اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدCluster Abell 520: a perspective based on member galaxies. A cluster forming at the crossing of three filaments?
43
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The connection of cluster mergers with the presence of extended, diffuse radio sources in galaxy clusters is still debated. An interesting case is the rich, merging cluster Abell 520, containing a radio halo. A recent gravitational analysis has shown in this cluster the presence of a massive dark core suggested to be a possible problem for the current cold dark matter paradigm. We aim to obtain new insights into the internal dynamics of Abell 520 analyzing velocities and positions of member galaxies. Our analysis is based on redshift data for 293 galaxies in the cluster field obtained combining new redshift data for 86 galaxies acquired at the TNG with data obtained by CNOC team and other few data from the literature. We also use new photometric data obtained at the INT telescope. We combine galaxy velocities and positions to select 167 cluster members around z~0.201. We analyze the cluster structure using the weighted gap analysis, the KMM method, the Dressler-Shectman statistics and the analysis of the velocity dispersion profiles. We compare our results with those from X-ray, radio and gravitational lensing analyses. We find that Abell 520 is definitely a very complex system. Our results suggest that we are looking at a cluster forming at the crossing of three filaments of the large scale structure. In particular, we detect a filament aligned with the LOS and projected onto the center of the forming cluster. It might explain the apparent massive dark core shown by gravitational lensing analysis.
قيم البحث
اقرأ أيضاً
We examine the possible acceleration mechanisms of the relativistic particles responsible for the extended radio emission in Abell 520. We used new LOFAR 145 MHz, archival GMRT 323 MHz and VLA 1.5 GHz data to study the morphological and spectral prop
erties of extended cluster emission. The observational properties are discussed in the framework of particle acceleration models associated with cluster merger turbulence and shocks. In Abell 520, we confirm the presence of extended synchrotron radio emission that has been classified as a radio halo. The comparison between the radio and X-ray brightness suggests that the halo might originate in a cocoon rather than from the central X-ray bright regions of the cluster. The halo spectrum is roughly uniform on the scale of 66 kpc. There is a hint of spectral steepening from the SW edge towards the cluster centre. Assuming DSA, the radio data are suggestive of a shock of $mathcal{M}_{SW}=2.6_{-0.2}^{+0.3}$ that is consistent with the X-ray derived estimates. This is in line with the scenario in which relativistic electrons in the SW radio edge gain their energies at the shock front via acceleration of either thermal or fossil electrons. We do not detect extended radio emission ahead of the SW shock that is predicted if the emission is the result of adiabatic compression. An X-ray surface brightness discontinuity is detected towards the NE region that may be a counter shock of $mathcal{M}_{NE}^{X}=1.52pm0.05$. This is lower than the value predicted from the radio emission ($mathcal{M}_{NE}=2.1pm0.2$). Our observations indicate that the SW radio emission in Abell 520 is likely effected by the prominent X-ray detected shock in which radio emitting particles are (re-)accelerated through the Fermi-I mechanism. The NE X-ray discontinuity that is approximately collocated with an edge in the radio emission hints at the presence of a counter shock.
We analyze the dynamical state of Abell 1914, a merging cluster hosting a radio halo, quite unusual for its structure. Our study considers spectroscopic data for 119 galaxies obtained with the Italian Telescopio Nazionale Galileo. We select 89 cluste
r members from spatial and velocity distributions. We also use photometry Canada-France-Hawaii Telescope archives. We compute the mean cluster redshift, <z>=0.168, and the velocity dispersion which shows a high value, sigma_v=1210_{-110}^{+125} km/s. From the 2D analysis we find that Abell 1914 has a NE-SW elongated structure with two galaxy clumps, that mostly merge in the plane of the sky. Our best, but very uncertain estimate of the velocity dispersion of the main system is sigma_v~1000 km/s. We estimate a virial mass M_sys=1.4--2.6 10^{15} h_{70}^{-1} Msun for the whole system. We study the merger through a simple two-body model and find that data are consistent with a bound, outgoing substructure observed just after the core crossing. By studying the 2D distribution of the red galaxies, photometrically selected, we show that Abell 1914 is contained in a rich large scale structure, with two close companion galaxy systems, known to be at z~0.17. The system at SW supports the idea that the cluster is accreting groups from a filament aligned in the NE-SW direction, while that at NW suggests a second direction of the accretion NW-SE. We conclude that Abell 1914 well fits among typical clusters with radio halos. We argue that the unusual radio emission is connected to the complex cluster accretion and suggest that Abell 1914 resembles the well-known nearby merging cluster Abell 754 for its particular observed phenomenology.
Merging clusters of galaxies are unique in their power to directly probe and place limits on the self-interaction cross-section of dark matter. Detailed observations of several merging clusters have shown the intracluster gas to be displaced from the
centroids of dark matter and galaxy density by ram pressure, while the latter components are spatially coincident, consistent with collisionless dark matter. This has been used to place upper limits on the dark matter particle self-inteaction cross-section of order 1 cm^2/g. The cluster Abell 520 has been seen as a possible exception. We revisit A520 presenting new HST ACS mosaic images and a Magellan image set. We perform a detailed weak lensing analysis and show that the weak lensing mass measurements and morphologies of the core galaxy-filled structures are mostly in good agreement with previous works. There is however one significant difference -- we do not detect the previously claimed dark core that contains excess mass with no significant galaxy overdensity at the location of the X-ray plasma. This peak has been suggested to be indicative of a large self-interaction cross-section for dark matter (at least ~5 sigma larger than the upper limit of 0.7 cm^2/g determined by observations of the Bullet Cluster). We find no such indication and instead find that the mass distribution of A520, after subtraction of the X-ray plasma mass, is in good agreement with the luminosity distribution of the cluster galaxies. We conclude that A520 shows no evidence to contradict the collisionless dark matter scenario.
We present a dynamical analysis of the galaxy cluster Abell 376 based on a set of 73 velocities, most of them measured at Pic du Midi and Haute-Provence observatories and completed with data from the literature. Data on individual galaxies are presen
ted and the accuracy of the determined velocities is discussed as well as some properties of the cluster. We obtained an improved mean redshift value z=0.0478^{+0.005}_{-0.006} and velocity dispersion sigma=852^{+120}_{-76}km/s. Our analysis indicates that inside a radius of 900h_{70}^{-1}kpc (15 arcmin) the cluster is well relaxed without any remarkable feature and the X-ray emission traces fairly well the galaxy distribution. A possible substructure is seen at 20 arcmin from the centre towards the Southwest direction, but is not confirmed by the velocity field. This SW clump is, however, kinematically bound to the main structure of Abell 376. A dense condensation of galaxies is detected at 46 arcmin (projected distance 2.6h_{70}^{-1}Mpc) from the centre towards the Northwest and analysis of the apparent luminosity distribution of its galaxies suggests that this clump is part of the large scale structure of Abell 376. X-ray spectroscopic analysis of ASCA data resulted in a temperature kT = 4.3+/-0.4 keV and metal abundance Z = 0.32+/-0.08 Z_solar. The velocity dispersion corresponding to this temperature using the T_X-sigma scaling relation is in agreement with the measured galaxies velocities.
The rich cluster Abell 520 (z=0.201) exhibits truly extreme and puzzling multi-wavelength characteristics. It may best be described as a cosmic train wreck. It is a major merger showing abundant evidence for ram pressure stripping, with a clear offse
t in the gas distribution compared to the galaxies (as in the bullet cluster 1E 0657-558). However, the most striking feature is a massive dark core (721 h_70 M_sun/L_sun) in our weak lensing mass reconstruction. The core coincides with the central X-ray emission peak, but is largely devoid of galaxies. An unusually low mass to light ratio region lies 500 kpc to the east, and coincides with a shock feature visible in radio observations of the cluster. Although a displacement between the X-ray gas and the galaxy/dark matter distributions may be expected in a merger, a mass peak without galaxies cannot be easily explained within the current collisionless dark matter paradigm. Interestingly, the integrated gas mass fraction (~0.15), mass-to-light ratio (220 h_70 M_sun/L_sun), and position on the X-ray luminosity-temperature and mass-temperature relations are unremarkable. Thus gross properties and scaling relations are not always useful indicators of the dynamical state of clusters.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
