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R. J. Rand؛ S. R. Kulkarni؛ J. J. Hester (1992). "Warm ionized gas in the edge-on galaxies NGC 4565 and NGC 4631". Astrophysical Journal. ج. 396: 97–103. Bibcode:1992ApJ...396...97R. DOI:10.1086/171699.