2D velocity fields of simulated interacting disc galaxies

We investigate distortions in the velocity fields of disc galaxies and their use to reveal the dynamical state of interacting galaxies at different redshift. For that purpose, we model disc galaxies in combined N-body/hydrodynamic simulations. 2D velocity fields of the gas are extracted from these simulations which we place at different redshifts from z=0 to z=1 to investigate resolution effects on the properties of the velocity field. To quantify the structure of the velocity field we also perform a kinemetry analysis. If the galaxy is undisturbed we find that the rotation curve extracted from the 2D field agrees well with long-slit rotation curves. This is not true for interacting systems, as the kinematic axis is not well defined and does in general not coincide with the photometric axis of the system. For large (Milky way type) galaxies we find that distortions are still visible at intermediate redshifts but partly smeared out. Thus a careful analysis of the velocity field is necessary before using it for a Tully-Fisher study. For small galaxies (disc scale length ~2 kpc) even strong distortions are not visible in the velocity field at z~0.5 with currently available angular resolution. Therefore we conclude that current distant Tully-Fisher studies cannot give reliable results for low-mass systems. Additionally to these studies we confirm the power of near-infrared integral field spectrometers in combination with adaptive optics (such as SINFONI) to study velocity fields of galaxies at high redshift (z~2).Comment: 12 pages, 18 figures, accepted for publication in A&A, high resolution version can be found at http://astro.uibk.ac.at/~thomas/kronberger.pd

A Close Look at Star Formation around Active Galactic Nuclei

We analyse star formation in the nuclei of 9 Seyfert galaxies at spatial resolutions down to 0.085arcsec, corresponding to length scales of less than 10pc in some objects. Our data were taken mostly with the near infrared adaptive optics integral field spectrograph SINFONI. The stellar light profiles typically have size scales of a few tens of parsecs. In two cases there is unambiguous kinematic evidence for stellar disks on these scales. In the nuclear regions there appear to have been recent - but no longer active - starbursts in the last 10-300Myr. The stellar luminosity is less than a few percent of the AGN in the central 10pc, whereas on kiloparsec scales the luminosities are comparable. The surface stellar luminosity density follows a similar trend in all the objects, increasing steadily at smaller radii up to 10^{13}L_sun/kpc^2 in the central few parsecs, where the mass surface density exceeds 10^4M_sun/pc^2. The intense starbursts were probably Eddington limited and hence inevitably short-lived, implying that the starbursts occur in multiple short bursts. The data hint at a delay of 50--100Myr between the onset of star formation and subsequent fuelling of the black hole. We discuss whether this may be a consequence of the role that stellar ejecta could play in fuelling the black hole. While a significant mass is ejected by OB winds and supernovae, their high velocity means that very little of it can be accreted. On the other hand winds from AGB stars ultimately dominate the total mass loss, and they can also be accreted very efficiently because of their slow speeds.Comment: 51 pages, including 27 figures; accepted by ApJ (paper reorganised, but results & conclusions the same

The effects of ram-pressure stripping on the internal kinematics of simulated spiral galaxies

We investigate the influence of ram-pressure stripping on the internal gas kinematics of simulated spiral galaxies. Additional emphasis is put on the question of how the resulting distortions of the gaseous disc are visible in the rotation curve and/or the full 2D velocity field of galaxies at different redshifts. A Milky-Way type disc galaxy is modelled in combined N-body/hydrodynamic simulations with prescriptions for cooling, star formation, stellar feedback, and galactic winds. This model galaxy moves through a constant density and temperature gas, which has parameters similar to the intra-cluster medium (ICM). Rotation curves (RCs) and 2D velocity fields 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 find that the appearance of distortions of the gaseous disc due to ram-pressure stripping depends on the direction of the acting ram pressure. In the case of face-on ram pressure, the distortions mainly appear in the outer parts of the galaxy in a very symmetric way. In contrast, in the case of edge-on ram pressure we find stronger distortions. The 2D velocity field also shows signatures of the interaction in the inner part of the disc. At angles smaller than 45 degrees between the ICM wind direction and the disc, the velocity field asymmetry increases significantly compared to larger angles. Compared to distortions caused by tidal interactions, the effects of ram-pressure stripping on the velocity field are relatively low in all cases and difficult to observe at intermediate redshift in seeing-limited observations. (abridged)Comment: 9 pages, 11 figures, accepted for publication in A&

Adaptive optics near infrared integral field spectroscopy of NGC 2992

NGC 2992 is an intermediate Seyfert 1 galaxy showing outflows on kilo parsec scales which might be due either to AGN or starburst activity. We therefore aim at investigating its central region for a putative starburst in the past and its connection to the AGN and the outflows. Observations were performed with the adaptive optics near infrared integral field spectrograph SINFONI on the VLT, complemented by longslit observations with ISAAC on the VLT, as well as N- and Q-band data from the Spitzer archive. The spatial and spectral resolutions of the SINFONI data are 50 pc and 83 km/s, respectively. The field of view of 3" x 3" corresponds to 450 pc x 450 pc. Br_gamma equivalent width and line fluxes from PAHs were compared to stellar population models to constrain the age of the putative recent star formation. A simple geometric model of two mutually inclined disks and an additional cone to describe an outflow was developed to explain the observed complex velocity field in H_2 1-0S(1). The morphologies of the Br_gamma and the stellar continuum are different suggesting that at least part of the Br_gamma emission comes from the AGN. This is confirmed by PAH emission lines at 6.2 micron and 11.2 micron and the strength of the silicon absorption feature at 9.7 micron, which point to dominant AGN activity with a relatively minor starburst contribution. We find a starburst age of 40 Myr - 50 Myr from Br_gamma line diagnostics and the radio continuum; ongoing star formation can be excluded. Both the energetics and the timescales indicate that the outflows are driven by the AGN rather than the starburst. The complex velocity field observed in H_2 1-0S(1) in the central 450 pc can be explained by the superposition of the galaxy rotation and an outflow.Comment: 10 pages, 8 figures, accepted for publication in A&

Hickson 62.I. Kinematics of NGC4778

Detailed studies of the photometric and kinematical properties of compact groups of galaxies are crucial to understand the physics of galaxy interactions and to shed light on some aspects of galaxy formation and evolution. In this paper we present a kinematical and photometrical study of a member, NGC4778, of the nearest (z=0.0137) compact group: Hickson 62. Aims: The aim of this work was to investigate the existence of kinematical anomalies in the brightest group member, NGC4778 in order to constrain the dynamical status and the formation history of the group. Methods: We used long-slit spectra obtained with FORS1 at VLT, to measure line-of-sight velocity distributions by means of the Fourier Correlation Quotient method, and to derive the galaxy rotation curve and velocity dispersion profile. Results: Our analysis reveals that Hickson 62a, also known as NGC4778, is an S0 galaxy with kinematical and morphological peculiarities, both in its central regions (r < 5'') and in the outer halo. In the central regions, the rotation curve shows the existence of a kinematically decoupled stellar component, offset with respect to the photometric center. In the outer halo we find an asymmetric rotation curve and a velocity dispersion profile showing a rise on the SW side, in direction of the galaxy NGC4776. Conclusions: The nuclear counterrotation, the distorted kinematics in the outer halo and the X-ray properties of the group suggest that NGC4778 may be the product of a recent minor merger, more reliable with a small late-type galaxy.Comment: 18 pages, 8 figures, accepted for pubblication in Astronomy and Astrophysic

Star formation and figure rotation in the early-type galaxy NGC2974

We present Galaxy Evolution Explorer (GALEX) far (FUV) and near (NUV) ultraviolet imaging of the nearby early-type galaxy NGC2974, along with complementary ground-based optical imaging. In the ultraviolet, the galaxy reveals a central spheroid-like component and a newly discovered complete outer ring of radius 6.2kpc, with suggestions of another partial ring at an even larger radius. Blue FUV-NUV and UV-optical colours are observed in the centre of the galaxy and from the outer ring outward, suggesting young stellar populations (< 1Gyr) and recent star formation in both locations. This is supported by a simple stellar population model which assumes two bursts of star formation, allowing us to constrain the age, mass fraction and surface mass density of the young component pixel by pixel. Overall, the mass fraction of the young component appears to be just under 1per cent (lower limit, uncorrected for dust extinction). The additional presence of a nuclear and an inner ring (radii 1.4 and 2.9kpc, respectively), as traced by [OIII] emission, suggests ring formation through resonances. All three rings are consistent with a single pattern speed of $78\pm6$ km/s/kpc, typical of S0 galaxies and only marginally slower than expected for a fast bar if traced by a small observed surface brightness plateau. This thus suggests that star formation and morphological evolution in NGC2974 at the present epoch are primarily driven by a rotating asymmetry (probably a large-scale bar), despite the standard classification of NGC2974 as an E4 elliptical.Comment: 13 pages, 10 figures, Changed content, Accepted for publication in MNRA

The ATLAS3D project - XXV: Two-dimensional kinematic analysis of simulated galaxies and the cosmological origin of fast and slow rotators

We present a detailed two-dimensional stellar dynamical analysis of as ample of 44 cosmological hydrodynamical simulations of individual central galaxies with stellar masses of 2 x 1010Msun ∼≤ Mstar ∼≤ 6x 1011Msun. Kinematic maps of the stellar line-of-sight velocity, velocity dispersion, and higher-order Gauss-Hermite moments h3 and h4 are constructed for each central galaxy and for the most massive satellites. The amount of rotation is quantified using the λR-parameter. The velocity, velocity dispersion, h3, and h4 fields of the simulated galaxies show a diversity similar to observed kinematic maps of early-type galaxies in the ATLAS3D survey. This includes fast (regular), slow, and misaligned rotation, hot spheroids with embedded cold disk components as well as galaxies with counter-rotating cores or central depressions in the velocity dispersion. We link the present-day kinematic properties to the individual cosmological formation histories of the galaxies. In general, major galaxy mergers have a significant influence on the rotation properties resulting in both a spin-down as well as a spin-up of the merger remnant. Lower mass galaxies with significant in-situ formation of stars, or with additional gas-rich major mergers - resulting in a spin-up - in their formation history, form elongated fast rotators with a clear anti-correlation of h3 and v/σ. An additional formation path for fast rotators includes gas-poor major mergers leading to a spin-up of the remnants. This formation path does not result in anti-correlated h3 and v/σ. The galaxies most consistent with the rare class of non-rotating round early-type galaxies grow by gas-poor minor mergers alone. In general, more massive galaxies have less in-situ star formation since z ∼ 2, rotate slower and have older stellar populations. (shortened)PostprintPeer reviewe

元代散曲と険韻としての「車遮韻」

Visualization of fluid flows at a high-Reynolds number (Re similar to 10(5)) presents difficulties for user comprehension due to density and ambiguous interactions between vortices. Prior work has used cluster-based reduced-order modelling (CROM) to analyze the wake of a High-Speed Train (HST) with Re = 86,000. In this paper, we present a novel surface visualization to convey the spatiotemporal changes undergone by clustered vortices in the HST wake. This visualization is accomplished through dimensional reduction of 3D volumetric vortices into 1D ridges, and physics-based feature tracking. The result is 3D surfaces visualizing the behavior of the vortices in the HST wake. Compared to conventional still-image representations, these surfaces allow the user to quickly compare and analyze the two shedding cycles identified via CROM. The spatiotemporal differences of the primary vortices in these shedding cycles provide analytic insight to influence the aerodynamics of the HST