Publications by Michele Cappellari


An Oxford SWIFT Integral Field Spectroscopy study of 14 early-type galaxies in the Coma cluster

ArXiv (0)

N Scott, RCW Houghton, RL Davies, M Cappellari, N Thatte, FJ Clarke, M Tecza

As a demonstration of the capabilities of the new Oxford SWIFT integral field spectrograph, we present first observations for a set of 14 early-type galaxies in the core of the Coma cluster. Our data consist of I- and z-band spatially resolved spectroscopy obtained with the Oxford SWIFT spectrograph, combined with r-band photometry from the SDSS archive for 14 early- type galaxies. We derive spatially resolved kinematics for all objects from observations of the calcium triplet absorption features at \sim 8500 {AA} . Using this kinematic information we classify galaxies as either Fast Rotators or Slow Rotators. We compare the fraction of fast and slow rotators in our sample, representing the densest environment in the nearby Universe, to results from the ATLAS3D survey, finding the slow rotator fraction is \sim 50 per cent larger in the core of the Coma cluster than in the Virgo cluster or field, a 1.2 {\sigma} increase given our selection criteria. Comparing our sample to the Virgo cluster core only (which is 24 times less dense than the Coma core) we find no evidence of an increase in the slow rotator fraction. Combining measurements of the effective velocity dispersion {\sigma_e} with the photometric data we determine the Fundamental Plane for our sample of galaxies. We find the use of the average velocity dispersion within 1 effective radius, {\sigma_e}, reduces the residuals by 13 per cent with respect to comparable studies using central velocity dispersions, consistent with other recent integral field Fundamental Plane determinations.


Circumnuclear Keplerian disks in galaxies

ASTR SOC P 182 (1999) 229-230

JG Funes, F Bertola, M Cappellari, EM Corsini, A Pizzella, JCV Beltran


A UV flare at the center of the elliptical galaxy NGC 4552

IAU SYMP (1999) 389-393

LM Buson, F Bertola, D Burstein, M Cappellari, SD Alighieri, L Greggio, A Renzini

A self-consistent analysis of near-UV, HST/FOC images of the elliptical galaxy NGC 4552 is used to show that its central spike has brightened by a factor similar to 4.5 between 1991 and 1993, and has decreased its luminositv by a factor similar to 2.0 between 1993 and 1996. A strong UV continuum over the energy distribution of the underlying galaxy is concurrently revealed shortward of lambda similar to 3200 Angstrom by our FOS spectra extending from the near-UV to red wavelengths. Nuclear emission-line profiles of both permitted and forbidden lines are best modelled with a combination of broad and narrow components, with FWHM of similar to 3000 km s(-1) and similar to 700 km s(-1), respectively. Current diagnostics based on the emission line intensity ratios definitely places the spike among AGNs, just at the border between Seyferts and LINERs. This evidence argues for the variable central spike being produced by a modest accretion event onto a central massive black hole (BH), with the accreted material having possibly being stripped from a star in a close fly-by with the BH. In this regard, one has to look at NGC 4552 as the faintest known AGN.


Searching for low-mass supermassive black holes

IAU SYMP (1999) 422-423

M Cappellari, F Bertola, EM Corsini, JG Funes, A Pizzella, JCV Beltran


The mini-active galactic nucleus at the center of the elliptical galaxy NGC 4552 with hubble space telescope

Astrophysical Journal 519 (1999) 117-133

M Cappellari, A Renzini, L Gregoio, S Di Serego Alighieri, LM Buson, D Burstein, F Bertola

The complex phenomenology shown by the UV-bright, variable spike first detected with the Hubble Space Telescope (HST) at the center of the otherwise normal galaxy NGC 4552 is further investigated with both HST imaging (FOC) and spectroscopy (FOS). HST/FOC images taken in 1991, 1993, and 1996 in the near-UV have been analyzed in a homogeneous fashion, showing that the central spike has brightened by a factor ∼4.5 between 1991 and 1993 and has decreased its luminosity by a factor ∼2.0 between 1993 and 1996. FOS spectroscopy extending from the near-UV to the red side of the optical spectrum reveals a strong UV continuum over the spectrum of the underlying galaxy, along with several emission lines in both the UV and the optical ranges. In spite of the low luminosity of the UV continuum of the spike (∼3 x 105 L⊙), the spike is definitely placed among active galactic nuclei (AGNs) by current diagnostics based on the emission-line intensity ratios, being just on the borderline between Seyfert galaxies and LINERs. Line profiles are very broad, and both permitted and forbidden lines are best modeled with a combination of broad and narrow components, with FWHM of ∼3000 km s-1 and ∼700 km s-1, respectively. This evidence argues for the variable central spike being produced by a modest accretion event onto a central massive black hole (BH), with the accreted material having possibly being stripped from a star in a close flyby with the BH. The 1996 broad Hα luminosity of this mini-AGN is ∼5.6 x 1037 ergs s-1, about a factor of 2 less than that of the nucleus of NGC 4395, heretofore considered to be the faintest known AGN. Combining all observational constraints, we estimate the mass of the BH at the center of NGC 4552 to be in the range between 3 x 108 and 2 x 109 L⊙. The relevance for the demography of BHs in galaxies of the high (HST) resolution imaging and spectroscopy capable of revealing an extremely low level AGN activity in normal galaxies is briefly discussed.


Objects in NGC 205 resolved into stellar associations by hubble space telescope ultraviolet imaging

Astrophysical Journal 515 (1999)

M Cappellari, F Bertola, D Burstein, LM Buson, L Greggio, A Renzini

We have obtained high-resolution UV images with the Hubble Space Telescope/Wide-Field Planetary Camera 2 of the central region of the dwarf elliptical galaxy NGC 205. Our images reveal that many of the hot UV stars previously detected and studied from the ground are actually multiple systems, open clusters, and star associations. We have performed photometry of two such clusters, and we find that our data are consistent with stellar ages of 50 and 100 Myr, respectively. From the number of massive stars in NGC 205, we estimate that the star formation episode in this galaxy has turned ∼1000 M⊙ of gas into stars over the last 100 Myr.


Objects in NGC 205 resolved into stellar associations by Hubble Space Telescope ultraviolet imaging

ASTROPHYSICAL JOURNAL 515 (1999) L17-L20

M Cappellari, F Bertola, D Burstein, LM Buson, L Greggio, A Renzini


Ground-based detection of circumnuclear Keplerian disks of ionized gas in early-type disk galaxies

(1999) 232-236

JG Funes, F Bertola, M Cappellari, EM Corsini, A Pizzella, JCV Beltran

We demonstrate the possibility of detecting mass concentrations (down to the level of 5 x 10(7) M.) in the center of galaxies with ground-based optical telescopes properly equipped, using Keplerian gaseous disks as probes. We predict that the high spatial resolution of HST equipped with STIS will allow to detect central mass concentrations down to the level of 5 x 10(6) M.. As a consequence, the detection of low mass concentrations in the range 10(6) - 10(7) M. will constitute a very appropriate use of HST.


Kinematically decoupled bulges in spirals: NGC 4698

ASTR SOC P 182 (1999) 241-242

M Sarzi, EM Corsini, M Cappellari, JG Funes, F Bertola, JCV Beltran, A Pizzella


Circumnuclear Keplerian disks in galaxies

ASTROPHYSICAL JOURNAL 509 (1998) L93-L96

F Bertola, M Cappellari, JG Funes, EM Corsini, A Pizzella, JCV Beltran


UV imaging of the galaxy cluster CL0939+72 at z similar to 0.4

ASTR SOC P 146 (1998) 488-491

LM Buson, F Bertola, M Cappellari, C Chiosi, A Dressler, A Oemler


The variable UV central spike of NGC 4552

ASTR SOC P 117 (1997) 545-549

M Cappellari, D Burstein, LM Buson, SD Alighieri, L Greggio, A Renzini, J Funes, F Bertola

The nature of the UV-bright spike at the center of the otherwise normal galaxy NGC 4552 is investigated by means of both Hubble Space Telescope (HST) imaging (FOC) and spectroscopy (FOS). This central feature-which underwent a recent dramatic UV flare-provides a potential new tool for revealing the presence of massive black holes in normal galaxies. In particular the sub-arcsec FOS spectra of the nucleus suggest that NGC 4552 does harbor an object with mass M > 4 x 10(8) M. within the central 2 pc.


AN ULTRAVIOLET FLARE AT THE CENTER OF THE ELLIPTIC GALAXY NGC4552

NATURE 378 (1995) 39-41

A RENZINI, L GREGGIO, SD ALIGHIERI, M CAPPELLARI, D BURSTEIN, F BERTOLA


Anisotropic Jeans models of stellar kinematics: second moments including proper motions and radial velocities

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M Cappellari

This is an addendum to the paper by Cappellari (2008, MNRAS, 390, 71), which presented a simple and efficient method to model the stellar kinematics of axisymmetric stellar systems. The technique reproduces well the integral-field kinematics of real galaxies. It allows for orbital anisotropy (three-integral distribution function), multiple kinematic components, supermassive black holes and dark matter. The paper described the derivation of the projected second moments and we provided a reference software implementation. However only the line-of-sight component was given in the paper. For completeness we provide here all the six projected second moments, including radial velocities and proper motions. We present a test against realistic N-body galaxy simulations.


Voronoi binning: Optimal adaptive tessellations of multi-dimensional data

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MICHELE Cappellari

We review the concepts of the Voronoi binning technique (Cappellari & Copin 2003), which optimally solves the problem of preserving the maximum spatial resolution of general two-dimensional data, given a constraint on the minimum signal-to-noise ratio (S/N). This is achieved by partitioning the data in an adaptive fashion using a Voronoi tessellation with nearly hexagonal lattice. We review astrophysical applications of the method to X-ray data, integral-field spectroscopy, Fabry-Perot interferometry, N-body simulations, standard images and other regularly or irregularly sampled data. Voronoi binning, unlike adaptive smoothing, produces maps where the noise in the data can be visually assessed and spurious artifacts can be recognized. The method can be used to bin data according to any general criterion and not just S/N. It can be applied to higher dimensions and it can be used to generate optimal adaptive meshes for numerical simulations.


Dynamical modeling of SAURON galaxies

Proceedings of IUTAM Symposia and Summer Schools IUTAM 3 (0)

M Cappellari, RCEVD Bosch, EK Verolme, R Bacon, M Bureau, Y Copin, RL Davies, E Emsellem, D Krajnovic, H Kuntschner, R McDermid, BW Miller, RF Peletier, PTD Zeeuw

<p style="text-align:justify;"> We describe our program for the dynamical modeling of early-type galaxies observed with the panoramic integral-field spectrograph SAURON. We are using Schwarzschild's numerical orbit superposition method to reproduce in detail all kinematical and photometric observables, and recover the intrinsic orbital structure of the galaxies. Since catastrophes are the most prominent features in the orbital observables, two-dimensional kinematical coverage is essential to constrain the dynamical models. </p>


Efficient solution of the anisotropic spherically-aligned axisymmetric Jeans equations of stellar hydrodynamics for galactic dynamics

ArXiv (0)

M Cappellari

I present a flexible solution for the axisymmetric Jeans equations of stellar hydrodynamics under the assumption of an anisotropic (three-integrals) velocity ellipsoid aligned with the spherical polar coordinate system. I describe and test a robust and efficient algorithm for its numerical computation. I outline the evaluation of the intrinsic velocity moments and the projection of all first and second velocity moments, including both the line-of-sight velocities and the proper motions. This spherically-aligned Jeans Anisotropic Modelling (JAM_sph) method can describe in detail the photometry and kinematics of real galaxies. It allows for a spatially-varying anisotropy, or stellar mass-to-light ratios gradients, as well as for the inclusion of general dark matter distributions and supermassive black holes. The JAM_sph method complements my previously derived cylindrically-aligned and spherical Jeans solutions, which I also summarize in this paper. I will include a reference software implementation of JAM_sph in the publicly-available JAM software package.


Erratum: “The Structure of Nuclear Star Clusters in Nearby Late-type Spiral Galaxies from Hubble Space Telescope Wide Field Camera 3 Imaging” (2015, AJ, 149 170)

The Astronomical Journal American Astronomical Society 158 (0) 260-260

DJ Carson, AJ Barth, AC Seth, MD Brok, M Cappellari, JE Greene, LC Ho, N Neumayer

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