Publications by Michele Cappellari


The intrinsic shape of bulges

ASTR SOC P 197 (2000) 245-246

M Cappellari, F Bertola, LM Buson, EM Corsini, JG Funes, A Pizzella, M Sarzi


Kinematic properties of the gas in the central region of galaxies

ASTR SOC P 197 (2000) 131-132

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


Central UV spikes in two galactic spheroids

Formation of Galactic Bulges Cambridge University Press (2000) 191-194

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

FOS spectra and FOC photometry of two centrally located, UV-bright spikes in the elliptical galaxy NGC 4552 and the bulge-dominated early spiral NGC 2681, are presented. These spectra reveal that such point-like UV sources detected by means of HST within a relatively large fraction ~15% of bulges can be related to radically different phenomena. While the UV unresolved emission in NGC 4552 represents a transient event likely induced by an accretion event onto a supermassive black hole, the spike seen at the center of NGC 2681 is not variable and it is stellar in nature.


NGC 4672: A candidate for bulge-to-disk decoupling in spirals

ASTR SOC P 197 (2000) 139-140

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


Counterrotating gaseous components in the early-type galaxy IC 4889

ASTR SOC P 197 (2000) 251-252

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


Isolated cores in early-type disk galaxies: NGC 4672

ASTR SOC P 221 (2000) 249-252

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

The morphological features of the early-type disk galaxy NGC 4672 are discussed as well as the velocity curves and velocity dispersion profiles of stars and ionized gas along both its major and minor axes. We conclude that NGC 4672 has structural (i.e. a bulge elongated perpendicularly to the disk) and kinematical (i.e, a stellar core rotating perpendicularly to the disk) properties similar to those of the Sa NGC 4698. The presence of the isolated core suggests that the disk component is the end result of the acquisition of external material in polar orbits around a pre-existing oblate spheroid, as in the case of the ring component of AM 2020-504, the prototype of polar ring ellipticals.


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.


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 Greggio, SD Alighieri, LM Buson, D Burstein, F Bertola


The bulge-disk orthogonal decoupling in galaxies: NGC 4698

ASTROPHYSICAL JOURNAL 519 (1999) L127-L130

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


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.


The bulge-disk orthogonal decoupling in galaxies: NGC 4698

Astrophysical Journal 519 (1999)

F Bertola, EM Corsini, JC Vega Beltrán, A Pizzella, M Sarzi, M Cappellari, JGSJ Funes

The R-band isophotal map of the Sa galaxy NGC 4698 shows that the inner region of the bulge structure is elongated perpendicularly to the major axis of the disk; this is also true for the outer parts of the bulge if a parametric photometric decomposition is adopted. At the same time, the stellar component is characterized by an inner velocity gradient and a central zero-velocity plateau along the minor and major axes of the disk, respectively. This remarkable geometric and kinematic decoupling suggests that a second event occurred in the formation history of this galaxy.


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.

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