Browsing by Author "Buta, Ronald J."
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Item A Comparative Study of Morphological Classifications of APM Galaxies(1995-06-15) Buta, Ronald J.; University of Alabama TuscaloosaWe investigate the consistency of visual morphological classifications of galaxies by comparing classifications for 831 galaxies from six independent observers. The galaxies were classified on laser print copy images or on computer screen using scans made with the Automated Plate Measuring (APM) machine. Classifications are compared using the Revised Hubble numerical type index T. We find that individual observers agree with one another with rms combined dispersions of between 1.3 and 2.3 type units, typically about 1.8 units. The dispersions tend to decrease slightly with increasing angular diameter and, in some cases, with increasing axial ratio (b/a). The agreement between independent observers is reasonably good but the scatter is non-negligible. In spite of the scatter, the Revised Hubble T system can be used to train an automated galaxy classifier, e.g. an artificial neural network, to handle the large number of galaxy images that are being compiled in the APM and other surveys.Item Discovery of a strong spiral magnetic field crossing the inner pseudoring of NGC 4736(IOP Publishing, 2008-04-10) Chyzy, Krzysztof T.; Buta, Ronald J.; Jagiellonian University; University of Alabama TuscaloosaWe report the discovery of a coherent magnetic spiral structure within the nearby ringed Sab galaxy NGC 4736. High-sensitivity radio polarimetric data obtained with the VLA at 8.46 and 4.86 GHz show a distinct ring of total radio emission precisely corresponding to the bright inner pseudoring visible in other wavelengths. However, unlike the total radio emission, the polarized radio emission reveals a clear pattern of ordered magnetic field of spiral shape, emerging from the galactic center. The magnetic vectors do not follow the tightly wrapped spiral arms that characterize the inner pseudoring, but instead cross the ring with a constant and large pitch angle of about 35 degrees. The ordered field is thus not locally adjusted to the pattern of star formation activity, unlike what is usually observed in grand-design spirals. The observed asymmetric distribution of Faraday rotation suggests the possible action of a large-scale MHD dynamo. The strong magnetic total and regular field within the ring ( up to 30 and 13 mu G, respectively) indicates that a highly efficient process of magnetic field amplification is under way, probably related to secular evolutionary processes in the galaxy.Item 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 WitwatersrandWe 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.Item GRAND DESIGN AND FLOCCULENT SPIRALS IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G)(IOP Publishing, 2011-07-26) Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Yau, Andrew; Athanassoula, E.; Bosma, Albert; Buta, Ronald J.; Helou, George; Ho, Luis C.; Gadotti, Dimitri A.; Knapen, Johan H.; Laurikainen, Eija; Madore, Barry F.; Masters, Karen L.; Meidt, Sharon E.; Menendez-Delmestre, Karin; Regan, Michael W.; Salo, Heikki; Sheth, Kartik; Zaritsky, Dennis; Aravena, Manuel; Skibba, Ramin; Hinz, Joannah L.; Laine, Jarkko; Gil de Paz, Armando; Munoz-Mateos, Juan-Carlos; Seibert, Mark; Mizusawa, Trisha; Kim, Taehyun; Erroz Ferrer, Santiago; Vassar College; International Business Machines (IBM); Centre National de la Recherche Scientifique (CNRS); UDICE-French Research Universities; Aix-Marseille Universite; University of Alabama Tuscaloosa; California Institute of Technology; Carnegie Institution for Science; Max Planck Society; European Southern Observatory; Instituto de Astrofisica de Canarias; Universidad de la Laguna; University of Oulu; University of Turku; University of Portsmouth; Space Telescope Science Institute; National Radio Astronomy Observatory (NRAO); University of Arizona; Complutense University of Madrid; Seoul National University (SNU)Spiral arm properties of 46 galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S(4)G) were measured at 3.6 mu m, where extinction is small and the old stars dominate. The sample includes flocculent, multiple arm, and grand design types with a wide range of Hubble and bar types. We find that most optically flocculent galaxies are also flocculent in the mid-IR because of star formation uncorrelated with stellar density waves, whereas multiple arm and grand design galaxies have underlying stellar waves. Arm-interarm contrasts increase from flocculent to multiple arm to grand design galaxies and with later Hubble types. Structure can be traced further out in the disk than in previous surveys. Some spirals peak at mid-radius while others continuously rise or fall, depending on Hubble and bar type. We find evidence for regular and symmetric modulations of the arm strength in NGC 4321. Bars tend to be long, high amplitude, and flat-profiled in early-type spirals, with arm contrasts that decrease with radius beyond the end of the bar, and they tend to be short, low amplitude, and exponential-profiled in late Hubble types, with arm contrasts that are constant or increase with radius. Longer bars tend to have larger amplitudes and stronger arms.Item H alpha kinematics of S(4)G spiral galaxies - I. NGC 864(Oxford University Press, 2012-12-21) Erroz-Ferrer, Santiago; Knapen, Johan H.; Font, Joan; Beckman, John E.; Falcon-Barroso, Jesus; Ramon Sanchez-Gallego, Jose; Athanassoula, E.; Bosma, Albert; Gadotti, Dimitri A.; Munoz-Mateos, Juan Carlos; Sheth, Kartik; Buta, Ronald J.; Comeron, Sebastien; Gil de Paz, Armando; Hinz, Joannah L.; Ho, Luis C.; Kim, Taehyun; Laine, Jarkko; Laurikainen, Eija; Madore, Barry F.; Menendez-Delmestre, Karin; Mizusawa, Trisha; Regan, Michael W.; Salo, Heikki; Seibert, Mark; Instituto de Astrofisica de Canarias; Universidad de la Laguna; Centre National de la Recherche Scientifique (CNRS); CNRS - National Institute for Earth Sciences & Astronomy (INSU); UDICE-French Research Universities; Aix-Marseille Universite; European Southern Observatory; National Radio Astronomy Observatory (NRAO); California Institute of Technology; University of Alabama Tuscaloosa; Korea Astronomy & Space Science Institute (KASI); Complutense University of Madrid; University of Arizona; Carnegie Institution for Science; Seoul National University (SNU); University of Oulu; University of Turku; Universidade Federal do Rio de Janeiro; Space Telescope Science InstituteWe present a study of the kinematics of the isolated spiral galaxy NGC 864, using H alpha Fabry-Perot data obtained with the Galaxy H alpha Fabry-Perot System (GH alpha FaS) instrument at the William Herschel Telescope in La Palma, complemented with images at 3.6 mu m, in the R band and in H alpha filter, and integral-field spectroscopic data. The resulting data cubes and velocity maps allow the study of the kinematics of the galaxy, including in-depth investigations of the rotation curve, velocity moment maps, velocity residual maps, gradient maps and position-velocity diagrams. We find asymmetries in the velocity field in the bar zone, caused by non-circular motions, probably in response to the potential of the bar. We also find a flat-profile bar, in agreement with the strong bar, with the grand design spiral pattern, and with the gap between the ends of the bar and the start of the spiral arms. We quantify the rate of massive star formation, which is concentrated in the two spiral arms.Item MID-INFRARED GALAXY MORPHOLOGY FROM THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G): THE IMPRINT OF THE DE VAUCOULEURS REVISED HUBBLE-SANDAGE CLASSIFICATION SYSTEM AT 3.6 mu m(IOP Publishing, 2010-08-31) Buta, Ronald J.; Sheth, Kartik; Regan, Michael; Hinz, Joannah L.; Gil de Paz, Armando; Menendez-Delmestre, Karin; Munoz-Mateos, Juan-Carlos; Seibert, Mark; Laurikainen, Eija; Salo, Heikki; Gadotti, Dimitri A.; Athanassoula, E.; Bosma, Albert; Knapen, Johan H.; Ho, Luis C.; Madore, Barry F.; Elmegreen, Debra M.; Masters, Karen L.; Comeron, Sebastien; Aravena, Manuel; Kim, Taehyun; University of Alabama Tuscaloosa; National Radio Astronomy Observatory (NRAO); Space Telescope Science Institute; University of Arizona; Complutense University of Madrid; California Institute of Technology; Carnegie Institution for Science; University of Oulu; European Southern Observatory; Centre National de la Recherche Scientifique (CNRS); UDICE-French Research Universities; Aix-Marseille Universite; Instituto de Astrofisica de Canarias; Universidad de la Laguna; Vassar College; University of Portsmouth; Korea Astronomy & Space Science Institute (KASI); Seoul National University (SNU)Spitzer Space Telescope Infrared Array Camera imaging provides an opportunity to study all known morphological types of galaxies in the mid-IR at a depth significantly better than ground-based near-infrared and optical images. The goal of this study is to examine the imprint of the de Vaucouleurs classification volume in the 3.6 mu m band, which is the best Spitzer waveband for galactic stellar mass morphology owing to its depth and its reddening-free sensitivity mainly to older stars. For this purpose, we have prepared classification images for 207 galaxies from the Spitzer archive, most of which are formally part of the Spitzer Survey of Stellar Structure in Galaxies (S(4)G), a Spitzer post-cryogenic ("warm") mission Exploration Science Legacy Program survey of 2331 galaxies closer than 40 Mpc. For the purposes of morphology, the galaxies are interpreted as if the images are blue light, the historical waveband for classical galaxy classification studies. We find that 3.6 mu m classifications are well correlated with blue-light classifications, to the point where the essential features of many galaxies look very similar in the two very different wavelength regimes. Drastic differences are found only for the most dusty galaxies. Consistent with a previous study by Eskridge et al., the main difference between blue-light and mid-IR types is an approximate to 1 stage interval difference for S0/a to Sbc or Sc galaxies, which tend to appear "earlier" in type at 3.6 mu m due to the slightly increased prominence of the bulge, the reduced effects of extinction, and the reduced (but not completely eliminated) effect of the extreme population I stellar component. We present an atlas of all of the 207 galaxies analyzed here and bring attention to special features or galaxy types, such as nuclear rings, pseudobulges, flocculent spiral galaxies, I0 galaxies, double-stage and double-variety galaxies, and outer rings, that are particularly distinctive in the mid-IR.Item PATTERN COROTATION RADII FROM POTENTIAL-DENSITY PHASE-SHIFTS FOR 153 OSUBGS SAMPLE GALAXIES(IOP Publishing, 2009-05-19) Buta, Ronald J.; Zhang, Xiaolei; University of Alabama Tuscaloosa; George Mason UniversityThe potential-density phase-shift method is an effective new tool for investigating the structure and evolution of galaxies. In this paper, we apply the method to 153 galaxies in the Ohio State University Bright Galaxy Survey (OSUBGS) to study the general relationship between pattern corotation radii and the morphology of spiral galaxies. The analysis is based on near-infrared H-band images that have been deprojected and decomposed assuming a spherical bulge. We find that multiple pattern speeds are common in disk galaxies. By selecting those corotation radii close to or slightly larger than the bar radius as being the bar corotation (CR) radius, we find that the average and standard deviation of the ratio R = r(CR)/r(bar), is 1.20 +/- 0.52 for 101 galaxies having well-defined bars. There is an indication that this ratio depends weakly on galaxy type in the sense that the average ranges from 1.03 +/- 0.37 for 65 galaxies of type Sbc and earlier, to 1.50 +/- 0.63 for 36 galaxies of type Sc and later. Our bar corotation radii are on average smaller than those estimated from single-pattern-speed numerical simulations, most likely because these simulations tend to find the pattern speed which generates a density response in the gas that best matches the morphology of the outer spiral structure. Although we find CR radii in most of the sample galaxies that satisfy conventional ideas about the extent of bars, we also consider the alternative interpretation that in many cases the bar CR is actually inside the bar and that the bar ends close to its outer Lindblad resonance instead of its CR. These "superfast" bars are the most controversial finding from our study. We see evidence in the phase-shift distributions for ongoing decoupling of patterns, which hints at the formation pathways of nested patterns, and which in turn further hints at the longevity of the density wave patterns in galaxies. We also examine how uncertainties in the orientation parameters of galaxies and in the shapes of bulges affect our results.Item The Potential-Density Phase-Shift Method for Determining the Corotation Radii in Spiral and Barred Galaxies(American Astronomical Society, 2007-04-20) Zhang, Xiaolei; Buta, Ronald J.; University of Alabama TuscaloosaWe have developed a new method for determining the corotation radii of density waves in disk galaxies, which makes use of the calculated radial distribution of an azimuthal phase shift between the potential and density wave patterns. The approach originated from improved theoretical understanding of the relation between the morphology and kinematics of galaxies and of the dynamical interaction between density waves and the basic-state disk stars, which results in the secular evolution of disk galaxies. In this paper we present the rationales behind the method and the first application of it to several representative barred and grand-design spiral galaxies, using near-infrared images to trace the mass distributions, as well as to calculate the potential distributions used in the phase-shift calculations. We compare our results with those from other existing methods for locating the corotations and show that the new method both confirms the previously established trends of bar-length dependence on galaxy morphological types and provides new insights into the possible extent of bars in disk galaxies. The method also facilitates the estimation of mass accretion/excretion rates due to bar and spiral density waves, providing an alternative way of quantifying the importance of these features in disk galaxies. A preliminary analysis of a larger sample shows that the phase-shift method is likely to be a generally applicable, accurate, and essentially model-independent method for determining the pattern speeds and corotation radii of single or nested density wave patterns in galaxies. Other implications of the results of this work include that most of the nearby bright disk galaxies appear to possess quasi-stationary spiral modes; that these density wave modes, as well as the associated basic states of the galactic disks, slowly transform over the time span of a Hubble time due to a collective dissipation process directly related to the presence of the phase shift between the potential and density patterns; and that self-consistent N-particle systems contain physics not revealed by the passive orbit analysis approaches.Item Reconstructing the Stellar Mass Distributions of S⁴G Galaxies using IRAC 3.6 and 4.5 μm Images. I. Correcting for Contamination by PAH, Hot Dust, and Intermediate Age Stars(2011-12-07) Buta, Ronald J.; University of Alabama TuscaloosaWith the aim of constructing accurate two-dimensional maps of the stellar mass distribution in nearby galaxies from Spitzer Survey of Stellar Structure in Galaxies 3.6 and 4.5 μm images, we report on the separation of the light from old stars from the emission contributed by contaminants. Results for a small sample of six disk galaxies (NGC 1566, NGC 2976, NGC 3031, NGC 3184, NGC 4321, and NGC 5194) with a range of morphological properties, dust content, and star formation histories are presented to demonstrate our approach. To isolate the old stellar light from contaminant emission (e.g., hot dust and the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature) in the IRAC 3.6 and 4.5 μm bands we use an independent component analysis (ICA) technique designed to separate statistically independent source distributions, maximizing the distinction in the [3.6]-[4.5] colors of the sources. The technique also removes emission from evolved red objects with a low mass-to-light ratio, such as asymptotic giant branch (AGB) and red supergiant (RSG) stars, revealing maps of the underlying old distribution of light with [3.6]-[4.5] colors consistent with the colors of K and M giants. The contaminants are studied by comparison with the non-stellar emission imaged at 8 μm, which is dominated by the broad PAH feature. Using the measured 3.6 μm/8 μm ratio to select individual contaminants, we find that hot dust and PAHs together contribute between ~5% and 15% to the integrated light at 3.6 μm, while light from regions dominated by intermediate-age (AGB and RSG) stars accounts for only 1%-5%. Locally, however, the contribution from either contaminant can reach much higher levels; dust contributes on average 22% to the emission in star-forming regions throughout the sample, while intermediate-age stars contribute upward of 50% in localized knots. The removal of these contaminants with ICA leaves maps of the old stellar disk that retain a high degree of structural information and are ideally suited for tracing stellar mass, as will be the focus in a companion paper.Item Ringed spiral galaxy NGC4622. II. An independent determination that the two outer arms lead(IOP Publishing, 2007-12-12) Byrd, Gene G.; Freeman, Tarsh; Howard, Sethanne; Buta, Ronald J.; University of Alabama Tuscaloosa; United States Department of Defense; United States NavyThe spiral galaxy NGC4622 was recognized by Byrd et al. (1989, Celest. Mech., 45, 31) to have a single inner arm winding outward counterclockwise (CCW) and an outer pair of arms winding outward clockwise (CW). Using HST and ground-based observations, Buta et al. (2003, AJ, 125, 634) used a dust silhouette method to determine that the disk of NGC4622 rotates CW on the sky. The outer pair of arms winding outward CW on the sky should thus lead (wind outward in the direction of disk orbital motion), contrary to most expectations. We have discovered in Fourier component images an additional pair of weak CCW arms: this pair is inside the already-known strong outer CW pair. We also find an additional weak single CW arm component: this arm is outside the strong, already-known, CCW single inner arm. Thus, regardless of disk rotation sense, NGC4622 has a pair of leading arms as well as a single leading arm. NGC4622's moderate (19 degrees) tilt is a plus for the methods in the present paper. We use a well-demonstrated IVB color/age method to locate co-rotation (CR) radii. At CR, the Fourier position angle peaks switch position angle sequence (e.g., IVB to BVI or the reverse). We find two possible CR radii (21.4 '' and 36 ''). The boundary between the outer CW arms and the inner CCW arms is between these two radii. From the IVB switching senses crossing the CR radii and the observed orbital angular rate decline with increasing radius across the first CR, the orbit sense is CW and the outer pair thus is the leading pair. We thus place on a firm footing for future research our earlier conclusions about the unusual nature of the NGC4622 spiral pattern.Item THE THICK DISK IN THE GALAXY NGC 4244 FROM S(4)G IMAGING(IOP Publishing, 2011-02-07) Comeron, Sebastien; Knapen, Johan H.; Sheth, Kartik; Regan, Michael W.; Hinz, Joannah L.; Gil de Paz, Armando; Menendez-Delmestre, Karin; Munoz-Mateos, Juan-Carlos; Seibert, Mark; Kim, Taehyun; Athanassoula, E.; Bosma, Albert; Buta, Ronald J.; Elmegreen, Bruce G.; Ho, Luis C.; Holwerda, Benne W.; Laurikainen, Eija; Salo, Heikki; Schinnerer, Eva; Korea Astronomy & Space Science Institute (KASI); Instituto de Astrofisica de Canarias; Universidad de la Laguna; National Radio Astronomy Observatory (NRAO); California Institute of Technology; Space Telescope Science Institute; University of Arizona; Complutense University of Madrid; Carnegie Institution for Science; Seoul National University (SNU); Centre National de la Recherche Scientifique (CNRS); UDICE-French Research Universities; Aix-Marseille Universite; University of Alabama Tuscaloosa; International Business Machines (IBM); University of Cape Town; University of Oulu; University of Turku; Max Planck SocietyIf thick disks are ubiquitous and a natural product of disk galaxy formation and/or evolution processes, all undisturbed galaxies that have evolved during a significant fraction of a Hubble time should have a thick disk. The late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick disk. Using data from the Spitzer Survey of Stellar Structure in Galaxies (S(4)G) we have identified signs of two disk components in this galaxy. The asymmetries between the light profiles on both sides of the mid-plane of NGC 4244 can be explained by a combination of the galaxy not being perfectly edge-on and a certain degree of opacity of the thin disk. We argue that the subtlety of the thick disk is a consequence of either a limited secular evolution in NGC 4244, a small fraction of stellar material in the fragments which built the galaxy, or a high amount of gaseous accretion after the formation of the galaxy.Item THE UNUSUAL VERTICAL MASS DISTRIBUTION OF NGC 4013 SEEN THROUGH THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G)(IOP Publishing, 2011-08-17) Comeron, Sebastien; Elmegreen, Bruce G.; Knapen, Johan H.; Sheth, Kartik; Hinz, Joannah L.; Regan, Michael W.; Gil de Paz, Armando; Munoz-Mateos, Juan-Carlos; Menendez-Delmestre, Karin; Seibert, Mark; Kim, Taehyun; Mizusawa, Trisha; Laurikainen, Eija; Salo, Heikki; Laine, Jarkko; Athanassoula, E.; Bosma, Albert; Buta, Ronald J.; Gadotti, Dimitri A.; Ho, Luis C.; Holwerda, Benne; Schinnerer, Eva; Zaritsky, Dennis; Korea Astronomy & Space Science Institute (KASI); International Business Machines (IBM); Instituto de Astrofisica de Canarias; Universidad de la Laguna; National Radio Astronomy Observatory (NRAO); University of Arizona; Space Telescope Science Institute; Complutense University of Madrid; Carnegie Institution for Science; University of Oulu; University of Turku; Centre National de la Recherche Scientifique (CNRS); UDICE-French Research Universities; Aix-Marseille Universite; University of Alabama Tuscaloosa; European Southern Observatory; European Space Agency; Max Planck SocietyNGC 4013 is a nearby Sb edge-on galaxy known for its "prodigious" Hi warp and its "giant" tidal stream. Previous work on this unusual object shows that it cannot be fitted satisfactorily by a canonical thin+thick disk structure. We have produced a new decomposition of NGC 4013, considering three stellar flattened components (thin+thick disk plus an extra and more extended component) and one gaseous disk. All four components are considered to be gravitationally coupled and isothermal. To do so, we have used the 3.6 mu m images from the Spitzer Survey of Stellar Structure in Galaxies. We find evidence for NGC 4013 indeed having a thin and a thick disk and an extra flattened component. This smooth and extended component (scale height z(EC) similar to 3 kpc) could be interpreted as a thick disk or as a squashed ellipsoidal halo and contains similar to 20% of the total mass of all three stellar components. We argue it is unlikely to be related to the ongoing merger or due to the off-plane stars from a warp in the other two disk components. Instead, we favor a scenario in which the thick disk and the extended component were formed in a two-stage process, in which an initially thick disk has been dynamically heated by a merger soon enough in the galaxy history to have a new thick disk formed within it.Item 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 ElectronicaK-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.