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Register a new userDYNAMO II: Coupled Stellar and Ionized Gas Kinematics in Two Low Redshift Clumpy Disks
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We study the spatially resolved stellar kinematics of two star-forming galaxies at z = 0.1 from the larger DYnamics of Newly Assembled Massive Objects (DYNAMO) sample. These galaxies, which have been characterized by high levels of star formation and large ionized gas velocity dispersions, are considered possible analogs to high-redshift clumpy disks. They were observed using the GMOS instrument in integral field spectroscopy (IFS) mode at the Gemini Observatory with high spectral resolution (R=5400, equivalent to 24 km/s at the observed wavelengths) and 6 hour exposure times in order to measure the resolved stellar kinematics via absorption lines. We also obtain higher-quality emission line kinematics than previous observations. The spatial resolution (1.2 kpc) is sufficient to show that the ionized gas in these galaxies (as traced by H-beta emission) is morphologically irregular, forming multiple giant clumps while stellar continuum light is smooth and well described by an exponential profile. Clumpy gas morphologies observed in IFS data are confirmed by complementary narrow band H-alpha imaging from the Hubble Space Telescope. Morphological differences between the stars and ionized gas are not reflected dynamically as stellar kinematics are found the be closely coupled to the kinematics of the ionized gas: both components are smoothly rotating with large velocity dispersions (~40 km/s) suggesting that the high gas dispersions are not primarily driven by star-formation feedback. In addition, the stellar population ages of these galaxies are estimated to be quite young (60-500 Myr). The large velocity dispersions measured for these young stars suggest that we are seeing the formation of thick disks and/or stellar bulges in support of recent models which produce these from clumpy galaxies at high redshift.
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We present molecular gas mass estimates for a sample of 13 local galaxies whose kinematic and star forming properties closely resemble those observed in $zapprox 1.5$ main-sequence galaxies. Plateau de Bure observations of the CO[1-0] emission line and Herschel Space Observatory observations of the dust emission both suggest molecular gas mass fractions of ~20%. Moreover, dust emission modeling finds $T_{dust}<$30K, suggesting a cold dust distribution compared to their high infrared luminosity. The gas mass estimates argue that $zsim$0.1 DYNAMO galaxies not only share similar kinematic properties with high-z disks, but they are also similarly rich in molecular material. Pairing the gas mass fractions with existing kinematics reveals a linear relationship between $f_{gas}$ and $sigma$/$v_{c}$, consistent with predictions from stability theory of a self-gravitating disk. It thus follows that high gas velocity dispersions are a natural consequence of large gas fractions. We also find that the systems with lowest depletion times ($sim$0.5 Gyr) have the highest ratios of $sigma$/$v_{c}$ and more pronounced clumps, even at the same high molecular gas fraction.
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