuclear ring in the Galactic centre

Mapping photodissociation and shocks in the vicinity of Sagittarius A∗

The Galactic centre mini-spiral in the mm-regime

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Mapping photodissociation and shocks in the vicinity of Sagittarius A^∗