Kinematic Structure of Merger Remnants

We use numerical simulations to study the kinematic structure of remnants formed from mergers of equal-mass disk galaxies. In particular, we show that remnants of dissipational mergers, which include the radiative cooling of gas, star formation, feedback from supernovae, and the growth of supermassive black holes, are smaller, rounder, have, on average, a larger central velocity dispersion, and show significant rotation compared to remnants of dissipationless mergers. The increased rotation speed of dissipational remnants owes its origin to star formation that occurs in the central regions during the galaxy merger. We have further quantified the anisotropy, three-dimensional shape, minor axis rotation, and isophotal shape of each merger remnant, finding that dissipational remnants are more isotropic, closer to oblate, have the majority of their rotation along their major axis, and are more disky than dissipationless remnants. Individual remnants display a wide variety of kinematic properties. A large fraction of the dissipational remnants are oblate isotropic rotators. Many dissipational, and all of the dissipationless, are slowly rotating and anisotropic. The remnants of gas-rich major mergers can well-reproduce the observed distribution of projected ellipticities, rotation parameter (V/\sigma)*, kinematic misalignments, Psi, and isophotal shapes. The dissipationless remnants are a poor match to this data. Our results support the merger hypothesis for the origin of low-luminosity elliptical galaxies provided that the progenitor disks are sufficiently gas-rich, however our remnants are a poor match to the bright ellipticals that are slowly rotating and uniformly boxy.Comment: 22 pages, 17 figures, accepted to Ap

Dissipation and Extra Light in Galactic Nuclei: I. Gas-Rich Merger Remnants

We study the origin and properties of 'extra' or 'excess' central light in the surface brightness profiles of gas-rich merger remnants. Combining a large set of hydrodynamical simulations with data on observed mergers (spanning a broad range of profiles at various masses and degrees of relaxation), we show how to robustly separate the physically meaningful extra light -- stellar populations formed in a compact central starburst during a gas-rich merger -- from the outer profile established by violent relaxation acting on stars already present in the progenitors prior to the final merger. This separation is sensitive to the profile treatment, and we demonstrate that certain fitting procedures can yield physically misleading results. We show that our method reliably recovers the younger starburst population, and examine how the properties of this component scale with mass, gas content, and other aspects of the progenitors. We consider the time evolution of profiles in different bands, and estimate biases introduced by observational studies at different times and wavelengths. We show that extra light is ubiquitous in observed and simulated gas-rich merger remnants, with sufficient mass (~3-30% of the stellar mass) to explain the discrepancy in the maximum phase-space densities of ellipticals and their progenitor spirals. The nature of this central component provides powerful new constraints on the formation histories of observed systems.Comment: 36 pages, 38 figures, accepted for publication in ApJ (minor revisions to match accepted version

Dissipation and Extra Light in Galactic Nuclei: II. 'Cusp' Ellipticals

We study the origin and properties of 'extra' or 'excess' central light in the surface brightness profiles of cusp or power-law ellipticals. Dissipational mergers give rise to two-component profiles: an outer profile established by violent relaxation acting on stars present in the progenitors prior to the final merger, and an inner stellar population comprising the extra light, formed in a compact starburst. Combining a large set of hydrodynamical simulations with data that span a broad range of profiles and masses, we show that this picture is borne out -- cusp ellipticals are indeed 'extra light' ellipticals -- and examine how the properties of this component scale with global galaxy properties. We show how to robustly separate the 'extra' light, and demonstrate that observed cusps are reliable tracers of the degree of dissipation in the spheroid-forming merger. We show that the typical degree of dissipation is a strong function of stellar mass, tracing observed disk gas fractions at each mass. We demonstrate a correlation between extra light content and effective radius at fixed mass: systems with more dissipation are more compact. The outer shape of the light profile does not depend on mass, with a mean outer Sersic index ~2.5. We explore how this relates to shapes, kinematics, and stellar population gradients. Simulations with the gas content needed to match observed profiles also reproduce observed age, metallicity, and color gradients, and we show how these can be used as tracers of the degree of dissipation in spheroid formation.Comment: 40 pages, 32 figures, accepted to ApJ (revised to match accepted version

Search for exotic resonances decaying into WZ/ZZ in pp collisions at √s=7 TeV

Journal of High Energy Physics 2013.2 (2013): 036 reproduced by permission of Scuola Internazionale Superiore di Studi Avanzati (SISSA)Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMA search for new exotic particles decaying to the VZ final state is performed, where V is either a W or a Z boson decaying into two overlapping jets and the Z decays into a pair of electrons, muons or neutrinos. The analysis uses a data sample of pp collisions corresponding to an integrated luminosity of 5 fb-1 collected by the CMS experiment at the LHC at √s=7 TeV in 2011. No significant excess is observed in the mass distribution of the VZ candidates compared with the background expectation from standard model processes. Model-dependent upper limits at the 95% confidence level are set on the product of the cross section times the branching fraction of hypothetical particles decaying to the VZ final state as a function of mass. Sequential standard model W′ bosons with masses between 700 and 940 GeV are excluded. In the Randall-Sundrum model for graviton resonances with a coupling parameter of 0.05, masses between 750 and 880 GeV are also exclude

Searches for long-lived charged particles in pp collisions at √s =7 and 8 TeV

Results of searches for heavy stable charged particles produced in pp collisions at √s =7 and 8 TeV are presented corresponding to an integrated luminosity of 5.0 fb⁻¹ and 18.8 fb⁻¹, respectively. Data collected with the CMS detector are used to study the momentum, energy deposition, and time-of-flight of signal candidates. Leptons with an electric charge between e/3 and 8e, as well as bound states that can undergo charge exchange with the detector material, are studied. Analysis results are presented for various combinations of signatures in the inner tracker only, inner tracker and muon detector, and muon detector only. Detector signatures utilized are long time-of-flight to the outer muon system and anomalously high (or low) energy deposition in the inner tracker. The data are consistent with the expected background, and upper limits are set on the production cross section of long-lived gluinos, scalar top quarks, and scalar τ leptons, as well as pair produced long-lived leptons. Corresponding lower mass limits, ranging up to 1322 GeV/c² for gluinos, are the most stringent to date