The metal-poor dwarf irregular galaxy candidate next to Mrk 1172

Abstract

In this work we characterise the properties of the object SDSS J020536.84-081424.7, an extended nebular region with projected extension of $14\times 14$ 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 ($1\times 10^{11}{M}_{\odot }$) and our object of study ($3\times 10^9{M}_{\odot }$). While the stellar content of Mrk 1172 is dominated by an old ($\sim 10$ Gyr) stellar population, the extended nebular emission has its light dominated by young to intermediate age populations (from $\sim 100$ Myr to $\sim 1$ Gyr) and presents strong emission lines such as: H$\beta$, [O III] $\lambda \lambda$4959,5007, H$\alpha$, [N II] $\lambda \lambda$6549,6585 and [S II] $\lambda \lambda$6717,6732. Using these emission lines we find that it is metal-poor (with $Z\sim$ 1/3 $Z_{\odot }$, comparable to the LMC) and is actively forming stars ($0.70$ M${}_{\odot }$ yr${}^{-1}$), especially in a few bright clumpy knots that are readily visible in H$\alpha$. The object has an ionised gas mass $\ge 3.8\times 10^5$ M${}_{\odot }$. Moreover, the motion of the gas is well described by a gas in circular orbit in the plane of a disk and is being affected by interaction with Mrk 1172. We conclude that SDSS J020536.84-081424.7 is most likely a dwarf irregular galaxy (dIGal).

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