An optical and HI study of the dwarf Local Group galaxy VV124=UGC4879. A
  gas-poor dwarf with a stellar disk?
  We present a detailed study of the dwarf galaxy VV124, recently recognized as
a isolated member of the Local Group. We have obtained deep (r=26.5) wide-field
g,r photometry of individual stars with the LBT under sub-arcsec seeing
conditions. The Color-Magnitude Diagram suggests that the stellar content of
the galaxy is dominated by an old, metal-poor population, with a significant
metallicity spread. A very clean detection of the RGB tip allows us to derive
an accurate distance of D=1.3 +/- 0.1 Mpc. Combining surface photometry with
star counts, we are able to trace the surface brightness profile of VV124 out
to ~ 5' = 1.9 kpc radius (where mu_r=30 mag/arcsec^2), showing that it is much
more extended than previously believed. Moreover, the surface density map
reveals the presence of two symmetric flattened wings emanating from the
central elongated spheroid and aligned with its major axis, resembling a
stellar disk seen nearly edge-on. We also present HI observations obtained with
the WSRT, the first ever of this object. A total amount of 10^6 M_sun of HI gas
is detected in VV124. Compared to the total luminosity, this gives a value of
M_HI/L_V=0.11, which is particularly low for isolated Local Group dwarfs. The
spatial distribution of the gas does not correlate with the observed stellar
wings. The systemic velocity of the HI in the region superposed to the stellar
main body of the galaxy is V_h=-25 km/s. The velocity field shows substructures
typical of galaxies of this size but no sign of rotation. The HI spectra
indicates the presence of a two-phase interstellar medium, again typical of
many dwarf galaxies.
