arXiv subjects
Publications and source records attributed to R. F. Peletier.
Early results are reported from the SAURON survey of the kinematics and stellar populations of nearby cluster and field E, S0, and Sa galaxies. We present maps of the Hbeta and [OIII] emission-line distribution and kinematics for NGC 5813 and NGC 7742.
By combining surface brightness profiles from images taken in the HST/NICMOS F160W and ground-based (GB) $K$ bands, we have obtained NIR profiles for a well studied sample of inclined disk galaxies, spanning radial ranges from 20 pc to a few kpc. We fit PSF-convolved Sersic-plus-exponential laws to the profiles, and compare the results with the fits to the ground-based data alone. HST profiles show light excesses over the best-fit Sersic law in the inner ~1 arcsec. This is often as a result of inner power-law cusps similar to the inner profiles of intermediate-luminosity elliptical galaxies.
Andredakis, Peletier & Balcells (1995) fit Sersic's law $μ(r) \sim r^{1/n}$ to the bulges of the Balcells & Peletier (1994) galaxy sample, and infer that $n$ drops with morphological type T from $n \approx$ 4--6 for S0 to $n=1$ (exponential) for Sc's. We use collisionless N body simulations to test the assumption that initially the surface brightness profiles of all bulges were exponential, and that the steepening of the profiles toward the early-types is due to satellite accretion. The results are positive. After the accretion of a satellite, bulge-disk fits show that the bulge grows and that the bulge profile index $n$ increases proportional to the satellite mass. For a satellite as massive as the bulge, $n$ rises from 1 to 4. We present kinematic diagnostics on the remnants and disk thickening. The latter suggests that the bulge growth must have occurred before the last formation of a thin disk in the galaxy. The thick disks created by the merger are reminiscent of thick disks seen in early-type edge-on galaxies. The efficiency of the process suggests that present day bulges of late-type spirals showing exponential profiles cannot have grown significantly by collisionless mergers.
We present Two-Dimensional Spectroscopy of the 9x12 arcsec^2 central region of M32 obtained with the 2D_FIS fibre spectrograph installed at the William Herschel Telescope. From these spectra line strength maps have been reconstructed for about 20 absorption lines, mostly belonging to the Lick system. We find good agreement with long-slit line strength profiles in the literature. In contrast with previous studies, indices were azimuthally averaged along continuum isophotes of M32. A remarkable result is that no gradients are presented in the spectral indices. So, we have fitted the mean values of each spectral index and central colours to the models of Vazdekis et al. (1996) and Worthey (1994), finding that an intermediate age (~4 Gyr) and metallicity similar to solar (Z=0.02) are the best fitted values for the innermost region of M32.
We present sub-arcsecond resolution ground-based near-infrared images of the central regions of a sample of twelve barred galaxies with circumnuclear star formation activity, which is organized in ring-like regions typically one kiloparsec in diameter. We also present Hubble Space Telescope near-infrared images of ten of our sample galaxies, and compare them with our ground-based data. Although our sample galaxies were selected for the presence of circumnuclear star formation activity, our broad-band near-infrared images are heterogeneous, showing a substantial amount of small-scale structure in some galaxies, and practically none in others. We argue that, where it exists, this structure is caused by young stars, which also cause the characteristic bumps or changes in slope in the radial profiles of ellipticity, major axis position angle, surface brightness and colour at the radius of the circumnuclear ring in most of our sample galaxies. In 7 out of 10 HST images, star formation in the nuclear ring is clearly visible as a large number of small emitting regions, organised into spiral arm fragments, which are accompanied by dust lanes. NIR colour index maps show much more clearly the location of dust lanes and, in certain cases, regions of star formation than single broad-band images. Circumnuclear spiral structure thus outlined appears to be common in barred spiral galaxies with circumnuclear star formation.
We compare two methods of distance determination to spiral galaxies using optical/near-infrared (NIR) observations, the (I-K) versus M_K colour - absolute magnitude (CM) relation and the I and K-band Tully-Fisher relation (TFR). Dust-free colours and NIR absolute magnitudes greatly enhance the usefulness of the NIR CM relation as a distance indicator for moderately to highly inclined_spiral_ galaxies_in the field_ (inclinations between ~ 80 and 90 deg); by avoiding contamination by dust the scatter in the CM relation is significantly reduced, compared to similar galaxy samples published previously. The CM relation can be used to determine distances to field spiral galaxies with M_K > -25.5, to at least M_K ~ -20. Our results, supplemented with previously published observations for which we can - to some degree - control the effects of extinction, are consistent with a universal nature of the CM relation for field spiral galaxies. High-resolution observations done with the Hubble Space Telescope can provide a powerful tool to calibrate the relation and extend the useful distance range by more than a factor of 2 compared to ground-based observations. The intrinsic scatter in the NIR CM relation in the absolute K-band magnitudes is ~0.5 mag, yielding a lower limit to the accuracy of distance determinations on the order of 25%. Although we find an unusually low scatter in the TFR (probably a statistical accident), a typical scatter in the TFR would yield distances to our sample galaxies with uncertainties of only about 15%. However, one of the main advantages of the use of the NIR CM relation is that_we only need photometric data_ to obtain distance estimates; use of the TFR requires additional kinematic data, although it can be used to significantly greater distances.
We present new high-resolution near-infrared observations in the J,H and K bands, obtained to study the properties of Seyfert host galaxies. The dataset consists of images in the three bands of practically the entire CfA sample of Seyfert galaxies, and K-band images of a control sample of non-active, `normal', galaxies, matched to the Seyfert sample in the distribution of type and inclination. The spatial resolution and sampling of the new images is a factor 2 better than previously published K-band data. In this paper, we present the data in the form of profiles of surface brightness and color, ellipticity and major axis position angle, as well as greyscale maps of surface brightness in H or K and both J-H and H-K colors. We compare our surface brightness and color profiles with the literature, and find good agreement. Our data are discussed in detail in three subsequent publications, where we analyze the morphologies of Seyfert and normal hosts, quantify the strength of nonaxisymmetric features in disks and their relationship to nuclear activity, address the question of bar fraction in Seyferts and normal galaxies, and analyze the color information in the framework of emission mechanisms in Seyfert 1s and 2s, and in non-active galaxies.
Low dispersion spectra have been obtained of five planetary nebulae in the elliptical galaxy NGC 5128 (Centaurus-A) from the catalogue of Hui et al. (1993). The planetary nebulae (PN) cover a range of galactocentric radius from 7.9 to 17.7 arcmin (8 to 18Kpc). The spectra display typical emission lines of H I, He I, He II, [O III], [N II] and [S II] and appear very similar to high excitation planetary nebulae in the Galaxy. This implies that, from a stellar evolution viewpoint, there should be no peculiar effects introduced by considering the bright cut-off of the PN luminosity function for distance estimation. In particular the brightest PN detected in NGC 5128 is not spectroscopically unusual. One of the PN shows relatively strong He II and [N II] lines and the derived N/O ratio indicates that it may be a Type I nebula, considered to arise from a high mass progenitor star. Determinations of the oxygen abundance of the five PN shows a mean value 0.5 dex below solar. Given that NGC 5128 is an elliptical galaxy with a presumably metal rich stellar content, the low metallicities of the PN are unexpected, although a similar situation has been observed in the bulge of M 31.
We present observations of the (field of the) Seyfert galaxy Mark290, which probes the high-velocity cloud (HVC) complex C, one of the largest HVCs. We find that this object has a metallicity of 0.094pm0.020(+0.022-0.019) times solar. We determine a lower limit to its distance of 5 kpc (z>3.5 kpc). If the gas is in thermal equilibrium with a hot halo, then it is also likely that D<30 kpc, putting the HVC in the Galactic Halo, as was the case for HVC complex~A (for which z=2.5--7 kpc). We find that, on this sightline, H+ represents 23pm10% of the hydrogen in the HVC. The total gaseous mass is 2x10^6 (D/5 kpc)^2 Msun and, depending on whether the space velocity is completely radial or vertical, the HVC represents a downward mass flux of ~0.036-0.083 (D/5 kpc) Msun/yr, or 2.9--6.7x10^{-3} (D/5 kpc)^{-1} Msun/yr/kpc^2. The low metallicity and large mass suggest that complex C is unlikely to be part of a Galactic Fountain, but rather represents accreting low-metallicity material. It may be a present-day analogue of the damped Ly-alpha absorbers seen in QSO spectra. Our abundance result provides the first direct observational evidence for the infall of low-metallicity gas on the Milky Way, required in models of galactic chemical evolution. It remains to be seen whether ultimately complex C is a remnant of the formation of the Milky Way (Oort 1970), a gas cloud orbiting the Galaxy (Kerr & Sullivan 1969), a Local Group object (Verschuur 1969, Blitz et al. 1996), the result of tidal interactions between the Magellanic System and the Galaxy >3 Gyr ago (an "Old Magellanic Stream"; Toomre, quoted in Kerr & Sullivan 1969), or was formed when hot, ionized intergalactic gas was compressed by the motion of the Milky Way (Silk et al. 1987).
We have determined a dust-free colour-magnitude (CM) relation for spiral galaxies, by using I-K colours in edge-on galaxies above the plane. We find that the scatter in this relation is small and approximately as large as can be explained by observational uncertainties. The slope of the near-IR CM relation is steeper for spirals than for elliptical galaxies. We suggest two possible explanations. First, the difference could be caused by vertical colour gradients in spiral galaxies. In that case these gradients should be similar for all galaxies, on average 0.15 dex in [Fe/H] per scale height, and increase for later galaxy types. The most likely explanation, however, is that spirals and ellipticals have intrinsically different CM relations. This means that the stars in spirals are younger than those in ellipticals. The age, however, or the fraction of young stars in spiral galaxies, would be determined solely by the galaxy's luminosity, and not by its environment.
We present a detailed study of a statistically complete sample of highly inclined disk galaxies in the near-infrared K' band. Since the K'-band light is relatively insensitive to contamination by galactic dust, we have been able to follow the vertical light distributions all the way down to the galaxy planes. The mean levels for the sharpness of the K'-band luminosity peaks indicate that the vertical luminosity distributions are more peaked than expected for the intermediate sech(z) distribution, but rounder than exponential. Since projection of not completely edge-on galaxies onto the plane of the sky causes vertical luminosity profiles to become rounder, we have performed simulations that show that it is possible that all our galaxies can have intrinsically exponential vertical surface brightness distributions. We find that the profile shape is independent of galaxy type, and varies little with position along the major axis. The fact that we observe this in all our sample galaxies indicates that the formation process of the galaxy disks perpendicular to the galaxy planes is a process intrinsic to the disks themselves.
We discuss some results of a morphological study of edge-on galaxies, based on optical and especially near-infrared surface photometry. We find that the vertical surface brightness distributions of galaxies are fitted very well by exponential profiles, much better than by isothermal distributions. We find that in general the vertical scale height increases when going outward. This increase is strong for early-type spiral galaxies and very small for late types. We argue that it can be due to the presence of thick discs with scale lengths larger than the galaxy's main disc. Finally we discuss the colour-magnitude relation in I-K for spiral galaxies. We find that it is a tight relation, for which the scatter is similar to the observational uncertainties, with a steeper slope than for elliptical galaxies.
We present the results of a detailed study of vertical surface brightness profiles of edge-on disk galaxies. Although the exponential disk scale height is constant to first order approximation, we show that for the large majority of galaxies in our sample, the scale height increases with distance along the major axis. The effect is strongest for early-type galaxies, where the increase of the scale height can be as much as a factor of 1.5 per scalelength, but is almost 0 for the latest-type galaxies. The effect can be understood if early-type disk galaxies have thick disks with both scale lengths and scale heights larger than those of the dominant disk component. Its origin appears to be linked to the processes that have formed the thick disk.
We present optical and near-infrared (NIR) surface brightness and colour profiles,in bands ranging from U to K, for the disk and bulge components of a complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than 50 degrees. We describe in detail the observations and the determination of colour parameters. Calibrated monochromatic and real-colour images are presented, as well as colour index maps. This data set, tailored for the study of the population characteristics of galaxy bulges, provides useful information on the colours of inner disks as well. In related papers, we have used them to quantify colour gradients in bulges, and age differentials between bulge and inner disk.
We present here the results of applying a new chemo-evolutionary stellar population model developed by ourselves in a previous paper (Vazdekis et al. 1996) to new high quality observational data of the nuclear regions of two representative elliptical galaxies and the bulge of the Sombrero galaxy. Here we fit in detail about 20 absorption lines and 6 optical and near-infrared colors following two approaches: fitting a single-age single-metallicity model and fitting our full chemical evolutionary model. We find that all of the iron lines are weaker than the best fitting models predict, indicating that the iron-abundance is anomalous and deficient. We also find that the Ca_I index at 4227 A is much lower than predicted by the models. We can obtain good fits for all the other lines and observed colors with models of old and metal-rich stellar populations, and can show that the observed radial gradients are due to metallicity decreasing outward. We find that good fits are obtained both with fully evolutionary models and with single-age single-metallicity models. This is due to the fact that in the evolutionary model more than 80% of stars form with in 1.5 Gyr after the formation of the galaxies. The fact that slightly better fits are obtained with evolutionary models indicates these galaxies contain a small spread in metallicity.
We have developed a new stellar population synthesis model designed to study early-type galaxies. It provides optical and near-infrared colors, and line indices for 25 absorption lines. It can synthesize single age, single metallicity stellar populations or follow the galaxy through its evolution from an initial gas cloud to the present time. The model incorporates the new isochrones of the Padova group and the latest stellar spectral libraries. The model has been extensively compared with previous ones in the literature to establish its accuracy as well as the accuracy of this kind of models in general. Using the evolutionary version of the model we find that we cannot fit the most metal-rich elliptical galaxies if we keep the IMF constant and do not allow infall of gas. We do however reproduce the results of Arimoto \& Yoshii (1986) for the evolution of the gas, and produce colors, and, for the first time with this type of models, absorption line-strengths. It is in fact possible to fit the data for the elliptical galaxies by varying the IMF with time. Our numerical model is in good broad agreement with the analytical 'simple model'. In the present paper we describe the model, and compare a few key observables with new data for three early-type {\em standard} galaxies. However the data, as well as our fits, will be discussed in much more detail in a second paper (Vazdekis {\it et al.} 1996), where some conclusions will be drawn about elliptical galaxies on the basis of this model.
We have found that the bulge of the large, nearby Sb galaxy NGC 7331 rotates retrograde to its disk. Analysis of spectra in the region of the near-IR Ca II triplet along the major axis shows that, in the radial range between 5'' and ~20'', the line of sight velocity distribution of the absorption lines has two distinct peaks, and can be decomposed into a fast-rotating component with v/sigma > 3, and a slower rotating, retrograde component with v/sigma between 1 -- 1.5. The radial surface brightness profile of the counter-rotating component follows that of the bulge, obtained from a 2-dimensional bulge-disk decomposition of a near-infrared K-band image, while the fast rotating component follows the disk. At the radius where the disk starts to dominate the isophotes change from being considerably boxy to very disky. Although a number of spiral galaxies have been found that contain cold, couter-rotating disks, this is the first galaxy known to have a boxy, probably triaxial, fairly warm, counter-rotating component, which is dominating in the central regions. If it is a bar seen end-on, this bar has to be thicker than the disk. We find that NGC 7331, even though it is a fairly early-type spiral, does not have a conventional, co-rotating bulge. The fact that the inner component is retrograde makes us believe that it was formed from infalling material, in either stellar or gaseous form (e.g. Balcells & Quinn 1990). Another possibility however is that the structure has been there since the formation of the galaxy. In this case it will be a challenge to explain the large change in orientation of the angular momentum when going outward radially.
We compare optical and near-infrared colors of disks and bulges in a diameter-limited sample of inclined, bright, nearby, early-type spirals. Color profiles along wedge apertures at 15 degree from the major axis and on the minor axis on the side of the galaxy opposite to the dust lane are used to assign nominal colors for the inner disks (at 2 scale length) and for the bulges (~ 0.5 r_eff), respectively. We estimate that the effects of dust reddening and the cross-talk between the colors of the two components is negligible. We find that color differences (bulge -- disk) are very small: Delta(U-R)=0.126 +/- 0.165, Delta(R-K)=0.078 +/- 0.165. Disks tend to be bluer by an amount three times smaller than that reported by Bothun & Gregg (1990) for S0's. Color variations from galaxy to galaxy are much larger than color differences between disk and bulge in each galaxy. Probably, the underlying old population of disks and bulges is much more similar than the population paradigm would lead us to believe. Implied age differences, assuming identical metallicities, are less than 30%.