Markus Kissler-Patig

SINFONI in the galactic center: young stars and infrared flares in the central light-month

We report 75 milli-arcsec resolution, near-IR imaging spectroscopy within the central 30 light days of the Galactic Center [...]. To a limiting magnitude of K~16, 9 of 10 stars in the central 0.4 arcsec, and 13 of 17 stars out to 0.7 arcsec from the central black hole have spectral properties of B0-B9, main sequence stars. [...] all brighter early type stars have normal rotation velocities, similar to solar neighborhood stars. We [...] derive improved 3d stellar orbits for six of these S-stars in the central 0.5 arcsec. Their orientations in space appear random. Their orbital planes are not co-aligned with those of the two disks of massive young stars 1-10 arcsec from SgrA*. We can thus exclude [...] that the S-stars as a group inhabit the inner regions of these disks. They also cannot have been located/formed in these disks [...]. [...] we conclude that the S-stars were most likely brought into the central light month by strong individual scattering events. The updated estimate of distance to the Galactic center from the S2 orbit fit is Ro = 7.62 +/- 0.32 kpc, resulting in a central mass value of 3.61 +/- 0.32 x 10^6 Msun. We happened to catch two smaller flaring events from SgrA* [...]. The 1.7-2.45 mum spectral energy distributions of these flares are fit by a featureless, red power law [...]. The observed spectral slope is in good agreement with synchrotron models in which the infrared emission comes from [...] radiative inefficient accretion flow in the central R~10 Rs region.

SINFONI: integral field spectroscopy at 50-milli-arcsecond resolution with the ESO VLT

SINFONI is an adaptive optics assisted near-infrared integral field spectrometer for the ESO VLT. The Adaptive OPtics Module (built by the ESO Adaptive Optics Group) is a 60-elements curvature-sensor based system, designed for operations with natural or sodium laser guide stars. The near-infrared integral field spectrometer SPIFFI (built by the Infrared Group of MPE) provides simultaneous spectroscopy of 32 x 32 spatial pixels, and a spectral resolving power of up to 3300. The adaptive optics module is in the phase of integration; the spectrometer is presented tested in the laboratory. We provide an overview of the project, with particular emphasis on the problems encountered in designing and building an adaptive optics assisted spectrometer.

Commissioning and performances of the VLT-VIMOS

The Visible Multi-Object Spectrograph VIMOS is a wide field survey instrument in the process of being commissioned for operations at the ESO-VLT. During the first commissioning period, the instrument has confirmed its excellent performances in its three basic modes of operation: direct imaging, multi-slit spectroscopy, and integral field spectroscopy. VIMOS provides the largest imaging field at the VLT with 224 arcmin2. It offers an unprecedented multiplex gain in multi-slit spectroscopy, with on order 800 slits which can be observed simultaneously. The integral field unit has a field up to 54x54 arcsec2, with 6400 spectra recorded at once. The overall efficiency of VIMOS combined to the Melipal unit #3 is confirmed to be as computed on the basis of the measured transmission of optical elements. Image quality is confirmed to be excellent, providing images limited by natural seeing in most conditions. High quality slit masks cut by the laser machine coupled to excellent geometric mask to CCD mapping lead to multi-slit spectra of excellent quality. VIMOS is expected to be offered to the ESO community for reguglar observations in early 2003.

The Nature of UCDs: Internal Dynamics from an Expanded Sample and Homogeneous Database

Context. The internal dynamics of ultra-compact dwarf galaxies (UCDs) has attracted increasing attention, with most of the UCDs studied to date located in the Virgo cluster.

The dynamical mass of the young cluster W3 in NGC 7252. Heavy-weight globular cluster or ultra compact dwarf galaxy?

We have determined the dynamical mass of the most luminous stellar cluster known to date, i.e. object W3 in the merger remnant galaxy NGC 7252. The dynamical mass is estimated from the velocity dispersion measured with the high-resolution spectrograph UVES on VLT. Our result is the astonishingly high velocity dispersion of sigma=45 +- 5 km/s. Combined with the large cluster size R_eff=17.5 +-1.8 pc, this translates into a dynamical virial mass for W3 of 8 +- 2 x 10^7 Msun. This mass is in excellent agreement with the value 7.2 x 10^7 Msun we previously estimated from the cluster luminosity M_V=-16.2 by means of stellar M/L ratios predicted by Simple Stellar Population models (with a Salpeter IMF) and confirms the heavy-weight nature of this object. This results points out that the NGC 7252-type of mergers are able to form stellar systems with masses up to ~ 10^8 Msun. We find that W3, when evolved to ~ 10 Gyr, lies far from the typical Milky Way globular clusters, but appears to be also separated from omegaCen in the Milky Way and G1 in M31, the most massive old stellar clusters of the Local Group, because it is too extended for a given mass, and from dwarf elliptical galaxies because it is much more compact for its mass. Instead the aged W3 is amazingly close to the compact objects named ultracompact dwarf galaxies (UCDGs) found in the Fornax cluster (Hilker et al. 1999; Drinkwater et al. 2000), and to a miniature version of the compact elliptical M32. These objects start populating a previously deserted region of the fundamental plane.

Keck Spectroscopy of Globular Clusters around NGC 1399

We report moderate-resolution, high signal-to-noise ratio spectroscopy of globular clusters around NGC 1399, the central cD galaxy in the Fornax Cluster. We address issues as diverse as elemental abundances of globular clusters versus stellar populations in elliptical galaxies, blue horizontal branches in metal-rich globular clusters, broadband colors as metallicity tracers, possible overestimation of the age-metallicity degeneracy in globular clusters, and dark matter in the halo of NGC 1399. We obtained spectra for 21 globular cluster candidates with multislit spectroscopy using the Low Resolution Imaging Spectrograph on the Keck I Telescope. Our sample turned out to include 18 globular clusters, one star, and two low-redshift late-type galaxies (z 0.3). The mean velocity of our globular cluster sample is 1293 ± 71 km s-1, and its velocity dispersion is 302 ± 51 km s-1. Both are slightly lower than, but in agreement with, previously derived values. We derive a mass of (1–5) × 1012 M☉ within 28 kpc for the galaxy, and an M/LB ratio of 36 ± 20 or 76 ± 40 M☉/L☉B, depending on the mass estimator. Both estimates indicate that dark matter dominates the potential at 6reff. The derived elemental abundances for the globular clusters span the entire range observed in the Milky Way and M31, with a mean metallicity of our sample around [Fe/H] -0.8 dex. This implies that the two major subpopulations reported from photometry could have formed by the same processes that formed halo and disk/bulge globular clusters in the Local Group spiral galaxies. Two globular clusters, which we associate with a group of very red globular clusters, representing about 5% of the total system, clearly stand out and exhibit metal abundances as high as those observed for stellar populations in giant elliptical galaxies. In addition, they display surprisingly high Hβ and Hγ indices that are not explained by any age/metallicity combination of existing models. The high Mg and Hβ values in these clusters could, however, be explained by the presence of blue horizontal branches. Finally, we find that V - I and metallicity are well correlated in the globular cluster system, but also that the slope of the relation is twice as flat at high metallicities as an extrapolation from the relation for Milky Way globular clusters. This implies that the mean metallicities of globular cluster systems in elliptical galaxies are lower, and cover a smaller range, than ones previously derived from broadband V - I colors.

The ACS Virgo Cluster Survey. XIV. Analysis of Color-Magnitude Relations in Globular Cluster Systems*

We examine the correlation between globular cluster (GC) color and magnitude using HST ACS imaging for a sample of 79 early-type galaxies (-21.7 < MB < -15.2 mag) with accurate SBF distances from the ACS Virgo Cluster Survey. Using the KMM mixture modeling algorithm, we find a highly significant correlation, ?z ? d(g - z)/dz = -0.037 ? 0.004, between color and magnitude for the subpopulation of blue GCs in the co-added GC color-magnitude diagram of the three brightest Virgo Cluster galaxies (M49, M87, and M60): brighter GCs are redder than their fainter counterparts. For the single GC systems of M87 and M60, we find similar correlations; M49 does not appear to show a significant trend. There is no correlation between (g - z) and Mz for GCs of the red subpopulation. The correlation ?g ? d(g - z)/dg for the blue subpopulation is much weaker than d(g - z)/dz. Using Monte Carlo simulations, we attribute this finding to the fact that the blue subpopulation in Mg extends to higher luminosities than does the red subpopulation, which biases the KMM fit results. The correlation between color and Mz thus is a real effect: this conclusion is supported by biweight fits to the same color distributions. We identify two environmental dependencies that influence the derived color-magnitude relation: (1) the slope decreases in significance with decreasing galaxy luminosity; and (2) the slope is stronger for GC populations located at smaller galactocentric distances. We examine several physical mechanisms that might give rise to the observed color-magnitude relation: (1) presence of contaminators; (2) accretion of GCs from low-mass galaxies; (3) stochastic effects; (4) the capture of field stars by individual GCs; and (5) GC self-enrichment. We conclude that self-enrichment and field-star capture, or a combination of these processes, offer the most promising means of explaining our observations.

MASSIV: Mass Assembly Survey with SINFONI in VVDS - II. Kinematics and close environment classification

Context. Processes driving mass assembly are expected to evolve on different timescales along cosmic time. A transition might happen around z similar to 1 as the cosmic star formation rate starts its decrease. Aims. We aim to identify the dynamical nature of galaxies in a representative sample to be able to infer and compare the mass assembly mechanisms across cosmic time. Methods. We present an analysis of the kinematics properties of 50 galaxies with redshifts 0.9 \textless z \textless 1.6 from the MASSIV sample observed with SINFONI/VLT with a mass range from 4.5 x 10(9) M-circle dot to 1.7 x 10(11) M-circle dot and a star formation rate from 6 M-circle dot yr(-1) to 300 M-circle dot yr(-1). This is the largest sample with 2D kinematics in this redshift range. We provide a classification based on kinematics as well as on close galaxy environment. Results. We find that a significant fraction of galaxies in our sample (29%) experience merging or have close companions that may be gravitationally linked. This places a lower limit on the fraction of interacting galaxies because ongoing mergers are probably also present but harder to identify. We find that at least 44% of the galaxies in our sample display ordered rotation, whereas at least 35% are non-rotating objects. All rotators except one are compatible with rotation-dominated (V-max/sigma \textgreater 1) systems. Non-rotating objects are mainly small objects (R-e \textless 4 kpc). They show an anti-correlation of their velocity dispersion and their effective radius. These low-mass objects (log M-star \textless 10.5) may be ongoing mergers in a transient state, galaxies with only one unresolved star-forming region, galaxies with an unstable gaseous phase or, less probably, spheroids. Combining our sample with other 3D-spectroscopy samples, we find that the local velocity dispersion of the ionized gas component decreases continuously from z similar to 3 to z = 0. The proportion of disks also seems to be increasing in star-forming galaxies when the redshift decreases. The number of interacting galaxies seems to be at a maximum at z similar to 1.2. Conclusions. These results draw a picture in which cold gas accretion may still be efficient at z similar to 1.2 but in which mergers may play a much more significant role at z similar to 1.2 than at higher redshift. From a dynamical point of view, the redshift range 1 \textless z \textless 2 therefore appears as a transition period in the galaxy mass assembly process(star star star star).

Extragalactic globular clusters in the near-infrared - II. The globular clusters systems of NGC 3115 and NGC 4365

We combine near-infrared photometry obtained with the VLT/ISAAC instrument and archival HST/WFPC2 optical images to determine VIK magnitudes and colours of globular clusters in two early-type galaxies, NGC 3115 and NGC 4365. The combination of near-IR and optical photometry provides a way to lift the age-metallicity degeneracy. For NGC 3115, the globular cluster colours reveal two major sub-populations, consistent with previous studies. By comparing the V I, V K colours of the NGC 3115 globular clusters with stellar populations models, we find that the colour dierence between the two >10 Gyr old major sub-populations is primarily due to a dierence in metallicity. We find(Fe/H) = 1:0 0: 3d ex and the blue (metal-poor) and red (metal-rich) globular cluster sub-populations being coeval within 3 Gyr. In contrast to the NGC 3115 globular clusters, the globular cluster system in NGC 4365 exhibits a more complex age and metallicity structure. We find a significant population of intermediate-age very metal-rich globular clusters along with an old population of both metal-rich and metal-poor clusters. Specifically, we observe a large population of globular clusters with red V K colours but intermediate V I colours, for which all current stellar population models give ages and metallicities in the range2 8G yr and0:5 Z 3 Z, respectively. After 10 Gyr of passive evolution, the intermediate-age globular clusters in NGC 4365 will have colours which are consistent with the very metal-rich population of globular clusters in giant elliptical galaxies, such as M 87. Our results for both globular cluster systems are consistent with previous age and metallicity studies of the diuse galactic light. In addition to the major globular cluster populations in NGC 3115 and NGC 4365 we report on the detection of objects with extremely red colours (V K> 3:8 mag), whose nature could not ultimately be revealed with the present data.

MASSIV: Mass Assembly Survey with SINFONI in VVDS - III. Evidence for positive metallicity gradients in z ~ 1.2 star-forming galaxies

Aims. The estimate of radial abundance gradients in high-redshift galaxies allows to constrain their star formation history and their interplay with the surrounding intergalactic medium. Methods. We present VLT/SINFONI integral-field spectroscopy of a first sample of 50 galaxies at z similar to 1.2 in the MASSIV survey. Using the N2 ratio between the [N II]6584 and H alpha rest-frame optical emission lines as a proxy for oxygen abundance in the interstellar medium, we measured the metallicity of the sample galaxies. We developed a tool to extract spectra in annular regions, leading to a spatially resolved estimate of the oxygen abundance in each galaxy. We were able to derive a metallicity gradient for 26 galaxies in our sample and discovered a significant fraction of galaxies with a “positive” gradient. Using a simple chemical evolution model, we derived infall rates of pristine gas onto the disks. Results. Seven galaxies display a positive gradient at a high confidence level. Four out of these are interacting, and one is a chain galaxy. We suggest that interactions might be responsible for shallowing and even inverting the abundance gradient. We also identify two interesting correlations in our sample: a) galaxies with higher gas velocity dispersion have shallower/positive gradients; and b) metal-poor galaxies tend to show a positive gradient, whereas metal-rich ones tend to show a negative one. This last observation can be explained by the infall of metal-poor gas into the center of the disks. We address the question of the origin of this infall under the influence of gas flows triggered by interactions and/or cold gas accretion. All the data published in this paper are publicly available at the time of publication following this link: http://cosmosdb.lambrate.inaf.it/VVDS-SINFONI.