A New Galaxy Cluster Merger Capable of Probing Dark Matter: Abell 56

We report the discovery of a binary galaxy cluster merger via a search of the redMaPPer optical cluster catalog, with a projected separation of 535 kpc between the BCGs. Archival XMM-Newton spectro-imaging reveals a gas peak between the BCGs, suggesting a recent pericenter passage. We conduct a galaxy redshift survey to quantify the line-of-sight velocity difference ($153\pm281$ km/s) between the two subclusters. We present weak lensing mass maps from archival HST/ACS imaging, revealing masses of $M_{200}=4.5\pm0.8\times10^{14}$ and $2.8\pm0.7\times10^{14}$ M$_\odot$ associated with the southern and northern galaxy subclusters respectively. We also present deep GMRT 650 MHz data revealing extended emission, 420 kpc long, which may be an AGN tail but is potentially also a candidate radio relic. We draw from cosmological n-body simulations to find analog systems, which imply that this system is observed fairly soon (60-271 Myr) after pericenter, and that the subcluster separation vector is within 22$^\circ$ of the plane of the sky, making it suitable for an estimate of the dark matter scattering cross section. We find $\sigma_{\rm DM}=1.1\pm0.6$ cm$^2$/g, suggesting that further study of this system could support interestingly tight constraints.Comment: accepted to Ap

Termodinâmica de um gelo de spin artificial regravável

Exportado OPUSMade available in DSpace on 2019-08-13T10:50:13Z (GMT). No. of bitstreams: 1 rodrigo_alves_stancioli___disserta__o.pdf: 3401031 bytes, checksum: 63dbb0f10e09a08f8cf9eafb4a2a9189 (MD5) Previous issue date: 29Gelos de spin artificiais (ASI) são redes bidimensionais de nanoilhas magnéticas geometricamente frustradas, originalmente concebidas para mimetizar o comportamento de materiais com a estrutura cristalina do pirocloro comumente conhecidos como gelos de spin. Diferentes tipos de ASI vêm sendo desenvolvidos recentemente, ensejando a observação de fenômenos interessantes como o aparecimento de excitações que se comportam como monopolos magnéticos, bem como sugerindo a possibilidade de novas aplicações. Uma nova geometria de ASI recentemente proposta na literatura foi denominada gelo de spin artificial "regravável", por possibilitar total controle sobre os microestados do sistema à temperatura ambiente. Apesar de a realização experimental desse sistema ser essencialmente atérmica, técnicas recentes permitem a fabricação de nanoilhas suscetíveisa flutuações térmicas, o que torna importante investigar o comportamento termodinâmico dos ASI. Neste trabalho, realizamos simulações de Monte Carlo de um modelo do ASI regravável, em que as nanoilhas são tratadas como spins do tipo Ising com interaçõesdipolares, no intuito de estudar suas transições de fase na ausência de campo magnético. Tanto condições de contorno abertas quanto periódicas foram consideradas. O estado fundamental encontrado é maximamente magnetizado, e uma fase ordenada é observadaem baixas temperaturas. No limite termodinâmico, uma transição contínua entre essa fase ordenada e uma fase paramagnética é evidenciada pela divergência do calor específico na temperatura crítica. Em sistemas finitos, no entanto, ocorre uma pseudo-transição de fasede baixa temperatura, introduzindo uma fase intermediária entre as fases paramagnética e maximamente magnetizada que se caracteriza pela pequena quantidade de excitações locais e por baixos valores de magnetização total. A temperatura crítica foi determinada mediante o cálculo dos zeros da distribuição de probabilidade da energia. Em trabalhos futuros, pretendemos elucidar a natureza dessa pseudo-transição, bem como investigar o comportamento das excitações na rede.Artificial spin ices (ASI) are geometrically frustrated, two-dimensional arrays of magnetic nanoislands, originally designed to mimic the behavior of pyrochlore spin ice materials. Different types of ASI have been developed lately, giving rise to interesting phenomena such as magnetic monopole-like excitations, as well as suggesting the possibility of newapplications. A novel geometry of ASI recently proposed in the literature has been termed "rewritable" artificial spin ice, for it allows total control over the microstates of the system at room temperature. Although the reported experimental realization of this particular system is essentially athermal, recent techniques permit the fabrication of nanoislandssusceptible to thermal fluctuations, which makes it important to investigate the thermal behavior of ASI. We have performed Monte Carlo simulations of a model of the rewritable ASI, with nanoislands being treated as Ising macrospins with dipolar interactions, in orderto study its phase transitions in the absence of a magnetic field. Both periodic and open boundary conditions have been considered. The ground state has been determined to be maximally magnetized, and an ordered phase has been observed at low temperatures.In the thermodynamic limit, a continuous transition between this ordered phase and a paramagnetic one is evidenced by the divergence of the specific heat curve at the critical temperature. In finite systems, however, a low temperature pseudo-phase transition takes place, introducing an intermediary phase between the paramagnetic and fully magnetizedphases which has few local excitations and shows low net magnetization values. The critical temperature has been determined by means of a new method based upon the energy probability distribution zeros. In future works, we intend to further investigate the nature of this pseudo-transition, as well as the behavior of excitations in the lattice

A New Dissociative Galaxy Cluster Merger: RM J150822.0+575515.2

Abstract: Galaxy cluster mergers that exhibit clear dissociation between their dark matter, intracluster gas, and stellar components are great laboratories for probing dark matter properties. Mergers that are binary and in the plane of the sky have the additional advantage of being simpler to model, allowing for a better understanding of the merger dynamics. We report the discovery of a galaxy cluster merger with all these characteristics and present a multiwavelength analysis of the system, which was found via a search in the redMaPPer optical cluster catalog. We perform a galaxy redshift survey to confirm the two subclusters are at the same redshift (0.541, with 368 ± 519 km s−1 line-of-sight velocity difference between them). The X-ray morphology shows two surface brightness peaks between the brightest cluster galaxies (BCGs). We construct weak-lensing mass maps that reveal a mass peak associated with each subcluster. Fitting Navarro–Frenk–White profiles to the lensing data, we find masses of M 200c = 36 ± 11 × 1013 and 38 ± 11 × 1013 M ⊙ h −1 for the southern and northern subclusters, respectively. From the mass maps, we infer that the two mass peaks are separated by 520 − 125 + 162 kpc along the merger axis, whereas the two BCGs are separated by 697 kpc. We also present deep GMRT 650 MHz data to search for a radio relic or halo and find none. Using the observed merger parameters, we find analog systems in cosmological n-body simulations and infer that this system is observed between 96 and 236 Myr after pericenter, with the merger axis within 28° of the plane of the sky

A New Galaxy Cluster Merger Capable of Probing Dark Matter: A56

We report the discovery of a binary galaxy cluster merger via a search of the redMaPPer optical cluster catalog, with a projected separation of 535 kpc between the brightest cluster galaxies (BCGs). Archival XMM-Newton spectro-imaging reveals a gas peak between the BCGs, suggesting a recent pericenter passage. We conduct a galaxy redshift survey to quantify the line-of-sight velocity difference (153 ± 281 km s−1) between the two subclusters. We present weak-lensing mass maps from archival Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) imaging, revealing masses of M 200 = 4.5 ± 0.8 × 1014 and 2.8 ± 0.7 × 1014 M ⊙ associated with the southern and northern galaxy subclusters, respectively. We also present deep GMRT 650 MHz data revealing extended emission, 420 kpc long, which may be an active galactic nucleus (AGN) tail but is potentially also a candidate radio relic. We draw from cosmological n-body simulations to find analog systems, which imply that this system is observed fairly soon (60-271 Myr) after pericenter, and that the subcluster separation vector is within 22° of the plane of the sky, making it suitable for an estimate of the dark matter scattering cross section. We find σ DM m = 1.1 ± 0.6 cm2 g−1, suggesting that further study of this system could support interestingly tight constraints