A compound which is represented by a formula (IIa), wherein each of Y1 to Y8 independently represents a chemical single bond, —O—, —S—, —O—C(═O)—, —C(═O)—O—, —O—C(═O)—O—, —NR1—C(═O)—, —C(═O)—NR1—, —O—C(═O)—NR1—, —NR1—C(═O)—O—, —NR1—C(═O)—NR1—, —O—NR1—, or —NR1—O—, R1 represents a hydrogen atom or an alkyl group; each of G1 and G2 independently represents a divalent linear aliphatic group; each of Z1 and Z2 independently represents an alkenyl group; Ax represents a group represented by a formula (II), wherein X represents —NR2—, an oxygen atom, a sulfur atom, and R2 represents a hydrogen atom or an alkyl group; D represents an alkylene group or a cycloalkanediyl group; A1 represents a trivalent aromatic group; each of A2 and A3 independently represents a divalent alicyclic hydrocarbon group; each of A4 and A5 independently represents a divalent aromatic group; Q1 represents a hydrogen atom, or an alkyl group.