Browsing by Subject "massive galaxies"
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Item Extreme Gas Fractions in Clumpy, Turbulent Disk Galaxies at Z Similar To 0.1(2014-08) Fisher, David B.; Glazebrook, Karl; Bolatto, Alberto; Obreschkow, Danail; Cooper, Erin Mentuch; Wisnioski, Emily; Bassett, Robert; Abraham, Roberto G.; Damjanov, Ivana; Green, Andy; McGregor, Peter; Cooper, Erin MentuchIn this Letter, we report the discovery of CO fluxes, suggesting very high gas fractions in three disk galaxies seen in the nearby universe (z similar to 0.1). These galaxies were investigated as part of the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey. High-resolution Hubble Space Telescope imaging of these objects reveals the presence of large star forming clumps in the bodies of the galaxies, while spatially resolved spectroscopy of redshifted II alpha reveals the presence of high dispersion rotating disks. The internal dynamical state of these galaxies resembles that of disk systems seen at much higher redshifts (1 < z < 3). Using CO(1-0) observations made with the Plateau de Bure Interferometer, we find gas fractions of 20%-30% and depletion times of t(dep) similar to 0.5 Gyr (assuming aMilky-Way-like alpha(CO)). These properties are unlike those expected for low-redshift galaxies of comparable specific star Formation rate, but they are normal for their high-z counterparts. DYNAMO galaxies break the degeneracy between gas fraction and redshift, and we show that the depletion time per specific star Formation rate for galaxies is closely tied to gas fraction, independent of redshift. We also show that the gas dynamics of two of our local targets corresponds to those expected from unstable disks, again resembling the dynamics of high-z disks. These results provide evidence that DYNAMO galaxies are local analogs to the clumpy, turbulent disks, which are often found at high redshift.Item The Role Of Bulge Formation In The Homogenization Of Stellar Populations At Z Similar To 2 As Revealed By Internal Color Dispersion In CANDELS(2015-04) Boada, Steven; Tilvi, Vithal; Papovich, Casey; Quadri, R. F.; Hilton, M.; Finkelstein, Steven L.; Guo, Y. C.; Bond, N.; Conselice, C.; Dekel, Avishai; Ferguson, H.; Giavalisco, Mauro; Grogin, N. A.; Kocevski, D. D.; Koekemoer, A. M.; Koo, D. C.; Finkelstein, Steven L.We use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey to study how the spatial variation in the stellar populations of galaxies relates to the formation of galaxies at 1.5 < z < 3.5. We use the internal color dispersion (ICD), measured between the rest-frame UV and optical bands, which is sensitive to age (and dust attenuation) variations in stellar populations. The ICD shows a relation with the stellar masses and morphologies of the galaxies. Galaxies with the largest variation in their stellar populations as evidenced by high ICD have disk-dominated morphologies (with Sersic indexes < 2) and stellar masses between 10 < log (M/M-circle dot) < 11. There is a marked decrease in the ICD as the stellar mass and/or the Sersic index increases. By studying the relations between the ICD and other galaxy properties including size, total color, star formation rate, and dust attenuation, we conclude that the largest variations in stellar populations occur in galaxies where the light from newly, high star-forming clumps contrasts older stellar disk populations. This phase reaches a peak for galaxies only with a specific stellar mass range, 10 < log (M/M-circle dot) < 11, and prior to the formation of a substantial bulge/spheroid. In contrast, galaxies at higher or lower stellar masses and/or higher Sersic index (n > 2) show reduced ICD values, implying a greater homogeneity of their stellar populations. This indicates that if a galaxy is to have a quiescent bulge along with a star-forming disk, typical of Hubble sequence galaxies, this is most common for stellar masses 10 < log (M/M-circle dot) < 11 and when the bulge component remains relatively small (n < 2).