We present dynamically-determined rotation-curve mass decompositions of 30 spiral galaxies, which were carried out to test the maximum-disk hypothesis and to quantify properties of their dark-matter halos. We used measured vertical velocity dispersions of the disk stars to calculate dynamical mass surface densities (Σ dyn ). By subtracting our observed atomic and inferred molecular gas mass surface densities from Σ dyn , we derived the stellar mass surface densities (Σ * ), and thus have absolute measurements of all dominant baryonic components of the galaxies. Using K-band surface brightness profiles (I K ), we calculated the K-band mass-to-light ratio of the stellar disks (Υ * = Σ * /I K ) and adopted the radial mean (Υ * ) for each galaxy to extrapolate Σ * beyond the outermost kinematic measurement. The derived Υ * of individual galaxies are consistent with all galaxies in the sample having equal Υ * . We find a sample average and scatter of Υ * = 0.31 ± 0.07. Rotation curves of the baryonic components were calculated from their deprojected mass surface densities. These were used with circular-speed measurements to derive the structural parameters of the dark-matter halos, modeled as either a pseudo-isothermal sphere (pISO) or a Navarro-Frenk-White (NFW) halo. In addition to our dynamically determined mass decompositions, we also performed alternative rotation-curve decompositions by adopting the traditional maximumdisk hypothesis. However, the galaxies in our sample are submaximal, such that at 2.2 disk scale lengths (h R ) the ratios between the baryonic and total rotation curves (F 2.2h R b ) are less than 0.75. We find this ratio to be nearly constant between 1-6h R within individual galaxies. We find a sample average and scatter of F 2.2h R b = 0.57 ± 0.07, with trends of larger F 2.2h R b for more luminous and higher-surface-brightness galaxies. To enforce these being maximal, we need to scale Υ * by a factor 3.6 on average. In general, the dark-matter rotation curves are marginally better fit by a pISO than by an NFW halo. For the nominal-Υ * (submaximal) case, we find that the derived NFW-halo parameters have values consistent with ΛCDM N-body simulations, suggesting that the baryonic matter in our sample of galaxies has only had a minor effect on the dark-matter distribution. In contrast, maximum-Υ * decompositions yield halo-concentration parameters that are too low compared to the ΛCDM simulations.

We present a survey of the mass surface-density of spiral disks, motivated by outstanding uncertainties in rotation-curve decompositions. Our method exploits integral-field spectroscopy to measure stellar and gas kinematics in nearly face-on galaxies sampled at 515, 660, and 860 nm, using the custom-built SparsePak and PPak instruments. A two-tiered sample, selected from the UGC, includes 146 nearly face-on galaxies, with B < 14.7 and disk scale-lengths between 10 and 20 arcsec, for which we have obtained Hα velocity-fields; and a representative 46-galaxy subset for which we have obtained stellar velocities and velocity dispersions. Based on re-calibration of extant photometric and spectroscopic data, we show these galaxies span factors of 100 in L K (0.03 < L/L * K < 3), 8 in L B /L K , 10 in R-band disk central surface-brightness, with distances between 15 and 200 Mpc. The survey is augmented by 4-70 µm Spitzer IRAC and MIPS photometry, ground-based UBV RIJHK photometry, and H I aperture-synthesis imaging. We outline the spectroscopic analysis protocol for deriving precise and accurate line-of-sight stellar velocity dispersions. Our key measurement is the dynamical disk-mass surface-density. Star-formation rates and kinematic and photometric regularity of galaxy disks are also central products of the study. The survey is designed to yield random and systematic errors small enough (i) to confirm or disprove the maximum-disk hypothesis for intermediate-type disk galaxies, (ii)

We present ionized-gas ([Oiii]λ5007 Å) and stellar kinematics (velocities and velocity dispersions) for 30 nearly face-on spiral galaxies out to as many as three K-band disk scale lengths (h R ). These data have been derived from PPak integral-field-unit spectroscopy from 4980−5370 Å observed at a mean resolution of λ/Δλ = 7700 (σ inst = 17 km s −1 ). These data are a fundamental product of our survey and will be used in companion papers to, e.g., derive the detailed (baryonic+dark) mass budget of each galaxy in our sample. Our presentation provides a comprehensive description of the observing strategy and data reduction, including a robust measurement and removal of shift, scale, and rotation effects in the data due to instrumental flexure. Using an in-plane coordinate system determined by fitting circular-speed curves to our velocity fields, we derive azimuthally averaged rotation curves and line-of-sight velocity dispersion (σ LOS ) and luminosity profiles for both the stars and [Oiii]-emitting gas. Along with a clear presentation of the data, we demonstrate: (1) The [Oiii] and stellar rotation curves exhibit a clear signature of asymmetric drift with a rotation difference that is 11% of the maximum rotation speed of the galaxy disk, comparable to measurements in the solar neighborhood in the Milky Way.(2) The e-folding length of the stellar velocity dispersion (h σ ) is 2h R on average, as expected for a disk with a constant scale height and mass-to-light ratio, with a scatter that is notably smaller for massive, high-surface-brightness disks in the most luminous galaxies. (3) At radii larger than 1.5h R , σ LOS tends to decline slower than the best-fitting exponential function, which may be due to an increase in the disk mass-to-light ratio, disk flaring, or disk heating by the dark-matter halo. (4) A strong correlation exists between the central vertical stellar velocity dispersion of the disks (σ z,0 ) and their circular rotational speed at 2.2h R (V OIII 2.2h R ), with a zero point indicating that galaxy disks are submaximal. Moreover, weak but consistent correlations exist between σ z,0 /V OIII 2.2h R and global galaxy properties such that disks with a fainter central surface brightness in bluer and less luminous galaxies of later morphological types are kinematically colder with respect to their rotational velocities.

We present our Disk Mass project as the main science case for building a new fiber IFU-module for the PMAS spectrograph, currently mounted at the Cassegrain focus of the 3.5m telescope on Calar Alto. Compared to traditional long-slit observations, the large light collecting power of 2-dimensional Integral Field Units dramatically improves the prospects for performing spectroscopy on extended low surface brightness objects with high spectral resolution. This enables us to measure stellar velocity dispersions in the outer disk of normal spiral galaxies. We describe some results from a PMAS pilot study using the existing lenslet array, and provide a basic description of the new fiber IFU-module for PMAS.Comment: 4 pages, 5 figures. Refereed proceeding for the `Euro3D Science Workshop'. Contains updated layout of PPAK fibers, and improved M/L value for N398

We measure the contribution of galaxy disks to the overall gravitational potential of 30 nearly face-on intermediateto-late-type spirals from the DiskMass Survey. The central vertical velocity dispersion of the disk stars (σ disk z,R=0) is related to the maximum rotation speed (V max) as σ disk z,R=0 ∼ 0.26V max , consistent with previous measurements for edge-on disk galaxies and a mean stellar velocity ellipsoid axial ratio α ≡ σ z /σ R = 0.6. For reasonable values of disk oblateness, this relation implies these galaxy disks are submaximal. We find disks in our sample contribute only 15%-30% of the dynamical mass within 2.2 disk scale lengths (h R), with percentages increasing systematically with luminosity, rotation speed, and redder color. These trends indicate that the mass ratio of disk-to-total matter remains at or below 50% at 2.2 h R even for the most extreme, fast-rotating disks (V max 300 km s −1) of the reddest rest frame, face-on color (B − K ∼ 4 mag), and highest luminosity (M K < −26.5 mag). Therefore, spiral disks in general should be submaximal. Our results imply that the stellar mass-to-light ratio and hence the accounting of baryons in stars should be lowered by at least a factor of three.