Interferometer

A high resolution interferometer is described. The interferometer is insensitive to slight misalignment of its elements, avoids channeling in the spectrum, generates a maximum equal path fringe contrast, produces an even two sided interferogram without critical matching of the wedge angles of the beamsplitter and compensator wedges, and is optically phase tunable. The interferometer includes a mirror along the path of each beam component produced by the beamsplitter, for reflecting the beam component from the beamsplitter, for reflecting the beam component from the beamsplitter to a corresponding retroreflector and for reflecting the beam returned by the retroreflector back to the beamsplitter. A wedge located along each beam component path, is large enough to cover the retroreflector, so that each beam component passes through the wedge during movement towards the retroreflector and away therefrom

Internal kinematics of isolated modelled disk galaxies

We present a systematic investigation of rotation curves (RCs) of fully hydrodynamically simulated galaxies, including cooling, star formation with associated feedback and galactic winds. Applying two commonly used fitting formulae to characterize the RCs, we investigate systematic effects on the shape of RCs both by observational constraints and internal properties of the galaxies. We mainly focus on effects that occur in measurements of intermediate and high redshift galaxies. We find that RC parameters are affected by the observational setup, like slit misalignment or the spatial resolution and also depend on the evolution of a galaxy. Therefore, a direct comparison of quantities derived from measured RCs with predictions of semi-analytic models is difficult. The virial velocity V_c, which is usually calculated and used by semi-analytic models can differ significantly from fit parameters like V_max or V_opt inferred from RCs. We find that V_c is usually lower than typical characteristic velocities derived from RCs. V_max alone is in general not a robust estimator for the virial mass.Comment: 9 pages, 15 figures, accepted for publication in A&

Internal kinematics of modelled interacting disc galaxies

We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of disc galaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, and galactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys disturb the velocity fields significantly and hence the RCs of the interacting galaxies, leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are significantly rising or falling profiles in the direction of the companion galaxy and pronounced bumps in the RCs. In addition, tidal tails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshift galaxies, on which we focus our investigations. We use a quantitative measure for the asymmetry of rotation curves to show that the appearance of these distortions strongly depends on the viewing angle. We also find in this way that the velocity fields settle back into relatively undisturbed equilibrium states after unequal mass mergers and fly-bys. About 1 Gyr after the first encounter, the RCs show no severe distortions anymore. These results are consistent with previous theoretical and observational studies. As an illustration of our results, we compare our simulated velocity fields and direct images with rotation curves from VLT/FORS spectroscopy and ACS images of a cluster at z=0.53 and find remarkable similarities.Comment: 13 pages, 14 figures, accepted for publication in A&A, some improvements and changes, main conclusions are unaffecte

The Dwarf Irregular Galaxy UGC 7636 Exposed: Stripping At Work In The Virgo Cluster

We present the results of optical spectroscopy of a newly discovered H II region residing in the H I gas cloud located between the dwarf irregular galaxy UGC 7636 and the giant elliptical galaxy NGC 4472 in the Virgo Cluster. By comparing UGC 7636 with dwarf irregular galaxies in the field, we show that the H I cloud must have originated from UGC 7636 because (1) the oxygen abundance of the cloud agrees with that expected for a galaxy with the blue luminosity of UGC 7636, and (2) M_{H I}/L_B for UGC 7636 becomes consistent with the measured oxygen abundance of the cloud if the H I mass of the cloud is added back into UGC 7636. It is likely that tides from NGC 4472 first loosened the H I gas, after which ram-pressure stripping removed the gas from UGC 7636.Comment: 12 pages, 2 eps figures (AASTeX 5.0); accepted for publication in ApJ Letter

Nonlinear breathers with crystalline symmetries

Nonlinear lattice models can support "discrete breather" excitations that stay localized in space for all time. By contrast, the localized Wannier states of linear lattice models are dynamically unstable. Nevertheless, symmetric and exponentially localized Wannier states are a central tool in the classification of band structures with crystalline symmetries. Moreover, the quantized transport observed in nonlinear Thouless pumps relies on the fact that -- at least in a specific model -- discrete breathers recover Wannier states in the limit of vanishing nonlinearity. Motivated by these observations, we investigate the correspondence between nonlinear breathers and linear Wannier states for a family of discrete nonlinear Schr\"odinger equations with crystalline symmetries. We develop a formalism to analytically predict the breathers' spectrum, center of mass and symmetry representations, and apply this to nonlinear generalizations of the Su-Schrieffer-Heeger chain and the breathing kagome lattice.Comment: 16+4 pages, 8+1 figure

Non-Thermal Emission from Relativistic Electrons in Clusters of Galaxies: A Merger Shock Acceleration Model

We have investigated evolution of non-thermal emission from relativistic electrons accelerated at around the shock fronts during merger of clusters of galaxies. We estimate synchrotron radio emission and inverse Compton scattering of cosmic microwave background photons from extreme ultraviolet (EUV) to hard X-ray range. The hard X-ray emission is most luminous in the later stage of merger. Both hard X-ray and radio emissions are luminous only while signatures of merging events are clearly seen in thermal intracluster medium (ICM). On the other hand, EUV radiation is still luminous after the system has relaxed. Propagation of shock waves and bulk-flow motion of ICM play crucial roles to extend radio halos. In the contracting phase, radio halos are located at the hot region of ICM, or between two substructures. In the expanding phase, on the other hand, radio halos are located between two ICM hot regions and shows rather diffuse distribution.Comment: 19 pages, 5 figures, accepted for publication in Ap

The Star-Forming Dwarf Galaxy Populations of two z ~ 0.4 Clusters: MS1512.4+3647 and Abell 851

We present the results of a deep narrow-band [OII] 3727 \AA emission-line search for faint ($g <$ 27), star-forming galaxies in the field of the $z=0.37$ MS1512.4+3647 cluster. We find no evidence for an over-density of emission-line sources relative to the field at $z \sim$ 0.4 (Hogg et al. 1998), and therefore conclude that the MS1512.4+3647 sample is dominated by field [OII] emission-line galaxies which lie along the $\sim$ 180 Mpc line of sight immediately in front and behind the cluster. This is surprising, given that the previously surveyed $z=0.41$ cluster Abell 851 has 3-4 times the field emission-line galaxy density (Martin et al. 2000). We find that the MS1512.4+3647 sample is deficient in galaxies with intermediate colors (1.0 $< g-i <$ 2.0) and implied star-formation exponential decay timescales $\tau \sim$ 100 Myr - 1 Gyr that dominate the Abell 851 emission-line galaxy population. Instead, the majority of [OII] emission-line galaxies surrounding the MS1512.4+3647 cluster are blue ($g-i \leq 1.0$) and forming stars in bursts with $\tau <$ 100 Myr. In both samples, galaxies with the shortest star-formation timescales are preferentially among the faintest star-forming objects. Their i luminosities are consistent with young stellar populations \sim 10^8 - 10^9 \Msun, although an additional factor of ten in stellar mass could be hiding in underlying old stellar populations. We discuss the implications for the star-formation histories of dwarf galaxies in the field and rich clusters.Comment: 26 pages, including 5 tables and 13 figures; accepted for publication in the Astrophysical Journa

A Two-Temperature Model of the Intracluster Medium

We investigate evolution of the intracluster medium (ICM), considering the relaxation process between the ions and electrons. According to the standard scenario of structure formation, ICM is heated by the shock in the accretion flow to the gravitational potential well of the dark halo. The shock primarily heats the ions because the kinetic energy of an ion entering the shock is larger than that of an electron by the ratio of masses. Then the electrons and ions exchange the energy through coulomb collisions and reach the equilibrium. From simple order estimation we find that the region where the electron temperature is considerably lower than the ion temperature spreads out on a Mpc scale. We then calculate the ion and electron temperature profiles by combining the adiabatic model of two-temperature plasma by Fox & Loeb (1997) with spherically symmetric N-body and hydrodynamic simulations based on three different cosmological models. It is found that the electron temperature is about a half of the mean temperature at radii $\sim$ 1 Mpc. This could lead to an about 50 % underestimation in the total mass contained within $\sim$ 1 Mpc when the electron temperature profiles are used. The polytropic indices of the electron temperature profiles are $\simeq 1.5$ whereas those of mean temperature $\simeq 1.3$ for $r \geq 1$ Mpc. This result is consistent both with the X-ray observations on electron temperature profiles and with some theoretical and numerical predictions about mean temperature profiles.Comment: 20 pages with 6 figures. Accepted for publication in Ap