Are infrared dark clouds really quiescent? | Astronomy & Astrophysics (A&A)

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Table 8

CO depletion, HNC/HCN ratio, lower limit of ionization, and velocity asymmetric degree of H¹³CO⁺ in four IRDCs.

Source

D_GC ^a

I_{0.87 mm}

T_g

N_H₂

D_CO ^b

x(e) ^e

δ V_H¹³CO⁺ ^f

(^o)

(kpc)

(Jy/beam)

(K)

10²² (cm^-2)

C¹⁸O

¹³CO

C¹⁷O

(10^-7)

G28.34 S

28.324

0.067

4.6

0.77 ± 0.10

13.23 ± 0.17

15.22 ± 2.19

13.71 ± 6.51

14.54 ± 2.55

1.56 ± 0.77

1.10

−0.51 ± 0.01

IRDC 18530

35.431

0.137

4.5

0.56 ± 0.07

17.12 ± 0.21

36.47 ± 5.24

19.54 ± 6.83

−

0.64 ± 0.22

3.66

−0.19 ± 0.002

IRDC 18306

23.296

0.056

3.6

0.48 ± 0.12

19.10 ± 0.48

49.81 ± 13.46

21.52 ± 6.51

41.20 ± 11.87

− ^d

6.89

0.30 ± 0.02

IRDC 18308

23.251

0.017

4.4

0.36 ± 0.07

6.12 ± 1.20

19.45 ± 4.31

12.16 ± 4.69

24.04 ± 7.03

− ^d

0.51

0.0009 ± 0.005

Notes.

^(a)

Assuming the galactocentric distance of the Sun is 8 kpc.

^(b)

Estimated from C¹⁸O and optical depth corrected ¹³CO with Eqs. (B.2)–(B.4).

^(c)

Measured with the optical depth corrected HNC and hyperfine fitted HCN at the same gas temperature T_ex,CO.

^(d)

The value is not given because of large uncertainties in HCN abundance, see Table A.4.

^(e)

Lower limit is measured from Eq. (17), with hyperfine fitted N₂H⁺, the optical depth corrected ¹³CO, and H¹³CO⁺ at the same gas temperature T_ex,CO.

^(f)

δV_H¹³CO⁺ = (V_HCO⁺−V_H¹³CO⁺)/Δυ_H¹³CO⁺, Mardones et al. (1997).

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