arXiv subjects

Jens Thomas

Publications and source records attributed to Jens Thomas.

At least 37 records · Page 2Linked to original sources

arXiv2021

The two phases of core formation -- orbital evolution in the centres of ellipticals with supermassive black hole binaries

The flat stellar density cores of massive elliptical galaxies form rapidly due to sinking supermassive black holes (SMBH) in gas-poor galaxy mergers. After the SMBHs form a bound binary, gravitational slingshot interactions with nearby stars drive the core regions towards a tangentially biased stellar velocity distribution. We use collisionless galaxy merger simulations with accurate collisional orbit integration around the central SMBHs to demonstrate that the removal of stars from the centre by slingshot kicks accounts for the entire change in velocity anisotropy. The rate of strong (unbinding) kicks is constant over several hundred Myr at $\sim 3 \ M_\odot \rm yr^{-1}$ for our most massive SMBH binary ($M_{\rm BH} = 1.7 \times 10^{10} M_\odot$). Using a frequency-based orbit classification scheme (box, x-tube, z-tube, rosette) we demonstrate that slingshot kicks mostly affect box orbits with small pericentre distances, leading to a velocity anisotropy of $β\lesssim -0.6$ within several hundred Myr as observed in massive ellipticals with large cores. We show how different SMBH masses affect the orbital structure of the merger remnants and present a kinematic tomography connecting orbit families to integral field kinematic features. Our direct orbit classification agrees remarkably well with a modern triaxial Schwarzschild analysis applied to simulated mock kinematic maps.

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arXiv2021

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

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 regularisation directly from the data. Altogether, this leads to a significant improvement of the constraining power of the modeling technique. We show with simulations that one can reconstruct the mass, anisotropy and viewing angle of an axisymmetric galaxy with a few percent 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 disk galaxy NGC 3368 to within 5 degree 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.

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arXiv2021

Composite Bulges -- II. Classical Bulges and Nuclear Discs in Barred Galaxies: The Contrasting Cases of NGC 4608 and NGC 4643

We present detailed morphological, photometric, and stellar-kinematic analyses of the central regions of two massive, early-type barred galaxies with nearly identical large-scale morphologies. Both have large, strong bars with prominent inner photometric excesses that we associate with boxy/peanut-shaped (B/P) bulges; the latter constitute ~ 30% of the galaxy light. Inside its B/P bulge, NGC 4608 has a compact, almost circular structure (half-light radius R_e approx. 310 pc, Sérsic n = 2.2) we identify as a classical bulge, amounting to 12.1% of the total light, along with a nuclear star cluster (R_e ~ 4 pc). NGC 4643, in contrast, has a nuclear disc with an unusual broken-exponential surface-brightness profile (13.2% of the light), and a very small spheroidal component (R_e approx. 35 pc, n = 1.6; 0.5% of the light). IFU stellar kinematics support this picture, with NGC 4608's classical bulge slowly rotating and dominated by high velocity dispersion, while NGC 4643's nuclear disc shows a drop to lower dispersion, rapid rotation, V-h3 anticorrelation, and elevated h4. Both galaxies show at least some evidence for V-h3 correlation in the bar (outside the respective classical bulge and nuclear disc), in agreement with model predictions. Standard 2-component (bulge/disc) decompositions yield B/T ~ 0.5-0.7 (and bulge n > 2) for both galaxies. This overestimates the true "spheroid" components by factors of four (NGC 4608) and over 100 (NGC 4643), illustrating the perils of naive bulge-disc decompositions applied to massive barred galaxies.

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arXiv2020

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

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 ~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.

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arXiv2020

Non-parametric Triaxial Deprojection of Elliptical Galaxies

We present a grid-based non-parametric approach to obtain a triaxial three-dimensional luminosity density from its surface brightness distribution. Triaxial deprojection is highly degenerate and our approach illustrates the resulting difficulties. Fortunately, for massive elliptical galaxies, many deprojections for a particular line of sight can be discarded, because their projection along other lines of sight does not resemble elliptical galaxies. The near-elliptical isophotes of these objects imply near ellipsoidal intrinsic shapes. In fact, deprojection is unique for densities distributed on ellipsoidal shells. The constrained non-parametric deprojection method we present here relaxes this constraint and assumes that the contours of the luminosity density are boxy/discy ellipsoids with radially varying axis ratios. With this approach we are able to reconstruct the intrinsic triaxial densities of our test models, including one drawn from an $N$-body simulation. The method also allows to compare the relative likelihood of deprojections at different viewing angles. We show that the viewing orientations of individual galaxies with nearly ellipsoidal isophotal shapes can be constrained from photometric data alone.

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arXiv2020

The MASSIVE Survey XIV -- Stellar Velocity Profiles and Kinematic Misalignments from 200 pc to 20 kpc in Massive Early-type Galaxies

We use high spatial resolution stellar velocity maps from the Gemini GMOS integral-field spectrograph (IFS) and wide-field velocity maps from the McDonald Mitchell IFS to study the stellar velocity profiles and kinematic misalignments from $\sim 200$ pc to $\sim 20$ kpc in 20 early-type galaxies with stellar mass $M_* > 10^{11.7} M_\odot$ in the MASSIVE survey. While 80% of the galaxies have low spins ($λ< 0.1$) and low rotational velocities ($< 50$ km/s) in both the central region and the main body, we find a diverse range of velocity features and misalignment angles. For the 18 galaxies with measurable central kinematic axes, 10 have well aligned kinematic axis and photometric major axis, and the other 8 galaxies have misalignment angles that are distributed quite evenly from $15^\circ$ to the maximal value of $90^\circ$. There is a strong correlation between central kinematic misalignment and galaxy spin, where all 4 galaxies with significant spins have well aligned kinematic and photometric axes, but only 43% of the low-spin galaxies are well aligned. The central and main-body kinematic axes within a galaxy are not always aligned. When the two kinematic axes are aligned ($\sim 60$% of the cases), they are either also aligned with the photometric major axis or orthogonal to it. We find 13 galaxies to also exhibit noticeable local kinematic twists, and one galaxy to have a counter-rotating core. A diverse assembly history consisting of multiple gas-poor mergers of a variety of progenitor mass ratios and orbits is likely to be needed to account for the predominance of low spins and the wide range of central and main-body velocity features reported here for local massive ETGs.

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arXiv2019

The MASSIVE Survey XIII -- Spatially Resolved Stellar Kinematics in the Central 1 kpc of 20 Massive Elliptical Galaxies with the GMOS-North Integral-Field Spectrograph

We use observations from the GEMINI-N/GMOS integral-field spectrograph (IFS) to obtain spatially resolved stellar kinematics of the central $\sim 1$ kpc of 20 early-type galaxies (ETGs) with stellar masses greater than $10^{11.7} M_\odot$ in the MASSIVE survey. Together with observations from the wide-field Mitchell IFS at McDonald Observatory in our earlier work, we obtain unprecedentedly detailed kinematic maps of local massive ETGs, covering a scale of $\sim 0.1-30$ kpc. The high ($\sim 120$) signal-to-noise of the GMOS spectra enable us to obtain two-dimensional maps of the line-of-sight velocity, velocity dispersion $σ$, as well as the skewness $h_3$ and kurtosis $h_4$ of the stellar velocity distributions. All but one galaxy in the sample have $σ(R)$ profiles that increase towards the center, whereas the slope of $σ(R)$ at one effective radius ($R_e$) can be of either sign. The $h_4$ is generally positive, with 14 of the 20 galaxies having positive $h_4$ within the GMOS aperture and 18 having positive $h_4$ within $1 R_e$. The positive $h_4$ and rising $σ(R)$ towards small radii are indicative of a central black hole and velocity anisotropy. We demonstrate the constraining power of the data on the mass distributions in ETGs by applying Jeans anisotropic modeling (JAM) to NGC~1453, the most regular fast rotator in the sample. Despite the limitations of JAM, we obtain a clear $χ^2$ minimum in black hole mass, stellar mass-to-light ratio, velocity anisotropy parameters, and the circular velocity of the dark matter halo.

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arXiv2019

The simultaneous formation of cored, tangentially biased, and kinematically decoupled centers in massive early-type galaxies

We study the impact of merging supermassive black holes (SMBHs) on the central regions of massive early-type galaxies (ETGs) using a series of merger simulations with varying mass ratios. The ETG models include realistic stellar and dark matter components and are evolved with the GADGET based regularized tree code KETJU. We show that observed key properties of the nuclear stellar populations of massive ETGs, namely flat stellar density distributions (cores), tangentially biased velocity distributions and kinematically decoupled (counter-)rotation can naturally result from a single process $-$ the scouring by SMBHs. Major mergers with mass ratios of $q>1/3$ produce flat, tangentially biased cores with kinematically distinct components. These features originate from spin reversals during the decay of the SMBH orbits caused by gravitational torques from tidally expelled nuclear material. Minor mergers ($q\lesssim1/3$) on the other hand, form non-rotating cores and the tidal reversal becomes less important. Low-density stellar cores scoured in (multiple) minor mergers are less tangentially biased. This implies that the nuclear stellar properties of massive ETGs can be solely explained by stellar dynamical processes during their final assembly without any need for `feedback' from accreting black holes. We predict a strong correlation between decoupled cores, central anisotropy and merger history: decoupled cores form in binary mergers and we predict them to occur in elliptical galaxies with the strongest central anisotropy. Measurements of the central orbital structure are the key to understanding the number of mergers a given galaxy has experienced.

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arXiv2019

The MASSIVE Survey - XII Connecting Stellar Populations of Early-Type Galaxies to Kinematics and Environment

We measure the stellar populations as a function of radius for 90 early-type galaxies (ETGs) in the MASSIVE survey, a volume-limited integral-field spectroscopic (IFS) galaxy survey targeting all northern-sky ETGs with absolute K-band magnitude M_K < -25.3 mag, or stellar mass M* 4x10^11 M_sun, within 108 Mpc. We are able to measure reliable stellar population parameters for individual galaxies out to 10-20 kpc (1-3 R_e) depending on the galaxy. Focusing on ~R_e (~10 kpc), we find significant correlations between the abundance ratios, sigma, and M* at large radius, but we also find that the abundance ratios saturate in the highest-mass bin. We see a strong correlation between the kurtosis of the line of sight velocity distribution (h4) and the stellar population parameters beyond R_e. Galaxies with higher radial anisotropy appear to be older, with metal-poorer stars and enhanced [alpha/Fe]. We suggest that the higher radial anisotropy may derive from more accretion of small satellites. Finally, we see some evidence for correlations between environmental metrics (measured locally and on >5 Mpc scales) and the stellar populations, as expected if satellites are quenched earlier in denser environments.

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arXiv2018

The formation of extremely diffuse galaxy cores by merging supermassive black holes

Given its velocity dispersion, the early-type galaxy NGC 1600 has an unusually massive ($M_\bullet = 1.7 \times 10^{10} M_\odot$) central supermassive black hole (SMBH), surrounded by a large core ($r_\mathrm{b} = 0.7$ kpc) with a tangentially biased stellar distribution. We present high-resolution equal-mass merger simulations including SMBHs to study the formation of such systems. The structural parameters of the progenitor ellipticals were chosen to produce merger remnants resembling NGC 1600. We test initial stellar density slopes of $ρ\propto r^{-1}$ and $ρ\propto r^{-3/2}$ and vary the initial SMBH masses from $8.5 \times 10^8$ to $8.5 \times 10^9$ $M_\odot$. With increasing SMBH mass the merger remnants show a systematic decrease in central surface brightness, an increasing core size, and an increasingly tangentially biased central velocity anisotropy. Two-dimensional kinematic maps reveal decoupled, rotating core regions for the most massive SMBHs. The stellar cores form rapidly as the SMBHs become bound, while the velocity anisotropy develops more slowly after the SMBH binaries become hard. The simulated merger remnants follow distinct relations between the core radius and the sphere-of-influence, and the SMBH mass, similar to observed systems. We find a systematic change in the relations as a function of the progenitor density slope, and present a simple scouring model reproducing this behavior. Finally, we find the best agreement with NGC 1600 using SMBH masses totaling the observed value of $M_\bullet = 1.7 \times 10^{10} M_\odot$. In general, density slopes of $ρ\propto r^{-3/2}$ for the progenitor galaxies are strongly favored for the equal-mass merger scenario.

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arXiv2018

The MICADO first light imager for the ELT: overview, operation, simulation

MICADO will enable the ELT to perform diffraction limited near-infrared observations at first light. The instrument's capabilities focus on imaging (including astrometric and high contrast) as well as single object spectroscopy. This contribution looks at how requirements from the observing modes have driven the instrument design and functionality. Using examples from specific science cases, and making use of the data simulation tool, an outline is presented of what we can expect the instrument to achieve.

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arXiv2018

The MASSIVE Survey - X. Misalignment between Kinematic and Photometric Axes and Intrinsic Shapes of Massive Early-Type Galaxies

We use spatially resolved two-dimensional stellar velocity maps over a $107"\times 107"$ field of view to investigate the kinematic features of 90 early-type galaxies above stellar mass $10^{11.5}M_\odot$ in the MASSIVE survey. We measure the misalignment angle $Ψ$ between the kinematic and photometric axes and identify local features such as velocity twists and kinematically distinct components. We find 46% of the sample to be well aligned ($Ψ< 15^{\circ}$), 33% misaligned, and 21% without detectable rotation (non-rotators). Only 24% of the sample are fast rotators, the majority of which (91%) are aligned, whereas 57% of the slow rotators are misaligned with a nearly flat distribution of $Ψ$ from $15^{\circ}$ to $90^{\circ}$. 11 galaxies have $Ψ\gtrsim 60^{\circ}$ and thus exhibit minor-axis ("prolate") rotation in which the rotation is preferentially around the photometric major axis. Kinematic misalignments occur more frequently for lower galaxy spin or denser galaxy environments. Using the observed misalignment and ellipticity distributions, we infer the intrinsic shape distribution of our sample and find that MASSIVE slow rotators are consistent with being mildly triaxial, with mean axis ratios of $b/a=0.88$ and $c/a=0.65$. In terms of local kinematic features, 51% of the sample exhibit kinematic twists of larger than $20^{\circ}$, and 2 galaxies have kinematically distinct components. The frequency of misalignment and the broad distribution of $Ψ$ reported here suggest that the most massive early-type galaxies are mildly triaxial, and that formation processes resulting in kinematically misaligned slow rotators such as gas-poor mergers occur frequently in this mass range.

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arXiv2018

The MASSIVE Survey IX: Photometric Analysis of 35 High Mass Early-Type Galaxies with HST WFC3/IR

We present near-infrared observations of 35 of the most massive early-type galaxies in the local universe. The observations were made using the infrared channel of the Hubble Space Telescope Wide Field Camera 3 in the F110W (1.1 $μ$m) filter. We measured surface brightness profiles and elliptical isophotal fit parameters from the nuclear regions out to a radius of ~10 kpc in most cases. We find that 37% (13) of the galaxies in our sample have isophotal position angle rotations greater than 20 degrees over the radial range imaged by WFC3/IR, which is often due to the presence of neighbors or multiple nuclei. Most galaxies in our sample are significantly rounder near the center than in the outer regions. This sample contains six fast rotators and 28 slow rotators. We find that all fast rotators are either disky or show no measurable deviation from purely elliptical isophotes. Among slow rotators, significantly disky and boxy galaxies occur with nearly equal frequency. The galaxies in our sample often exhibit changing isophotal shapes, sometimes showing both significantly disky and boxy isophotes at different radii. The fact that parameters vary widely between galaxies and within individual galaxies is evidence that these massive galaxies have complicated formation histories, and some of them have experienced recent mergers and have not fully relaxed. These data demonstrate the value of high spatial resolution IR imaging of galaxies and provide measurements necessary for determining stellar masses, dynamics, and black hole masses in high mass galaxies.

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arXiv2017

The MASSIVE Survey - VIII. Stellar Velocity Dispersion Profiles and Environmental Dependence of Early-Type Galaxies

We measure the radial profiles of the stellar velocity dispersions, $σ(R)$, for 90 early-type galaxies (ETGs) in the MASSIVE survey, a volume-limited integral-field spectroscopic (IFS) galaxy survey targeting all northern-sky ETGs with absolute $K$-band magnitude $M_K < -25.3$ mag, or stellar mass $M_* > 4 \times 10^{11} M_\odot$, within 108 Mpc. Our wide-field 107" $\times$ 107" IFS data cover radii as large as 40 kpc, for which we quantify separately the inner (2 kpc) and outer (20 kpc) logarithmic slopes $γ_{\rm inner}$ and $γ_{\rm outer}$ of $σ(R)$. While $γ_{\rm inner}$ is mostly negative, of the 56 galaxies with sufficient radial coverage to determine $γ_{\rm outer}$ we find 36% to have rising outer dispersion profiles, 30% to be flat within the uncertainties, and 34% to be falling. The fraction of galaxies with rising outer profiles increases with $M_*$ and in denser galaxy environment, with 10 of the 11 most massive galaxies in our sample having flat or rising dispersion profiles. The strongest environmental correlations are with local density and halo mass, but a weaker correlation with large-scale density also exists. The average $γ_{\rm outer}$ is similar for brightest group galaxies, satellites, and isolated galaxies in our sample. We find a clear positive correlation between the gradients of the outer dispersion profile and the gradients of the velocity kurtosis $h_4$. Altogether, our kinematic results suggest that the increasing fraction of rising dispersion profiles in the most massive ETGs are caused (at least in part) by variations in the total mass profiles rather than in the velocity anisotropy alone.

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arXiv2017

NGC 307 and the Effects of Dark-Matter Haloes on Measuring Supermassive Black Holes in Disc Galaxies

We present stellar-dynamical measurements of the central supermassive black hole (SMBH) in the S0 galaxy NGC 307, using adaptive-optics IFU data from VLT-SINFONI. We investigate the effects of including dark-matter haloes as well as multiple stellar components with different mass-to-light (M/L) ratios in the dynamical modeling. Models with no halo and a single stellar component yield a relatively poor fit with a low value for the SMBH mass ($7.0 \pm 1.0 \times 10^{7} M_{\odot}$) and a high stellar M/L ratio (K-band M/L = $1.3 \pm 0.1$). Adding a halo produces a much better fit, with a significantly larger SMBH mass ($2.0 \pm 0.5 \times 10^{8} M_{\odot}$) and a lower M/L ratio ($1.1 \pm 0.1$). A model with no halo but with separate bulge and disc components produces a similarly good fit, with a slightly larger SMBH mass ($3.0 \pm 0.5 \times 10^{8} M_{\odot}$) and an identical M/L ratio for the bulge component, though the disc M/L ratio is biased high (disc M/L $ = 1.9 \pm 0.1$). Adding a halo to the two-stellar-component model results in a much more plausible disc M/L ratio of $1.0 \pm 0.1$, but has only a modest effect on the SMBH mass ($2.2 \pm 0.6 \times 10^{8} M_{\odot}$) and leaves the bulge M/L ratio unchanged. This suggests that measuring SMBH masses in disc galaxies using just a single stellar component and no halo has the same drawbacks as it does for elliptical galaxies, but also that reasonably accurate SMBH masses and bulge M/L ratios can be recovered (without the added computational expense of modeling haloes) by using separate bulge and disc components.

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arXiv2017

The MASSIVE Survey - VII. The Relationship of Angular Momentum, Stellar Mass and Environment of Early-Type Galaxies

We analyse the environmental properties of 370 local early-type galaxies (ETGs) in the MASSIVE and ATLAS3D surveys, two complementary volume-limited integral-field spectroscopic (IFS) galaxy surveys spanning absolute $K$-band magnitude $-21.5 > M_K > -26.6$, or stellar mass $8 \times 10^{9} < M_* < 2 \times 10^{12} M_\odot$. We find these galaxies to reside in a diverse range of environments measured by four methods: group membership (whether a galaxy is a brightest group/cluster galaxy, satellite, or isolated), halo mass, large-scale mass density (measured over a few Mpc), and local mass density (measured within the $N$th neighbour). The spatially resolved IFS stellar kinematics provide robust measurements of the spin parameter $λ_e$ and enable us to examine the relationship among $λ_e$, $M_*$, and galaxy environment. We find a strong correlation between $λ_e$ and $M_*$, where the average $λ_e$ decreases from $\sim 0.4$ to below 0.1 with increasing mass, and the fraction of slow rotators $f_{\rm slow}$ increases from $\sim 10$% to 90%. We show for the first time that at fixed $M_*$, there are almost no trends between galaxy spin and environment; the apparent kinematic morphology-density relation for ETGs is therefore primarily driven by $M_*$ and is accounted for by the joint correlations between $M_*$ and spin, and between $M_*$ and environment. A possible exception is that the increased $f_{\rm slow}$ at high local density is slightly more than expected based only on these joint correlations. Our results suggest that the physical processes responsible for building up the present-day stellar masses of massive galaxies are also very efficient at reducing their spin, in any environment.

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arXiv2017

The MASSIVE Survey VI: The Spatial Distribution and Kinematics of Warm Ionized Gas in the Most Massive Local Early-type Galaxies

We present the first systematic investigation of the existence, spatial distribution, and kinematics of warm ionized gas as traced by the [O II] 3727AA emission line in 74 of the most massive galaxies in the local Universe. All of our galaxies have deep integral field spectroscopy from the volume- and magnitude-limited MASSIVE survey of early-type galaxies with stellar mass log(M_*/M_sun) > 11.5 (M_K < -25.3 mag) and distance D < 108 Mpc. Of the 74 galaxies in our sample, we detect warm ionized gas in 28, which yields a global detection fraction of 38\pm6% down to a typical [O II] equivalent width limit of 2AA. MASSIVE fast rotators are more likely to have gas than MASSIVE slow rotators with detection fractions of 80\pm10% and 28\pm6%, respectively. The spatial extents span a wide range of radii (0.6 - 18.2 kpc; 0.1 - 4R_e), and the gas morphologies are diverse, with 17/28 = 61\pm9% being centrally concentrated, 8/28 = 29\pm9% exhibiting clear rotation out to several kpc, and 3/28 = 11\pm6% being extended but patchy. Three out of four fast rotators show kinematic alignment between the stars and gas, whereas the two slow rotators with robust kinematic measurements available exhibit kinematic misalignment. Our inferred warm ionized gas masses are roughly ~10^5M_sun. The emission line ratios and radial equivalent width profiles are generally consistent with excitation of the gas by the old underlying stellar population. We explore different gas origin scenarios for MASSIVE galaxies and find that a variety of physical processes are likely at play, including internal gas recycling, cooling out of the hot gaseous halo, and gas acquired via mergers.

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arXiv2016

The MASSIVE Survey - V. Spatially-Resolved Stellar Angular Momentum, Velocity Dispersion, and Higher Moments of the 41 Most Massive Local Early-Type Galaxies

We present spatially-resolved two-dimensional stellar kinematics for the 41 most massive early-type galaxies (MK <~ -25.7 mag, stellar mass M* >~ 10^11.8 Msun) of the volume-limited (D < 108 Mpc) MASSIVE survey. For each galaxy, we obtain high-quality spectra in the wavelength range of 3650 to 5850 A from the 246-fiber Mitchell integral-field spectrograph (IFS) at McDonald Observatory, covering a 107" x 107" field of view (often reaching 2 to 3 effective radii). We measure the 2-D spatial distribution of each galaxy's angular momentum (lambda and fast or slow rotator status), velocity dispersion (sigma), and higher-order non-Gaussian velocity features (Gauss-Hermite moments h3 to h6). Our sample contains a high fraction (~80% ) of slow and non-rotators with lambda <~ 0.2. When combined with the lower-mass ETGs in the ATLAS3D survey, we find the fraction of slow-rotators to increase dramatically with galaxy mass, reaching ~50% at MK ~ -25.5 mag and ~90% at MK <~ -26 mag. All of our fast rotators show a clear anti-correlation between h3 and V/sigma, and the slope of the anti-correlation is steeper in more round galaxies. The radial profiles of sigma show a clear luminosity and environmental dependence: the 12 most luminous galaxies in our sample (MK <~ -26 mag) are all brightest cluster/group galaxies (except NGC 4874) and all have rising or nearly flat sigma profiles, whereas five of the seven "isolated" galaxies are all fainter than MK = -25.8 mag and have falling sigma. All of our galaxies have positive average h4; the most luminous galaxies have average h4 ~ 0.05 while less luminous galaxies have a range of values between 0 and 0.05. Most of our galaxies show positive radial gradients in h4, and those galaxies also tend to have rising sigma profiles. We discuss the implications for the relationship among dynamical mass, sigma, h4, and velocity anisotropy for these massive galaxies.

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