arXiv subjects

Peter J. Teuben

Publications and source records attributed to Peter J. Teuben.

25 records · Page 2Linked to original sources

arXiv2002

Molecular Gas and Star Formation in Bars of Nearby Spiral Galaxies

We compare the distribution of molecular gas and star formation activity in the bar region of six spirals (NGC 2903, NGC 3627, NGC 4321, NGC 5457, NGC 6946, & IC 342) from the BIMA Survey of Nearby Galaxies (SONG). The molecular gas, traced using the CO (J=1--0) emission line, is brightest along the leading edge of the stellar bar in the bar dust lanes. The star formation activity, traced using the Halpha emission line, is offset towards the leading side of the CO emission. A cross-correlation analysis shows that a) the HII regions are offset 0--800 pc on the leading side of the CO emission, b) the largest offsets are found in the strongest bars, and c) there is a wide range in offsets in a single bar with no systematic pattern as a function of the galacto-centric radius. The CO-Halpha offset constrains how stars may form depending on the gas flow. We examine possible star formation scenarios in context of the two main classes of bar gas flow simulations, the N-body/sticky particle and hydrodynamic models. Though both model gas flows are generally consistent with the observed offsets, we suggest the inclusion of a two- or multi-phase medium to improve the agreement between models and observation.

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arXiv2002

Inner Molecular Rings in Barred Galaxies: BIMA SONG CO Observations

Although inner star-forming rings are common in optical images of barred spiral galaxies, observational evidence for the accompanying molecular gas has been scarce. In this paper we present images of molecular inner rings, traced using the CO (1-0) emission line, from the Berkeley-Illinois-Maryland-Association Survey of Nearby Galaxies (BIMA SONG). We detect inner ring CO emission from all five SONG barred galaxies classified as inner ring (type (r)). We also examine the seven SONG barred galaxies classified as inner spiral (type (s)); in one of these, NGC 3627, we find morphological and kinematic evidence for a molecular inner ring. Inner ring galaxies have been classified as such based on optical images, which emphasize recent star formation. We consider the possibility that there may exist inner rings in which star formation efficiency is not enhanced. However, we find that in NGC 3627 the inner ring star formation efficiency is enhanced relative to most other regions in that galaxy. We note that the SONG (r) galaxies have a paucity of CO and H alpha emission interior to the inner ring (except near the nucleus), while NGC 3627 has relatively bright bar CO and H alpha emission; we suggest that galaxies with inner rings such as NGC 3627 may be misclassified if there are significant amounts of gas and star formation in the bar.

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arXiv2001

Gas Inflow in Barred Galaxies - Effects of Secondary Bars

We report here results of high-resolution hydrodynamical simulations of gas flows in barred galaxies, with a focus on gas dynamics in the central kiloparsec. In a single bar with an Inner Lindblad Resonance, we find either near-circular motion of gas in the nuclear ring, or a spiral shock extending towards the galaxy center, depending on the sound speed in the gas. From a simple model of a dynamically-possible doubly barred galaxy with resonant coupling, we infer that the secondary bar is likely to end well inside its corotation. Such a bar cannot create shocks in the gas flow, and therefore will not reveal itself in color maps through straight dust lanes: the gas flows induced by it are different from those caused by the rapidly rotating main bars. In particular, we find that secondary stellar bars are unlikely to increase the mass inflow rate into the galactic nucleus.

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arXiv1999

Molecular Gas, Dust and Star Formation in the Barred Spiral NGC 5383

We present multi-wavelength (interferometer and single-dish CO J=1-0, Halpha, broadband optical and near-infrared) observations of the classic barred spiral NGC 5383. We compare the observed central gas and dust morphology to the predictions of recent hydrodynamic simulations. In the nuclear region, our observations reveal three peaks lying along a S-shaped gas and dust distribution. In contrast, the model predicts a circumnuclear ring, not the observed S-shaped distribution; moreover, the predicted surface density contrast between the central gas accumulation and the bar dust lanes is an order of magnitude larger than observed. The discrepancies are not due to unexplored model parameter space or a nuclear bar but are probably due to the vigorous (7 solar masses per year) star formation activity in the center. As is common in similar bars, the star formation rate in the bar between the bar ends and the central region is low (~0.5 solar masses per yr), despite the high gas column density in the bar dust lanes; this is generally attributed to shear and shocks. We note a tendency for the HII regions to be associated with the spurs feeding the main bar dust lanes, but these are located on the leading side of the bar. We propose that stars form in the spurs, which provide a high column density but low shear environment. HII regions can therefore be found even on the leading side of the bar because the ionizing stars pass ballistically through the dust lane

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arXiv1999

High Velocity Clouds: the Missing Link

Hierarchical structure formation models predict the existence of large numbers of low velocity dispersion dark halos. Galaxy surveys find far fewer galaxies than predicted by analytical estimates and numerical simulations. In this paper, we suggest that these dark halos are not missing, but have been merely misplaced in the galactic astronomy section of the journals: they are the High Velocity Clouds (HVCs). We review the predictions of our model for the Local Group origin of the HVCs and its implications for the formation and the evolution of our Galaxy. We describe recent observations that confirm many of earlier predictions and discuss future tests of the model.

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arXiv1998

High Velocity Clouds: Building Blocks of the Local Group

We suggest that the high--velocity clouds (HVCs) are large clouds, with typical diameters of 25 kpc and containing 5e7 solar masses of neutral gas and 3e8 solar masses of dark matter, falling onto the Local Group; altogether the HVCs contain 10$^{11}$ solar masses of neutral gas. Our reexamination of the Local-Group hypothesis for the HVCs connects their properties to the hierarchical structure formation scenario and to the gas seen in absorbtion towards quasars. We begin by showing that at least one HVC complex (besides the Magellanic Stream) must be extragalactic at a distance > 40 kpc from the Galactic center, with a diameter > 20 kpc and a mass > 1e8 solar masses. We interpret the more distant HVCs as dark matter ``mini--halos'' moving along filaments towards the Local Group. Most poor galaxy groups should contain HI structures to large distances bound to the group. The HVCs are local analogues of the Lyman--limit clouds We argue that there is a Galactic fountain in the Milky Way, but that the fountain does not explain the origin of the HVCs. Our analysis of the HI data leads to the detection of a vertical infall of low-velocity gas towards the plane. This implies that the chemical evolution of the Galactic disk is governed by episodic infall of metal-poor HVC gas that only slowly mixes with the rest of the interstellar medium. The Local--Group infall hypothesis makes a number of testable predictions. The HVCs should have sub-solar metallicities. Their H$α$ emission should be less than that seen from the Magellanic Stream. The clouds should not be seen in absorption to nearby stars. The clouds should be detectable in both emission and absorption around other groups.

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arXiv1997

The Mass Inflow Rate in the Barred Galaxy NGC 1530

Mass inflow in barred galaxies has been invoked to account for a wide variety of phenomena, but until now direct evidence for inflow has been lacking. We present Fabry-Perot H-alpha observations of the barred spiral galaxy NGC 1530 from which we determine velocities of the ionized gas for the entire region swept by the bar. We compare the velocity field to models of gas flow in barred spirals and show that it is well reproduced by ideal gas hydrodynamic models. Inspection of the models and observations reveals that gas entering the bar dust lanes streams directly down the dust lanes toward the 2 kpc radius nuclear ring. The models predict that approximately 20% of the gas flowing down the dust lane enters the nuclear ring; the remaining gas sprays around the ring to the other bar dust lane. The fraction of the gas entering the ring is relatively insensitive to the shape or size of the bar. Our observations of the velocity field and dust optical depth yield a mass inflow rate into the nuclear ring of 1 solar mass per year.

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