Showing papers by "Ralf Bender published in 2007"

The Sloan Digital Sky Survey-II Supernova Survey: Technical Summary

Abstract: The Sloan Digital Sky Survey-II (SDSS-II) has embarked on a multi-year project to identify and measure light curves for intermediate-redshift (0.05 < z < 0.35) Type Ia supernovae (SNe Ia) using repeated five-band (ugriz) imaging over an area of 300 sq. deg. The survey region is a stripe 2.5 degrees wide centered on the celestial equator in the Southern Galactic Cap that has been imaged numerous times in earlier years, enabling construction of a deep reference image for discovery of new objects. Supernova imaging observations are being acquired between 1 September and 30 November of 2005-7. During the first two seasons, each region was imaged on average every five nights. Spectroscopic follow-up observations to determine supernova type and redshift are carried out on a large number of telescopes. In its first two three-month seasons, the survey has discovered and measured light curves for 327 spectroscopically confirmed SNe Ia, 30 probable SNe Ia, 14 confirmed SNe Ib/c, 32 confirmed SNe II, plus a large number of photometrically identified SNe Ia, 94 of which have host-galaxy spectra taken so far. This paper provides an overview of the project and briefly describes the observations completed during the first two seasons of operation.

The centers of early-type galaxies with hubble space telescope. VI. Bimodal central surface brightness profiles

Abstract: We combine several HST investigations on the central structure of early-type galaxies to generate a large sample of surface photometry. The studies selected were those that used the Nuker law to characterize the inner light distributions of the galaxies. The sample comprises WFPC1 and WFPC2 V-band observations published earlier by our group, R-band WFPC2 photometry of Rest et al., NICMOS H-band photometry by Ravindranath et al. and Quillen et al., and the brightest cluster galaxy WFPC2 I-band photometry of Laine et al. The distribution of the logarithmic slopes of the central brightness profiles strongly affirms that the central structure of elliptical galaxies with MV < -19 is bimodal, based on both parametric and nonparametric analysis. At the HST resolution limit, most galaxies are either power-law systems, which have steep cusps in surface brightness, or core systems, which have shallow cusps interior to a steeper envelope brightness distribution. A rapid transition between the two forms occurs over the luminosity range -22 < MV < -20, with cores dominating at the highest luminosities and power laws at the lowest. There are a few intermediate systems that have both cusp slopes and total luminosities that fall within the core/power-law transition, but they are rare and do not fill in the overall bimodal distribution.

Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies

Abstract: Dynamical models for 17 early-type galaxies in the Coma cluster are presented. The galaxy sample consists of flattened, rotating as well as non-rotating early-types including cD and S0 galaxies with luminosities between MB = 18.79 and MB = 22.56. Kinematical long-slit observations cover at least the major and minor axis and extend to 1 4 reff. Axisymmetric Schwarzschild models are used to derive stellar mass-tolight ratios and dark halo parameters. In every galaxy the best fit with dark matter matches the data better than the best fit without. The statistical significance is over 95 percent for 8 galaxies, around 90 percent for 5 galaxies and for four galaxies it is not significant. For the highly significant cases systematic deviations between observed and modelled kinematics are clearly seen; for the remaining galaxies differences are more statistical in nature. Best-fit models contain 10-50 percent dark matter inside the half-light radius. The central dark matter density is at least one order of magnitude lower than the luminous mass density, independent of the assumed dark matter density profile. The central phase-space density of dark matter is often orders of magnitude lower than in the luminous component, especially when the halo core radius is large. The orbital system of the stars along the major-axis is slightly dominated by radial motions. Some galaxies show tangential anisotropy along the minor-axis, which is correlated with the minor-axis Gauss-Hermite coefficientH4. Changing the balance between data-fit and regularisation constraints does not change the reconstructed mass structure significantly: model anisotropies tend to strengthen if the weight on regularisation is reduced, but the general property of a galaxy to be radially or tangentially anisotropic, respectively, does not change. This paper is aimed to set the basis for a subsequent detailed analysis of luminous and dark matter scaling relations, orbital dynamics and stellar populations.

The Kormendy relation of massive elliptical galaxies at z ~ 1.5: evidence for size evolution

Abstract: We present the morphological analysis based on HST-NIC2 (0.075 arcsec pixel -1 ) images in the F160W filter of a sample of nine massive field (>10 11 M ⊙ ) galaxies spectroscopically classified as early-types at 1.2 < z < 1.7. Our analysis shows that all of them are bulge-dominated systems. In particular, six of them are well fitted by a de Vaucouleurs profile (n = 4) suggesting that they can be considered pure elliptical galaxies. The remaining three galaxies are better fitted by a Sersic profile with index 1.9 < n fit < 2.3 suggesting that a disc-like component could contribute up to 30 per cent to the total light of these galaxies. We derived the effective radius R e and the mean surface brightness (SB) (μ) e within R e of our galaxies and we compared them with those of early-types at lower redshifts. We find that the SB (μ) e of our galaxies should get fainter by 2.5 mag from z ∼ 1.5 to ∼0 to match the SB of the local ellipticals with comparable R e , that is, the local Kormendy relation. Luminosity evolution without morphological changes can only explain half of this effect, as the maximum dimming expected for an elliptical galaxy is ∼ 1.6 mag in this redshift range. Thus, other parameters, possibly structural, may undergo evolution and play an important role in reconciling models and observations. Hypothesizing an evolution of the effective radius of galaxies we find that R e should increase by a factor of 1.5 from z ∼ 1.5 to ∼0.

X-ray monitoring of optical novae in M 31 from July 2004 to February 2005

Abstract: Context. Optical novae have recently been identified as the major class of supersoft X-ray sources in M 31 based on ROSAT and early XMM-Newton and Chandra observations. Aims. This paper reports on a search for X-ray counterparts of optical novae in M 31 based on archival Chandra HRC-I and ACIS-I as well as XMM-Newton observations of the galaxy center region obtained from July 2004 to February 2005. Methods. We systematically determine X-ray brightness or upper limit for counterparts of all known optical novae with outbursts between November 2003 to the end of the X-ray coverage. In addition, we determine the X-ray brightnesses for counterparts of four novae with earlier outbursts. Results. For comparison with the X-ray data we created a catalogue of optical novae in M 31 based on our own nova search programs and on all novae reported in the literature. We collected all known properties and named the novae consistently following the CBAT scheme. We detect eleven out of 34 novae within a year after the optical outburst in X-rays. While for eleven novae we detect the end of the supersoft source phase, seven novae are still bright more than 1200, 1600, 1950, 2650, 3100, 3370 and 3380 d after outburst. One nova is detected to turn on 50 d, another 200 d after outburst. Three novae unexpectedly showed short X-ray outbursts starting within 50 d after the optical outburst and lasting only two to three months. The X-ray emission of several of the novae can be characterized as supersoft from hardness ratios and/or X-ray spectra or by comparing HRC-I count rates with ACIS-I count rates or upper limits. Conclusions. The number of detected optical novae at supersoft X-rays is much higher than previously estimated (>30%). We use the X-ray light curves to estimate the burned masses of the White Dwarf and of the ejecta.

The black hole mass and extreme orbital structure in ngc 1399

Abstract: The largest galaxies, and in particular central galaxies in clusters, offer unique insight into understanding the mechanism for the growth of nuclear black holes. We present Hubble Space Telescopekinematics for NGC 1399, the central galaxy in Fornax. We find the best-fit model contai ns a black hole of (5: 1� 0: 7)� 10 8 M� (at a distance of 21.1 Mpc), a factor of over 2 below the correlation of black hole mass and velocity dispersion. We also find a dramatic signature for central tangential anisotropy. Th e velocity profiles on adjacent sides 0.5 00 away from the nucleus show strong bimodality, and the central spectrum shows a large drop in the dispersion. Both of these observations point to an orbital distribution that is tange ntially biased. The best-fit orbital model suggests a ratio of the tangential to radial internal velocity dispersions o f three. This ratio is the largest seen in any galaxy to date and will provide an important measure for the mode by which the central black hole has grown. Subject headings: galaxies: nuclei — galaxies: statistics — galaxies: genera l

The supermassive black hole in NGC 4486a detected with SINFONI at the Very Large Telescope

Abstract: The near-infrared (IR) integral field spectrograph SINFONI at the European Southern Observatory Very Large Telescope opens a new window for the study of central supermassive black holes. With a near-IR spatial resolution similar to Hubble Space Telescope optical and the ability to penetrate dust, it provides the possibility to explore the low-mass end of the M•‐σ relation ( σ< 120 km s −1 ) where so far very few black hole masses were measured with stellar dynamics. With SINFONI, we observed the central region of the low-luminosity elliptical galaxy NGC 4486a at a spatial resolution of ≈0.1 arcsec in the K band. The stellar kinematics were measured with a maximum penalized likelihood method considering the region around the CO absorption band heads. We determined a black hole mass of M• = (1.25 +0.75 −0.79) × 10 7 M� (90 per cent confidence limit) using the Schwarzschild orbit superposition method including the full two-dimensional spatial information. This mass agrees with the predictions of the M•‐σ relation, strengthening its validity at the lower σ end.

The Black Hole Mass and Extreme Orbital Structure in NGC1399

Abstract: The largest galaxies, and in particular central galaxies in clusters, offer unique insight into understanding the mechanism for the growth of nuclear black holes. We present Hubble Space Telescope kinematics for NGC1399, the central galaxy in Fornax. We find the best-fit model contains a black hole of 5.1 +-0.7 x 10^8 Msun (at a distance of 21.1 Mpc), a factor of over 2 below the correlation of black hole mass and velocity dispersion. We also find a dramatic signature for central tangential anisotropy. The velocity profiles on adjacent sides 0.5" away from the nucleus show strong bimodality, and the central spectrum shows a large drop in the dispersion. Both of these observations point to an orbital distribution that is tangentially biased. The best-fit orbital model suggests a ratio of the tangential to radial internal velocity dispersions of three. This ratio is the largest seen in any galaxy to date and will provide an important measure for the mode by which the central black hole has grown.

Intense Star Formation and Feedback at High Redshift: Spatially Resolved Properties of the z?=?2.6 Submillimeter Galaxy SMM J14011+0252

Abstract: We present a detailed analysis of the spatially resolved properties of the lensed submillimeter galaxy (SMG) SMM J14011+0252 at z = 2.56, combining deep near-infrared integral-field data obtained with SPIFFI on the VLT with other multiwavelength data sets. As previously discussed by other authors, the broad characteristics of SMM J14011+0252 in particular and submillimeter galaxies in general are in agreement with what is expected for the early evolution of local massive spheroidal galaxies. From continuum and line flux, velocity, and dispersion maps, we measure the kinematics, star formation rates, gas densities, and extinction for individual subcomponents. The star formation intensity is similar to low-redshift "maximal starbursts," while the line fluxes and the dynamics of the emission line gas provide direct evidence for a starburst-driven wind with physical properties very similar to local superwinds. We also find circumstantial evidence for "self-regulated" star formation within J1. The relative velocity of the bluer companion J2 yields a dynamical mass estimate for J1 within ~20 kpc of Mdyn ~ 1 × 1011 M☉. The relative metallicity of J2 is 0.4 dex lower than in J1n/J1s, suggesting different star formation histories. Spectral energy distribution fitting of the continuum peak J1c confirms and substantiates previous suggestions that this component is a z = 0.25 interloper. When removing J1c, the stellar continuum and Hα line emission appear well aligned spatially in two individual components, J1n and J1s, and coincide with two kinematically distinct regions in the velocity map, which might well indicate a merging system. This highlights the close similarity between SMGs and ultraluminous infrared galaxies (ULIRGs), which are often merger-driven maximal starbursts, and suggests that the intrinsic mechanisms of star formation and related feedback are in fact similar to low-redshift strongly star-forming systems.

Axisymmetric orbit models of N-body merger remnants: a dependency of reconstructed mass on viewing angle

Abstract: We model mock observations of collisionless N-body disc-disc mergers with the same axisymmetric orbit superposition program that has been used to model elliptical galaxies in Coma. The remnants sample representatively the shape distribution of disc-disc mergers, including the most extreme cases, like highly prolate, maximally triaxial and dominantly oblate objects. The aim of our study is to better understand how the assumption of axial symmetry affects reconstructed masses and stellar motions of systems which are intrinsically not axisymmetric, whether the axisymmetry assumption then leads to a bias and how such a potential bias can be recognized in models of real galaxies. The mass recovery at the half-light radius depends on viewing angle and intrinsic shape: edge-on views allow to reconstruct total masses with an accuracy between 20 per cent (triaxial/prolate remnants) and 3 per cent (oblate remnant). Masses of highly flattened, face-on systems are underestimated by up to 50 per cent. Deviations in local mass densities can be larger where remnants are strongly triaxial or prolate. Luminous mass-to-light ratios are sensitive to box orbits in the remnants. Box orbits cause the central value of the Gauss-Hermite parameter H 4 to vary with viewing angle. Reconstructed luminous mass-to-light ratios, as well as reconstructed central masses, follow this variation. Luminous mass-to-light ratios are always underestimated (up to a factor of 2.5). Respective dark haloes in the models can be overestimated by about the same amount, depending again on viewing angle. Reconstructed velocity anisotropies ft depend on viewing angle as well as on the orbital composition of the remnant and are mostly accurate to about A/? = 0.2. Larger deviations can occur towards the centre or the outer regions, respectively. We construct N-body realizations of the Schwarzschild models to discuss chaotic orbits and the virial equilibrium in our models. In this study we explore the extreme limits of axisymmetric models. Apparently flattened, rotating ellipticals of intermediate mass are likely close to both, axial symmetry and edge-on orientation. Our results imply that Schwarzschild models allow a reconstruction of their masses and stellar anisotropies with high accuracy.

Astro-WISE: Chaining to the Universe

Abstract: The recent explosion of recorded digital data and its processed derivatives threatens to overwhelm researchers when analysing their experimental data or when looking up data items in archives and file systems. While current hardware developments allow to acquire, process and store 100s of terabytes of data at the cost of a modern sports car, the software systems to handle these data are lagging behind. This general problem is recognized and addressed by various scientific communities, e.g., DATAGRID/EGEE federates compute and storage power over the high-energy physical community, while the astronomical community is building an Internet geared Virtual Observatory, connecting archival data. These large projects either focus on a specific distribution aspect or aim to connect many sub-communities and have a relatively long trajectory for setting standards and a common layer. Here, we report "first light" of a very different solution to the problem initiated by a smaller astronomical IT community. It provides the abstract "scientific information layer" which integrates distributed scientific analysis with distributed processing and federated archiving and publishing. By designing new abstractions and mixing in old ones, a Science Information System with fully scalable cornerstones has been achieved, transforming data systems into knowledge systems. This break-through is facilitated by the full end-to-end linking of all dependent data items, which allows full backward chaining from the observer/researcher to the experiment. Key is the notion that information is intrinsic in nature and thus is the data acquired by a scientific experiment. The new abstraction is that software systems guide the user to that intrinsic information by forcing full backward and forward chaining in the data modelling.

The Munich Near-Infrared Cluster Survey (MUNICS) - IX. Galaxy Evolution to z ~ 2 From Optically Selected Catalogues

Abstract: (Abridged) We present B, R, and I-band selected galaxy catalogues based on the Munich Near-Infrared Cluster Survey (MUNICS) which, together with the K-selected sample, serve as an important probe of galaxy evolution in the redshift range 0 < z < 2. Furthermore, used in comparison they are ideally suited to study selection effects. The construction of the B, R, and I-selected photometric catalogues, containing ~9000, ~9000, and ~6000 galaxies, respectively, is described in detail. The catalogues reach 50% completeness limits for point sources of B ~ 24.5mag, R ~ 23.5mag, and I ~ 22.5mag and cover an area of about 0.3 square degrees. Photometric redshifts are derived for all galaxies with an accuracy of dz/(1+z) ~ 0.057. We investigate the influence of selection band and environment on the specific star formation rate (SSFR). We find that K-band selection indeed comes close to selection in stellar mass, while B-band selection purely selects galaxies in star formation rate. We use a galaxy group catalogue constructed on the K-band selected MUNICS sample to study possible differences of the SSFR between the field and the group environment, finding a marginally lower average SSFR in groups as compared to the field, especially at lower redshifts. The field-galaxy luminosity function in the B and R band as derived from the R-selected sample evolves out to z ~ 2 in the sense that the characteristic luminosity increases but the number density decreases. This effect is smaller at longer rest-frame wavelengths and gets more pronounced at shorter wavelengths. Parametrising the redshift evolution of the Schechter parameters as M*(z) = M*(0) + a ln(1+z) and Phi*(z) = Phi*(0) (1+z)^b we find evolutionary parameters a ~ -2.1 and b ~ -2.5 for the B band, and a ~ -1.4 and b ~ -1.8 for the R band.

The Munich Near-Infrared Cluster Survey – IX. Galaxy evolution to z ~ 2 from optically selected catalogues

Abstract: We present B-, R- and I-band-selected galaxy catalogues based on the Munich Near-Infrared Cluster Survey (MUNICS) which, together with the previously used K-selected sample, serve as an important probe of galaxy evolution in the redshift range 0 ≤ z ≤ 2. Furthermore, used in comparison they are ideally suited to study selection effects in extragalactic astronomy. The construction of the B-, R- and I-selected photometric catalogues, containing ∼9000, ∼9000 and ∼6000 galaxies, respectively, is described in detail. The catalogues reach 50 per cent completeness limits for point sources of B ≃ 24.5 mag, R ≃ 23.5 mag and I ≃ 22.5 mag and cover an area of about 0.3 deg 2 . Photometric redshifts are derived for all galaxies with an accuracy of δz/(1 + z) ≃ 0.057, very similar to the K-selected sample. Galaxy number counts in the B, V, R, I, J and K bands demonstrate the quality of the data set. The rest-frame colour distributions of galaxies at different selection bands and redshifts suggest that the most-massive galaxies have formed the bulk of their stellar population at earlier times and are essentially in place at redshift unity. We investigate the influence of selection band and environment on the specific star formation rate (SSFR). We find that K-band selection indeed comes close to selection in stellar mass, while B-band selection purely selects galaxies in SFR. We use a galaxy group catalogue constructed on the K-band-selected MUNICS sample to study possible differences of the SSFR between the field and the group environment, finding a marginally lower average SSFR in groups as compared to the field, especially at lower redshifts. The field-galaxy luminosity function in the B and R band as derived from the R-selected sample evolves out to z ≃ 2 in the sense that the characteristic luminosity increases but the number density decreases. This effect is smaller at longer rest-frame wavelengths and gets more pronounced at shorter wavelengths. Parametrizing the redshift evolution of the Schechter parameters as M*(z) = M* (0) + a In (1 + z) and Φ*(z) = Φ* (0) (1 + z) b , we find evolutionary parameters a ≃ -2.1 and b ≃ -2.5 for the B band, and a ≃ - 1.4 and b ≃ -1.8 for the R band.

Black holes in low-mass bulges and pseudobulges

Abstract: We are investigating whether the well-known relations between the mass of a central supermassive black hole and the mass or velocity dispersion of its surrounding bulge (the M•-σ relation) remain valid—or how they change—when galaxies with pseudobulges or low-mass bulges are considered. Possible differences in these relations can tell us about the relative importance of different growing mechanisms. We present the data collected with the adaptive optics assisted near-infrared integral field spectrograph SINFONI at the VLT and show some first results.

VIRUS-W: a fiber based integral field unit spectrograph for the study of galaxy bulges

Abstract: We presented the design for a fiber based integral field unit spectrograph for the new two meter class Wendelstein telescope in Bavaria, Germany. The proposed spectrograph will feature a fiberhead consisting of 246 individual optical fibers and a field of view of approximately 1′ × 2′ and two different spectral resolution modes optimized for the study of bulges of local latetype galaxies.

Axisymmetric orbit models of N-body merger remnants: a dependency of reconstructed mass on viewing angle

Abstract: We model mock observations of collisionless N-body disc-disc mergers with an axisymmetric orbit superposition program that has been used to model Coma ellipticals. The remnants sample representatively the shapes of disc-disc mergers including prolate, triaxial and oblate objects. The aim is to better understand how the assumption of axial symmetry affects reconstructed masses and stellar motions of systems which are intrinsically not axisymmetric, whether it leads to a bias and how such a potential bias can be recognised in models of real galaxies. The mass recovery at the half-light radius depends on viewing-angle and intrinsic shape: edge-on views allow to reconstruct total masses with an accuracy between 20% (triaxial/prolate remnants) and 3% (oblate remnant). Masses of highly flattened, face-on systems are underestimated by up to 50%. Deviations in local mass densities can be larger where remnants are strongly triaxial or prolate. Luminous M/L are sensitive to box orbits in the remnants. Box orbits cause the central kinematics to vary with viewing-angle. Reconstructed luminous M/L and central masses follow this variation. Luminous M/L are always underestimated (up to a factor of 2.5). Respective dark halos in the models can be overestimated by about the same amount, depending again on viewing angle. Reconstructed velocity anisotropies depend on viewing angle and on the orbital composition of the remnant. We construct N-body realisations of the Schwarzschild models to discuss chaotic orbits and the virial equilibrium in our models. Apparently flattened, rotating ellipticals of intermediate mass are likely close to both, axial symmetry and edge-on orientation. Our results imply that Schwarzschild models allow a reconstruction of their masses and stellar anisotropies with high accuracy. (abridged)

Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies

Abstract: Dynamical models for 17 Coma early-type galaxies are presented. The galaxy sample consists of flattened, rotating as well as non-rotating early-types including cD and S0 galaxies with luminosities between M=-18.79 and M=-22.56. Kinematical long-slit observations cover at least the major and minor axis and extend to 1-4 effective radii. Axisymmetric Schwarzschild models are used to derive stellar mass-to-light ratios and dark halo parameters. In every galaxy models with a dark matter halo match the data better than models without. The statistical significance is over 95 percent for 8 galaxies, around 90 percent for 5 galaxies and for four galaxies it is not significant. For the highly significant cases systematic deviations between observed and modelled kinematics are clearly seen; for the remaining galaxies differences are more statistical in nature. Best-fit models contain 10-50 percent dark matter inside the half-light radius. The central dark matter density is at least one order of magnitude lower than the luminous mass density. The central phase-space density of dark matter is often orders of magnitude lower than in the luminous component, especially when the halo core radius is large. The orbital system of the stars along the major-axis is slightly dominated by radial motions. Some galaxies show tangential anisotropy along the minor-axis, which is correlated with the minor-axis Gauss-Hermite coefficient H4. Changing the balance between data-fit and regularisation constraints does not change the reconstructed mass structure significantly. Model anisotropies tend to strengthen if the weight on regularisation is reduced, but the general property of a galaxy to be radially or tangentially anisotropic, respectively, does not change. (abridged)