[1] P. Baird, Harmonic maps with symmetry, harmonic morphism and deformations of matrics, Research Notes in Mathematics, 87, Pitman (Advanced Publishing Program), Boston, MA, 1983.
[2] P. Baird and S. Gudmundsson, p-harmonic maps and minimal submanifolds, Math. Ann., 294 (1992) 611–624.
[3] P. Baird and J. C. Wood, Harmonic morphisms between Riemannian manifolds, London Mathematical Society Monographs. New Series, 29, The Clarendon Press, Oxford University Press, Oxford, 2003.
[4] M. P. Do Carmo and J. Flaherty Francis, Riemannian geometry, 6, Springer, 1992.
[5] B. Fuglede, Harmonic morphisms between Riemannian manifolds, Ann. Inst. Fourier (Grenoble), 28 (1978) 107–144.
[6] E. Ghandour and Y.-L. Ou, Generalized harmonic morphisms and horizontally weakly conformal biharmonic maps, J. Math. Anal. Appl., 464 (2018) 924–938.
[7] A. Kasue and T. Washio, Growth of equivariant harmonic maps and harmonic morphisms, Osaka J. Math., 27 (1990) 899–928.
[8] J. M. Lee, Introduction to smooth manifolds, Second edition. Graduate Texts in Mathematics, 218, Springer, New York, 2013.
[9] B. O’neill, Semi-Riemannian geometry with applications to relativity, Pure and Applied Mathematics, 103, Academic Press, Inc. [Harcourt Brace Jovanovich, Publishers], New York, 1983.
[10] G. Yun, Harmonicity of horizontally conformal maps and spectrum of the laplacian, Int. J. Math. Math. Sci., 30 (2002) 709–715.
)