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Astron. Astrophys. 364, 613-624 (2000)

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1. Introduction

Massive stars strongly influence the dynamical and chemical evolution of the interstellar medium. The formation of massive stars may lead both to a destruction of molecular cloud cores and disks around young stars by their intense UV radiation and strong outflows and to shock waves which may trigger the formation of a new generation of stars.

Despite the importance of massive stars, we do not know if they form by accretion (see, e.g., Jijina & Adams 1996) or/and the coalescence of intermediate-mass stars (Bonnell et al. 1998). The detection of disks around and outflows from massive young stellar objects (YSOs) would favour the accretion scenario. This is a strong motivation for our search of energetic outflows associated with such objects. In a recent very comprehensive review, Garay & Lizano (1999) summarized evidence for the presence of disk-like structures and outflows associated with massive YSOs.

The few outflows from massive star-forming regions detected so far are much more energetic and carry more mass and momentum than outflows from low-mass stars (Shepherd & Churchwell 1996a,b; Shepherd et al. 1998; Henning et al. 2000b). In this paper, we report the detection of a very massive molecular outflow and discuss the properties of the driving source.

IRAS 12326-6245 is known as a luminous far-infrared source with a bolometric luminosity of [FORMULA] = 3.8 105 [FORMULA] at a kinematically estimated distance of [FORMULA] kpc (Zinchenko et al. 1995; Osterloh et al. 1997). This distance is adopted throughout the paper.

This remarkable object is associated with several molecular masers including H2O, OH and methanol masers (e.g. Braz & Epchtein 1983, 1987; Caswell & Haynes 1987; Cohen et al. 1988; Caswell et al. 1995; MacLeod et al. 1998) which were found at the position of IRAS 12326-6245. However, most of these measurements were performed with beam sizes larger than 2 arcmin. Recent interferometer observations by Caswell (1998) show an OH maser very close to the IRAS position. Although Walsh et al. (1998) reported the presence of two UC H II regions close to the IRAS position, they detected no 6.7 GHz methanol maser emission (resolution 1.8") in the region of IRAS 12326-6245.

Strong thermal molecular emission towards IRAS 12326-6245 was mapped in CS(2-1) and CO(2-1) by Zinchenko et al. (1995) and Osterloh et al. (1997) as well as in CS(3-2), C34S(2-1) and C18O(1-0) by Lapinov et al. (1998). These maps show that the dense molecular core is compact ([FORMULA]) and elongated approximately in the E-W direction. The CO spectra exhibit extended wings suggesting the presence of a massive molecular outflow. In a beam of 23[FORMULA] a cloud mass of 320 [FORMULA] was derived by Osterloh et al. (1997).

Wood & Churchwell (1989) defined a "very red" region in the IRAS log[[FORMULA](60[FORMULA])/[FORMULA](12[FORMULA])] versus log[[FORMULA](25[FORMULA])/[FORMULA](12[FORMULA])] colour diagram, where UC H II regions are located. The comparison of the colours of IRAS 12326-6245, having log[[FORMULA](60[FORMULA])/[FORMULA](12[FORMULA])] = 2.99 and log[[FORMULA](25[FORMULA])/[FORMULA](12[FORMULA])] = 1.60, with this region demonstrates that IRAS 12326-6245 is an extremely red and cold object (see also Osterloh et al. 1997).

In general, the available data imply a rather isolated region of high-mass star formation at an early stage. According to available distance estimates it is located almost 10 times farther away than the Orion Molecular Cloud, but the intensities of the line emission are comparable. The goal of the present study is to investigate in more detail this remarkable object. Here, we report the results of additional observations of IRAS 12326-6245 in the near- and mid-infrared, in several molecular lines as well as in the 1.3 mm continuum emission, and we discuss the whole available data set.

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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