Dark Matter and Stellar Mass in the Luminous Regions of Disk Galaxies
Abstract
We investigate the correlations among stellar mass (M_{*}), disk scale length (R_{d}), and rotation velocity at 2.2 disk scale lengths (V_{2.2}) for a sample of 81 diskdominated galaxies (disk/total>=0.9) selected from the SDSS. We measure V_{2.2} from longslit Hα rotation curves and infer M_{*} from galaxy iband luminosities (L_{i}) and gr colors. We find logarithmic slopes of 2.60+/0.13 and 3.05+/0.12 for the (forward fit) L_{i}V_{2.2} and M_{*}V_{2.2} relations, somewhat shallower than most previous studies, with intrinsic scatter of 0.13 and 0.16 dex, respectively. Our direct estimates of the totaltostellar mass ratio within 2.2R_{d}, assuming a Kroupa IMF, yield a median ratio of 2.4 for M_{*}>10^{10} M_{solar} and 4.4 for M_{*}=10^{9}10^{10} M_{solar}, with large scatter at a given M_{*} and R_{d}. The typical ratio of the rotation speed predicted for the stellar disk alone to the observed rotation speed at 2.2R_{d} is ~0.65. The distribution of scale lengths at fixed M_{*} is broad, but we find no correlation between disk size and the residual from the M_{*}V_{2.2} relation, implying that the M_{*}V_{2.2} relation is an approximately edgeon view of the disk galaxy fundamental plane. Independent of the assumed IMF, this result implies that stellar disks do not, on average, dominate the mass within 2.2R_{d}. We discuss our results in the context of infall models where disks form in adiabatically contracted cold dark matter halos. A model with a disktohalo mass ratio m_{d}=0.05 provides a reasonable match to the R_{d}M_{*} distribution for spin parameters λ ranging from ~0.04 to 0.08, and it yields a reasonable match to the mean M_{*}V_{2.2} relation. A model with m_{d}=0.1 predicts overly strong correlations between disk size and M_{*}V_{2.2} residual. Explaining the wide range of halotodisk mass ratios within 2.2R_{d} requires significant scatter in m_{d} values, with systematically lower m_{d} for galaxies with lower M_{*} or lower stellar surface density Σ_{*}.
 Publication:

The Astrophysical Journal
 Pub Date:
 November 2005
 DOI:
 10.1086/491614
 arXiv:
 arXiv:astroph/0504581
 Bibcode:
 2005ApJ...633..844P
 Keywords:

 Cosmology: Dark Matter;
 Galaxies: Kinematics and Dynamics;
 Galaxies: Photometry;
 Astrophysics
 EPrint:
 18 pages, 2 tables, 7 figures, Accepted to ApJ, Table 1 updated, otherwise minor changes