ALBERT

Description: We present a complete sample of molecular clumps containing compact and ultracompact H ii (UC H ii ) regions between  = 10° and 60° and | b | 〈 1°, identified by combining the APEX Telescope Large Area Survey of the Galaxy submm and CORNISH radio continuum surveys with visual examination of archival infrared data. Our sample is complete to optically thin, compact and UC H ii regions driven by a zero-age main-sequence star of spectral type B0 or earlier embedded within a 1000 M clump. In total we identify 213 compact and UC H ii regions, associated with 170 clumps. Unambiguous kinematic distances are derived for these clumps and used to estimate their masses and physical sizes, as well as the Lyman continuum fluxes and sizes of their embedded H ii regions. We find a clear lower envelope for the surface density of molecular clumps hosting massive star formation of 0.05 g cm –2 , which is consistent with a similar sample of clumps associated with 6.7 GHz masers. The mass of the most massive embedded stars is closely correlated with the mass of their natal clump. Young B stars appear to be significantly more luminous in the ultraviolet than predicted by current stellar atmosphere models. The properties of clumps associated with compact and UC H ii regions are very similar to those associated with 6.7 GHz methanol masers and we speculate that there is little evolution in the structure of the molecular clumps between these two phases. Finally, we identify a significant peak in the surface density of compact and UC H ii -regions associated with the W49A star-forming complex, noting that this complex is truly one of the most massive and intense regions of star formation in the Galaxy.

Description: Most runaway OB stars, like the majority of massive stars residing in their parent clusters, go through the red supergiant (RSG) phase during their lifetimes. Nonetheless, although many dozens of massive runaways were found to be associated with bow shocks, only two RSG bow-shock-producing stars, Betelgeuse and μ Cep, are known to date. In this paper, we report the discovery of an arc-like nebula around the late M-type star IRC –10414 using the SuperCOSMOS H-alpha Survey. Our spectroscopic follow-up of IRC –10414 with the Southern African Large Telescope (SALT) showed that it is a M7 supergiant, which supports previous claims on the RSG nature of this star based on observations of its maser emission. This was reinforced by our new radio- and (sub)millimetre-wavelength molecular line observations made with the Atacama Pathfinder Experiment 12-m telescope and the Effelsberg 100-m radio telescope, respectively. The SALT spectrum of the nebula indicates that its emission is the result of shock excitation. This finding along with the arc-like shape of the nebula and an estimate of the space velocity of IRC –10414 (70 ± 20 km s –1 ) imply the bow shock interpretation for the nebula. Thus, IRC –10414 represents the third case of a bow-shock-producing RSG and the first one with a bow shock visible at optical wavelengths. We discuss the smooth appearance of the bow shocks around IRC –10414 and Betelgeuse and propose that one of the necessary conditions for stability of bow shocks generated by RSGs is the ionization of the stellar wind. Possible ionization sources of the wind of IRC –10414 are proposed and discussed.

Description: We report the results of 870-μm continuum observations, using the Large APEX Bolometer Camera, towards 77 class-II, 6.7-GHz methanol masers identified by the Methanol MultiBeam (MMB) survey to map the thermal emission from cool dust towards these objects. These data complement a study of 630 methanol masers associated with compact dense clumps identified from the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. Compact dust emission is detected towards 70 sources, which implies a dust-association rate of 99 per cent for the full MMB catalogue. Evaluation of the derived dust and maser properties leads us to conclude that the combined sample represents a single population tracing the same phenomenon. We find median clump masses of a few 10 3  M and that all but a handful of sources satisfy the mass–size criterion required for massive star formation. This study provides the strongest evidence of the almost ubiquitous association of methanol masers with massive, star-forming clumps. The fraction of methanol-maser associated clumps is a factor of ~2 lower in the outer Galaxy than the inner Galaxy, possibly a result of the lower metallicity environment of the former. We find no difference in the clump-mass and maser-luminosity distributions of the inner and outer Galaxy. The maser-pumping and clump formation mechanisms are therefore likely to be relatively invariant to Galactic location. Finally, we use the ratio of maser luminosity and clump mass to investigate the hypothesis that the maser luminosity is a good indicator of the evolutionary stage of the embedded source, however, we find no evidence to support this.

Description: We use sensitive observations of three high-redshift sources: [C  ii ] $^2\text{P}_{3/2}$ -〉 $^2\text{P}_{1/2}$ fine-structure and CO ( J = 2 -〉 1) rotational transitions for the z  = 6.4 quasar (QSO) host galaxy J1148+5251 taken with the Plateau de Bure Interferometer (PdBI) and Jansky Very Large Array, respectively, and [C  ii ] and CO ( J = 5 -〉 4) transitions from the QSO BR1202–0725 and its companion sub-millimetre galaxy (SMG) at z  = 4.7 taken with the Atacama Large Millimeter Array and the PdBI. We use these observations to place constraints on the quantity $\Delta z = z_{\rm CO} - z_{\text{C}{\,\small {ii}}}$ for each source where z CO and $z_{\text{C}{\,\small {ii}}}$ are the observed redshifts of the CO rotational transition and [C  ii ] fine-structure transition, respectively, using a combination of approaches: (1) modelling the emission line profiles using ‘shapelets’ – a complete orthonormal set of basis functions that allow us to recreate most physical line shapes – to compare both the emission redshifts and the line profiles themselves, in order to make inferences about the intrinsic velocity differences between the molecular and atomic gas, and (2) performing a marginalization over all model parameters in order to calculate a non-parametric estimate of z . We derive 99 per cent confidence intervals for the marginalized posterior of z of (–1.9 ± 1.3)  x 10 –3 , (–3 ± 8)  x 10 –4 and (–2 ± 4)  x 10 –3 for J1148+5251, and the BR1202–0725 QSO and SMG, respectively. We show that the [C  ii ] and CO ( J = 2 -〉 1) line profiles for J1148+5251 are consistent with each other within the limits of the data, whilst the [C  ii ] and CO ( J = 5 -〉 4) line profiles from the BR1202–0725 QSO and SMG, respectively, have 65 and 〉99.9 per cent probabilities of being inconsistent, with the CO ( J = 5 -〉 4) lines ~30 per cent wider than the [C  ii ] lines. Therefore, whilst the observed values of z can correspond to variations in the quantity F / F with cosmic time, where F  = α 2 /μ, with α the fine-structure constant and μ the proton-to-electron mass ratio, of both (–3.3 ± 2.3)  x 10 –4 for a look-back time of 12.9 Gyr and of (–5 ± 15)  x 10 –5 for a look-back time of 12.4 Gyr, we propose that they are the result of the two species of gas being spatially separated as indicated by the inconsistencies in their line profiles.

Description: We report the first counts of faint submillimetre galaxies (SMGs) in the 870-μm band derived from arcsecond-resolution observations with the Atacama Large Millimeter Array (ALMA). We have used ALMA to map a sample of 122 870-μm-selected submillimetre sources drawn from the 0 ${^{\circ}_{.}}$ 5 x 0 ${^{\circ}_{.}}$ 5 the Large Apex BOlometer CAmera (LABOCA) Extended Chandra Deep Field South submillimetre survey (LESS). These ALMA maps have an average depth of 870 μm ~ 0.4 mJy, some approximately three times deeper than the original LABOCA survey and critically the angular resolution is more than an order of magnitude higher, FWHM of ~1.5 arcsec compared to ~19 arcsec for the LABOCA discovery map. This combination of sensitivity and resolution allows us to precisely pinpoint the SMGs contributing to the submillimetre sources from the LABOCA map, free from the effects of confusion. We show that our ALMA-derived SMG counts broadly agree with the submillimetre source counts from previous, lower resolution single-dish surveys, demonstrating that the bulk of the submillimetre sources are not caused by blending of unresolved SMGs. The difficulty which well-constrained theoretical models have in reproducing the high surface densities of SMGs, thus remains. However, our observations do show that all of the very brightest sources in the LESS sample, S 870 μm 12 mJy, comprise emission from multiple, fainter SMGs, each with 870-μm fluxes of 9 mJy. This implies a natural limit to the star formation rate in SMGs of 10 3  M  yr –1 , which in turn suggests that the space densities of z  〉 1 galaxies with gas masses in excess of ~5  x 10 10  M is 〈10 –5  Mpc –3 . We also discuss the influence of this blending on the identification and characterization of the SMG counterparts to these bright submillimetre sources and suggest that it may be responsible for previous claims that they lie at higher redshifts than fainter SMGs.

Description: By matching infrared-selected, massive young stellar objects (MYSOs) and compact H ii regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey, we have identified ~1000 embedded young massive stars between 280° 〈  〈 350° and 10° 〈  〈 60° with | b | 〈 1 $_{.}^{\circ}$ 5. Combined with an existing sample of radio-selected methanol masers and compact H ii regions, the result is a catalogue of ~1700 massive stars embedded within ~1300 clumps located across the inner Galaxy, containing three observationally distinct subsamples, methanol-maser, MYSO and H ii -region associations, covering the most important tracers of massive star formation, thought to represent key stages of evolution. We find that massive star formation is strongly correlated with the regions of highest column density in spherical, centrally condensed clumps. We find no significant differences between the three samples in clump structure or the relative location of the embedded stars, which suggests that the structure of a clump is set before the onset of star formation, and changes little as the embedded object evolves towards the main sequence. There is a strong linear correlation between clump mass and bolometric luminosity, with the most massive stars forming in the most massive clumps. We find that the MYSO and H ii -region subsamples are likely to cover a similar range of evolutionary stages and that the majority are near the end of their main accretion phase. We find few infrared-bright MYSOs associated with the most massive clumps, probably due to very short pre-main-sequence lifetimes in the most luminous sources.

Description: Using the 870 μm APEX Telescope large area survey of the Galaxy, we have identified 577 submillimetre continuum sources with masers from the methanol multibeam survey in the region 280° 〈  〈 20°; | b | 〈 1 ${^{\circ}_{.}}$ 5. 94 per cent of methanol masers in the region are associated with submillimetre dust emission. We estimate masses for ~450 maser-associated sources and find that methanol masers are preferentially associated with massive clumps. These clumps are centrally condensed, with envelope structures that appear to be scale-free, the mean maser position being offset from the peak column density by 0 ± 4 arcsec. Assuming a Kroupa initial mass function and a star formation efficiency of ~30 per cent, we find that over two-thirds of the clumps are likely to form clusters with masses 〉20 M . Furthermore, almost all clumps satisfy the empirical mass–size criterion for massive star formation. Bolometric luminosities taken from the literature for ~100 clumps range between ~100 and 10 6  L . This confirms the link between methanol masers and massive young stars for 90 per cent of our sample. The Galactic distribution of sources suggests that the star formation efficiency is significantly reduced in the Galactic Centre region, compared to the rest of the survey area, where it is broadly constant, and shows a significant drop in the massive star formation rate density in the outer Galaxy. We find no enhancement in source counts towards the southern Scutum–Centaurus arm tangent at  ~ 315°, which suggests that this arm is not actively forming stars.

Description: Maser lines of OH, H 2 O and SiO are commonly observed in O-rich asymptotic giant branch (AGB) stars, but their presence after the end of the AGB phase is linked to non-spherical mass-loss processes. IRAS 15452 – 5459 is a post-AGB star with an hourglass nebula whose maser lines are quite peculiar. We observed all of the three maser species with the Australia Telescope Compact Array with angular resolutions of 6, 0.6, 0.3 and 1.7 arcsec at 18 cm, 13 mm, 7 mm and 3 mm, respectively. While double peaks are routinely seen in OH and water masers and interpreted as due to expanding envelopes, only very few sources display SiO lines with a similar spectral profile. Our observations confirm the detection of the double peak of SiO at 86 GHz; the same spectral shape is seen in the lower J maser at 43 GHz. A double peak is also detected in the water line, which covers the same velocity range as the SiO masers. Thermally excited lines of SiO are detected at 7 and 3 mm and span the same velocity range as the maser lines of this species. Although observations at higher angular resolution are desirable to further investigate the spatial distributions of the maser spots, the current data allow us to conclude that the SiO masers are distributed in an hourglass shape and are likely due to the sputtering of dust grains caused by shock propagation. The complex OH profile would instead be due to emission from the fast outflow and an orthogonal structure.