No abstract

We present a new deep spectroscopic catalogue for Abell 85, within 3.0 × 2.6 Mpc 2 and down to M r ∼ M * r +6. Using the Visible Multi-Object Spectrograph at the Very Large Telescope and the AutoFiber 2 at the William Herschel Telescope, we obtained almost 1430 new redshifts for galaxies with m r ≤ 21 mag and µ e,r ≤ 24 mag arcsec −2 . These redshifts, together with SDSS-DR6 and NED spectroscopic information, result in 460 confirmed cluster members. This data set allows the study of the luminosity function (LF) of the cluster galaxies covering three orders of magnitudes in luminosities. The total and radial LFs are best modelled by a double Schechter function. The normalized LFs show that their bright (M r ≤ −21.5) and faint (M r ≥ −18.0) ends are independent of clustercentric distance and similar to the field LFs unlike the intermediate luminosity range (−21.5 ≤ M r ≤ −18.0). Similar results are found for the LFs of the dominant types of galaxies: red, passive, virialized and early-infall members. On the contrary, the LFs of blue, star-forming, non-virialized and recent-infall galaxies are well described by a single Schechter function. These populations contribute to a small fraction of the galaxy density in the innermost cluster region. However, in the outskirts of the cluster, they have similar densities to red, passive, virialized and early-infall members at the LF faint end. These results confirm a clear dependence of the colour and star formation of Abell 85 members in the cluster centric distance.

Context. The ubiquitous presence of the Fe line complex in the X-ray spectra of galaxy clusters offers the possibility of measuring their redshift without resorting to spectroscopic follow-up observations. In practice, the blind search of the Fe line in X-ray spectra is a difficult task and is affected not only by limited S/N (particularly at high redshift), but also by several systematic errors, associated with varying Fe abundance values, ICM temperature gradients, and instrumental characteristics. Aims. We assess the accuracy with which the redshift of galaxy clusters can be recovered from an X-ray spectral analysis of Chandra archival data. We present a strategy to compile large surveys of clusters whose identification and redshift measurement are both based on X-ray data alone. Methods. We apply a blind search for K-shell and L-shell Fe line complexes in X-ray cluster spectra using Chandra archival observations of galaxy clusters. The Fe line can be detected in the ICM spectra by simply analyzing the C-statistics variation ΔC stat as a function of the redshift parameter, when all the other model parameters are frozen to the best-fit values. We repeat the measurement under different conditions, and compare the X-ray derived redshift z X with the one obtained by means of optical spectroscopy z o . We explore how a number of priors on metallicity and luminosity can be effectively used to reduce catastrophic errors. The ΔC stat provides the most effective means of discarding wrong redshift measurements and estimating the actual error in z X . Results. We identify a simple and efficient procedure for optimally measuring the redshifts from the X-ray spectral analysis of clusters of galaxies. When this procedure is applied to mock catalogs extracted from high sensitivity, wide-area cluster surveys, such as those proposed with Wide Field X-ray Telescope (WFXT) mission, it is possible to obtain complete samples of X-ray clusters with reliable redshift measurements, thus avoiding time-consuming optical spectroscopic observations. Our analysis shows that, in the case of WFXT, a blind Fe line search is 95% successful for spectra with more than 1000 net counts, whenever ΔC stat > 9, corresponding formally to a 3σ confidence level. The average error in the redshift z X decreases rapidly for higher values of ΔC stat . Finally, we discuss how to estimate the completeness of a large cluster samples with measured z X . This methodology will make it possible to trace cosmic growth by studying the evolution of the cluster mass function directly using X-ray data.

We propose a strategy to search for bulk motions in the intracluster medium (ICM) of merging clusters based on Chandra CCD data. Our goal is to derive robust measurements of the average redshift of projected ICM regions obtained from the centroid of the K α line emission. We thoroughly explore the effect of the unknown temperature structure along the line of sight to accurately evaluate the systematic uncertainties on the ICM redshift. We apply our method to the "Bullet cluster" (1E 0657-56). We directly identify 23 independent regions on the basis of the surface brightness contours, and measure the redshift of the ICM averaged along the line of sight in each. We find that the redshift distribution across these regions is marginally inconsistent with the null hypothesis of a constant redshift or no bulk motion in the ICM, at a confidence level of about 2 σ. We tentatively identify the regions most likely affected by bulk motions and find a maximum velocity gradient of about (46 ± 13) km s −1 kpc −1 along the line of sight on a scale of ∼ 260 kpc along the path of the "bullet". We interpret this as the possible signature of a significant mass of ICM pushed away along a direction perpendicular to the merging. This preliminary result is promising for a systematic search for bulk motions in bright, moderate-redshift clusters based on spatially resolved spectral analysis of Chandra CCD data. This preliminary result is promising for a systematic search for bulk motions in bright, moderate-redshift clusters based on spatially resolved spectral analysis of Chandra CCD data.

We investigate the power of the caustic technique for identifying substructures of galaxy clusters from optical redshift data alone. The caustic technique is designed to estimate the mass profile of galaxy clusters to radii well beyond the virial radius, where dynamical equilibrium does not hold. Two by-products of this technique are the identification of the cluster members and the identification of the cluster substructures. We test the caustic technique as a substructure detector on two samples of 150 mock redshift surveys of clusters; the clusters are extracted from a large cosmological N -body simulation of a ΛCDM model and have masses of M 200 ∼ 10 14 h −1 M and M 200 ∼ 10 15 h −1 M in the two samples. We limit our analysis to substructures identified in the simulation with masses larger than 10 13 h −1 M . With mock redshift surveys with 200 galaxies within 3R 200 , (1) the caustic technique recovers ∼ 30 − 50% of the real substructures, and (2) ∼ 15 − 20% of the substructures identified by the caustic technique correspond to real substructures of the central cluster, the remaining fraction being low-mass substructures, groups or substructures of clusters in the surrounding region, or chance alignments of unrelated galaxies. These encouraging results show that the caustic technique is a promising approach for investigating the complex dynamics of galaxy clusters.

We investigate the spatial distribution of iron in the intra-cluster medium in a selected sample of 41 relaxed clusters in the redshift range 0.05 < z < 1.03 using Chandra archival data. We compute the azimuthally-averaged, deprojected Z Fe profile of each cluster out to ∼ 0.4r 500 , and identify a peak in the distribution of iron followed by a flatter distribution at larger radii. Due to the steep gradient both in gas density and abundance, we find that the emission-weighted iron abundance within 0.2r 500 , which entirely includes the iron peak in most of the cases, is on average ∼25% higher than the mass-weighted value, showing that spatially resolved analysis and accurate deprojection are key to study the evolution of iron enrichment in the very central regions of cool core clusters. We quantify the extent of the iron distribution in each cluster with a normalized scale parameter r Fe , defined as the radius where the iron abundance excess is half of its peak value. We find that r Fe increases by a factor of ∼ 3 from z ∼ 1 to z ∼ 0.1, suggesting that the spatial distribution of iron in the ICM extends with time, possibly due to the mixing with the mechanical-mode feedback from the central galaxy. We also find that the iron mass excess within 0.3r 500 , when normalized to the total baryonic mass within the same region, does not evolve significantly, showing that this iron mass component is already established at z ∼ 1.

For the first time, we explore the dynamics of the central region of a galaxy cluster within r 500 ∼600 h −1 kpc from its center by combining optical and X-ray spectroscopy. We use (1) the caustic technique, whichidentifies the cluster substructures and their galaxy members with optical spectroscopic data, and (2) the X-ray redshift fitting procedure, which estimates the redshift distribution of the intracluster medium (ICM). We use the spatial and redshift distributions of the galaxies and of the X-ray-emitting gas to associate the optical substructures to the X-ray regions. When we apply this approach to Abell 85 (A85), a complex dynamic structure of A85 emerges from our analysis: a galaxy group, with redshift z=0.0509±0.0021 is passing through the cluster center along the line of sight dragging part of the ICM present in the cluster core; two additional groups, at redshift z=0.0547±0.0022 and z=0.0570±0.0020, are going through the cluster in opposite directions, almost perpendicularly to the line of sight, and have substantially perturbed the dynamics of the ICM. An additional group in the outskirts of A85, at redshift z=0.0561±0.0023, is associated with a secondary peak of X-ray emission, at redshift = -+ z 0.0583 0.0047 0.0039 . Although our analysis and results on A85 need to be confirmed by high-resolution spectroscopy, they demonstrate how our new approach can be a powerful tool to constrain the formation history of galaxy clusters by unveiling their central and surrounding structures.

In this study, two Ni(II) complexes, namely [Ni(HL1)2(OAc)2] (1) and [Ni(L2)2] (2) (where HL1 and HL2 are (E)-1-((1-(2-hydroxyethyl)-1H-pyrazol-5-ylimino)methyl)-naphthalen-2-ol) and (E)-ethyl-5-((2-hydroxynaphthalen-1-yl)methyleneamino)-1-methyl-1H-pyrazole-4-carboxylate, respectively), were synthesized and characterized by X-ray crystallography, Electrospray Ionization Mass Spectrometry (ESI-MS), elemental analysis, and IR. Their uptake in biological macromolecules and cancer cells were preliminarily investigated through electronic absorption (UV-Vis), circular dichroism (CD) and fluorescence quenching measurements. Bovine serum albumin (BSA) interaction experiments were investigated by spectroscopy which showed that the complexes and ligands could quench the intrinsic fluorescence of BSA through an obvious static quenching process. The spectroscopic studies indicated that these complexes could bind to DNA via groove, non-covalent, and electrostatic interactions. Furthermore, in vitro methyl thiazolyl tetrazolium (MTT) assays and Annexin V/PI flow cytometry experiments were performed to assess the antitumor capacity of the complexes against eight cell lines. The results show that both of the complexes possess reasonable cytotoxicities.