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Reexamination of the Radial Abundance Gradient Break in NGC 3359  [PDF]
H. Jabran Zahid,Fabio Bresolin
Physics , 2011, DOI: 10.1088/0004-6256/141/6/192
Abstract: In this contribution, we reexamine the radial oxygen abundance gradient in the strongly barred spiral galaxy NGC 3359, for which, using an imaging spectrophotometric technique, Martin & Roy detected a break near the effective radius of the galaxy. We have new emission line flux measurements of HII regions in NGC 3359 from spectra obtained with the Subaru telescope to further investigate this claim. We find that there are small systematic variations in the line ratios determined from narrow-band imaging as compared to our spectroscopic measurements. We derive and apply a correction to the line ratios found by Martin & Roy and statistically examine the validity of the gradient break proposed for NGC 3359 using recently developed metallicity diagnostics. We find that, with a high degree of confidence, a model with a break fits the data significantly better than one without it. This suggests that the presence of a strong bar in spiral galaxies can generate measurable changes in the radial distribution of metals.
The Abundance Gradient of NGC 1365: Evidence for a Recently Formed Bar in an Archetype Barred Spiral Galaxy?  [PDF]
J. -R. Roy,J. R. Walsh
Physics , 1997, DOI: 10.1093/mnras/288.3.715
Abstract: Emission-line optical spectrophotometry for 55 H II regions in the prominent southern barred spiral galaxy NGC 1365 is presented. Nebular diagnostic diagrams such as [N II]/[O II] and [S II]/[O II] versus [O II]/{O III] show that the H II regions of the barred galaxy have the same range of physical conditions as found in non-barred late-type galaxies. Extinction is moderately high across the disc and there is evidence for a slight trend of extinction with galactocentric distance; the logarithmic extinction at H-beta falls from about c = 1.2 in the centre to 0.6 -- 0.8 in the outer regions. The global O/H distribution has a moderate gradient of about -0.5 dex/rho0 (about -0.02 dex/kpc) consistent with the known trend between the slope of the abundance gradient and the strength of the bar. A break is seen in the O/H gradient just beyond the -4/1 resonance, the gradient being moderately steep at about -0.8 dex/rho0 (-0.05 dex/kpc) inside this resonance, and flat beyond rho/rho0 > 0.55. The abundance distribution is compared with another barred spiral galaxy, NGC 3359, and with that of two well-sampled normal spiral galaxies, NGC 2997 and M 101. The possibility that the bar formed recently in NGC 1365 is considered. The difficulties encountered in doing spectrophotometry with fibre optics are discussed and shown not to be insurmountable.
Soft X-ray Emission from the Spiral Galaxy NGC 1313  [PDF]
E. J. M. Colbert,R. Petre,E. M. Schlegel,S. D. Ryder
Physics , 1995, DOI: 10.1086/175777
Abstract: The nearby barred spiral galaxy NGC 1313 has been observed with the PSPC instr- ument on board the ROSAT X-ray satellite. Ten individual sources are found. Three sources (X-1, X-2 and X-3 [SN~1978K]) are very bright (~10^40 erg/s) and are unusual in that analogous objects do not exist in our Galaxy. We present an X-ray image of NGC~1313 and \xray spectra for the three bright sources. The emission from the nuclear region (R ~< 2 kpc) is dominated by source X-1, which is located ~1 kpc north of the photometric (and dynamical) center of NGC~1313. Optical, far-infrared and radio images do not indicate the presence of an active galactic nucleus at that position; however, the compact nature of the \xray source (X-1) suggests that it is an accretion-powered object with central mass M >~ 10^3 Msun. Additional emission (L_X ~ 10^39 erg/s) in the nuclear region extends out to ~2.6 kpc and roughly follows the spiral arms. This emission is from 4 sources with luminosity of several x 10^38 erg/s, two of which are consistent with emission from population I sources (e.g., supernova remnants, and hot interstellar gas which has been heated by supernova remnants). The other two sources could be emission from population II sources (e.g., low-mass \xray binaries). The bright sources X-2 and SN~1978K are positioned in the southern disk of NGC~1313. X-2 is variable and has no optical counterpart brighter than 20.8 mag (V-band). It is likely that it is an accretion-powered object in NGC~1313. The type-II supernova SN~1978K (Ryder \etal 1993) has become extra- ordinarily luminous in X-rays $\sim$13 years after optical maximum.
The population of ULXs in the spiral galaxy NGC 2276  [PDF]
Anna Wolter,Fabio Pizzolato,Stefano Rota,Michela Mapelli,Emanuele Ripamonti
Physics , 2010, DOI: 10.1002/asna.201011499
Abstract: We present results for X-ray point sources in the Sc galaxy NGC 2276, obtained by analyzing Chandra data. The galaxy is known to be very active in many wavelengths, possibly due to gravitational interaction with the central elliptical of the group, NGC 2300. However, previous XMM-Newton observations resulted in the detection of only one bright ULX and extended hot gas emission. We present here the X-ray population in NGC 2276 which comprises 17 sources. We found that 6 of them are new ULX sources in this spiral galaxy resolved for the first time by Chandra. We constructed the Luminosity Function that can be interpreted as mainly due of High Mass X-ray binaries, and estimate the Star Formation rate (SFR) to be SFR ~ 5-10 M_sun/yr.
Atomic hydrogen in the spiral galaxy NGC 3631  [PDF]
J. H. Knapen
Physics , 1996, DOI: 10.1093/mnras/286.2.403
Abstract: New high resolution, high sensitivity WSRT HI synthesis observations of the spiral galaxy NGC 3631 are presented. In the total atomic hydrogen map, the spiral arms are well distinguished from the interarm regions, while the sensitivity allows detection of HI in all but a few isolated regions of the areas between the spiral arms. Most of the atomic hydrogen is located within the optical disc, but the HI extends to some 1.5R_opt. The HI follows the spiral arms, and streaming motions of up to ~15 kms (projected) can be identified from the velocity field. Assuming a constant inclination angle of 17 deg, a rotation curve is derived which is slightly falling in the outer parts of the disc. Analysis of a residual velocity field, obtained after subtraction of an axisymmetric model based on the rotation curve, confirms the existence of streaming motions near the spiral arms in an otherwise undisturbed disc.
Gas motions in the plane of the spiral galaxy NGC 3631  [PDF]
A. M. Fridman,O. V. Khoruzhii,E. V. Polyachenko,A. V. Zasov,O. K. Sil'chenko,A. V. Moiseev,A. N. Burlak,V. L. Afanasiev,S. N. Dodonov,J. H. Knapen
Physics , 2000, DOI: 10.1046/j.1365-8711.2001.04218.x
Abstract: The velocity field of the nearly face-on galaxy NGC 3631, derived from observations in the H alpha line and the HI radio line, is analysed to study perturbations related to the spiral structure of the galaxy. We confirm our previous conclusion that the line-of-sight velocity field gives evidence of the wave nature of the observed two-armed spiral structure. Fourier analysis of the observed velocity field is used to determine the location of corotation of the spiral structure of this galaxy, and the radius of corotation R_c is found to be about 42 arcsec, or 3.2 kpc. The vector velocity field of the gas in the plane of the disc is restored, and taking into account that we previously investigated vertical motions, we now have a full 3D gaseous velocity field of the galaxy. We show clear evidence of the existence of two anticyclonic and four cyclonic vortices near corotation in a frame of reference rotating with the spiral pattern. The centres of the anticyclones lie between the observed spiral arms. The cyclones lie close to the observed spirals, but their centres are shifted from the maxima in brightness.
The Void in the Sculptor Group Spiral Galaxy NGC 247  [PDF]
R. Wagner-Kaiser,T. Demaio,A. Sarajedini,S. Chakrabarti
Physics , 2014, DOI: 10.1093/mnras/stu1327
Abstract: The dwarf galaxy NGC 247, located in the Sculptor Filament, displays an apparent void on the north side of its spiral disk. The existence of the void in the disk of this dwarf galaxy has been known for some time, but the exact nature and cause of this strange feature has remained unclear. We investigate the properties of the void in the disk of NGC 247 using photometry of archival Hubble Space Telescope data to analyze the stars in and around this region. Based on a grid of isochrones from log(t)=6.8 to log(t)=10.0, we assign ages using nearest-neighbor interpolation. Examination of the spatial variation of these ages across the galaxy reveals an age difference between stars located inside the void region and stars located outside this region. We speculate that the void in NGC 247's stellar disk may be due to a recent interaction with a nearly dark sub-halo that collided with the disk and could account for the long-lived nature of the void.
Hydrodynamical Simulations of the Barred Spiral Galaxy NGC 1097  [PDF]
Lien-Hsuan Lin,Hsiang-Hsu Wang,Pei-Ying Hsieh,Ronald E. Taam,Chao-Chin Yang,David C. C. Yen
Physics , 2013, DOI: 10.1088/0004-637X/771/1/8
Abstract: NGC 1097 is a nearby barred spiral galaxy believed to be interacting with the elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1 nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes connected to the ring extend almost continuously out to the bar. The other ends of the dust lanes attach to two main spiral arms. To provide a physical understanding of its structural and kinematical properties, two-dimensional hydrodynamical simulations have been carried out. Numerical calculations reveal that many features of the gas morphology and kinematics can be reproduced provided that the gas flow is governed by a gravitational potential associated with a slowly rotating strong bar. By including the self-gravity of the gas disk in our calculation, we have found the starburst ring to be gravitationally unstable which is consistent with the observation in \citet{hsieh11}. Our simulations show that the gas inflow rate is 0.17 M$_\sun$ yr$^{-1}$ into the region within the starburst ring even after its formation, leading to the coexistence of both a nuclear ring and a circumnuclear disk.
The Hαemission of the spiral galaxy NGC 7479  [PDF]
Almudena Zurita,Maite Rozas,John E. Beckman
Physics , 1999, DOI: 10.1023/A:1017500812701
Abstract: We use the catalogue of HII regions obtained from a high quality continuum-subtracted H$\alpha$ image of the grand design spiral galaxy NGC 7479, to construct the luminosity function (LF) for the HII regions (over 1000) of the whole galaxy. Although its slope is within the published range for spirals of the same morphological type, the unusually strong star formation along the intense bar of NGC 7479 prompted us to analyze separately the HII regions in the bar and in the disc. We have calculated the physical properties of a group of HII regions in the bar and in the disc selected for their regular shapes and absence of blending. We have obtained galaxy-wide relations for the HII region set: diameter distribution function and also the global H$\alpha$ surface density distribution. As found previously for late-type spirals, the disc LF shows clear double-linear behaviour with a break at log L$_{H\alpha}$=38.6 (in erg/s). The bar LF is less regular. This reflects a physical difference between the bar and the disc in the properties of their populations of regions.
Global Structure and Kinematics of the Spiral Galaxy NGC 2841  [PDF]
V. L. Afanasiev,O. K. Sil'chenko
Physics , 1998, DOI: 10.1086/300798
Abstract: Investigation of gaseous and stellar kinematics and of broad-band VRI and narrow-band H-alpha and [NII]6583 images is performed for the central part (R < 4 kpc) of the regular spiral galaxy NGC 2841. We have found emission-line splitting at R < 20" and three-component LOSVD for the stars in the radius range 6" - 100". Morphological analysis reveals strong narrow shock fronts close to the major axis in the radius range of 30" - 50", a turn of the isophote major axis by 5 degrees and strongly negative Fourier coefficient a4 (boxy isophotes) in the radius range of 15" - 33". In principle, all these features may be explained in the frame of a triaxial bulge hypothesis.
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