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Table 1 of McClure-Griffiths et al. (2013), which presents a catalog of H i clouds, contains an error in the properties of one of the clouds. The Australia Telescope Compact Array (ATCA) 21 cm H i spectrum toward the cloud G1.4−1.8+87 at its cataloged position of ℓ = 1
38 b = −177 and vLSR = 87 km s−1 is shown in Figure 1. Superimposed on the broad emission feature centered around 87 km s−1 is a 2.3 K spike of emission in a single 0.82 km s−1 channel. The software used to extract cloud properties from the data mistakenly fitted a Gaussian to this single channel and reported a cloud with a peak brightness temperature of 4.3 K and a line FWHM of 1 km s−1. Given that adjacent pixels in the datacube do not show a similarly narrow peak, and that the spectrum contains other single-channel fluctuations of this magnitude, it is quite unlikely that the "spike" is real.
Figure 1. H i spectrum toward the originally cataloged position for the cloud G1.4−1.8+87 showing the single noise spike at vLSR = 87 km s−1 and a better fit (shown in red), with an amplitude of Tb = 1.5 K and a FWHM of 19.1 km s−1.
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| Name | l | b | VLSR | Peak Tb | Δv | NH max | Mc | r |
|---|---|---|---|---|---|---|---|---|
| (deg) | (deg) | (km s−1) | (K) | (km s−1) | (×1019 cm−2) | (M☉) | (pc) | |
| G0.2+3.8+65 | 0.23 | 3.81 | 63.7 | 4.4 | 5.9 | 5.7 | 25 | 6.6 |
| G0.2−1.6−170 | 0.27 | −1.62 | −169.6 | 4.9 | 17.5 | 17.6 | 2190 | 32.9 |
| G0.3+2.8+195 | 0.30 | 2.84 | 200.8 | 1.4 | 28.6 | 9.7 | 220 | 12.2 |
| G0.3+3.7−82 | 0.36 | 3.74 | −74.3 | 3.7 | 13.7 | 11.1 | 706 | 22.4 |
| G0.7+4.5+61 | 0.68 | 4.52 | 63.3 | 9.6 | 5.3 | 10.8 | 287 | 14.2 |
Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available.
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We have re-examined the ATCA datacube and determined a new, more robust, peak position. We have extracted spectra from the newly derived peak position. The spectrum toward the new peak position is shown in Figure 2 and is representative of spectra from adjacent pixels. The noise fluctuations in this spectrum are typical for the datacube. We have fit a Gaussian to the new spectrum and derive new properties for the cloud: ℓ = 138, b = −179, Tpk = 2.2 K, FWHM = 14.7 km s−1, VLSR = 86.5 km s−1. The values for the peak column density, NH, and the mass, M, are unchanged from the published values with peak NH i = 2.05 × 1019 cm−2 and M = 17 M⊙.
Figure 2. H i spectrum toward the newly derived peak position at ℓ = 134, b = −181 with a representative fit (shown in red) with a peak Tb = 2.25 K with FWHM of 14.7 km s−1.
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We have corrected the entry for G1.4−1.8+87 in the data Table 1and provide the correct, full table electronically. We regret the error.