# Radiative torques of irregular grains: Describing the alignment of a grain ensemble

## TL;DR

This paper investigates how irregular grain shapes affect radiative torque alignment efficiency, confirming the importance of superparamagnetic inclusions and refining theoretical predictions for grain alignment in astrophysics.

## Contribution

It provides a detailed analysis of the distribution of RAT components for various grain shapes and confirms the RAT efficiency scaling law, enhancing the predictive power of grain alignment models.

## Key findings

- Distribution of RAT amplitude ratios varies with grain shape
- RAT efficiency scales as (λ/a)^-3 for λ≫a
- Superparamagnetic inclusions are essential for high alignment

## Abstract

The radiative torque (RAT) mechanism is the most promising way of explaining observed polarization arising from aligned grains. We explore the efficiency of the grain alignment by an anisotropic radiation flow for an extensive ensemble of grain shapes. We calculate the distribution of the ratios of the amplitudes of the two major components of the RATs, that is an essential parameter that enters the theory of RAT alignment in Lazarian & Hoang (2007, LH07). While this distribution is different for different classes of grain shapes that we considered, the most probable values of the parameter are centered in the range of $q^{max}\sim 0.5-1.5$. The functional form from RATs calculated is in good agreement with the analytical model (AMO). We find that the RAT efficiency scales as $(\lambda/a)^{-3}$ for $\lambda\gg a$ as previously found in LH07. This increases the power of predictions obtained with the RAT theory. We also confirm that superparamagnetic inclusions are necessary in achieving high degrees of alignment, and constrain the parameter space describing the requirements for achieving these alignment degrees.