Publications (17)0 Total impact
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Article: HST Observations of the Interacting Galaxies NGC 2207 and IC 2163
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ABSTRACT: Hubble Space Telescope images of the galaxies NGC 2207 and IC 2163 show star formation and dust structures in a system that has experienced a recent grazing encounter. Tidal forces from NGC 2207 compressed and elongated the disk of IC 2163, forming an oval ridge of star formation. Gas flowing away from this ridge has thin parallel dust filaments transverse to the direction of motion. Numerical models suggest that the filaments come from flocculent spiral arms that were present before the interaction. A dust lane at the outer edge of the tidal tail is a shock front where the flow abruptly changes direction. A spiral arm of NGC 2207 that is backlit by IC 2163 is seen to contain several parallel, knotty filaments that are probably shock fronts in a density wave. Blue clusters of star formation inside these dust lanes show density wave triggering by local gravitational collapse. Spiral arms inside the oval of IC 2163 could be the result of ILR-related orbits in the tidal potential that formed the oval. Their presence suggests that tidal forces alone may initiate a temporary nuclear gas flow and eventual starburst without first forming a stellar bar. Several emission structures resembling jets 100-1000 pc long appear. There is a dense dark cloud with a conical shape 400 pc long and a bright compact cluster at the tip, and with a conical emission nebula of the same length that points away from the cluster in the other direction. This region coincides with a non-thermal radio continuum source that is 1000 times the luminosity of Cas A at 20 cm. Comment: 20 pgs, 8 figs as jpeg (3 color), to appear in Astronomical Journal, August 200007/2000; -
Article: HST Observations of Dust and Star-Forming Regions in the Ocular Galaxy IC 2163 and Its Spiral Companion NGC2207
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ABSTRACT: IC 2163 has a central eye-shaped ("ocular") structure with two long tidal arms indicative of a very recent, close, tidal encounter. It is partially obscured by its spiral companion NGC 2207. Numerical models (Elmegreen et al. 1995, ApJ, 453,139) suggest that perigalacticon occurred 40 Myr ago. We use UBVI images taken with the WFPC2 camera of HST to study the star-forming regions and to make a direct measurement of extinction through the disk of NGC 2207. We find no evidence for super star clusters (SSCs) and no difference between the star-forming regions in the fast-streaming gas on the compressed rim of the ocular oval and those elsewhere in the system. The star-forming regions have luminosity functions typical of intermediate and late-type spiral galaxies, with ages of a few times 106 to a few times 107 years and masses of 103 Msun to 106 Msun. Either the 40 Myr since perigalacticon is too small for SSCs to have formed yet or the interaction was too weak to produce them. For the part of NGC 2207 that overlaps IC 2163 along the line of sight, AV 1.1 mag for the dust lanes and AV 0.4 mag for the inter-lane disk of NGC 2207. Our values for the extinction of NGC 2207 in B, V, and I are closer to a Whitford reddening curve than Berlind et al. (1997, AJ, 114, 107) derived from ground-based measurements because of our higher resolution images. This result supports their interpretation that extinction becomes grey when patchy dust is unresolved. Support for this work was provided by NASA through grant number GO-06483-95A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.11/1999; 31:1524. -
Article: Dust Spirals and Acoustic Noise in the Nucleus of the Galaxy NGC 2207
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ABSTRACT: Observations with the Hubble Space Telescope reveal an irregular network of dust spiral arms in the nuclear region of the interacting disk galaxy NGC 2207. The spirals extend from ~50 pc to ~300 pc in galactocentric radius, with a projected width of ~20 pc. Radiative transfer calculations determine the gas properties of the spirals and the inner disk, and imply a factor of ~4 local gas compression in the spirals. The gas is not strongly self-gravitating, nor is there a nuclear bar, so the spirals could not have formed by the usual mechanisms applied to main galaxy disks. Instead, they may result from acoustic instabilities that amplify at small galactic radii. Such instabilities may promote gas accretion into the nucleus.08/1998; -
Article: An interaction model for the formation of dwarf galaxies and 10 exp 8 solar mass clouds in spiral disks
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ABSTRACT: Ten H I clouds with masses larger than 10 exp 8 solar masses in the interacting galaxies IC 2163/NGC 2207 are identified. Twenty-eight other interacting pairs of galaxies with large knots or star formation structures in their optical images are also tabulated. It is suggested that interactions can lead to the formation of greater than 10 solar mass clouds and young stellar regions in the outer parts of galactic disks, and that some of these regions may become gravitationally bound dwarf galaxies if they are ejected in tidal arms. It is proposed that the key to the origin of clouds of greater than 10 exp 8 solar mass in interacting systems lies in the high velocity dispersion of the interstellar gas. Numerical N-body simulations of the interacting galaxies suggest that the complete detachment of an unbound dwarf galaxy requires a companion mass comparable to or larger than the galaxy mass.Astrophysical Journal. 07/1993; 412:90-98. -
Article: An Interaction Model for the Formation of Dwarf Galaxies and 10(8) Msun Clouds in Spiral Disks
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ABSTRACT: Galaxy interactions that agitate the interstellar medium by increasing the gas velocity dispersion and removing peripheral gas in tidal arms should lead to the formation and possible ejection of self-gravitationally bound cloud complexes with masses in excess of 10(8) Msun. Some of these complexes may eventually appear as independent dwarf galaxies. The formation of clouds with masses exceeding 10(8) Msun is the result of gravitational instabilities in gas disks with high velocity dispersions. Such masses and high dispersions were observed with the VLA for the interacting pair IC 2163/NGC 2207, which contains 10 clouds with HI masses >10(8) Msun and widespread velocity dispersions 4 times larger than in normal spiral galaxies. A giant cloud that forms by an instability in a high-dispersion ISM should also have a high internal dispersion, and it should produce stars with a greater efficiency than in normal galaxies because of the cloud's greater resistance to self-destruction. Such clouds should also have a larger fraction of massive stars than normal clouds because of the larger temperatures that follow from the high efficiency. Thus agitated galaxies should produce peripheral or nuclear starbursts partly because of their high gas velocity dispersions. Numerical N-body simulations of interacting galaxies illustrate the proposed formation of 10(8) Msun cloud complexes by gravitational instabilities. The masses and dispersions of the clouds that form increase with the strength of the perturbation. The simulations suggest that the complete detachment of an unbound dwarf galaxy requires a companion mass comparable to or larger than the galaxy mass. Dwarf galaxies that form this way should contain old stars from the original disk plus new stars from the cloud complex/starburst phase of its interaction-induced formation. This work was supported in part by NSF Grant AST-8914969 to M.K..11/1992; 24:1267. -
Article: A High Resolution Neutral Hydrogen Line Study of the Ocular Galaxy IC 2163 Interacting with NGC 2207
08/1991; 23:1456. -
Article: The grazing encounter between IC 2163 and NGC 2207: pushing the limits of observational modelling
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Article: Observations of the Ocular Galaxy NGC 2535 and its Starburst Companion NGC 2536.
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Article: Interaction Between NGC 5394 and NGC 5395.
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Article: The interacting galaxies NGC 5394/5395: a post-ocular galaxy and its ring/spiral companion.
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Article: A Bird's Eye View of Ocular Galaxies.
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Article: Interaction between the Galaxies IC 2163 and NGC 2207.
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Article: CO Observations of the Interacting Galaxy Pair NGC 5394/95
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Article: Spitzer Space Telescope IRAC and MIPS observations of the interacting galaxies Ic 2163 and NGC 2207: clumpy emission.
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Article: Effects of Grazing Encounters on Spiral Galaxies.
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Article: Hubble Space Telescope Observations of Dust and Star-forming Regions in the Ocular Galaxy IC 2163 and its Spiral Companion NGC 2207
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Article: Ocular Galaxies: NGC 2535 and its Starburst Companion NGC 2536.
