Observational Test of Environmental Effects on The Local Group Dwarf Spheroidal Galaxies

In this paper, we examine whether tidal forces exerted by the Galaxy or M31 have an influence on the Local Group dwarf spheroidal galaxies (dSphs) which are their companions. We focus on the surface brightness profiles of the dSphs, especially their core radii because it is suggested based on the numerical simulations that tidal disturbance can make core radii extended. We examine the correlation for the dSphs between the distances from their parent galaxy (the Galaxy or M31) and the compactnesses of their surface brightness profiles by using a parameter ``C'' defined newly in this paper. Consequently, we find no significant correlation. We make some remarks on the origin of this result by considering three possible scenarios; tidal picture, dark matter picture, and heterogeneity of the group of dSphs, each of which has been often discussed to understand fundamental properties and formation processes of dSphs.Comment: 14 pages LaTeX, 2 PostScript figures, to appear in ApJ Letter

Analysis of linearized inverse problems in ultrasound transmission imaging

The purpose of this paper is to analyze the linearized inverse problem during the iterativesolution process of the ill-posed nonlinear inverse problem of image reconstruction for ultra-sound transmission imaging. We show that the conjugate gradient applied to normal equation(CGNE) method gives more reliable solutions for linearized systems than Tikhonov regular-ization methods. The linearized systems are more sensitive when treated by CGNE than byTikhonov regularization methods. The Tikhonov regularization is less effective at the be-ginning of the outer-loop iteration, where the nonlinearity is dominating while the conjugategradient for the linearized system stops earlier. Only when the linear approximation is goodenough to describe the whole system, Tikhonov regularization can fully play its role and giveslightly better reconstruction results as compared to CGNE in a very noisy case

The Wendelstein Calar Alto Pixellensing Project (WeCAPP): the M31 Nova catalogue

We present light curves from the novae detected in the long-term, M31 monitoring WeCAPP project. The goal of WeCAPP is to constrain the compact dark matter fraction of the M31 halo with microlensing observations. As a by product we have detected 91 novae benefiting from the high cadence and highly sensitive difference imaging technique required for pixellensing. We thus can now present the largest CCD and optical filters based nova light curve sample up-to-date towards M31. We also obtained thorough coverage of the light curve before and after the eruption thanks to the long-term monitoring. We apply the nova taxonomy proposed by Strope et al. (2010) to our nova candidates and found 29 S-class novae, 10 C-class novae, 2 O-class novae and 1 J-class nova. We have investigated the universal decline law advocated by Hachichu and Kato (2006) on the S-class novae. In addition, we correlated our catalogue with the literature and found 4 potential recurrent novae. Part of our catalogue has been used to search for optical counter-parts of the super soft X-ray sources detected in M31 (Pietsch et al. 2005). Optical surveys like WeCAPP, and coordinated with multi-wavelength observation, will continue to shed light on the underlying physical mechanism of novae in the future.Comment: 15 pages, 15 figures, 7 tables, A&A accepted for publication. The appendix is stored in the Data Conservanc

Central rotations of Milky Way Globular Clusters

Most Milky Way globular clusters (GCs) exhibit measurable flattening, even if on a very low level. Both cluster rotation and tidal fields are thought to cause this flattening. Nevertheless, rotation has only been confirmed in a handful of GCs, based mostly on individual radial velocities at large radii. We are conducting a survey of the central kinematics of Galactic GCs using the new Integral Field Unit instrument VIRUS-W. We detect rotation in all 11 GCs that we have observed so far, rendering it likely that a large majority of the Milky Way GCs rotate. We use published catalogs of the ACS survey of GCs to derive central ellipticities and position angles. We show that in all cases where the central ellipticity permits an accurate measurement of the position angle, those angles are in excellent agreement with the kinematic position angles that we derive from the VIRUS-W velocity fields. We find an unexpected tight correlation between central rotation and outer ellipticity, indicating that rotation drives flattening for the objects in our sample. We also find a tight correlation between central rotation and published values for the central velocity dispersion, most likely due to rotation impacting the old dispersion measurements.Comment: 6 pages, 3 figures; accepted for publication in ApJ Letter

The old and heavy bulge of M31 I. Kinematics and stellar populations

We present new optical long-slit data along 6 position angles of the bulge region of M31. We derive accurate stellar and gas kinematics reaching 5 arcmin from the center, where the disk light contribution is always less than 30%, and out to 8 arcmin along the major axis, where the disk makes 55% of the total light. We show that the velocity dispersions of McElroy (1983) are severely underestimated (by up to 50 km/s) and previous dynamical models have underestimated the stellar mass of M31's bulge by a factor 2. Moreover, the light-weighted velocity dispersion of the galaxy grows to 166 km/s, thus reducing the discrepancy between the predicted and measured mass of the black hole at the center of M31. The kinematic position angle varies with distance, pointing to triaxiality. We detect gas counterrotation near the bulge minor axis. We measure eight emission-corrected Lick indices. They are approximately constant on circles. We derive the age, metallicity and alpha-element overabundance profiles. Except for the region in the inner arcsecs of the galaxy, the bulge of M31 is uniformly old (>12 Gyr, with many best-fit ages at the model grid limit of 15 Gyr), slightly alpha-elements overabundant ([alpha/Fe]~0.2) and at solar metallicity, in agreement with studies of the resolved stellar components. The predicted u-g, g-r and r-i Sloan color profiles match reasonably well the dust-corrected observations. The stellar populations have approximately radially constant mass-to-light ratios (M/L_R ~ 4-4.5 for a Kroupa IMF), in agreement with stellar dynamical estimates based on our new velocity dispersions. In the inner arcsecs the luminosity-weighted age drops to 4-8 Gyr, while the metallicity increases to above 3 times the solar value.Comment: Accepted for publication in A&

USCT Image Reconstruction: Acceleration using Gauss-Newton Preconditioned Conjugate Gradient

Ultrasound transmission tomography offers quantitative characterization of the tissue or materials by their speed of sound and attenuation. Reconstruction of such images is an inverse problem which is solved iteratively based on a forward model of the Helmholtz equation by paraxial approximation and thus is time-consuming. Hence, developing optimizers that decrease this time, in particular reducing the number of forward propagations is of high relevance in order to bring this technology into clinical practice. In this paper, we solve the inverse problem of reconstruction in a two-level strategy, by an outer and an inner loop. At each iteration of the outer loop, the system is linearized and this linear subproblem is solved in the inner loop with a preconditioned conjugate gradient (CG). A standard Cholesky preconditioning method based on the system matrix is compared with a matrix-free Quasi-Newton update approach, where a preconditioned matrix-vector product is computed at the beginning of every CG iteration. We also use a multigrid scheme with multi-frequency reconstruction to get a convergent rough reconstruction at a lower frequency and then refine it on a higher-resolution grid. The Cholesky preconditioning reduces the number of CG iterations by approx. 70%~85%; but the computation time for determining the system matrix for the Cholesky preconditioner is dominating, offsetting the gains of the reduction of iterations. The matrix-free preconditioning method saves approx. 30% of the computation time on average for single-frequency and multi-frequency reconstruction. For the robust multifrequency reconstruction, we test three breast-like numerical phantoms resulting in a deviation of 0.13 m/s on average in speed of sound reconstruction and a deviation of 5.4% on average in attenuation reconstruction, from the ground truth simulation

More evidence for an intracluster planetary nebulae population in the Virgo cluster

We surveyed a 50 sq arcmin region in the Virgo cluster core to search for intergalactic planetary nebulae, and found 11 candidates in the surveyed area. The measured fluxes of these unresolved sources are consistent with these objects being planetary nebulae from an intracluster population of stars. We compute the cumulative luminosity function of these 11 planetary nebula candidates. If we assume that they belong to the Virgo cluster, their cumulative luminosity function is in good agreement with planetary nebula luminosity function simulations. This comparison allows us to estimate the surface mass density of the intracluster stellar population at the surveyed field in the cluster core.Comment: ApJ Letters, in press. A .ps file is also available at: http://www.usm.uni-muenchen.de:8001/people/mendez/preprints/preprints.htm

SBS 0335-052W - an Extremely Low Metallicity Dwarf Galaxy

We present Multiple Mirror Telescope (MMT) and Keck II telescope spectrophotometry and 3.5m Calar Alto telescope R, I photometry of the western component of the extremely low-metallicity blue compact galaxy SBS 0335-052. The components, separated by 22 kpc, appear to be members of a unique, physically connected system. It is shown that SBS 0335-052W consists of at least three stellar clusters and has the same redshift as SBS 0335-052. The oxygen abundance in its two brightest knots is extremely low, 12+log(O/H)= 7.22+/-0.03 and 7.13+/-0.08, respectively. These values are lower than in SBS 0335-052 and are nearly the same as those in I Zw 18. The (R-I) color profiles are very blue in both galaxies due to the combined effects of ionized gas and a young stellar population emission. We argue that SBS 0335-052W is likely to be a nearby, young dwarf galaxy.Comment: 18 pages, 4 EPS figures, to appear in ApJ, 1 July 199