We present optical long-slit spectroscopy and far-ultraviolet to mid-infrared spectral energy distribution fitting of two diffuse dwarf galaxies , LSBG-285 and LSBG-750 , which were recently discovered by the Hyper Suprime-Cam Subaru Strategic Program ( HSC-SSP ) .
We measure redshifts using H \alpha line emission , and find that these galaxies are at comoving distances of { \approx } 25 and { \approx } 41 Mpc , respectively , after correcting for the local velocity field .
They have effective radii of r _ { \mathrm { eff } } = 1.2 and 1.8 kpc and stellar masses of M _ { \star } \approx 2 - 3 \times 10 ^ { 7 } ~ { } M _ { \odot } .
There are no massive galaxies ( M _ { \star } > 10 ^ { 10 } ~ { } M _ { \odot } ) within a comoving separation of at least 1.5 Mpc from LSBG-285 and 2 Mpc from LSBG-750 .
These sources are similar in size and surface brightness to ultra-diffuse galaxies , except they are isolated , star-forming objects that were optically selected in an environmentally blind survey .
Both galaxies likely have low stellar metallicities [ Z _ { \star } / Z _ { \odot } ] < -1.0 and are consistent with the stellar mass–metallicity relation for dwarf galaxies .
We set an upper limit on LSBG-750 ’ s rotational velocity of { \sim } 50 km s ^ { -1 } , which is comparable to dwarf galaxies of similar stellar mass with estimated halo masses < 10 ^ { 11 } ~ { } M _ { \odot } .
We find tentative evidence that the gas-phase metallicities in both of these diffuse systems are high for their stellar mass , though a statistically complete , optically-selected galaxy sample at very low surface brightness will be necessary to place these results into context with the higher-surface-brightness galaxy population .