The anomalous properties of Markarian 1460

Abstract

We present and discuss optical, near-infrared and H i measurements of the galaxy Markarian 1460 at a distance of 19 Mpc in the Ursa Major Cluster. This low-luminosity (MB=−14) galaxy is unusual because (i) it is blue (B−R=0.8) and has the spectrum of an H ii galaxy, (ii) it has a light profile that is smooth and well fitted by an r1/4 and not an exponential function at all radii larger than the seeing, and (iii) it has an observed central brightness of about μB=20 mag arcsec-2, intermediate between those of elliptical galaxies (on the bright μB side) and normal low-luminosity dwarf irregular (on the low μB side) galaxies. No other known galaxy exhibits all these properties in conjunction. On morphological grounds this galaxy looks like a normal distant luminous elliptical galaxy, since the Fundamental Plane tells us that higher luminosity normal elliptical galaxies tend to have lower surface-brightnesses. Markarian 1460 has 2×107 Mo of H i and a ratio M(H i)/LB of 0.2, which is low compared to the typical values for star-forming dwarf galaxies. From the high surface-brightness and r1/4 profile, we infer that the baryonic component of Markarian 1460 has become self-gravitating through dissipative processes. From the colours, radio continuum, H i and optical emission line properties, and yet smooth texture, we infer that Markarian 1460 has had significant star formation as recently as ~1 Gyr ago but not today.