Session 38 - Dwarf Galaxies.
Display session, Tuesday, January 14
Metropolitan Ballroom,

## [38.10] The \underlineTotal Mass of DDO154

C. R. Purton (DRAO), C. Carignan (U. de Montréal)

HI spectral-line data for the dwarf irregular galaxy DDO154 has been obtained from both the DRAO synthesis telescope and the VLA. Combining the two sets of data yields a total HI flux consistent with single-dish measurements. The VLA data on its own misses an extended component which contributes \sim30% of the flux.

The combined data traces the HI disk out to \sim6 optical (Holmberg) radii and gives a total HI mass of 2.5\times10^8 M_ødot, from which (M_H_I/L_B) \sim8, making DDO154 one of the most gas-rich galaxies known.

The rotation curve obtained from the combined data is one of the most extended, relative to the optical size of the galaxy, ever derived. It extends 33% further than that obtained from the VLA data alone, and confirms that the rotation curve is declining in the outer parts.

Detailed mass models show that the HI measurements have likely reached the edge of the mass distribution, allowing for the first time an estimate of the total mass and total extent of a galaxy. The derived total mass of DDO154 is M_t_o_t = 3.0\times10^9 M_ødot, and the radial extent R_t_o_t \leq 8 kpc.