First detections of CO absorption in the Magellanic Clouds and direct measurement of the CO-to-H2 ratio

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Table C.1.

CO and H₂ measurements towards LMC and SMC sightlines.

Star	log N(HI)^a	v_LSR	log N(H₂)^b	log N(CO)^c	log N(CI)^d	instrument	comment
	[cm⁻²]	km s⁻¹	[cm⁻²]	[cm⁻²]	[cm⁻²]
LMC
SK −67 2	21.00	254	$20 . 46_{- 0.46}^{+ 0.15}$ $20.46^{+0.15}_{-0.46}$	< 15.0	$13 . 89_{- 0.09}^{+ 0.02}$ $13.89^{+0.02}_{-0.09}$	STIS
		263	$20 . 40_{- 0.20}^{+ 0.14}$ $20.40^{+0.14}_{-0.20}$	$15 . 42_{- 0.28}^{+ 0.35}$ $15.42^{+0.35}_{-0.28}$	$14 . 32_{- 0.04}^{+ 0.04}$ $14.32^{+0.04}_{-0.04}$	STIS	CH, CH⁺, CN (Welty et al. 2006)
SK −68 137	21.50	255	$20 . 31_{- 0.32}^{+ 0.05}$ $20.31^{+0.05}_{-0.32}$	< 13.7	$14 . 29_{- 0.02}^{+ 0.02} c$ $14.29^{+0.02}_{-0.02}$ ^c	COS
		281	$20 . 53_{- 0.11}^{+ 0.05}$ $20.53^{+0.05}_{-0.11}$	$14 . 88_{- 0.19}^{+ 0.33}$ $14.88^{+0.33}_{-0.19}$	$16 . 2_{- 0.3}^{+ 0.6} c, e$ $16.2^{+0.6}_{-0.3}$ ^c,e	COS
SK −67 5	21.00	278	$19 . 47_{- 0.01}^{+ 0.01}$ $19.47^{+0.01}_{-0.01}$	< 12.9	$14 . 02_{- 0.02}^{+ 0.02}$ $14.02^{+0.02}_{-0.02}$	STIS	André et al. (2004)
SK −68 135	21.46	262	$19 . 99_{- 0.01}^{+ 0.01}$ $19.99^{+0.01}_{-0.01}$	< 13.2	$14 . 43_{- 0.03}^{+ 0.04}$ $14.43^{+0.04}_{-0.03}$	STIS	André et al. (2004), CH, CH⁺ (Welty et al. 2006)
SK −69 246	21.47	267	$19 . 76_{- 0.01}^{+ 0.01}$ $19.76^{+0.01}_{-0.01}$	< 13.0	$14 . 18_{- 0.03}^{+ 0.04}$ $14.18^{+0.04}_{-0.03}$	STIS	Bluhm & de Boer (2001), André et al. (2004),
							CH, CH⁺ (Welty et al. 2006)
SK −68 52	21.30	229	$19 . 51_{- 0.01}^{+ 0.01}$ $19.51^{+0.01}_{-0.01}$	< 13.0	$14 . 07_{- 0.04}^{+ 0.04}$ $14.07^{+0.04}_{-0.04}$	STIS	CH, CH⁺ (Welty et al. 2006)
SK −68 73	21.66	279	$20 . 24_{- 0.01}^{+ 0.01}$ $20.24^{+0.01}_{-0.01}$	< 13.0	$14 . 59_{- 0.03}^{+ 0.06}$ $14.59^{+0.06}_{-0.03}$	COS+STIS	CH, CH⁺ (Welty et al. 2006)
SK −68 129	21.72	259	$20 . 53_{- 0.03}^{+ 0.07}$ $20.53^{+0.07}_{-0.03}$	< 12.6	$14 . 05_{- 0.01}^{+ 0.01}$ $14.05^{+0.01}_{-0.01}$	COS
SK −68 140	21.47	261	$20 . 40_{- 0.03}^{+ 0.03}$ $20.40^{+0.03}_{-0.03}$	< 13.2	$14 . 12_{- 0.01}^{+ 0.01}$ $14.12^{+0.01}_{-0.01}$	COS
SK −68 155	21.44	279	$20 . 02_{- 0.05}^{+ 0.03}$ $20.02^{+0.03}_{-0.05}$	< 12.9	$14 . 00_{- 0.01}^{+ 0.01}$ $14.00^{+0.01}_{-0.01}$	COS
SK −69 279	21.59	262	$20 . 54_{- 0.03}^{+ 0.01}$ $20.54^{+0.01}_{-0.03}$	< 12.8	$13 . 96_{- 0.20}^{+ 0.43}$ $13.96^{+0.43}_{-0.20}$	COS
SK −70 79	21.26	220	$20 . 38_{- 0.01}^{+ 0.01}$ $20.38^{+0.01}_{-0.01}$	< 13.5	$14 . 31_{- 0.01}^{+ 0.01}$ $14.31^{+0.01}_{-0.01}$	STIS
SK −70 115	21.13	208	$19 . 97_{- 0.01}^{+ 0.01}$ $19.97^{+0.01}_{-0.01}$	< 12.6	$13 . 91_{- 0.01}^{+ 0.01}$ $13.91^{+0.01}_{-0.01}$	STIS(H+M)	CH, CH⁺ (Welty et al. 2006)
SK −71 46	–	227	$20 . 32_{- 0.04}^{+ 0.03}$ $20.32^{+0.03}_{-0.04}$	< 13.2	$14 . 09_{- 0.04}^{+ 0.04}$ $14.09^{+0.04}_{-0.04}$	COS
SK −71 50	21.18	262	$19 . 47_{- 0.04}^{+ 0.03}$ $19.47^{+0.03}_{-0.04}$	< 12.7	$13 . 77_{- 0.03}^{+ 0.03}$ $13.77^{+0.03}_{-0.03}$	STIS
BI 184	21.12	239	$19 . 89_{- 0.02}^{+ 0.01}$ $19.89^{+0.01}_{-0.02}$	< 12.6	$13 . 92_{- 0.03}^{+ 0.04}$ $13.92^{+0.04}_{-0.03}$	COS
BI 237	21.62	276	$20 . 20_{- 0.01}^{+ 0.01}$ $20.20^{+0.01}_{-0.01}$	< 13.0	$13 . 74_{- 0.02}^{+ 0.03}$ $13.74^{+0.03}_{-0.02}$	COS
BI 253	21.67	260	$20 . 01_{- 0.01}^{+ 0.01}$ $20.01^{+0.01}_{-0.01}$	< 13.0	$14 . 00_{- 0.03}^{+ 0.02}$ $14.00^{+0.02}_{-0.03}$	COS

SMC

SK 143	21.00	124	$20 . 93_{- 0.09}^{+ 0.09} f$ $20.93^{+0.09}_{-0.09}$ ^f	$16 . 85_{- 0.02}^{+ 0.02}$ $16.85^{+0.02}_{-0.02}$	$14 . 93_{- 0.06}^{+ 0.06} c$ $14.93^{+0.06}_{-0.06}$ ^c	STIS(H)+COS	CH, CN, C₂, C₃ (Welty et al. 2013)
AV 16	–	117	$20 . 33_{- 0.06}^{+ 0.07}$ $20.33^{+0.07}_{-0.06}$	< 13.3	$13 . 86_{- 0.05}^{+ 0.04} c$ $13.86^{+0.04}_{-0.05}$ ^c	STIS
AV 18	22.04	139	$20 . 46_{- 0.02}^{+ 0.03}$ $20.46^{+0.03}_{-0.02}$	< 12.7	$13 . 42_{- 0.03}^{+ 0.03} c$ $13.42^{+0.03}_{-0.03}$ ^c	STIS
AV 26	21.70	116	$20 . 70_{- 0.01}^{+ 0.02}$ $20.70^{+0.02}_{-0.01}$	< 13.3	$15 . 15_{- 0.10}^{+ 0.12}$ $15.15^{+0.12}_{-0.10}$	STIS(H+M)	CH (Welty et al. 2006)
AV 80	21.81	110	$20 . 24_{- 0.01}^{+ 0.01}$ $20.24^{+0.01}_{-0.01}$	< 12.6	$13 . 61_{- 0.03}^{+ 0.03}$ $13.61^{+0.03}_{-0.03}$	STIS
AV 170	21.14	118	$19 . 73_{- 0.01}^{+ 0.01}$ $19.73^{+0.01}_{-0.01}$	< 12.7	$13 . 41_{- 0.06}^{+ 0.06}$ $13.41^{+0.06}_{-0.06}$	STIS
AV 175	–	137	$20 . 05_{- 0.09}^{+ 0.10}$ $20.05^{+0.10}_{-0.09}$	< 12.9	$13 . 20_{- 0.09}^{+ 0.05}$ $13.20^{+0.05}_{-0.09}$	COS
AV 207	21.43	153	$19 . 52_{- 0.04}^{+ 0.02}$ $19.52^{+0.02}_{-0.04}$	< 13.2	$13 . 59_{- 0.03}^{+ 0.03}$ $13.59^{+0.03}_{-0.03}$	COS
AV 215	21.86	123	$19 . 52_{- 0.05}^{+ 0.06}$ $19.52^{+0.06}_{-0.05}$	< 12.9	$13 . 79_{- 0.12}^{+ 0.14}$ $13.79^{+0.14}_{-0.12}$	STIS
AV 266	–	119	$19 . 81_{- 0.02}^{+ 0.01}$ $19.81^{+0.01}_{-0.02}$	< 12.9	$13 . 48_{- 0.11}^{+ 0.12}$ $13.48^{+0.12}_{-0.11}$	STIS
AV 304	21.48	114	$19 . 55_{- 0.03}^{+ 0.03}$ $19.55^{+0.03}_{-0.03}$	< 12.6	$13 . 47_{- 0.03}^{+ 0.04} c$ $13.47^{+0.04}_{-0.03}$ ^c	COS
AV 435	21.54	176	$19 . 92_{- 0.01}^{+ 0.01}$ $19.92^{+0.01}_{-0.01}$	< 12.7	$13 . 29_{- 0.04}^{+ 0.05} c$ $13.29^{+0.05}_{-0.04}$ ^c	COS
AV 472	–	119	$20 . 38_{- 0.01}^{+ 0.01}$ $20.38^{+0.01}_{-0.01}$	< 12.8	$13 . 7_{- 0.4}^{+ 0.5} c$ $13.7^{+0.5}_{-0.4}$ ^c	COS
AV 476	21.85	160	$20 . 84_{- 0.05}^{+ 0.03}$ $20.84^{+0.03}_{-0.05}$	< 12.9	$14 . 62_{- 0.11}^{+ 0.12}$ $14.62^{+0.12}_{-0.11}$	COS	CH, CH⁺ (Welty et al. 2006)
AV 490	21.46	125	$19 . 88_{- 0.01}^{+ 0.01}$ $19.88^{+0.01}_{-0.01}$	< 12.5	$13 . 63_{- 0.01}^{+ 0.01}$ $13.63^{+0.01}_{-0.01}$	STIS
SK 191	21.51	145	$20 . 78_{- 0.03}^{+ 0.02}$ $20.78^{+0.02}_{-0.03}$	< 12.9	$13 . 77_{- 0.02}^{+ 0.03}$ $13.77^{+0.03}_{-0.02}$	STIS+COS

References. aWelty et al. (2012), Roman-Duval et al. (2019); b Kosenko & Balashev (2023, unless specified otherwise); c This work; d Kosenko et al. (2024, unless specified otherwise); eThe line profiles are saturated in COS spectrum, and therefore we propose considering this value with caution. fCartledge et al. (2005);

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