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Register a new userStudying the kinematic asymmetries of disks and post-coalescence mergers using a new `kinemetry criterion
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We have obtained VIMOS/VLT optical integral field spectroscopy (IFS) data for a sample of 4 LIRGs which have been selected at a similar distance ($sim$ 70 Mpc) to avoid relative resolution effects. They have been classified in two groups (isolated disk and post-coalescence mergers) according to their morphology. The $kinemetry$ method (developed by Krajnovic and coworkers) is used to characterize the kinematic properties of these galaxies and to discuss new criteria for distinguishing their status. We present and discuss new kinematic maps (i.e., velocity field and velocity dispersion) for these four galaxies. The morphological and kinematic classifications of these systems are consistent, with disks having lower kinematic asymmetries than post-coalescence mergers. We then propose and discuss a new kinematic criterion to differentiate these two groups. This criterion distinguishes better these two categories and has the advantage of being less sensitive to angular resolution effects. According to the previous criteria,the present post-coalescence systems would have been classified as disks. This indicates that the separation of disks from mergers is subjective to the definition of `merger. It also suggests that previous estimates of the merger/disk ratio could have been underestimated, but larger samples are necessary to establish a firmer conclusion.
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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 H-alpha) 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 co-workers), 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 non-merging 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.
Galaxies in clusters are more likely to be of early type and to have lower star formation rates than galaxies in the field. Recent observations and simulations suggest that cluster galaxies may be `pre-processed by group or filament environments and that galaxies that fall into a cluster as part of a larger group can stay coherent within the cluster for up to one orbital period (`post-processing). We investigate these ideas by means of a cosmological $N$-body simulation and idealized $N$-body plus hydrodynamics simulations of a group-cluster merger. We find that group environments can contribute significantly to galaxy pre-processing by means of enhanced galaxy-galaxy merger rates, removal of galaxies hot halo gas by ram pressure stripping, and tidal truncation of their galaxies. Tidal distortion of the group during infall does not contribute to pre-processing. Post-processing is also shown to be effective: galaxy-galaxy collisions are enhanced during a groups pericentric passage within a cluster, the merger shock enhances the ram pressure on group and cluster galaxies, and an increase in local density during the merger leads to greater galactic tidal truncation.
Observations of debris disks, the products of the collisional evolution of rocky planetesimals, can be used to trace planetary activity across a wide range of stellar types. The most common end points of stellar evolution are no exception as debris disks have been observed around several dozen white dwarf stars. But instead of planetary formation, post-main-sequence debris disks are a signpost of planetary destruction, resulting in compact debris disks from the tidal disruption of remnant planetesimals. In this work, we present the discovery of five new debris disks around white dwarf stars with gaseous debris in emission. All five systems exhibit excess infrared radiation from dusty debris, emission lines from gaseous debris, and atmospheric absorption features indicating on-going accretion of metal-rich debris. In four of the systems, we detect multiple metal species in emission, some of which occur at strengths and transitions previously unseen in debris disks around white dwarf stars. Our first year of spectroscopic follow-up hints at strong variability in the emission lines that can be studied in the future, expanding the range of phenomena these post-main-sequence debris disks exhibit.
Context. Outflows powered by the injection of kinetic energy from massive stars can strongly affect the chemical evolution of galaxies, in particular of dwarf galaxies, as their lower gravitational potentials enhance the chance of a galactic wind. Aims. We therefore performed a detailed kinematic analysis of the neutral and ionised gas components in the nearby star-forming irregular dwarf galaxy NGC 4861. Similar to a recently published study of NGC 2366, we want to make predictions about the fate of the gas and to discuss some general issues about this galaxy. Methods. Fabry-Perot interferometric data centred on the Halpha line were obtained with the 1.93m telescope at the Observatoire de Haute-Provence. They were complemented by HI synthesis data from the VLA. We performed a Gaussian decomposition of both the Halpha and the HI emission lines in order to search for multiple components indicating outflowing gas. The expansion velocities of the detected outflows were compared to the escape velocity of NGC 4861, which was modelled with a pseudo-isothermal halo. Results. Both in Halpha and HI the galaxy shows several outflows, three directly connected to the disc and probably forming the edges of a supergiant shell, and one at kpc-distance from the disc. We measured velocity offsets of 20 to 30 km/s, which are low in comparison to the escape velocity of the galaxy and therefore minimise the chance of a galactic wind.
Double-peaked line profiles are commonly considered a hallmark of rotating disks, with the distance between the peaks a measure of the rotation velocity. However, double-peaks can arise also from radiative transfer effects in optically thick non-rotating sources. Utilizing exact solutions of the line transfer problem we present a detailed study of line emission from geometrically thin Keplerian disks. We derive the conditions for emergence of kinematic double peaks in optically thin and thick disks, and find that it is generally impossible to disentangle the effects of kinematics and line opacity in observed double-peaked profiles. Unless supplemented by additional information, a double-peaked profile alone is not a reliable indicator of a rotating disk. In certain circumstances, triple and quadruple profiles might be better indicators of rotation in optically thick disks.
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