Radio Continuum Surveys Research Articles

The Marseille Observatory Hα Survey: Comparisons by CO, 6 CM and IRAS Data

The Marseille Observatory Hα survey supplies Hα velocities of the ionized hydrogen over large zones of the sky towards the galactic plane. This survey, led at the ESO La Silla, uses a 36 cm telescope equiped with a scanning Fabry-Perot interferometer and a photon counting camera (Le Coarer et al. 1992). About 250 fields (39′×39′) toward the galactic plane have already been covered (see Figure 1) with a spatial resolution of 9″×9″ and a spectral resolution of 5 km s–1. This allows us to observe the discrete HII regions and the diffuse ionized gas widely distributed between them and to separate the distinct layers found along the line of sight. HII regions are often grouped on the molecular cloud surface, then CO, radio continuum and recombination lines surveys of the galactic plane are also essential to distinguish the HII region-molecular cloud complexes met on the line of sight, and in order to take dynamical effects into account, such as the champagne effect, for the kinematic distance determination. Indeed, the spiral structure pattern determination requires avoiding any artificial spread by clearly identifying the giant complexes composed of molecular clouds, HII regions, diffuse ionized hydrogen widely surrounding them, and exciting stars. On the other hand the ionized gas data (Hα and recombination lines) associated with IRAS data help us to study the nature of the young objects constituent of these complexes and to assess their detectability. We present two fields from the Hα survey and parallel large scale investigations.

All‐Sky 4.85 GHz Flux Measurements of HiiRegions

We present an all-sky flux catalog of 760 H II regions with angular sizes ranging up to 10' at 4.85 GHz. The data were compiled in a self-consistent manner from existing images of the Green Bank and Parkes-MIT-NRAO 4.85 GHz radio continuum surveys. Nearly 35% of these H II regions have fluxes measured from these surveys for the first time. We compared our results to the previously published source catalogs that fit the same data. The new flux measurements agree within 5%-7% of these values and fall well within the formal errors. The diameters fall within 16% of the previously published fits to the same data, which is within the formal uncertainties of these values.

A Three‐dimensional Decomposition of the Infrared Emission from Dust in the Milky Way

We have constructed a three-dimensional model of the Galactic large-scale infrared emission from dust associated with the molecular neutral atomic (H I), and extended low-density cm~3) (H 2 ), (n e D 1E100 ionized (H II) gas phases of the interstellar medium. The model incorporates a three-dimensional map of the molecular and neutral atomic hydrogen gas distributions, derived from available 12CO and H I surveys by using the radial velocity information in the spectral lines as a distance indicator, and available 5 and 19 GHz radio continuum surveys to trace the column density of ionized gas. We use the model to decompose the Di†use Infrared Background Experiment (DIRBE) 12E240 km obserCOBE5 vations of the Galactic plane region ( o b o „ 5i), from which the zodiacal light and stellar emission have been subtracted, into distinct emission components associated with each gas phase within selected ranges of Galactocentric distance. An interstellar dust model is ‐tted to the resulting infrared spectra to derive the following quantities within each Galactocentric distance interval: (1) the abundance and equilibrium temperature of the large dust grain component within each gas phase; (2) estimates of the abundance of very small (\200 transiently heated dust grains and polycyclic aromatic hydrocarbon (PAH) mol”) ecules; and (3) constraints on various model parameters, such as the energy density of the ambient interstellar radiation ‐eld, which heats the dust within the H I gas phase. Our results show steep negative Galactocentric gradients in the equilibrium temperature of the large dust grain component within the H I, and H II gas phases, the GalaxyIs ambient interstellar radiH 2 , ation ‐eld, and the dust-to-gas mass ratio for each gas phase. The intensity of the ambient interstellar radiation ‐eld increases by a factor of D3 between the solar circle (8.5 kpc) and the molecular ring at a Galactocentric distance of D5 kpc. The dust abundance gradient of ([0.05 ^ 0.03) dex kpc~1 is equivalent, within the uncertainties, to the metallicity gradient in the Galactic disk. The derived emission spectra are consistent with a model in which very small transiently heated dust grains and PAHs are abundant and the dominant contributors to the mid-infrared (5 km \j 40 km) luminosity from a Galactocentric distance of 2 kpc out to a Galactocentric distance of at least 12 kpc, and indicate that the relative abundance of the PAHs is signi‐cantly higher in the outer region of the Galactic disk than inside the solar circle. We combine the results of our decomposition algorithm with the results of a study of optical extinction at high Galactic latitude to derive the radial distribution of optical opacity in the Galactic disk and ‐nd that our Galaxy would be e†ectively transparent Galaxy) 0.2 mag] to an external obser[A B (total ver viewing it at a low inclination (i 30i). All of the Galactic infrared emission observed by the DIRBE can be accounted for by dust associated with gas that is detected by current radio surveys, refuting the recent suggestion that a large fraction of the dynamically inferred hidden mass in spiral galaxies may be due to unseen gas and stars in the disk of the galaxies. Subject headings: di†use radiation E dust, extinction E Galaxy: structure E infrared: ISM: continuum E ISM: abundances E ISM: molecules

Magnetic Fields in the Irregular Galaxy LMC

New radio continuum surveys allowed the determination of the magnetic field in the Large Magellanic Cloud. The magnetic field is filamentary, extending to the south of the 30 Doradus nebula. Some possible explanations for this unusual morphology are discussed.

The extended non-thermal radio emission from the Small Magellanic Cloud

Radio continuum surveys of the Small Magellanic Cloud (SMC) at 843 MHz have been made using the Parkes 64-m radio telescope. After subtracting non-thermal emission from background sources, identified supernova remnants and thermal emissions scaled from an Hα map, the resulting large-scale non-thermal emission is used to estimate the distribution of the magnetic field of the SMC

Radio continuum emission from the Magellanic Clouds

New radio continuum surveys of the Large and the Small Magellanic Cloud have been completed recently at four frequencies, using the Parkes 64-m telescope. Here we shall discuss briefly the overall radio morphology of the Clouds at different frequencies and discuss the detected linear polarization. A preliminary integrated radio continuum spectrum of the Large Magellanic Cloud is also presented. Various aspects of future studies will be outlined.

Radio Studies of Cosmic Rays in the Galaxy

Changes of the cosmic ray electron spectrum throughout the Galaxy have been found, based on the comparison of large-scale radio continuum surveys. These observations are not compatible with the assumption of a static Galactic halo, but indicate the existence of a Galactic wind. Galactic plane surveys reveal sources of cosmic ray electrons in the Galactic disk. Recent studies of the population of radio sources show no evidence for a large number of compact Galactic non-thermal sources. Most of the extended sources are probably HII-regions. Relatively few new supernova remnants (SNRs) with low surface brightness could be identified. Most of the non-thermal emission in the disk-halo interface seems diffuse or unresolved, even at arcmin angular resolution.

Multi-epoch radio continuum surveys of the Rho Ophiuchi dark cloud

view Abstract Citations (61) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multi-Epoch Radio Continuum Surveys of the Rho Ophiuchi Dark Cloud Stine, P. C. ; Feigelson, E. D. ; Andre, P. ; Montmerle, T. Abstract Radio-continuum surveys of 4 sq. deg of the ρ Ophiuchi cloud were conducted on four occasions at 1.4 GHz with the Very Large Array to study the variability of radio counterparts of over one hundred pre-main-sequence stars detected at X-ray, infrared, and optical wavelengths. These observations are supplemented with 5 GHz observations of the dense core region of the cloud and pointed observations of selected sources. This work significantly increases the sensitivity of a previous study by André, Montmerle, and Feigelson (1987), in which eight definite young stellar radio sources were uncovered. In this study, only one new reliable stellar source was found, located near the cloud core. The overwhelming majority (≡90%) of young stellar objects over a large area remain undetected to low flux-density levels (≡1 mJy). The failure to detect most PMS stars in ρ Ophiuchi and other star-formation regions may be explained by a sufficiently dense layer of circumstellar ionized material, such as a weak stellar wind, that absorbs nonthermal surface radio emission but is not itself detectable in radio. It seems that the stellar radio sources in the ρ Ophiuchi cloud are the prototypes of a new, rare class of young stellar objects. These sources are characterized by an absence of dense circumstellar ionized material and by extended magnetic structures with sizes ⪆3 stellar radii. Publication: The Astronomical Journal Pub Date: October 1988 DOI: 10.1086/114889 Bibcode: 1988AJ.....96.1394S Keywords: Early Stars; Ophiuchi Clouds; Pre-Main Sequence Stars; Sky Surveys (Astronomy); Stellar Flares; Very Large Array (Vla); Radio Emission; Stellar Activity; Stellar Mass; X Ray Sources; Astrophysics; STARS: PRE-MAIN-SEQUENCE full text sources ADS | data products SIMBAD (220)

Radio Continuum Surveys Of The Sky

Radio continuum surveys give us the fundamental information about the distribution of the radio intensity across the sky. The radio waves originate in three fundamental emitting processes and are measured superposed in the antenna beam. At the lowest radio frequencies (below 10 GHz) the nonthermal emission process (synchrotron radiation) predominates. This radio emission comes from supernova remnants, from the “galactic background” (relativistic electrons diffusing in galactic magnetic fields), but also from extragalactic objects (galaxies, quasars, radio galaxies, etc.). In the frequency range 10 GHz < f < 300 GHz the thermal (free-free) process becomes dominant. In the Galaxy we see the HII regions along the galactic plane. In nearby galaxies we can identify the thermal emission in the disks. Above 300 GHz the dust is seen. This is the boundary region between radio and far-infrared radiation.

New Supernova Remnants from Deep Radio Continuum Surveys

AbstractBased on radio continuum surveys of the Galactic plane at wavelengths of 21 cm and 11 cm we have so far identified about 32 new supernova remnants in the area 357°.4 ≤ℓ≤ 76°. |b| ≤ 5°. This increases the number of known objects in this field by about 68%. Most of them are in the Galactic latitude range |b| 〉 0°.5. Some implications are discussed.

Star Formation in the Large Magellanic Cloud

Methods used in pattern recognition and cluster analysis are applied to investigate the spatial distribution of the star forming regions. The fractal dimension of these structures is deduced. The new 21 cm, radio continuum (1.4 GHz) and IRAS surveys reveal scale structures of 700 pc to 1500 pc being identical with the optically identified star forming sites. The morphological structures delineated by young stars reflect physical parameters which determine the star formation in this galaxy. The formation of spiral arm filaments is understandable by stochastic selfpropagating star formation processes.

The All-Sky 408 MHz Survey

The 408 MHz All-sky Survey has been made from four radio continuum surveys observed between 1965 and 1978, using the Jodrell Bank MKI telescope, the Effelsberg 100 metre telescope and the Parkes 64 metre telescope. A detailed description of the survey data reduction and calibration methods, with preliminary astronomical results will soon be published and a second paper will give an atlas of maps at the full survey resolution of 51′ arc between half power points.

Far-infrared survey of Cygnus X

Results of a new far-infrared survey of Cygnus X conducted with 12-arcmin resolution are presented. Forty-nine sources were observed, 39 of them for the first time. Associations are made with sources from mid-infrared, radio continuum, and CO radio line surveys.