Maximal Disks and the Tully-Fisher Relation

Details Maximal Disks and the Tully-Fisher Relation Maximal Disks and the Tully-Fisher Relation

Mar 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...513..561c&link_type=abstract

The Astrophysical Journal, Volume 513, Issue 2, pp. 561-571.

Astronomy and Astrophysics

Astronomy

157

Galaxies: Halos, Galaxies: Kinematics And Dynamics, Galaxies: Spiral, Galaxies: Structure

Scientific paper

We show that for luminous, nonbarred, high surface brightness (HSB) spirals the Tully-Fisher relation (TFR) residuals can be used to estimate the relative mass contributions of the stellar disk and the dark halo at the peak of the disk rotation, near 2.2 exponential scale lengths. For ``maximal disks,'' a large fraction (0.85+/-0.1) of the total rotational support, V_2.2, at such radii should arise from their stellar mass. Therefore, the disk size or surface-brightness should be a significant additional parameter in the TFR. At a given absolute luminosity, M_r, more compact disks (as measured by the disk scale length R_exp) should have higher rotation speeds, V_2.2. Using a well-defined sample of late-type spirals, deviations, DeltalogV_2.2, and DeltalogR_exp, from the mean relations, V_2.2(M_r) and R_exp(M_r), are not significantly correlated. The case of ∂logV_2.2/∂logR_exp=-0.5 expected for a maximal disk is ruled out for the majority of these HSB galaxies. We model adiabatic infall of varying amounts of luminous matter into dark matter halos to explore the range of possible values for ∂logV_2.2/∂logR_exp. From this, we find that the TFR residuals require a mean value of V_disk~0.6V_total, fairly insensitive to the details of the initial dark matter halo and to the presence of a bulge. This translates to M_halo~0.6M_total within 2.2R_exp or roughly twice more dark matter in the inner parts of late-type spirals than previously accounted for by maximum disk fits. We show that any stellar population differences between disks of different scale lengths lead to lower values of V_disk/V_total. Our result is independent of the shape of the luminosity profile and relies only on the assumption of adiabatic contraction and that the dark matter halo rotation rises in the central parts of the galaxy. Submaximal disks establish a natural continuity between HSB and low surface brightness galaxies, which appear to be completely dark matter dominated even in their inner regions.

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