Richard Davies

Kinemetry of SINS high-redshift star-forming galaxies: distinguishing rotating disks from major mergers

We present a simple set of kinematic criteria that can distinguish between galaxies dominated by ordered rotational motion and those involved in major merger events. Our criteria are based on the dynamics of the warm ionized gas (as traced by Hα) within galaxies, making this analysis accessible to high-redshift systems, whose kinematics are primarily traceable through emission features. Using the method of kinemetry (developed by Krajnovic and coworkers), we quantify asymmetries in both the velocity and velocity dispersion maps of the warm gas, and the resulting criteria enable us to empirically differentiate between nonmerging and merging systems at high redshift. We apply these criteria to 11 of our best-studied rest-frame UV/optical-selected z ~ 2 galaxies for which we have near-infrared integral-field spectroscopic data from SINFONI on the VLT. Of these 11 systems, we find that >50% have kinematics consistent with a single rotating disk interpretation, while the remaining systems are more likely undergoing major mergers. This result, combined with the short formation timescales of these systems, provides evidence that rapid, smooth accretion of gas plays a significant role in galaxy formation at high redshift.

Mergers and Mass Accretion Rates in Galaxy Assembly: The Millennium Simulation Compared to Observations of z ≈ 2 Galaxies

Recent observations of UV/optically selected, massive star-forming galaxies at z ≈ 2 indicate that the baryonic mass assembly and star formation history is dominated by continuous rapid accretion of gas and internal secular evolution, rather than by major mergers. We use the Millennium Simulation to build new halo merger trees and extract halo merger fractions and mass accretion rates. We find that, even for halos not undergoing major mergers, the mass accretion rates are plausibly sufficient to account for the high star formation rates observed in z ≈ 2 disks. On the other hand, the fraction of major mergers in the Millennium Simulation is sufficient to account for the number counts of submillimeter galaxies (SMGs), in support of observational evidence that these are major mergers. When following the fate of these two populations in the Millennium Simulation to z = 0, we find that subsequent mergers are not frequent enough to convert all z ≈ 2 turbulent disks into elliptical galaxies at z = 0. Similarly, mergers cannot transform the compact SMGs/red sequence galaxies at z ≈ 2 into observed massive cluster ellipticals at z = 0. We argue therefore, that secular and internal evolution must play an important role in the evolution of a significant fraction of z ≈ 2 UV/optically and submillimeter-selected galaxy populations.

Adaptive optics for astronomy

Adaptive Optics is a prime example of how progress in observational astronomy can be driven by technological developments. At many observatories it is now considered to be part of a standard instrumentation suite, enabling ground-based telescopes to reach the diffraction limit and thus providing spatial resolution superior to that achievable from space with current or planned satellites. In this review we consider adaptive optics from the astrophysical perspective. We show that adaptive optics has led to important advances in our understanding of a multitude of astrophysical processes, and describe how the requirements from science applications are now driving the development of the next generation of novel adaptive optics techniques.

Do black hole masses scale with classical bulge luminosities only? The case of the two composite pseudo-bulge galaxies NGC 3368 and NGC 3489

It is now well established that all galaxies with a massive bulge component harbour a central supermassive black hole (SMBH). The mass of the SMBH correlates with bulge properties such as the bulge mass and the velocity dispersion, which implies that the bulge and the central black hole of a galaxy have grown together during the formation process. As part of an investigation of the dependence of the SMBH mass on bulge types and formation mechanisms, we present measurements of SMBH masses in two pseudobulge galaxies. The spiral galaxy NGC 3368 is double-barred and hosts a large pseudobulge with a tiny classical bulge component at the very centre. The S0 galaxy NGC 3489 has only a weak large-scale bar, a small pseudobulge and a small classical bulge. Both galaxies show weak nuclear activity in the optical, indicative of the presence of a supermassive black hole. We present high resolution, adaptive-optics-assisted, near-infrared integral field data of these two galaxies, taken with SINFONI at the Very Large Telescope, and use axisymmetric orbit models to determine the masses of the SMBHs. The SMBH mass of NGC 3368, averaged over the four quadrants, ishM i = 7:5 10 6 M with an error of 1:5 10 6 M , which mostly comes from the non-axisymmetry in the data. For NGC 3489, a solution without black hole cannot be excluded when modelling the SINFONI data alone, but can be clearly ruled out when modelling a combination of SINFONI, OASIS and SAURON data, for which we obtain M = (6:00 +0:56 0:54 jstat 0:64jsys) 10 6 M . Although both galaxies seem to be consistent with the M - relation, at face value they do not agree with the relation between bulge magnitude and black hole mass when the total bulge magnitude (i.e., including both classical bulge and pseudobulge) is considered; the agreement is better when only the small classical bulge components are considered. However, taking into account the ageing of the stellar population could change this conclusion.

The SINS Survey: Broad Emission Lines in High-Redshift Star-Forming Galaxies

High signal-to-noise, representative spectra of star-forming galaxies at z ~ 2, obtained via stacking, reveal a high-velocity component underneath the narrow Hα and [NII] emission lines. When modeled as a single Gaussian, this broad component has FWHM 1500 km s–1; when modeled as broad wings on the Hα and [N II] features, it has FWHM ≳ 500 km s^(–1). This feature is preferentially found in the more massive and more rapidly star-forming systems, which also tend to be older and larger galaxies. We interpret this emission as evidence of either powerful starburst-driven galactic winds or active supermassive black holes (SMBHs). If galactic winds are responsible for the broad emission, the observed luminosity and velocity of this gas imply mass outflow rates comparable to the star formation rate. On the other hand, if the broad-line regions of active black holes account for the broad feature, the corresponding black holes masses are estimated to be an order of magnitude lower than those predicted by local scaling relations, suggesting a delayed assembly of SMBHs with respect to their host bulges.

What is limiting near‐infrared astrometry in the Galactic Centre?

We systematically investigate the error sources for high-precision astrometry from adaptive optics (AO) based near-infrared imaging data. We focus on the application in the crowded stellar field in the Galactic Centre. We show that at the level of ≲ 100 μas a number of effects are limiting the accuracy. Most important are the imperfectly subtracted seeing haloes of neighbouring stars, residual image distortions and unrecognized confusion of the target source with fainter sources in the background. Further contributors to the error budget are the uncertainty in estimating the point-spread function, the signal-to-noise ratio induced statistical uncertainty, coordinate transformation errors, the chromaticity of refraction in Earths atmosphere, the post-AO differential tilt jitter and anisoplanatism. For stars as bright as m K = 14, residual image distortions limit the astrometry, for fainter stars the limitation is set by the seeing haloes of the surrounding stars. In order to improve the astrometry substantially at the current generation of telescopes, an AO system with high performance and weak seeing haloes over a relatively small field (r ≲ 3 arcsec) is suited best. Furthermore, techniques to estimate or reconstruct the seeing halo could be promising.

NGC 6240: merger-induced star formation and gas dynamics

We present spatially resolved integral field spectroscopic K-band data at a resolution of 0.13 �� (60 pc) and interferometric CO(2–1) line observations of the prototypical merging system NGC 6240. Despite the clear rotational signature, the stellar kinematics in the two nuclei are dominated by dispersion. We use Jeans modelling to derive the masses and the mass-to-light ratios of the nuclei. Combining the luminosities with the spatially resolved Brγ equivalent width shows that only 1/ 3o f theK-band continuum from the nuclei is associated with the most recent star forming episode; and that less than 30% of the system’s bolometric luminosity and only 9% of its stellar mass is due to this starburst. The star formation properties, calculated from typical merger star formation histories, demonstrate the impact of different assumptions about the star formation history. The properties of the nuclei, and the existence of a prominent old stellar population, indicate that the nuclei are remnants of the progenitor galaxies’ bulges.

Star formation in the circumnuclear environment of NGC 1068

ABSTRA C T We present near-infrared emission-line images of the circumnuclear ring in NGC 1068. We have measured the Brg fluxes in a number of star-forming complexes and derived the extinction for each of these by comparison with Ha. We investigate the star-forming histories of these regions and find that a short burst of star formation occurred coevally throughout the ring within the last 30‐40 Myr, and perhaps as recently as 4‐7 Myr ago. The 1‐0 S(1) flux and S(1)/Brg ratios indicate that as well as fluorescence, shock-excited H2 emission contributes to the total flux. There is excess H2 flux to the north-west where the ionization cone crosses the ring, and we show that it is possible that the non-stellar continuum from the Seyfert nucleus which produces the high-excitation lines could also be causing fluorescence at the edges of molecular clouds in the ring. The nuclear 1‐0 S(1) is more extended than previously realized but only along the bar’s major axis, and we consider mechanisms for its excitation.

High-velocity bipolar molecular emission from an AGN torus

We have detected in ALMA observations CO J = 6 - 5 emission from the nucleus of the Seyfert galaxy NGC 1068. The low-velocity (up to +/- 70 km/s relative to systemic) CO emission resolves into a 12x7 pc structure, roughly aligned with the nuclear radio source. Higher-velocity emission (up to +/- 400 km/s) is consistent with a bipolar outflow in a direction nearly perpendicular (roughly 80 degrees) to the nuclear disk. The position-velocity diagram shows that in addition to the outflow, the velocity field may also contain rotation about the disk axis. These observations provide compelling evidence in support of the disk-wind scenario for the AGN obscuring torus.

MICADO: the E-ELT adaptive optics imaging camera

MICADO is the adaptive optics imaging camera for the E-ELT. It has been designed and optimised to be mounted to the LGS-MCAO system MAORY, and will provide diffraction limited imaging over a wide (~1 arcmin) field of view. For initial operations, it can also be used with its own simpler AO module that provides on-axis diffraction limited performance using natural guide stars. We discuss the instruments key capabilities and expected performance, and show how the science drivers have shaped its design. We outline the technical concept, from the opto-mechanical design to operations and data processing. We describe the AO module, summarise the instrument performance, and indicate some possible future developments.