Kinematics across bulge types a longslit kinematic survey and dedicated instrumentation

Der erste Teil dieser Arbeit stellt die Konstruktion, Inbetriebnahme und ersteDaten eines neuen optischen, faserbasierten Feldspektrographen namens VIRUS-Wvor. Die Entwicklung wurde durch den Bau des neuen 2 m Fraunhofer Teleskops aufdem Berg Wendelstein in den Bayrischen Alpen motiviert. Die besondereEigenschaft dieses Instruments liegt zum einen in der Fähigkeit, Spektren ineinem zweidimensionalen Sichtfeld aufzuzeichnen, und zum anderen in derKombina- tion eines grossen Sichtfeldes von 105 ′′ × 55 ′′ mit einer relativgrossen instrumentellen Auflösung von R = 8700. Diese Auflösung erlaubt es,Geschwindigkeitsdispersionen von Sternen und Gas bis hinunter zu 15 kms−1aufzulösen. Es wird im Allgemeinen erwartet, dass dies dem Regime entspricht,in dem sich Sterne in Scheiben bilden. Der abgedeckte Spektralbereich diesesDynamikmodus beträgt 4850 A bis 5480 A. Zusätzlich bietet VIRUS-W einen zweiten Modus, welcher der Studie der Zusammensetzung von stellarenPopulationen, also z.B. deren Alter und Metal- lizität, gewidmet ist. Diespektrale Auflösung ist hier geringer (R = 3300), aber der abgedeckteSpektralbereich ist weiter und beträgt 4340 A bis 6040 A. Dies deckt einegrössere Zahl von Absorptionsbanden im stellaren Spektrum ab. Insbesondere isthier Hβ enthalten, welches eine wichtige Grundlage zur Bestimmung des Alterseiner Stellaren Population liefert. Bis zur Fertigstellung des WendelsteinTeleskops wird sich der Spektrograph an dem 2.7m Harlan J. Smith Teleskop des McDonald Observatoriums in Texas befinden. Dort nahm er im November 2010 erfolgreich seinen Betrieb auf. Die bei der Inbetriebnahme gewonnenen Daten erlauben uns, die genaue spektrale Auflösung und die Effizienz zu bestimmen. Durch den Vergle- ich der aufgezeichneten Daten eines spektrophotometrischen Standardsterns mit veröffentlichten Werten errechnen wir fu ̈r das gesamte Atmosphären-Teleskop-Spektrographen-System eine Ef- fizient von 37% im hochauflösenden Dynamikmodus und von 40% im niedriger auflösenden Modus. Wir schliessen diesen Teil mit der Diskussion der Beobachtungen der drei Galaxien NGC2903, NGC205 und NGC3091 aus den November- und Dezember- Kampagnen ab und präsentieren erste Geschwindigkeitsfelder und Messungen von Absorptionen. Der Vergleich mit Literaturdaten für NGC205 zeigt, dass wir in der Lage sind, diese sehr niedrigen Dispersionen von ≃ 20km/s zuverlässig wiederzugeben. Der zweite Teil dieser Arbeit befasst sich mit einer Beobachtungsreihe von Bulgeregionen be- nachbarter Spiralgalaxien, die wir am Hobby-Eberly-Teleskop des McDonald Observatoriums mit dem LRS Langspaltspektrographen durchgefu ̈rht haben. Wir präsentieren kinematische Profile entlang der Hauptachse von 46 Galaxien der Hubbletypen S0 bis Sc. Für 28 dieser Objekte stellen wir ausserdem Profile entlang der kleineren Halbachse vor. Ein systematischer Vergleich der gewonnenen Daten mit photometrischen Dekompositionen erlaubt es uns zu zeigen, dass die Unterscheide, die verschiedene Bulgetypen in ihrem so genan- nten Sersic-Index zeigen, auch in der Kinematik widergespiegelt werden. Pseudobulges zeigen oft eine scheibenartige Morphologie und haben niedrigere Sersic-Indizes — also ein Leuchtkraft- profil, das eher demjenigen einer Scheibe entspricht. Klassische Bulges haben im Allgemeinen grössere Sersic-Indizes (n > 2). Wir zeigen, dass Pseudobulges auch schwächere Gradienten der Geschwindigkeitsdispersion als Funktion des Radius aufweisen — ihre Dispersionsprofile sind also vorwiegend flach. Höhere Sersic-Indizes hingegen treten in Galaxien mit steiler abfallenden Dispersionprofilen auf. Ausserdem beobachten wir, dass Pseudobulges vorwiegend in Galaxien mit nierigeren zentralen Geschwindigkeitsdispersionen auftreten und einen grösseren Grad von Rotation im Verhältnis zu ihrer mittleren Geschwindigkeitsdispersion zeigen

Evidence for non-axisymmetry in M31 from wide-field kinematics of stars and gas

As the nearest large spiral galaxy, M31 provides a unique opportunity to learn about the structure and evolutionary history of this galaxy type in great detail. Among the many observing programs aimed at M31 are microlensing studies, which require good three-dimensional models of the stellar mass distribution. Possible non-axisymmetric structures like a bar need to be taken into account. Due to M31's high inclination, the bar is difficult to detect in photometry alone. Therefore, detailed kinematic measurements are needed to constrain the possible existence and position of a bar in M31. We obtained $\approx$ 220 separate fields with the optical IFU spectrograph VIRUS-W, covering the whole bulge region of M31 and parts of the disk. We derive stellar line-of-sight velocity distributions from the stellar absorption lines, as well as velocity distributions and line fluxes of the emission lines H$\beta$, [OIII] and [NI]. Our data supersede any previous study in terms of spacial coverage and spectral resolution. We find several features that are indicative of a bar in the kinematics of the stars, we see intermediate plateaus in the velocity and the velocity dispersion, and correlation between the higher moment $h3$ and the velocity. The gas kinematics is highly irregular, but is consistent with non-triaxial streaming motions caused by a bar. The morphology of the gas shows a spiral pattern, with seemingly lower inclination than the stellar disk. We also look at the ionization mechanisms of the gas, which happens mostly through shocks and not through starbursts.Comment: 23 pages, 39 figures; accepted for publication in A&

Re-growth of stellar disks in mature galaxies: The two component nature of NGC 7217 revisited with VIRUS-W

Previous studies have reported the existence of two counter-rotating stellar disks in the early-type spiral galaxy NGC7217. We have obtained high-resolution optical spectroscopic data (R ~ 9000) with the new fiber-based Integral Field Unit instrument VIRUS-W at the 2.7m telescope of the McDonald Observatory in Texas. Our analysis confirms the existence of two components. However, we find them to be co-rotating. The first component is the more luminous (~ 77% of the total light), has the higher velocity dispersion (~ 170 km/s) and rotates relatively slowly (projected $v_{max}$ = 50 km/s). The lower luminosity second component, (~ 23% of the total light), has a low velocity dispersion (~ 20 km/s) and rotates quickly (projected $v_{max}$ = 150 km/s). The difference in the kinematics of the two stellar components allows us to perform a kinematic decomposition and to measure the strengths of their Mg and Fe Lick indices separately. The rotational velocities and dispersions of the less luminous and faster component are very similar to those of the interstellar gas as measured from the [OIII] emission. Morphological evidence of active star formation in this component further suggests that NGC7217 may be in the process of (re)growing a disk inside a more massive and higher dispersion stellar halo. The kinematically cold and regular structure of the gas disk in combination with the central almost dust-free morphology allows us to compare the dynamical mass inside of the central 500pc with predictions from a stellar population analysis. We find agreement between the two if a Kroupa stellar initial mass function is assumed.Comment: accepted for publication by MNRA

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

Using 3D Spectroscopy to Probe the Orbital Structure of Composite Bulges

Detailed imaging and spectroscopic analysis of the centers of nearby S0 and spiral galaxies shows the existence of "composite bulges", where both classical bulges and disky pseudobulges coexist in the same galaxy. As part of a search for supermassive black holes in nearby galaxy nuclei, we obtained VLT-SINFONI observations in adaptive-optics mode of several of these galaxies. Schwarzschild dynamical modeling enables us to disentangle the stellar orbital structure of the different central components, and to distinguish the differing contributions of kinematically hot (classical bulge) and kinematically cool (pseudobulge) components in the same galaxy.Comment: LaTeX, 2 pages, 1 PDF figure. To appear in "Proceedings of IAU Symposium 309: Galaxies in 3D across the Universe", eds. B. L. Ziegler, F. Combes, H. Dannerbauer, and M. Verdug

The properties and the formation mechanism of the stellar counter-rotating components in NGC 4191

We disentangle two counter-rotating stellar components in NGC 4191 and characterize their physical properties (kinematics, morphology, age, metallicity, and abundance ratio). We performed a spectroscopic decomposition on integral field data to separate the contribution of two stellar components to the observed galaxy spectrum across the field of view. We also performed a photometric decomposition, modelling the galaxy with a S\'ersic bulge and two exponential disks of different scale length, with the aim of associating these structural components with the kinematic components. We measured the equivalent width of the absorption line indices on the best fit that represent the kinematic components and compared our measurements to the predictions of stellar population models. We have evidence that the line-of-sight velocity distributions (LOSVDs) are consistent with the presence of two distinct kinematic components. The combined information of the intensity of the LOSVDs and photometry allows us to associate the S\'ersic bulge and the outer disk with the main kinematic component, and the inner disk with the secondary kinematic component. The two kinematic stellar components counter-rotate with respect to each other. The main component is the most luminous and massive, and it rotates slower than the secondary component, which rotates along the same direction as the ionized gas. We also found that the two kinematic components have the same solar metallicity and sub-solar abundance ratio, without the presence of significant radial gradients. On the other hand, their ages show strong negative gradients and the possible indication that the secondary component is the youngest. We interpret our results in light of recent cosmological simulations and suggest gas accretion along two filaments as the formation mechanism of the stellar counter-rotating components in NGC 4191 (Abridged).Comment: 10 pages, 10 figure. Accepted for publication in Astronomy and Astrophysic

Spectroscopic decomposition of NGC 3521: unveiling the properties of the bulge and disc

We study the kinematics and the stellar populations of the bulge and disc of the spiral galaxy NGC 3521. At each position in the field of view, we separate the contributions of the bulge and the disc from the total observed spectrum and study their kinematics, age, and metallicities independently. Their properties are clearly distinct: the bulge rotates more slowly, has a higher velocity dispersion, and is less luminous than the disc. We identify three main populations of stars in NGC 3521: old ($\geq7$ Gyr), intermediate ($\approx$ 3 Gyr), and young ($\leq$1 Gyr). The mass and light of NGC 3521 are dominated by the intermediate stellar population. The youngest population contributes mostly to the disc component and its contribution increases with radius. We also study the luminosity-weighed properties of the stars in NGC 3521. Along the photometric major axis, we find: i) no age gradient for the stars in the bulge, and a negative age gradient for the stars in the disc; ii) negative metallicity gradients and sub-solar $\alpha$-enhancement for both the bulge and the disc. We propose the following picture for the formation of NGC 3521: initial formation a long time ago ($\geq 7$ Gyr), followed by a second burst of star formation or a merger ($\approx$ 3 Gyrs ago), which contributed predominantly to the mass-build up of the bulge. Recently ($\leq 1$ Gyr), the disc of NGC 3521 experienced an additional episode of star formation that started in the innermost regions.Comment: 13 pages, 11 figures, accepted for publication in MNRA