SIMBAD references

We present the discovery of a peculiar blue core in the elliptical galaxy IC 225 by using images and spectra from the Sloan Digital Sky Survey (SDSS). The outer parts of the surface brightness profiles of u-, g-, r-, i-, and z-band SDSS images for IC 225 are well fitted with an exponential function. The fitting results show that IC 225 follows the same relations between the magnitude, scale length, and central surface brightness as for dwarf elliptical galaxies and that its absolute blue magnitude (M_B) is -17.14 mag, all of which suggests that IC 225 is a typical dwarf elliptical galaxy. The g-r color profile indicates a very blue core with a radius of 2", which is also clearly seen in the RGB image made of g-, r-, and i-band SDSS images. The SDSS optical spectrum exhibits strong and very narrow nebular emission lines. The metal abundances derived by the standard methods, which are 12+log(O/H)=8.98, log(N/O)=-0.77, and 12+log(S⁺/H⁺)=6.76, turn out to be significantly higher than those predicted by the well-known luminosity-metallicity relation. After carefully inspecting the central region of IC 225, we find that there are two distinct nuclei, separated by 1".4; the off-nuclear one is even bluer than the nucleus of IC 225. The asymmetric line profiles of higher order Balmer lines indicate that the emission lines are more blueshifted relative to the absorption lines, suggesting that the line emission arises from the off-center core, a metal-rich H II region. To the best of our knowledge, it is the first high-metallicity H II region detected in a dwarf elliptical galaxy.