ABSTRACT This paper introduces and describes the data cubes from GHIGLS, deep Green Bank Telescope (GBT) surveys of the 21 cm line emission of H i in 37 targeted fields at intermediate Galactic ...latitude. The GHIGLS fields together cover over 1000 deg2 at spatial resolution. The H i spectra have an effective velocity resolution of about 1.0 km s−1 and cover at least km s−1, extending to km s−1 for most fields. As illustrated with various visualizations of the H i data cubes, GHIGLS highlights that even at intermediate Galactic latitude the interstellar medium is very complex. Spatial structure of the H i is quantified through power spectra of maps of the integrated line emission or column density, . For our featured representative field, centered on the north ecliptic pole, the scaling exponents in power-law representations of the power spectra of maps for low-, intermediate-, and high-velocity gas components (LVC, IVC, and HVC) are , , and , respectively. After Gaussian decomposition of the line profiles, 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 , reflecting more small-scale structure in the cold neutral medium (CNM). There is evidence that filamentary structure in the H i 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, yielding values close to those obtained using diagnostics developed in our earlier independent analysis. The effect of 21 cm line opacity on the GHIGLS maps is estimated. Comparisons of the GBT data in a few of the GHIGLS fields with data from the EBHIS and GASS surveys explore potential issues in data reduction and calibration and reveal good agreement. The high quality of the GHIGLS data enables a variety of studies in directions of low Galactic column density, as already demonstrated by the Planck Collaboration. Fully reduced GHIGLS H i data cubes and other data products are available at www.cita.utoronto.ca/GHIGLS.
We present the first results from the science demonstration phase for the Hi-GAL survey, the Herschel key program 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° × 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 AV ~ 1 is exceeded for the regions in the l = 59° field; a AV value between 5 and 10 is found for the l = 30° field, likely due to the relatively higher 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.
ABSTRACT Observations of Galactic H i gas for seven targeted regions at intermediate Galactic latitude are presented at angular resolution using data from the DRAO Synthesis Telescope (ST) and the ...Green Bank Telescope (GBT). The DHIGLS data are the most extensive arcminute-resolution measurements of the diffuse atomic interstellar medium beyond those in the Galactic plane. The acquisition, reduction, calibration, and mosaicking of the DRAO ST data and the cross calibration and incorporation of the short-spacing information from the GBT are described. The high quality of the resulting DHIGLS products enables a variety of new studies in directions of low Galactic column density. We analyze the angular power spectra of maps of the integrated H i emission (column density) from the data cubes for several distinct velocity ranges. In fitting power-spectrum models based on a power law, but including the effects of the synthesized beam and noise at high spatial frequencies, we find exponents ranging from −2.5 to −3.0. Power spectra of maps of the centroid velocity for these components give similar results. These exponents are interpreted as being representative of the three-dimensional density and velocity fields of the atomic gas, respectively. We find evidence for dramatic changes in the H i structures in channel maps over even small changes in velocity. This narrow line emission has counterparts in absorption spectra against bright background radio sources, quantifying that the gas is cold and dense and can be identified as the cold neutral medium phase. Fully reduced DHIGLS H i data cubes and other data products are available at www.cita.utoronto.ca/DHIGLS.
Hi-GAL: The Herschel Infrared Galactic Plane Survey Molinari, S.; Swinyard, B.; Bernard, J.-P. ...
Publications of the Astronomical Society of the Pacific,
03/2010, Letnik:
122, Številka:
889
Journal Article
Recenzirano
Odprti dostop
Hi-GAL, the Herschel infrared Galactic Plane Survey, is an Open Time Key Project of theHerschel Space Observatory. It will make an unbiased photometric survey of the inner Galactic plane by mapping ...a2°
2
°
wide strip in the longitude range∣l∣ < 60°
∣
l
∣
<
60
°
in five wavebands between 70 μm and 500 μm. The aim of Hi-GAL is to detect the earliest phases of the formation of molecular clouds and high-mass stars and to use the optimum combination ofHerschelwavelength coverage, sensitivity, mapping strategy, and speed to deliver a homogeneous census of star-forming regions and cold structures in the interstellar medium. The resulting representative samples will yield the variation of source temperature, luminosity, mass and age in a wide range of Galactic environments at all scales from massive YSOs in protoclusters to entire spiral arms, providing an evolutionary sequence for the formation of intermediate and high-mass stars. This information is essential to the formulation of a predictive global model of the role of environment and feedback in regulating the star-formation process. Such a model is vital to understanding star formation on galactic scales and in the early universe. Hi-GAL will also provide a science legacy for decades to come with incalculable potential for systematic and serendipitous science in a wide range of astronomical fields, enabling the optimum use of future major facilities such asJWSTand ALMA.
Abstract
We present the first data release of the James Clerk Maxwell Telescope Plane Survey (JPS), the JPS Public Release 1. JPS is an 850-μm continuum survey of six fields in the northern inner ...Galactic plane in a longitude range of ℓ = 7°–63°, made with the Submillimetre Common-User Bolometer Array 2. This first data release consists of emission maps of the six JPS regions with an average pixel-to-pixel noise of 7.19 mJy beam−1, when smoothed over the beam, and a compact source catalogue containing 7813 sources. The 95 per cent completeness limits of the catalogue are estimated at 0.04 Jy beam−1 and 0.3 Jy for the peak and integrated flux densities, respectively. The emission contained in the compact source catalogue is 42 ± 5 per cent of the total and, apart from the large-scale (greater than 8 arcmin) emission, there is excellent correspondence with features in the 500-μm Herschel maps. We find that, with two-dimensional matching, 98 ± 2 per cent of sources within the fields centred at ℓ = 20°, 30°, 40° and 50° are associated with molecular clouds, with 91 ± 3 per cent of the ℓ = 30° and 40° sources associated with dense molecular clumps. Matching the JPS catalogue to Herschel 70-μm sources, we find that 38 ± 1 per cent of sources show evidence of ongoing star formation. The JPS Public Release 1 images and catalogue will be a valuable resource for studies of star formation in the Galaxy and the role of environment and spiral arms in the star formation process.
We present early results from the JCMT (James Clerk Maxwell Telescope) Plane Survey (JPS), which has surveyed the northern inner Galactic plane between longitudes ... = 7... and ... = 63... in the ...850-...m continuum with SCUBA-2 (Submm Common-User Bolometer Array 2), as part of the JCMT Legacy Survey programme. Data from the ... = 30... survey region, which contains the massive-star-forming regions W43 and G29.96, are analysed after approximately 40 per cent of the observations had been completed. The pixel-to-pixel noise is found to be 19 mJy beam... after a smooth over the beam area, and the projected equivalent noise levels in the final survey are expected to be around 10 mJy beam... An initial extraction of compact sources was performed using the FellWalker method, resulting in the detection of 1029 sources above a 5... surface-brightness threshold. The completeness limits in these data are estimated to be around 0.2 Jy beam... (peak flux density) and 0.8 Jy (integrated flux density) and are therefore probably already dominated by source confusion in this relatively crowded section of the survey. The flux densities of extracted compact sources are consistent with those of matching detections in the shallower APEX (Atacama Pathfinder Experiment) Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. We analyse the virial and evolutionary state of the detected clumps in the W43 star-forming complex and find that they appear younger than the Galactic-plane average. (ProQuest: ... denotes formulae/symbols omitted.)
We present the JCMT Gould Belt Survey's first look results of the southern extent of the Orion A Molecular Cloud (δ ≤ −5:31:27.5). Employing a two-step structure identification process, we construct ...individual catalogues for large-scale regions of significant emission labelled as islands and smaller-scale subregions called fragments using the 850 μm continuum maps obtained using SCUBA-2. We calculate object masses, sizes, column densities, and concentrations. We discuss fragmentation in terms of a Jeans instability analysis and highlight interesting structures as candidates for follow-up studies. Furthermore, we associate the detected emission with young stellar objects (YSOs) identified by Spitzer and Herschel. We find that although the population of active star-forming regions contains a wide variety of sizes and morphologies, there is a strong positive correlation between the concentration of an emission region and its calculated Jeans instability. There are, however, a number of highly unstable subregions in dense areas of the map that show no evidence of star formation. We find that only ∼72 per cent of the YSOs defined as Class 0+I and flat-spectrum protostars coincide with dense 850 μm emission structures (column densities >3.7 × 1021 cm−2). The remaining 28 per cent of these objects, which are expected to be embedded in dust and gas, may be misclassified. Finally, we suggest that there is an evolution in the velocity dispersion of YSOs such that sources which are more evolved are associated with higher velocities.
Abstract
Massive star formation occurs in the interior of giant molecular clouds and proceeds through many stages. In this work, we focus on massive young stellar objects (MYSOs) and ultracompact H
...ii
regions (UCH
ii
), where the former are enshrouded in dense envelopes of dust and gas, the latter of which has begun dispersing. By selecting a complete sample of MYSOs and UCH
ii
from the Red MSX Source (RMS) survey database, we combine Planck and IRAS data and build their spectral energy distributions. With these, we estimate the physical properties (dust temperatures, mass, luminosity) of the sample. Because the RMS database provides unique solar distances, it also allows the instantaneous star formation efficiency (SFE) to be investigated as a function of Galactocentric radius. We find that the SFE increases between 2 and 4.5 kpc, where it reaches a peak, likely in correspondence with the accumulation of molecular material at the end of the Galactic bar. It then stays approximately constant up to 9 kpc, after which it linearly declines, in agreement with predictions from extragalactic studies. This behavior suggests the presence of a significant amount of undetected molecular gas at
R
G
> 8 kpc. Finally, we present diagnostic colors that can be used to identify sites of massive star formation.
Context. The Draco nebula is a high Galactic latitude interstellar cloud observed at velocities corresponding to the intermediate velocity cloud regime. This nebula shows unusually strong CO emission ...and remarkably high-contrast small-scale structures for such a diffuse high Galactic latitude cloud. The 21 cm emission of the Draco nebula reveals that it is likely to have been formed by the collision of a cloud entering the disk of the Milky Way. Such physical conditions are ideal to study the formation of cold and dense gas in colliding flows of diffuse and warm gas. Aims. The objective of this study is to better understand the process of structure formation in a colliding flow and to describe the effects of matter entering the disk on the interstellar medium. Methods. We conducted Herschel-SPIRE observations of the Draco nebula. The clumpfind algorithm was used to identify and characterize the small-scale structures of the cloud. Results. The high-resolution SPIRE map reveals the fragmented structure of the interface between the infalling cloud and the Galactic layer. This front is characterized by a Rayleigh-Taylor (RT) instability structure. From the determination of the typical length of the periodic structure (2.2 pc) we estimated the gas kinematic viscosity. This allowed us to estimate the dissipation scale of the warm neutral medium (0.1 pc), which was found to be compatible with that expected if ambipolar diffusion were the main mechanism of turbulent energy dissipation. The statistical properties of the small-scale structures identified with clumpfind are found to be typical of that seen in molecular clouds and hydrodynamical turbulence in general. The density of the gas has a log-normal distribution with an average value of 103 cm-3. The typical size of the structures is 0.1−0.2 pc, but this estimate is limited by the resolution of the observations. The mass of these structures ranges from 0.2 to 20 M⊙ and the distribution of the more massive structures follows a power-law dN/ dlog (M) ~ M-1.4. We identify a mass-size relation with the same exponent as that found in molecular clouds (M ~ L2.3). On the other hand, we found that only 15% of the mass of the cloud is in gravitationally bound structures. Conclusions. We conclude that the collision of diffuse gas from the Galactic halo with the diffuse interstellar medium of the outer layer of the disk is an efficient mechanism for producing dense structures. The increase of pressure induced by the collision is strong enough to trigger the formation of cold neutral medium out of the warm gas. It is likely that ambipolar diffusion is the mechanism dominating the turbulent energy dissipation. In that case the cold structures are a few times larger than the energy dissipation scale. The dense structures of Draco are the result of the interplay between magnetohydrodynamical turbulence and thermal instability as self-gravity is not dominating the dynamics. Interestingly they have properties typical of those found in more classical molecular clouds.
New 1665- and 1667-MHz OH observations were made with the Green Bank Telescope at an angular resolution of 7 arcmin of 108 locations over two diffuse gas clouds at high Galactic latitude. A linear ...correlation is observed between the IRAS 100 μm infrared intensity, which traces all the gas, and the OH column density, indicating that the amount of OH increases with the visual extinction above a threshold value of AV≈ 0.5. N(OH) increases monotonically with N(H i) in up to N(OH) ≈ 0.25–0.3 × 1014 cm−2. At greater values of N(OH) the H i column density saturates at N(H i) ≈ 5 × 1020 cm−2, suggesting that there is molecular gas not traced by H i. No correlation is found between the 12CO integrated intensity and the OH column density, indicating that OH might be a better tracer of H2 than CO in those diffuse regions. An H i column density of at least ≈2.2–2.9 × 1020 cm−2 is needed for the formation of OH, but in regions where the cloud is less shielded from the interstellar radiation field the value rises to N(H i) = 3.3 × 1020 cm−2.
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