Science with an ngVLA: Tracing the Water Snowline in Protoplanetary disks with the ngVLA

TL;DR

The paper discusses how the ngVLA telescope can trace the water snowline in protoplanetary disks by detecting changes in dust properties and using ammonia as a proxy, crucial for understanding planet formation.

Contribution

It demonstrates the ngVLA's capability to map the water snowline through continuum spectral index changes and ammonia snowline detection, advancing planet formation studies.

Findings

Sharp spectral index transitions can be detected in bright disks.

NH3 snowline detection is challenging but feasible under certain conditions.

ngVLA is uniquely capable of studying water snowline evolution in disks.

Abstract

The water snowline in protoplanetary disks is one of the most pivotal locations for planet formation: it sets a critical boundary of chemical composition in the disk and likely serves as a favorable site of planetesimal growth and planet formation. However, the water snowline at the mid-plane cannot be directly traced by water line observations as the dust emission around the water snowline is highly optically thick at these line frequencies. Alternatively, the water snowline maybe traced through the sharp changes in physical properties (surface density and dust size distribution) at this transition or through the snowlines of other molecules that sublimate co-spatially with water. In this chapter, we discuss the ngVLA's capability of tracing the mid-plane water snowline through mapping sharp transitions in the continuum spectral index caused by changes of dust size distributions and by using the NH3 snowline as a proxy. We found that with the current design of the ngVLA ability, a sharp transition in spectral index across the water snowline can be readily traced in relatively bright disks. A detection of the NH3 snowline is challenging under the current design, but may still be possible if the NH3-to-water abundance in the disk is close to that of the ISM ices. In summary, the proposed ngVLA is the only facility can provide sufficient sensitivity and spatial resolution to trace the evolution of water snowline at the disk mid-plane and to reveal its role in accelerating the planetesimal formation and in building the architecture of planetary systems.