Emergence of streamers in simulations of late infall

TL;DR

The paper investigates how late infall from the environment can create streamer-like structures feeding Class II protoplanetary disks. It uses 3D hydrodynamic simulations with FARGO3D and RADMC3D post-processing to compare two scenarios: a single cloudlet encounter and a disk moving through a turbulent ISM, generating synthetic CO and scattered-light observables. The results show that cloudlet-driven streamers are bright but short-lived, while turbulence-driven accretion can produce multiple arced streamers and straight BHL tails depending on v_sys and σ_turb, potentially making streamers a common, long-lived feature in dense environments. This work highlights the sensitivity of streamer morphology to environmental conditions and suggests that observed inflows can constrain local cloud properties and inform theories of disk evolution and planet formation.

Abstract

Growing observational evidence suggests that Class II protoplanetary disks may undergo substantial interactions with their environment in the form of late infall. This mass inflow predominantly manifests itself in the form of so-called streamers: filaments and arcs of gas connecting large-scale, extended gas structures to disk scales. Prevalent late infall has far-reaching consequences for planet formation theory, challenging the long-standing treatment of evolved disks in isolation. In this work, we investigate the emergence of late-infall streamers in different formation scenarios, their morphology and multiplicity, as well as their dependence on environmental conditions. We conduct this investigation by performing 3D hydrodynamical simulation using the grid-based code FARGO3D, which we post-process to obtain synthetic observations using the Monte Carlo radiative transfer code RADMC3D. We find that, while a late infall event in the form of a single encounter with a "cloudlet" of gas can produce a streamer via an interplay between the fallback of bound material and shocks, such features dissipate quickly, on a timescale of ~10 kyr. Furthermore, we find that streamers can also form naturally in a turbulent, dense environment without the need for such encounters, which could act to reconcile short-lived streamers with ubiquitous detection of these structures. Here, we find multiple co-existing streamers for a disk velocity relative to the interstellar medium of $v_\mathrm{sys}=0.5~\mathrm{km}~\mathrm{s}^{-1}$ and a turbulent velocity dispersion of $σ_\mathrm{turb}=0.5~\mathrm{km}~\mathrm{s}^{-1}$. We find considerable dependence of the streamer morphology on the environment, which may act as a utility to constrain the physical conditions of the gas surrounding planet-forming disk, and therefore the conditions under which planets form.

Figures (14)

• Figure 1: Gas column density of the cloudlet encounter simulation, for six different points in time. The perspective is face-on. The white arrows show the velocity streamlines, computed as a mass-weighted average along the line of sight. The color scale was chosen to highlight low-density features, thereby saturating the protoplanetary disk.
• Figure 2: Polarized scattered light ($\lambda=1.245µm$) intensity at $t=17.07k$ for the cloudlet encounter simulation. The inclination of the camera is $i=40°$. The white arrow represents the original orbital velocity of the cloudlet, and the white dashed line is the 0.1m″ contour line.
• Figure 3: Synthetic CO line emission (J 2-1) at $t=17.07k$ for the cloudlet encounter simulation. The left panel shows the moment 1 map, with the gray dashed line showing the $600m\jansky\per″\squared km\per s$ moment 0 contour. The right panel shows the peak brightness temperature on a square root scale. The gray and white arrows represent the initial orbital velocity of the cloudlet. The white dashed line in the right panel represents the $T_\mathrm{b,peak}=20K$ contour line.
• Figure 4: Absolute value of the angular momentum flux through a spherical shell with radius $R_\mathrm{bound}$ as a function of time. The differently colored lines denote different simulations from Table \ref{['tab:bh_params']}. Unless stated otherwise, the shown simulations have $v_\mathrm{sys}=0.5km\per s$ and $k_\mathrm{min}=2\pi/50\astronomicalunit$. The round markers show the physical time of the snapshot used for the synthetic observations. The cross markers show the physical time of the snapshots used for the time series in Fig. \ref{['fig:b_0.5_0.5_d2_t']}.
• Figure 5: Orientation of the non-systemic momentum flux through a spherical shell with radius $R_\mathrm{bound}$ as a function of time. The differently colored lines denote different simulations from Table \ref{['tab:bh_params']}. Unless stated otherwise, the shown simulations have $v_\mathrm{sys}=0.5km\per s$ and $k_\mathrm{min}=2\pi/50\astronomicalunit$. The round markers show the physical time of the snapshot used for the synthetic observations. The cross markers show the physical time of the snapshots used for the time series in Fig. \ref{['fig:b_0.5_0.5_d2_t']}. The left panel shows the azimuthal angle $\theta$, and the right panel shows the polar angle $\phi$.