Ultraviolet absorption observations of intermediate-velocity cloud gas detected towards the M 15 globular cluster

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Table 4

Predicted and observed high ion column density ratios for different ionization models.

Ionization method	Ion ratio	Predicted ratio	g1 cloud	M5-HVC¹	Complex M-HVC²

Radiative cooling^a.....	N(CIV)/N(SiIV)	8.7–33.0	3.9 ± 1.5	4.2 ± 0.7	<1.0
	N(CIV)/N(NV)	0.9–2.7	>10.5	>3.3	<1.05
	N(CIV)/N(OVI)	0–0.2	0.83 ± 0.37	>2.1	<0.35

Conductive interface^b.....	N(CIV/N(SiIV)	5.5–30.9	3.9 ± 1.5	4.2 ± 0.7	<1.0
	N(CIV)/N(NV)	0.8–2.6	>10.5	>3.3	<1.05
	N(CIV)/N(OVI)	0.1–0.9	0.83 ± 0.37	>2.1	<0.35

Turbulent mixing layers^c.....	N(CIV/N(SiIV)	0.9–28.8	3.9 ± 1.5	4.2 ± 0.7	<1.0
(non-equilibrium ionization)	N(CIV)/N(NV)	7.4–29.5	>10.5	>3.3	<1.05
	N(CIV)/N(OVI)	1.1–7.4	0.83 ± 0.37	>2.1	<0.35

Shock ionization^d.....	N(CIV/N(SiIV)	1.3–33.0	3.9 ± 1.5	4.2 ± 0.7	<1.0
	N(CIV)/N(NV)	0.7–38.6	>10.5	>3.3	1.0
	N(CIV)/N(OVI)	0–1.1	0.83 ± 0.37	>2.1	<0.35

Halo SNR^e.....	N(CIV/N(SiIV)	–	3.9 ± 1.5	4.2 ± 0.7	<1.0
	N(CIV)/N(NV)	1.8–9.0	>10.5	>3.3	1.0
	N(CIV)/N(OVI)	0.1–3.0	0.83 ± 0.37	>2.1	<0.35

Notes. 1 = –142 km s^-1 HVC towards M5 (Zech et al. 2008), 2 = –131 km s^-1 Complex M HVC towards Mrk 421 (Yao et al. 2011).

= Edgar and Chevalier (1986),

= Borkowski et al. (1990),

= Slavin et al. (1993),

= Dopita and Sutherland (1996),

= Shelton (1998).

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