Spatially correlated stellar accretion in the Lupus star forming region: Evidence for ongoing infall from the interstellar medium

Abstract

Growing evidence suggests that protoplanetary discs may be influenced by late stage infall from the interstellar medium (ISM). It remains unclear the degree to which infall shapes disc populations at ages $\gtrsim 1$~Myr. We explore possible spatial correlations between stellar accretion rates in the Lupus star forming region, which would support the hypothesis that infall can regulate stellar accretion. We consider both the `clustered' stars towards the center of Lupus 3, and the `distributed' stars that are more sparsely distributed across the Lupus complex. We take the observed accretion rates in the literature and explore spatial correlations. In particular, we test whether the clustered stars exhibit a radial gradient in normalised accretion rates, and whether the distributed stars have spatially correlated accretion rates. We find statistically significant correlations for both the clustered and distributed samples. The clustered sample exhibits higher accretion rates in the central region, consistent with the expected Bondi-Hoyle-Lyttleton accretion rate. Stars that are spatially closer among the distributed population also exhibit more similar accretion rates. These results cannot be explained by the stellar mass distribution for either sample. Age gradients are disfavoured, though not discounted, because normalised disc dust masses are not spatially correlated across the region. Spatially correlated stellar accretion rates within the Lupus star forming region argue in favour of an environmental influence on stellar accretion, possibly combined with internal processes in the inner disc. Refined age measurements and searches for evidence of infalling material are potential ways to further test this finding.