Optical Spectroscopy

To confirm that the galaxies visible in Figure \ref{fig:images} correspond to the clouds discussed in Section \ref{ssec:hi}, we observed both galaxies in twilight with the Double Spectrograph on the Palomar Hale 200 inch telescope on UT 2014 February 6. The slit positions are shown in the upper panels of Figure \ref{fig:images}. The observations were wavelength calibrated, bias- and sky-subtracted using standard longslit techniques. We show the spectra of these objects in Figure \ref{fig:spectra}, with the lower panels showing the wavelengths near H\(\alpha\) and the upper panels displaying the emission.

The optical spectra reveal H\(\alpha\) emission. Other emission lines were not detected, but flux estimates of other lines assuming typical starforming dwarf galaxies suggest they should have \({\rm S/N} \lesssim 1\), due to poor observing conditions. We fit the H\(\alpha\) emission with Gaussian profiles, yielding a central velocity offset from the by only \(3 \pm 34\) and \(10 \pm 35 {\, {\rm km}\, {\rm s}^{-1}}\) (see Table \ref{tab:props}). This is well within the H\(\alpha\) \(1\sigma\) uncertainties¹, implying that the optical galaxies are indeed associated with the clouds. Because flux calibration was not possible for these observations due to non-photometric conditions, we cannot quantify the magnitude of star formation implied by the emission. However, the presence of any detectable H\(\alpha\) emission implies star formation is ongoing (or only ceased within the last \(\sim 10\) Myr) in at least some part of these galaxies.