arXiv subjects

E. M. Corsini

Publications and source records attributed to E. M. Corsini.

At least 163 records · Page 9Linked to original sources

arXiv2002

Measurement of fast bars in a sample of early-type barred galaxies

We present surface photometry and stellar kinematics of a sample of 5 SB0 galaxies: ESO 139-G009, IC 874, NGC 1308, NGC 1440 and NGC 3412. We measured their bar pattern speed using the Tremaine-Weinberg method, and derived the ratio, R, of the corotation radius to the length of the bar semi-major axis. For all the galaxies, R is consistent with being in the range from 1.0 and 1.4, i.e. that they host fast bars. This represents the largest sample of galaxies for which R has been measured this way. Taking into account the measured distribution of R and our measurement uncertainties, we argue that this is probably the true distribution of R. If this is the case, then the Tremaine-Weinberg method finds a distribution of R which is in agreement with that obtained by hydrodynamical simulations. We compared this result with recent high-resolution N-body simulations of bars in cosmologically-motivated dark matter halos,and conclude that these bars are not located inside centrally concentrated dark matter halos.

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arXiv2002

Position-velocity diagrams of ionized gas in the inner regions of disk galaxies

We use long-slit spectroscopy along the major axis of a sample of 23 nearby disk galaxies to study the kinematic properties of the ionized-gas component in their inner regions. For each galaxy, we derive the position-velocity diagram of the ionized gas from its emission lines. We discuss the variety of shapes observed in such position-velocity diagrams by comparing the gas velocity gradient, velocity dispersion and integrated flux measured in the inner (r +/-1'') and outer regions (r +/-4''). This kind of analysis allows the identification of galaxies which are good candidates to host a circumnuclear Keplerian gaseous disk rotating around a central mass concentration, and to follow up with Hubble Space Telescope observations.

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arXiv2002

Nuclear Stellar Disks in Spiral Galaxies

We report evidence for nuclear stellar disks in 3 early-type spirals, namely NGC 1425, NGC 3898 and NGC 4698, revealed by WFPC2/F606W images out of a sample of 38 spiral galaxies, selected from the Hubble Space Telescope Data Archive. Adopting the photometric method introduced by Scorza & Bender we derived their central surface brightness and scalelength by assuming them to be infinitesimally thin exponential disks. No nuclear disk was found in barred galaxies or galaxies of Hubble type later than Sb. The external origin of the disk in NGC 4698 is strongly suggested by its orthogonal geometrical decoupling with respect to the host galaxy.

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arXiv2001

The Orthogonal Gaseous Kinematical Decoupling in the Sa Spiral NGC 2855

We present major and minor-axis kinematics of stars and ionized gas as well as narrow and broad-band surface photometry of the Sa spiral NGC 2855. In the nuclear regions of this unbarred and apparently undisturbed spiral galaxy the gas is rotating perpendicularly to the galaxy disk. We suggest that this kinematically-decoupled component is the signature of an acquisition process in the history of this galaxy.

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arXiv2001

Kinematic properties of gas and stars in 20 disc galaxies

Ionized gas and stellar kinematical parameters have been measured along the major axis of 20 nearby disc galaxies. We discuss the properties of each sample galaxy distinguishing between those characterized by regular or peculiar kinematics. In early-type disc galaxies ionized gas tends to rotate faster than stars and to have a lower velocity dispersion, whereas in late-type spirals gas and stars show almost the same rotation velocities and velocity dispersions. Incorporating the early-type disc galaxies studied by Bertola et al. (1995), Fisher (1997) and Corsini et al. (1999), we have compiled a sample of some 40 galaxies for which the major-axis radial profiles of both the stellar and gaseous components have been measured. The value of the stellar velocity dispersion measured at Re/4 turns out to be strongly correlated with the galaxy morphological type, while the gaseous velocity dispersion is not and sometimes takes values above the range expected from thermal motions or small-scale turbulence.

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arXiv2000

Modelling gaseous and stellar kinematics in the disc galaxies NGC 772, NGC 3898, and NGC 7782

We present V-band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, NGC 3898 and NGC 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allowed us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects. NGC 772 and NGC 7782 have apparently normal kinematics with the ionized gas tracing the gravitational equilibrium circular speed. This is not true in the innermost region (r < 8'') of NGC 3898 where the ionized gas is rotating more slowly than the circular velocity predicted by dynamical modelling. This phenomenon is common in the bulge-dominated galaxies for which dynamical modelling enables us to make the direct comparison between the gas velocity and the circular speed, and it poses questions about the reliability of galaxy mass distributions derived by the direct decomposition of the observed ionized-gas rotation curve into the contributions of luminous and dark matter.

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arXiv2000

Modeling gas and stellar kinematics in disc galaxies

We present V-band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, NGC 3898 and NGC 7782. For each galaxy we built a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allowed us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects. We found that the observed gas rotation corresponds to the circular velocity except for the innermost region (|r|<8") of NGC 3898. This behaviour is quite common, although not ubiquitous, in the few bulge-dominated galaxies, for which dynamical modeling allows the comparison between the gas velocity and the circular speed.

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arXiv2000

Disk Galaxies and Galaxy Disks

The conference Galaxy Disks and Disk Galaxies, sponsored by the Vatican Observatory, was held in June 12-16, 2000 at the Pontifical Gregorian University, in Rome (Italy). The meeting hosted about 230 participants coming from 30 countries. The very full program consisted of 29 review papers, 34 invited talks, and more than 180 posters. The meeting covered topics regarding the structure, formation and evolution of galaxies with disks. Particular attention was dedicated to the stellar and gaseous disk of the Milky Way, the global characteristics of galaxy disks, their structure, morphology and dynamics, the gaseous components, star formation, and chemical evolution, the interactions, accretion, mergers and starbursts, the dark and luminous matter, the establishment of the scaling laws, and the formation and evolution of disk galaxies from a theoretical and observational point of view.

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arXiv2000

NGC 4672: a new case of an early-type disk galaxy with an orthogonally decoupled core

We report the case of the early-type disk galaxy NGC 4672 as a new example of a galaxy characterized by the orthogonal geometrical decoupling between bulge and disk. The morphological features of this galaxy are discussed as well as the velocity curves and velocity dispersion profiles of stars and ionized gas along both its major and minor axis. 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.

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arXiv1999

Minor-Axis Stellar Velocity Gradients in Disk and Polar-Ring Galaxies

Kinematical decoupling between two components of a galaxy suggests the occurrence of a second event. In disk galaxies it is usually observed as a counterrotation of the stellar disk with respect to the gaseous component and/or with respect to a second stellar disk. We discuss here three cases of kinematical orthogonal decoupling of the innermost region of the spheroidal component with respect to the disk (or ring) component in the two Sa spirals NGC 4698 and NGC 4672, and in the elliptical galaxy with a polar ring AM 2020-504. Moreover the major axis of the disk (or ring) component forms an angle of 90 degrees with the major axis of the bulge (or elliptical) component. The above phenomena lead us to face a scenario in which the disk of a spiral galaxy might have been formed as a second event by accretion around a pre-existing bare spheroid.

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arXiv1999

Correlation between kinematics and Hubble Sequence in disk galaxies?

We present a comparison between ionized gas and stellar kinematics for a sample of 5 early-to-intermediate disc galaxies. We measured the major axis V and sigma radial profiles for both gas and stars, and the h3 and h4 radial profiles of the stars. We also derived from the R-band surface photometry of each galaxy the light contribution of their bulges and discs. In order to investigate the differences between the velocity fields of the sample galaxies we adopted the self-consistent dynamical model by Pignatelli & Galletta (1999), which takes into account the asymmetric drift effects, the projection effects along the line-of-sight and the non-Gaussian shape of the line profiles due to the presence of different components with distinct dynamical behavior. We find for the stellar component a sizeable asymmetric drift effect in the inner regions of all the sample galaxies, as it results by comparing their stellar rotation curves with the circular velocity predicted by the models. The galaxy sample is not wide enough to draw general conclusions. However, we have found a possible correlation between the presence of slowly-rising gas rotation curves and the ratio of the bulge/disc half luminosity radii, while there is no obvious correlation with the key parameter represented by the morphological classification, namely the bulge/disc luminosity ratio. Systems with a diffuse dynamically hot component (bulge or lens) with a scale length comparable to that of the disc are characterized by slowly-rising gas rotation curves. On the other hand, in systems with a small bulge the gas follows almost circular motions, regardless of the luminosity of the bulge itself.

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arXiv1999

The Bulge-Disk Orthogonal Decoupling in Galaxies: NGC 4698

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 axis of the disk respectively. This remarkable geometric and kinematic decoupling suggests that a second event occurred in the formation history of this galaxy.

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arXiv1999

The kinematics and the origin of ionized gas in NGC 4036

We present the kinematics and photometry of the stars and of the ionized gas near the centre of the S0 galaxy NGC4036. Dynamical models based on the Jeans Equation have been constructed from the stellar data to determine the gravitational potential in which the ionized gas is expected to orbit. Inside 10'', the observed gas rotation curve falls well short of the predicted circular velocity. Over a comparable radial region the observed gas velocity dispersion is far higher than the one expected from thermal motions or small scale turbulence, corroborating that the gas cannot be following the streamlines of nearly closed orbits. We explore several avenues to understand the dynamical state of the gas: (1) We treat the gas as a collisionless ensemble of cloudlets and apply the Jeans Equation to it; this modeling shows that inside 4'' the gas velocity dispersion is just high enough to explain quantitatively the absence of rotation. (2) Alternatively, we explore whether the gas may arise from the `just shed' mass-loss envelopes of the bulge stars, in which case their kinematics should simply mimic that of the stars. he latter approach matches the data better than (1), but still fails to explain the low velocity dispersion and slow rotation velocity of the gas for 5''<r<10''. (3) Finally, we explore, whether drag forces on the ionized gas may aid in explaining its peculiar kinematics. While all these approaches provide a much better description of the data than cold gas on closed orbits, we do not yet have a definitive model to describe the observed gas kinematics at all radii.

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arXiv1999

The kinematics and the origin of the ionized gas in NGC 4036

The kinematics of stars and ionized gas has been studied near the center of the S0 galaxy NGC 4036. Dynamical models based both on stellar photometry and kinematics have been built in order to derive the gravitational potential in which the gas is expected to orbit. The observed gas rotation curve falls short of the circular velocity curve inferred from these models. Inside 10'' the observed gas velocity dispersion is found to be comparable to the predicted circular velocity, showing that the gas cannot be considered on circular orbits. The understanding of the observed gas kinematics is improved by models based on the Jeans Equations, which assume the ionized gas as an ensemble of collisionless cloudlets distributed in a spheroidal and in a disk component.

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arXiv1999

The bulge-disk orthogonal decoupling in galaxies: NGC 4698 and NGC 4672

We report the case of the geometrical and kinematical decoupling between the bulge and the disk of the Sa galaxy NGC 4698. The R-band isophotal map of this spiral shows that the bulge structure is elongated perpendicularly to the major axis of the disk. At the same time a central stellar velocity gradient is found along the major axis of the bulge. We also present the Sa NGC 4672 as good candidate of a spiral hosting a bulge and a disk orthogonally decoupled with respect to one other. This decoupling of the two fundamental components of a visible galaxy suggests that the disk could represent a second event in the history of early-type spirals.

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arXiv1998

Kinematics of Gas and Stars in Early-type Disk Galaxies

We present a comparison between ionized gas and stellar kinematics for a sample of 5 early-to-intermediate disk galaxies. We measured the major axis V and velocity dispersion radial profiles for both gas and stars, and the h_3 and h_4 radial profiles of the stars. We also derived from the R-band surface photometry of each galaxy the light contribution of their bulges and disks. In order to investigate the differences in the velocity fields of our sample galaxies we adopted the self-consistent dynamical model by Pignatelli & Galletta (1998), which takes into account the asymmetric drift effects, the projection effects along the line-of-sight and the non-Gaussian shape of the line profiles due to the presence of different components with distinct dynamical behavior.

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arXiv1998

Dark matter in early-type spiral galaxies: the case of NGC 2179 and of NGC 2775

We present stellar and ionized-gas velocity curves and velocity dispersion profiles for the Sa galaxies NGC 2179 and NGC 2775. Using their luminosity profiles and modeling both their stellar and gaseous kinematics, we have derived the mass distribution of the dark and the luminous matter. This unambiguously shows that, inside one disk length-scale R_D, the stellar bulge and disk account for the whole gravitating mass. The dark matter halo, likely present also at inner radii, becomes an important mass component only for R > 2 R_D. Giving the quantity and quality of the data, our results on these two luminous galaxies serve as strong counter-example to the recent claim according to which also high-luminosity spirals are dark matter dominated at essentially all radii.

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arXiv1998

Circumnuclear Keplerian Disks in Galaxies

In this paper we demonstrate the possibility of inferring the presence of Keplerian gaseous disks using optical ground-based telescopes properly equipped. We have modeled the peculiar bidimensional shape of the emission lines in a sample of five S0-Sa galaxies as due to the motion of a gaseous disk rotating in the combined potential of a central point-like mass and of an extended stellar disk. The value of the central mass concentration estimated for four galaxies of the sample (NGC 2179, NGC 4343, NGC 4435 and NGC 4459) is ~10^9 Msolar. For the remaining galaxy NGC 5064 an upper limit of 5*10^7 Msolar is estimated.

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