The Metal-Poor Dwarf Irregular Galaxy Candidate Next To Mrk 1172

In this work, we characterize the properties of the object SDSS J020536.84-081424.7, an extended nebular region with projected extension of 14 x 14 kpc(2) in the line of sight of the ETG Mrk 1172, using unprecedented spectroscopic data from MUSE. We perform a spatially resolved stellar population synthesis and estimate the stellar mass for both Mrk 1172 (1 x 10(11) M-circle dot) and our object of study (3 x 10(9) M-circle dot). While the stellar content of Mrk 1172 is dominated by an old (similar to 10 Gyr) stellar population, the extended nebular emission has its light dominated by young to intermediate age populations (from similar to 100 Myr to similar to 1 Gyr) and presents strong emission lines such as H beta; [O III] lambda lambda 4959, 5007 angstrom; H alpha; [N II] lambda lambda 6549, 6585 angstrom; and [S II] lambda lambda 6717, 6732 A. Using these emission lines, we find that it is metal poor (with Z similar to 1/3 Z(circle dot), comparable to the LMC) and is actively forming stars (0.70 M-circle dot yr(-1)), especially in a few bright clumpy knots that are readily visible in H alpha. The object has an ionized gas mass >= 3.8 x 10(5) M-circle dot. Moreover, the motion of the gas is well described by a gas in circular orbit in the plane of a disc and is being affected by interaction wtih Mrk 1172. We conclude that SDSS J020536.84-081424.7 is most likely a dwarf irregular galaxy (the dIGal).