NGC1333/IRAS4: A multiple star formation laboratory

We present SCUBA observations of the protomultiple system NGC1333/IRAS4 at 450um and 850um. The 850um map shows significant extended emission which is most probably a remnant of the initial cloud core. At 450um, the component 4A is seen to have an elongated shape suggestive of a disk. Also we confirm that in addition to the 4A and 4B system, there exists another component 4C, which appears to lie out of the plane of the system and of the extended emission. Deconvolution of the beam reveals a binary companion to IRAS4B. Simple considerations of binary dynamics suggest that this triple 4A-4BI-4BII system is unstable and will probably not survive in its current form. Thus IRAS4 provides evidence that systems can evolve from higher to lower multiplicity as they move towards the main sequence. We construct a map of spectral index from the two wavelengths, and comment on the implications of this for dust evolution and temperature differences across the map. There is evidence that in the region of component 4A the dust has evolved, probably by coagulating into larger or more complex grains. Furthermore, there is evidence from the spectral index maps that dust from this object is being entrained in its associated outflow.Comment: 10 pages, 10 figures. To appear in MNRAS. Uses mn.sty. Also available at http://www.astro.phys.ethz.ch/papers/smith/smith_p_m.htm

Extinction correction and on-sky calibration of SCUBA-2

Commissioning of SCUBA-2 included a program of skydips and observations of calibration sources intended to be folded into regular observing as standard methods of source flux calibration and to monitor the atmospheric opacity and stability. During commissioning, it was found that these methods could also be utilised to characterise the fundamental instrument response to sky noise and astronomical signals. Novel techniques for analysing on-sky performance and atmospheric conditions are presented, along with results from the calibration observations and skydips.Comment: 10 pages, 7 figure

New light on the S235A-B star forming region

The S235A-B star forming region has been extensively observed in the past from the radio to the near-IR, but what was happening in the immediate surroundings of the water maser, placed in between the two nebulosities, was still unclear because of insufficient resolution especially in the spectral range from the Far-IR to the mm, even though there were sound indications that new young stellar objects (YSOs) are being formed there. We present here new high resolution maps at mm wavelengths in different molecules (HCO+, C34S, H2CS, SO2 and CH3CN), as well as in the 1.2 and 3.3 mm continuum obtained with the Plateau de Bure interferometer, and JCMT observations at 450 micron and 850 micron that unambiguously reveal the presence of new YSOs placed in between the two HII regions S235A and S235B and associated with the water maser. A molecular core and an unresolved source in the mm and in the sub-mm are centred on the maser, with indication of mass infall onto the core. Two molecular bipolar outflows and a jet originate from the same position. Weak evidence is found for a molecular rotating disk perpendicular to the direction of the main bipolar outflow. The derived parameters indicate that one of the YSOs is an intermediate luminosity object (L~1000 Lsun) in a very early evolutionary phase, embedded in a molecular core of ~100 Msun, with a temperature of 30 K. The main source of energy for the YSO could come from gravitational infall, thus making of this YSO a rare example of intermediate luminosity protostar representing a link between the earliest evolutionary phases of massive stars and low mass protostars of class 0-I.Comment: 19 pages, 22 figures, to be published in Astronomy & Astrophysic

NGC 1333/IRAS 4: a multiple star formation laboratory

We present SCUBA observations of the protomultiple system NGC 1333/IRAS 4 at 450 and 850 μm. The 850-μm map shows significant extended emission which is most probably a remnant of the initial cloud core. At 450 μm, the component 4A is seen to have an elongated shape suggestive of a disc. Also we confirm that, in addition to the 4A and 4B system, there exists another component 4C, which appears to lie out of the plane of the system and of the extended emission. Deconvolution of the beam reveals a binary companion to IRAS 4B. Simple considerations of binary dynamics suggest that this triple 4A-4BI-4BII system is unstable and will probably not survive in its current form. Thus IRAS 4 provides evidence that systems can evolve from higher to lower multiplicity as they move towards the main sequence. We construct a map of spectral index from the two wavelengths, and comment on the implications of this for dust evolution and temperature differences across the map. There is evidence that in the region of component 4A the dust has evolved, probably by coagulating into larger or more complex grains. Furthermore, there is evidence from the spectral index maps that dust from this object is being entrained in its associated outflo

Resolving the Submillimeter Background: the 850-micron Galaxy Counts

Recent deep blank field submillimeter surveys have revealed a population of luminous high redshift galaxies that emit most of their energy in the submillimeter. The results suggest that much of the star formation at high redshift may be hidden to optical observations. In this paper we present wide-area 850-micron SCUBA data on the Hawaii Survey Fields SSA13, SSA17, and SSA22. Combining these new data with our previous deep field data, we establish the 850-micron galaxy counts from 2 mJy to 10 mJy with a >3-sigma detection limit. The area coverage is 104 square arcmin to 8 mJy and 7.7 square arcmin to 2.3 mJy. The differential 850-micron counts are well described by the function n(S)=N_0/(a+S^3.2), where S is the flux in mJy, N_0=3.0 x 10^4 per square degree per mJy, and a=0.4-1.0 is chosen to match the 850-micron extragalactic background light. Between 20 to 30 per cent of the 850-micron background resides in sources brighter than 2 mJy. Using an empirical fit to our >2 mJy data constrained by the EBL at lower fluxes, we argue that the bulk of the 850-micron extragalactic background light resides in sources with fluxes near 1 mJy. The submillimeter sources are plausible progenitors of the present-day spheroidal population.Comment: 5 pages, accepted by The Astrophysical Journal Letter

The Submillimeter Properties of the 1 Ms Chandra Deep Field North X-ray Sample

We present submillimeter observations for 136 of the 370 X-ray sources detected in the 1 Ms exposure of the Chandra Deep Field North. Ten of the X-ray sources are significantly detected in the submillimeter. The average X-ray source in the sample has a significant 850 micron flux of 1.69+/-0.27 mJy. This value shows little dependence on the 2-8 keV flux from 5e-16 erg/cm^2/s to 1e-14 erg/cm^2/s. The ensemble of X-ray sources contribute about 10% of the extragalactic background light at 850 microns. The submillimeter excess is found to be strongest in the optically faint X-ray sources that are also seen at 20 cm, which is consistent with these X-ray sources being obscured and at high redshift (z>1).Comment: 5 pages, submitted to The Astrophysical Journal Letter

Effects of Contact Network Models on Stochastic Epidemic Simulations

The importance of modeling the spread of epidemics through a population has led to the development of mathematical models for infectious disease propagation. A number of empirical studies have collected and analyzed data on contacts between individuals using a variety of sensors. Typically one uses such data to fit a probabilistic model of network contacts over which a disease may propagate. In this paper, we investigate the effects of different contact network models with varying levels of complexity on the outcomes of simulated epidemics using a stochastic Susceptible-Infectious-Recovered (SIR) model. We evaluate these network models on six datasets of contacts between people in a variety of settings. Our results demonstrate that the choice of network model can have a significant effect on how closely the outcomes of an epidemic simulation on a simulated network match the outcomes on the actual network constructed from the sensor data. In particular, preserving degrees of nodes appears to be much more important than preserving cluster structure for accurate epidemic simulations.Comment: To appear at International Conference on Social Informatics (SocInfo) 201

CHIMPS: the ¹³CO/C¹⁸O (<i>J</i> = 3 → 2) Heterodyne Inner Milky Way Plane Survey

We present the 13CO/C18O (J = 3 → 2) Heterodyne Inner Milky Way Plane Survey (CHIMPS) which has been carried out using the Heterodyne Array Receiver Program on the 15 m James Clerk Maxwell Telescope (JCMT) in Hawaii. The high-resolution spectral survey currently covers |b| ≤ 0.5° and 28° ≲ l ≲ 46°, with an angular resolution of 15 arcsec in 0.5 km s-1 velocity channels. The spectra have a median rms of ˜0.6 K at this resolution, and for optically thin gas at an excitation temperature of 10 K, this sensitivity corresponds to column densities of NH2 ˜ 3 × 1020 cm-2 and NH2 ˜ 4 × 1021 cm-2 for 13CO and C18O, respectively. The molecular gas that CHIMPS traces is at higher column densities and is also more optically thin than in other publicly available CO surveys due to its rarer isotopologues, and thus more representative of the three-dimensional structure of the clouds. The critical density of the J = 3 → 2 transition of CO is ≳104 cm-3 at temperatures of ≤20 K, and so the higher density gas associated with star formation is well traced. These data complement other existing Galactic plane surveys, especially the JCMT Galactic Plane Survey which has similar spatial resolution and column density sensitivity, and the Herschel infrared Galactic Plane Survey. In this paper, we discuss the observations, data reduction and characteristics of the survey, presenting integrated-emission maps for the region covered. Position-velocity diagrams allow comparison with Galactic structure models of the Milky Way, and while we find good agreement with a particular four-arm model, there are some significant deviations

The sub-millimetre evolution of V4334 Sgr (Sakurai's Object)

We report the results of monitoring of V4334 Sgr (Sakurai's Object) at 450 microns and 850 microns with SCUBA on the James Clerk Maxwell Telescope. The flux density at both wavelengths has increased dramatically since 2001, and is consistent with continued cooling of the dust shell in which Sakurai's Object is still enshrouded, and which still dominates the near-infrared emission. Assuming that the dust shell is optically thin at sub-millimetre wavelengths and optically thick in the near-infrared, the sub-millimetre data imply a mass-loss rate during 2003 of ~3.4(+/0.2)E-5 for a gas-to-dust ratio of 75. This is consistent with the evidence from 1-5micron observations that the mass-loss is steadily increasing.Comment: 5 pages, 4 eps figures, accepted for publication in MNRA

Submillimeter detection of the Sunyaev -- Zel'dovich effect toward the most luminous X-ray cluster at z=0.45

We report on the detection of the Sunyaev -- Zel'dovich (SZ) signals toward the most luminous X-ray cluster RXJ1347-1145 at Nobeyama Radio Observatory (21 and 43 GHz) and at James Clerk Maxwell Telescope (350 GHz). In particular the latter is the first successful detection of the SZ temperature increment in the submillimeter band which resolved the profile of a cluster of galaxies. Both the observed spectral dependence and the radial profile of the SZ signals are fully consistent with those expected from the X-ray observation of the cluster. The combined analysis of 21GHz and 350GHz data reproduces the temperature and core-radius of the cluster determined with the ROSAT and ASCA satellites when we adopt the slope of the density profile from the X-ray observations. Therefore our present data provide the strongest and most convincing case for the detection of the submillimeter SZ signal from the cluster, as well as in the Rayleigh -- Jeans regime. We also discuss briefly the cosmological implications of the present results.Comment: 11 pages, The Astrophysical Journal (Letters), in pres