404 research outputs found
The connection between X-ray Clusters and Star Formation
The properties of X-ray clusters of galaxies can be well understood in terms
of a competition between shock heating and adiabatic compression. Strong shocks
are expected to be important for massive clusters, while adiabatic compression
is dominant for small clusters and groups. The scale of the shock/adiabatic
transition is marked by a change of slope of the L-T relation and in the global
properties of the emitting plasma. This scale is connected to star formation
processes. Two quantities are crucial: the average energy injected in the IGM
from stars and SNe, and the epoch of the energy injection. We show how these
quantities can be synthesized in terms of specific entropy, which ultimately
determines the X-ray emission from groups and clusters.Comment: 4 pages, including 2 figures, LaTex2e. To be published in the
Proceedings of the ``VLT Opening Symposium'', Antofagasta (Chile), 1-4 March
1999. Typos changed in eq. (3
Emission Lines in X-ray Spectra of Clusters of Galaxies
Emission lines in X-ray spectra of clusters of galaxies reveal the presence
of heavy elements in the diffuse hot plasma (the Intra Cluster Medium, or ICM)
in virial equilibrium in the dark matter potential well. The relatively simple
physical state of the ICM allows us to estimate, with good accuracy, its
thermodynamical properties and chemical abundances. These measures put strong
constraints on the interaction processes between the galaxies and the
surrounding medium, and have significant impact on models of galaxy formation
as well. This field is rapidly evolving thanks to the X-ray satellites Chandra
and XMM-Newton. Among the most relevant progresses in the last years, we
briefly discuss the nature of cool cores and the measure of the Iron abundance
in high redshift clusters. Future X-ray missions with bolometers promise to
provide a substantial step forward to a more comprehensive understanding of the
complex physics of the ICM.Comment: 8 pages, 3 figures, Proceedings of the VI Serbian Conference on
Spectral Line Shapes in Astrophysics, Sremski Karlovci, Serbia June 11-15
200
Searching for bulk motions in the ICM of massive, merging clusters with Chandra CCD data
We search for bulk motions in the intracluster medium (ICM) of massive
clusters showing evidence of an ongoing or recent major merger with spatially
resolved spectroscopy in {\sl Chandra} CCD data. We identify a sample of 6
merging clusters with 150 ks {\sl Chandra} exposure in the redshift range
. By performing X-ray spectral analysis of projected ICM regions
selected according to their surface brightness, we obtain the projected
redshift maps for all of these clusters. After performing a robust analysis of
the statistical and systematic uncertainties in the measured X-ray redshift
, we check whether or not the global distribution
differs from that expected when the ICM is at rest. We find evidence of
significant bulk motions at more than 3 in A2142 and A115, and less
than 2 in A2034 and A520. Focusing on single regions, we identify
significant localized velocity differences in all of the merging clusters. We
also perform the same analysis on two relaxed clusters with no signatures of
recent mergers, finding no signs of bulk motions, as expected. Our results
indicate that deep {\sl Chandra} CCD data enable us to identify the presence of
bulk motions at the level of 1000\ in the ICM
of massive merging clusters at . Although the CCD spectral
resolution is not sufficient for a detailed analysis of the ICM dynamics, {\sl
Chandra} CCD data constitute a key diagnostic tool complementing X-ray
bolometers on board future X-ray missions
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