Discovery of a huge low-surface-brightness galaxy - A protodisk galaxy at low redshift?

Abstract

The authors report on the accidental discovery of an extremely large, extremely H I-rich low-surface-brightness galaxy located at a redshift of z = 0.083. Its nuclear spectrum exhibits broad, low-level emission lines. Surface photometry at V indicates the presence of a bulge component and a very extended disk, with scale length of ≈45arcsec (55 kpc for H<SUB>0</SUB> = 100) and with central surface brightness of V(0) ≈ 25.5 mag arcsec<SUP>-2</SUP>. The total amount of H I is at least 1.0×10<SUP>11</SUP>M_sun;. This amount of H I is at least 5 times more H I than any spiral galaxy previously observed. If disk formation is a quiescent process, then it is likely that the authors have caught a disk in the process of formation. They also point out that the properties of this disk are likely to be similar to the suspected sources that produce the observed damped Lyα absorption profiles that are so conspicuous at z ≈ 2.