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The Astronomical Journal, 143:97 (8pp), 2012 April

Allen et al.

Figure 3. 21 cm H i profiles in the survey area. Brightness temperature (TB ) and LSR velocity scales are given in the panel at the lower left corner.

mosaic of H i profiles is shown in Figure 3. As we have asserted earlier, the spatial and velocity extent of the 1667 MHz OH emission is very similar to that of the 21 cm H i emission.
3.1.1. A detailed comparison of OH and H i profiles

A more detailed comparison of a typical OH velocity profile with the corresponding H i profile structure is made in Figure 4, which shows the 21 cm H i profile obtained from the Leiden/Argentine/Bonn (LAB) survey (Kalberla et al. 2005)8 and plotted at a greatly reduced scale on our most sensitive OH 1667 profile constructed from the average of all observations at l = 107 5, b = +4 8. This OH profile provides an . . important check on the sensitivity and repeatability of our survey, and it is described in more detail in the Appendix. The noise level in the OH profile of Figure 4 is 3 mK (in TB units); the


The Astronomical Journal, 143:97 (8pp), 2012 April

Allen et al.

Figure 2. Mosaic of OH profiles recorded by our survey. Antenna temperature (TA ) and LSR velocity scales are given in the panel at the lower left corner. The grid of profiles is oriented in Galactic longitude and latitude, and centered at l = 107 5,b = 4 8. The grid separation is 30 , which is closely equal to the telescope beam . . FWHM. The velocity resolution in this plot has been smoothed to 1 km s-1 for comparison with the H i profiles in Figure 3.

shown here is typically 3 hr after the removal of scans deemed to be of insufficient quality. The signal peaks are generally about TA 20­40 mK, and the noise levels in these final profiles as established from the baseline fits vary from 3 to 5 mK in TA units. The central pixel at offset (0,0) was observed more often (total 10.0 hr) as a check on system performance; the noise level on this profile is 2.0 mK (see the Appendix for further discussion of this profile). One of the most striking results of our survey is the ubiquity of the OH emission. As can be seen from Figure 2, significant OH profiles were recorded at all survey positions, and roughly with the same levels of intensity. This may at first sight seem

3.1. Correspondence of OH with H i The spatial and velocity extents of the OH profiles in our survey resemble those of the H i. In order to illustrate this point we have constructed H i profiles at each position of our survey using data from the "Atlas of Galactic Neutral Hydrogen" (Hartmann et al. 1997). This Atlas collects the spectra of the Leiden/Dwingeloo H i survey that was carried out using a 25 m telescope. The angular resolution of that telescope at 21 cm is also 30 , matching closely with our OH observations, so no additional spatial smoothing was applied. The full velocity range of the H i survey covers from -450 to +400 km s-1 ,
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Instituto de Astrofґ isica de Andalucґ P.O. Box 3004, E-18080 Granada, Spain; mrm@iaa.es ia, 3 Onsala Space Observatory, Onsala, SE-439 92, Sweden; John.Black@chalmers.se SKA, Cape Town; SKA - SA, The Park, Park Road, Pinelands 7405, South Africa; roy@hartrao.ac.za Received 2012 November 1; published 2013 February 14

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An error has been discovered in the production of Figures 6 and 7 in the published article. Owing to a misunderstanding on our part concerning the operation of the software we used to smooth and resample the archival CfA data, the 12 CO(1­0) profiles shown in these two figures are not correct. The corrected versions of Figures 6 and 7 and their respective captions are shown below. The conclusions of our paper remain unchanged. We are grateful to Dr. Thomas Dame for calling our attention to discrepancies in the original version of Figure 6, and for providing a properly smoothed and sampled set of 12 CO(1­0) profile data in units of the "main beam brightness" scale Tmb (brightness units corrected for lthe main.beam efficiency),Jwhich we have used to correct the figures. A len et. al (2013}, Astron. ., 145: 85

Figure 6.

12

CO(1­0) profiles in the survey area. Main beam brightness temperature Tmb and LSR velocity scales are given in the panel at the lower left corner.

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