Observations of the galaxy cluster MACS J2135-0102 (z cl =0.325) were made with the LABOCA 870µm bolometer camera 29 on the APEX telescope on 2009 May 8 for a total of 3.2hours (1200 seconds on-source) in excellent conditions (PWV=0.35-0.40mm). We used a 6 arcminute spiral pattern scan, centered at α:21:35:12.706 δ:-01:01:43.27 (J2000). For flux calibration, Mars and Uranus were both observed immediately prior to the science observations. The data were reduced using the minicrush reduction package, which includes temperature drift correction, flat-fielding, opacity correction, bad bolometer masking and de-spiking 29 . The final map appears flat, and has an r.m.s. of 3.5mJy/beam. Including systematic effects, we estimate calibration and fitting uncertainties as ~4% and 6% respectively. Visual inspection of the image shows a bright 30σ source centered at α:21:35:11.6 δ:-01:02:52.0 with an 870µm flux of 106.0±3.5mJy. Given the uncertainties in the calibration we adopt the flux of the SMG as S 870 =106.5±7.0mJy, and derive S 870 =24.2±7.0mJy for the counter-image.We followed up SMMJ2135-0102 with the Submillimetre APEX Bolometer CAmera (SABOCA, Siringo et al., in prep.) on the APEX telescope on UT 2009 September 20 and 21. SABOCA is a 37 superconducting Transition Edge Sensing (TES) bolometer array with hexagonal layout and twobeam separation on sky Its filter transmission curve is optimised to cover the 350µm window, and has a central wavelength of 352µm (852 GHz) for flat spectrum sources. SABOCA operates at a temperature of 300mK and is installed in the Cassegrain cabin of APEX. We observed SMMJ2135-0102 in a 20"x20" raster of spirals with 35 seconds duration in order to obtain a fully sampled map.

Aims. We study the dust properties of four low metallicity galaxies by modelling their spectral energy distributions. This modelling enables us to constrain the dust properties such as the mass, the temperature or the composition to characterise the global ISM properties in dwarf galaxies. Methods. We present 870 μm images of four low metallicity galaxies (NGC 1705, Haro 11, Mrk 1089 and UM 311) observed with the Large APEX BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment (APEX) telescope. We modeled their spectral energy distributions combining the submm observations of LABOCA, 2MASS, IRAS, Spitzer photometric data, and the IRS data for Haro 11. Results. We found that the PAH mass abundance is very low in these galaxies, 5 to 50 times lower than the PAH mass fraction of our Galaxy. We also found that a significant mass of dust is revealed when using submm constraints compared to that measured with only mid-IR to far-IR observations extending only to 160 μm. For NGC 1705 and Haro 11, an excess in submillimeter wavelengths was detected when we used our standard dust SED model. We rerun our SED procedure adding a cold dust component (10 K) to better describe the high 870 μm flux derived from LABOCA observations, which significantly improves the fit. We found that at least 70% of the dust mass of these two galaxies can reside in a cold dust component. We also showed that the subsequent dust-to-gas mass ratios, considering HI and CO observations, can be strikingly high for Haro 11 in comparison with what is usually expected for these low-metallicity environments. Furthermore, we derived the star formation rate of our galaxies and compared them to the Schmidt law. Haro 11 falls anomalously far from the Schmidt relation. These results may suggest that a reservoir of hidden gas could be present in molecular form not traced by the current CO observations. While there can be a significant cold dust mass found in Haro 11, the SED peaks at exceptionally short wavelengths (36 μm), also highlighting the importance of the much warmer dust component heated by the massive star clusters in Haro 11. We also derived the total IR luminosities derived from our models and compared them with relations that derive this luminosity from Spitzer bands. We found that the Draine & Li (2007) formula compares well to our direct IR determinations.

Tracing molecular hydrogen content with carbon monoxide in low-metallicity galaxies has been exceedingly difficult. Here we present a new effort, with IRAM 30-m observations of 12 CO(1-0) of a sample of 8 dwarf galaxies having oxygen abundances ranging from 12 + log(O/H) ∼ 7.7 to 8.4. CO emission is detected in all galaxies, including the most metal-poor galaxy of our sample (0.1 Z ); to our knowledge this is the largest number of 12 CO(1-0) detections ever reported for galaxies with 12 + log(O/H) < ∼ 8 (0.2 Z ) outside the Local Group. We calculate stellar masses, M star , and star-formation rates (SFRs), and analyze our results in conjunction with galaxy samples from the literature. Extending previous results for a correlation of the molecular gas depletion time, τ dep , with M star and specific SFR (sSFR), we find a variation in τ dep of a factor of 200 or more (from < ∼ 50 Myr to ∼10 Gyr) over a spread of ∼10 3 in sSFR and M star . We exploit the variation of τ dep to constrain the CO-to-H 2 mass conversion factor α CO at low metallicity, and assuming a power-law variation find α CO ∝ Z/Z −2 , similar to results based on dust continuum measurements compared with gas mass. By including H I measurements, we show that the fraction of total gas mass relative to the baryonic mass is higher in galaxies that are metal poor, of low mass, and with high sSFR. Finally, comparisons of the data with star-formation models of the molecular gas phases show that the models are generally quite successful, but at metallicities Z/Z < ∼ 0.2, there are some discrepancies.

We present an analysis of the molecular and atomic gas emission in the rest-frame far-infrared and submillimetre from the lensed z = 2.3 submillimetre galaxy SMM J2135−0102. We obtain very high signal-to-noise ratio detections of 11 transitions from three species and limits on a further 20 transitions from nine species. We use the 12 CO, [C I] and HCN line strengths to investigate the gas mass, kinematic structure and interstellar medium (ISM) chemistry and find strong evidence for a two-phase medium within this high-redshift starburst galaxy, comprising a hot, dense, luminous component and an underlying extended cool, low-excitation massive component. Employing a suite of photodissociation region models, we show that on average the molecular gas is exposed to an ultraviolet (UV) radiation field that is ∼1000 times more intense than the Milky Way, with star-forming regions having a characteristic density of n ∼ 10 4 cm −3 . Thus, the average ISM density and far-UV radiation field intensity are similar to those found in local ultraluminous infrared galaxies (ULIRGs) and to those found in the central regions of typical starburst galaxies, even though the star formation rate is far higher in this system. The 12 CO spectral line energy distribution and line profiles give strong evidence that the system comprises multiple kinematic components with different conditions, including temperature, and line ratios suggestive of high cosmic-ray flux within clouds, likely as a result of high star formation density. We find tentative evidence of a factor of ∼4 temperature range within the system. We expect that such internal structures are common in high-redshift ULIRGs but are missed due to the poor signal-to-noise ratio of typical observations. We show that, when integrated over the galaxy, the gas and star formation surface densities appear to follow the Kennicutt-Schmidt relation, although by comparing our data to high-resolution submillimetre imaging, our data suggest that this relation breaks down on scales of <100 pc. By virtue of the lens amplification, these observations uncover a wealth of information on the star formation and ISM at z ∼ 2.3 at a level of detail that has only recently become possible at z < 0.1 and show the potential physical properties that will be studied in unlensed galaxies when the Atacama Large Millimeter Array is in full operation.

Aims. New SiO multi-transition millimetre line observations of a sample of carbon stars, including J = 8 → 7 observations with the APEX telescope, are used to probe the role of non-equilibrium chemistry and the influence of grains in circumstellar envelopes of carbon stars. Methods. A detailed radiative transfer modelling, including the effect of dust emission in the excitation analysis, of the observed SiO line emission is performed. A combination of low-and high-energy lines are important in constraining the abundance distribution. Results. It is found that the fractional abundance of SiO in these C-rich environments can be several orders of magnitude higher than predicted by equilibrium stellar atmosphere chemistry. In fact, the SiO abundance distribution of carbon stars closely mimic that of M-type (O-rich) AGB stars. A possible explanation for this behaviour is a shock-induced chemistry, but also the influence of dust grains, both as a source for depletion as well as production of SiO, needs to be further investigated. As observed for M-type AGB stars, a clear trend that the SiO fractional abundance decreases as the mass-loss rate of the star increases is found for the carbon stars. This indicates that SiO is accreted onto dust grains in the circumstellar envelopes.