Radio Emission Of Galaxies Research Articles

Simulating Electron Transport and Synchrotron Emission in Radio Galaxies: Shock Acceleration and Synchrotron Aging in Axisymmetric Flows

We introduce a simple and economical but effective method for including relativistic electron transport in multidimensional simulations of radio galaxies. The method is designed to follow explicitly diffusive acceleration at shocks, and, in smooth flows, second-order Fermi acceleration, plus adiabatic and synchrotron losses for electrons in the energy range responsible for radio emission in these objects. We are able to follow both the spatial and the energy (momentum) distributions of the electrons, so that direct synchrotron emission properties can be modeled in time-dependent simulated flows of this type for the first time. That feature is essential if simulations are to bridge successfully the fundamental physical gap between flow dynamics and observed emissions. As an initial step toward that goal, we present results from some axisymmetric MHD simulations of Mach 20 light jet flows. These explicitly explore the effects of shock acceleration, as well as adiabatic expansion and synchrotron aging in smooth flows. The simulations demonstrate the importance of the fact that even for steady inflows jet terminal shocks are not simple, steady plane structures. Most importantly, this should play a very major role in determining the properties of synchrotron emission within the terminal hot spot and in the lobes generated by the jet back flow. In fact, the outflows are inherently complex, because of the basic "driven" character of a jet flow. Consequently, the nonthermal electron population emerging from the jet may encounter a wide range of shock types and strengths, as well as of magnetic field environments. We may expect to find a complex range in synchrotron spectral and brightness patterns associated with terminal hot spots and lobes. These include the possibility of steep spectral gradients (of either sign) within hot spots, the potential in lobes for islands of flat-spectrum electrons within steeper spectral regions (or the reverse), and spectral gradients coming from the dynamical history of a given flow element rather than from synchrotron aging of the embedded electrons. Finally, synchrotron "aging" in the lobes tends to proceed more slowly than one would estimate from regions of high emissivity. This is a consequence of the fact that those regions are ordinarily places where the magnetic fields are the strongest, so that the instantaneous rates of energy loss are atypical of the full history of the electron population. This feature supports earlier suggestions that nonuniform field structures may help to explain why dynamical ages of FR II sources often seem to be greater than the apparent age of the electrons radiating in the lobes, as measured in terms of spectral steepening, or the absence thereof.

Energy distributions of radio galaxies

Far-infrared observations of 140 radio galaxies which span a range of over four orders of magnitude in radio power, (from weak nuclear sources in nearby galaxies, to powerful FR II doubled lobed sources at moderate redshift) are presented. The strength of the far-infrared emission is more closely correlated with core than total radio emission. Far-infrared emission in radio galaxies represents star formation that is more closely tied to the active nucleus than to the global properties of the galaxy. The far-infrared luminosity function shows good continuity between radio galaxies and radio loud quasars.

The spatial correlation between far-infrared and radio emission in galaxies - II. Far-infrared models of NGC 6946

The far-infrared colour of NGC 6946 is observed to vary across the disc of the galaxy. In this paper we examine three models for these colour variations to learn about possible heating sources for the dust, and the relationship of the far-infrared and non-thermal radio emissions. A model with a single dust component in which the dust temperature varies with position leads to a far-infrared-radio correlation which shows some non-linearity, especially in the nuclear region. Two models, each with two dust components, are also considered: one model has differing contributions of warm and cold dust (cirrus) with the temperature of each component the same throughout the galaxy, while the second allows the temperature of the cirrus component to vary with position

The spatial correlation between far-infrared and radio emission in galaxies – I. NGC 6946, M51, NGC 2997 and M83

This paper presents high-resolution far-infrared images of four galaxies using 50- and 100-μm data from the Chopped Photometric Channel instrument of the IRAS satellite. By careful calibration we produce far-infrared colour (temperature) maps, and compare them quantitatively with non-thermal radio images.

VLA observations of unidentified Leiden-Berkeley Deep-Survey sources - Luminosity and redshift dependence of spectral properties

VLA observations of a complete subset of the Leiden-Berkeley Deep Survey sources that have S(1.4 GHz) greater than 10 mJy and are not optically identified down to F=22 mag are reported. By comparing the spectral and structural properties of the sources with samples from the literature, an attempt was made to disentangle the luminosity and redshift dependence of the spectral indices of extended emission in radio galaxies and of the incidence of compact steep-spectrum sources. It is found that the fraction of compact sources among those with a steep spectrum is related primarily to redshift, being much larger at high redshifts for sources of similar radio luminosity. Only a weak and marginally significant dependence of spectral indices of the extended sources on luminosity and redshift is found in samples selected at 1.4 and 2.7 GHz. It is pointed out that the much stronger correlation of spectral indices with luminosity may be arising partly from spectral curvature, and partly due to the preferential inclusion of very steep-spectrum sources from high redshift in low-frequency surveys.

The radio emission of galaxies with low-luminosity active nuclei

We have compared the radio continuum emission of three samples of bright (Bto<13) galaxies with LINER,HII region-like, and Seyfert nuclei. Basically, we have found that the objects of the first class are the weakest total and central radio emitters (for total and central unit light, respectively), whereas the Seyfert galaxies contain the most powerful central radio sources.

The Role of Environment in the Origin of Radio Emission from Galaxies

The influence of the environment on the origin of radio radiation from galaxies is studied by compairing the occurence of radio emission in galaxies in compact high density groups of Hickson (1982) with that in field galaxies of similar types. The study shows that the fractional luminosity functions of elliptical and spiral galaxies in compact groups are similar in shape to that of field galaxies but the probability of a compact group galaxy being a radio source is 5 to 10 times greater than that of an isolated galaxy of the same type. Radio Loud group ellipticals tend to be the optically brightest galaxy in the group independent of their absolute luminosity.

Statistical methods for astronomical data with upper limits. II - Correlation and regression

Statistical methods for calculating correlations and regressions in bivariate censored data where the dependent variable can have upper or lower limits are presented. Cox's regression and the generalization of Kendall's rank correlation coefficient provide significant levels of correlations, and the EM algorithm, under the assumption of normally distributed errors, and its nonparametric analog using the Kaplan-Meier estimator, give estimates for the slope of a regression line. Monte Carlo simulations demonstrate that survival analysis is reliable in determining correlations between luminosities at different bands. Survival analysis is applied to CO emission in infrared galaxies, X-ray emission in radio galaxies, H-alpha emission in cooling cluster cores, and radio emission in Seyfert galaxies.

Aperture-synthesis systems for meter and decimeter wavelengths (survey)

As is well known, the results of radioastronomical observations in the meter and decimeter wavelength range are quite informative and offer great interest for astrophysics. In this range extragalactic sources, their structure, the mechanisms of radio emission, and spectra are studied and the "outer" regions of emission of radio galaxies are investigated. This wavelength range is also very informative for the study of galactic objects (nebulae, supernova remnants, etc.).

Optical spectroscopy of the radio-loud nuclei of spiral galaxies - Starbursts or monsters?

view Abstract Citations (80) References (68) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical spectroscopy of the radio-cloud nuclei of spiral galaxies : starbursts or monsters ? Heckman, T. M. ; van Breugel, W. ; Miley, G. K. ; Butcher, H. R. Abstract Optical spectroscopic data pertaining to the physical state, kinematics and spatial extent of emission line gas near the radio-loud nuclei of spiral galaxies are combined with published optical, radio and IR data, in an examination of the Condon et al (1982) suggestion that the nuclear radio emission in galaxies of this class is produced by multiple SNRs generated by a nuclear starburst. It is found that only about 1/3 of the spiral galaxies examined have optical spectroscopic properties consistent with those of 'extranuclear starbursts'. Evidence is adduced for the view that the putative nuclear starbursts must differ significantly from extranuclear starbursts. While giant H II regions generally have thermal radio emission, the radio-loud nuclei exhibit nonthermal radio emission whose spectrum is much steeper than that of SNRs. Publication: The Astronomical Journal Pub Date: August 1983 DOI: 10.1086/113397 Bibcode: 1983AJ.....88.1077H Keywords: Astronomical Spectroscopy; Galactic Nuclei; Radio Sources (Astronomy); Spiral Galaxies; Bursts; Galactic Structure; H Ii Regions; Infrared Astronomy; Nonthermal Radiation; Optical Emission Spectroscopy; Starburst Galaxies; Supernova Remnants; Astronomy full text sources ADS | data products SIMBAD (43) NED (38)

X-ray emission around radio galaxies in non-Abell clusters - A possible physical link between environment and nonthermal radio emission

X-ray observations of a sample of 11 4C radio galaxies in clusters with z< or approx. =0.1 were performed with the IPC (resolution FWHMapprox.1'.5) on the Einstein Observatory. The sample galaxies lie in the directions of non-Abell Zwicky clusters; these clusters are generally poor, ranging in effective Abell richness class from < or approx. =0 to 1. In 10 out of the 11 observed fields 1--3 keV emission was detected. In nearly every case, the X-ray emission is centered on the radio galaxy; 5 out of 10 of the X-ray sources are resolved with HWHM of 70--300 kpc. The X-ray luminosities are (1--60) x 10/sup 42/ ergs s/sup -1/ (H/sub 0/ = 75 km s/sup -1/ Mpc/sup -1/), generally less than the richer Abell clusters and undetectable with previous satellites. Examinations of the optical fields and preliminary velocity data suggest that most of the radio sources are associated with dominant galaxies which are at rest at the gravitational centers of the clusters. Internal relativistic particle and magnetic field pressures of the relaxed outer radio structures are on the same order as the thermal pressure produced by the X-ray emitting gas. We argue that this class of radio source is confinedmore » (and possibly triggered) by gas accumulated at the cluster centers. The X-ray emission is a cosmic signpost indicating the presence of large quantities of gas around the central radio galaxies. Recent radio observations indicate that the probability of galaxy radio emission is much higher for cluster galaxies than for very isolated galaxies; these new X-ray observations of poor clusters combined with previous data on Abell clusters suggest that the presence of cluster gas is the important factor in determining the link between cluster environment and radio emission.« less

Radio emission in the directions of cD and related galaxies in poor clusters. II - 1400-MHz pencil beam observations

The results of a 1400-MHz survey with the NRAO 91-m telescope for radio emission in the directions of poor clusters that contain cD or other related galaxies are reported. A total of 51 clusters was observed and 37 sources with S/sub 1400/>150 mJy in 28 clusters were detected. We estimate that 16 +- 6% (8 +- 3 sources) of the poor clusters contain radio sources within 5 arcmin. The potential effects of cluster richness upon the probability of galaxy radio emission are discussed using this poor cluster sample and a similar radio survey of rich Abell clusters.

Mean surface brightnesses and radio emission of galaxies

Mean surface brightnesses and radio emission of galaxies

Optimum algorithm for processing the observational data on polarization of distributed Galaxy radio emission

Optimum algorithm for processing the observational data on polarization of distributed Galaxy radio emission

The Magnetic Fields and Radio Emission of Galaxies

The Magnetic Fields and Radio Emission of Galaxies