Ices in Young Embedded Disks

Ices in embedded protostellar disks provide one of the earliest observable records of the volatile material available for planet formation, but their interpretation is complicated by the surrounding infalling envelope. In particular, it remains unclear whether infrared ice absorption features observed toward highly inclined Class 0/I systems primarily trace disk ices or envelope ices. We investigate this question using RADMC-3D radiative transfer models of parameterized disk+envelope structures. We introduce three cases for each model to separate the intrinsic disk-ice signal from the effects of envelope scattering and thermal emission, as well as envelope ice absorption. We find that the H$_2$O 3 $\mu$m and CO$_2$ 4.3 $\mu$m bands are strongly affected by the envelope because they lie in a scattering-dominated wavelength regime. In contrast, the CO$_2$ 15.2 $\mu$m band is dominated by more direct thermal emission and remains a more robust tracer of disk ices across most parameter variations. Other ice features in between show behavior that reflect their absorption and scattering opacities at their respective wavelengths. Disk contribution ratios in the observed ice optical depths are the highest for the extracted spectra from the disk center, and decrease as one moves farther away in each direction. Surprisingly, apertures located outside the disk show signatures from the ices in the disk, showcasing the impact of scattering. We confirm that $\sim70^\circ$ is the critical angle for the best view of ices in the disk for short wavelength features. Moreover, our results show that the inferred disk contribution depends strongly on envelope infall rate, disk mass, size and vertical extent. Higher envelope infall rate results in higher envelope contribution, bringing disk contribution to almost non-existent at ^{-5} M_\odot{\rm yr}^{-1}$ for the scattering-dominated bands, while for the 15 $\mu$m feature disk contribution still stays significant. Meanwhile, higher disk mass does not necessarily result in higher disk contribution to the ice absorption features. Grain size distribution, especially in the envelope, may also significantly alter the contribution ratios since they are an important factor in determining absorption and scattering opacities. We then proceed to reveal the ice inventory in the ‘Butterfly Star’ IRAS04302, and reveal spatial distribution of its ice features with an empirical approach before performing detailed radiative transfer modeling.