Neutral gas in the central 2 parsecs of the Galaxy

Jackson, J. M.; Geis, N.; Genzel, R.; Harris, A. I.; Madden, S. C.; Poglitsch, A.; Stacey, G. J.; Townes, C. H.

doi:10.1086/172120

Cited by 209 publications

(347 citation statements)

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“…The inner ring has a mass of ∼ 4 × 10 3 − 1.2 × 10 4 M ⊙ , larger than the estimated mass of neutral gas observed in the central cavity ( > ∼ 300 M ⊙ , Jackson et al 1993). We argue that the formation of the CW disc and that of the CNR in our Galaxy might be both associated with the disruption of a molecular cloud.…”

Section: Discussionmentioning

confidence: 51%

“…The mass of the inner ring in runs R1, R2 and R4 is 4 × 10 3 − 1.2 × 10 4 M ⊙ (Table 2), and its temperature spans from ∼ 100 K to ∼ 500 K, indicating that the inner ring is composed of warm, but mostly neutral gas. Jackson et al (1993) found that > ∼ 300 M ⊙ of neutral gas lie in the central cavity inside the CNR, but this measurement is quite uncertain and might be an underestimate (see also Goicoechea et al 2013). The inner ring in our simulations is a factor of 10 − 40 more massive than this estimate.…”

Section: The Cnr In Our Galaxymentioning

confidence: 51%

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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: Discussionmentioning

confidence: 51%

Section: The Cnr In Our Galaxymentioning

confidence: 51%

Modelling the formation of the circumnuclear ring in the Galactic centre

Mapelli

Trani

2016

A&A

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“…Carral et al (1994) and Lord et al (1996) present energetic and spectroscopic arguments that the [CII] and [OI] generally originate in PDRs in starburst nuclei, and not in shocks driven by stellar winds and supernovae or x rays from supernovae blast waves. Typically, the beam size for 16 In [OI] these include Genzel et al, 1984Genzel et al, , 1985Jackson et al, 1993;see Fig. 35;in [CII] Genzel et al, 1985;Lugten et al, 1986;Poglitsch et al, 1991;in [CI] Serabyn et al, 1994; these observations is of order 1Ј, which corresponds to 1.4 kpc at a distance of 5 Mpc.…”

Section: Starburst Galactic Nucleimentioning

confidence: 99%

Photodissociation regions in the interstellar medium of galaxies

Hollenbach

Tielens²

1999

Rev. Mod. Phys.

751

712

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The interstellar medium of galaxies is the reservoir out of which stars are born and into which stars inject newly created elements as they age. The physical properties of the interstellar medium are governed in part by the radiation emitted by these stars. Far-ultraviolet (6 eVϽh Ͻ13.6 eV) photons from massive stars dominate the heating and influence the chemistry of the neutral atomic gas and much of the molecular gas in galaxies. Predominantly neutral regions of the interstellar medium in which the heating and chemistry are regulated by far ultraviolet photons are termed PhotoDissociation Regions (PDRs). These regions are the origin of most of the non-stellar infrared (IR) and the millimeter and submillimeter CO emission from galaxies. The importance of PDRs has become increasingly apparent with advances in IR and submillimeter astronomy. The IR emission from PDRs includes fine structure lines of C, C ϩ , and O; rovibrational lines of H 2 ; rotational lines of CO; broad mid-IR features of polycyclic aromatic hydrocarbons; and a luminous underlying IR continuum from interstellar dust. The transition of H to H 2 and C ϩ to CO occurs within PDRs. Comparison of observations with theoretical models of PDRs enables one to determine the density and temperature structure, the elemental abundances, the level of ionization, and the radiation field. PDR models have been applied to interstellar clouds near massive stars, planetary nebulae, red giant outflows, photoevaporating planetary disks around newly formed stars, diffuse clouds, the neutral intercloud medium, and molecular clouds in the interstellar radiation field-in summary, much of the interstellar medium in galaxies. Theoretical PDR models explain the observed correlations of the [CII] 158 m with the CO Jϭ1 -0 emission, the CO Jϭ1 -0 luminosity with the interstellar molecular mass, and the [CII] 158 m plus [OI] 63 m luminosity with the IR continuum luminosity. On a more global scale, PDR models predict the existence of two stable neutral phases of the interstellar medium, elucidate the formation and destruction of star-forming molecular clouds, and suggest radiation-induced feedback mechanisms that may regulate star formation rates and the column density of gas through giant molecular clouds. [S0034-6861(99)01001-6] CONTENTS

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“…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%

“…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. : Güsten et al 1987;Jackson et al 1993;Marshall et al 1995;Shukla et al 2004;Christopher et al 2005). The CND does not appear to be an equilibrium structure.…”

Section: Introductionmentioning

confidence: 99%

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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Neutral gas in the central 2 parsecs of the Galaxy

Cited by 209 publications

References 0 publications

Modelling the formation of the circumnuclear ring in the Galactic centre

Modelling the formation of the circumnuclear ring in the Galactic centre

Photodissociation regions in the interstellar medium of galaxies

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

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Neutral gas in the central 2 parsecs of the Galaxy

Cited by 209 publications

References 0 publications

Modelling the formation of the circumnuclear ring in the Galactic centre

Modelling the formation of the circumnuclear ring in the Galactic centre

Photodissociation regions in the interstellar medium of galaxies

Mapping photodissociation and shocks in the vicinity of Sagittarius A∗

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