A star-forming dwarf galaxy candidate in the halo of NGC 4634
  The halos of disk galaxies form a crucial connection between the galaxy disk
and the intergalactic medium. Massive stars, HII regions, or dwarf galaxies
located in the halos of galaxies are potential tracers of recent accretion
and/or outflows of gas, and are additional contributors to the photon field and
the gas phase metallicity. We investigate the nature and origin of a
star-forming dwarf galaxy candidate located in the halo of the edge-on Virgo
galaxy NGC 4634 with a projected distance of 1.4 kpc and a H$\alpha$ star
formation rate of $\sim 4.7 \times 10^{-3} \text{M}_\odot \text{yr}^{-1}$ in
order to increase our understanding of these disk-halo processes. With optical
long-slit spectra we measured fluxes of optical nebula emission lines to derive
the oxygen abundance 12 + log(O/H) of an HII region in the disk of NGC 4634 and
in the star-forming dwarf galaxy candidate. Abundances derived from optical
long-slit data and from Hubble Space Telescope (HST) r-band data, H$\alpha$
data, Giant Metrewave Radio Telescope (GMRT) HI data, and photometry of SDSS
and GALEX data were used for further analysis. With additional probes of the
luminosity-metallicity relation in the $B$-band from the H$\alpha$-luminosity,
the HI map, and the relative velocities, we are able to constrain a possible
origin of the dwarf galaxy candidate. The high oxygen abundance (12 + log(O/H)
$\approx$ 8.72) of the dwarf galaxy candidate leads to the conclusion that it
was formed from pre-enriched material. Analysis of auxiliary data shows that
the dwarf galaxy candidate is composed of material originating from NGC 4634.
We cannot determine whether this material has been ejected tidally or through
other processes, which makes the system highly interesting for follow up
observations.
