Detection of a Star Forming Galaxy in the Center of a Low-Mass Galaxy Cluster

Brightest Cluster Galaxies (BCGs) residing in the centers of galaxy clusters are typically quenched giant ellipticals. A recent study hinted that star-forming galaxies with large disks, so-called superluminous spirals and lenticulars, are the BCGs of a subset of galaxy clusters. Based on the existing optical data it was not possible to constrain whether the superluminous disk galaxies reside at the center of galaxy clusters. In this work, we utilize XMM-Newton X-ray observations of five galaxy clusters to map the morphology of the intracluster medium (ICM), characterize the galaxy clusters, determine the position of the cluster center, and measure the offset between the cluster center and the superluminous disk galaxies. We demonstrate that one superluminous lenticular galaxy, 2MASX J10405643-0103584, resides at the center of a low-mass ($M_{\rm 500} = 10^{14} \ \rm{M_{\odot}}$) galaxy cluster. This represents the first conclusive evidence that a superluminous disk galaxy is the central BCG of a galaxy cluster. We speculate that the progenitor of 2MASX J10405643-0103584 was an elliptical galaxy, whose extended disk was re-formed due to the merger of galaxies. We exclude the possibility that the other four superluminous disk galaxies reside at the center of galaxy clusters, as their projected distance from the cluster center is $150-1070$ kpc, which corresponds to $(0.27-1.18)R_{\rm 500}$. We conclude that these clusters host quiescent massive elliptical galaxies at their center.Comment: 7 pages, 3 figures, accepted for publication in the Astrophysical Journa

A New Method to Quantify X-ray Substructures in Clusters of Galaxies

We present a new method to quantify substructures in clusters of galaxies, based on the analysis of the intensity of structures. This analysis is done in a residual image that is the result of the subtraction of a surface brightness model, obtained by fitting a two-dimensional analytical model (beta-model or S\'ersic profile) with elliptical symmetry, from the X-ray image. Our method is applied to 34 clusters observed by the Chandra Space Telescope that are in the redshift range 0.02<z<0.2 and have a signal-to-noise ratio greater than 100. We present the calibration of the method and the relations between the substructure level with physical quantities, such as the mass, X-ray luminosity, temperature, and cluster redshift. We use our method to separate the clusters in two sub-samples of high and low substructure levels. We conclude, using Monte Carlo simulations, that the method recuperates very well the true amount of substructure for small angular core radii clusters (with respect to the whole image size) and good signal-to-noise observations. We find no evidence of correlation between the substructure level and physical properties of the clusters such as mass, gas temperature, X-ray luminosity and redshift. The scaling relations for the two sub-samples (high and low substructure level clusters) are different (they present an off-set, i.e., given a fixed mass or temperature, low substructure clusters tend to be more X-ray luminous), which is an important result for cosmological tests using the mass-luminosity relation to obtain the cluster mass function, since they rely on the assumption that clusters do not present different scaling relations according to their dynamical state.Comment: 13 pages, 17 figures, accepted for publication in ApJ (http://iopscience.iop.org/0004-637X/746/2/139/

Do sonho de vida ao insucesso empresarial: a saga do jovem empreendedor Narciso

No abstract.NenhumaEste caso traz a história do jovem Empreendedor Narciso, que no ano eleitoral de 2018 abriu uma empresa no setor de comunicação digital. Sem nenhum preparo gerencial, Narciso vivencia muitas situações constrangedoras, incluindo relações difíceis com seus colaboradores. O caso relata a situação sob o ponto de vista de Lírio, amigo de Narciso que foi contratado para realizar algumas funções de comando na ausência do chefe. Mesmo Lírio tendo liberdade de comandar, ele se viu em muitas histórias complicadas de se resolver, já que envolviam outros funcionários insatisfeitos e os desmandos de Narciso. O dilema do caso envolve os comportamentos gerenciais de Narciso e suas implicações no fechamento da empresa

Dark Matter Subhalos and the X-ray Morphology of the Coma Cluster

Structure formation models predict that clusters of galaxies contain numerous massive subhalos. The gravity of a subhalo in a cluster compresses the surrounding intracluster gas and enhances its X-ray emission. We present a simple model, which treats subhalos as slow moving and gasless, for computing this effect. Recent weak lensing measurements by Okabe et al. have determined masses of ~ 10^13 solar masses for three mass concentrations projected within 300 kpc of the center of the Coma Cluster, two of which are centered on the giant elliptical galaxies NGC 4889 and NGC 4874. Adopting a smooth spheroidal beta-model for the gas distribution in the unperturbed cluster, we model the effect of these subhalos on the X-ray morphology of the Coma Cluster, comparing our results to Chandra and XMM-Newton X-ray data. The agreement between the models and the X-ray morphology of the central Coma Cluster is striking. With subhalo parameters from the lensing measurements, the distances of the three subhalos from the Coma Cluster midplane along our line of sight are all tightly constrained. Using the model to fit the subhalo masses for NGC 4889 and NGC 4874 gives 9.1 x 10^12 and 7.6 x 10^12 solar masses, respectively, in good agreement with the lensing masses. These results lend strong support to the argument that NGC 4889 and NGC 4874 are each associated with a subhalo that resides near the center of the Coma Cluster. In addition to constraining the masses and 3-d location of subhalos, the X-ray data show promise as a means of probing the structure of central subhalos.Comment: ApJ, in press. Matches the published versio