Objection 1. It would seem that an aureole is due to the angels. For Jerome (Serm. de Assump. [Ep. ad Paul. et Eustoch. ix]) speaking of virginity says: "To live without the flesh while living in the flesh is to live as an angel rather than as a man": and a gloss on 1 Corinthians 7:26, "For the present necessity," says that "virginity is the portion of the angels." Since then an aureole corresponds to virginity, it would seem due to the angels.
Objection 2. Further, incorruption of the spirit is more excellent than incorruption of the flesh. Now there is incorruption of spirit in the angels, since they never sinned. Therefore an aureole is due to them rather than to men incorrupt in the flesh and who have sinned at some time.
Objection 3. Further, an aureole is due to teaching. Now angels teach us by cleansing, enlightening, and perfecting [Cf. I, 111, 1] us, as Dionysius says (Hier. Eccles. vi). Therefore at least the aureole of doctors is due to them.
On the contrary, It is written (2 Timothy 2:5): "He... shall not be [Vulgate: 'is not'] crowned, except he strive lawfully." But there is no conflict in the angels. Therefore an aureole is not due to them.
Further, an aureole is not due to an act that is not performed through the body: wherefore it is not due to lovers of virginity, martyrdom or teaching, if they do not practice them outwardly. But angels are incorporeal spirits. Therefore they have no aureole.
I answer that, An aureole is not due to the angels. The reason of this is that an aureole, properly speaking, corresponds to some perfection of surpassing merit. Now those things which make for perfect merit in man are connatural to angels, or belong to their state in general, or to their essential reward. Wherefore the angels have not an aureole in the same sense as an aureole is due to men.
Reply to Objection 1. Virginity is said to be an angelic life, in so far as virgins imitate by grace what angels have by nature. For it is not owing to a virtue that angels abstain altogether from pleasures of the flesh, since they are incapable of such pleasures.
Reply to Objection 2. Perpetual incorruption of the spirit in the angels merits their essential reward: because it is necessary for their salvation, since in them recovery is impossible after they have fallen [Cf. I, 64, 2].
Reply to Objection 3. The acts whereby the angels teach us belong to their glory and their common state: wherefore they do not merit an aureole thereby.
Source: Summa Theologica (New Advent)