A MALT90 study of the chemical properties of massive clumps and filaments of infrared dark clouds

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Volume 562 (February 2014)

A&A, 562 (2014) A3

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Issue		A&A Volume 562, February 2014


Article Number		A3
Number of page(s)		42
Section		Interstellar and circumstellar matter
DOI		https://doi.org/10.1051/0004-6361/201322596
Published online		29 January 2014

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Appendix A: Kinematic distances and physical properties of the clumps

The kinematic distances of the clumps listed in Col. (4) of Table 1 are based on the Galactic rotation curve model by Reid et al. (2009). As the sources are associated with IRDCs, it is assumed that they lie at a near distance in which case there is more IR background radiation against which to see the source in absorption. The clump distances were adopted from Paper I with the following exception. In Paper I, for the first quadrant field G1.87 we had radial velocity data only towards a filamentary cloud near the field centre (see Figs. 1 and 5 in Paper I). As discussed in Paper I, the negative radial velocity of the cloud (~−41 km s^-1) suggests that it lies at a far distance. The far distance solution (~10.6 kpc) was therefore adopted for all the clumps in the field. In the present paper, we used the MALT90 N₂H⁺(1−0) radial velocity data to determine the G1.87 clump distances. As a high-density gas tracer, N₂H⁺ is expected to be well-suited for this purpose. Moreover, N₂H⁺(1−0) was detected towards all sources in the present study. The radial velocities of the clumps were typically found to be ~40−50 km s^-1 (i.e. positive rather than negative), and the corresponding near kinematic distances were derived to be ~7 kpc as shown in Table 1. We note that the near-far kinematic distance ambiguity towards G13.22−SMM 29 (IRAS 18117-1738) was resolved by Sewilo et al. (2004). This source was placed at the far distance because H₂CO absorption was seen between the source velocity and the velocity at the tangent point.

The clump effective radii listed in Table 1 correspond to the kinematic distances explained above. The rest of the physical properties of the clumps listed in Table 1 were revised from those presented in Paper I by making the following modifications. The masses and densities of the clumps were previously calculated by assuming that the dust-to-gas mass ratio is 1/100. However, this value refers to the canonical dust-to-hydrogen mass ratio, M_dust/M_H (e.g. Draine 2011; Table 23.1 therein). Assuming that the clumps’ chemical composition is similar to the solar mixture, i.e. the mass fractions for hydrogen, helium, and heavier elements are X = 0.71, Y = 0.27, and Z = 0.02, respectively, the ratio of total mass (H+He+metals) to hydrogen mass is 1/X ≃ 1.41. The total dust-to-gas mass ratio is therefore M_dust/M_gas = M_dust/(1.41M_H) = 1/141. For the assumed gas composition, the mean molecular weight per H₂ molecule, needed in the calculation of the column and number densities, is μ_H₂ ≃ 2.82 (Kauffmann et al. 2008; Appendix A.1 therein). As explained in Paper I, the dust temperature was assumed to be T_dust = 15 K for IR-dark clumps, and 20 K for clumps associated with Spitzer IR emission. For G2.11−SMM 5 and G13.22−SMM 29, which are associated with IRAS sources, the dust colour temperatures were derived to be 30 and 18.9 K, respectively (Paper I). For G13.22−SMM 32, which is associated with an H ii region, we adopted the value¹⁰T_dust = 30 K. Finally, the dust opacity per unit dust mass at 870 μm was taken to be κ₈₇₀ = 1.38 cm² g^-1, the value interpolated from the widely used Ossenkopf & Henning (1994) model describing graphite-silicate dust grains that have coagulated and accreted thin ice mantles over a period of 10⁵ yr at a gas density of 10⁵ cm^-3.

Appendix B: Maps of spectral-line emission

The integrated intensity maps of the detected spectral lines are presented in Figs. B.1−B.14. In each panel, the line emission is shown as contours overlaid on the Spitzer 8 μm image.

Fig. B.1

Contour maps of integrated intensity of the MALT90 lines detected towards G1.87−SMM 1. In each panel, the contours are overlaid on the arcsinh-scaled Spitzer 8 μm image (cf. Fig. 1). The contour levels start at 3σ for H¹³CO⁺, SiO, HN¹³C, C₂H, CH₃CN, and ¹³CS. For HNCO(4_0, 4 − 3_0, 3), HCN, HCO⁺, HNC, HC₃N, and N₂H⁺, the contours start at 26σ, 23σ, 20σ, 30σ, 6σ, and 15σ, respectively. In all cases, the contours go in steps of 3σ. The average 1σ value in T_MB units is ~ 0.69 K km s^-1. The red plus sign marks the LABOCA 870 μm peak position of the clump. A scale bar indicating the 1 pc projected length is indicated. The line emission is extended in many cases, and the HCN, HCO⁺, and HNC emissions are well correlated with each other. The N₂H⁺ emission also shows some resemblance to these species. The spatial distributions of HNCO and HC₃N appear to be similar to each other, while weak CH₃CN emission traces reasonably well the 8 μm absorption feature.

	Fig. C.2 Same as Fig. C.1 but towards G1.87−SMM 8.
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	Fig. C.3 Same as Fig. C.1 but towards G1.87−SMM 10.
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	Fig. C.4 Same as Fig. C.1 but towards G1.87−SMM 12. We note that the velocity range for the SiO and C₂H spectra is wider for illustrative purposes. The vertical red line marks the radial velocity of the optically thin HC₃N line.
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	Fig. C.5 Same as Fig. C.1 but towards G1.87−SMM 14. We note that the velocity range for the SiO and C₂H spectra is wider for illustrative purposes. The vertical red line marks the radial velocity of the optically thin HC₃N line.
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	Fig. C.6 Same as Fig. C.1 but towards G1.87−SMM 15. The vertical red line indicates the radial velocity of the optically thin HNCO line.
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	Fig. C.7 Same as Fig. C.1 but towards G1.87−SMM 16. In some of the spectra, the velocity range shown is wider for illustrative purposes. The vertical red line mark the velocity of the HNCO line.
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	Fig. C.8 Same as Fig. C.1 but towards G1.87−SMM 20.
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	Fig. C.9 Same as Fig. C.1 but towards G1.87−SMM 21. The vertical red line indicates the radial velocity of the HNCO line.
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	Fig. C.10 Same as Fig. C.1 but towards G1.87−SMM 23. We note that the velocity range for the HCN and HCO⁺ spectra is wider for illustrative purposes. The vertical red line indicates the radial velocity of the optically thin HC₃N line.
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	Fig. C.11 Same as Fig. C.1 but towards G1.87−SMM 24. The vertical red line indicates the radial velocity of the HNCO line.
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	Fig. C.12 Same as Fig. C.1 but towards G1.87−SMM 27. The velocity range shown is wider for the C₂H and HCO⁺ spectra. The vertical red line indicates the radial velocity of the optically thin HNCO line.
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	Fig. C.13 Same as Fig. C.1 but towards G1.87−SMM 28. The velocity range shown is wider for the C₂H spectrum. The vertical red line indicates the radial velocity of the optically thin HNCO line.
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	Fig. C.14 Same as Fig. C.1 but towards G1.87−SMM 30. The vertical red line indicates the radial velocity of the optically thin HC₃N line.
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	Fig. C.15 Same as Fig. C.1 but towards G1.87−SMM 31. The velocity range is wider for the HCN spectrum. The vertical red line indicates the radial velocity of the optically thin HNCO line.
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	Fig. C.16 Same as Fig. C.1 but towards G1.87−SMM 38.
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	Fig. C.17 Same as Fig. C.1 but towards G2.11−SMM 5. A wider velocity range for the HCO⁺ spectrum is shown because of the additional velocity component.
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	Fig. C.18 Same as Fig. C.1 but towards G11.36−SMM 1.
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	Fig. C.19 Same as Fig. C.1 but towards G11.36−SMM 2.
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	Fig. C.20 Same as Fig. C.1 but towards G11.36−SMM 3.
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	Fig. C.21 Same as Fig. C.1 but towards G11.36−SMM 4.
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Online material

Appendix A: Kinematic distances and physical properties of the clumps

Appendix B: Maps of spectral-line emission

Appendix C: Spectra

	Fig. C.22 Same as Fig. C.1 but towards G11.36−SMM 5.
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	Fig. C.23 Same as Fig. C.1 but towards G11.36−SMM 6.
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	Fig. C.24 Same as Fig. C.1 but towards G11.36−SMM 7.
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	Fig. C.25 Same as Fig. C.1 but towards G13.22−SMM 4. There is an additional velocity component in the HCO⁺ spectrum.
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	Fig. C.26 Same as Fig. C.1 but towards G13.22−SMM 5. The velocity range is wider for the two C₂H spectra.
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	Fig. C.27 Same as Fig. C.1 but towards G13.22−SMM 6.
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	Fig. C.28 Same as Fig. C.1 but towards G13.22−SMM 7. The C₂H spectrum has a wider velocity range. Two velocity components are seen in the HCO⁺ and HNC spectra.
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	Fig. C.29 Same as Fig. C.1 but towards G13.22−SMM 11. Two velocity components are seen in the HCO⁺ and HNC spectra.
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	Fig. C.30 Same as Fig. C.1 but towards G13.22−SMM 23. Three velocity components are seen in the HCO⁺ spectrum, while two are visible in the HNC spectrum.
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	Fig. C.31 Same as Fig. C.1 but towards G13.22−SMM 27. The velocity range in the C₂H spectrum is wider.
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