arXiv subjects

K. T. Chyzy

Publications and source records attributed to K. T. Chyzy.

26 records · Page 2Linked to original sources

arXiv2006

A method of estimation of the dynamical age of FR II-type radio sources from multifrequency data

We propose a new approach in determining ages of FR II type radio sources. We apply the assumed dynamical model of Kaiser et al. (1997) to a number of FR II type radio galaxies observed at different radio frequencies, and fit - for each frequency separately - the model free parameters to the observed sources' quantities. Such a procedure, using enlarged in fact a number of observables, enables us to determine relatively precise ages and other crucial characteristics of the analyzed sources. The resulting age estimates agree very well with those obtained by means of `classical' spectral ageing method for objects not older than 10 Myr, for which good-quality spectral data are available. The presented method is however also applicable in the case of the sources older than this, and/or the ones for which the only available low-resolution radio data do not allow for detailed spectral ageing studies. Our analysis indicates that the main factor precluding precise age determination for FR II type radio galaxies regards the poorly known shape of the initial electron energy distribution injected by the jet terminal shocks to the expanding lobes/cocoons. We briefly consider this issue, and conclude that the broad-band single power-law form assumed here may be accurate enough for the presented estimates, although most likely it does not strictly correspond to some well-defined realistic particle acceleration process. Instead, it should be considered as a simplest model approximation of the initial electron continuum, averaged over a very broad energy range and over the age of the source, with the effective spectral index which may be different for different sources.

astro-ph↗

arXiv2005

Gradient and dispersion analyses of the WMAP data

We studied the WMAP temperature anisotropy data using two different methods. The derived signal gradient maps show regions with low mean gradients in structures near the ecliptic poles and higher gradient values in the wide ecliptic equatorial zone, being the result of non-uniform observational time sky coverage. We show that the distinct observational time pattern present in the raw (cleaned) data leaves also its imprints on the composite CMB maps. Next, studying distribution of the signal dispersion we show that the north-south asymmetry of the WMAP signal diminishes with galactic altitude, confirming the earlier conclusions that it possibly reveals galactic foreground effects. As based on these results, one can suspect that the instrumental noise sky distribution and non-removed foregrounds can have affected some of the analyses of the CMB signal. We show that actually the different characteristic axes of the CMB sky distribution derived by numerous authors are preferentially oriented towards some distinguished regions on the sky, defined by the observational time pattern and the galactic plane orientation.

astro-ph↗

arXiv2005

Large-scale magnetized outflows from the Virgo Cluster spiral NGC4569

Using the Effelsberg radio telescope at 4.85GHz and 8.35 GHz we discovered large symmetric lobes of polarized radio emission around the strongly HI deficient Virgo cluster spiral galaxy NGC4569. These lobes extend up to 24 kpc from the galactic disk. Our observations were complemented by 1.4 GHz continuum emission from existing HI observations. This is the first time that such huge radio continuum lobes are observed in a cluster spiral galaxy. The eastern lobe seems detached and has a flat spectrum typical for in-situ cosmic ray electron acceleration. The western lobe is diffuse and possesses vertical magnetic fields over its whole volume. The lobes are not powered by an AGN, but probably by a nuclear starburst producing >10^5 supernovae which occurred ~30 Myr ago. Since the radio lobes are symmetric, they resist ram pressure due to the galaxy's rapid motion within the intracluster medium.

astro-ph↗

arXiv2004

Giant Radio Sources in View of the Dynamical Evolution of FRII-type Population. I. The Observational Data, and Basic Physical Parameters of Sources Derived from the Analytical Model

The time evolution of giant lobe-dominated radio galaxies (with projected linear size D>1 Mpc if H_{0}=50 km/s/Mpc and q_{0}=0.5 is analysed on the basis of dynamical evolution of the entire FRII-type population. Two basic physical parameters, namely the jet power Q_{0} and central density of the galaxy nucleus rho0 are derived for a sample of giants with synchrotron ages reliably determined, and compared with the relevant parameters in a comparison sample of normal-size sources consisting of 3C, B2, and other sources. Having the apparent radio luminosity P and linear size D of each sample source, Q_{0} and rho_{0} are obtained by fitting the dynamical model of Kaiser et al. (1997). We find that: (i) there is not a unique factor governing the source size; they are old sources with temperate jet power (Q_{0}) evolved in a relatively low-density environment (rho_{0}). The size is dependent, in order of decreasing partial correlation coefficients, on age; then on Q_{0}; next on rho_{0}. (ii) A self-similar expansion of the sources' cocoon seems to be feasible if the power supplied by the jets is a few orders of magnitude above the minimum-energy value. In other cases the expansion can only initially be self-similar; a departure from self-similarity for large and old sources is justified by observational data of giant sources. (iii) An apparent increase of the lowest internal pressure value observed within the largest sources' cocoon with redshift is obscured by the intrinsic dependence of their size on age and the age on redshift, which hinders us from making definite conclusions about a cosmological evolution of intergalactic medium (IGM) pressure.

astro-ph↗

arXiv2004

Giant Radio Sources in View of the Dynamical Evolution of FRII-type Population. II. The Evolutionary Tracks on the P-D and u_{c}-E_{tot} Planes

The time evolution of `fiducial' radio sources derived from fitting the dynamical model of Kaiser et al. (1997) is compared with the observational data for the `clan' sources found in the sample of giant and normal-size FRII-type sources published Paper I (Machalski et al. 2004). Each `clan' comprises 3, 4 or 5 sample sources having similar values of the two basic physical parameters: the jet power Q_{0} and central density of the galaxy nucleus rho_{0} (determined in Paper I) but different ages, radio luminosities and axial ratios. These sources are considered as the `same' source observed at different epochs of its lifetime and used to fit the evolutionary luminosity-size (P-D) and energy density-total energy (u_{c}-E_{tot}) tracks derived from the model for a `fiducial' source with Q0 and rho_{0} equal to the means of relevant values obtained for the `clan' members, as well as to constrain the evolutionary model of the source dynamics used. In the result we find that (i) The best fit is achieved when the Kaiser et al.'s model is modified by allowing an evolution of the sources' cocoon axial ratio with time as suggested by Blundell et al. (1999). (ii) A slow acceleration of the average expansion speed of the cocoon along the jet axis is suggested by the `clan' sources. We argue that this acceleration, although minor, may be real and some supporting arguments come from the well known hydrodynamical considerations.

astro-ph↗

arXiv2003

Magnetic Fields and Ionized Gas in the Local Group Irregular Galaxies IC10 and NGC6822

We performed a high-sensitivity search for galaxy-scale magnetic fields by radio polarimetry at 10.45GHz and 4.85GHz with the Effelsberg 100m radio telescope, accompanied by Halpha imaging, for the two Local Group irregular galaxies IC10 and NGC6822. Their star-forming bodies are small and rotate slowly. IC10 is known to have a very high star-forming activity, resembling blue compact dwarfs, while NGC6822 has a low overall star-formation level. Despite very different current star formation rates, our Halpha imaging revealed a large web of diffuse Halpha filaments and shells in both IC10 and NGC6822. Some of them extend far away from the galaxy's main body. The total power emission of both objects shows bright peaks either at the positions of optically strong star-forming clumps (IC10) or individual HII regions or supernova remnants (NGC6822). However, in both cases we detect a smoothly distributed, extended component. In IC10 we found clear evidence for the presence of a diffuse, mostly random magnetic field of ~14muG strength, probably generated by a fluctuation dynamo. One of the Halpha-emitting filaments appears to be associated with enhanced magnetic fields. We also rediscuss the reddening of IC10 and its implications for its distance. In the case of NGC6822 we found only very weak evidence for nonthermal emission, except perhaps for some regions associated with local gas compression. We detect in both galaxies small spots of polarized emission, indicative of regular fields (~3muG), at least partly associated with local compressional phenomena.

astro-ph↗

arXiv2002

On the time evolution of giant radio galaxies

A time evolution of giant lobe-dominated radio galaxies (with projected linear size $D>1$ Mpc) is analysed on the basis of dynamical evolution of the entire FRII-type population. Two basic physical parameters, namely the jet power $Q_{0}$ and central density of the galaxy nucleus $ρ_{0}$ are derived for a sample of giants with synchrotron ages reliably determined, and compared with the relevant parameters in a comparison sample of normal-size sources consisting of 3C, B2, and other sources. Having apparent luminosity (power) $P$ and linear size $D$ of each sample source, $Q_{0}$ and $ρ_{0}$ are fitted using the dynamical model of Kaiser et al. (1997) but modified by allowing an evolution of the cocoon axial ratio with time as suggested by Blundell et al. (1999). In a result, we found that: (i) there is not a unique factor governing the source size; giants are old sources with high enough jet power evolved in a relatively low-density environment. The size is dependent, in order of decreasing partial correlation coefficients, on age; then on $Q_{0}$; next on $ρ_{0}$, (ii) a number of the sample sources, having similar $Q_{0}$ and $ρ_{0}$ but different ages and axial ratios (called a `clan'), fit very well the evolutionary luminosity-size ($P$-$D$) and energy density-total energy tracks derived from the model for a `fiducial' source with $Q_{0}$ and $ρ_{0}$ equal to the means of relevant values obtained for the `clan' members. Therefore, these sources can be considered as `the same' source observed at different epochs of its lifetime, and hence very useful for an observational constraint of evolutionary models of the source dynamics, (iii) in some cases a slow acceleration of the average expansion speed of the cocoon along the jet axis seems to be present.

astro-ph↗

arXiv2000

Regular magnetic fields in the dwarf irregular galaxy NGC 4449

We present a high-resolution VLA study of the total power and polarized radio continuum emission at 8.46 and 4.86 GHz of the irregular galaxy NGC 4449, known for its weak rotation and non-systematic gas motions. We found strong galaxy-scale regular magnetic fields, which is surprising because of a lack of ordered rotation required for the dynamo action. The strength of the regular field reaches 8 $μ$G and that of the total field 14 $μ$G, comparable to that of the total magnetic field strength in radio-bright spirals. The magnetic vectors in NGC 4449 form radial ``fans'' in the central region and fragments of a spiral pattern in the galaxy's outskirts. These structures are associated with large regions of systematic Faraday rotation, implying genuine galaxy-scale magnetic fields rather than random ones compressed and stretched by gas flows. The observed pattern of polarization B-vectors is similar to dynamo-type fields in normal spirals. Nonstandard, fast dynamo concepts are required to explain the observed field strengths, though it is unknown what kind of magnetic field geometry can be produced in slowly and chaotically rotating objects. The so far neglected role of magnetic fields for the dynamics and star formation in dwarf irregulars also needs to be revised.

astro-ph↗