Millimetre continuum observations of southern massive star formation regions -- I. SIMBA observations of cold cores

Abstract

We report the results of a 1.2-mm continuum emission survey toward 131 star-forming complexes suspected of undergoing massive star formation. These regions have previously been identified as harbouring a methanol maser and/or a radio continuum source [ultracompact (UC) H II region], the presence of which is in most instances indicative of massive star formation. The 1.2-mm emission was mapped using the SIMBA instrument on the 15-m Swedish ESO Submillimetre Telescope (SEST). Emission is detected toward all of the methanol maser and UC H II regions targeted, as well as towards 20 others lying within the fields mapped, implying that these objects are associated with cold, deeply embedded objects. Interestingly, there are also 20 methanol maser sites and nine UC H II regions within the fields mapped which are devoid of millimetre continuum emission.In addition to the maser and UC H II regions detected, we have also identified 253 other sources within the SIMBA maps. All of these (253) are new sources, detected solely from their millimetre continuum emission. These 'mm-only' cores are devoid of the traditional indicators of massive star formation, (i.e. methanol/OH maser, UC H II regions or IRAS point sources). At least 45 per cent of these mm-only cores are also without mid-infrared Mid-course Space Experiment (MSX) emission. The 'mm-only' core may be an entirely new class of source that represents an earlier stage in the evolution of massive stars, prior to the onset of methanol maser emission. Or, they may harbour protoclusters which do not contain any high-mass stars (i.e. below the H II region limit).In total, 404 sources are detected, representing four classes of sources which are distinguished by the presence of the different combination of associated tracer/s. Their masses, estimated assuming a dust temperature of 20 K and adopting kinematic distances, range from 0.5 × 10 1 to 3.7 × 10 4 M , with an average mass for the sample of 1.5 × 10 3 M . The H 2 number density (n H 2 ) of the source sample ranges from 1.4 × 10 3 to 1.9 × 10 6 cm −3 , with an average of 8.7 × 10 4 cm −3 . The average radius of the sample is 0.5 pc. The visual extinction ranges from 10 to 500 mag with an average of 80 mag, which implies a high degree of embedding. The surface density ( ) varies from 0.2 to 18.0 kg m −2 with an average of 2.8 kg m −2 .Analysis of the millimetre-only sources shows that they are less massive (M = 0.9 × 10 3 M ) and smaller (R = 0.4 pc) than sources with methanol maser and/or radio continuum emission, which collectively have a mean mass of 2.5 × 10 3 M and a mean radius of 0.7 pc.

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

“…The Cygnus X histograms are also compared to density spectra of nearby dense cores (Motte et al 1998;Ward-Thompson et al 1999) and ρ Oph condensations (Motte et al 1998). dish studies of high-mass star-forming regions (see Table 4 and also Reid & Wilson 2005;Hill et al 2005). Using the terminology mentioned above, HMPOs (for high-mass protostellar objects, Beuther et al 2002) and IRDCs (for infrared dark clouds, e.g.…”

“…Serendipitous discoveries of a few infrared-quiet massive young stellar objects have been made in submillimeter continuum maps (e.g. Molinari et al 1998;Motte et al 2003;Sandell & Sievers 2004;Hill et al 2005) and as absorption regions in mid-infrared images (often called "infrared dark clouds", e.g. Carey et al 2000;Rathborne et al 2006).…”

The Dust and [C ii] Morphologies of Redshift ∼4.5 Sub-millimeter Galaxies at ∼200 pc Resolution: The Absence of Large Clumps in the Interstellar Medium at High-redshift

“…In a study of 16 ALESS SMGs at 0 16 resolution (∼1 kpc), Hodge et al (2016) identified disk-like morphologies with no significant evidence for clumps in dust emission in the majority of their galaxies. However, giant H II regions in local galaxies are a few hundred parsecs across (e.g., Hill et al 2005;Sakamoto et al 2008). This means that, although this study measures structures on ∼1 kpc scales, even higher resolution is required to search for extended clumpy disks with 200-500 pc size clumps, as seen in some simulations (Dekel et al 2009;Bournaud et al 2014) and locally (e.g., Hill et al 2005;Sakamoto et al 2008).…”

Characterizing the properties of cluster precursors in the MALT90 survey

“…This fit is done independently for each line of sight, taking into account differences in temperature across the clump better than previous studies (e.g. Faúndez et al 2004;Hill et al 2005), in which a single temperature is assumed for the entire clump. However, for clumps with active star formation, it is possible that the column density is underestimated due temperature gradients along the line of sight.…”