The kinematics of distant galaxies from z = 0.1 to z > 2 play a key role in our understanding of galaxy evolution from early times to the present. One of the important parameters is the intrinsic, or ...local, velocity dispersion of a galaxy, which allows one to quantify the degree of non-circular motions such as pressure support. However, this is difficult to measure because the observed dispersion includes the effects of (often severe) beam smearing on the velocity gradient. Here we investigate four methods of measuring the dispersion that have been used in the literature, to assess their effectiveness at recovering the intrinsic dispersion. We discuss the biases inherent in each method, and apply them to model disk galaxies in order to determine which methods yield meaningful quantities and under what conditions. All the mean-weighted dispersion estimators are affected by (residual) beam smearing. In contrast, the dispersion recovered by fitting a spatially and spectrally convolved disk model to the data is unbiased by the beam smearing it is trying to compensate. Because of this, and because the bias it does exhibit depends only on the signal-to-noise ratio (S/N), it can be considered reliable. However, at very low S/N, all methods should be used with caution.
We present the Spectroscopic Imaging survey in the near-infrared (near-IR) with SINFONI (SINS) of high-redshift galaxies. With 80 objects observed and 63 detected in at least one rest-frame optical ...nebular emission line, mainly Halpha, SINS represents the largest survey of spatially resolved gas kinematics, morphologies, and physical properties of star-forming galaxies at z approx 1-3. We describe the selection of the targets, the observations, and the data reduction. We then focus on the 'SINS Halpha sample', consisting of 62 rest-UV/optically selected sources at 1.3 < z < 2.6 for which we targeted primarily the Halpha and N II emission lines. Only approx30% of this sample had previous near-IR spectroscopic observations. The galaxies were drawn from various imaging surveys with different photometric criteria; as a whole, the SINS Halpha sample covers a reasonable representation of massive M{sub *} approx> 10{sup 10} M{sub sun} star-forming galaxies at z approx 1.5-2.5, with some bias toward bluer systems compared to pure K-selected samples due to the requirement of secure optical redshift. The sample spans 2 orders of magnitude in stellar mass and in absolute and specific star formation rates, with median values approx3 x 10{sup 10} M{sub sun}, approx70 M{sub sun} yr{sup -1}, and approx3 Gyr{sup -1}. The ionized gas distribution and kinematics are spatially resolved on scales ranging from approx1.5 kpc for adaptive optics assisted observations to typically approx4-5 kpc for seeing-limited data. The Halpha morphologies tend to be irregular and/or clumpy. About one-third of the SINS Halpha sample galaxies are rotation-dominated yet turbulent disks, another one-third comprises compact and velocity dispersion-dominated objects, and the remaining galaxies are clear interacting/merging systems; the fraction of rotation-dominated systems increases among the more massive part of the sample. The Halpha luminosities and equivalent widths suggest on average roughly twice higher dust attenuation toward the H II regions relative to the bulk of the stars, and comparable current and past-averaged star formation rates.
We present the modeling of SINFONI integral field dynamics of 18 star-forming galaxies at z {approx} 2 from H{alpha} line emission. The galaxies are selected from the larger sample of the SINS ...survey, based on the prominence of ordered rotational motions with respect to more complex merger-induced dynamics. The quality of the data allows us to carefully select systems with kinematics dominated by rotation, and to model the gas dynamics across the whole galaxy using suitable exponential disk models. We obtain a good correlation between the dynamical mass and the stellar mass, finding that large gas fractions (M {sub gas} {approx} M {sub *}) are required to explain the difference between the two quantities. We use the derived stellar mass and maximum rotational velocity V {sub max} from the modeling to construct for the first time the stellar mass Tully-Fisher relation at z {approx} 2.2. The relation obtained shows a slope similar to what is observed at lower redshift, but we detect an evolution of the zero point. We find that at z {approx} 2.2 there is an offset in log(M {sub *}) for a given rotational velocity of 0.41 {+-} 0.11 with respect to the local universe. This result is consistent with the predictions of the latest N-body/hydrodynamical simulations of disk formation and evolution, which invoke gas accretion onto the forming disk in filaments and cooling flows. This scenario is in agreement with other dynamical evidence from SINS, where gas accretion from the halo is required to reproduce the observed properties of a large fraction of the z {approx} 2 galaxies.
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