Gas Density, Stability, and Starbursts near the Inner Lindblad Resonance of the Milky Way

Stark, A. A.; Martin, Christopher L.; Walsh, Wilfred M.; Xiao, Kecheng; Lane, Alan M.; Walker, Christopher K.

doi:10.1086/425304

Cited by 39 publications

(52 citation statements)

References 25 publications

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“…• 3 and in Sgr C complexes correspond to the locations where interactions between the X1 and X2 orbits are expected (see, Binney et al 1991;Stark et al 2004). The CO and SiO(2−1) maps of these regions (Tanaka et al 2007;Amo-Baladrón et al, in prep.…”

Section: Observationsmentioning

confidence: 99%

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Tracing gas accretion in the Galactic center using isotopic ratios

Riquelme

Amo-Baladrón

Martı́n-Pintado

et al. 2010

A&A

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Aims. We study the 12 C/ 13 C isotopic ratio in the disk of the central molecular zone and in the halo to trace gas accretion toward the Galactic center region in the Milky Way. Methods. Using the IRAM 30m telescope, we observed the J = 1−0 rotational transition of HCO + , HCN, HNC, and their 13 C isotopic substitutions in order to measure the 12 C/ 13 C isotopic ratio. We observed 9 positions selected throughout the Galactic center region, including clouds at high latitude, locations where the X1 and X2 orbits associated with the barred potential are expected to intersect, and typical Galactic center molecular clouds. Results. We find a systematically higher 12 C/ 13 C isotopic ratio (>40) toward the halo and the X1 orbits than for the Galactic center molecular clouds (20-25). Our results point to molecular gas that has undergone a different degree of nuclear processing than observed in the gas towards the inner Galactic center region. Conclusions. The high isotopic ratios are consistent with the accretion of the gas from the halo and from the outskirts of the Galactic disk.

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Section: Observationsmentioning

confidence: 99%

“…Left: spectra toward the 1.3 complex. Center: l-v diagram showing the X1 and X2 orbits superimposed (Stark et al 2004). Right: spectra toward Sgr C region.…”

Section: Opacity Effects Isotopic Fractionation and Selective Photomentioning

confidence: 99%

Tracing gas accretion in the Galactic center using isotopic ratios

Riquelme

Amo-Baladrón

Martı́n-Pintado

et al. 2010

A&A

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“…This mechanism is based on the gravitational collapse of the gas into giant gas clouds in the ILR ring suggested by Elmegreen (1994). Stark et al (2004) used the properties of the Galactic center molecular gas derived by Martin et al (2004) to estimate a critical density of n(H 2 ) $ 10 3:5 cm À3 above which the molecular gas in the ILR will become instable and self-gravitating. The sudden formation of these clouds can result in a starburst.…”

Section: Is the Center Of Ngc 6946 Peculiar?mentioning

confidence: 99%

Molecular Gas Dynamics in NGC 6946: A Bar‐driven Nuclear Starburst “Caught in the Act”

Schinnerer

Böker

Emsellem³

et al. 2006

ApJ

134

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We present high angular resolution ($1 00 and 0B6) millimeter interferometric observations of the 12 CO(1À0) and 12 CO(2À1) line emission in the central 300 pc of the late-type spiral galaxy NGC 6946. The data, obtained with the IRAM Plateau de Bure Interferometer (PdBI), allow the first detection of a molecular gas spiral in the inner $10 00 (270 pc) with a large concentration of molecular gas (M H 2 $ 1:6 ; 10 7 M ) within the inner 60 pc. This nuclear clump shows evidence for a ringlike geometry with a radius of $10 pc as inferred from the position-velocity diagrams. Both the distribution of the molecular gas and its kinematics can be well explained by the influence of an inner stellar bar of about 400 pc length. A qualitative model of the expected gas flow shows that streaming motions along the leading sides of this bar are a plausible explanation for the high nuclear gas density. Thus, NGC 6946 is a prime example of molecular gas kinematics being driven by a small-scale, secondary stellar bar.

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“…In the Milky Way the nuclear star-forming ring should probably be identified with the continuum sources Sgr A-E, but any such match remains to be assessed quantitatively (however, see Stark et al 2004): here (Sect. 4) we show that the kinematics of the inner-galaxy HII regions in fact fit the expected pattern and define fairly well a ring of radius ≈ 70 = 175 pc.…”

Section: Introductionmentioning

confidence: 99%

Molecular cloud shredding in the Galactic Bar

Liszt¹

2006

A&A

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Seen just outside the innermost regions of the galactic center, the kinematics of molecular gas are dominated by a handful of compact but unusually broad-lined features of enigmatic origin. We show, using previous data, that there is a family of such features whose members are distinguished morphologically by their extreme vertical extension, perpendicular to the inclined plane of the overall gas tilt. Having isolated the features spatially, we mapped them with varying degrees of completeness at high resolution (1 ) in lines of 12 CO, 13 CO and CS. Although very broad profiles exist in some individual beams, more generally we resolved the kinematics into spatial gradients which earlier were smeared in broader beams to form wider lines. The largest apparent velocity gradients are typically with respect to galactic latitude but motions are confined to the range of velocities inside the galactic terminal velocity, indicating that it is the galactic gravitational potential which is being tapped to create the observed kinematics. We interpret the broad-lined features qualitatively in terms of recent hydrodynamical models of gas flow in strongly barred galaxies: standing shocks which occur where gas enters the Galactic dust lane can account for the presence of broad lines over small spatial volumes wherever molecular gas is actually engaged in this process. To interpret the dynamical sequencing of the complex behaviour seen within the broad-line features we discuss how the Sun must be oriented with respect to the bar. In doing so, we identify the nuclear star-forming rings seen in other galaxies with the complex of giant H II regions Sgr A, B, C etc. and show that the kinematics are as expected for a ring of radius 175 pc (for a Sun-center distance of 8.5 kpc) rotating at about 210 km s −1 . Gas having clear and strong outward-directed non-circular motion around l = 0• (the famous "expanding molecular ring") is then associated with the "spray" of incoming gas at the inner ends of the dust lane, defining a more nearly end-on viewing angle for the bar.Using the inferred geometry, we construct a narrative for the behaviour of the feature most completely mapped here, at l = 5.4• , whereby gas basically falls out of the sky and is concentrated into the observed dense, bright molecular core before being shredded and sucked into the inflow of the dust lane 100 pc or more below the nominal galactic equator. From there it is recycled and lifted back into the more nearly equatorial region of the nuclear ring. Of course, the vertical structure of this and the other features, and the overall tilt of the dust lane and inner-galaxy gas layer, all remain to be discussed theoretically.

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Gas Density, Stability, and Starbursts near the Inner Lindblad Resonance of the Milky Way

Cited by 39 publications

References 25 publications

Tracing gas accretion in the Galactic center using isotopic ratios

Tracing gas accretion in the Galactic center using isotopic ratios

Molecular Gas Dynamics in NGC 6946: A Bar‐driven Nuclear Starburst “Caught in the Act”

Molecular cloud shredding in the Galactic Bar

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