Browsing by Author "Sheth, Kartik"

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    Lenticular galaxies - the one in the middle
    (2016) Malinga, Simon; Barway, Sudhanshu; Sheth, Kartik; Van der Heyden, Kurt
    The lenticular (S0) galaxies introduced by Hubble (1936) as a morphological transition class between elliptical and early-type spiral galaxies, which have the most massive bulges among disk galaxies, may have formed in several different ways as suggested by theoretical and numerical simulation studies. A sample of lenticular galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S4G) using the Spitzer Space Telescope along with Sloan Digital Sky Survey (SDSS) was used for this project to study molecular gas properties as well morphologies associated with dust where molecular gas is present. A variety of image processing techniques are employed to study the details of galaxies to uncover the presence of molecular gas in S0 galaxies. We obtained colour maps using 3:6 and 4:5 micron images and SDSS r and i band images to find these galaxies have sufficient amount of dust and molecular gas along with variety of dust morphologies. In this thesis, we have shown, for the first time that the mass of molecular gas obtained by Carbon Monoxide (CO) is correlated to colour excess measured from (r - 3:6) and (i - 4:5) colour maps. It would be important to study this relation using advance facilities such as ALMA and MeerKAT to explore properties of molecular gas in nearby early-type galaxies in detail.
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    Thick disks of edge-on galaxies seen through the spitzer survey of stellar structure in galaxies (s 4 g): lair of missing baryons?
    (2011) Comerón, Sébastien; Elmegreen, Bruce G; Knapen, Johan H; Salo, Heikki; Laurikainen, Eija; Laine, Jarkko; Athanassoula, E; Bosma, Albert; Sheth, Kartik; Regan, Michael W; Hinz, Joannah L; de Paz, Armando Gil; Menéndez-Delmestre, Karín; Mizusawa, Trisha; Muñoz-Mateos, Juan-Carlos; Seibert, Mark; Kim, Taehyun; Elmegreen, Debra M; Gadotti, Dimitri A; Ho, Luis C; Holwerda, Benne W; Lappalainen, Jani; Schinnerer, Eva; Skibba, Ramin
    Most, if not all, disk galaxies have a thin (classical) disk and a thick disk. In most models thick disks are thought to be a necessary consequence of the disk formation and/or evolution of the galaxy. We present the results of a study of the thick disk properties in a sample of carefully selected edge-on galaxies with types ranging from T = 3 to T = 8. We fitted one-dimensional luminosity profiles with physically motivated functions-the solutions of two stellar and one gaseous isothermal coupled disks in equilibrium-which are likely to yield more accurate results than other functions used in previous studies. The images used for the fits come from the Spitzer Survey of Stellar Structure in Galaxies (S(4)G). We found that thick disks are on average more massive than previously reported, mostly due to the selected fitting function. Typically, the thin and thick disks have similar masses. We also found that thick disks do not flare significantly within the observed range in galactocentric radii and that the ratio of thick-to-thin disk scale heights is higher for galaxies of earlier types. Our results tend to favor an in situ origin for most of the stars in the thick disk. In addition, the thick disk may contain a significant amount of stars coming from satellites accreted after the initial buildup of the galaxy and an extra fraction of stars coming from the secular heating of the thin disk by its own overdensities. Assigning thick disk light to the thin disk component may lead to an underestimate of the overall stellar mass in galaxies because of different mass-to-light ratios in the two disk components. On the basis of our new results, we estimate that disk stellar masses are between 10% and 50% higher than previously thought and we suggest that thick disks are a reservoir of “local missing baryons.”