ترغب بنشر مسار تعليمي؟ اضغط هنا

The double galaxy cluster Abell 2465 - II. Star formation in the cluster

494   0   0.0 ( 0 )
 نشر من قبل Gary Wegner
 تاريخ النشر 2014
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We investigate the star formation rate and its location in the major merger cluster Abell 2465 at $z$ = 0.245. Optical properties of the cluster are described in Paper I. Measurements of the H$alpha$ and infrared dust emission of galaxies in the cluster were made with an interference filter centred on the redshifted line at a wavelength of 817 nm and utilized data from the WISE satellite 12 $mu$m band. Imaging in the Johnson $U$ and $B$ bands was obtained, and along with SDSS $u$ and $r$ was used to study the blue fraction, which appears enhanced, as a further signatures of star formation in the cluster. Star formation rates were calculated using standard calibrations. The total star formation rate normalized by the cluster mass, $Sigma SFR/M_{cl}$ compared to compilations for other clusters indicate that the components of Abell 2465 lie above the mean $z$ and $M_{cl}$ relations, suggestive that interacting galaxy clusters have enhanced star formation. The projected radial distribution of the star forming galaxies does not follow a NFW profile and is relatively flat indicating that fewer star forming galaxies are in the cluster centre. The morphologies of the H$alpha$ sources within $R_{200}$ for the cluster as a whole indicate that many are disturbed or merging, suggesting that a combination of merging or harassment is working.



قيم البحث

اقرأ أيضاً

We report Chandra X-ray observations and optical weak-lensing measurements from Subaru/Suprime-Cam images of the double galaxy cluster Abell 2465 (z=0.245). The X-ray brightness data are fit to a beta-model to obtain the radial gas density profiles o f the northeast (NE) and southwest (SW) sub-components, which are seen to differ in structure. We determine core radii, central temperatures, the gas masses within $r_{500c}$, and the total masses for the broader NE and sharper SW components assuming hydrostatic equilibrium. The central entropy of the NE clump is about two times higher than the SW. Along with its structural properties, this suggests that it has undergone merging on its own. The weak-lensing analysis gives virial masses for each substructure, which compare well with earlier dynamical results. The derived outer mass contours of the SW sub-component from weak lensing are more irregular and extended than those of the NE. Although there is a weak enhancement and small offsets between X-ray gas and mass centers from weak lensing, the lack of large amounts of gas between the two sub-clusters indicates that Abell 2465 is in a pre-merger state. A dynamical model that is consistent with the observed cluster data, based on the FLASH program and the radial infall model, is constructed, where the subclusters currently separated by ~1.2Mpc are approaching each other at ~2000km/s and will meet in ~0.4Gyr.
Magnetic fields are ubiquitous in galaxy clusters, yet their radial profile, power spectrum, and connection to host cluster properties are poorly known. Merging galaxy clusters hosting diffuse polarized emission in the form of radio relics offer a un ique possibility to study the magnetic fields in these complex systems. In this paper, we investigate the intra-cluster magnetic field in Abell 2345. This cluster hosts two radio relics that we detected in polarization with 1-2 GHz JVLA observations. X-ray XMM-Newton images show a very disturbed morphology. We derived the Rotation Measure (RM) of five polarized sources within $sim$ 1 Mpc from the cluster center applying the RM synthesis. Both, the average RM and the RM dispersion radial profiles probe the presence of intra-cluster magnetic fields. Using the thermal electron density profile derived from X-ray analysis and simulating a 3D magnetic field with fluctuations following a power spectrum derived from magneto-hydrodynamical cosmological simulations, we build mock RM images of the cluster. We constrained the magnetic field profile in the eastern radio relic sector by comparing simulated and observed RM images. We find that, within the framework of our model, the data require a magnetic field scaling with thermal electron density as $B(r)propto n_e(r)$. The best model has a central magnetic field (within a 200 kpc radius) of $2.8pm0.1$ $mu$G. The average magnetic field at the position of the eastern relic is $sim$0.3 $mu$G, a factor 2.7 lower than the equipartition estimate.
We present LOFAR $120-168$ MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the GMRT $595-629$ MHz and VLA $2-4$ GHz data, we characterised the spectral and polarimetric properties of the radio e mission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration (DSA), we obtain shock Mach numbers of $mathcal{M}=2.4$ and $2.3$ for the northern and southern shocks, respectively. For $mathcal{M}lesssim3$ shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high ($>10$ per cent) particle acceleration efficiency required. However, for $mathcal{M}gtrsim4$ shocks the required efficiency is $gtrsim1%$ and $gtrsim0.5%$, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to $geqslant(53pm3)^circ$ and $geqslant(39pm5)^circ$ for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics ($sim1.8,text{Mpc}$) our upper limit on the power is $P_text{1.4 GHz}=(1.4pm0.6)times10^{23},text{W}text{Hz}^{-1}$ which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous.
We present results from Chandra and XMM-Newton observations of Abell 98 (A98), a galaxy cluster with three major components: a relatively bright subcluster to the north (A98N), a disturbed subcluster to the south (A98S), and a fainter subcluster to t he far south (A98SS). We find evidence for surface brightness and temperature asymmetries in A98N consistent with a shock-heated region to the south, which could be created by an early stage merger between A98N and A98S. Deeper observations are required to confirm this result. We also find that A98S has an asymmetric core temperature structure, likely due to a separate ongoing merger. Evidence for this is also seen in optical data. A98S hosts a wide-angle tail (WAT) radio source powered by a central active galactic nucleus (AGN). We find evidence for a cavity in the intracluster medium (ICM) that has been evacuated by one of the radio lobes, suggesting that AGN feedback is operating in this system. Examples of cavities in non-cool core clusters are relatively rare. The three subclusters lie along a line in projection, suggesting the presence of a large-scale filament. We observe emission along the filament between A98N and A98S, and a surface brightness profile shows emission consistent with the overlap of the subcluster extended gas haloes. We find the temperature of this region is consistent with the temperature of the gas at similar radii outside this bridge region. Lastly, we examine the cluster dynamics using optical data. We conclude A98N and A98S are likely bound to one another, with a 67% probability, while A98S and A98SS are not bound at a high level of significance.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا