Publications by Michele Cappellari

The Kinematics of Core and Cusp Galaxies: Comparing HST Imaging and Integral-Field Observations


J Falcon-Barroso, R Bacon, M Cappellari, RL Davies, PT de Zeeuw, E Emsellem, D Krajnovic, H Kuntschner, RM McDermid, RF Peletier, M Sarzi, G van de Yen

Measuring the Low Mass End of the M center dot - sigma Relation


D Krajnovic, RM McDermid, M Cappellari, RL Davies

Formation of slowly rotating elliptical galaxies in major mergers. A resolution study

AIP Conference Proceedings 1240 (2010) 405-406

M Bois, F Bournaud, E Emsellem, K Alatalo, L Blitz, M Bureau, M Cappellari, RL Davies, TA Davis, PT De Zeeuw, J Falcón-Barroso, S Khochfar, D Krajnović, H Kuntschner, PY Lablanche, RM McDermid, R Morganti, T Naab, M Sarzi, N Scott, P Serra, RCE Van Den Bosch, G Van De Ven, A Weijmans, LM Young

We study resolution effects in numerical simulations of gas-rich (20% of the total baryonic mass) major mergers, and show that the formation of slowly-rotating elliptical galaxies requires a resolution that is beyond the present-day standards to be properly modelled. Our findings show that a high-enough resolution is required to accurately model the global properties of merger remnants and the evolution of their angular momentum. The role of wet mergers of spiral galaxies in the formation of slow-rotating ellipticals may therefore have been underestimated. © 2010 American Institute of Physics.

Searching for the Supermassive Black Hole in NGC 1265 (3C 83.1B)


A Beifiori, M Sarzi, RL Davies, M Cappellari, RCW Houghton

Early-type Galaxies in Isolation: an H I Perspective with ATLAS(3D)


P Serra, R Morganti, TA Oosterloo, K Alatalo, L Blitz, M Bois, RCE van den Bosch, F Bournaud, M Bureau, M Cappellari, RL Davies, TA Davis, P Duc, E Emsellem, J Falcon-Barroso, S Khochfar, D Krajnovic, H Kuntschner, PY Lablanche, RM McDermid, T Naab, M Sarzi, N Scott, G van de Ven, A Weijmans, LM Young, PT de Zeeuw

The NGC 404 nucleus: Star cluster and possible intermediate-mass black hole

Astrophysical Journal 714 (2010) 713-731

AC Seth, M Cappellari, N Neumayer, N Caldwell, N Bastian, K Olsen, RD Blum, VP Debattista, R McDermid, T Puzia, A Stephens

We examine the nuclear morphology, kinematics, and stellar populations in nearby S0 galaxy NGC 404 using a combination of adaptive optics assisted near-IR integral-field spectroscopy, optical spectroscopy, and Hubble Space Telescope imaging. These observations enable study of the NGC 404 nucleus at a level of detail possible only in the nearest galaxies. The surface brightness profile suggests the presence of three components: a bulge, a nuclear star cluster (NSC), and a central light excess within the cluster at radii < 3 pc. These components have distinct kinematics with modest rotation seen in the NSC and counter-rotation seen in the central excess. Molecular hydrogen emission traces a disk with rotation nearly orthogonal to that of the stars. The stellar populations of the three components are also distinct, with half of the mass of the NSC having ages of ∼ 1 Gyr (perhaps resulting from a galaxy merger), while the bulge is dominated by much older stars. Dynamical modeling of the stellar kinematics gives a total NSC mass of 1.1 × 107 M ⊙. Dynamical detection of a possible intermediate-mass black hole (BH) is hindered by uncertainties in the central stellar mass profile. Assuming a constant mass-to-light ratio, the stellar dynamical modeling suggests a BH mass of <1 × 105 M ⊙, while the molecular hydrogen gas kinematics are best fitted by a BH with a mass of 4.5+3.5-2.0 × 105 M ⊙. Unresolved and possibly variable dust emission in the near-infrared and active galactic nucleus-like molecular hydrogen emission-line ratios do suggest the presence of an accreting BH in this nearby LINER galaxy. © 2010. The American Astronomical Society. All rights reserved.

Lenticular vs spiral galaxies: dark matter content and the Tully-Fisher relation


M Bureau, MJ Williams, M Cappellari

Determination of masses of the central black holes in NGC 524 and 2549 using laser guide star adaptive optics

Monthly Notices of the Royal Astronomical Society 399 (2009) 1839-1857

D Krajnović, RM McDermid, M Cappellari, RL Davies

We present observations of early-type galaxies NGC 524 and 2549 with laser guide star adaptive optics (LGS AO) obtained at GEMINI North telescope using the Near-infrared Integral Field Spectrograph (NIFS) integral field unit (IFU) in the K band. The purpose of these observations is to determine high spatial resolution stellar kinematics within the nuclei of these galaxies and, in combination with previously obtained large-scale observations with the SAURON IFU, to determine the masses (M•) of the supermassive black holes (SMBH). The targeted galaxies were chosen to have central light profiles showing a core (NGC 524) and a cusp (NGC 2549), to probe the feasibility of using the galaxy centre as the natural guide source required for LGS AO. We employ an innovative technique where the focus compensation due to the changing distance to the sodium layer is made 'open loop', allowing the extended galaxy nucleus to be used only for tip-tilt correction. The data have spatial resolution of 0.23 and 0.17 arcsec full-width at half maximum (FWHM), where at least ∼40 per cent of flux comes within 0.2, showing that high quality LGS AO observations of these objects are possible. The achieved signal-to-noise ratio (S/N ∼ 50) is sufficiently high to reliably determine the shape of the line-of-sight velocity distribution. We construct axisymmetric three-integral dynamical models which are constrained with both the NIFS and SAURON data. The best-fitting models yield M• = (8.3+2.7-1.3) × 108 M⊙ and (M/L)I = 5.8 ± 0.4 for NGC 524 and M• = (1.4 +0.2-1.3) × 107 M⊙ and (M/L)R = 4.7 ± 0.2 for NGC 2549 (all errors are at the 3σ level). We demonstrate that the wide-field SAURON data play a crucial role in the M/L determination increasing the accuracy of M/L by a factor of at least 5, and constraining the upper limits on black hole masses. The NIFS data are crucial in constraining the lower limits of M• and in combination with the large-scale data reducing the uncertainty by a factor of 2 or more. We find that the orbital structure of NGC 524 shows significant tangential anisotropy, while at larger radii both galaxies are consistent with having almost perfectly oblate velocity ellipsoids. Tangential anisotropy in NGC 524 coincides with the size of SMBH sphere of influence and the core region in the light profile. This agrees with predictions from numerical simulations where core profiles are the result of SMBH binaries evacuating the centre nuclear regions following a galaxy merger. However, being a disc dominated fast rotating galaxy, NGC 524 has probably undergone through a more complex evolution. We test the accuracy to which M• can be measured using seeings obtained from typical LGS AO observations, and conclude that for a typical conditions and M• the expected uncertainty is of the order of 50 per cent. © 2009 RAS.



M Cappellari, SDS Alighieri, A Cimatti, E Daddi, A Renzini, JD Kurk, P Cassata, M Dickinson, A Franceschini, M Mignoli, L Pozzetti, G Rodighiero, P Rosati, G Zamorani

The mass of the black hole in Centaurus A from SINFONI AO-assisted integral-field observations of stellar kinematics

Monthly Notices of the Royal Astronomical Society 394 (2009) 660-674

M Cappellari, N Neumayer, J Reunanen, PP Van Der Werf, PT De Zeeuw, HW Rix

We present a determination of the mass of the supermassive black hole (BH) and the nuclear stellar orbital distribution of the elliptical galaxy Centaurus A (Cen A) (NGC 5128) using high-resolution integral-field observations of the stellar kinematics. The observations were obtained with SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared) at the European Southern Observatory Very Large Telescope in the near-infrared (IR) (K band), using adaptive optics (AO) to correct for the blurring effect of the Earth's atmosphere. The data have a spatial resolution of 0.17 arcsec full width at half-maximum and high signal-to-noise ratios (S/N) ≳ 80 per spectral pixel so that the shape of the stellar line-of-sight velocity distribution can be reliably extracted. We detect clear low-level stellar rotation, which is counter-rotating with respect to the gas. We fit axisymmetric three-integral dynamical models to the data to determine the best-fitting values for the BH mass M BH = (5.5 ± 3.0) × 10 7 M ⊙ (3σ errors) and (M/L) K = (0.65 ± 0.15) in solar units. These values are in excellent agreement with previous determinations from the gas kinematics, and in particular with our own published value, extracted from the same data. This provides one of the cleanest gas versus stars comparisons of M BH determination, due to the use of integral-field data for both dynamical tracers and due to a very well-resolved BH sphere of influence R BH ≈ 0.70 arcsec. We derive an accurate profile of the orbital anisotropy, and carefully test its reliability using spherical Jeans models with radially varying anisotropy. We find an increase in the tangential anisotropy close to the BH, but the spatial extent of this effect seems restricted to the size of R BH instead of that of R b ≈ 3.9 arcsec of the core in the surface brightness profile, contrary to detailed predictions of current simulations of the binary BH scouring mechanism. More realistic simulations would be required to draw conclusions from this observation. © 2009 RAS.

Dynamical masses of early-type galaxies at z ∼ 2: Are they truly superdense?

Astrophysical Journal 704 (2009)

M Cappellari, S Di Serego Alighieri, A Cimatti, E Daddi, A Renzini, JD Kurk, P Cassata, M Dickinson, A Franceschini, M Mignoli, L Pozzetti, G Rodighiero, P Rosati, G Zamorani

We measured stellar velocity dispersions σ and derived dynamical masses of nine massive (M ≈ 1011 M ⊙) early-type galaxies (ETGs) from the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample at redshift 1.4 ≲ z ≲ 2.0. The σ are based on individual spectra for two galaxies at z ≈ 1.4 and on a stacked spectrum for seven galaxies with 1.6 < z < 2.0, with 202 hr of exposure at the ESO Very Large Telescope. We constructed detailed axisymmetric dynamical models for the objects, based on the Jeans equations, taking the observed surface brightness (from deep HST/ACS observations), point-spread function, and slit effects into account. Our dynamical masses M Jeans agree within ≲30% with virial estimates M vir = 5 × Reσ2/ G, although the latter tend to be smaller. Our M Jeans also agrees within a factor ≲2 with the M pop previously derived using stellar population models and 11 bands photometry. This confirms that the galaxies are intrinsically massive. The inferred mass-to-light ratios (M/L) U in the very age-sensitive rest-frame U band are consistent with passive evolution in the past 1 Gyr (formation redshift zf ∼3). A "bottom-light" stellar initial mass function appears to be required to ensure close agreement between M Jeans and M pop at z ∼2, as it does at z ∼0. The GMASS ETGs are on average more dense than their local counterpart. However, a few percent of local ETGs of similar dynamical masses also have comparable σ and mass surface density Σ50 inside R e. © 2009. The American Astronomical Society. All rights reserved.

The SAURON Project - XIV. No escape from V<inf>esc</inf>: A global and local parameter in early-type galaxy evolution

Monthly Notices of the Royal Astronomical Society 398 (2009) 1835-1857

N Scott, M Cappellari, RL Davies, R Bacon, PT De Zeeuw, E Emsellem, J Falcón-Barroso, D Krajnović, H Kuntschner, RM McDermid, RF Peletier, A Pipino, M Sarzi, RCE Van Den Bosch, G Van De Ven, E Van Scherpenzeel

We present the results of an investigation of the local escape velocity (Vesc) - line strength index relationship for 48 early-type galaxies from the SAURON sample, the first such study based on a large sample of galaxies with both detailed integral field observations and extensive dynamical modelling. Values of Vesc are computed using multi-Gaussian expansion (MGE) photometric fitting and axisymmetric, anisotropic Jeans' dynamical modelling simultaneously on Hubble Space Telescope and ground-based images. We determine line strengths and escape velocities at multiple radii within each galaxy, allowing an investigation of the correlation within individual galaxies as well as amongst galaxies. We find a tight correlation between Vesc and the line-strength indices. For Mgb, we find that this correlation exists not only between different galaxies but also inside individual galaxies - it is both a local and global correlation. The Mgb-Vesc relation has the form: log(Mgb/4 Å) = (0.32 ± 0.03) log(Vesc/500 km s-1) - (0.031 ± 0.007) with an rms scatter σ = 0.033. The relation within individual galaxies has the same slope and offset as the global relation to a good level of agreement, though there is significant intrinsic scatter in the local gradients. We transform our line strength index measurements to the single stellar population (SSP) equivalent ages (t), metallicity ([Z/H]) and enhancement ([α/Fe]) and carry out a principal component analysis of our SSP and Vesc data. We find that in this four-dimensional parameter space the galaxies in our sample are to a good approximation confined to a plane, given by log (V esc/500 km s -1) = 0.85 [Z/H] + 0.43 log (t/Gyr) - 0.29. It is surprising that a combination of age and metallicity is conserved; this may indicate a 'conspiracy' between age and metallicity or a weakness in the SSP models. How the connection between stellar populations and the gravitational potential, both locally and globally, is preserved as galaxies assemble hierarchically may provide an important constraint on modelling. © 2009 RAS.

Stellar populations of early-type galaxies in the ATLAS<sup>3D</sup> sample

AIP Conference Proceedings 1111 (2009) 111-114

P Serra, RM McDermid, K Alatalo, L Blitz, M Bois, F Bournaud, M Bureau, M Cappellari, RL Davies, TA Davis, PT De Zeeuw, E Emsellem, J Falcón-Barroso, S Khochfar, D Krajnović, H Kuntschner, PY Lablanche, R Morganti, T Naab, M Sarzi, N Scott, RCE Van Den Bosch, G Van De Ven, A Weijmans, LM Young

ATLAS3D is a multi-wavelength, volume-limited survey of 263 morphologicallyselected early-type galaxies within a distance of 42 Mpc and complete to MK ≤ -21.5. Here we present the ATLAS3D project and our first results on the stellar populations of galaxies in the ATLAS3Dsample based on SAURON integral-field spectroscopy. We show relations between integrated line-strength indices and stellar velocity dispersion o in the range 55 ≤ Σ(km/s) ≤ 350. We derive simple-stellar-population-equivalent age, metallicity and α/Fe abundance ratio and discuss their relation to stellar velocity dispersion, environment and galaxy internal kinematics. These preliminary results indicate that slow rotators tend to be older and have less variation in age than fast rotators. We also find that galaxies in lower density environments are on average younger than those in denser environments, as found by other authors. © 2009 American Institute of Physics.

The SAURON project - XIII. SAURON-GALEX study of early-type galaxies: The ultraviolet colour-magnitude relations and Fundamental Planes

Monthly Notices of the Royal Astronomical Society 398 (2009) 2028-2048

H Jeong, SK Yi, M Bureau, RL Davies, J Falcón-Barroso, G Van De Ven, RF Peletier, R Bacon, M Cappellari, T De Zeeuw, E Emsellem, D Krajnović, H Kuntschner, RM McDermid, M Sarzi, RCE Van Den Bosch

We present Galaxy Evolution Explorer far-ultraviolet (FUV) and near-ultraviolet (NUV) imaging of 34 nearby early-type galaxies from the SAURON representative sample of 48 E/S0 galaxies, all of which have ground-based optical imaging from the MDM Observatory. The surface brightness profiles of nine galaxies (≈26 per cent) show regions with blue UV-optical colours suggesting RSF. Five of these (≈15 per cent) show blue integrated UV-optical colours that set them aside in the NUV integrated colour-magnitude relation. These are objects with either exceptionally intense and localized NUV fluxes or blue UV-optical colours throughout. They also have other properties confirming they have had RSF, in particular Hβ absorption higher than expected for a quiescent population and a higher CO detection rate. This suggests that residual star formation is more common in early-type galaxies than we are used to believe. NUV blue galaxies are generally drawn from the lower stellar velocity dispersion (σe < 200 km s-1) and thus lower dynamical mass part of the sample. We have also constructed the first UV Fundamental Planes and show that NUV blue galaxies bias the slopes and increase the scatters. If they are eliminated, the fits get closer to expectations from the virial theorem. Although our analysis is based on a limited sample, it seems that a dominant fraction of the tilt and scatter of the UV Fundamental Planes is due to the presence of young stars in preferentially low-mass early-type galaxies. Interestingly, the UV-optical radial colour profiles reveal a variety of behaviours, with many galaxies showing signs of RSF, a central UV-upturn phenomenon, smooth but large-scale age and metallicity gradients and in many cases a combination of these. In addition, FUV-NUV and FUV-V colours even bluer than those normally associated with UV-upturn galaxies are observed at the centre of some quiescent galaxies. Four out of the five UV-upturn galaxies are slow rotators. These objects should thus pose interesting challenges to stellar evolutionary models of the UV upturn. © 2009 RAS.

Kinematic constraints on the stellar and dark matter content of spiral and S0 galaxies

Monthly Notices of the Royal Astronomical Society 400 (2009) 1665-1689

MJ Williams, M Bureau, M Cappellari

We present mass models of a sample of 14 spiral and 14 S0 galaxies that constrain their stellar and dark matter content. For each galaxy, we derive the stellar mass distribution from near-infrared photometry under the assumptions of axisymmetry and a constant KS-band stellar mass-to-light ratio. To this we add a dark halo assumed to follow a spherically symmetric Navarro, Frenk and White profile and a correlation between concentration and dark mass within the virial radius, MDM. We solve the Jeans equations for the corresponding potential under the assumption of constant anisotropy in the meridional plane, βz. By comparing the predicted second velocity moment to observed long-slit stellar kinematics, we determine the three best-fitting parameters of the model: and βz. These simple axisymmetric Jeans models are able to accurately reproduce the wide range of observed stellar kinematics, which typically extend to ≈2-3Re or, equivalently, ≈0.5-1R25. Although our sample contains barred galaxies, we argue a posteriori that the assumption of axisymmetry does not significantly bias our results. We find a median stellar mass-to-light ratio at KS-band of with an rms scatter of 0.31. We present preliminary comparisons between this large sample of dynamically determined stellar mass-to-light ratios and the predictions of stellar population models. The stellar population models predict slightly lower mass-to-light ratios than we measure. The mass models contain a median of 15 per cent dark matter by mass within an effective radius Re (defined here as the semimajor axis of the ellipse containing half the KS-band light) and 49 per cent within the optical radius R25. Dark and stellar matter contribute equally to the mass within a sphere of radius 4.1Re or 1.0 R25. There is no evidence of any significant difference in the dark matter content of the spirals and S0s in our sample. Models without dark matter are also able to satisfactorily reproduce the observed kinematics in most cases. The improvement when a halo is added is statistically significant, however, and the stellar mass-to-light ratios of mass models with dark haloes match the independent expectations of stellar population models better. © 2009 RAS.

Galactic Bulges: the SAURON Perspective


J Falcon-Barroso, RF Peletier, R Bacon, M Cappellari, RL Davies, PT de Zeeuw, E Emsellem, D Krajnovic, H Kuntschner, RM McDermid, M Sarzi, RCE van den Bosch, G van de Ven

Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and 821

Monthly Notices of the Royal Astronomical Society 398 (2009) 561-574

AM Weijmans, M Cappellari, R Bacon, PT De Zeeuw, E Emsellem, J Falcón-Barroso, H Kuntschner, RM McDermid, RCE Van Den Bosch, G Van De Ven

We use the integral-field spectrograph SAURON to measure the stellar line-of-sight velocity distribution and absorption line strengths out to four effective radii (Re) in the early-type galaxies NGC 3379 and 821. With our newly developed observing technique, we can now probe these faint regions in galaxies that were previously not accessible with traditional long-slit spectroscopy. We make optimal use of the large field-of-view and high throughput of the spectrograph: by adding the signal of all ∼1400 lenslets into one spectrum, we obtain sufficient signal-to-noise in a few hours of observing time to reliably measure the absorption line kinematics and line strengths out to large radius. We find that the line strength gradients previously observed within 1 Re remain constant out to at least 4 Re, which puts constraints on the merger histories of these galaxies. The stellar halo populations are old and metal poor. By constructing orbit-based Schwarzschild dynamical models, we find that dark matter is necessary to explain the observed kinematics in NGC 3379 and 821, with 30-50 per cent of the total matter being dark within 4 Re. The radial anisotropy in our best-fitting halo models is less than in our models without halo, due to differences in orbital structure. The halo also has an effect on the Mg b-Vesc relation: its slope is steeper when a dark matter halo is added to the model. © 2009 RAS.

A Shared Tully-Fisher Relation for Spirals and S0 Galaxies


MJ Williams, M Bureau, M Cappellari

Stellar Velocity Profiles and Line-Strengths out to Four Effective Radii in the Early-Type Galaxy NGC 3379


A Weijmans, M Cappellari, PT de Zeeuw, E Emsellem, J Falcon-Barroso, H Kuntschner, RM McDermid, RCE van den Bosch, G van de Ven

Specific angular momentum of disc merger remnants and the λ<inf>r</inf>-parameter

Monthly Notices of the Royal Astronomical Society 397 (2009) 1202-1214

R Jesseit, M Cappellari, T Naab, E Emsellem, A Burkert

We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the λR-parameter, which is a luminosity-weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early-type galaxies in so-called fast λR > 0.1 and slow rotators λR < 0.1. Tests on merger remnants reveal that λR is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of λR values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in transforming fast rotators into slow rotators in a single binary merger, the latter being created mostly in an equal-mass merger. Slow rotators have a λR which does not vary with projection. The confusion rate with face-on fast rotators is very small. Mergers with a gas component form slow rotators with smaller ellipticities than collisionless merger remnants have, and are in much better agreement with the SAURON slow rotators. Remergers of merger remnants are slow rotators, but tend to have too high ellipticities. Fast rotators maintain the angular momentum content from the progenitor disc galaxy if merger mass ratio is high. Some SAURON galaxies have values of λR as high as our progenitor disc galaxies. © 2009 RAS.