Wyniki wyszukiwania - BazTech

1

HI Mass Fraction as a Measure of Physical Processes Efficiency in Cluster Environment of A262

Hassan M. S. R., Abidin Z. Z., Ibrahim U. F. S. U., Hashim N.

Acta Astronomica

|

2023

|

Vol. 73, No. 1

87--104

EN

We present our results on measurements of the neutral hydrogen (HI) mass fraction in galaxy cluster environment of a nearby cluster Abell 262 (A262), and investigate the possible physical processes that lead to our estimation of HI mass fraction in this cluster. We conduct a spectroscopic analysis to define a true cluster membership around Abell radius of the cluster, from which we estimate the virial mass of the whole cluster based on the velocity dispersion analysis, and later use data from a 21-cm single-pointing observation to deduce the global HI mass fraction in the cluster. It is found that the HI mass, MHI, and HI mass fraction, FHI, of A262 are equal to be about (4.33±0.32)×1011M☉ and (1.01±0.09)×10-3, respectively, in which the latter agrees with previous findings. We have also shown that the fraction of stellar mass in A262 is about (8.25±0.14)×10-3, and falls within the range of the widely accepted value. We discuss several physical mechanisms that contribute to the derived HI mass fraction of A262. We also emphasize that the FHI can be used as a proxy of efficiency of physical processes in clusters, if we have a large sample of galaxy clusters with available HI data.

2

1.4-GHz Observations of Extended Giant Radio Galaxies

Weżgowiec M., Jamrozy M., Mack K.-H.

Acta Astronomica

|

2016

|

Vol. 66, No. 1

85--119

EN

This paper presents 1.4-GHz radio continuum observations of fifteen very extended radio galaxies. These sources are so large that most interferometers lose partly their structure and total flux density. Therefore, single-dish detections are required to fill in the central (u,v) gap of interferometric data and obtain reliable spectral index patterns across the structures, and thus also an integrated radio continuum spectrum. We have obtained such 1.4-GHz maps with the 100-m Effelsberg telescope and combined them with the corresponding maps available from the NVSS. The aggregated data allow us to produce high-quality images, which can be used to obtain physical parameters of the mapped sources. The combined images reveal in many cases extended low surface-brightness cocoons.

3

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

Machalski J., Chyży K. T., Jamrozy M.

Acta Astronomica

|

2004

|

Vol. 54, No. 3

249--279

EN

The time evolution of giant lobe-dominated radio galaxies (with projected linear size D>1 Mpc if H0=50 km/s Mpc and q0=0.5) is analyzed on the basis of dynamical evolution of the entire FRII-type population. Two basic physical parameters, namely the jet power Q0 and central density of the galaxy nucleus ρ0 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, Q0 and ρ0 are obtained by fitting the dynamical model of Kaiser et al. We find that: (i) There is no unique factor governing the source size. The sources are old, with temperate jet power (Q0) and are evolved in a relatively low-density environment (ρ0). The size is dependent, in order of decreasing partial correlation coefficients, on age, then on Q0, next on ρ0. (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.

4

Giant Radio Sources in View of the Dynamical Evolution of FRII-Type Population. II. The Evolutionary Tracks on the P-D and uc - Etot Planes

Machalski J., Chyży K. T., Jamrozy M.

Acta Astronomica

|

2004

|

Vol. 54, No. 4

391--403

EN

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 in 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 Q0 and central density of the galaxy nucleus ρ0 (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 (uc-Etot) tracks derived from the model for a "fiducial" source with Q0 and ρ0 equal to the averages 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.

5

Spectral Energy and Age Distributions for 51 Globular Cluster Candidates

Ma J., Zhou X., Chen J., Wu H., Kong X., Jiang Z., Zhu J., Xue S.

Acta Astronomica

|

2002

|

Vol. 52, No. 4

453--470

EN

This paper is the fourth in a series presenting spectrophotometry of 51 globular cluster candidates, that were detected by Mochejska et al. in the nearby galaxy M33 using the data collected by the DIRECT project. The frames of M33 in this study were taken as a part of the BATC Multicolor Sky Survey. We obtained the spectral energy distributions of these candidates in 13 intermediate-band filters. By comparing the integrated photometric measurements with theoretical stellar population synthesis models of Bruzual and Charlot, we estimated their ages. The BC96 models provide the evolution in time of the spectrophotometric properties of simple stellar populations for a wide range of stellar metallicity. Our results show that half of the candidates are younger than 108 years. We also find that globular clusters formed continuously in M33 from ≈4×106 to 1010 years. Our results are in agreement with Chandar et al. who estimated ages for 35 globular clusters candidates from our list by comparing the photometric measurements to integrated colors from theoretical models by Bertelli et al. The Kolmogorov-Smirnov test shows that the maximum value of the absolute difference of estimated ages between Chandar et al. and us is 0.48, and the significance level probability is 100.00%.