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Register a new userMapping the Kinematically Decoupled Core in NGC 1407 with MUSE
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Studies of the kinematics of NGC 1407 have revealed complex kinematical structure, consisting of the outer galaxy, an embedded disc within a radius of $sim60$ arcsec, and a kinematically decoupled core (KDC) with a radius of less than 30arcsec. However, the size of the KDC and the amplitude of the kinematic misalignment it induces have not yet been determined. In this paper, we explore the properties of the KDC using observations from the MUSE Integral Field Spectrograph to map out the kinematics in the central arcminute of NGC 1407. Velocity and kinemetry maps of the galaxy reveal a twist of $sim$148 degree in the central $10$ arcseconds of the galaxy, and the higher-order moments of the kinematics reveal that within the same region, this slowly-rotating galaxy displays no net rotation. Analysis of the stellar populations across the galaxy found no evidence of younger stellar populations in the region of the KDC, instead finding uniform age and super-solar $alpha$-enhancement across the galaxy, and a smoothly decreasing metallicity gradient with radius. We therefore conclude that NGC 1407 contains a triaxial, kiloparsec-scale KDC with distinct kinematics relative to the rest of the galaxy, and which is likely to have formed through either a major merger or a series of minor mergers early in the lifetime of the galaxy. With a radius of $sim$5 arcseconds or $sim0.6$ kpc, NGC 1407 contains the smallest KDC mapped by MUSE to date in terms of both its physical and angular size.
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MUSE observations of NGC5813 reveal a complex structure in the velocity dispersion map, previously hinted by SAURON observations. The structure is reminiscent of velocity dispersion maps of galaxies comprising two counter-rotating discs, and may explain the existence of the kinematically distinct core (KDC). Further evidence for two counter-rotating components comes from the analysis of the higher moments of the stellar line-of-sight velocity distributions and fitting MUSE spectra with two separate Gaussian line-of-sight velocity distributions. The emission-line kinematics show evidence of being linked to the present cooling flows and the buoyant cavities seen in X-rays. We detect ionised gas in a nuclear disc-like structure, oriented like the KDC, which is, however, not directly related to the KDC. We build an axisymmetric Schwarzschild dynamical model, which shows that the MUSE kinematics can be reproduced well with two counter-rotating orbit families, characterised by relatively low angular momentum components, but clearly separated in integral phase space and with radially varying contributions. The model indicates that the counter-rotating components in NGC5813 are not thin discs, but dynamically hot structures. Our findings give further evidence that KDCs in massive galaxies should not necessarily be considered as structurally or dynamically decoupled regions, but as the outcomes of the mixing of different orbital families, where the balance in the distribution of mass of the orbital families is crucial. We discuss the formation of the KDC in NGC5813 within the framework of gas accretion, binary mergers and formation of turbulent thick discs from cold streams at high redshift.
We present evidence for the presence of a low-amplitude kinematically distinct component in the giant early-type galaxy M87, via datasets obtained with the SAURON and MUSE integral-field spectroscopic units. The MUSE velocity field reveals a strong twist of ~140 deg within the central 30 arcsec connecting outwards such a kinematically distinct core to a prolate-like rotation around the large-scale photometric major-axis of the galaxy. The existence of these kinematic features within the apparently round central regions of M87 implies a non-axisymmetric and complex shape for this galaxy, which could be further constrained using the presented kinematics. The associated orbital structure should be interpreted together with other tracers of the gravitational potential probed at larger scales (e.g., Globular Clusters, Ultra Compact Dwarfs, Planetary Nebulae): it would offer an insight in the assembly history of one of the brightest galaxies in the Virgo Cluster. These data also demonstrate the potential of the MUSE spectrograph to uncover low-amplitude spectral signatures.
We study the properties of 66 galaxies with kinematically misaligned gas and stars from MaNGA survey. The fraction of kinematically misaligned galaxies varies with galaxy physical parameters, i.e. M*, SFR and sSFR. According to their sSFR, we further classify these 66 galaxies into three categories, 10 star-forming, 26 Green Valley and 30 quiescent ones. The properties of different types of kinematically misaligned galaxies are different in that the star-forming ones have positive gradient in D4000 and higher gas-phase metallicity, while the green valley/quiescent ones have negative D4000 gradients and lower gas-phase metallicity on average. There is evidence that all types of the kinematically misaligned galaxies tend to live in more isolated environment. Based on all these observational results, we propose a scenario for the formation of star forming galaxies with kinematically misaligned gas and stars - the progenitor accretes misaligned gas from a gas-rich dwarf or cosmic web, the cancellation of angular momentum from gas-gas collisions between the pre-existing gas and the accreted gas largely accelerates gas inflow, leading to fast centrally-concentrated star-formation. The higher metallicity is due to enrichment from this star formation. For the kinematically misaligned green valley and quiescent galaxies, they might be formed through gas-poor progenitors accreting kinematically misaligned gas from satellites which are smaller in mass.
We present results from our ongoing effort to understand the nature and evolution of nearby galaxies using the SAURON integral-field spectrograph. In this proceeding we focus on the study of the particular case formed by the interacting galaxies NGC5953 and NGC5954. We present stellar and gas kinematics of the central regions of NGC5953. We use a simple procedure to determine the age of the stellar populations in the central regions and argue that we may be witnessing the formation of a kinematically decoupled component from cold gas being acquired during the ongoing interaction with NGC5954.
We introduce VLT-MUSE observations of the central 2$times2$ (30$times$30 pc) of the Tarantula Nebula in the Large Magellanic Cloud. The observations provide an unprecedented spectroscopic census of the massive stars and ionised gas in the vicinity of R136, the young, dense star cluster located in NGC 2070, at the heart of the richest star-forming region in the Local Group. Spectrophotometry and radial-velocity estimates of the nebular gas (superimposed on the stellar spectra) are provided for 2255 point sources extracted from the MUSE datacubes, and we present estimates of stellar radial velocities for 270 early-type stars (finding an average systemic velocity of 271$pm$41 km/s). We present an extinction map constructed from the nebular Balmer lines, with electron densities and temperatures estimated from intensity ratios of the [SII], [NII], and [SIII] lines. The interstellar medium, as traced by H$alpha$ and [NII] $lambda$6583, provides new insights in regions where stars are probably forming. The gas kinematics are complex, but with a clear bi-modal, blue- and red-shifted distribution compared to the systemic velocity of the gas centred on R136. Interesting point-like sources are also seen in the eastern cavity, western shell, and around R136; these might be related to phenomena such as runaway stars, jets, formation of new stars, or the interaction of the gas with the population of Wolf--Rayet stars. Closer inspection of the core reveals red-shifted material surrounding the strongest X-ray sources, although we are unable to investigate the kinematics in detail as the stars are spatially unresolved in the MUSE data. Further papers in this series will discuss the detailed stellar content of NGC 2070 and its integrated stellar and nebular properties.
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