"Murder is the unlawful killing of a human being with malice aforethought." ( 187, subd. (a).) A defendant who commits an intentional and unlawful killing but who lacks malice is guilty of . . . voluntary manslaughter. ( 192.)' Generally, the intent to unlawfully kill constitutes malice. 'But a defendant who intentionally and unlawfully kills lacks malice . . . in limited, explicitly defined circumstances: either when the defendant acts in a "sudden quarrel or heat of passion" ( 192, subd. (a)), or when the defendant kills in "unreasonable self-defense"--the unreasonable but good faith belief in having to act in self-defense.' Because heat of passion and unreasonable self-defense reduce an intentional, unlawful killing from murder to voluntary manslaughter by negating the element of malice that otherwise inheres in such a homicide, voluntary manslaughter of these two forms is considered a lesser necessarily included offense of intentional murder." (People v. Breverman (1998) 19 Cal. 4th 142, 153-154 [77 Cal. Rptr. 2d 870, 960 P.2d 1094], italics in original; People v. Barton (1995) 12 Cal. 4th 186, 199 [47 Cal. Rptr. 2d 569, 906 P.2d 531]; see also People v. Ochoa (1998) 19 Cal. 4th 353, 422 [79 Cal. Rptr. 2d 408, 966 P.2d 442]; People v. Coad (1986) 181 Cal. App. 3d 1094, 1106 [226 Cal. Rptr. 386].)