The Formation of Dust Lanes

Dust lanes are a common feature of edge-on disk galaxies. However, they are largely absent in low mass galaxies. Surprisingly, there have been few systematic studies of the properties and origins of dust lanes. This oversight is particularly striking given the close correlation between dust extinction and cold molecular gas. During a large study of edge-on late-type galaxies, we noticed that the dust lane phenomena disappears abruptly when the rotation speed of a galaxy falls below 120 km/s. We find that below this rotation speed all galaxies are stable to gravitational pertubations, suggesting that disk instabilities are linked to the formation of dust lanes in undistiburbed late-type galaxies. This connection has several implications for the Kennicutt star formation law, for the metallicities of galaxies as a function of rotation speed, for the formation of bulges, and for the thicknesses of dwarf galaxies.

Images from the HST archive showing the distribution of dust in massive galaxies (V>120km/s, left) and low mass galaxies (V<120km/s, right). All images have been scaled to a common distance. The low mass galaxies clearly have dust, but with a larger scale height
Vertical color gradients for low mass galaxies (100km/s<V<120km/s, left) and high mass galaxies (V>120km/s, right). The gradients are plotted for the dust sensitive R-Ks color. The high mass galaxies are dramatically redder in the midplane, indicating a well-confined layer of dust. The lower mass galaxies have flat color gradients.
The stellar, gas, and total central surface density of the edge-on disks as a function of rotation speed. There is no sharp change in the surface density at V=120km/s
The stability of low mass galaxies (100km/s<V<120km/s, left) and high mass galaxies (V>120km/s, right), as a function of radius (dark portions indicate the inner scale length). Regions above the dashed line are gravitationally unstable. The high mass galaxies are all unstable in their inner regions, while the low mass galaxies are stable everywhere. This suggests that gravitational instabilities play a role in the formation of dust lanes.
On-going Work
CO & HI mapping of Edge-on Galaxies: To test if the molecular gas content is coupled to the morphology of the dust, Erik Rosolowsky and our collaborators have begun mapping the distribution of molecular and atomic gas in galaxies with rotation speeds above and below the 120 km/s transition where dust lanes disappear.
ACS mapping of dust in Edge-on Galaxies: Roelof de Jong, Anil Seth, Eric Bell, Simone Bianchi and I are using multicolor ACS snapshot imaging to constrain the detailed dust morphology in galaxies with and without dust lanes. We are also examining the radial variation of the dust morphology to test for possible links with disk stability.
  • Dalcanton, J. J., Yoachim, P., & Bernstein R. A. 2004, "The
    Formation of Dust Lanes: Implications for Galaxy Evolution
    ", Ap. J., submitted.
  • Dalcanton, J. J., Yoachim, P., & Bernstein R. A. 2003, "The
    Formation of Dust Lanes
    ", BAAS
Graduate Students: Peter Yoachim
  Anil Seth
  Erik Rosolowsky (UCBerkeley)
Other Collaborators: Rebecca Bernstein (UMichigan)
Roelof deJong (STScI)
Eric Bell (MPIA-Heidelberg)
Simone Bianchi (Arcetri)