The SAMI Galaxy Survey: gas streaming and dynamical M/L in rotationally supported systems

• Published in: Monthly Notices of the Royal Astronomical Society
• Main Authors: Cecil, G., Fogarty, L. M. R., Richards, S., Bland-Hawthorn, J., Lange, R., Moffett, A., Catinella, B., Cortese, L., Ho, I.-T., Taylor, E. N., Bryant, J. J., Allen, J. T., Sweet, S. M., Croom, S. M., Driver, S. P., Goodwin, M., Kelvin, L., Green, A. W., Konstantopoulos, I. S., Owers, M. S., Lawrence, J. S., Lorente, N. P. F.
• Format: Text
• Language: English
• Published: Oxford University Press 2015
• Subjects: Article; Starlight; sami
• Online Access: http://mnras.oxfordjournals.org/cgi/content/short/456/2/1299; https://doi.org/10.1093/mnras/stv2643

Line-of-sight velocities of gas and stars can constrain dark matter (DM) within rotationally supported galaxies if they trace circular orbits extensively. Photometric asymmetries may signify non-circular motions, requiring spectra with dense spatial coverage. Our integral-field spectroscopy of 178 galaxies spanned the mass range of the Sydney-AAO Multi-object integral field spectrograph (SAMI) Galaxy Survey. We derived circular speed curves (CSCs) of gas and stars from non-parametric fits out to r ∼ 2 r e . For 12/14 with measured H <scp>i</scp> profiles, ionized gas and H <scp>i</scp> maximum velocities agreed. We fitted mass-follows-light models to 163 galaxies by approximating the radial light profile as nested, very flattened mass homeoids viewed as a S e ´ rsic form. Fitting broad-band spectral energy distributions to Sloan Digital Sky Survey images gave median stellar mass/light 1.7 assuming a Kroupa initial mass function (IMF) versus 2.6 dynamically. Two-thirds of the dynamical mass/light measures were consistent with star+remnant IMFs. One-fifth required upscaled starlight to fit, hence comparable mass of unobserved baryons and/or DM distributed like starlight across the SAMI aperture that came to dominate motions as the starlight CSCs declined rapidly. The rest had mass distributed differently from light. Subtracting fits of S e ´ rsic radial profiles to 13 VIKING Z -band images revealed residual weak bars. Near the bar major axis, we assessed m = 2 streaming velocities, and found deviations usually <30 km s−1 from the CSC; three showed no deviation. Thus, asymmetries rarely influenced the CSC despite colocated shock-indicating, emission-line flux ratios in more than 2/3 of our sample.