Green’s Dictionary of Slang

to go away, to leave; usu. as imper. jow! go away! be off!

1864, 1867, 1870		Hotten Sl. Dict. 163: JOW, be off, be gone immediately. If the word jehanum be added, it forms a peremptory order to go to the place unmentionable to ears polite [...] Anglo-Indian.
1873		Sl. Dict.
1891		A. Day Mysterious Beggar 249: You young gully-fluff! You can’t play this racket on me. I’ll make things fake: I’ll jow in time!
1981		(con. 1920s) P. Crosbie Your Dinner’s Poured Out! 220: jow off buzz off.
1987		L. Redmond Emerald Square 132: The biggest of them was shouting at me. ‘Jow off!’.