Dark Matter Distribution in the Galaxy IC 2574

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Session 6 -- Normal Galaxies: Structure and Dynamics
Display presentation, Monday, 9:20-6:30, Pauley Room

[6.12] Dark Matter Distribution in the Galaxy IC 2574

N. Martimbeau (SFSU), C. Carignan (Universit\'e de Montr\'eal)

We present new studies on the dwarf spiral galaxy IC 2574 (SAB(sm),D = 3 Mpc). Broad--band photometry is done on photographic plates (B and R) taken from Kitt Peak National Observatory. Luminosity profiles are then extracted and the extrapolated central surface brightness B(0)$_c$ = 23.44 mag arcsec$^{-2}$, a scale lenght of $\alpha^{-1}$ = 2.2 kpc, and a color index of $<$ B -- R $>$ = 0.96 are derived.

21 cm aperture synthesis observations from Westerbork Synthesis Radio Telescope give a rotation curve that reaches nearly 8 kpc. We were able to trace a HI radial distribution of surface density over $\sim$ 1.8 D$_{25}$. The rotation curve rises slowly, barely flattening at its end, with a maximum rotational velocity of $\sim$ 67 km s$^{-1}$.

With the B luminosity profile, the HI radial distribution and the HI rotation curve, a mass model is suggested for IC 2574. The best solutions found are: a (M/L$_B$) = 0.4 M$_\odot$/L$_\odot$ for the luminous stellar disk, and a core radius r$_c$ = 8 kpc and a central surface density $\rho_0$ = 0.0064 M$_\odot$ pc$^{-3}$ for the dark halo.

This model shows us that the luminous components (star and gas) contribute very little to the total mass of the galaxy, and in fact, the dark component account for $\sim$ 90 \% of the mass at the last measured point. This is not uncommon in dwarf galaxies, and it has been found for example in NGC 3109 (Jobin \& Carignan 1990) and NGC5585 (C\^ot\'e \& Carignan 1991).

{\noindent \bf{References}}

{\noindent C\^ot\'e, S. \& Carignan, C. 1991, AJ, 102, 904}

{\noindent Jobin, M. \& Carignan, C. 1990, AJ, 100, 648}

Monday program listing