Browsing by Author "Block, David L."

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    DO BARS DRIVE SPIRAL DENSITY WAVES?
    (IOP Publishing, 2009-05) Buta, Ronald J.; Knapen, Johan H.; Elmegreen, Bruce G.; Salo, Heikki; Laurikainen, Eija; Elmegreen, Debra Meloy; Puerari, Ivanio; Block, David L.; University of Alabama Tuscaloosa; Instituto de Astrofisica de Canarias; International Business Machines (IBM); University of Oulu; Vassar College; Instituto Nacional de Astrofisica, Optica y Electronica; University of Witwatersrand
    We present deep near-infrared Ks-band Anglo-Australian Telescope Infrared Imager and Spectrograph observations of a selected sample of nearby barred spiral galaxies, including some with the strongest known bars. The sample covers a range of Hubble types from SB0(-) to SBc. The goal is to determine if the torque strengths of the spirals correlate with those of the bars, which might be expected if the bars actually drive the spirals as has been predicted by theoretical studies. This issue has implications for interpreting bar and spiral fractions at high redshift. Analysis of previous samples suggested that such a correlation exists in the near-infrared, where effects of extinction and star formation are less important. However, the earlier samples had only a few excessively strong bars. Our new sample largely confirms our previous studies, but still any correlation is relatively weak. We find two galaxies, NGC 7513 and UGC 10862, where there is only a weak spiral in the presence of a very strong bar. We suggest that some spirals probably are driven by their bars at the same pattern speed, but that this may be only when the bar is growing or if there is abundant gas and dissipation.
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    Variation of galactic bar length with amplitude and density as evidence for bar growth over a Hubble time
    (IOP Publishing, 2007-12-01) Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Knapen, Johan H.; Buta, Ronald J.; Block, David L.; Puerari, Ivanio; International Business Machines (IBM); Vassar College; Instituto de Astrofisica de Canarias; University of Alabama Tuscaloosa; University of Witwatersrand; Instituto Nacional de Astrofisica, Optica y Electronica
    K-s-band images of 20 barred galaxies show an increase in the peak amplitude of the normalized m = 2 Fourier component with the R-25-normalized radius at this peak. This implies that longer bars have higher m = 2 amplitudes. The long bars also correlate with an increased density in the central parts of the disks, as measured by the luminosity inside 0.25R(25) divided by the cube of this radius in kpc. Because denser galaxies evolve faster, these correlations suggest that bars grow in length and amplitude over a Hubble time, with the fastest evolution occurring in the densest galaxies. All but three of the sample have early-type flat bars; there is no clear correlation between the correlated quantities and the Hubble type.