arXiv subjects

Reynier F. Peletier

Publications and source records attributed to Reynier F. Peletier.

89 records · Page 5Linked to original sources

arXiv2005

Cool Gas and Massive Stars - the Nuclear Ring in M100

The SAURON integral field spectrograph was used to observe the central area of the barred spiral galaxy M100 (NGC 4321). M100 contains a nuclear ring of star formation, fueled by gas channeled inward by the galaxy's bar. We present maps of emission line strengths, absorption line strength indices, and the gas velocity dispersion across the field. The H beta emission is strongest in the ring, along two curved bar dustlanes and at the ends of the bar. The Mg b absorption line strength shows a younger population of stars within the ring as compared to the surrounding area. The gas velocity dispersion is notably smaller than elsewhere in the field both in the ring and along the leading edge of the dustlanes. Low gas dispersion is correlated spatially with the H beta emission. We thus see stars being formed from cold (low dispersion) gas which is being channeled inward along the dustlanes under the influence of a large bar, and accumulated into a ring near the location of the inner Lindblad resonances. This lends further strong support to the interpretation of nuclear rings in barred galaxies as resonance phenomena.

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arXiv2005

A Bar Signature and Central Disk in the Gaseous and Stellar Velocity Fields of NGC5448

We analyse SAURON kinematic maps of the inner kpc of the early-type (Sa) barred spiral galaxy NGC5448. The observed morphology and kinematics of the emission-line gas is patchy and perturbed, indicating clear departures from circular motion. The kinematics of the stars is more regular, and display a small inner disk-like system embedded in a large-scale rotating structure. We focus on the [OIII] gas, and use a harmonic decomposition formalism to analyse the gas velocity field. The higher-order harmonic terms and the main kinematic features of the observed data are consistent with an analytically constructed simple bar model. The bar model is derived using linear theory, considering an m=2 perturbation mode, and with bar parameters which are consistent with the large-scale bar detected via imaging. We also study optical and near infra-red images to reveal the asymmetric extinction in NGC5448, and we recognise that some of the deviations between the data and the analytical bar model may be due to these complex dust features. Our study illustrates how the harmonic decomposition formalism can be used as a powerful tool to quantify non-circular motions in observed gas velocity fields.

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arXiv2004

Kinematics in the starbursting circumnuclear region of M100

We have obtained integral-field spectroscopic data, using the SAURON instrument, of the bar and starbursting circumnuclear region in the barred spiral galaxy M100. From our data we have derived kinematic maps of the mean velocity and velocity dispersion of the stars and the gas, which we present here. We have also produced maps of the total, [OIII], and Hbeta intensity. The gas velocity field shows significant kinematic signatures of gas streaming along the inner part of the bar, and of density wave streaming motions across the miniature spiral arms in the nuclear pseudo-ring. The stellar velocity field shows similar non-circular motions. The gas velocity dispersion is notably smaller where the star formation occurs in the nuclear zone and HII regions.

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arXiv2004

Long-Lived Triaxiality in the Dynamically Old Elliptical Galaxy NGC 4365: A Limit on Chaos and Black Hole Mass

Supermassive black holes in the centres of giant elliptical galaxies are thought to induce chaos and eliminate triaxiality in their hosts. We address whether this process operates in real systems, by modeling the stellar kinematics of the old elliptical NGC 4365. This galaxy has a mean stellar population age > 12 Gyr and is known for its kinematically decoupled core and skew rotation at larger radii. We fit the two-dimensional mean velocity field obtained by the SAURON integral-field spectrograph, and the isophotal ellipticity and position-angle profiles, using the velocity field fitting approach. We find NGC 4365 to be strongly triaxial (triaxiality parameter T approximately 0.45) and somewhat flatter than it appears. Axisymmetry or near axisymmetry (T < 0.1) is ruled out at > 95% confidence. In the most probable orientation the long axis points roughly toward the observer, extending to the southwest in projection. Strong triaxiality has persisted for hundreds of dynamical times, ruling out black holes above 3 x 10^9 solar masses. The M-sigma relation predicts 4 x 10^8 solar masses, which would not preclude long-lived triaxiality and is consistent with the observations. NGC 4365 lends support to a picture in which supermassive black holes, while omnipresent in luminous giant elliptical galaxies, are not massive enough to alter their global structure through chaos.

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arXiv2003

Minor axis kinematics of 19 S0-Sbc bulges

We present minor axis kinematic profiles for a well-studied sample of 19 early- to intermediate-type disk galaxies. We introduce, for the first time, the use of single-burst stellar population (SSP) models to obtain stellar velocities, velocity dispersions and higher order Gauss-Hermite moments (h3,h4) from galaxy spectra in the near-infrared Ca II triplet region. SSP models, which employs the synthetic spectra of Vazdekis et al. 2003, provide a means to address the template-mismatch problem, and are shown to provide as good or better fits as traditional stellar templates. We anticipate the technique to be of particular use for high-redshift galaxy kinematics. We give the measurement of a recently defined CaT* index Cenarro et al. 2001a, and describe the global properties of the bulge kinematics as derived from the kinematic profiles. We detect small-amplitude minor-axis rotation, generally due to inner isophotal twists as a result of slightly triaxial bulges or misaligned inner disks; such inner features do not show peculiar colors or distinct CaT* index values. Velocity dispersion profiles, which extend well into the disk region, show a wide range of slopes. Flattened bulges tend to have shallower velocity dispersion profiles. The inferred similarity of bulge and disk radial velocity dispersions supports the interpretation of these bulges as thickened disks.

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arXiv2003

The near-IR Ca II triplet - sigma relation for bulges of spiral galaxies

We present measurements of the near-infrared Calcium II triplet (CaT, CaT*), Paschen (PaT) and Magnesium (MgI) indices for a well-studied sample of 19 bulges of early to intermediate spiral galaxies. We find that both the CaT* and CaT indices decrease with central velocity dispersion (sigma) with small scatter. This dependence is similar to that recently found by Cenarro (2002) for elliptical galaxies, implying an uniform CaT* -- sigma relation that applies to galaxies from ellipticals to intermediate-type spirals. The decrease of CaT and CaT* with sigma contrasts with the well-known increase of another alpha-element index, Mg_2, with sigma. We discuss the role of Ca underabundance ([Ca/Fe]<0) and IMF variations in the onset of the observed relations.

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arXiv2002

The Peculiar Galaxy NGC7332

We present a detailed study of the edge-on S0 galaxy NGC7332. We show that this object lies significantly below the fundamental plane of early-type galaxies. To understand this behaviour, we have carried out observations with the Integral Field Spectrograph SAURON, which give us a detailed view of the internal kinematics and gas and stars in this galaxy.

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arXiv2002

Bulges on the Fundamental Plane of Early-Type Galaxies

In an ongoing effort to study the formation and evolution of galactic bulges we have investigated the position of 19 bulges of type S0-Sbc on the fundamental plane (FP). We find that bulges, both in B and K band, lie close to but slightly below the FP defined by ellipticals and S0s, i.e. are slightly brighter. There are hints that bulges of later morphological type are situated below the other bulges in our sample. The FP results are consistent with the picture, obtained from our recent analysis of HST-colours, that bulges are old, except for the Sbc galaxies. The fact that bulges lie so close to the FP of ellipticals and S0s implies that their formation epoch must have been similar, at most about 2.5 Gyr earlier, than cluster Es and S0s, and and that the surrounding disk does not significantly affect their structure.

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arXiv2001

Nested and Single Bars in Seyfert and Non-Seyfert Galaxies

We analyze the observed properties of nested and single stellar bar systems in disk galaxies. The 112 galaxies in our sample comprise the largest matched Seyfert vs. non-Seyfert sample of nearby galaxies with complete near-infrared or optical imaging sensitive to lengthscales ranging from tens of pc to tens of kpc. We find that a significant fraction of the sample galaxies, 17% +/- 4%, has more than one bar, and that 28% +/- 5% of barred galaxies have nested bars. The bar fractions appear to be stable according to reasonable changes in our adopted bar criteria. For these nested bars, we detect a clear division in length between the large-scale (primary) bars and small-scale (secondary) bars, both in absolute and normalized (to the size of the galaxy) length. We argue that this bimodal distribution can be understood within the framework of the inner Lindblad resonances (ILRs), which are located where the gravitational potential of the innermost galaxy switches effectively from 3D to 2D. While primary bars are found to correlate with the host galaxy sizes, no such correlation is observed for the secondary bars. Moreover, we find that secondary bars differ morphologically from single bars. Overall, our matched Seyfert and non-Seyfert samples show a statistically significant excess of bars among the Seyfert galaxies at practically all lengthscales. We confirm our previous result that Seyfert galaxies always show a preponderance of "thick" bars compared to the bars in non-Seyfert galaxies. Finally, no correlation is observed between the presence of a bar and that of companion galaxies, even relatively bright ones.

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arXiv2001

The SAURON project. I. The panoramic integral-field spectrograph

A new integral-field spectrograph, SAURON, is described. It is based on the Tiger principle, and uses a lenslet array. SAURON has a large field of view and high throughput, and allows simultaneous sky subtraction. Its design is optimized for studies of the stellar kinematics, gas kinematics, and line-strength distributions of nearby early-type galaxies. The instrument design and specifications are described, as well as the extensive analysis software which was developed to obtain fully calibrated spectra, and the associated kinematic and line-strength measurements. A companion paper reports on the first results obtained with SAURON on the William Herschel Telescope.

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arXiv2000

Galaxy mapping with the SAURON integral-field spectrograph: The star formation history of NGC 4365

We report the first wide-field mapping of the kinematics and stellar populations in the E3 galaxy NGC 4365. The velocity maps extend previous long-slit work. They show two independent kinematic subsystems: the central 300 x 700 pc rotates about the projected minor axis, and the main body of the galaxy, 3 x 4 kpc, rotates almost at right angles to this. The line-strength maps show that the metallicity of the stellar population decreases from a central value greater than solar, to one-half solar at a radius of 2 kpc. The decoupled core and main body of the galaxy have the same luminosity-weighted age, of ~14 Gyr, and the same elevated magnesium-to-iron ratio. The two kinematically distinct components have thus shared a common star formation history. We infer that the galaxy underwent a sequence of mergers associated with dissipative star formation that ended >12 Gyr ago. The misalignment between the photometric and kinematic axes of the main body is unambiguous evidence of triaxiality. The similarity of the stellar populations in the two components suggests that the observed kinematic structure has not changed substantially in 12 Gyr.

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arXiv2000

SAURON Observations of Disks in Early-Type Galaxies

We briefly describe the SAURON project, aimed at determining the intrinsic shape and internal dynamics of spheroids. We focus here on the ability of SAURON to identify gaseous and stellar disks and to measure their morphology and kinematics. We illustrate some of our results with complete maps of NGC3377, NGC3623, and NGC4365.

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arXiv2000

Deficiency of `Thin' Stellar Bars in Seyfert Host Galaxies

Using all available major samples of Seyfert galaxies and their corresponding control samples of closely matched non-active galaxies, we find that the bar ellipticities (or axial ratios) in Seyfert galaxies are systematically different from those in non-active galaxies. Overall, there is a deficiency of bars with large ellipticities (i.e., `fat' or `weak' bars) in Seyferts, compared to non-active galaxies. Accompanied with a large dispersion due to small number statistics, this effect is strictly speaking at the `2sigma' level. To obtain this result, the active galaxy samples of near-infrared surface photometry were matched to those of normal galaxies in type, host galaxy ellipticity, absolute magnitude, and, to some extent, in redshift. We discuss possible theoretical explanations of this phenomenon within the framework of galactic evolution, and, in particular, of radial gas redistribution in barred galaxies. Our conclusions provide further evidence that Seyfert hosts differ systematically from their non-active counterparts on scales of a few kpc.

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arXiv1999

Tracing the vertical composition of disc galaxies through colour gradients

(Abbreviated) Optical observations of a statistically complete sample of edge-on disc galaxies are used to study the intrinsic vertical colour gradients in the galactic discs, to constrain the effects of population gradients, residual dust extinction and gradients in the galaxies' metal abundance. It appears that the intrinsic vertical colour gradients are either non-existent, or small and relatively constant as a function of position along the galaxies' major axes. Our results are consistent with the absence of any vertical colour gradient in the discs of the early-type sample galaxies. In most galaxies small-scale variations in the magnitude and even the direction of the vertical gradient are observed: at larger galactocentric distances they generally display redder colours with increasing z height, whereas the opposite is often observed in and near the galactic centres. For a significant fraction of our sample galaxies another mechanism in addition to the effects of stellar population gradients is required to explain the magnitude of the observed gradients. The non-zero colour gradients in a significant fraction of our sample galaxies are likely (at least) partially due to residual dust extinction at these z heights, as is also evidenced from the sometimes significant differences between the vertical colour gradients measured on either side of the galactic planes. We suggest that initial vertical metallicity gradients, if any, have likely not been accentuated by accretion or merging events over the lifetimes of our sample galaxies. On the other hand, they may have weakened any existing vertical metallicity gradients, although they also may have left the existing correlations unchanged.

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arXiv1999

Two-Dimensional Line Strength Maps in Three Well-studied Early-Type Galaxies

Integral field spectroscopy has been obtained for the nuclear regions of 3 large, well-studied, early-type galaxies. From these spectra we have obtained line strength maps for about 20 absorption lines, mostly belonging to the Lick system. An extensive comparison with multi-lenslet spectroscopy shows that accurate kinematic maps can be obtained, and also reproducible line strength maps. Comparison with long-slit spectroscopy also produces good agreement. We show that Mg is enhanced with respect to Fe in the inner disk of one of the three galaxies studied, the Sombrero. [Mg/Fe] there is larger than in the rest of the bulge. The large values of Mg/Fe in the central disk are consistent with the centres of other early-type galaxies, and not with large disks, like the disk of our Galaxy, where [Mg/Fe] is approximately 0. We confirm with this observation a recent result of Worthey (1998) that Mg/Fe is determined by the central kinetic energy, or escape velocity, of the stars, only, and not by the formation time scale of the stars. A stellar population analysis using the models of Vazdekis et al. (1996) shows that our observed H gamma agrees well with what is predicted based on the other lines. Using the line strength of the Ca II IR triplet as an indicator of the abundance of Ca, we find that Ca follows Fe, and not Mg, in these galaxies. This is peculiar, given the fact that Ca is an alpha-element. Finally, by combining the results of this paper with those of Vazdekis et al. (1997) we find that the line strength gradients in the three galaxies are primarily caused by variations in metallicity.

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arXiv1999

A subarcsecond resolution near-infrared study of Seyfert and `normal' galaxies: II. Morphology

We present a detailed study of the bar fraction in the CfA sample of Seyfert galaxies, and in a carefully selected control sample of non-active galaxies, to investigate the relation between the presence of bars and of nuclear activity. To avoid the problems related to bar classification in the RC3, e.g., subjectivity, low resolution and contamination by dust, we have developed an objective bar classification method, which we conservatively apply to our new sub-arcsecond resolution near-infrared imaging data set (Peletier et al. 1999). We are able to use stringent criteria based on radial profiles of ellipticity and major axis position angle to determine the presence of a bar and its axial ratio. Concentrating on non-interacting galaxies in our sample for which morphological information can be obtained, we find that Seyfert hosts are barred more often (79% +/- 7.5%) than the non-active galaxies in our control sample (59% +/- 9%), a result which is at the 2.5 sigma significance level. The fraction of non-axisymmetric hosts becomes even larger when interacting galaxies are taken into account. We discuss the implications of this result for the fueling of central activity by large-scale bars. This paper improves on previous work by means of imaging at higher spatial resolution and by the use of a set of stringent criteria for bar presence, and confirms that the use of NIR is superior to optical imaging for detection of bars in disk galaxies.

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arXiv1999

A confirmed location in the Galactic halo for the high-velocity cloud 'chain A'

The high-velocity clouds of atomic hydrogen, discovered about 35 years ago, have velocities inconsistent with simple Galactic rotation models that generally fit the stars and gas in the Milky Way disk. Their origins and role in Galactic evolution remain poorly understood, largely for lack of information on their distances. The high-velocity clouds might result from gas blown from the Milky Way disk into the halo by supernovae, in which case they would enrich the Galaxy with heavy elements as they fall back onto the disk. Alternatively, they may consist of metal-poor gas -- remnants of the era of galaxy formation, accreted by the Galaxy and reducing its metal abundance. Or they might be truly extragalactic objects in the Local Group of galaxies. Here we report a firm distance bracket for a large high-velocity cloud, Chain A, which places it in the Milky Way halo (2.5 to 7 kiloparsecs above the Galactic plane), rather than at an extragalactic distance, and constrains its gas mass to between 10^5 and 2 times 10^6 solar masses.

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