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J. Machalski

Publications and source records attributed to J. Machalski.

36 records · Page 2Linked to original sources
arXiv2007

A multifrequency study of giant radio sources I. Low-frequency Giant Metrewave Radio Telescope observations of selected sources

We present low-frequency observations with the Giant Metrewave Radio Telescope (GMRT) of a sample of giant radio sources (GRSs), and high-frequency observations of three of these sources with the Very Large Array (VLA). From multifrequency observations of the lobes we estimate the magnetic field strengths using three different approaches, and show that these differ at most by a factor of $\sim$3. For these large radio sources the inverse-Compton losses usually dominate over synchrotron losses when estimates of the classical minimum energy magnetic field are used, consistent with earlier studies. However, this is often not true if the magnetic fields are close to the values estimated using the formalism of Beck & Krause. We also examine the spectral indices of the cores and any evidence of recurrent activity in these sources. We probe the environment using the symmetry parameters of these sources and suggest that their environments are often asymmetric on scales of $\sim$1 Mpc, consistent with earlier studies.

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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.

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arXiv2006

Spectral ageing analysis of the double-double radio galaxy J1453+3308

We present new radio observations at frequencies ranging from 240 to 4860 MHz of the well-known, double-double radio galaxy (DDRG), J1453+3308, using both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). These observations enable us to determine the spectra of the inner and outer lobes over a large frequency range and demonstrate that while the spectrum of the outer lobes exhibits significant curvature, that of the inner lobes appears practically straight. The break frequency, and hence the inferred synchrotron age of the outer structure, determined from 16$-$arcsec strips transverse to the source axis, increases with distance from the heads of the lobes. The maximum spectral ages for the northern and southern lobes are $\sim$47 and 58 Myr respectively. Because of the difference in the lengths of the lobes these ages imply a mean separation velocity of the heads of the lobes from the emitting plasma of 0.036c for both the northern and southern lobes. The synchrotron age of the inner double is about 2 Myr which implies an advance velocity of $\sim$0.1c, but these values have large uncertainties because the spectrum is practically straight.

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arXiv2006

The new sample of giant radio sources III. Statistical trends and correlations

In this paper we analyse whether `giant' radio galaxies (GRGs) differ from `normal'-size galaxies (NSGs) except for the linear extent of their radio structure. We compare a number of properties of GRGs with the corresponding properties of NSGs, and analyse the statistical trends and correlations of physical parameters, homogeneously determined for the sources, with their `fundamental' parameters. Using the Pearson partial-correlation test on the correlation between two variables in the presence of one or two other variables, we examine which correlation is the strongest. The analysis clearly shows that GRGs do not form a separate class of radio sources. They most likely evolve with time from smaller sources, however under specific circumstances. Analysing properties of GRGs and NSGs together, we find that (i) the core prominence does not correlate with the total radio luminosity (as does the core power), but it anti-correlates with the surface brightness of the lobes of sources, (ii) the energy density (and possibly the internal pressure) in the lobes is independent of redshift for constant radio luminosity and size of the sources, (iii) the equipartition magnetic-field strength, transformed into constant source luminosity and redshift, strongly correlates with the source size. We argue that this B_{eq} - D correlation reflects a more fundamental correlation between B_{eq} and the source age, (iv) both the rotation and depolarisation measures suggest Faraday screens local to the lobes of sources, however their geometry and the composition of intervening material cannot be determined from the global polarisation characteristics.

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arXiv2006

The new sample of giant radio sources II. Update of optical counterparts, further spectroscopy of identified faint host galaxies, high-frequency radio maps, and polarisation properties of the sources

Our sample of giant radio-source candidates, published in Paper I (Machalski et al. 2001), is updated and supplemented with further radio and optical data. In this paper we present: (i) newly detected host galaxies, their photometric magnitude, and redshift estimate for the sample sources not identified yet, (ii) optical spectra and spectroscopic redshift for the host galaxies fainter than about 18.5 mag taken with the Apache Point Observatory 3.5m telescope, and (iii) the VLA 4.9 GHz total-intensity and polarised-intensity radio maps of the sample members. In a few cases they reveal extremely faint radio cores undetected before, which confirm the previously uncertain optical identifications. The radio maps are analysed and the polarisation properties of the sample sources summarised. A comparison of our updated sample with three samples published by other authors implies that all these four samples probe the same part of the population of extragalactic radio sources. There is no significant difference between the distributions of intrinsic size and radio power among these samples. The median redshift of 0.38 +/- 0.07 in our sample is the highest among the corresponding values in the four samples, indicating that the angular size and flux-density limits in our sample, lower than those for the other three samples, result in effective detections of more distant, giant-size galaxies compared to those detected in the other samples. This sample and a comparison sample of `normal'-size radio galaxies will be used in Paper III (Machalski & Jamrozy 2006) to investigate of a number of trends and correlations in the entire data.

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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.

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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.

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arXiv2004

Large-Scale Radio Structure in the Universe: Giant Radio Galaxies

Giant radio galaxies (GRGs), with linear sizes larger than 1 Mpc (H0=50 km/s/Mpc), represent the biggest single objects in the Universe. GRGs are rare among the entire population of radio galaxies (RGs) and their physical evolution is not well understood though for many years they have been of special interest for several reasons. The lobes of radio sources can compress cold gas clumps and trigger star or even dwarf galaxy formation, they can also transport gas from a host galaxy to large distances and seed the IGM with magnetic fields. Since GRGs have about 10 to 100 times larger sizes than normal RGs, their influence on the ambient medium is correspondingly wider and is pronounced on scales comparable to those of clusters of galaxies or larger. Therefore `giants' could play an important role in the process of large-scale structure formation in the Universe. Recently, thanks to the new all sky radio surveys, significant progress in searching for new GRGs has been made.

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arXiv2004

Search for Southern-Hemisphere Giant Radio Galaxies with SALT

An extensive search for distant Giant radio galaxies on the southern hemisphere is justified. We emphasize the crucial role of optical spectroscopy in determination of their basic physical parameters, i.e. the distance, projected linear size, volume of their lobes or cocoon, luminosity, etc., and argue that SALT will be the best instrument for such a task.

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arXiv2003

Redshift Measurements of Faint Distant Giant Radio Galaxies and Observational Constraints on their Jet Power and Dynamical Age

The redshifts of faint radio galaxies identified with giant radio source candidates selected from the sample of Machalski et al. (2001) have been measured. Given the redshift, the projected linear size and radio luminosity are then determined. The above, supplemented with the axial ratio of the sources (evaluated from the radio maps) allows to constrain their jet power and the dynamical age using the analytical model of Kaiser et al. (1997) but modified by allowing the axial ratio of the source's cocoon to evolve in time.

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arXiv2003

Spectral-ageing analysis of selected distant giant radio galaxies

Very deep 4.9 GHz observations with the VLA are used to supplement available radio maps at the frequencies of 325 MHz (WENSS survey) and 1.4 GHz (NVSS survey) in order to study the synchrotron spectra and radiative ages of relativistic particles in the extended lobes of distant giant radio galaxies selected from the sample of Machalski et al. (2001).

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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.

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arXiv2001

The new sample of Giant radio sources: I. Radio imaging, optical identification and spectroscopy of selected candidates

A new sample of very large angular size radio sources has been selected from the 1.4 GHz VLA surveys: FIRST and NVSS. This sample will be very useful for an observational constraint on the time evolution of double radio sources, especially their size, predicted by numerous analytical models of such evolution (cf. Introduction). In this paper we present radio and optical data for a large fraction of the sample sources. They are: high-frequency VLA maps with very weak radio cores detected, deep optical images showing the identified faint host galaxies not visible on the DSS images, and optical spectra of the identified galaxies brighter than about R ~ 18.5 mag taken with the McDonald Observatory 2.1m telescope. For 15 galaxies (of which 4 do not belong to the complete sample) the redshift has been determined. In the result, 44 per cent of galaxies in the complete sample have redshift data (with one exception all redshifts are less than 0.33), of which 70 per cent have a linear size exceeding 1 Mpc. The photometric redshift estimates for other 11 galaxies with 19 mag<R<21.7 mag (0.3<z<0.5) predict their sizes much over 1 Mpc.

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arXiv2000

J1343+3758: The third largest FRII-type radio galaxy

A radio source of the Fanaroff--Riley type II with the angular size of 11.3 arc min is identified with an optical galaxy at z=0.229. Thus, the projected linear extent of the radio structure is 3.14 Mpc which makes it the third largest classical double radio source known after 3C236 and WNB2147+816. The high-frequency VLA observations, a galaxy identification and its optical spectroscopy are reported. The equipartition magnetic field and energy density in the source is calculated and compared with corresponding parameters of other giants known, indicating that either parameter of the source investigated is extremely low. On the other hand, the age estimate of relativistic electrons and the advance speed of the lobe material are comparable to the respective parameters characterizing other low-luminosity giant sources, as well as much smaller and brighter 3CR sources. The environment analysis suggests that J1343+3758 lies in a significantly poor region of intergalactic medium.

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arXiv1999

GB2 0909+353: One of the Largest Double Radio Source

The evidence are given that the radio source GB2 0909+353 (GB2 catalogue: Machalski 1978; ICRS 2000.0 coordinates: 09 12 51.7, +35 10 10) is likely one of the largest classical doubles known, though its optical identification is not certain. Our deep VLA observations at 5 GHz did not reveal a radio core brighter than 0.5 mJy/beam at this frequency. Thus a distance to the source is evaluated using photometric -- redshift estimates of the faint galaxies in the optical field. The equipartition magnetic field and energy density in the source is calculated and compared with corresponding parameters of other `giant' radio sources known, showing extremely low values of both physical parameters of the source investigated. On the other hand, the age of relativistic electrons, and the advance speed of the `hot spot' in the source are typical for much smaller and brighter 3CR sources.

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arXiv1998

Observed Redshift Distributions and Cosmological Evolution of Radio Sources

It is shown that the new observed redshift distributions of various flux-limited samples of radio sources in general are consistent with the predictions of two basic evolutionary models published by Condon (1984) and Dunlop and Peacock (1990), i.e. none of them can be rejected at the confidence level of about 95 per cent. However, the models allowing a free-form evolution and suggesting both density and luminosity evolution are more consistent with the observational data at lower redshifts, while the 'pure luminosity evolution' model fits better the data at higher redshifts. This leads to a suspicion that the same evolution governing all radio sources, suggested by Condon (1984), might not be the case.

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