233 research outputs found
Feedback from intra-cluster supernovae on the ICM in cooling flow galaxy clusters
No full textWe study the effect of heating and metal enrichment from supernovae (SNe) residing between galaxies on the Intra-Cluster Medium (ICM). Recent observations indicate that a considerable fraction ( ̃20%) of the SN Ia parent stellar population in galaxy clusters is intergalactic. By considering their effect on the relaxed progenitors of cooling flow clusters we propose that intra-cluster SNe can act as a distributed heating source which may influence the initial stages of the formation of cooling flows. We investigate the increase in cooling time as a function of the energy input supplied by SNe and their assumed spatial distribution, and conclude that intra-cluster SNe represent a heating source which in some clusters can cause a delay of the formation of cooling flows. This would imply that some cooling flows are younger than previously thought. We also discuss the impact that a large population of intra-cluster SNe could have on the chemical evolution of the ICM in cooling flow clusters
Enrichment of the ICM of galaxy clusters due to ram-pressure stripping
No full textWe investigate the impact of galactic mass loss
triggered by ram-pressure stripping of cluster galaxies on the evolution of the
intra-cluster medium (ICM).
We use combined N-body and hydrodynamic simulations together with a phenomenological galaxy formation model and a prescription of the effect of ram-pressure stripping on the galaxies. We analyze the effect of galaxy – ICM interaction for different model clusters with different
masses and different merger histories.
Our simulations show that ram-pressure stripping can account for
~10% of the overall observed level of enrichment in the ICM
within a radius of 1.3 Mpc. The efficiency of metal ejection of cluster galaxies depends in the first few Gyr of the simulation mainly on the cluster mass and is significantly increased
during major merger events. Additionally we show that ram-pressure
stripping is most efficient in the center of the galaxy cluster and the level of enrichment drops quite fast at larger radii. We present emission-weighted metallicity maps of the
ICM which can be compared with X-ray observations. The resulting distribution
of metals in the ICM shows a complex pattern with stripes and plumes of metal-rich material.
The metallicity maps can be used to trace the
present and past interactions between the ICM and cluster galaxies
H.E.S.S. observations of galaxy clusters
No full textClusters of galaxies, the largest gravitationally bound objects in the universe, are expected to contain a significant population of hadronic and leptonic cosmic rays. Potential sources for these particles are merger and accretion shocks, starburst driven galactic winds and radio galaxies. Furthermore, since galaxy clusters confine cosmic ray protons up to energies of at least 1 PeV for a time longer than the Hubble time they act as storehouses and accumulate all the hadronic particles which are accelerated within them. Consequently clusters of galaxies are potential sources of VHE (> 100 GeV) gamma rays. Motivated by these considerations, promising galaxy clusters are observed with the H.E.S.S. experiment as part of an ongoing campaign. Here, upper limits for the VHE gamma ray emission for the Abell 496 and Coma cluster systems are reported.W. Domainko, W. Benbow, J. A. Hinton, O. Martineau-Huynh, M. de Naurois, D. Nedbal, G. Pedaletti, G. Rowell for the H.E.S.S. Collaboratio
Finding short GRB remnants in globular clusters: the VHE gamma-ray source in Terzan 5
No full textContext. Globular cluster are believed to boost the rate of compact binary mergers that may launch a certain type of cosmological gamma-ray burst (GRB). Therefore globular clusters appear to be potential sites to search for remnants of such GRBs.
Aims. The very-high-energy (VHE) gamma-ray source HESS J1747-248 recently discovered in the direction of the Galactic globular cluster Terzan 5 is investigated for being a GRB remnant.
Methods. Signatures created by the ultrarelativistic outflow, the subrelativistic ejecta and the ionizing radiation of a short GRB are estimated for an expected age of such a remnant of t ≳ 104 years.
Results. The kinetic energy of a short GRB could roughly be adequate for powering the VHE source in a hadronic scenario. The age of the proposed remnant estimated from its extension possibly agrees with the occurrence of such events in the Galaxy. Subrelativistic merger ejecta could shock-heat the ambient medium.
Conclusions. Further VHE observations can probe for the presence of a break towards lower energies expected for particle acceleration in ultrarelativistic shocks. Deep X-ray observations would have the potential to examine whether there is any thermal plasma heated by the subrelativistic ejecta. The identification of a GRB remnant in our own Galaxy may also help to explore the effect of such a highly energetic event on the Earth
A search for diffuse X-ray emission from GeV-detected Galactic globular clusters
No full textContext. Recently, diffuse and extended sources in TeV γ-rays as well as in X-rays have been detected in the direction of the Galactic globular cluster (GC) Terzan 5. Remarkably, this is among the brightest GCs detected in the GeV regime. The nature of neither the TeV nor the diffuse X-ray signal from Terzan 5 is not yet settled. These emissions most likely indicate the presence of several non-thermal radiation processes in addition to those that give rise to the GeV signal. Aims. The aim of this work is to search for diffuse X-ray emission from all GeV-detected GCs where appropriate X-ray observations are available, and to compare the obtained results with the signal detected from Terzan 5. This study will help to determine whether Terzan 5 stands out among other GC or whether a whole population of globular clusters feature similar properties. Methods. After assessing all archival X-ray observations of GeV detected GCs, we analyzed the data of six Chandra observation
Exploring the nature of the unidentified very-high-energy gamma-ray source HESS J1507-622
No full textContext. Several extended sources of very-high-energy (VHE; E > 100 GeV) gamma rays have been found that lack counterparts belonging to an established class of VHE gamma-ray emitters.
Aims. The nature of the first unidentified VHE gamma-ray source with significant angular offset from the Galactic plane of 3.5°, HESS J1507–622, is explored.
Methods.Fermi-LAT data in the high-energy (HE, 100 MeV < E < 100 GeV) gamma-ray range collected over 34 month are used to describe the spectral energy distribution (SED) of the source. Additionally, implications of the off-plane location of the source for a leptonic and hadronic gamma-ray emission model are investigated.
Results. HESS J1507–622 is detected in the Fermi energy range and its spectrum is best described by a power law in energy with Γ = 1.7 ± 0.1stat ± 0.2sys and integral flux between (0.3−300) GeV of F = (2.0 ± 0.5stat ± 1.0sys) × 10-9 cm-2 s-1. The SED constructed from the Fermi and H.E.S.S. data for this source does not support a smooth power-law continuation from the VHE to the HE gamma-ray range. With the available data it is not possible to discriminate between a hadronic and a leptonic scenario for HESS J1507–622. The location and compactness of the source indicate a considerable physical offset from the Galactic plane for this object. In case of a multiple-kpc distance, this challenges a pulsar wind nebula (PWN) origin for HESS J1507–622 since the time of travel for a pulsar born in the Galactic disk to reach such a location would exceed the inverse Compton (IC) cooling time of electrons that are energetic enough to produce VHE gamma-rays. However, an origin of this gamma-ray source connected to a pulsar that was born off the Galactic plane in the explosion of a hypervelocity star cannot be excluded.
Conclusions. The nature of HESS J1507–622 is still unknown to date, and a PWN scenario cannot be ruled out in general. On the contrary HESS J1507–622 could be the first discovered representative of a population of spatially extended VHE gamma-ray emitters with HE gamma-ray counterpart that are located at considerable offsets from the Galactic plane. Future surveys in the VHE gamma-ray range are necessary to probe the presence or absence of such a source population
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