Publications by Michele Cappellari

A Shared Tully-Fisher Relation for Spirals and S0 Galaxies


MJ Williams, M Bureau, M Cappellari

The continuing formation of early-type galaxies: an HI survey

AIP CONF PROC 1035 (2008) 129-131

R Morganti, E Manthey, A Crocker, T Oosterloo, PT de Zeeuw, RM McDermid, D Krajnovic, M Cappellari, A Weijmans, M Sarzi

A deep H I survey of nearby early-type galaxies carried out with the Westerbork Radio Synthesis telescope has shown that, contrary to expectation, neutral hydrogen is a significant constituent of the ISM in this type of objects located in low density environment. The studied galaxies are part of a representative sample of nearby E and SO for which integral-field spectroscopy using the SAURON spectrograph is available. We present preliminary results on the comparison of the characteristics of the H I with those of the molecular and ionised gas as well as the stellar dynamics and population.

Triaxial orbit based galaxy models with an application to the (apparent) decoupled core galaxy NGC 4365

Monthly Notices of the Royal Astronomical Society 385 (2008) 647-666

RCE Van Den Bosch, G Van De Ven, EK Verolme, M Cappellari, PT De Zeeuw

We present a flexible and efficient method to construct triaxial dynamical models of galaxies with a central black hole, using Schwarzschild's orbital superposition approach. Our method is general and can deal with realistic luminosity distributions, which project to surface brightness distributions that may show position angle twists and ellipticity variations. The models are fit to measurements of the full line-of-sight velocity distribution (wherever available). We verify that our method is able to reproduce theoretical predictions of a three-integral triaxial Abel model. In a companion paper by Ven, de Zeeuw & van den Bosch, we demonstrate that the method recovers the phase-space distribution function. We apply our method to two-dimensional observations of the E3 galaxy NGC 4365, obtained with the integral-field spectrograph SAURON, and study its internal structure, showing that the observed kinematically decoupled core is not physically distinct from the main body and the inner region is close to oblate axisymmetric. © 2008 RAS.

Towards a new classification of early-type galaxies: An integral-field view


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

Structure and kinematics of molecular disks in fast-rqtator early-type galaxies

Astrophysical Journal 676 (2008) 317-334

LM Young, M Bureau, M Cappellari

We present interferometru; observations resolving the CO emission in the four gas-rich lenticular galaxies NGC 3 032, NGC 4150, NGC 4459, and NGC 4526, and we compare the CO distribution and kinematics to those of the stars and ionized gas. Counterrotation documents an external origin for the gas in at least one case (NGC 3032), and the comparisons to stellar and ionized gas substructures in all four galaxies offer insights into their formation histories. The molecular gas is found in kpc-scale disks with mostly regular kinematics and average surface densities of 100-200 M⊙ pc -2. The disks are well aligned with the stellar photometric and kinematic axes. In the two more luminous Virgo Cluster members NGC 4459 and NGC 4526 the molecular gas shows excellent agreement with circular velocities derived independently from detailed modeling of stellar kinematic data. There are also two puzzling instances of disagreements between stellar kinematics and gas kinematics on subkiloparsec scales. In the inner arcseconds of NGC 3032 the CO velocities are significantly lower than the inferred circular velocities, and the reasons may possibly be related to the external origin of the gas but are not well understood. In addition, the very young population of stars in the core of NGC 4150 appears to have the opposite sense of rotation from the molecular gas. © 2008. The American Astronomical Society. All rights reserved.

Recent star formation in nearby early-type galaxies

ASTR SOC P 390 (2008) 218-226

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

Motivated by recent progress in the study of early-type galaxies owing to technological advances, the launch of new space telescopes, and large ground-based surveys, we attempt a short review of our current understanding of the recent star formation activity in such intriguing galactic systems.

Star formation in nearby early-type galaxies: Mapping in UV, optical, and CO


M Bureau, R Bacon, M Cappellari, F Combes, RL Davies, PT de Zeeuw, E Emsellem, J Falcon-Barroso, H Jeong, D Krajnovic, H Kuntschner, RM McDermid, RF Peletier, M Sarzi, KL Shapiro, GV de Ven, SK Yi, LM Young

The SAURON project - XII. Kinematic substructures in early-type galaxies: Evidence for discs in fast rotators

Monthly Notices of the Royal Astronomical Society 390 (2008) 93-117

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

We analysed two-dimensional maps of 48 early-type galaxies obtained with the SAURON and OASIS integral-field spectrographs using kinemetry, a generalization of surface photometry to the higher order moments of the line-of-sight velocity distribution (LOSVD). The maps analysed include: reconstructed image, mean velocity, velocity dispersion, h3 and h4 Gauss-Hermite moments. Kinemetry is a good method to recognize structures otherwise missed by using surface photometry, such as embedded discs and kinematic subcomponents. In the SAURON sample, we find that 31 per cent of early-type galaxies are single component systems. 91 per cent of the multicomponents systems have two kinematic subcomponents, the rest having three. In addition, 29 per cent of galaxies have kinematically decoupled components, nuclear components with significant kinematic twists. We differentiate between slow and fast rotators using velocity maps only and find that fast-rotating galaxies contain discs with a large range in mass fractions to the main body. Specifically, we find that the velocity maps of fast rotators closely resemble those of inclined discs, except in the transition regions between kinematic subcomponents. This deviation is measured with the kinemetric k 5/k1 ratio, which is large and noisy in slow rotators and about 2 per cent in fast rotators. In terms of E/S0 classification, this means that 74 per cent of Es and 92 per cent of S0s have components with disc-like kinematics. We suggest that differences in k5/k1 values for the fast and slow rotators arise from their different intrinsic structure which is reflected on the velocity maps. For the majority of fast rotators, the kinematic axial ratios are equal to or less than their photometric axial ratios, contrary to what is predicted with isotropic Jeans models viewed at different inclinations. The position angles of fast rotators are constant, while they vary abruptly in slow rotators. Velocity dispersion maps of face-on galaxies have shapes similar to the distribution of light. Velocity dispersion maps of the edge-on fast rotators and all slow rotators show differences which can only be partially explained with isotropic models and, in the case of fast rotators, often require additional cold components. We constructed local (bin-by-bin) h3-V/σ and h4-V/σ diagrams from SAURON observations. We confirm the classical anticorrelation of h3 and V/σ, but we also find that h3 is almost zero in some objects or even weakly correlated with V/σ. The distribution of h4 for fast and slow rotators is mildly positive on average. In general, fast rotators contain flattened components characterized by a disc-like rotation. The difference between slow and fast rotators is traceable throughout all moments of the LOSVD, with evidence for different intrinsic shapes and orbital contents and, hence, likely different evolutionary paths. © 2008 RAS.

Measuring the inclination and mass-to-light ratio of axisymmetric galaxies via anisotropic Jeans models of stellar kinematics

Monthly Notices of the Royal Astronomical Society 390 (2008) 71-86

M Cappellari

We present a simple and efficient anisotropic generalization of the semi-isotropic (two-integral) axisymmetric Jeans formalism, which is used to model the stellar kinematics of galaxies. The following is assumed: (i) a constant mass-to-light ratio (M/L) and (ii) a velocity ellipsoid that is aligned with cylindrical coordinates (R, z) and characterized by the classic anisotropy parameter. Our simple models are fit to SAURON integral-field observations of the stellar kinematics for a set of fast-rotator early-type galaxies. With only two free parameters (βz and the inclination), the models generally provide remarkably good descriptions of the shape of the first (V) and second () velocity moments, once a detailed description of the surface brightness is given. This is consistent with previous findings on the dynamical structure of these objects. With the observationally motivated assumption that βz ≳ 0, the method is able to recover the inclination. The technique can be used to determine the dynamical M/L and angular momenta of early-type fast-rotators and spiral galaxies, especially when the quality of the data does not justify more sophisticated modelling approaches. This formalism allows for the inclusion of dark matter, supermassive black holes, spatially varying anisotropy and multiple kinematic components. © 2008 RAS.

Galactic Bulges and Inner Disks, as Seen by SAURON


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

The SAURON project - XI. Stellar populations from absorption-line strength maps of 24 early-type spirals

Monthly Notices of the Royal Astronomical Society 379 (2007) 445-468

RF Peletier, J Falcón-Barroso, R Bacon, M Cappellari, RL Davies, PT De Zeeuw, E Emsellem, K Ganda, D Krajnović, H Kuntschner, RM McDermid, M Sarzi, G Van De Ven

We present absorption-line strength maps of a sample of 24 representative early-type spiral galaxies, mostly of type Sa, obtained as part of the SAURON (Spectrographic Areal Unit for Research on Optical Nebulae) survey of nearby galaxies using our custom-built integral-field spectrograph. Using high-quality spectra, spatially binned to a constant signal-to-noise ratio, we measure several key age, metallicity and abundance ratio sensitive indices from the Lick Observatory Image Dissector Scanner (Lick/IDS) system over a contiguous two-dimensional field including bulge and inner disc. We present maps of Hβ, Fe 5015 and Mg b for each galaxy. We find that Sa galaxies on the average have slightly smaller Mg b and Fe 5015 line strengths than ellipticals and S0s, and higher Hβ values, but with a much larger scatter. The absorption-line maps show that many galaxies contain some younger populations (≤1 Gyr), distributed in small or large inner discs, or in circumnuclear star-forming rings. In many cases these young stars are formed in circumnuclear ministarbursts, which are dominating the light in the centres of some of the early-type spirals. These ministarburst cause a considerable scatter in index-index diagrams such as Mg b-Hβ and Mg b-Fe 5015, more than is measured for early-type galaxies. We find that the central regions of Sa galaxies display a wide range in ages, even within the galaxies. We find that the central regions of early-type spirals are often dusty, with a good correlation between the presence of young central stellar populations and a significant amount of dust extinction. 50 per cent of the sample show velocity dispersion drops in their centres. All of the galaxies of our sample lie on or below the Mg b -σ relation for elliptical galaxies in the Coma cluster, and above the Hβ absorption line-σ relation for elliptical galaxies. If those relations are considered to be relations for the oldest local galaxies we see that our sample of spirals has a considerable scatter in age, with the largest scatter at the lowest σ. This is in disagreement with highly inclined samples, in which generally only old stellar populations are found in the central regions. The discrepancy between our sample and highly inclined samples, and the presence of so many stellar velocity dispersion dips, i.e. so-called σ drops, in these spiral galaxies with large bulges (type Sa) can be understood if the central regions of Sa galaxies contain at least two components: a thin, disc-like component, often containing recent star formation, and another, elliptical-like component, consisting of old stars and rotating more slowly, dominating the light above the plane. These components together form the photometrically defined bulge, in the same way as the thin and the thick disc co-exist in the solar neighbourhood. In this picture, consistent with the current literature, part of the bulge, the thicker component, formed a very long time ago. Later, stars continued to form in the central regions of the disc, rejuvenating in this way the bulge through dynamical processes. This picture is able to explain in a natural way the heterogeneous stellar populations and star formation characteristics that we are seeing in detailed observations of early-type spiral galaxies. © 2007 RAS.

Fast and slow rotators: The build-up of the red sequence

Proceedings of the International Astronomical Union 3 (2007) 11-14

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

Using the unique dataset obtained within the course of the SAURON project, a radically new view of the structure, dynamics and stellar populations of early-type galaxies has emerged. We show that galaxies come in two broad flavours (slow and fast rotators), depending on whether or not they exhibit clear large-scale rotation, as indicated via a robust measure of the specific angular momentum of baryons. This property is also linked with other physical characteristics of early-type galaxies, such as: the presence of dynamically decoupled cores, orbital structure and anisotropy, stellar populations and dark matter content. I here report on the observed link between this baryonic angular momentum and a mass sequence, and how this uniquely relates to the building of the red sequence via dissipative/dissipationless mergers and secular evolution. © 2008 Copyright International Astronomical Union 2008.

Revisiting the (V/sigma)-epsilon anisotropy diagram of early-type galaxies using integral-field kinematics


M Cappellari, R Bacon, M Bureau, RL Davies, PTD Zeeuw, E Emsellem, J Falcon-Barroso, D Krajnovic, H Kuntschner, RM McDermid, RF Peletier, M Sarzi, RCEVD Bosch, GVD Ven

We use integral-field observation of the stellar kinematics obtained with SAURON in combination with Schwarzschild dynamical models to revisit our understanding of the classic (V /σ) − ε anisotropy diagram of early-type galaxies.

Stars and gas in the inner parts of galaxies seen in SAURON integral field observations

\nar 51 (2007) 29-33-29-33

RF Peletier, K Fathi, EL Allard, JH Knapen, M Sarzi, G van de Ven, J Falcon-Barroso, M Cappellari, PT de Zeeuw, E Emsellem

The SAURON project - X. The orbital anisotropy of elliptical and lenticular galaxies: revisiting the (V/sigma,epsilon) diagram with integral-field stellar kinematics

Monthly Notices of the Royal Astronomical Society 379 (2007) 418-444

M Cappellari, Bacon, R., Bureau, M., Emsellem, E.

The central parsecs of centaurus A: High-excitation gas, a molecular disk, and the mass of the black hole

Astrophysical Journal 671 (2007) 1329-1344

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

We present two-dimensional gas-kinematic maps of the central region in Centauras A. The adaptive optics (AO) assisted SINFONI data from the VLT have aresolutionof 0.12″ in K band. The ionized gas species (Brγ, [Fe II], [Si VI]) show a rotational partern that is increasingly overlaid by nonrotational motion for higher excitation lines in the direction of Cen A's radio jet. The emission lines of molecular hydrogen (H2) show regular rotation and no distortion due to the jet. The molecular gas seems to be well settled in the gravitational potential of the stars and the central supermassive black hole, and we thus use it as a tracer to model the mass in the central ± 1.5Prime;. These are the first AO integral-field observations on the nucleus of Cen A, enabling us to study the regularity of the rotation around the black hole, well inside the radius of influence, and to determine the inclination angle of the gas disk in a robust way. The gas kinematics are best modeled through a tilted-ring model that describes the warped gas disk; its mean inclination angle is ∼34° and the mean position angle of the major axis is ∼155°. The best-fit black hole mass is MBH = (4.5 -1.0-1.7) 7times; 107 M⊙ (3 σ error), based on a kinematically hot disk model where the velocity dispersion is included through the Jeans equation. This black hole mass estimate is somewhat lower than, but consistent with, the mass values previously derived from ionized gas kinematics. It is also consistent with the stellar dynamical measurement from the same AO observations, which we present in a separate paper. It brings Cen A into agreement with the MBH-σ relation. © 2007. The American Astronomical Society. All rights reserved.

Supermassive black holes from OASIS and SAURON integral-field kinematics

Proceedings of the International Astronomical Union 3 (2007) 215-218

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

Supermassive black holes are a key element in our understanding of how galaxies form. Most of the progress in this very active field of research is based on just ~30 determination of black hole masses, accumulated over the past decade. We illustrate how integral-field spectroscopy, and in particular our OASIS modeling effort can help improve the current situation. © 2008 Copyright International Astronomical Union 2008.

The SAURON project - IX. A kinematic classification for early-type galaxies

Monthly Notices of the Royal Astronomical Society 379 (2007) 401-417

RL Davies, Eric Emsellem, Michele Cappellari, Davor Krajnovic

Spiral galaxies in the SAURON survey

Proceedings of the International Astronomical Union 3 (2007) 271-276

RF Peletier, K Ganda, J Falcón-Barroso, R Bacon, M Cappellari, RL Davies, PT De Zeeuw, E Emsellem, D Krajnović, H Kuntschner, RM McDermid, M Sarzi, G Van De Ven

We discuss some recent integral field spectroscopy using the SAURON instrument of a sample consisting of 24 early-type spirals, part of the SAURON Survey, and 18 late-type spirals. Using 2-dimensional maps of their stellar radial velocity, velocity dispersion, and absorption line strength, it is now much easier to understand the nature of nearby galactic bulges. We discuss a few highlights of this work, and point out some new ideas about the formation of galactic bulges. © 2008 Copyright International Astronomical Union 2008.

Absorption-line strengths of 18 late-type spiral galaxies observed with SAURON

Monthly Notices of the Royal Astronomical Society 380 (2007) 506-540

K Ganda, RF Peletier, RM McDermid, J Falcón-Barroso, PT De Zeeuw, R Bacon, M Cappellari, RL Davies, E Emsellem, D Krajnović, H Kuntschner, M Sarzi, G Van De Ven

ABSTRACT We present absorption line strength maps for a sample of 18 Sb-Sd galaxies observed using the integral-field spectrograph SAURON operating at the William Herschel Telescope on La Palma, as part of a project devoted to the investigation of the kinematics and stellar populations of late-type spirals, a relatively unexplored field. The SAURON spectral range allows the measurement of the Lick/IDS indices Hβ, Fe5015 and Mgb, which can be used to estimate the stellar population parameters. We present here the two-dimensional line strength maps for each galaxy. From the maps, we learn that late-type spiral galaxies tend to have high Hβ and low Fe5015 and Mgb values, and that the Hβ index has often a positive gradient over the field, while the metal indices peak in the central region. We investigate the relations between the central line strength indices and their correlations with morphological type and central velocity dispersion, and compare the observed behaviour with that for ellipticals, lenticulars and early-type spirals from the SAURON survey. We find that our galaxies lie below the Mg-σ relation determined for elliptical galaxies and that the indices show a clear trend with morphological type. From the line strength maps we calculate age, metallicity and abundance ratio maps via a comparison with model predictions; we discuss the results from a one-SSP (single stellar population) approach and from a two-SSP approach, considering the galaxy as a superposition of an old (≈13 Gyr) and a younger (age ≤5 Gyr) population. We confirm that late-type galaxies are generally younger and more metal-poor than ellipticals and have abundance ratios closer to solar values. We also explore a continuous star formation scenario, and try to recover the star formation history using the evolutionary models of Bruzual & Charlot, assuming constant or exponentially declining star formation rate. In this last case, fixing the galaxy age to 10 Gyr, we find a correlation between the e-folding time-scale τ of the starburst and the central velocity dispersion, in the sense that more massive galaxies tend to have shorter τ, suggesting that the star formation happened long ago and has now basically ended, while for smaller objects with larger values of τ it is still active now. © 2007 The Authors. Journal compilation © 2007 RAS.