scholarly journals A coordinated radio and optical survey of M31

1985 ◽  
Vol 106 ◽  
pp. 435-436
Author(s):  
R.A.M. Walterbos ◽  
R. C. Kennicutt
Keyword(s):  
Large Scale ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Small Scale ◽  
Surface Photometry ◽  
Optical Surface ◽  
Schmidt Telescope ◽  
Infrared Observations ◽  
Andromeda Galaxy ◽  
Optical Surveys

At Leiden we are obtaining coordinated radio, optical and infrared observations of the Andromeda galaxy, M31. Its proximity offers us a unique opportunity to study both the large-scale and small-scale structure of a galaxy which is similar in many respects to the Milky Way. The WSRT has been used to obtain high-resolution (24″ × 36″) maps of M31 in the HI line and 21-and 49-cm radio-continuum emission. Recently the radio data have been complemented with optical surface photometry in UBVR and Hα, using the Burrell Schmidt telescope at Kitt Peak and the Palomar Schmidt. Results from the HI and IRAS infrared observations are presented elsewhere. Here we present some preliminary results from the radio-continuum and optical surveys.

scholarly journals The Large-Scale Radio Continuum Structure of Spiral Galaxies

1978 ◽  
Vol 77 ◽  
pp. 33-48 ◽  
Author(s):  
P.C. van der Kruit
Keyword(s):  
Large Scale ◽  
Spiral Galaxies ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Optical Image ◽  
Radio Continuum ◽  
Continuum Emission ◽  
The Galaxy ◽  
Continuum Structure ◽  
Disk Component

This review concerns the large-scale structure of radio continuum emission in spiral galaxies (“the smooth background”), by which we mean the distribution of radio surface brightness at scales larger than, say, 1 kpc. Accordingly the nuclear emission and structure due to spiral arms and HII regions will not be a major topic of discussion here. Already the first mappings of the galactic background suggested that there is indeed a distribution of radio continuum emission extending throughout the Galaxy. This conclusion has been reinforced by the earliest observations of M31 by showing that the general emission from this object extended over at least the whole optical image. More recently, van der Kruit (1973a, b, c) separated the radio emission from a sample of spiral galaxies observed at 1415 MHz with the Westerbork Synthesis Radio Telescope (WSRT) into a nuclear, spiral arm and “base disk” component, showing that the latter component usually contains most of the flux density. This latter component is largely non-thermal and extends over the whole optical image (see also van der Kruit and Allen, 1976). Clearly it is astrophysically interesting to discuss the large-scale structure of the radio continuum emission.

scholarly journals The Circumstellar Environment of LkHα 234

1987 ◽  
Vol 115 ◽  
pp. 368-368
Author(s):  
B. A. Wilking ◽  
L. G. Mundy ◽  
R. D. Schwartz
Keyword(s):  
High Resolution ◽  
Millimeter Wave ◽  
Spectral Dependence ◽  
Large Scale ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Owens Valley ◽  
Molecular Line ◽  
Continuum Source ◽  
Circumstellar Environment

We present high resolution (HPBW = 5 arcsec) continuum and molecular-line observations of the circumstellar environment of the emission-line star LkHα 234 made with the Owens Valley Millimeter-Wave Interferometer. These 98 GHz observations have revealed an unresolved continuum source coincident with the star and a 10 000 by 17000 A.U. ridge of enhanced CS(2-1) emission which peaks ∼ 4″ east of the star. The resulting spectral dependence for the radio continuum emission of ν1.5 is most easily interpreted as arising from a partially ionized stellar wind. Attempts are made to describe the properties of the CS emission in terms of a rotating molecular disk which would link LkHα 234 with large scale mass loss activity in the cloud. However, it appears most likely that the CS emission is arising from a dense (n(H2) ∼ 106 cm −3) condensation of gas adjacent to, but not dynamically associated with, the star.

scholarly journals Magnetism in galaxies – Observational overview and next generation radio telescopes

2010 ◽  
Vol 6 (S274) ◽  
pp. 325-332 ◽  
Author(s):  
Rainer Beck
Keyword(s):  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Milky Way ◽  
Cosmic Ray ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Radio Telescopes ◽  
Spiral Arms ◽  
Central Regions

AbstractThe strength and structure of cosmic magnetic fields is best studied by observations of radio continuum emission, its polarization and its Faraday rotation. Fields with a well-ordered spiral structure exist in many types of galaxies. Total field strengths in spiral arms and bars are 20–30 μG and dynamically important. Strong fields in central regions can drive gas inflows towards an active nucleus. The strongest regular fields (10–15 μG) are found in interarm regions, sometimes forming “magnetic spiral arms” between the optical arms. The typical degree of polarization is a few % in spiral arms, but high (up to 50%) in interarm regions. The detailed field structures suggest interaction with gas flows. Faraday rotation measures of the polarization vectors reveals large-scale patterns in several spiral galaxies which are regarded as signatures of large-scale (coherent) fields generated by dynamos. – Polarization observations with the forthcoming large radio telescopes will open a new era in the observation of magnetic fields and should help to understand their origin. Low-frequency radio synchrotron emission traces low-energy cosmic ray electrons which can propagate further away from their origin. LOFAR (30–240 MHz) will allow us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in galaxy clusters and in the Milky Way. Polarization at higher frequencies (1–10 GHz), to be observed with the EVLA, MeerKAT, APERTIF and the SKA, will trace magnetic fields in the disks and central regions of galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources with ASKAP and the SKA are dedicated to measure magnetic fields in distant intervening galaxies and clusters, and will be used to model the overall structure and strength of the magnetic field in the Milky Way.

scholarly journals Proceedings of Observatories: Nuffield Radio Astronomy Laboratories Jodrell Bank

1971 ◽  
Vol 8 ◽  
pp. 65-75
Author(s):  
Bernard Lovell
Keyword(s):  
Recent Work ◽  
Radio Astronomy ◽  
Supernova Remnants ◽  
Large Scale ◽  
Continuum Emission ◽  
Small Scale ◽  
Line Radiation ◽  
Transmission Properties ◽  
The Galaxy ◽  
The Continuum

The structure of the Galaxy can be studied by the following techniques: (i) measurements of the continuum emission, both on the large scale and from discrete objects such as supernova remnants; (ii) measurements of line radiation, again both from large and small scale features; and (iii) measurements of the transmission properties of the interstellar medium. All these techniques have been pursued in recent work at Jodrell Bank. This section describes work in the categories (i) and (iii); work under (ii) is described in Sections 6 and 7.

scholarly journals Molecular Gas Distribution and Dynamics in the Central Region of Galaxies

1994 ◽  
Vol 140 ◽  
pp. 293-299
Author(s):  
Sumio Ishizuki
Keyword(s):  
High Resolution ◽  
Central Region ◽  
Large Scale ◽  
Starburst Galaxies ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Molecular Gas ◽  
Gas Distribution

AbstractTo investigate the relation between a large-scale stellar bar and circumnuclear starburst, the CO (J=1→0) emission of circumnuclear regions of three starburst galaxies NGC2782, NGC3504, and M83 (NGC5236) have been mapped with the Nobeyama Millimeter Array. The high resolution CO (J=1→0) images indicate that the molecular gas in the three starburst galaxies is located interior to the innermost ends of the paired straight dust lanes. The molecular gas at the small radii is associated with their circumnuclear starburst sites which are indicated by radio continuum emission.

Deep Survey of the Radio Continuum Emission along the Southern Galactic Plane at 2·4 GHz

1995 ◽  
Vol 12 (1) ◽  
pp. 54-59 ◽  
Author(s):  
A. R. Duncan ◽  
R. T. Stewart ◽  
R. F. Haynes ◽  
K. L. Jones
Keyword(s):  
Large Scale ◽  
Galactic Plane ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Total Power ◽  
Latitude Range ◽  
Power Maps ◽  
Deep Survey ◽  
5 Ghz ◽  
Linear Polarisation

AbstractWe have just completed the observational stage of a 2·4 GHz survey of the Southern Galactic Plane, using the Parkes radiotelescope, between 238° ≤ l ≤ 365° and with a latitude range of at least |b| ≤ 5° (beamwidth ~9 arcmin). The survey details both continuum emission and linear polarisation down to rms noises of approximately 12 and 4 mJy/beam respectively. It is the most sensitive survey to date of the southern plane at this frequency and should nicely complement the Effelsberg northern plane surveys in addition to the recent southern surveys such as the 843 MHz MOST survey and the 5 GHz PMN survey. The total-power maps are now completed, and reduction of the polarisation data is still in progress. In addition to compact HII regions and extragalactic sources, we are detecting on our total-power images a considerable amount of large-scale structure, and a significant number of new SNR candidates and spur-like features.

scholarly journals Radio Continuum Emission in the Resonance-Ring Galaxies NGC 1433 and NGC 6300

1996 ◽  
Vol 157 ◽  
pp. 250-252
Author(s):  
Hemant Shukla ◽  
Stuart D. Ryder
Keyword(s):  
Radio Continuum ◽  
Continuum Emission ◽  
Surface Photometry ◽  
Orbital Resonance ◽  
Fabry Perot ◽  
Nuclear Ring ◽  
Ring Galaxies ◽  
Continuum Data ◽  
Compact Array

NGC 1433 is a nearly face-on prototypical ringed, barred galaxy. It has a nuclear ring, an inner ring and an outer pseudoring. Also present are symmetrical spiral arcs, also called “plumes”, leading the central bar. Based on a study using multicolor surface photometry and Hα Fabry-Perot interferometry, Buta (1986) was able to associate each of the ring features with a specific orbital resonance. NGC 6300, having almost an identical Hubble type and distance to that of NGC 1433, provides for an ideal comparison. It has no nuclear or outer rings. However, the inner ring is quite broad and dusty (Buta 1987). Radio continuum data were obtained with the Australia Telescope Compact Array (ATCA) at 1.38 GHz (bandwidth = 128.0 MHz) with maximum baselines of 1.5 km, yielding a resolution of ∼ 30″ and r.m.s. noise per map of 0.2 mJy Beam−1 for both of the galaxies. The Hα + N[II] images for both of the galaxies were obtained with the CTIO 1.5 m telescope.

scholarly journals Polarized Radio Emission from M51

1990 ◽  
Vol 140 ◽  
pp. 211-212 ◽  
Author(s):  
C. Horellou ◽  
R. Beck ◽  
U. Klein
Keyword(s):  
Large Scale ◽  
Azimuthal Angle ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Spiral Arms ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
First Time ◽  
Magnetic Spiral ◽  
Companion Galaxy

The polarized radio continuum emission of M51 is found to be strongest outside the optical spiral arms. The rotation measure varies double-sinusoidally with azimuthal angle which for the first time clearly shows a dominating bisymmetric spiral (BSS) structure of the large-scale magnetic field in M51. The pitch angle of the magnetic spiral is similar to that of the optical spiral arms. The lowest (axisymmetric) dynamo mode is possibly suppressed by interaction with the companion galaxy.

scholarly journals Radio constraints on dark matter annihilation in Canes Venatici I with LOFAR†

2020 ◽  
Vol 496 (3) ◽  
pp. 2663-2672 ◽  
Author(s):  
Martin Vollmann ◽  
Volker Heesen ◽  
Timothy W. Shimwell ◽  
Martin J Hardcastle ◽  
Marcus Brüggen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Dark Matter ◽  
Cross Section ◽  
Cosmic Ray ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Small Scale ◽  
Dark Matter Annihilation ◽  
Underlying Assumption ◽  
Field Strengths

ABSTRACT Dwarf galaxies are dark matter (DM) dominated and therefore promising targets for the search for weakly interacting massive particles (WIMPs), which are well-known candidates for DM. The annihilation of WIMPs produces ultrarelativistic cosmic ray electrons and positrons that emit synchrotron radiation in the presence of magnetic fields. For typical magnetic field strengths (few μG) and $\mathcal {O}$(GeV–TeV) WIMP masses, this emission peaks at hundreds of MHz. Here, we use the non-detection of 150-MHz radio continuum emission from the dwarf spheroidal galaxy Canes Venatici I with the Low-Frequency Array to derive constraints on the annihilation cross-section of WIMPs into primary electron–positron and other fundamental particle–antiparticle pairs. Our main underlying assumption is that the transport of the cosmic rays can be described by the diffusion approximation, thus requiring a non-zero magnetic field strength with small-scale structure. In particular, by adopting magnetic field strengths of $\mathcal {O}(1\, \mu$G) and diffusion coefficients $\sim \!10^{27}~\rm cm^2\, s^{-1}$, we obtain limits that are comparable with those set by the Fermi Large Area Telescope using gamma-ray observations of this particular galaxy. Assuming s-wave annihilation and WIMPs making up 100 per cent of the DM density, our benchmark limits exclude several thermal WIMP realizations in the [2, 20]-GeV mass range. We caution, however, that our limits for the cross-section are subject to enormous uncertainties that we also quantitatively assess. In particular, variations on the propagation parameters or on the DM halo can shift our limits up by several orders of magnitude (in the pessimistic scenario).

The radio continuum emission from the Galaxy

1964 ◽  
Vol 20 ◽  
pp. 102-106 ◽  
Author(s):  
B. Y. Mills
Keyword(s):  
Large Scale ◽  
Galactic Structure ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Physical Conditions ◽  
Galactic System ◽  
The Galaxy

Study of the radio continuum emission from the Galaxy is of interest both from the viewpoint of the physics of the radiating processes and the light which these shed on physical conditions within the Galaxy, and also because the large-scale organization of the emitting regions gives information about the structure of the Galaxy as a whole. We are concerned here particularly with the latter aspect, that is, the question of galactic structure, and for this we need to know the distribution of the emitting regions throughout the Galactic System.

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