scholarly journals ATLASGAL-selected massive clumps in the inner Galaxy

2020 ◽  
Vol 644 ◽  
pp. A160
Author(s):  
W.-J. Kim ◽  
F. Wyrowski ◽  
J. S. Urquhart ◽  
J. P. Pérez-Beaupuits ◽  
T. Pillai ◽  
...  
Keyword(s):  
Column Density ◽  
Detection Rate ◽  
Ultra Violet ◽  
Large Area ◽  
Detection Rates ◽  
Ultra Violet Radiation ◽  
The Galaxy ◽  
Area Survey ◽  
Far Ultraviolet ◽  
Grain Surface

Aims. We study ten molecular transitions obtained from an unbiased 3 mm molecular line survey using the IRAM 30 m telescope toward 409 compact dust clumps identified by the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) to better understand the photodissociation regions (PDRs) associated with these clumps. The main goal of this study is to investigate whether the abundances of the selected molecules show any variations resulting from the PDR chemistry in different clump environments. Methods. We selected HCO, HOC+, C2H, c-C3H2, CN, H13CN, HC15N, and HN13C as PDR tracers, and H13CO+ and C18O as dense gas tracers. By using estimated optical depths of C2H and H13CN and assuming optically thin emission for other molecular transitions, we derived the column densities of those molecules and their abundances. To assess the influence of the presence and strength of ultra-violet radiation, we compare abundances of three groups of the clumps: HII regions, infrared bright non-HII regions, and infrared dark non-HII regions. Results. We detected C18O, H13CO+, C2H, c-C3H2, CN, and HN13C toward most of the observed dust clumps (detection rate >94%), and H13CN is also detected with a detection rate of 75%. On the other hand, HCO and HC15N show detection rates of 32 and 39%, respectively, toward the clumps, which are mostly associated with HII region sources: detection rates of HCO and HC15N toward the HII regions are 66 and 79%. We find that the abundances of HCO, CN, C2H, and c-C3H2 decrease as the H2 column density increases, indicating high visual extinction, while those of high-density tracers (i.e., H13CO+ and HC15N) are constant. In addition, N(HCO)/N(H13CO+) ratios significantly decrease as H2 column density increases, and, in particular, 82 clumps have X(HCO) ≳ 10−10 and N(HCO)/N(H13CO+) ≳ 1, which are indications of far-ultraviolet (FUV) chemistry. This suggests the observed HCO abundances are likely associated with FUV radiation illuminating the PDRs. We also find that high N(c-C3H2)/N(C2H) ratios found for HII regions that have high HCO abundances (≳10−10) are associated with more evolved clumps with high Lbol/Mclump. This trend might be associated with grain-surface processes, which determine the initial abundances of these molecules, and time-dependent effects in the clumps corresponding to the envelopes around dense PDRs and HII regions. In addition, some fraction of the measured abundances of the small hydrocarbons of the HII sources may be the result of the photodissociation of PAH molecules.

scholarly journals ATLASGAL, the APEX Telescope Large Area Survey of the Galaxy

2009 ◽  
Vol 5 (H15) ◽  
pp. 780-780
Author(s):  
F. Schuller ◽  
K. M. Menten ◽  
F. Wyrowski ◽  
H. Beuther ◽  
S. Bontemps ◽  
...  
Keyword(s):  
Galactic Plane ◽  
High Mass ◽  
Current Status ◽  
Continuum Emission ◽  
Mass Star ◽  
Large Area ◽  
Submillimeter Wavelengths ◽  
The Galaxy ◽  
First Results ◽  
Area Survey

AbstractSubmillimeter continuum emission traces high molecular column densities and, thus, dense cloud regions in which new stars are forming. Surveys of the Galactic plane in such emission have the potential of delivering an unbiased view of high-mass star formation throughout the Milky Way. Here we present the scope, current status and first results of ATLASGAL, an ongoing survey of the Galactic plane using the Large APEX Bolometer Camera (LABOCA) on the Atacama Pathfinder Experiment (APEX) telescope at the Chajnantor plateau in Chile. Aimed at mapping 360 square degrees at 870 μm, with a uniform sensitivity of 50 mJy/beam, this survey will provide the first unbiased sample of cold dusty clumps in the Galaxy at submillimeter wavelengths. These will be targets for molecular line follow-up observations and high resolution studies with ALMA and the EVLA.

scholarly journals ATLASGAL – physical parameters of dust clumps associated with 6.7 GHz methanol masers

2019 ◽  
Author(s):  
S J Billington ◽  
J S Urquhart ◽  
C König ◽  
T J T Moore ◽  
D J Eden ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Evolutionary Process ◽  
Volume Density ◽  
High Mass ◽  
Physical Parameters ◽  
Mass Star ◽  
Large Area ◽  
The Galaxy ◽  
Area Survey ◽  
Methanol Masers

Abstract We have constructed the largest sample of dust-associated class II 6.7 GHz methanol masers yet obtained. New measurements from the the Methanol MultiBeam (MMB) Survey were combined with the 870 $\mu$m APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) and the 850 $\mu$m JCMT Plane Survey (JPS). Together with two previous studies we have now identified the host clumps for 958 methanol masers across the Galactic Plane, covering approximately 99 per cent of the MMB catalogue and increasing the known sample of dust-associated masers by over 30 per cent. We investigate correlations between the physical properties of the clumps and masers using distances and luminosities drawn from the literature. Clumps hosting methanol masers are significantly more compact and have higher volume densities than the general population of clumps. We determine a minimum volume density threshold of n(H2) ≥ 104 cm−3 for the efficient formation of intermediate- and high-mass stars. We find 6.7 GHz methanol masers are associated with a distinct part of the evolutionary process (Lbol/Mfwhm ratios of between 100.6 and 102.2) and have well defined turning on and termination points. We estimate the lower limit for the mass of embedded objects to be ≥6 M⊙ and the statistical lifetime of the methanol maser stage to be ∼3.3 × 104 yrs. This suggests that methanol masers are indeed reliable tracers of high mass star formation, and indicates that the evolutionary period traced by this marker is relatively rapid.

scholarly journals ATLASGAL – The APEX telescope large area survey of the galaxy at 870 $\mathsf{\mu}$m

2009 ◽  
Vol 504 (2) ◽  
pp. 415-427 ◽  
Author(s):  
F. Schuller ◽  
K. M. Menten ◽  
Y. Contreras ◽  
F. Wyrowski ◽  
P. Schilke ◽  
...  
Keyword(s):  
Large Area ◽  
The Galaxy ◽  
Area Survey

scholarly journals Modelled 3D distribution of OH/IR stars in the Galactic disc

2021 ◽  
Vol 502 (2) ◽  
pp. 3012-3020
Author(s):  
Y Uno ◽  
H Imai ◽  
K Shinano ◽  
H-H Qiao ◽  
J R Dawson ◽  
...  
Keyword(s):  
Simple Model ◽  
Galactic Plane ◽  
Phase 1 ◽  
Galactic Disc ◽  
Large Area ◽  
Luminosity Functions ◽  
Ir Stars ◽  
The Galaxy ◽  
Area Survey ◽  
Maser Sources

ABSTRACT We have modelled the 3D distribution of OH/IR stars in the Galactic plane, traced by 1612 MHz OH maser sources with classic double horned spectral profiles. We statistically analysed over 700 maser sources detected by the HI/OH/Recombination line survey of the Milky Way (THOR) and the Australia Telescope Compact Array interferometric follow-up observations of the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). With a simple model constructed from a classical density distribution of stars and luminosity functions of OH maser sources in the Galaxy, we estimate the scale height, or the half thickness of the OH/IR star distribution along the Galactic disc to be 90–290 pc. The simple model also implies that there are ∼4000 OH/IR stars hosting 1612 MHz OH masers along the Galactic Plane. Therefore, next generation telescopes such as the Australian Square Kilometre Array Pathfinder (ASKAP) and SKA Phase 1 will detect about 80 per cent of such OH/IR stars in the Galaxy at a 10 mJy detection limit. Comparing the data of previously detected circumstellar 1612 MHz OH maser sources with those of THOR and SPLASH, the maser source lifetime is estimated to be ∼300 yr. This is likely a lower limit, since non-detections of masers in some cases could be affected by the flux variation of the maser source.

scholarly journals ATLASGAL: the APEX Telescope Large Area Survey of the Galaxy

2011 ◽  
Vol 52 ◽  
pp. 129-134 ◽  
Author(s):  
F. Wyrowski ◽  
F. Schuller ◽  
K.M. Menten ◽  
L. Bronfman ◽  
T. Henning ◽  
...  
Keyword(s):  
Large Area ◽  
The Galaxy ◽  
Area Survey

scholarly journals Intense L-Band Solar Radio Bursts Detection Based on GNSS Carrier-To-Noise Ratio Decrease over Multi-Satellite and Multi-Station

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1405
Author(s):  
Fan Yang ◽  
Xuefen Zhu ◽  
Xiyuan Chen ◽  
Mengying Lin
Keyword(s):  
Detection Rate ◽  
Solar Radio ◽  
Detection Method ◽  
Radio Bursts ◽  
Large Area ◽  
Solar Radio Bursts ◽  
High Detection Rate ◽  
Detection Rates ◽  
L Band ◽  
Noise Ratio

Intense solar radio bursts (SRBs) can increase the energy noise and positioning error of the bandwidth of global navigation satellite system (GNSS). The study of the interference from intense L-band SRBs is of great importance to the steady operation of GNSS receivers. Based on the fact that intense L-band SRBs lead to a decrease in the carrier-to-noise ratio (C/N0) of multiple GNSS satellites over a large area of the sunlit hemisphere, an intense L-band SRB detection method without the aid of a radio telescope is proposed. Firstly, the valley period of a single satellite at a single monitoring station is detected. Then, the detection of SRBs is achieved by calculating the intersection of multiple satellites and multiple stations. The experimental results indicate that the detection rates of GPS L2 and GLONASS G2 are better than those of GPS L1 L5, GLONASS G1, and Galileo E1 E5. The detection rate of SRBs can reach 80% with a flux density above 800 solar flux unit (SFU) at the L2 frequency of GPS. Overall, the detection rate is not affected by the satellite distribution relative to the Sun. The proposed detection method is low-cost and has a high detection rate and low false alarm rate. This method is a noteworthy reference for coping with interference in GNSS from intense L-band SRBs.

Ultra-Fast Melting and Solidification Behaviour of Amorphous and Crystalline Silicon

1983 ◽  
Vol 23 ◽  
Author(s):  
A.G. Cullis ◽  
H.C. Webber ◽  
N.G. Chew
Keyword(s):  
Crystal Growth ◽  
Heat Flow ◽  
Crystalline Silicon ◽  
Computer Modelling ◽  
Ultra Violet ◽  
Large Area ◽  
Ultra Violet Radiation ◽  
Theoretical Predictions ◽  
Violet Radiation ◽  
Melting And Solidification

ABSTRACTSubnanosecond ultra-violet radiation pulses are used to produce relatively thick, large area amorphous layers onSi crystals by transient melting and solidification. The different behaviours of (001) and (111) Si orientations are highlighted. Observations of crystal growth phenomena during solidification at velocities lower than required for amorphization are correlated with theoretical predictions. Computer modelling of heat flow in amorphous silicon is refined.

Physical Characteristics of Very Low Temperature Anodic Oxides of Polycrystalline Si Films

1999 ◽  
Vol 558 ◽  
Author(s):  
H. Plantier ◽  
J. Pelletier ◽  
R. A. B. Devine ◽  
G. Vincent
Keyword(s):  
Low Temperature ◽  
Electric Fields ◽  
Single Crystal Silicon ◽  
Ultra Violet ◽  
Electrical Measurements ◽  
Large Area ◽  
Crystal Silicon ◽  
Technical Problems ◽  
Ultra Violet Radiation ◽  
Very Low Temperature

ABSTRACTControlled oxidation of polycrystalline and single crystal silicon has been carried out at temperatures < 100 °C using microwave excited, plasma assisted anodisation. Oxide thicknesses up to 30 nm have been obtained in times ∼ 15 minutes. The growth kinetics are similar for both types of Si. The results of infrared absorption measurements clearly indicate that the anodic oxides have a network structure significantly different to that of high temperature, thermally grown oxides and this is partly due to ultra-violet radiation present in the plasma during growth. Electrical measurements (CV, IV) are underway on simple MOS capacitors. The results indicate that the plasma oxides have acceptable levels of fixed oxide charge but that the breakdown electric fields are presently low. Preliminary data suggests that these very low temperature oxides are suitable for TFT applications though some technical problems need to be addressed. Given these reservations the processing of large area flat panel displays using this type of plasma assisted oxidation is perfectly feasible.

scholarly journals The Australia Telescope Large Area Survey: Measuring the AGN contribution to galaxies over cosmic time

2013 ◽  
Vol 9 (S304) ◽  
pp. 93-93
Author(s):  
Kate Chow
Keyword(s):  
Cosmic Time ◽  
Host Galaxy ◽  
Evolutionary Stage ◽  
Large Area ◽  
X Ray ◽  
Star Forming ◽  
Total Luminosity ◽  
The Galaxy ◽  
Area Survey ◽  
The Relationship

AbstractThe Australia Telescope Large Area Survey (ATLAS) is the widest deep radio survey ever attempted, covering ~7deg2 across its two fields, the Chandra Deep Field South (CDFS) and the European Large Area ISO Survey South 1 Region (ELAIS-S1). ATLAS has extensive multiwavelength data, including optical, infrared and X-ray, to complement its ~15μJy rms 1.4 GHz radio data. At these faint radio flux densities, the proportion of AGN to star-forming galaxies (SFGs) is high, and there are likely many composite objects, which have both an AGN and ongoing star formation. In ATLAS, we estimate that the number of AGN is approximately 50%, and this proportion will change with decreasing flux density. To understand the relationship between the AGN and the host galaxy, we need to measure the contribution of the AGN to the total luminosity, and determine how this varies with the evolutionary stage of the galaxy. Here I present results exploring the AGN contribution to galaxies over cosmic time, through the use of different multiwavelength discriminants.

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