arXiv subjects

R. F. Peletier

Publications and source records attributed to R. F. Peletier.

154 records · Page 9Linked to original sources

arXiv1996

Scale Lengths in Disk Surface Brightness as probes of Dust Extinction in 3 Spiral Galaxies: M 51, NGC 3631 and M 100

We have measured the radial brightness distributions in the disks of three nearby face-on spirals: M 51, NGC 3631, and NGC 4321 (M 100) in the photometric bands B through I, with the addition of the K band for M 51 only. The measurements were made by averaging azimuthally, in three modes, the two-dimensional surface brightness over the disks in photometric images of the objects in each band: (a) over each disk as a whole, (b) over the spiral arms alone, and (c) over the interarm zones alone. From these profiles scale-lengths were derived for comparison with schematic exponential disk models incorporating interstellar dust. These models include both absorption and scattering in their treatment of radiative transfer. The model fits show that the arms exhibit greater optical depth in dust than the interarm zones. The average fraction of emitted stellar light in V which is extinguished by dust within 3 scale-lengths of the center of each galaxy does not rise above 20% in any of them. We show that this conclusion is also valid for models with similar overall quantities of dust, but where this is concentrated in lanes. These can also account for the observed scale-lengths, and their variations.

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arXiv1995

NIR imaging and modeling of the core of M100

High-resolution NIR and optical images are used to constrain a dynamical model of the circumnuclear star forming (SF) region in the barred galaxy M100 (=NGC 4321). Subarcsecond resolution allowed us to distinguish important morphological details which are easily misinterpreted when using images at lower resolution. Small leading arms observed in our K-band image of the nuclear region are reproduced in the gas flow in our model, and lead us to believe that part of the K light comes from young stars, which trace the gas flow.

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arXiv1995

Stellar Populations of Bulges and Disks: New Insights from Near-IR Colours

Colours of spiral galaxies generally are affected by the underlying old stellar population, younger stars, and extinction by dust. Old and young populations generally can be disentangled using a combination of blue and near-infrared colours. Extinction effects are very hard to take into account, except for galaxies with special orientations. In this paper we give some results of one of the first studies of galactic bulges and disks in various optical and near-infrared bands, and its implications for the stellar populations of spirals.

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arXiv1995

Ages of galaxy bulges and disks from optical and near-infrared colours

For a sample of bright nearby early-type galaxies we have obtained surface photometry in bands ranging from U to K. Since the galaxies have inclinations larger than 50 deg. it is easy to separate bulges and disks. By measuring the colours in special regions, we minimize the effects of extinction, and by looking at B-K colour gradients we can show that for these type of spirals the colours mainly give information about stellar populations, and not extinction. We find that the differences between bulges and disks in all colours is very small, and using simple population models we can show that on the average the age difference between the bulge and the disk at 2 scale length is smaller than 30%, and much smaller if part of the difference is caused by a gradient in metallicity.

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arXiv1995

The Kinematics of the Ionized and Molecular Hydrogen in the Starburst Galaxy NGC 253

Near-infrared H_2 1-0 S(1) and Br_gamma velocity curves along the major axis of NGC 253 have revealed a central velocity gradient that is seven times steeper than that shown by the optical velocity curve. This is interpreted as an optical depth effect due to dust. Approximately 35 mag of visual extinction in the center is required to match the SW side of the optical velocity curve. The spatial variation of the ratio of these lines to the CO (J=1-0) line is compared among starburst galaxies NGC 253, M82, and NGC 4945 to investigate the excitation mechanism responsible for the H_2 1-0 S(1) line.

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arXiv1995

The extinction by dust in the outer parts of spiral galaxies

To investigate the distribution of dust in Sb and Sc galaxies we have analyzed near-infrared and optical surface photometry for an unbiased sample of 37 galaxies. Since light in the $K$-band is very little affected by extinction by dust, the $B-K$ colour is a good indicator of the amount of extinction, and using the colour-inclination relation we can statistically determine the extinction for an average Sb/Sc galaxy. We find in general a considerable amount of extinction in spiral galaxies in the central regions, all the way out to their effective radii. In the outer parts, at D$_{K,21}$, or at 3 times the typical exponential scale lengths of the stellar distribution , we find a maximum optical depth of 0.5 in $B$ for a face-on galaxy. If we impose the condition that the dust is distributed in the same way as the stars, this upper limit would go down to 0.1.

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arXiv1995

THE STRIKING NEAR-INFRARED MORPHOLOGY OF THE INNER REGION IN M100

New optical and NIR K-band images of the inner 3 kpc region of the nearby Virgo spiral M100 (NGC 4321) display remarkable morphological changes with wavelength. While in the optical the light is dominated by a circumnuclear zone of enhanced star formation, the features in the 2.2\mum image correspond to a newly discovered kpc-size stellar bar, and a pair of leading arms situated inside an ovally-shaped region. Only 5% of the K flux is emitted in antisymmetric structures. This indicates that the morphology seen in the NIR is dominated by a global density wave. Making a first-order correction for the presence of localized dust extinction in K using the I-K image, we find that the observed leading arm morphology is slightly hidden by dust. Possible mechanisms responsible for the optical and NIR morphology are discussed, and tests are proposed to discriminate between them. Conclusions are supported with an evolutionary stellar population model reproducing the optical and NIR colors in a number of star forming zones. We argue that this morphology is compatible with the presence of a pair of inner Lindblad resonances in the region, and show this explicitly in an accompanying paper by detailed numerical modeling. The observed phenomena may provide insight into physical processes leading to central activity in galaxies.

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arXiv1993

Synthetic metal line indices for elliptical galaxies from super metal rich alpha-enhanced stellar models

There are strong indications from recent papers (e.g. Worthey et al. 1992) that the abundance ratio of Mg/Fe, and consequently also O/Fe in giant elliptical galaxies is not solar. The line strengths of two Fe lines at 5270 and 5335 A are weaker than one expects from the strength of the Mg b line if [Mg/Fe] = 0. We have synthesized absorption line indices to derive the Mg and Fe abundances of these galaxies. For these models we have calculated new evolutionary tracks of high metallicity stars with a range of Mg/Fe abundances. This is the first time that such tracks have been generated. Integrating along isochrones to synthesize metal line strengths we find that for a typical bright giant elliptical [Mg/Fe] has to be between +0.3 and +0.7. We show that this result is independent of other parameters such as age, total metal content and mixing length parameter. The total metal content is super-solar, but the iron metallicity of elliptical galaxies not necessarily has to be larger than solar. For the formation of elliptical galaxies our result on the Mg and Fe abundances has the implication that most of the enrichment of the gas has to come from SNe II, which have more massive progenitors and as such produce relatively more O and Mg than Fe. It means that most of the stars have to be formed within a period of $3 \times 10^8$ years, so that there can only be one major collapse phase of the galaxy.

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arXiv1993

Colors and color gradients in bulges of galaxies

We have obtained surface photometry in U, B, R and I for a complete optically selected sample of 45 early-type spiral galaxies, to investigate the colors and color gradients of spiral bulges. Color profiles in U-R, B-R, U-B and R-I have been determined in wedges opening on the minor axes. Based on several criteria, we have defined a subsample of 18 objects whose colors are largely unaffected by dust. We find that the colors of bulges are predominantly bluer than those of ellipticals. This result holds even when bulges are compared to ellipticals of the same luminosity, and indicates that bulges are younger and/or more metal-poor than elliptical galaxies. Most bulges do not reach solar metallicities. Bulges show predominantly negative color gradients (bluer outward) that increases with bulge luminosity. The similarity with ellipticals suggests that the formation of the disk did not affect the stellar populations of the bulge in a major way.

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arXiv1993

The Infrared Tully-Fisher Relation in the Ursa-Major Cluster

We present new magnitudes derived from 1.65 micron images for 23 galaxies in the Ursa Major cluster. Magnitudes now exist for all but one spiral meeting our criteria for cluster membership and having HI velocity width greater than 187 km/s and inclination greater than 45 deg. These spirals fit a Tully-Fisher relation with dispersion in intrinsic magnitudes (after known observational uncertainties and the effect of cluster depth are removed) of 0.36 and a slope of 10.2 +/- 0.6. The magnitude dispersion is smaller than found in the Virgo cluster but still significantly larger than claimed by some authors. We find a hint that the Tully-Fisher relation may turn over at the bright end. Adding the central surface brightness of the disk as a third parameter flattens the slope of the Tully- Fisher relation and may give a distance estimate with slightly less dispersion, but the significance of the decrease must be tested on an independent sample.

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