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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

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.

OGLE Collection of Star Clusters. New Objects in the Outskirts of the Large Magellanic Cloud

Sitek M., Szymański M. K., Skowron D. M., Udalski A., Kostrzewa-Rutkowska Z., Skowron J., Karczmarek P., Cieślar M., Wyrzykowski Ł., Kozłowski S., Pietrukowicz P., Soszyński I., Mróz P., Pawlak M., Poleski R., Ulaczyk K.

Acta Astronomica

2016

Vol. 66, No. 3

255--267

The Magellanic System (MS), consisting of the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) and the Magellanic Bridge (MBR), contains diverse sample of star clusters. Their spatial distribution, ages and chemical abundances may provide important information about the history of formation of the whole System. We use deep photometric maps derived from the images collected during the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV) to construct the most complete catalog of star clusters in the Large Magellanic Cloud using the homogeneous photometric data. In this paper we present the collection of star clusters found in the area of about 225 square degrees in the outer regions of the LMC. Our sample contains 679 visually identified star cluster candidates, 226 of which were not listed in any of the previously published catalogs. The new clusters are mainly young small open clusters or clusters similar to associations.

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

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%.