Clumpy Star Formation and AGN Activity in the 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 multiwavelength 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 similar to 10 kpc long string of young massive star clusters (t less than or similar to 10 Myr; M greater than or similar to 10(5) M (circle dot)) 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 (circle dot). Furthermore, we present additional evidence for a low-luminosity AGN in Mrk 709 S (first identified by Reines et al. 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.

Automated summary

The study provides a detailed investigation of star formation and BH activity in the low-metallicity dwarf-dwarf galaxy merger Mrk 709, revealing that the two dwarf galaxies are likely in the early stages of a merger and the southern galaxy is undergoing clumpy star formation resembling that seen in high-redshift galaxies. Additionally, evidence for a low-luminosity AGN in Mrk 709 S is presented, including the detection of the coronal [Fe x] optical emission line.