Volume 542, June 2012
|Number of page(s)||27|
|Section||Interstellar and circumstellar matter|
|Published online||25 May 2012|
Below we comment briefly on the eight bubble regions in our sample. The masses and temperatures quoted are those of the β = 2.0 trial.
We find a total associated mass for Sh 104 of ~4000 M⊙, which is in the middle of the range for the H II regions investigated here. This calculated mass is two-thirds that found in Deharveng et al. (2003) using molecular gas tracers. As mentioned previously, the interior of Sh 104 has more emission at all wavelengths than the other regions in the sample. Roughly 30% of the total FIR emission from the region comes from the interior region. We hypothesize that this is a result of Sh 104 being nearly complete – some of the radiation that would otherwise escape is trapped within the bubble.
In Fig. 1, there is a clear difference in temperature between Sh 104 itself and the local ambient medium. We find that its PDR is well-characterized by temperatures of 25 K. Local filaments are for the most part ~20 K, although “N. Filament 1” and “N. Filament 5” appear to be significantly colder at 15 K and 17 K respectively. The temperature map of Sh 104 (Fig. 4) is relatively smooth but there is a trend for hotter temperatures toward the southwest, and colder temperatures toward the north-west. The warmest region in the field is the separate H II region at (ℓ,b) = (73.790, +0.572). It has a mean dust temperature of 28 K and a total associated mass of ~400 M⊙. The other source found along the PDR, “CS” has a mass of ~100 M⊙.
The column density map in Fig. 6 shows the highest values, up to 1022 cm-2, along the PDR. Local filaments have mean column densities of >1021 cm-2. There are a number of prominent filaments that begin on the border of Sh 104 and lead radially away; these are prominent in the column density map.
The most surprising aspect of W5-E found here is that its dust temperatures vary little across the field. Figure 1 shows a narrow range of Herschel colors, which leads to relatively small variations in dust temperature. The dust temperature of the entire region is 24 K. The coldest regions of the field are to the east (“E. Filament 1” and “E. Filament 2”) and north (“N. Filament 1” and “N. Filament 2”) – they are between 16 and 18 K. There are other cold locations along the PDR, most notably behind the ionization front in “N. PDR 1” (BRC13) and “E. PDR 1 (BRC14)”. The total associated mass of W5-E, ~8000 M⊙, places it as the second most massive in the sample; it is the largest region in the sample in terms of physical diameter.
There are three other H II regions in the field of W5-E. With the exception of the separate H II region on the border of in RCW 79, these are the most massive secondary H II regions in our sample. The bipolar H II region Sh 201 at (ℓ,b) = (138.481, +1.637) is the hottest location in the field at 27 K and stands out clearly in Fig. 4. Its total associated mass is ~800 M⊙. The other H II regions on the eastern border are ~25 K; they have total associated masses of ~600 M⊙.
W5-E is unique in our sample in that it displays a number of features obviously affected by the impinging stellar radiation. These features are discussed in detail in Deharveng et al. (2012). The bright-rimmed clouds BRC12 and BRC13, which harbor embedded sources, have mean temperatures of 24 K and 22 K, respectively, while the dust associated with the embedded sources has a temperature of ~22 K. The embedded sources are conspicious in the temperature map (Fig. 4) as higher temperature regions within cold temperature clumps. The pillars detected with Spitzer seen to the southwest are also cool and have an average temperature of ~20 K. Many of these pillars have embedded stars forming at their “tips” detected by Herschel. This is consistent with a scenario where the majority of the pillar is shielded from impinging ratiation and is thus able to maintain the cold temperatures necessary for subsequent star formation.
The temperature map of Sh 241 in Fig. 4 shows relatively little variation across the field. The large high-temperature region to the north is probably not real as it is a region of very low intensity emission. The bubble H II region itself is 23 K. The prominant separate compact H II region is slightly warmer, 25 K while filaments average ~17 K. The total mass for Sh 241 is ~2000 M⊙ while that of the compact H II region is ~300 M⊙. Sh 241 is ringed by a region of cold emission to the north of temperature ~18 K. This region has a higher than average column density, >1021.5 cm-2. The colder emission appears to be part of a large filament running East-West that also contains another H II region and what appears to be cold protostars.
As a whole, RCW 71 is the warmest region in our sample at 30 K. RCW 71 is also the least massive region in the sample, with a total associated mass of just ~200 M⊙. This low mass estimate may be due to an inaccurate distance. As mentioned in Sect. 2, the kinematic and spectroscopic distances for this source do not agree. We note, however, that the PDR of RCW 71 has only marginally higher column density values than the background (Fig. 6), and therefore the low associated mass estimate may be real.
The temperature map of RCW 71 in Fig. 4 shows high temperatures in the PDR up to ~ 35 K (in apertures “E. PDR 1” and “E. PDR 2”). Material has accumulated into cold massive filaments most prominently to the east, but also to the west. The coldest of these, “N. Filament” has a temperature of 13 K – it is one of the coldest regions in the sample. The field of RCW 71 also has one of the coldest point sources, “S. PS 1”. It has a temperature of 15 K.
RCW 79 has a total associated mass of ~10 000 M⊙, which makes it the most massive in our sample. This mass does not include the secondary PDRs to the south, which are themselves ~3000 M⊙ combined. Our mass estimates are considerably higher than that of Zavagno et al. (2006), who found 2000 M⊙ for the entire region using 1.2 mm observations. Their observations, however, may not have been sensitive to the more diffuse emission detected by Herschel. The column density map in Fig. 6 has values in the PDR of up to ~1022.5 cm-2 and looks very similar to the 1.2 mm maps in Zavagno et al. (2006). Along the south-eastern border there is another H II region that has a total associated mass of ~2000 M⊙. This is the most massive secondary H II region in our sample – it is significantly more massive than RCW 71 and approximately the same mass as RCW 120.
RCW 79 is interesting in that there is significant patches of cold material ringing the PDR to the south and to the west. These colder areas are apparent in Fig. 4. The coldest objects in the field, the “N. Filament” and the “E. Filament” are 22 K and 24 K, respectively. There is ongoing star formation in the field. Within “E. Filament” there are two compact objects and there are compact sources detected in the “S. PDR” aperture.
Like RCW 71, the PDR of RCW 82 is filamentary, but its temperature of 25 K is cooler than that of RCW 71. The total associated mass of RCW 82 is ~3000 M⊙. This is significantly less than what was found by Pomarès et al. (2009) from CO observations. The temperature in the field of RCW 82 seen in Fig. 4 shows little variation. To the west, RCW 82 has what appears to be a second PDR (“W. PDR 2”). The IRDCs seen in the field range from ~20 K for “N. Filament” to <15 K for “E. Filemant 2”. As for Sh 104, there are a number of cool filaments leading radially away from RCW 82; these have column density values of ~1021.5 cm-2. The eastern PDR of RCW 82 has a number of cold locations. These are evident in the colors seen in Fig. 2, and also in the temperature map in Fig. 4.
G332.5−0.1 is angularly small and located along a prominent IRDC. The total associated mass of G332.5 − 0.1 is ~4000 M⊙ which is on the higher end of the range of H II regions masses studied here. The IRDC itself has a temperature of up to ~20 K, which is warmer than other IRDCs here studied. Indeed, as seen in Fig. 4, the IRDC is not well-separated in temperature from the surrounding region. The column density distribution (Fig. 6) shows the IRDC prominently – it has column density values of ~1022 cm-2.
Within the IRDC there are two prominent condensations: “W. PS” and “E. PS”. These condensations have masses of ~1000 M⊙. The PDR has massive condensations to the north, south, and east. The northern condensation contains an H II region, with a total associated mass of of ~600 M⊙. This location is the hottest in the field, 29 K.
The wide range of colors seen Fig. 1 indicates that RCW 120 also has a large range of dust temperatures, compared to the other
H II regions in the sample. RCW 120 has the largest concentration of IRDCs in its surroundings of any object in our sample. These IRDCs are the coldest objects found in our analysis, averaging 13 K. The largest of the IRDCs, “E. IRDC”, has a mass of ~500 M⊙ and has numerous protostars detected within it. This IRDC has a temperature derived from aperture photometry of 16 K. This temperature is almost certainly affected by the numerous embedded protostars which have not been removed when calculating temperatures. The temperature map (Fig. 4) shows temperatures of ≤15 K for quiescent parts of the cloud where there are no detected protostars. There are two large protostars detected in the “E. IRDC” aperture that are visible in the temperature map – they have temperatures of ~18 K.
A point source is detected within Condensation 1 at 70 μm and 100 μm (Zavagno et al. 2010) for which we find a total associated mass of ~300 M⊙. The entire condensation has a mass of ~800 M⊙. It is easily the most massive condensation in the field. In fact, it’s mass is one third that of the total associated mass for the RCW 120 region, which is only ~2000 M⊙. Using the same 870 μm APEX-LABOCA data used here, Deharveng et al. (2009) calculated a mass for the source within Condensation 1 of 140−250 M⊙ and a mass for the entire condensation of 460−800 M⊙; the range of values comes from estimates of the dust temperature from 30 K to 20 K.
The column density map of RCW 120 (Fig. 6) highlights the numerous filamentary structures. These are prominent in the source, but are also detected leading away from the “E. IRDC” region. The PDR and the local IRDCs have roughly the same value of NH ~ 1022 cm-2.
Anderson et al. (2010) found that for RCW 120, the ionization front appears “patchy” and that there are numerous locations where hot dust is detected beyond the ionization front. They hypothesized that these locations represent holes in the PDR where radiation may escape and heat the ambient medium. Such radiation may cause an increase in pressure which would aid in collapsing existing pre-stellar clumps. We confirm their results here; the same three warmer locations can again be identified beyond the ionization front of RCW 120. It is interesting, however, that RCW 120 remains the clearest example of this phenomenon. This may be due to its proximity to the Sun.
© ESO, 2012
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