Determine whether present-day dust alignment preserves a fossil transient-irradiation signature

Determine whether the alignment of interstellar and molecular-cloud dust grains is driven primarily by the present-day interstellar radiation field or instead preserves a fossil imprint of stronger irradiation from past transient events, such as nearby supernovae.

Background

The paper argues that transient irradiation can produce long-lived memory effects: fast alignment may persist after the transient fades, while RAT-driven disruption can permanently modify the grain-size distribution on observational timescales. Consequently, present-day polarization may encode the history of earlier, more intense radiation rather than responding only to the current radiation field.

The authors propose comparing the radiation strength required to produce the observed alignment, denoted by U_align, with the present radiation strength inferred from the dust temperature, U_current. A substantial discrepancy, particularly U_align much greater than U_current, could indicate that the alignment was established during an earlier transient episode. The paper does not resolve whether observed interstellar dust alignment generally has this fossil origin or is instead produced by the current interstellar radiation field.