Clumpy Star Formation and AGN Activity in Dwarf-Dwarf Galaxy Merger Mrk
  709
  Nearby, low-metallicity dwarf starburst galaxies hosting active galactic
nuclei (AGNs) offer the best local analogs to study the early evolution of
galaxies and their supermassive black holes (BHs). Here we present a detailed
multi-wavelength investigation of star formation and BH activity in the
low-metallicity dwarf-dwarf galaxy merger Mrk 709. Using Hubble Space Telescope
H$\alpha$ and continuum imaging combined with Keck spectroscopy, we determine
that the two dwarf galaxies are likely in the early stages of a merger (i.e.,
their first pass) and discover a spectacular $\sim 10$ kpc-long string of young
massive star clusters ($t \lesssim 10$ Myr; $M_\star \gtrsim 10^5~M_\odot$)
between the galaxies triggered by the interaction. We find that the southern
galaxy, Mrk 709 S, is undergoing a clumpy mode of star formation resembling
that seen in high-redshift galaxies, with multiple young clusters/clumps having
stellar masses between $10^7$ and $10^8~M_\odot$. Furthermore, we present
additional evidence for a low-luminosity AGN in Mrk 709 S (first identified by
Reines et al. 2014 (arXiv:1405.0278) using radio and X-ray observations),
including the detection of the coronal [Fe X] optical emission line. The work
presented here provides a unique glimpse into processes key to hierarchical
galaxy formation and BH growth in the early Universe.
