Inner disc and circumplanetary material in the PDS 70 system

TL;DR

This study uses archival ALMA data to detect and analyze circumplanetary material around PDS 70 c and possibly PDS 70 b, providing insights into ongoing planet formation and dust properties in the system.

Contribution

It presents the first detection of compact dust emission around PDS 70 c across multiple epochs and assesses its variability and dust characteristics, advancing understanding of circumplanetary environments.

Findings

Detected dust emission around PDS 70 c with >3.8σ significance.

Tentative detection of emission near PDS 70 b at ~3σ.

No significant flux variability observed in the inner disc.

Abstract

The two giant protoplanets directly imaged in the dust-depleted cavity of PDS 70 offer a unique opportunity to study ongoing planet formation. Both planets have been detected in infrared thermal emission and in H$\alpha$, indicating active accretion. We calibrate and analyse archival ALMA Band 6 and 7 observations of PDS 70 from 2019, 2021, and 2023 to search for circumplanetary material and assess its motion. Using 2D visibility modelling of the high-resolution (~0.11"x0.08" in Band 6; ~0.05"x0.05" in Band 7) dust continuum from the outer disc, we subtract the model and image the cavity at multiple epochs. We re-detect compact dust emission around PDS 70 c in all datasets with >$3.8\sigma$ significance, and tentatively detect emission near PDS 70 b at ~$3\sigma$ in Band 6, with peak fluxes of $59\pm17\mu$Jy/beam and $46\pm14\mu$Jy/beam. The relative astrometry of the compact emission around PDS 70 c is consistent with the expected position of the planet between 2019-2023. We find a peak flux difference up to $64\pm34\mu$Jy/beam at 1$\sigma$, but Bayesian analysis indicates no significant variability. We detect no flux variability in the inner disc. The inferred dust mass near PDS 70 c and in the inner disc ranges from $0.008$-$0.063 M_\oplus$ and $0.04$-$0.31 M_\oplus$, respectively, consistent with prior estimates. Finally, we measure Band 6-7 spectral indices of $2.5\pm1.2$ (PDS 70 c) and $3.2\pm0.5$ (inner disc), suggesting that the inner disc emission is dominated by optically thin dust.