We present the results of the spectral and temporal analysis of eight X-ray point sources in five nearby (distance < 20 Mpc) galaxies observed with Chandra. For spectral analysis, an absorbed powerlaw and an absorbed diskblackbody were used as empirical models. Six sources were found to be equally fitted by both the models while two sources were better fitted by the powerlaw model. Based on model parameters, we estimate the X-ray luminosity of these sources in the energy range 0.3 − 10.0 keV, to be of the order of ∼ 1039ergs s−1 except for one source (X-8) with LX > 1040ergs s−1. Five of these maybe classified as Ultraluminous X-ray sources (ULXs) with powerlaw photon index within the range, Γ ∼ 1.63−2.63 while the inner disk temperature, kT ∼ 0.68−1.93 keV, when fitted with the disk blackbody model. The black hole masses harboured by the X-ray point sources were estimated using the disk blackbody model to be in the stellar mass range, however, the black hole mass of one source (X-6) lies within the range 68.37M ≤ MBH ≤ 176.32M, which at the upper limit comes under the Intermediate mass black hole range. But if the emission is considered to be beamed by a factor ∼ 5, the black hole mass reduces to ∼ 75M. The timing analysis of these sources does not show the presence of any short term variations in the kiloseconds timescales.

We searched for X-ray emission from the 665 galaxies inside and towards the nearby voids by analyzing the ROSAT All-Sky Survey (RASS) data as well as the ROSAT pointed observations (PSPC). As a result we have detected six X-ray emitting galaxies. Two (UGC 10205 and NGC 7509) are in the high density region in the local void, three (UGC 749, MCG +11-10-073, and Mrk 464) are towards the nearby voids, and UGC 32 is located in the low density region. We carried out a timing analysis for both Mrk 464 and UGC 32, and a spectral analysis for Mrk 464. The light curve of Mrk 464 shows the possibility of periodic X-ray flux variation and UGC 32 shows weak, but rapid variation.

Galaxy clusters as the densest and most prominent regions within the large-scale structure can be used as well characterizable laboratories to study astrophysical processes on the largest scales. X-ray observations provide currently the best way to determine the physical properties of galaxy clusters and the environmental parameters that describe them as laboratories. We illustrate this use of galaxy clusters and the precision of our understanding of them as laboratory environments with several examples. Their application to determine the matter composition of the Universe shows good agreement with results from other methods and is therefore a good test of our understanding. We test the reliability of mass measurements and illustrate the use of X-ray diagnostics to study the dynamical state of clusters. We discuss further studies on turbulence in the cluster ICM, the interaction of central AGN with the radiatively cooling plasma in cluster cooling cores and the lessons learned from the ICM enrichment by heavy elements.

Observations with EUVE, ROSAT, and BeepoSAX have shown that some clusters of galaxies produce intense EUV emission. These findings have produced considerable interest; over 100 papers have been published on this topic in the refereed literature. A notable suggestion as to the source of this radiation is that it is a 'warm' (106 K) intracluster medium which, if present, would constitute the major baryonic component of the universe. A more recent variation of this theme is that this material is 'warm-hot' intergalactic material condensing onto clusters. Alternatively, inverse Compton scattering of low energy cosmic rays against cosmic microwave background photons has been proposed as the source of this emission. Various origins of these particles have been posited, including an old (${\~}$ 수식 이미지Giga year) population of cluster cosmic rays; particles associated with relativistic jets in the cluster; and cascading particles produced by shocks from sub-cluster merging. The observational situation has been quite uncertain with many reports of detections which have been subsequently contradicted by analyses carried out by other groups. Evidence supporting a thermal and a non-thermal origin has been reported. The existing EUV, FUV, and optical data will be briefly reviewed and clarified. Direct observational evidence from a number of different satellites now rules out a thermal origin for this radiation. A new examination of subtle details of the EUV data suggests a new source mechanism: inverse Compton scattered emission from secondary electrons in the cluster. This suggestion will be discussed in the context of the data.

We review recent observational results on early type galaxies obtained with high spatial resolution Chandra data. With its unprecedented high spatial resolution, Chandra reveals many intriguing features in early type galaxies which were not identified with the previous X-ray missions. In particular, various fine structures of the hot ISM in early type galaxies are detected, for example, X-ray cavities which are spatially coincident with radio jets/lobes, indicating the interaction between the hot ISM and radio jets. Also point sources (mostly LMXBs) are individually resolved down to Lx = a few x 10 37 erg sec-1 and it is for the first time possible to unequivocally investigate their properties and the X-ray luminosity function. After correcting for incompleteness, the XLF of LMXBs is well reproduced by a single power law with a slope of -1.0 - -1.5, which is in contrast to the previous report on the existence of the XLF break at Lx, Eddington = 2 x 10 38 erg sec-1 (i.e., Eddington luminosity of a neutron star binary). Carefully considering both detected and undetected, hidden populations of point sources we further discuss the XLF of LMXBs and the metal abundance of the hot ISM and their impact on the properties of early type galaxies.

We have measured the correlation functions of the optically selected clusters of galaxies in the Abell and the APM catalogs, and of the X-ray clusters in the X-ray-Brightest Abell-type Clusters of galaxies (XBACs) catalog and the Brightest Clusters Sample (BCS). The same analysis method and the same method of characterizing the resulting correlation functions are applied to all observational samples. We have found that the amplitude of the correlation function of the APM clusters is much higher than what has been previously claimed, in particular for richer subsamples. The correlation length of the APM clusters with the richness R ≥ 70 (as defined by the APM team) is found to be r0 = 25.4 -3.0 +3.1 h-1 Mpc. The amplitude of correlation function is about 2.4 times higher than that of Croft et al. (1997). The correlation lengths of the Abell clusters with the richness class RC ≥ 0 and 1 are measured to be r0 = 17.4 -1.1 +1.2 and 21.0 -2.8 +2.8 h-1 Mpc, respectively, which is consistent with our results for the APM sample at the similar level of richness. The richness dependence of cluster correlations is found to be r0= 0.40dc + 3.2 where dc is the mean intercluster separation. This is identical in slope with the Bahcall & West (1992)'s estimate, but is inconsistent with the weak dependence of Croft et al. (1997). The X-ray bright Abell clusters in the XBACs catalog and the X-ray selected clusters in the BCS catalog show strong clustering. The correlation length of the XBACs clusters with Lx ≥ 0.65×10 44 h-2 erg s-1 is 30.3 -6.5 +8.2 h-1 Mpc, and that of the BCS clusters with Lx ≥ 0.70×10 44 h-2erg s-1 is 30.2 -8.9 +9.8 h-1 Mpc. The clustering strength of the X-ray clusters is much weaker than what is expected from the optical clusters.

We have systematically investigated the X-ray spectra of normal galaxies, by using the Imaging Proportional Counter (IPC) data in the Einstein data base. We employed the X-ray color-color plot as well as the standard model fitting method which requires higher signal to noise ratio. We discuss X-ray emission mechanisms in terms of their spectral properties and the signature of cooling flows which are most likely present in X-ray bright early type galaxies. On the average, fits to absorbed thermal spectra show that the X-ray emission temperature of spirals is higher than that of ellipticals. This is consistent with our understanding that accreting binaries are a major X-ray source in spirals, while extended gaseous halos are present in ellipticals. The emission temperature becomes lower with increasing X-ray to optical luminosity ratio in E and S0 galaxies. This result is what we would expect if the emission of X-ray faint early type galaxies consists of a large evolved stellar component, while the gaseous emission becomes dominant in X-ray brighter galaxies. We also find a cool, self-absorbed core in some early type galaxies, which directly indicates the presence of cooling flows in such galaxies.