$\textbf{AdS}_3$ vacua and surface defects in massive IIA

We summarize the results and the ideas in 1707.06152, 1707.06154, 1807.07768 where new warped $\mathrm{AdS}_3$ backgrounds are derived in massive IIA string theory by uplifting exact solutions in $\mathcal N=1$, $d=7$ and $\mathcal N=(1,1)$, $d=6$ gauged supergravities. These solutions are respectively asymptotically $\mathrm{AdS}_7$ and $\mathrm{AdS}_6$ and they are related to the D2-D4-NS5-D6-D8 brane intersection. We provide a particular supergravity solution in 10d describing this bound state and we discuss the relations between its near-horizon geometry and the uplifts from 6d and 7d. Then we give the holographic interpretation of these $\mathrm{AdS}_3$ warped backgrounds in terms of $\mathcal N=(0,4)$ defect $\mathrm{SCFT}_2$ within the $\mathcal N=(1,0)$ $\mathrm{SCFT}_6$ and the $\mathcal N=2$ $\mathrm{SCFT}_5$.