arXiv subjects

G. Joncas

Publications and source records attributed to G. Joncas.

At least 37 records · Page 2Linked to original sources

arXiv2015

GHIGLS: HI mapping at intermediate Galactic latitude using the Green Bank Telescope

This paper introduces the data cubes from GHIGLS, deep Green Bank Telescope surveys of the 21-cm line emission of HI in 37 targeted fields at intermediate Galactic latitude. The GHIGLS fields together cover over 1000 square degrees at 9.55' spatial resolution. The HI spectra have an effective velocity resolution about 1.0 km/s and cover at least -450 < v < +250 km/s. GHIGLS highlights that even at intermediate Galactic latitude the interstellar medium is very complex. Spatial structure of the HI is quantified through power spectra of maps of the column density, NHI. For our featured representative field, centered on the North Ecliptic Pole, the scaling exponents in power-law representations of the power spectra of NHI maps for low, intermediate, and high velocity gas components (LVC, IVC, and HVC) are -2.86 +/- 0.04, -2.69 +/- 0.04, and -2.59 +/- 0.07, respectively. After Gaussian decomposition of the line profiles, NHI maps were also made corresponding to the narrow-line and broad-line components in the LVC range; for the narrow-line map the exponent is -1.9 +/- 0.1, reflecting more small scale structure in the cold neutral medium (CNM). There is evidence that filamentary structure in the HI CNM is oriented parallel to the Galactic magnetic field. The power spectrum analysis also offers insight into the various contributions to uncertainty in the data. The effect of 21-cm line opacity on the GHIGLS NHI maps is estimated.

astro-ph.GA↗

arXiv2015

The JCMT Gould Belt Survey: SCUBA-2 observations of circumstellar disks in L 1495

We present 850$μ$m and 450$μ$m data from the JCMT Gould Belt Survey obtained with SCUBA-2 and characterise the dust attributes of Class I, Class II and Class III disk sources in L1495. We detect 23% of the sample at both wavelengths, with the detection rate decreasing through the Classes from I--III. The median disk mask is 1.6$\times 10^{-3}$M$_{\odot}$, and only 7% of Class II sources have disk masses larger than 20 Jupiter masses. We detect a higher proportion of disks towards sources with stellar hosts of spectral type K than spectral type M. Class II disks with single stellar hosts of spectral type K have higher masses than those of spectral type M, supporting the hypothesis that higher mass stars have more massive disks. Variations in disk masses calculated at the two wavelengths suggests there may be differences in dust opacity and/or dust temperature between disks with hosts of spectral types K to those with spectral type M.

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arXiv2015

The JCMT Gould Belt Survey: First results from the SCUBA-2 observations of the Ophiuchus molecular cloud and a virial analysis of its prestellar core population

In this paper we present the first observations of the Ophiuchus molecular cloud performed as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) with the SCUBA-2 instrument. We demonstrate methods for combining these data with previous HARP CO, Herschel, and IRAM N$_{2}$H$^{+}$ observations in order to accurately quantify the properties of the SCUBA-2 sources in Ophiuchus. We produce a catalogue of all of the sources found by SCUBA-2. We separate these into protostars and starless cores. We list all of the starless cores and perform a full virial analysis, including external pressure. This is the first time that external pressure has been included in this level of detail. We find that the majority of our cores are either bound or virialised. Gravitational energy and external pressure are on average of a similar order of magnitude, but with some variation from region to region. We find that cores in the Oph A region are gravitationally bound prestellar cores, while cores in the Oph C and E regions are pressure-confined. We determine that N$_{2}$H$^{+}$ is a good tracer of the bound material of prestellar cores, although we find some evidence for N$_{2}$H$^{+}$ freeze-out at the very highest core densities. We find that non-thermal linewidths decrease substantially between the gas traced by C$^{18}$O and that traced by N$_{2}$H$^{+}$, indicating the dissipation of turbulence at higher densities. We find that the critical Bonnor-Ebert stability criterion is not a good indicator of the boundedness of our cores. We detect the pre-brown dwarf candidate Oph B-11 and find a flux density and mass consistent with previous work. We discuss regional variations in the nature of the cores and find further support for our previous hypothesis of a global evolutionary gradient across the cloud from southwest to northeast, indicating sequential star formation across the region.

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arXiv2014

The JCMT Gould Belt Survey: Evidence for radiative heating in Serpens MWC 297 and its influence on local star formation

We present SCUBA-2 450micron and 850micron observations of the Serpens MWC 297 region, part of the JCMT Gould Belt Survey of nearby star-forming regions. Simulations suggest that radiative feedback influences the star-formation process and we investigate observational evidence for this by constructing temperature maps. Maps are derived from the ratio of SCUBA-2 fluxes and a two component model of the JCMT beam for a fixed dust opacity spectral index of beta = 1.8. Within 40 of the B1.5Ve Herbig star MWC 297, the submillimetre fluxes are contaminated by free-free emission with a spectral index of 1.03+-0.02, consistent with an ultra-compact HII region and polar winds/jets. Contamination accounts for 73+-5 per cent and 82+-4 per cent of peak flux at 450micron and 850micron respectively. The residual thermal disk of the star is almost undetectable at these wavelengths. Young Stellar Objects are confirmed where SCUBA-2 850micron clumps identified by the fellwalker algorithm coincide with Spitzer Gould Belt Survey detections. We identify 23 objects and use Tbol to classify nine YSOs with masses 0.09 to 5.1 Msun. We find two Class 0, one Class 0/I, three Class I and three Class II sources. The mean temperature is 15+-2K for the nine YSOs and 32+-4K for the 14 starless clumps. We observe a starless clump with an abnormally high mean temperature of 46+-2K and conclude that it is radiatively heated by the star MWC 297. Jeans stability provides evidence that radiative heating by the star MWC 297 may be suppressing clump collapse.

astro-ph.SR↗

arXiv2014

Planck intermediate results. XVII. Emission of dust in the diffuse interstellar medium from the far-infrared to microwave frequencies

The dust-HI correlation is used to characterize the emission properties of dust in the diffuse interstellar medium. We cross-correlate sky maps from Planck, WMAP, and DIRBE, at 17 frequencies from 23 to 3000 GHz, with the Parkes survey of the 21-cm line emission of neutral atomic hydrogen, over a contiguous area of 7500 deg$^2$ centred on the southern Galactic pole. Our analysis yields four specific results. (1) The dust temperature is observed to be anti-correlated with the dust emissivity and opacity. We interpret this result as evidence for dust evolution within the diffuse ISM. The mean dust opacity is measured to be $(7.1 \pm 0.6) 10^{-27} cm^2/H \times (ν/353\, GHz)^{1.53\pm0.03}$ for $100 < ν<353$GHz. (2) We map the spectral index of dust emission at millimetre wavelengths, which is remarkably constant at $β_{mm} = 1.51\pm 0.13$. We compare it with the far infrared spectral index beta_FIR derived from greybody fits at higher frequencies, and find a systematic difference, $β_{mm}-β_{FIR} = -0.15$, which suggests that the dust SED flattens at $ν< 353\,$GHz. (3) We present spectral fits of the microwave emission correlated with HI from 23 to 353 GHz, which separate dust and anomalous microwave emission. The flattening of the dust SED can be accounted for with an additional component with a blackbody spectrum, which accounts for $(26 \pm 6)$% of the dust emission at 100 GHz and could represent magnetic dipole emission. Alternatively, it could account for an increasing contribution of carbon dust, or a flattening of the emissivity of amorphous silicates, at millimetre wavelengths. These interpretations make different predictions for the dust polarization SED. (4) We identify a Galactic contribution to the residuals of the dust-HI correlation, which we model with variations of the dust emissivity on angular scales smaller than that of our correlation analysis.

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arXiv2012

New scientific results with SpIOMM: a testbed for CFHT's imaging Fourier transform spectrometer SITELLE

We present new data obtained with SpIOMM, the imaging Fourier transform spectrometer attached to the 1.6-m telescope of the Observatoire du Mont-Mégantic in Québec. Recent technical and data reduction improvements have significantly increased SpIOMM's capabilities to observe fainter objects or weaker nebular lines, as well as continuum sources and absorption lines, and to increase its modulation efficiency in the near ultraviolet. To illustrate these improvements, we present data on the supernova remnant Cas A, planetary nebulae M27 and M97, the Wolf-Rayet ring nebula M1-67, spiral galaxies M63 and NGC 3344, as well as the interacting pair of galaxies Arp 84.

astro-ph.IM↗

arXiv2012

GASKAP -- The Galactic ASKAP Survey

A survey of the Milky Way disk and the Magellanic System at the wavelengths of the 21-cm atomic hydrogen (HI) line and three 18-cm lines of the OH molecule will be carried out with the Australian Square Kilometre Array Pathfinder telescope. The survey will study the distribution of HI emission and absorption with unprecedented angular and velocity resolution, as well as molecular line thermal emission, absorption, and maser lines. The area to be covered includes the Galactic plane (|b|< 10deg) at all declinations south of delta = +40deg, spanning longitudes 167deg through 360deg to 79deg at b=0deg, plus the entire area of the Magellanic Stream and Clouds, a total of 13,020 square degrees. The brightness temperature sensitivity will be very good, typically sigma_T ~ 1 K at resolution 30arcsec and 1 km/s. The survey has a wide spectrum of scientific goals, from studies of galaxy evolution to star formation, with particular contributions to understanding stellar wind kinematics, the thermal phases of the interstellar medium, the interaction between gas in the disk and halo, and the dynamical and thermal states of gas at various positions along the Magellanic Stream.

astro-ph.GA↗

arXiv2011

Planck Early Results XXIV: Dust in the diffuse interstellar medium and the Galactic halo

This paper presents the first results of comparison of Planck along with IRAS data with Green Bank Telescope 21-cm observations in 14 fields covering more than 800 square degrees at high Galactic latitude. Galactic dust emission for fields with average HI column density lower than 2 x 10^20 cm^-2 is well correlated with 21-cm emission. The residual emission in these fields, once the HI-correlated emission is removed, is consistent with the expected statistical properties of the cosmic infrared background fluctuations. Fields with larger column densities show significant excess dust emission compared to the HI column density. Regions of excess lie in organized structures that suggest the presence of hydrogen in molecular form, though they are not always correlated with CO emission. Dust emission from intermediate-velocity clouds is detected with high significance. Its spectral properties are consistent with, compared to the local ISM values, significantly hotter dust (T~20 K), lower sub-millimeter dust opacity, and a relative abundance of very small grains to large grains about four times higher. These results are compatible with expectations for clouds that are part of the Galactic fountain in which there is dust shattering and fragmentation. Correlated dust emission in HVCs is not detected; the average of the 99.9% confidence upper limits to the emissivity is 0.15 times the local ISM value at 857 and 3000 GHz, in accordance with gas phase evidence for lower metallicity and depletion in these clouds. Unexpected anti-correlated variations of the dust temperature and emission cross-section per H atom are identified in the local ISM and IVCs, a trend that continues into molecular environments. This suggests that dust growth through aggregation, seen in molecular clouds, is active much earlier in the cloud condensation and star formation processes.

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arXiv2011

Planck Early Results: The Galactic Cold Core Population revealed by the first all-sky survey

We present the statistical properties of the first version of the Cold Core Catalogue of Planck Objects (C3PO), in terms of their spatial distribution, temperature, distance, mass, and morphology. We also describe the statistics of the Early Cold Core Catalogue (ECC, delivered with the Early Release Compact Source Catalogue, ERCSC) that is the subset of the 915 most reliable detections of the complete catalogue. We have used the CoCoCoDeT algorithm to extract 10783 cold sources. Temperature and dust emission spectral index β values are derived using the fluxes in the IRAS 100 \mum band and the three highest frequency Planck bands. Temperature spans from 7K to 17K, and peaks around 13K. Data are not consistent with a constant value of β over the all temperature range. β ranges from 1.4 to 2.8 with a mean value around 2.1, and several possible scenarios are possible, including β(T) and the effect of multiple T components folded into the measurements. For one third of the objects the distances are obtained. Most of the detections are within 2 kpc in the Solar neighbourhood, but a few are at distances greater than 4 kpc. The cores are distributed from the deep Galactic plane, despite the confusion, to high latitudes (>30$^{\circle}$). The associated mass estimates range from 1 to $10^5$ solar masses. Using their physical properties these cold sources are shown to be cold clumps, defined as the intermediate cold sub-structures between clouds and cores. These cold clumps are not isolated but mostly organized in filaments associated with molecular clouds. The Cold Core Catalogue of Planck Objects (C3PO) is the first unbiased all-sky catalogue of cold objects. It gives an unprecedented statistical view to the properties of these potential pre-stellar clumps and offers a unique possibility for their classification in terms of their intrinsic properties and environment.

astro-ph.GA↗

arXiv2010

Clouds, filaments and protostars: the Herschel Hi-GAL Milky Way

We present the first results from the science demonstration phase for the Hi-GAL survey, the Herschel key-project that will map the inner Galactic Plane of the Milky Way in 5 bands. We outline our data reduction strategy and present some science highlights on the two observed 2° x 2° tiles approximately centered at l=30° and l=59°. The two regions are extremely rich in intense and highly structured extended emission which shows a widespread organization in filaments. Source SEDs can be built for hundreds of objects in the two fields, and physical parameters can be extracted, for a good fraction of them where the distance could be estimated. The compact sources (which we will call 'cores' in the following) are found for the most part to be associated with the filaments, and the relationship to the local beam-averaged column density of the filament itself shows that a core seems to appear when a threshold around A_V of about 1 is exceeded for the regions in the l=59° field; a A_V value between 5 and 10 is found for the l=30° field, likely due to the relatively larger distances of the sources. This outlines an exciting scenario where diffuse clouds first collapse into filaments, which later fragment to cores where the column density has reached a critical level. In spite of core L/M ratios being well in excess of a few for many sources, we find core surface densities between 0.03 and 0.5 g cm-2. Our results are in good agreement with recent MHD numerical simulations of filaments forming from large-scale converging flows.

astro-ph.GA↗

arXiv2010

Direct Estimate of Cirrus Noise in Herschel Hi-GAL Images

In Herschel images of the Galactic plane and many star forming regions, a major factor limiting our ability to extract faint compact sources is cirrus confusion noise, operationally defined as the "statistical error to be expected in photometric measurements due to confusion in a background of fluctuating surface brightness". The histogram of the flux densities of extracted sources shows a distinctive faint-end cutoff below which the catalog suffers from incompleteness and the flux densities become unreliable. This empirical cutoff should be closely related to the estimated cirrus noise and we show that this is the case. We compute the cirrus noise directly, both on Herschel images from which the bright sources have been removed and on simulated images of cirrus with statistically similar fluctuations. We connect these direct estimates with those from power spectrum analysis, which has been used extensively to predict the cirrus noise and provides insight into how it depends on various statistical properties and photometric operational parameters. We report multi-wavelength power spectra of diffuse Galactic dust emission from Hi-GAL observations at 70 to 500 microns within Galactic plane fields at l= 30 degrees and l= 59 degrees. We find that the exponent of the power spectrum is about -3. At 250 microns, the amplitude of the power spectrum increases roughly as the square of the median brightness of the map and so the expected cirrus noise scales linearly with the median brightness. Generally, the confusion noise will be a worse problem at longer wavelengths, because of the combination of lower angular resolution and the rising power spectrum of cirrus toward lower spatial frequencies, but the photometric signal to noise will also depend on the relative spectral energy distribution of the source compared to the cirrus.

astro-ph.GA↗

arXiv2009

Distribution and characteristics of Infrared Dark Clouds using genetic forward modelling

Infrared Dark Clouds (IRDCs) are dark clouds seen in silhouette in mid-infrared surveys. They are thought to be the birthplace of massive stars, yet remarkably little information exists on the properties of the population as a whole (e.g. mass spectrum, spatial distribution). Genetic forward modelling is used along with the Two Micron All Sky Survey and the Besancon Galactic model to deduce the three dimensional distribution of interstellar extinction towards previously identified IRDC candidates. This derived dust distribution can then be used to determine the distance and mass of IRDCs, independently of kinematic models of the Milky Way. Along a line of sight that crosses an IRDC, the extinction is seen to rise sharply at the distance of the cloud. Assuming a dust to gas ratio, the total mass of the cloud can be estimated. The method has been successfully applied to 1259 IRDCs, including over 1000 for which no distance or mass estimate currently exists. The IRDCs are seen to lie preferentially along the spiral arms and in the molecular ring of the Milky Way, reinforcing the idea that they are the birthplace of massive stars. Also, their mass spectrum is seen to follow a power law with an index of -1.75 +/- 0.06, steeper than giant molecular clouds in the inner Galaxy, but comparable to clumps in GMCs. This slope suggests that the IRDCs detected using the present method are not gravitationally bound, but are rather the result of density fluctuations induced by turbulence.

astro-ph.GA↗

arXiv2008

Science with ASKAP - the Australian Square Kilometre Array Pathfinder

[ABRIDGED VERSION] The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries. The SKA will be 50 times more sensitive than any existing radio facility. A majority of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from 300 MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phase-array feed systems on parabolic reflectors. This large field-of-view makes ASKAP an unprecedented synoptic telescope poised to achieve substantial advances in SKA key science. The central core of ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of the sites selected by the international community as a potential location for the SKA. Following an introductory description of ASKAP, this document contains 7 chapters describing specific science programmes for ASKAP. The combination of location, technological innovation and scientific program will ensure that ASKAP will be a world-leading radio astronomy facility, closely aligned with the scientific and technical direction of the SKA. A brief summary chapter emphasizes the point, and considers discovery space.

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arXiv2008

Science results from the imaging Fourier transform spectrometer SpIOMM

SpIOMM is an imaging Fourier transform spectrometer designed to obtain the visible range (350 to 850 nm) spectrum of every light source in a circular field of view of 12 arcminutes in diameter. It is attached to the 1.6-m telescope of the Observatoire du Mont Megantic in southern Quebec. We present here some results of three successful observing runs in 2007, which highlight SpIOMMs capabilities to map emission line objects over a very wide field of view and a broad spectral range. In particular, we discuss data cubes from the planetary nebula M27, the supernova remnants NGC 6992 and M1, the barred spiral galaxy NGC7479, as well as Stephans quintet, an interacting group of galaxies.

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arXiv2007

Detection of Endolithes Using Infrared Spectroscopy

On Earth, the Dry Valleys of Antarctica provide the closest martian-like environment for the study of extremophiles. Colonies of bacteries are protected from the freezing temperatures, the drought and UV light. They represent almost half of the biomass of those regions. Due to there resilience, endolithes are one possible model of martian biota. We propose to use infrared spectroscopy to remotely detect those colonies even if there is no obvious sign of their presence. This remote sensing approach reduces the risk of contamination or damage to the samples.

astro-ph↗

arXiv2007

The James Clerk Maxwell Telescope Legacy Survey of Nearby Star-forming Regions in the Gould Belt

This paper describes a James Clerk Maxwell Telescope (JCMT) legacy survey that has been awarded roughly 500 hrs of observing time to be carried out from 2007 to 2009. In this survey we will map with SCUBA-2 (Submillimetre Common User Bolometer Array 2) almost all of the well-known low-mass and intermediate-mass star-forming regions within 0.5 kpc that are accessible from the JCMT. Most of these locations are associated with the Gould Belt. From these observations we will produce a flux-limited snapshot of star formation near the Sun, providing a legacy of images, as well as point-source and extended-source catalogues, over almost 700 square degrees of sky. The resulting images will yield the first catalogue of prestellar and protostellar sources selected by submillimetre continuum emission, and should increase the number of known sources by more than an order of magnitude. We will also obtain CO maps with the array receiver HARP (Heterodyne Array Receiver Programme), in three CO isotopologues, of a large typical sample of prestellar and protostellar sources. We will then map the brightest hundred sources with the SCUBA-2 polarimeter (POL-2), producing the first statistically significant set of polarization maps in the submillimetre. The images and source catalogues will be a powerful reference set for astronomers, providing a detailed legacy archive for future telescopes, including ALMA, Herschel and JWST.

astro-ph↗

arXiv2007

Radio Polarimetry of the ELAIS N1 Field: Polarized Compact Sources

We present deep polarimetric observations at 1420 MHz of the European Large Area ISO Survey North 1 region (ELAIS N1) as part of the Dominion Radio Astrophysical Observatory Planck Deep Fields project. By combining closely spaced aperture synthesis fields, we image a region of 7.43 square degrees to a maximum sensitivity in Stokes Q and U of 78 microJy/beam, and detect 786 compact sources in Stokes I. Of these, 83 exhibit polarized emission. We find that the differential source counts (log N - log p) for polarized sources are nearly constant down to p > 500 microJy, and that these faint polarized radio sources are more highly polarized than the strong source population. The median fractional polarization is (4.8 +/- 0.7)% for polarized sources with Stokes I flux density between 1 and 30 mJy; approximately three times larger than sources with I > 100 mJy. The majority of the polarized sources have been identified with galaxies in the Spitzer Wide Area Infrared Extragalactic Survey (SWIRE) image of ELAIS N1. Most of the galaxies occupy regions in the IRAC 5.8/3.6 micron vs. 8.0/4.5 micron color-color diagram associated with dusty AGNs, or with ellipticals with an aging stellar population. A few host galaxies have colors that suggests significant PAH emission in the near-infrared. A small fraction, 12%, of the polarized sources are not detected in the SWIRE data. None of the polarized sources in our sample appears to be associated with an actively star-forming galaxy.

astro-ph↗

arXiv2007

The SCUBA-2 "All-Sky" Survey

The sub-millimetre wavelength regime is perhaps the most poorly explored over large areas of the sky, despite the considerable effort that has been expended in making deep maps over small regions. As a consequence the properties of the sub-millimetre sky as a whole, and of rare bright objects in particular, remains largely unknown. Here we describe a forthcoming survey (the SCUBA-2 ``All-Sky'' Survey, or SASSy) designed to address this issue by making a large-area map of approximately one-fifth of the sky visible from the JCMT (4800 square degrees) down to a 1 sigma noise level of 30 mJy/beam. This map forms the pilot for a much larger survey, which will potentially map the remaining sky visible from the JCMT, with the region also visible to ALMA as a priority. SASSy has been awarded 500 hours for the 4800 square degree pilot phase and will commence after the commissioning of SCUBA-2, expected in early 2008.

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