Protoplanetary disk masses in NGC 2024: Evidence for two populations

Abstract

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′× 2.9′ mosaic centered on NGC 2024 FIR 3 was observed at 225 GHz with a resolution of 0.25″, or ~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 ± 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 ± 7%. In the western population, towards IRS 1, only 15 ± 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.

Ionization: a possible explanation for the difference of mean disk sizes in star-forming regions

“…In agreement with this trend, the dust mass of Class II disks is about five times lower than the dust mass of Class I objects in Ophiuchus, as shown by Williams et al (2019), who compared the results of the sample of fainter (and generally more evolved star-disk systems) with the previous sample of brighter disks (Cieza et al 2019). Similarly, the dust masses in the ∼1 Myr old Orion Molecular Cloud 2 (OMC-2) are similar to the dust masses measured for Lupus and Taurus, which have similar ages (van Terwisga et al 2019). This correlation of decreasing dust mass with increasing age is consistent with the theory of a radial drift of dust grains in gaseous disks (Whipple 1972;Weidenschilling 1977;Birnstiel et al 2010).…”

Bridging the gap between protoplanetary and debris disks: separate evolution of millimeter and micrometer-sized dust

“…These regions include O/B stars and are thus subject to strong UV field radiation (Briceño et al 2005(Briceño et al , 2007Dahm & Hillenbrand 2007;Walter et al 2008;Bouy et al 2009). The disk fraction has been observed to decrease close to the central OB stars in Orion, Cygnus OB2, and NGC 2024 (Mann et al 2014;Guarcello et al 2016;van Terwisga et al 2020). Additionally, ALMA observations of protoplanetary disks in σ Ori by Ansdell et al (2017) demonstrate that disk dust masses also decrease the closer the YSOs are to the central O9 star; this has also been similarly demonstrated by Eisner et al (2018) with the disk flux emission of Orion objects as a function of distance to θ 1 Ori C, an O6 and B0 binary.…”

The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars V. A Characterization of Protostellar Multiplicity

“…This source was detected in the VLA data toward HOPS-384 presented in Paper I, but it was not identified as a multiple system there because its nature was uncertain, and there were no ALMA data covering that region in our survey. An ALMA survey of the region by van Terwisga et al (2020) associated the continuum at 1.3 mm emission with NGC 2024 FIR3, which was classified as a Class 0 system by Ren & Li (2016) with a bolometric luminosity of 220 L . Given the association with a bonafide protostar system, we include this detection in our multiplicity statistics with a separation of 1.…”

“…Given the association with a bonafide protostar system, we include this detection in our multiplicity statistics with a separation of 1. 46 (∼586 au) and show the ALMA 1.3 mm image from van Terwisga et al (2020) and the VLA images in Figure 5. While we zoom-in more closely on the source, the wider field image from van Terwisga et al (2020) shows significant extended structure associated with the envelope.…”

“…46 (∼586 au) and show the ALMA 1.3 mm image from van Terwisga et al (2020) and the VLA images in Figure 5. While we zoom-in more closely on the source, the wider field image from van Terwisga et al (2020) shows significant extended structure associated with the envelope.…”