individual (collapsed) white-light images with all entries in the *Gaia* [@GaiaCollaboration16a] DR1 [@GaiaCollaboration16]; see Fig \[fig1\]). For simplicity, and given the spaxel size of the WiFeS datacubes, we restrict ourselves to integer shifts when combining fields. We estimate that the resulting absolute and relative (field-to-field) alignment accuracy are both $\pm$1arc sec.

HST imaging of the cloudlets
----------------------------

We have downloaded all the HST ACS F475W and F658N images from the *Barbara A. Mikulski archive for space telescopes* (MAST). The former filter encompasses the full velocity range of the \[\]$\lambda\lambda$5959,5007Å emission, whereas the latter covers the rest-frame H$\alpha$ emission. The dataset comprises four exposures of 380s each with the F475W filter, and four exposures of 360s each using the F658N filter, all acquired in January 2004 under program \#12001 (PI Green).

We used the individual calibrated and CTE-corrected frames (<span style="font-variant:small-caps;">\*\_flc.fits</span>) retrieved from MAST to construct a combined, drizzled image in both filters using the following steps. We first correct the WCS solutions of each frame using the <span style="font-variant:small-caps;">tweakreg</span> routine from the <span style="font-variant:small-caps;">drizzlepac 2.1.13</span> package via a dedicated <span style="font-variant:small-caps;">python</span> script. We anchor the WCS solution to the *Gaia* [@GaiaCollaboration16a] DR1 [@GaiaCollaboration16] sources present within the images, retrieved automatically 