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Thirteen dwarf galaxies have recently been found to host radio-selectedaccreting massive black hole (MBH) candidates, some of which are ``wandering"in the outskirts of their hosts. We present 9 GHz Very Long Baseline Array(VLBA) observations of these sources at milliarcsecond resolution. Ourobservations have beam solid angles ${\sim}10^4$ times smaller than theprevious Very Large Array (VLA) observations at 9 GHz, with comparable pointsource sensitivities. We detect milliarcsecond-scale radio sources at thepositions of the four VLA sources most distant from the photo-centers of theirassociated dwarf galaxies. These sources have brightness temperatures of${>}10^6~\mathrm{K}$, consistent with active galactic nuclei (AGNs), but thesignificance of their preferential location at large distances($p$-value~$=0.0014$) favors a background AGN interpretation. The VLBAnon-detections toward the other 9 galaxies indicate that the VLA sources areresolved out on scales of tens of milliarcseconds, requiring extended radioemission and lower brightness temperatures consistent with either starformation or radio lobes associated with AGN activity. We explore the starformation explanation by calculating the expected radio emission for these nineVLBA non-detections, finding that about 5 have VLA luminosities that areinconsistent with this scenario. Of the remaining four, two are associated withspectroscopically confirmed AGNs that are consistent with being located attheir galaxy photo-centers. There are therefore between 5 and 7 wandering MBHcandidates out of the 13 galaxies we observed, although we cannot rule outbackground AGNs for five of them with the data in hand.

Wandering Black Hole Candidates in Dwarf Galaxies at VLBI Resolution