We present an analysis of the optical nuclear spectra from the active galactic nuclei (AGN) in a sample of giant low surface brightness (GLSB) galaxies. GLSB galaxies are extreme late type spirals that are large, isolated and poorly evolved compared
to regular spiral galaxies. Earlier studies have indicated that their nuclei have relatively low mass black holes. Using data from the Sloan Digital Sky Survey (SDSS), we selected a sample of 30 GLSB galaxies that showed broad H$alpha$ emission lines in their AGN spectra. In some galaxies such as UGC 6284, the broad component of H$alpha$ is more related to outflows rather than the black hole. One galaxy (UGC 6614) showed two broad components in H$alpha$, one associated with the black hole and the other associated with an outflow event. We derived the nuclear black hole (BH) masses of 29 galaxies from their broad H$alpha$ parameters. We find that the nuclear BH masses lie in the range $10^{5}-10^{7} M_{odot}$. The bulge stellar velocity dispersion $sigma_{e}$ was determined from the underlying stellar spectra. We compared our results with the existing BH mass - velocity dispersion ($M_{BH}-sigma_{e}$) correlations and found that the majority of our sample lie in the low BH mass regime and below the $M_{BH}-sigma_{e}$ correlation. The effects of galaxy orientation in the measurement of $sigma_e$ and the increase of $sigma_e$ due to the effects of bar are probable reasons for the observed offset for some galaxies, but in many galaxies the offset is real. A possible explanation for the $M_{BH}-sigma_{e}$ offset could be lack of mergers and accretion events in the history of these galaxies which leads to a lack of BH-bulge co-evolution. keywords{galaxies: active, galaxies: bulges, galaxies: nuclei}
The structural parameters, like the inclination, i and the position angle of the line of nodes (PA_lon) of the disk of the Large Magellanic Cloud (LMC) are estimated using the JH photometric data of red clump stars from the Infrared Survey Facility -
Magellanic Cloud Point Source Catalog (IRSF-MCPSC). The observed LMC region is divided into several sub-regions and stars in each region are cross identified with the optically identified red clump stars to obtain the near infrared magnitudes. The peak values of H magnitude and (J-H) colour of the observed red clump distribution are obtained by fitting a profile to the distributions and also by taking the average value of magnitude and colour of the red clump stars in the bin with largest number. Then the dereddened peak H0 magnitude of the red clump stars in each sub-region is obtained. The RA, Dec and relative distance from the center of each sub-region are converted into x, y & z Cartesian coordinates. A weighted least square plane fitting method is applied to this x,y,z data to estimate the structural parameters of the LMC disk. A reddening map based on (J-H) colour of the RC stars is presented. When the peaks of the red clump distribution were identified by averaging, an inclination of 25.7 +/- 1.6 and PA_lon = 141.5 +/- 4.5 were obtained. We estimate a distance modulus of 18.47 +/- 0.1 mag to the LMC. Extra-planar features which are in front as well as behind the fitted plane are identified which match with the optically identified extra-planar features. The bar of the LMC is found to be part of the disk within 500 pc. The estimates of the structural parameters are found to be independent of the photometric bands used for the analysis. We find that the inner disk, within 3.0, is less inclined and has larger value of PA_lon when compared to the outer disk.
The structural parameters of the disk of the Large Magellanic Cloud (LMC) are estimated.We used the red clump stars from the VI photometric data of the Optical Gravitational Lensing Experiment survey and from the Magellanic Cloud Photometric Survey f
or the estimation of inclination and position angle of line of nodes of the LMC disk. The dereddened peak I magnitude of the red clump stars in each subregion is used to obtain the relative distances and hence the z coordinate. The RA and Dec of each sub-region is converted into x & y cartesian coordinates. A weighted least square plane fitting method is applied to this x,y,z data to estimate the structural parameters of the LMC disk. We find an inclination of i =23.0 plus or minus 0.8 and PAlon = 163.7 plus or minus 1.5 for the LMC disk using the OGLE III data and an inclination of i=37.4 plus or minus 2.3 and PAlon= 141.2 plus or minus 3.7 for the LMC disk using the MCPS data. The effect of choice of center, reddening and area covered on the estimated parameters are discussed. Regions in the north west, south west and south east of the LMC disk are warped with respect to the fitted plane. We also identify a symmetric but offcentered warp in the inner LMC.We identify that the structure of the LMC disk inside the 3 degree radius is different from the outside disk such that the inner LMC has relatively less inclination and relatively large PAlon. The 3D plot of the LMC disk suggests an offcentered increase in the inclination for the north-eastern regions which might be due to tidal effects. We suggest that the variation in the planar parameters estimated by various authors as well as in this study is because of the difference in coverage and the complicated inner structure of the LMC disk. In the inner LMC, the stellar and HI disk are found to have similar properties.
The bar of the Large Magellanic Cloud (LMC) is one of the prominent, but controversial feature regarding its location with respect to the disk of the LMC. In order to study the relative location of the bar with respect to the disk, we present the hig
h resolution map of the structure across the LMC. We used the reddening corrected mean magnitudes ($I_0$) of red clump (RC) stars from the OGLE III catalogue to map the relative variation in distance (vertical structure) or variation in RC population across the LMC. The bar does not appear as an identifiable vertical feature in the map, as there is no difference in $I_0$ values between the bar and the disk regions. We conclude that the LMC bar is very much part of the disk, located in the plane of the disk (within 0.02 mag) and it is not a separate component. We identify warps or variation in RC population with increase in radial distance. %The structure map also suggests a %warp or a different RC population in the eastern part of the LMC disk.
RR Lyrae stars (RRLS) belong to population II and are generally used as a tracer of the host galaxy halo. The surface as well as vertical distribution of RRLS in the inner Large Magellanic Cloud (LMC) are studied to understand whether these stars are
actually formed in the halo. RRLS identified by the OGLE III survey are used to estimate their number density distribution. The scale-height of their distribution is estimated using extinction corrected average magnitudes of ab type stars. The density distribution mimics the bar, confirming results in the literature. The distribution of their scale height indicates that there may be two populations, one with smaller scale-height, very similar to the red clump stars and the other, much larger. The distribution of the reddening-corrected magnitude along the minor axis shows variation, suggesting an inclination. The inclination is estimated to be i = 31.3 (3.5) degrees, very similar to the inclination of the disk. Thus, the RRLS in the inner LMC mimic the bar and inclination of the disk, suggesting that a major fraction of RRLS is formed in the disk of the LMC. The results indicate that the RRLS in the inner LMC trace the disk and probably the inner halo. They do not trace the extended metal-poor halo of the LMC. We suggest that a major star formation event happened in the LMC at 10-12 Gyrs ago, resulting in the formation of most of the inner RRLS, as well as probably the globular clusters, inner halo and the disk of the LMC.
We used the red clump stars from the Optical Gravitational Lensing Experiment (OGLE II) survey and the the Magellanic Cloud Photometric Survey (MCPS), to estimate the line of sight depth. The observed dispersion in the magnitude and colour distributi
on of red clump stars is used to estimate the line of sight depth, after correcting for the contribution due to other effects. This dispersion due to depth, has a range from minimum dispersion that can be estimated, to 0.46 mag (a depth of 500 pc to 10.44 Kpc), in the LMC. In the case of SMC, the dispersion ranges from minimum dispersion to 0.35 magnitude (a depth of 665 pc to 9.53 Kpc). The thickness profile of LMC bar indicates that it is flared. The average depth in the bar region is 4.0$pm$1.4 kpc. The halo of the LMC (using RR Lyrea stars) is found to have larger depth compared to the disk/bar, which supports the presence of inner halo for the LMC. The large depth estimated for the LMC bar and the disk suggests that the LMC might have had minor mergers. In the case of SMC, the bar depth (4.90$pm$1.23 Kpc) and the disk depth (4.23$pm$1.48 Kpc) are found to be within the standard deviations. We find evidence for increase in depth near the optical center (up to 9 kpc). On the other hand, the estimated depth for the halo (RR Lyrea stars) and disk (RC stars) for the bar region of the SMC is found to be similar. Thus, increased depth and enhanced stellar as well as HI density near the optical center suggests that the SMC may have a bulge.
