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

We summarize the results and the ideas in 1707.06152, 1707.06154, 1807.07768 where new warped ${\mathrm{A}\mathrm{d}\mathrm{S}}_3$ 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 ${\mathrm{A}\mathrm{d}\mathrm{S}}_7$ and ${\mathrm{A}\mathrm{d}\mathrm{S}}_6$ 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 ${\mathrm{A}\mathrm{d}\mathrm{S}}_3$ warped backgrounds in terms of $\mathcal{N}=(0,4)$ defect ${\mathrm{S}\mathrm{C}\mathrm{F}\mathrm{T}}_2$ within the $\mathcal N=(1,0)$ ${\mathrm{S}\mathrm{C}\mathrm{F}\mathrm{T}}_6$ and the $\mathcal{N}=2$ ${\mathrm{S}\mathrm{C}\mathrm{F}\mathrm{T}}_5$.