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Astron. Astrophys. 357, 637-650 (2000)

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3. Images

Images of the 450 and 850µm emission surrounding the five UCHII regions are shown in Fig. 1. Detailed descriptions of each source, and what is known about them from other wavelengths, are given below.

3.1. G10.47

The G10.47+0.03 HII region containing the UCHII regions G10.47+0.03 A, B and C is coincident with the strong submm emission peak in the centre of the map and has been extensively observed at radio wavelengths (Garay et al. 1993b,c; WC89; Becker et al. 1994). G10.47+0.03A is marked with a cross in Fig. 1. This region shows OH, CH3OH and H2O maser emission (Caswell et al. 1995a,b,c,d; Caswell et al. 1993; Hofner & Churchwell 1996; Palagi et al. 1993; Braz & Epchtein 1983; Zheng & Ling 1997), and a hot, dense molecular core where many species have been detected (Garay et al. 1993a; Cesaroni et al. 1992, 1994a,b, 1998; Plume et al. 1992; Gensheimer et al. 1996;; Olmi et al. 1993, 1996a,b; Shepherd & Churchwell 1996; Hatchell et al. 1998a,b,c; 1999; Nummelin et al. 1998; Wyrowski et al. 1999). The large scale CO distribution was mapped by Scoville et al. (1987). Hoare et al. (1991) observed and modelled the submm emission from this source.

The southwestern peak lies towards the east section of the HII region G10.46+0.03 (the lowest cross on Fig. 1), close to G10.46+0.03A (Garay et al. 1993b; Becker et al. 1994; Zoonematkermani et al. 1990; Handa et al. 1987), and corresponds to the IRAS 18056-1952 position and a third NH3 peak (Garay et al. 1993a; Cesaroni et al. 1998). This region has also been extensively studied in molecular lines and also has hot molecular core characteristics (Wouterloot et al. 1993; Bronfman et al. 1996; Shepherd & Churchwell 1996) and associated CH3OH, OH and H2O masers (Cohen et al. 1991; Kalenskij et al. 1992; Palagi et al. 1993; Walsh et al. 1997; Zheng & Ling 1997). Chini et al. (1986a,b) measured the 1300µm flux. A trail of small HII regions, detected from 2-20cm and including G10.46+0.03 C and other small sources, extends south to the 1.5' limit of the SCUBA map in the direction of G10.44+0.01 but has no associated warm dust (Furst et al. 1990; Garay et al. 1993b; Griffith et al. 1994; Aliakberov et al. 1985).

The northern submm peak at [FORMULA] shows a compact NH3 clump (Garay et al. 1993a, marked with a cross on Fig. 1) and OH and CH3OH masers (Caswell et al. 1995c; Caswell 1998), but no radio emission has been detected at this position, suggesting that any UCHII region is still optically thick; this clump may be at an earlier stage of evolution than either G10.47+0.03 or G10.46+0.03.

3.2. G12.21

The 450 and 850µm maps show a central source with extensions to the northeast and southeast. The main submm peak is associated with the UCHII region G12.21-0.10; this has been detected at several radio wavelengths (WC89; Zoonematkermani et al. 1990; Becker et al. 1994) as well as at 70µm (Jaffe et al. 1982) and JHK (Testi et al. 1998), has OH, CH3OH and H2O masers (Braz & Ephchtein 1983; Hofner & Churchwell 1996; Walsh et al. 1997; Palagi et al. 1993; Bachiller et al. 1990; Jaffe et al. 1981), and associated molecular line emission from hot, dense, chemically rich gas (Hatchell et al. 1998a,b; Anglada et al. 1996; Cesaroni et al. 1992,1998; Plume et al. 1992; Churchwell et al. 1990b; Shepherd & Churchwell 1996; Olmi et al. 1993). The large scale CO distribution was mapped by Scoville et al. (1987). The extension to the northeast contains no radio sources, but the extension to the south contains a CH3OH maser [FORMULA] to the south of the peak (Caswell et al. 1995c).

To the east and southeast, at the edge of the 850µm map, are two further peaks. These appear as negative features in the northwest of the maps (not visible in Fig. 1) because the [FORMULA] chop throw has resulted in self-chopping. The eastern peak, G12.21-0.12, has been detected in molecular lines tracing dense, hot gas (Forster et al. 1985; Plume et al. 1992; Anglada et al. 1996) and also has OH, H2O and CH3OH masers (Roellig et al. 1999; Forster & Caswell 1989; Caswell 1998; Zheng & Ling 1997; Mehringer et al. 1995; Palagi et al. 1993; Menten 1991; Forster & Caswell 1989; Kemball et al. 1988; Braz & Epchtein 1983; Hofner & Churchwell 1996; Koo et al. 1988) but no known associated radio source, though further observations are needed to confirm this. IRAS 18097-1825A is centred [FORMULA] west of this clump.

The southeastern source has been detected at 6 and 11 cm and in hydrogen radio recombination lines (Aliakberov et al. 1985, Lockman 1989) and also has an associated CH3OH maser (Caswell et al. 1995c). Chini et al. (1986a,b) measured the 1300µm flux centred on this position.

3.3. G13.87

G13.87 appears as a single submm clump. The apparent elongation in the east-northeast/west-northwest direction is the effect of the SCUBA beam. A possible extension to the north appears at 850µm but is not seen at 450µm and is unlikely to be real. Associated with the central peak is the cometary HII region G13.87+0.28 (Garay et al. 1993c, 1994; Becker et al. 1994; Redman et al. 1998; Aliakberov et al. 1985; Wink et al. 1983; Griffith et al. 1994; Lockman 1989; Furst et al. 1990). [FORMULA] to the north lies a second radio source, G13.874+0.281, detected at 20 cm but undetected by SCUBA (Zoonematkermani et al. 1990). The clump has been detected in several molecular species (Olmi et al. 1993; Cesaroni et al. 1992; Plume et al. 1992; Churchwell et al. 1990b; Anglada et al. 1996; Bronfman et al. 1996; Shepherd & Churchwell 1996; Wouterloot et al. 1993) although it is not chemically rich (Hatchell et al. 1998a). The large scale molecular cloud was mapped in CO by Scoville et al. (1987). Chini et al. (1986a,b) made a flux measurement at 1300µm; the associated IRAS source is 18116-1646, and it has been extensively studied in the infrared (Kwok et al. 1997; Zavagno et al. 1992; Cox 1990; Jourdain de Muizon et al. 1990; Simpson & Rubin 1990; Volk & Cohen 1989; Jaffe et al. 1981,1982). Maser detections include H2O (Hofner & Churchwell 1996; Codella et al. 1995; Palagi et al. 1993) and CH3OH (Walsh et al. 1997; Koo et al. 1988; Braz & Epchtein 1983; van der Walt et al. 1995)

3.4. G31.41

G31.41+0.31 appears as a core-halo UCHII region in the survey of WC89, and has been detected at several radio wavelengths (Becker et al. 1994; Garay et al. 1993c; Wink et al. 1983; Zoonematkermani et al. 1990; Furst et al. 1990; Lockman 1989; Handa et al. 1987; Aliakberov et al. 1985). The submm emission shows one central peak with some extension to the south at 850µm. Again, the west-northwest/east-southeast elongation is likely to be due to the SCUBA beam. However, there are CH3OH masers detected [FORMULA] to the west of the submm peak (Walsh et al. 1997; Caswell et al. 1995b,c) and there is a radio detection [FORMULA] to the east (Aliakberov et al. 1985). The central peak also has associated H2O, OH and CH3OH maser emission (Hofner & Churchwell 1996; Tang et al. 1996; Gaylard et al. 1994; Palagi et al. 1993; Schutte et al. 1993; Cohen et al. 1991; Koo et al. 1988; Braz & Epchtein 1983; Gaume & Mutel 1987). The molecular line emission towards the UCHII region is chemically rich and many high-excitation transitions have been detected (Wyrowski et al. 1999; Hatchell et al. 1998a,b,c;1999; Cesaroni et al. 1991, 1992, 1994a,b, 1998; Nummelin et al. 1998; Olmi et al. 1996a,b; Bronfman et al. 1996; Shepherd & Churchwell 1996; Anglada et al. 1996; Tang et al. 1996; Wouterloot et al. 1993; Plume et al. 1992; Churchwell et al. 1990b, 1992; Wyrowski & Walmsley 1996; Gensheimer et al. 1996). Chini et al. (1986a,b) measured the 1300µm flux towards the central peak.

3.5. G43.89

The submm image for G43.89 shows a single peak towards the radio source G43.89-0.78; this is a cometary UCHII region of diameter [FORMULA] (WC89). H2O masers have been detected towards the peak (Hofner & Churchwell 1996; Brand et al. 1994), and also CH3OH and OH masers (Schutte et al. 1993; Bachiller et al. 1990) and it has been the subject of many radio observations (Wood et al. 1988; Zoonematkermani et al. 1990; Handa et al. 1987; Furst et al. 1990; Reich et al. 1990; Aliakberov et al. 1985; Lockman 1989). The infrared fluxes and spectrum were measured by IRAS (Zavagno et al. 1992; Jourdain de Muizon et al. 1990; Simpson & Rubin 1990; Olnon et al. 1986) and Doherty et al. (1994) carried out 2µm spectroscopy. Some molecular line emission has been detected, but the source is not chemically rich (Hatchell et al. 1998a; Baudry et al. 1997; Bronfman et al. 1996; Shepherd & Churchwell 1996; Churchwell et al. 1990b; Olmi et al. 1993); the large-scale CO distribution was mapped by Scoville et al. (1987). Chini et al. (1986a,b) measured the 1300µm flux.

3.6. Peaked vs. non-peaked sources

In all five sources there is strong submm emission which peaks towards the target UCHII region, within our [FORMULA]/[FORMULA] resolution and few arcsecond pointing accuracy. In at least two sources (G10.47 and G12.21) there are also secondary peaks. It is particularly evident at 450µm that three of the sources (G10.47, G12.21 and G31.41) have more pronounced central peaks compared to the surrounding low-level emission (the contour levels are the same for each source). This is also clear from Table 3: roughly [FORMULA] the map flux is contained in a single beam centred on the peak for G10.47, G12.21 and G31.41 whereas in G13.87 and G43.89 this figure is less than [FORMULA]. The difference between peaked and non-peaked sources also can be seen clearly in the radial profiles used for modelling in Sect. 4 (Figs. 5 and 7).

In our spectral line survey towards 14 UCHII regions (Hatchell et al. 1998) we noted that some sources were chemically rich, with many molecular species detected, including grain mantle species and their daughter products. We concluded that these sources contained hot, dense molecular cores. Other sources were line-poor, with only common molecules such as CO, SO, CS and CH3OH detected. Of the five sources in our SCUBA sample, the three peaked sources, G10.47, G12.21 and G31.41 were all line-rich in the molecular line survey, whereas G13.87 and G43.89 were line-poor. The peaked sources in the SCUBA sample can therefore be identified with the sources with hot molecular cores.

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© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000