Context : Protoplanetary disks in dense , massive star-forming regions are strongly affected by their environment .
How this environmental impact changes over time is an important constraint on disk evolution and external photoevaporation models .

Aims : We characterize the dust emission from 179 disks in the core of the young ( 0.5 Myr ) NGC 2024 cluster .
By studying how the disk mass varies within the cluster , and comparing these disks to those in other regions , we aim to determine how external photoevaporation influences disk properties over time .

Methods : Using the Atacama Large Millimeter/submillimeter Array , a 2.9 ^ { \prime } \times 2.9 ^ { \prime } mosaic centered on NGC 2024 FIR 3 was observed at 225 GHz with a resolution of 0.25 ^ { \prime \prime } , or \sim 100 AU .
The imaged region contains 179 disks identified at IR wavelengths , seven new disk candidates , and several protostars .

Results : The overall detection rate of disks is 32 \pm 4 \% .
Few of the disks are resolved , with the exception of a giant ( R = 300 AU ) transition disk .
Serendipitously , we observe a millimeter flare from an X-ray bright young stellar object ( YSO ) , and resolve continuum emission from a Class 0 YSO in the FIR 3 core .
Two distinct disk populations are present : a more massive one in the east , along the dense molecular ridge hosting the FIR 1-5 YSOs , with a detection rate of 45 \pm 7 \% .
In the western population , towards IRS 1 , only 15 \pm 4 \% of disks are detected .

Conclusions : NGC 2024 hosts two distinct disk populations .
Disks along the dense molecular ridge are young ( 0.2–0.5 Myr ) and partly shielded from the far ultraviolet radiation of IRS 2b ; their masses are similar to isolated 1–3 Myr old SFRs .
The western population is older and at lower extinctions , and may be affected by external photoevaporation from both IRS 1 and IRS 2b .
However , it is possible these disks had lower masses to begin with .