Line-of-sight Velocity Distribution Research Articles

Triaxial Schwarzschild models of NGC 708: a 10-billion solar mass black hole in a low-dispersion galaxy with a Kroupa IMF

ABSTRACT We report the discovery of a (1.0 ± 0.28) × 1010 M⊙ supermassive black hole (BH) at the centre of NGC 708, the Brightest Cluster Galaxy of Abell 262. Such high BH masses are very rare and allow to investigate BH–host galaxy scaling relations at the high mass end, which in turn provide hints about the (co)evolution of such systems. NGC 708 is found to be an outlier in all the canonical scaling relations except for those linking the BH mass to the core properties. The galaxy mass-to-light ratio points to a Kroupa IMF rather than Salpeter, with this finding confirmed using photometry in two different bands. We perform this analysis using our novel triaxial Schwarzschild code to integrate orbits in a five-dimensional space, using a semiparametric deprojected light density to build the potential and non-parametric line-of-sight velocity distributions (LOSVDs) derived from long-slit spectra recently acquired at Large Binocular Telescope (LBT) to exploit the full information in the kinematic. We find that the galaxy geometry changes as a function of the radius going from prolate, nearly spherical in the central regions to triaxial at large radii, highlighting the need to go beyond constant shape profiles. Our analysis is only the second of its kind and will systematically be used in the future to hunt supermassive BH in giant ellipticals.

Total mass slopes and enclosed mass constrained by globular cluster system dynamics

We study the total-mass density profiles of early-type galaxies (ETGs: ellipticals and lenticulars) with globular clusters (GCs) as kinematic tracers. The goal of this work is to probe the total mass distribution, parameterised with a double power-law profile, by constraining the parameters of the profile with a flexible modelling approach. To that end, we leverage the extended spatial distribution of GCs from the SLUGGS survey (⟨RGC,  max⟩∼8 Re) in combination with discrete dynamical modelling. We use discrete Jeans anisotropic modelling in cylindrical coordinates to determine the velocity moments at the location of the GCs in our sample. Assuming a Gaussian line-of-sight velocity distribution (LOSVD) and a combination of informative and uninformative priors we use a Bayesian framework to determine the best-fit parameters of the total mass density profile and orbital properties of the GCs. We find that the choice of informative priors does not impact the enclosed mass and inner slope measurements. Additionally, the orbital properties (anisotropy and rotation of the dispersion-dominated GC systems) minimally impact the measurements of the inner slope and enclosed mass. A strong presence of dynamically-distinct subpopulations or low numbers of kinematic tracers can bias the results. Owing to the large spatial extent of the tracers our method is sensitive to the intrinsic inner slope of the total mass profile and we find ᾱ = −1.88 ± 0.01 for 12 galaxies with robust measurements. To compare our results with literature values we fit a single power-law profile to the resulting total mass density. In the radial range 0.1–4 Re our measured slope has a value of ⟨γtot⟩= − 2.22 ± 0.14 and is in good agreement with the literature. Due to the increased flexibility in our modelling approach, our measurements exhibit larger uncertainties, thereby limiting our ability to constrain the intrinsic scatter σγ.

B/PS bulges and barlenses from a kinematic viewpoint – II

ABSTRACT Internal dynamics and kinematics of galaxies have imprints on the line-of-sight velocity distribution (LOSVD). Gauss–Hermite parametrization allows one to identify the kinematics features of the system in terms of skewness (h3) and broadness (h4) deviations of an LOSVD. Such a method provides information about the type of orbits since a $h_3\!-\!\overline{V}$ correlation is a sign of elongated orbits, and the anticorrelation is a sign of circular or near-circular orbits. In previous works, analysis of the $h_3\!-\!\overline{V}$ relation provided a tool to identify a hidden bar or B/PS bulge (edge-on, PA = 90°) and to probe their strength. We prepared two N-body galaxy models with clear B/PS bulges: one has an ordinary bar (the X model), and the second one has a barlens embedded into a bar (the BL model) to investigate the mechanism of formation of h3 features at any position of an observer. We show that the $h_3\!-\!\overline{V}$ correlation appears in the regions where bar and disc particles are mixing. We also reveal that the model with a barlens has an $h_3\!-\!\overline{V}$ anticorrelation in the centre, and we show that barlens-specific orbits are responsible for this signal. Moreover, this feature can be observed only for galaxies with compact bulges and barlenses. The results of this work are applicable for the interpretation of future integral-field unit (IFU) data for real galaxies with B/PS bulges, especially for objects with barlenses.

B/PS bulges and barlenses from a kinematic viewpoint – I

ABSTRACT A significant part of barred disc galaxies exhibits boxy/peanut-shaped structures (B/PS bulges) at high inclinations. Another structure also associated with the bar is a barlens, often observed in galaxies in a position close to face-on. At this viewing angle, special kinematic tests are required to detect a 3D extension of the bars in the vertical direction (B/PS bulges). We use four pure N-body models of galaxies with B/PS bulges, which have different bar morphology from bars with barlenses to the so-called face-on peanut bars. We analyse the kinematics of our models to establish how the structural features of B/PS bulges manifest themselves in the kinematics for galaxies at intermediate inclinations and whether these features are related to the barlenses. We apply the dissection of the bar into different orbital groups to determine which of them are responsible for the features of the LOSVD (line-of-sight velocity distribution), i.e. for the deep minima of the h4 parameter along the major axis of the bar. As a result, we claim that for our models at the face-on position, the kinematic signatures of a ‘peanut’ indeed track the vertical density distribution features. We conclude that orbits responsible for such kinematic signatures differ from model to model. We pay special attention to the barlens model. We show that orbits assembled into barlens are not responsible for the kinematic signatures of B/PS bulges. The results presented in this work are applicable to the interpretation of IFU observations of real galaxies.

Detailed Shapes of the Line-of-sight Velocity Distributions in Massive Early-type Galaxies from Nonparametric Spectral Models

We present the first systematic study of the detailed shapes of the line-of-sight velocity distributions (LOSVDs) in nine massive early-type galaxies (ETGs) using the novel nonparametric modeling code WINGFIT. High-signal spectral observations with the Multi-Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope allow us to measure between 40 and 400 individual LOSVDs in each galaxy at a signal-to-noise ratio level better than 100 per spectral bin and to trace the LOSVDs all the way out to the highest stellar velocities. We extensively discuss potential LOSVD distortions due to template mismatch and strategies to avoid them. Our analysis uncovers a plethora of complex, large-scale kinematic structures for the shapes of the LOSVDs. Most notably, in the centers of all ETGs in our sample, we detect faint, broad LOSVD “wings” extending the line-of-sight velocities, v los, well beyond 3σ to v los ∼ ± 1000–1500 km s−1 on both sides of the peak of the LOSVDs. These wings likely originate from point-spread function effects and contain velocity information about the very central unresolved regions of the galaxies. In several galaxies, we detect wings of similar shape also toward the outer parts of the MUSE field of view. We propose that these wings originate from faint halos of loosely bound stars around the ETGs, similar to the cluster-bound stellar envelopes found around many brightest cluster galaxies.

Accuracy and precision of triaxial orbit models I: SMBH mass, stellar mass, and dark-matter halo

ABSTRACT We investigate the accuracy and precision of triaxial dynamical orbit models by fitting 2D mock observations of a realistic N-body merger simulation resembling a massive early-type galaxy with a supermassive black hole. We show that we can reproduce the triaxial N-body merger remnant’s correct black hole mass, stellar mass-to-light ratio and total enclosed mass (inside the half-light radius) for several different tested orientations with an unprecedented accuracy of 5–10 per cent. Our dynamical models use the entire non-parametric line-of-sight velocity distribution (LOSVD) rather than parametric LOSVDs or velocity moments as constraints. Our results strongly suggest that state-of-the-art integral-field projected kinematic data contain only minor degeneracies with respect to the mass and anisotropy recovery. Moreover, this also demonstrates the strength of the Schwarzschild method in general. We achieve the proven high recovery accuracy and precision with our newly developed modelling machinery by combining several advancements: (i) our new semiparametric deprojection code probes degeneracies and allows us to constrain the viewing angles of a triaxial galaxy; (ii) our new orbit modelling code SMART uses a 5-dim orbital starting space to representatively sample in particular near-Keplerian orbits in galaxy centres; (iii) we use a generalized information criterion AICp to optimize the smoothing and to compare different mass models to avoid biases that occur in χ2-based models with varying model flexibilities.

Point-spread Function Deconvolution of the IFU Data and Restoration of Galaxy Stellar Kinematics

Abstract We present a performance test of the point-spread function (PSF) deconvolution algorithm applied to astronomical integral field unit (IFU) spectroscopy data for restoration of galaxy kinematics. We deconvolve the IFU data by applying the Lucy–Richardson algorithm to the 2D image slice at each wavelength. We demonstrate that the algorithm can effectively recover the true stellar kinematics of the galaxy, by using mock IFU data with a diverse combination of surface brightness profile, signal-to-noise ratio, line-of-sight geometry, and line-of-sight velocity distribution (LOSVD). In addition, we show that the proxy of the spin parameter λ R e can be accurately measured from the deconvolved IFU data. We apply the deconvolution algorithm to the actual SDSS-IV MaNGA IFU survey data. The 2D LOSVD, geometry, and λ R e measured from the deconvolved MaNGA IFU data exhibit noticeable differences compared to the ones measured from the original IFU data. The method can be applied to any other regular-grid IFU data to extract the PSF-deconvolved spatial information.

Detectability of large-scale counter-rotating stellar disks in galaxies with integral-field spectroscopy

Context. In recent years integral-field spectroscopic surveys have revealed that the presence of kinematically decoupled stellar components is not a rare phenomenon in nearby galaxies. However, complete statistics are still lacking because they depend on the detection limit of these objects. Aims. We investigate the kinematic signatures of two large-scale counter-rotating stellar disks in mock integral-field spectroscopic data to address their detection limits as a function of the galaxy properties and instrumental setup. Methods. We built a set of mock data of two large-scale counter-rotating stellar disks as if they were observed with the Multi Unit Spectroscopic Explorer (MUSE). We accounted for different photometric, kinematic, and stellar population properties of the two counter-rotating components as a function of galaxy inclination. We extracted the stellar kinematics in the wavelength region of the calcium triplet absorption lines by adopting a Gauss-Hermite (GH) parameterization of the line-of-sight velocity distribution (LOSVD). Results. We confirm that the strongest signature of the presence of two counter-rotating stellar disks is the symmetric double peak in the velocity dispersion map, already known as the 2σ feature. The size, shape, and slope of the 2σ peak strongly depend on the velocity separation and relative light contribution of the two counter-rotating stellar disks. When the 2σ peak is difficult to detect due to the low signal-to-noise ratio of the data, the large-scale structure in the h3 map can be used as a diagnostic for strong and weak counter-rotation. The counter-rotating kinematic signatures become fainter at lower viewing angles as an effect of the smaller projected velocity separation between the two counter-rotating components. We confirm that the observed frequency of 2σ galaxies represents only a lower limit of the stellar counter-rotation phenomenon. Conclusions. The parameterization with a single GH function does not provide a good description of the LOSVD in the presence of strong counter-rotation. However, using GH parametric solutions is a practical way to reveal the large-scale counter-rotating stellar disks and could be used to detect faint counter-rotating components to improve the statistics of stellar counter-rotation.

SDSS-IV MaNGA: Refining Strong Line Diagnostic Classifications Using Spatially Resolved Gas Dynamics

Abstract We use the statistical power of the MaNGA integral-field spectroscopic galaxy survey to improve the definition of strong line diagnostic boundaries used to classify gas ionization properties in galaxies. We detect line emission from 3.6 million spaxels distributed across 7400 individual galaxies spanning a wide range of stellar masses, star formation rates, and morphological types, and find that the gas-phase velocity dispersion σ Hα correlates strongly with traditional optical emission-line ratios such as [S ii]/Hα, [N ii]/Hα, [O i]/Hα, and [O iii]/Hβ. Spaxels whose line ratios are most consistent with ionization by galactic H ii regions exhibit a narrow range of dynamically cold line-of-sight velocity distributions (LOSVDs) peaked around 25 km s−1 corresponding to a galactic thin disk, while those consistent with ionization by active galactic nuclei (AGNs) and low-ionization emission-line regions (LI(N)ERs) have significantly broader LOSVDs extending to 200 km s−1. Star-forming, AGN, and LI(N)ER regions are additionally well separated from each other in terms of their stellar velocity dispersion, stellar population age, Hα equivalent width, and typical radius within a given galaxy. We use our observations to revise the traditional emission-line diagnostic classifications so that they reliably identify distinct dynamical samples both in two-dimensional representations of the diagnostic line ratio space and in a multidimensional space that accounts for the complex folding of the star-forming model surface. By comparing the MaNGA observations to the SDSS single-fiber galaxy sample, we note that the latter is systematically biased against young, low-metallicity star-forming regions that lie outside of the 3″ fiber footprint.

A novel approach to optimize the regularization and evaluation of dynamical models using a model selection framework

ABSTRACT Orbit superposition models are a non-parametric dynamical modelling technique to determine the mass of a galaxy’s central supermassive black hole (SMBH), its stars, or its dark matter halo. One of the main problems is how to decide which model out of a large pool of trial models based on different assumed mass distributions represents the true structure of an observed galaxy best. We show that the traditional approach to judge models solely by their goodness-of-fit can lead to substantial biases in estimated galaxy properties caused by varying model flexibilities. We demonstrate how the flexibility of the models can be estimated using bootstrap iterations and present a model selection framework that removes these biases by taking the variable flexibility into account in the model evaluation. We extend the model selection approach to optimize the degree of regularization directly from the data. Altogether, this leads to a significant improvement of the constraining power of the modelling technique. We show with simulations that one can reconstruct the mass, anisotropy, and viewing angle of an axisymmetric galaxy with a few per cent accuracy from realistic observational data with fully resolved line-of-sight velocity distributions (LOSVDs). In a first application, we reproduce a photometric estimate of the inclination of the disc galaxy NGC 3368 to within 5° accuracy from kinematic data that cover only a few sphere-of-influence radii around the galaxy’s SMBH. This demonstrates the constraining power that can be achieved with orbit models based on fully resolved LOSVDs and a model selection framework.

BAYES-LOSVD: A Bayesian framework for non-parametric extraction of the line-of-sight velocity distribution of galaxies

We introduce BAYES-LOSVD, a novel implementation of the non-parametric extraction of line-of-sight velocity distributions (LOSVDs) in galaxies. We employed Bayesian inference to obtain robust LOSVDs and associated uncertainties. Our method relies on a principal component analysis to reduce the dimensionality on the set of templates required for the extraction and thus increase the performance of the code. In addition, we implemented several options to regularise the output solutions. Our tests, conducted on mock spectra, confirm the ability of our approach to model a wide range of LOSVD shapes, overcoming limitations of the most widely used parametric methods (e.g., Gauss-Hermite expansion). We present examples of LOSVD extractions for real galaxies with known peculiar LOSVD shapes, including NGC 4371, IC 0719, and NGC 4550, using MUSE and SAURON integral-field unit (IFU) data. Our implementation can also handle data from other popular IFU surveys (e.g., ATLAS3D, CALIFA, MaNGA, SAMI).

SMART: A new implementation of Schwarzschild’s Orbit Superposition technique for triaxial galaxies and its application to an N-body merger simulation

Abstract We present SMART, a new 3D implementation of the Schwarzschild Method and its application to a triaxial N-body merger simulation. SMART fits full line-of-sight velocity distributions (LOSVDs) to determine the viewing angles, black hole, stellar and dark matter (DM) masses and the stellar orbit distribution of galaxies. Our model uses a 5D orbital starting space to ensure a representative set of stellar trajectories adaptable to the integrals-of-motion space and it is designed to deal with non-parametric stellar and DM densities. SMART’s efficiency is demonstrated by application to a realistic N-body merger simulation including supermassive black holes which we model from five different projections. When providing the true viewing angles, 3D stellar luminosity profile and normalized DM halo, we can (i) reproduce the intrinsic velocity moments and anisotropy profile with a precision of $\sim 1\%$ and (ii) recover the black hole mass, stellar mass-to-light ratio and DM normalization to better than a few percent accuracy. This precision is smaller than the currently discussed differences between initial-stellar-mass functions and scatter in black hole scaling relations. Further tests with toy models suggest that the recovery of the anisotropy in triaxial galaxies is almost unique when the potential is known and full LOSVDs are fitted. We show that orbit models even allow the reconstruction of full intrinsic velocity distributions, which contain more information than the classical anisotropy parameter. Surprisingly, the orbit library for the analysed N-body simulation’s gravitational potential contains orbits with net rotation around the intermediate axis that is stable over some Gyrs.

The MASSIVE Survey. XV. A Stellar Dynamical Mass Measurement of the Supermassive Black Hole in Massive Elliptical Galaxy NGC 1453

Abstract We present a new stellar dynamical mass measurement ( ) of the supermassive black hole (SMBH) in NGC 1453, a fast-rotating massive elliptical galaxy in the MASSIVE survey. We measure stellar kinematics in 135 spatial bins in the central 1.5 kpc × 2 kpc region of the galaxy using high signal-to-noise ratio (S/N ∼ 130) spectra from the Gemini-North GMOS integral field spectrograph (IFS). Combining with wide-field IFS kinematics out to ∼3 effective radii and stellar light distributions from Hubble Space Telescope Wide Field Camera 3 images, we perform Schwarzschild orbit-based mass modeling in the axisymmetric limit to constrain the mass components in NGC 1453. The best-fit black hole mass is ; the mass models without a central black hole are excluded at the 8.7σ level. The NGC 1453 black hole lies within the intrinsic scatter of the SMBH and galaxy scaling relations, unlike three other galaxies hosting SMBHs in the MASSIVE sample. The high-S/N GMOS spectra enable us to determine eight moments of the Gauss–Hermite expansion of the line-of-sight velocity distributions (LOSVDs), which are used as constraints in the orbit modeling. The stellar orbits in the mass models are further constrained to produce negligible h 9 through h 12 to minimize spurious behavior in the LOSVDs. We show that truncating the series at h 4, as was often done in prior work, leads to a much weaker constraint on the inferred for NGC 1453. Furthermore, we discuss precautions and modifications that are needed to achieve axisymmetry in triaxial orbit codes that use the Schwarzschild method to sample the start space of stellar orbits in triaxial gravitational potentials.

HALO7D I. The Line-of-sight Velocities of Distant Main-sequence Stars in the Milky Way Halo

Abstract The Halo Assembly in Lambda-CDM: Observations in 7 Dimensions (HALO7D) data set consists of Keck II/DEIMOS spectroscopy and Hubble Space Telescope–measured proper motions of Milky Way halo main-sequence turnoff stars in the CANDELS fields. In this paper, we present the spectroscopic component of this data set and discuss target selection, observing strategy, and survey properties. We present a new method of measuring line-of-sight (LOS) velocities by combining multiple spectroscopic observations of a given star, utilizing Bayesian hierarchical modeling. We present the LOS velocity distributions of the four HALO7D fields and estimate their means and dispersions. All of the LOS distributions are dominated by the “hot halo”: none of our fields are dominated by substructure that is kinematically cold in the LOS velocity component. Our estimates of the LOS velocity dispersions are consistent across the different fields, and these estimates are consistent with studies using other types of tracers. To complement our observations, we perform mock HALO7D surveys using the synthetic survey software Galaxia to “observe” the Bullock & Johnston accreted stellar halos. Based on these simulated data sets, the consistent LOS velocity distributions across the four HALO7D fields indicate that the HALO7D sample is dominated by stars from the same massive (or few relatively massive) accretion event(s).

Kinematics of the outer halo of M 87 as mapped by planetary nebulae

Aims. We present a kinematic study of a sample of 298 planetary nebulas (PNs) in the outer halo of the central Virgo galaxy M 87 (NGC 4486). The line-of-sight velocities of these PNs are used to identify subcomponents, to measure the angular momentum content of the main M 87 halo, and to constrain the orbital distribution of the stars at these large radii. Methods. We use Gaussian mixture modelling to statistically separate distinct velocity components and identify the M 87 smooth halo component, its unrelaxed substructures, and the intra-cluster (IC) PNs. We compute probability weighted velocity and velocity dispersion maps for the smooth halo, and its specific angular momentum profile (λR) and velocity dispersion profile. Results. The classification of the PNs into smooth halo and ICPNs is supported by their different PN luminosity functions. Based on a Kolmogorov–Smirnov (K–S) test, we conclude that the ICPN line-of-sight velocity distribution (LOSVD) is consistent with the LOSVD of the galaxies in Virgo subcluster A. The surface density profile of the ICPNS at 100 kpc radii has a shallow logarithmic slope, −αICL ≃ −0.8, dominating the light at the largest radii. Previous B − V colour and resolved star metallicity data indicate masses for the ICPN progenitor galaxies of a few ×108 M⊙. The angular momentum-related λR profile for the smooth halo remains below 0.1, in the slow rotator regime, out to 135 kpc average ellipse radius (170 kpc major axis distance). Combining the PN velocity dispersion measurements for the M 87 halo with literature data in the central 15 kpc, we obtain a complete velocity dispersion profile out to Ravg = 135 kpc. The σhalo profile decreases from the central 400 km s−1 to about 270 km s−1 at 2–10 kpc, then rises again to ≃300 ± 50 km s−1 at 50–70 kpc, to finally decrease sharply to σhalo ∼ 100 km s−1 at Ravg = 135 kpc. The steeply decreasing outer σhalo profile and the surface density profile of the smooth halo can be reconciled with the circular velocity curve inferred from assuming hydrostatic equilibrium for the hot X-ray gas. Because this rises to νc,X ∼ km s−1 at 200 kpc, the orbit distribution of the smooth M 87 halo is required to change strongly from approximately isotropic within Ravg ∼ 60 kpc to very radially anisotropic at the largest distances probed. Conclusions. The extended LOSVD of the PNs in the M 87 halo allows the identification of several subcomponents: the ICPNs, the “crown” accretion event, and the smooth M 87 halo. In galaxies like M 87, the presence of these subcomponents needs to be taken into account to avoid systematic biases in estimating the total enclosed mass. The dynamical structure inferred from the velocity dispersion profile indicates that the smooth halo of M 87 steepens beyond Ravg = 60 kpc and becomes strongly radially anisotropic, and that the velocity dispersion profile is consistent with the X-ray circular velocity curve at these radii without non-thermal pressure effects.

Shape of LOSVDs in Barred Disks: Implications for Future IFU Surveys

Abstract The shape of line-of-sight velocity distributions (LOSVDs) carries important information about the internal dynamics of galaxies. The skewness of LOSVDs represents their asymmetric deviation from a Gaussian profile. Correlations between the skewness parameter (h 3) and the mean velocity ( ) of a Gauss–Hermite series reflect the underlying stellar orbital configurations of different morphological components. Using two self-consistent N-body simulations of disk galaxies with different bar strengths, we investigate correlations at different inclination angles. Similar to previous studies, we find anticorrelations in the disk area, and positive correlations in the bar area when viewed edge-on. However, at intermediate inclinations, the outer parts of bars exhibit anticorrelations, while the core areas dominated by the boxy/peanut-shaped (B/PS) bulges still maintain weak positive correlations. When viewed edge-on, particles in the foreground/background disk (the wing region) in the bar area constitute the main velocity peak, whereas the particles in the bar contribute to the high-velocity tail, generating the correlation. If we remove the wing particles, the LOSVDs of the particles in the outer part of the bar only exhibit a low-velocity tail, resulting in a negative correlation, whereas the core areas in the central region still show weakly positive correlations. We discuss implications for IFU observations on bars, and show that the variation of the correlation in the disk galaxy may be used as a kinematic indicator of the bar and the B/PS bulge.

Sloshing in its cD halo: MUSE kinematics of the central galaxy NGC 3311 in the Hydra I cluster

Context.Early-type galaxies (ETGs) show a strong size evolution with redshift. This evolution is explained by fast “in-situ” star formation at high-zfollowed by a late mass assembly mostly driven by minor mergers that deposit stars primarily in the outer halo.Aims.We aim to identify the main structural components of the Hydra I cD galaxy NGC 3311 to investigate the connection between the central galaxy and the surrounding stellar halo.Methods.We produce maps of the line-of-sight velocity distribution (LOSVD) moments from a mosaic of MUSE pointings covering NGC 3311 out to 25 kpc. Combining deep photometric and spectroscopic data, we model the LOSVD maps using a finite mixture distribution, including four non-concentric components that are nearly isothermal spheroids, with different line-of-sight systemic velocitiesV, velocity dispersionsσ, and small (constant) values of the higher order Gauss-Hermite momentsh3andh4.Results.The kinemetry analysis indicates that NGC 3311 is classified as a slow rotator, although the galaxy shows a line-of-sight velocity gradient along the photometric major axis. The comparison of the correlations betweenh3andh4withV/σwith simulated galaxies indicates that NGC 3311 assembled mainly through dry mergers. Theσprofile rises to ≃ 400 km s-1at 20 kpc, a significant fraction (0.55) of the Hydra I cluster velocity dispersion, indicating that stars there were stripped from progenitors orbiting in the cluster core. The finite mixture distribution modeling supports three inner components related to the central galaxy and a fourth component with large effective radius (51 kpc) and velocity dispersion (327 km s-1) consistent with a cD envelope. We find that the cD envelope is offset from the center of NGC 3311 both spatially (8.6 kpc) and in velocity (ΔV= 204 km s-1), but coincides with the cluster core X-ray isophotes and the mean velocity of core galaxies. Also, the envelope contributes to the broad wings of the LOSVD measured by largeh4values within 10 kpc.Conclusions.The cD envelope of NGC 3311 is dynamically associated with the cluster core, which in Hydra I is in addition displaced from the cluster center, presumably due to a recent subcluster merger.

Predicted stellar kinematics of a kiloparsec-scale nuclear disc (or ring) in the Milky Way

In Debattista et al. (2015), we proposed that a kiloparsec-scale nuclear disc is responsible for the high-velocity secondary peak in the stellar line-of-sight velocity distributions (LOSVDs) seen at positive longitudes in the bulge by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Here, we make further qualitative but distinctive predictions of the kinematic properties of a nuclear disc, including for the LOSVDs at negative longitudes (which APOGEE-2 will observe) and examine the proper motions throughout the disc. Since a nuclear ring is also able to produce similar high-velocity LOSVD peaks, we present predictions for the proper motion signatures which distinguish between a nuclear disc and a nuclear ring. We also demonstrate that the stars in a nuclear disc, which would be on x2 orbits perpendicular to the bar, can remain on these orbits for a long time and can therefore be old. We show that such (old) nuclear discs of comparable size exist in external galaxies.

The Extended Baryonic Halo of NGC 3923

Galaxy halos and their globular cluster systems build up over time by the accretion of small satellites. We can learn about this process in detail by observing systems with ongoing accretion events and comparing the data with simulations. Elliptical shell galaxies are systems that are thought to be due to ongoing or recent minor mergers. We present preliminary results of an investigation of the baryonic halo—light profile, globular clusters, and shells/streams—of the shell galaxy NGC 3923 from deep Dark Energy Camera (DECam) g and i-band imaging. We present the 2D and radial distributions of the globular cluster candidates out to a projected radius of about 185 kpc, or ∼ 37 R e , making this one of the most extended cluster systems studied. The total number of clusters implies a halo mass of M h ∼ 3 × 10 13 M ⊙ . Previous studies had identified between 22 and 42 shells, making NGC 3923 the system with the largest number of shells. We identify 23 strong shells and 11 that are uncertain. Future work will measure the halo mass and mass profile from the radial distributions of the shell, N-body models, and line-of-sight velocity distribution (LOSVD) measurements of the shells using the Multi Unit Spectroscopic Explorer (MUSE).

Increase in the Amplitude of Line-of-sight Velocities of the Small-scale Motions in a Solar Filament before Eruption

Abstract We present a study on the evolution of the small-scale velocity field in a solar filament as it approaches the eruption. The observation was carried out by the Solar Dynamics Doppler Imager (SDDI) that was newly installed on the Solar Magnetic Activity Research Telescope at Hida Observatory. The SDDI obtains a narrowband full-disk image of the Sun at 73 channels from Hα − 9.0 Å to Hα + 9.0 Å, allowing us to study the line-of-sight (LOS) velocity of the filament before and during the eruption. The observed filament is a quiescent filament that erupted on 2016 November 5. We derived the LOS velocity at each pixel in the filament using the Becker’s cloud model, and made the histograms of the LOS velocity at each time. The standard deviation of the LOS velocity distribution can be regarded as a measure for the amplitude of the small-scale motion in the filament. We found that the standard deviation on the previous day of the eruption was mostly constant around 2–3 km s−1, and it slightly increased to 3–4 km s−1 on the day of the eruption. It shows a further increase, with a rate of 1.1 m s−2, about three hours before eruption, and another increase, with a rate of 2.8 m s−2, about an hour before eruption. From this result we suggest that the increase in the amplitude of the small-scale motions in a filament can be regarded as a precursor of the eruption.