Heavy Element Enrichment of the Cluster ICM

At the typical cluster temperatures of several keV, the K-shell line of iron (Fe Ly-a) is the most prominent line in the X-ray spectrum. Iron was therefore the first element that was detected in the X-ray spectrum of a galaxy cluster [101]. Figure 23.18, shows modern X-ray spectra of the Centaurus and Virgo clusters observed with ASCA and XMM-Newton, respectively, displaying lines of several heavy elements. The typical iron abundances found in the early observations were in the range of 0.3-0.5 solar [107]. With the capabilities of the ASCA satellite to perform spatially resolved spectroscopy the first look at abundance profiles was possible, involving mostly the elements Fe and Si, with a few exceptions of bright sources showing also emission lines of a few other abundant elements [66]. Additional information on the spatial distribution of these elements came subsequently also from observations

Fig. 23.17 Left: Chandra image of the X-ray halo around M87 showing a wealth of features due to the interaction of the jets from the central AGN in M87 and the cluster ICM. Sharp, concentric surface brightness edges with a significant brightening in the denser radio lobe regions indicate shock waves most probably created by the early supersonic expansion of the radio bubbles in the center. Right: Composite image of the M87 halo region with X-ray emission shown in red and radio emission shown in blue color. The spatial correlation of the radio and X-ray features (relativistic and thermal plasma) is obvious in several of the interaction zones (Forman et al. [64])

Fig. 23.17 Left: Chandra image of the X-ray halo around M87 showing a wealth of features due to the interaction of the jets from the central AGN in M87 and the cluster ICM. Sharp, concentric surface brightness edges with a significant brightening in the denser radio lobe regions indicate shock waves most probably created by the early supersonic expansion of the radio bubbles in the center. Right: Composite image of the M87 halo region with X-ray emission shown in red and radio emission shown in blue color. The spatial correlation of the radio and X-ray features (relativistic and thermal plasma) is obvious in several of the interaction zones (Forman et al. [64])

Energy (keV)

Fig. 23.18 X-ray spectra of the Centaurus cluster (left) observed with ASCA [76] and of the M87 X-ray halo studied with XMM-Newton (right) [12]

XMM-Newton M87

FeNe Tjjjt

Energy (keV)

Fig. 23.18 X-ray spectra of the Centaurus cluster (left) observed with ASCA [76] and of the M87 X-ray halo studied with XMM-Newton (right) [12]

Ni with the BeppoSAX satellite [40]. Two interesting discoveries were made with these studies. It was found that the Fe abundance profile in "cooling flow" clusters showed a pronounced central increase while the profile for "noncooling flow" clusters was essentially flat [40, 59,60,66,93] as shown in Fig. 23.19. In addition the ratio of the Si to Fe abundance increases with cluster radius such that the central abundance

Fig. 23.19 Left: Abundance profiles of Fe in noncooling flow clusters (left) and "cooling flow" clusters (middle) observed with BeppoSAX by DeGrandi and Molendi [40] in solar units. Right: Ratio of the abundance of Si and Fe as a function of cluster radius observed with ASCA by Finoguenov et al. [59]. Also indicated are the classical values for the yields of type Ia and type II supernovae

Fig. 23.19 Left: Abundance profiles of Fe in noncooling flow clusters (left) and "cooling flow" clusters (middle) observed with BeppoSAX by DeGrandi and Molendi [40] in solar units. Right: Ratio of the abundance of Si and Fe as a function of cluster radius observed with ASCA by Finoguenov et al. [59]. Also indicated are the classical values for the yields of type Ia and type II supernovae ratio is closer to the yields of supernovae type Ia, while the global cluster ratio is closer to the yields of SNII (Fig. 23.19) [59,60].

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