Marco Grossi
Observatório Astronómico de Lisboa, Portugal

Abstract
The late-type spiral galaxy M33 is the brightest of M31's satellite companions. While M31 is known to be a disturbed galaxy, M33 seems to have not undergone any recent or past mergers having a quite undisturbed stellar disc and no prominent bulge. On the other hand, a long-standing puzzle about M33 is the existence of an extremely warped HI disk, and to sustain its current star formation rate indicate that M33 needs toaccrete gas at a rate of about 1 M_☉/yr.
We used the 21-cm survey ALFALFA to inspect the neutral hydrogen distribution in the outer disk of M33 finding a varied population of HI clouds with masses up to few times 10⁶ M_☉. Particularly, we detected an extended HI complex at a projected distance of about 15 kpc. Deep optical images have been taken to search for optical counterparts to the clouds, and/or traces of stellar streams. In this talk I will present the results.

2010 February 24, 13:30

IA/U.Porto
Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto