Fourier phase analysis in radio-interferometry

Most statistical tools used to characterize the complex structures of the interstellar medium can be related to the power spectrum, and therefore to the Fourier amplitudes of the observed fields. To tap into the vast amount of information contained in the Fourier phases, one may consider the probability distribution function (PDF) of phase increments, and the related concepts of phase entropy and phase structure quantity. We use these ideas here with the purpose of assessing the ability of radio-interferometers to detect and recover this information. By comparing current arrays such as the VLA and Plateau de Bure to the future ALMA instrument, we show that the latter is definitely needed to achieve significant detection of phase structure, and that it will do so even in the presence of a fair amount of atmospheric phase fluctuations. We also show that ALMA will be able to recover the actual "amount'' of phase structure in the noise-free case, if multiple configurations are used.Comment: Accepted for publication in "Astronomy & Astrophysics

GMRT and VLA observations at 49cm and 20cm of the HII region near l=24.4d, b=0.1d

We report multifrequency radio continuum and hydrogen radio recombination line observations of HII regions near l=24.8d b=0.1d using the Giant Metrewave Radio Telescope (GMRT) at 1.28 GHz (n=172), 0.61 GHz (n=220) and the Very Large Array (VLA) at 1.42 GHz (n=166). The region consists of a large number of resolved HII regions and a few compact HII regions as seen in our continuum maps, many of which have associated infrared (IR) point sources. The largest HII region at l=24.83d and b=0.1d is a few arcmins in size and has a shell-type morphology. It is a massive HII region enclosing ~ 550 solar mass with a linear size of 7 pc and an rms electron density of ~ 110 cm^-3 at a kinematic distance of 6 kpc. The required ionization can be provided by a single star of spectral type O5.5. We also report detection of hydrogen recombination lines from the HII region at l=24.83d and b=0.1d at all observed frequencies near Vlsr=100 km/s. We model the observed integrated line flux density as arising in the diffuse HII region and find that the best fitting model has an electron density comparable to that derived from the continuum. We also report detection of hydrogen recombination lines from two other HII regions in the field.Comment: 14 pages, 8 Figures. Uses JAA style file. Accepted for publication in Journal of Astrophysics and Astronomy. High resolution figures (fig 1a, fig 1b and fig 2b) can be downloaded from http://www.ncra.tifr.res.in/~ngk/G2

Detection of extended molecular gas in the disk of the LSB galaxy Malin 2

International audience Aims: Our goal is to see if there is molecular gas extending throughout the optical low surface brightness disk of the galaxy Malin 2. Methods: We used the heterodyne receiver array (HERA) mounted on the IRAM 30 m telecope to make deep observations at the frequency of the CO(2-1) line at nine different positions of Malin 2. With a total observing time of 11 h at a velocity resolution of 11 km s-1 we achieve a sensitivity level of 1 mK. Results: We detect CO(2-1) line emission from Malin 2. The line is detected in four of the nine HERA beams; a fifth beam shows a marginal detection. These results not only confirm that there is molecular gas in the disk of Malin 2, but they also show that it is spread throughout the inner 34 kpc radius as sampled by the observations of the galaxy disk. The mean molecular gas surface density in the disk is 1.1 ± 0.2 M&sun; pc-2, and the molecular gas mass lies between the limits 4.9 × 108 to 8.3 × 108~M&sun;. The observed velocity dispersion of the molecular gas is higher (~13 km s-1) than in star-forming galactic disks. This could explain the disk stability and its low star-formation activity

GMRT and VLA Observations at 49 cm and 20 cm of the HII Region near l = 24.8°, b = 0.1°

International audienceWe report multi-frequency radio continuum and hydrogen radio recombination line observations of HII regions near l = 24.8°, b = 0.1° using the Giant Metrewave Radio Telescope(GMRT) at 1.28 GHz (n = 172), 0.61 GHz (n = 220) and the Very Large Array (VLA) at 1.42 GHz (n = 166). The region consists of a large number of resolved HII regions and a few compact HII regions as seen in our continuum maps, many of which have associated infrared (IR) point sources. The largest HII region at l = 24.83° and b = 0.1° is a few arcmins in size and has a shell-type morphology. It is a massive HII region enclosing ˜550M with a linear size of 7 pc and an rms electron density of ˜110 cm-3 at a kinematic distance of 6 kpc. The required ionization can be provided by a single star of spectral type Omicr 5.5

GMRT and VLA Observations at 49 cm and 20 cm of the HII Region near l = 24.8°, b = 0.1°

International audienceWe report multi-frequency radio continuum and hydrogen radio recombination line observations of HII regions near l = 24.8°, b = 0.1° using the Giant Metrewave Radio Telescope(GMRT) at 1.28 GHz (n = 172), 0.61 GHz (n = 220) and the Very Large Array (VLA) at 1.42 GHz (n = 166). The region consists of a large number of resolved HII regions and a few compact HII regions as seen in our continuum maps, many of which have associated infrared (IR) point sources. The largest HII region at l = 24.83° and b = 0.1° is a few arcmins in size and has a shell-type morphology. It is a massive HII region enclosing ˜550M with a linear size of 7 pc and an rms electron density of ˜110 cm-3 at a kinematic distance of 6 kpc. The required ionization can be provided by a single star of spectral type Omicr 5.5

GMRT and VLA Observations at 49 cm and 20 cm of the HII Region near l = 24.8°, b = 0.1°

International audienceWe report multi-frequency radio continuum and hydrogen radio recombination line observations of HII regions near l = 24.8°, b = 0.1° using the Giant Metrewave Radio Telescope(GMRT) at 1.28 GHz (n = 172), 0.61 GHz (n = 220) and the Very Large Array (VLA) at 1.42 GHz (n = 166). The region consists of a large number of resolved HII regions and a few compact HII regions as seen in our continuum maps, many of which have associated infrared (IR) point sources. The largest HII region at l = 24.83° and b = 0.1° is a few arcmins in size and has a shell-type morphology. It is a massive HII region enclosing ˜550M with a linear size of 7 pc and an rms electron density of ˜110 cm-3 at a kinematic distance of 6 kpc. The required ionization can be provided by a single star of spectral type Omicr 5.5

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International audienceVO Paris Federation is a partnership between Paris Obser-vatory, IAP, IPSL and CEA. Its objectives are to provide VO access toits databases ressources, contribute to international standards develop-ments, implement VO compliant simulation codes and data visualisa-tion and analysis software. The various activities are organised into por-tals whose functions are (i) to provide visibility and information on theprojects and (ii) to encourage collaborations. The portals are linked tothematic activities and resources: solar system (ephemerides, astrometry,physical characteristic of small bodies of the solar system, planetology),reference systems, exoplanet database, legacy (archives from the Nan ̧cayRadio Telescope, some specific data from the DENIS and EROS surveys,MAMA), solar physics, stellar and galactic databases and services, atomicand molecular databases and services, simulation codes and data analysis

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