The H I content of the recently discovered field dwarf galaxy APPLES 1

¹ INAF - Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy e-mail: a.tarchi@ira.cnr.it
² INAF - Osservatorio Astronomico di Cagliari, Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy
³ CSIRO Australia Telescope National Facility, Cnr Vimiera & Pembroke Roads, Marsfield NSW 2122, Australia
⁴ Institute of Astronomy, ETH, Hönggerberg, HPF, 8093 Zürich, Switzerland
⁵ Department of Physics and Astronomy, University College London, Gower St., London WC1E 6BT, UK
⁶ Università di Cagliari, Dipartimento di Fisica, Cittadella Universitaria, 09042 Monserrato (CA), Italy
⁷ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany

Received: 14 June 2005
Accepted: 12 August 2005

Abstract

We present observations in a search for neutral hydrogen associated with the recently detected field dwarf galaxy APPLES 1, performed with the Parkes radiotelescope. The observed radio spectrum shows no evident (>3σ rms) line emission indicating an upper limit for the H i content of the galaxy of ~ and providing an upper value for the M_HI/L_B ratio equal to 2.4 /. The low value of the H i content suggested by the observations, together with the galaxy optical morphology, might indicate that APPLES 1 is a dwarf spheroidal. This indication is in contrast with the evidence of recent star formation, which is typical for dwarf irregular galaxies. This may suggest that APPLES 1 belongs to the class of mixed dwarf irregular/spheroidal transition-type galaxies. We also conclude that the relatively low neutral gas mass in APPLES 1 can be explained by an extended and inefficient star formation process, without the need for a dramatic event such as enhanced star formation or a past encounter with a massive galaxy or galaxy group.