Free Access
Issue
A&A
Volume 578, June 2015
Article Number A41
Number of page(s) 19
Section Interstellar and circumstellar matter
DOI https://doi.org/10.1051/0004-6361/201525881
Published online 01 June 2015

Online material

Appendix A: Comments on the selected positions

(0′′, 0′′). The position of HD 37903. Probably a blend of two PDRs, although they are too close together in velocity to separated. South of HD 37903 the high-J CO lines split into two components, but at the position of the star they are close to the cloud velocity. [C ii] is much broader and it was with two velocity components. [C ii] also shows a red-shifted wing. This red-shifted emission extends toward SW and is roughly coincident with the somewhat blue-shifted ridge of CO emission curving out toward HD 37903.

(30′′, +15′′). This is the position where [C ii] peaks, Tmb ~ 80 K. It is close to and probably associated with the bright fluorescent H2 ridge Field et al. (1998) call the Seahorse. Two velocity components were fitted to all observed lines, one close to the systemic velocity of the molecular cloud, 10.5 km s-1, and one which is blue-shifted, 9.19.4 km s-1 ( Table 2).

(13′′,79′′). This position is centered on the southern ridge (SR), one of the most extensively modeled PDRs in NGC 2023. It is, however, a difficult position to model, because it coincides with the blue outflow lobe from Sellgren C (Sandell et al., in prep.) and the [C ii] line and high-J CO lines show two velocity components: one blue-shifted, and one red-shifted. The SR is definitely associated with the red-shifted velocity component (Vlsr ~ 10.7 km s-1), because north-south cuts through the SR show that this velocity component coincides with the SR. The SR also stands out in the high-J CO channel maps, most prominently in the channel centered on 11 km s-1, see Figs. 6, B.3, and B.4. It is still seen even in CO(43), but not as clearly (Fig. B.2). The good agreement in velocity between [C ii] and CO(11−10) emission suggest that the [C ii] emission originates from the dense PDR. The blue-shifted emission component has a systemic velocity of 10 km s-1, and almost certainly corresponds to a PDR on the front side of the C ii region. This PDR is less dense than the SR, and not detected in CO(11−10). Although it is clearly seen in CO(76) and CO(65) it is hard to reliably estimate how much of the emission is associated with the PDR, since both lines are affected by the blue outflow lobe from Sellgren C. The [C ii] line is more blue-shifted than the CO lines and may include low density gas from the C ii region. Therefore only the PDR component directly associated with the PDR is modeled. It is likely that the intensity of the high-J CO transitions is somewhat underestimated since our observations are centered on the ridge and the emission only fills about half the beam. However, since our PDR modeling only use line ratios, the error from ignoring beam filling is relatively minor.

(53′′,13′′) and (23′′,60′′). The position (53′′, 13′′) coincides with the peak of CO(11−10) emission peak as well as with the C91α clump no. 3 (Wyrowski et al. 2000), while (53′′, 13′′) is approximately centered on the C91α clump no. 2. No attempt was made to model the C91α clump no.1, because the CO emission is contaminated by the strong red-shifted outflow from Sellgren D. For both positions strong [C ii] emission is seen at about the same velocity as C91α, but at (23′′, 60′′) the [C ii] line is much broader, 2.5 km s-1 vs. 0.8 km s-1 for the C91α emission line, probably because more of the extended

emission associated with the ridge is included and because [C ii] is not very sensitive to the density of the emitting gas. A relatively strong blue-shifted [C ii] emission feature is also seen at both positions without any counterpart in high-J CO emission.

(45′′,45′′) and (60′′,60′′). These two positions probe the strong PDR ridge southeast of HD 37903. A “long” integration spectrum in [C ii] and CO(11−10) was obtained on (45′′, 45′′), which is close to the peak position in CO(11−10). The position (60′′, 60′′) coincides with the peak in low-J CO lines. Both positions show emission from two blended PDR components in [C ii] (Fig. 10, Table 2). At (45′′, 45′′) the red-shifted component dominates the emission in both [C ii] and CO(11−10). The second component is close to the cloud velocity. Here [C ii] shows a strong blue-shifted wing making it difficult to separate the emission from the PDR from the low density [C ii] inside the C ii region, although PDR modeling was done for both components. At (60′′,60′′) our high-J CO spectra only show emission from the PDR on the backside of the C ii region. The blue-shifted [C ii] component is almost certainly dominated by lower density gas inside the nebula. Here only the red-shifted PDR component is modeled. The (60′′,60′′) position was also observed by Jaffe et al. (1990) in CO(76) with a 34′′-beam. Their results agree well with our findings.

(50′′, +53′′). This position is close to the symmetry axis in the northwestern part of the nebula. All lines, except 13CO(32) show double split lines. This is not due to self-absorption, since there is no foreground gas that could absorb the CO(76) and CO(65) emission. At CO(43) the emission from the backside of the nebula is probably affected by self-absorption near the cloud velocity, making the emission somewhat more red-shifted than the higher J transitions. The PDR modeling therefore only uses the CO(76) and CO(65) transitions and both PDRs are modeled separately.

(+17′′, +113′′). This position coincides with the northern 13CO(32) peak and close to the crossing H2 filaments, which Field et al. (1998) called the “triangle” (located at 16′′, +129′′). Here all the lines show only one velocity component at the cloud velocity (Table 2). The triangle was observed by Takami et al. (2000) in several H2 emission lines in the near-IR with a Fabry-Perot spectrometer providing spectral resolution, R, of 5002200. This position is also close to the position (+33′′, +105′′) observed by (Burton et al. 1998), who obtained spectra from 12.5 μm, at 230430 spectral resolution.

Appendix B: CO channel maps

Figures B.1 to B.3 show the channel maps of CO(32), CO(43), CO(65), and CO(76). The fields of view of the CO(65) (Fig. B.3) and CO(76) (Fig. B.4) channel maps were restricted to the southeastern and central part of the nebula, in order to visualize the strong CO emission from the PDR better. Figures B.5 and B.6 show the channel maps for CO(65) and CO(76) but smoothed to the 16.̋1 resolution of the [C ii] data in order to capture the fainter emission in the northwestern part of the map better.

thumbnail Fig. B.1

Velocity-channel map for CO(32) with contours at 2, 5, 10 to 80 K in steps of 10 K. The “+” shows the position of HD 37903.

Open with DEXTER

thumbnail Fig. B.2

Velocity-channel map for CO(43) with contours at 2, 5, 10 to 110 K in steps of 10 K. The “+” shows the position of HD 37903.

Open with DEXTER

thumbnail Fig. B.3

Velocity-channel map for CO(65) showing the southeastern and central part of the map with full resolution. The contour levels start at 10 K and go to 100 K in steps of 10 K. The “+” shows the position of HD 37903.

Open with DEXTER

thumbnail Fig. B.4

Velocity-channel map for CO(76) showing the southeastern and central part of the map with full resolution. The contour levels are at 15 K, and from 20 K to 100 K in steps of 10 K. The “+” shows the position of HD 37903.

Open with DEXTER

thumbnail Fig. B.5

Velocity-channel map for CO(65) smoothed to 16.̋1 resolution showing the whole area that was mapped. The contour levels go from 8 K to 80 K in steps of 8 K. The “+” shows the position of HD 37903.

Open with DEXTER

thumbnail Fig. B.6

Velocity-channel map for CO(76) smoothed to 16.̋1 resolution showing the whole area that was mapped. The contour levels go from 6.3 K to 63 K in steps of 6.3 K. The “+” shows the position of HD 37903.

Open with DEXTER


© ESO, 2015

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.