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Aims. In this work we derive clues to the formation scenario and ionisation source of the lenticular galaxy NGC 3607 by means of metallicity gradients, stellar population, and emission lines properties.

Context. Studies of interacting galaxies have shown that dwarf galaxies may be produced in tidal tails during collisions. Numerical simulations suggest that the total detachment of the tidal dwarf requires the companion's mass to be comparable to or higher than that of the parent galaxy. This would imply that minor mergers (interaction between unequal mass galaxies) might not form tidal dwarf galaxies (TDGs).

Context.Understanding how each early-type galaxy forms and evolves is one of the objectives of extragalactic astrophysics and cosmology. The spatial distribution of the stellar populations inside a spheroidal system and their kinematic properties supply important information about the formation process. The reconstruction of the star formation history is crucial in this context.

Context.NGC 1380 is a lenticular galaxy located near the centre of the Fornax Cluster, northeast of NGC 1399. The globular cluster system of this galaxy has hitherto only been studied from the ground. Recent studies of similar early-type galaxies, specially lenticular ones, reveal the existence of star clusters that apparently break up the traditional open/globular cluster dichotomy.

Aims.We present a near-infrared spectral atlas of 47 active galactic nuclei (AGN) of all degrees of activity in the wavelength interval of 0.8–2.4 μm, including the fluxes of the observed emission lines. We analyze the spectroscopic properties of the continuum and emission line spectra of the sources.

Context.NGC 5846 is a giant elliptical galaxy with a previously well studied globular cluster system (GCS), known to have a bimodal colour distribution with a remarkably high red fraction.

The stellar population of the central region of the galaxy NGC 720has been investigated through longslit optical spectroscopy. The velocity dispersion and 13 Lick indices were obtained as a function of the radius along the semimajor axis of the galaxy. The Mg2index presents a gradient of ${\rm d\,Mg}_2\,/\,{\rm d\,log}\,r=-0.079$which behaves similarly to the $\ion{Fe}{i}$lines, indicating no enhancement of Mg2in relation to $\ion{Fe}{i}$. The stellar population ages and metallicities were derived by a population synthesis method using available evolutive spectrophotometric models. The synthesis indicates a strong age gradient along the semimajor axis of NGC 720. In the central region a 13 Gyr and solar metallicity stellar population dominates the flux at 5870 Å; the contribution of this component vanishes at a radius of 0.73 kpc, where the total flux is accounted for by a younger, 5 Gyr and solar metallicity stellar population. For distances larger than 1 kpc a 2.5 Gyr component becomes very important. Moreover, NGC 720is probably overabundant in CN in the center with respect to the solar abundance. The estimated total mass ($3.29\times10^{11}~M_\odot$) and the Mg2gradient values suggest that this galaxy might have undergone a merger event. The correspondence between the J-band brightness profile decomposition and the result of the spectral synthesis shows that this galaxy is formed by an old (13–5 Gyr), bulge-like, small-scale and massive spheroid and a younger (5–2.5 Gyr), large-scale disk component. We discuss our results in comparison with available numerical simulations and propose that the merger event must have occurred about 4 Gyr ago.

We present the results of the B, Vand Iphotometry of eleven southern minor mergers. The total apparent Bmagnitude, integrated $B-V$and $V-I$colours were measured. We built B, V, and Iequivalent profiles for each galaxy and decomposed them into bulge and disk components when possible. From Hα+N[II] images we have estimated the basic photometric parameters of the HII regions, such as position, size, $B-V$and $V-I$colours, Hα+[NII] luminosity and $EW(\rm H\alpha+[NII])$equivalent width. Primary components have blue absolute magnitudes in the range $-22 < M\!_B <-18$, with a peak at $M\!_B = - 22$. The magnitudes of the secondary components are in the range $-22 < M\!_B < -16$with a maximum at $M\!_B = -19$. Most pairs have Δ$M\!_B \sim 2$, which means that in luminosity the primary galaxy is on average about 6 times brighter than the secondary. We found a linear correlation between the luminosity ratios of the components and their ratio of major diameters, leading to mass ratios between $0.04 < \cal M_{\rm secondary}$/$\cal M$$_{\rm primary} < 0.2$, suggesting indeed that our sample is formed by minor mergers. On average the galaxies have colours bluer than those of isolated galaxies with the same morphological type. Most of the HII regions and evolved star-forming regions of the sample were formed between 3.6 to 13.7 Myr ago with an average of ($6.3\pm0.7$) Myr. The HII region properties, luminosity, sizes and ages are similar in both components. The HII regions have log (Hα+[NII]) luminosity between 38.6 and 41.7. The HII region luminosity function for the whole sample fits a power law of index α= –1.33. The linear correlation between the luminosity $\cal L$(Hα+[NII]) and the size of the HII regions has slope of $2.12\pm0.06$. We found that the disk of the primary component is more luminous than those of Lu's sample, while the disk of the secondary is smaller and fainter. A plot of the disk parameters does not change with colour. This indicates that the different stellar populations in the disks were affected in the same way.

Near-infrared spectroscopy is used to study the kinematics and excitation mechanisms of H2and [Fe ii] lines in a sample of mostly Seyfert 1 galaxies. The spectral coverage allows simultaneous observation of the JHKbands, thus eliminating the aperture and seeing effects that have usually plagued previous works. The H2lines are unresolved in all objects in which they were detected while the [Fe ii] lines have widths implying gas velocities of up to 650  km s-1. This suggests that, very likely, the H2and [Fe ii] emission does not originate from the same parcel of gas. Molecular H2lines were detected in 90% of the sample, including PG objects, indicating detectable amounts of molecular material even in objects with low levels of circumnuclear starburst activity. Analysis of the observations favors thermal excitation mechanisms for the H2lines. Indeed, in NGC 3227, Mrk 766, NGC 4051 and NGC 4151, the molecular emission is found to be purely thermal but with heating processes that vary between the objects. Thermal excitation is also confirmed by the rather similar vibrational and rotational temperatures in the objects for which data were available. [Fe ii] lines are detected in all of the sample AGN. The [Fe ii] 1.254 μm/Paβratio is compatible with excitation of the [Fe ii] lines by the active nucleus in most Seyfert 1 galaxies, but in Mrk 766 the ratio implies a stellar origin. A correlation between H2/Brγand [Fe ii]/Paβis found for our sample objects supplemented by data from the literature. The correlation of these line ratios is a useful diagnostic tool in the NIR to separate emitting line objects by their level of nuclear activity. X-ray excitation models are able to explain the observed H2and part of the [Fe ii] emission but fail to explain the observations in Seyfert 2 galaxies. Most likely, a combination of X-ray heating, shocks driven by the radio jet and circumnuclear star formation contributes, in different proportions, to the H2and [Fe ii] lines observed. In most of our sample objects, the [Fe ii] 1.257 μm/1.644 μm ratio is found to be 30% lower than the intrinsic value based on current atomic data. This implies either that the extinction towards the [Fe ii]-emitting clouds is very similar in most objects or there are possible inaccuracies in the A-values in the $\ion{Fe}{ii}$transitions.

In this work we investigate the stellar population, metallicity distribution and ionized gas in the elliptical galaxy NGC 5044, using long-slit spectroscopy and a stellar population synthesis method. We found differences in the slope of metal-line profiles along the galaxy which suggests an enhancement of αelements, particularly towards the central region. The stellar population synthesis showed that the component with $[Z/Z_\odot]\sim0.0$dominates the $\lambda5870$Å flux in the central region of NGC 5044, contributing with ~$42\%$of the total flux, while in the external regions the contribution decreases to ~$8.0\%$. The component with $[Z/Z_\odot]\sim-0.4$contributes with ~$32\%$in the central region, and ~$55\%$in the external regions. The component with $[Z/Z_\odot]\sim-1.1$contributes with ~$26\%$in the central region, and ~$37\%$in the external regions. The three components have ~1010years. The presence of a non-thermal ionization source, such as a low-luminosity AGN and/or shock ionization, is implied by the large values of the ratio $\frac{\ion{[N}{ii]}}{\rm H\alpha}$observed in all sampled regions. However, the emission lines observed in the external regions indicate the presence of an additional ionization source, probably hot, post-AGB stars.

CCD infrared (JHKs) photometry was performed on a sample of 10 elliptical and 2 lenticular galaxies. Isophotal parameters, brightness profiles, integrated colors and color gradients are presented. Color gradients found are very weak, showing bluer colors towards the outer regions. The colors of the sample galaxies are compatible with stellar populations like those found in metal-rich clusters of the Galaxy; objects NGC 7192, NGC 7562 and NGC 7619 are compatible with less metal-rich populations. The brightness profile of most galaxies is well described by the $r^{1/4}$law. The profiles of NGC 1600 and NGC 720 are described by Sérsic's law with $n\sim{1.5}$and $n\sim{1.8}$respectively. The infrared effective radius of the objects studied is typically one half of its counterpart in the Bband, which can be an indication that the stellar population that dominates the infrared emission is more concentrated in the central regions. We show that the sample satisfies the Fundamental Plane relation of elliptical galaxies in the infrared, with an rms scatter of 0.20 for Jand Hand 0.23 for Ks.

We present mid-IR photometric properties for a sample of 28 early-type galaxies observed at 6.75, 9.63 and 15 $\mu{} $m with the ISOCAM instrument on board the ISO satellite. We find total mid-IR luminosities in the range $(3{-}42) \times{} 10^{8}$$ L_{\odot}$. The spectral energy distributions (SED) of the galaxies were derived using the mid-IR data together with previously published UV, optical and near-IR data. These SEDs clearly show a mid-IR emission coming from dust heated at $T \simeq 260$K. Dust grains properties are inferred from the mid-IR colors. The masses of the hot dust component are in the range $10{-}400$$M_{\odot}$. The relationship between the masses derived from mid-IR observations and those derived from visual extinction are discussed. The possible common heating source for the gas and dust is investigated through the correlations between ${\rm H}\alpha$and mid-IR luminosities.

We present new valuable BVIphotometry of ten Seyfert 1 galaxies and narrow band Hαimages for six of these objects. The results indicate that the distribution of the luminosity of the sample has an amplitude of almost 4 mag with an average of MB=-20.7. The observed morphologies are confined to early type galaxies. A barred structure is found in only 2 objects. Despite that early morphological types are dominant in this sample, integrated ($B-V$) colors are very blue. For instance, the SO galaxies show, on average, a $(B-V)=0.78$. This effect seems to be caused by the luminosity contribution of the active nucleus and/or the disk to the total luminosity of the galaxy. In the Bband, the contribution of the active galactic nucleus to the total luminosity of the galaxy varies from 3% to almost 60% and the bulge to disk luminosity ratio ($L_{\rm bulge}/L_{\rm disk}$) ranges from 0.6 to 22. Signs of tidal interactions seem to be a common characteristic since they are observed in 6 of the objects and one of them seems to be located in a poor cluster not yet identified in the literature. In contrast, Hαextended emission is rare, with only 1 galaxy showing clear evidence of it. Luminosity profile decomposition shows that the model Gauss + bulge + disk properly reproduces the surface brightness of the galaxies. However, in order to account for the luminosity profile, most of the disk galaxies need the inner truncated exponential form with a central cutoff radius ranging from 3 to 10 kpc. This is interpreted in terms of reddened regions that are well identified in the $B-V$color maps. These regions present very similar colors among them, with $(B-V)\sim1.2$. This fact could be associated with the presence of dust confined in the inner regions of the galaxies.

Optical spectra were used to study the stellar population and gas emission, when present, in the central parts of the elliptical galaxies NGC$ $6958, NGC$ $6851 and ESO$ $185-G54, and the spiral galaxies NGC$ $5757, NGC$ $7412 and IC$ $4214. Stellar population properties were derived by comparing the equivalent widths of the absorption lines with those of galaxy templates built from star clusters, as well as by applying a method of stellar population synthesis based on the same star clusters. For the galaxies with emission lines, the underlying stellar population was subtracted to obtain the pure emission spectrum, and the resulting emission line intensities were measured to determine the mechanism responsible for the gas excitation. From this analysis we concluded that the galaxies have solar metallicity except the elliptical ESO$ $185-G54 that reached metallicity slightly above solar. The three ellipticals and the Sa galaxy IC$ $4214 have their nuclei dominated by old stellar populations, although IC$ $4214 appears to have some contribution from the young generation stars. Recent star formation ($t < 500$Myr) is prominent in the nucleus of the SBb galaxy NGC$ $5757, and is also present to a lesser degree in the Sbc NGC$ $7412. In these two galaxies, the recent star formation is responsible for the observed Hiitype emission lines, while IC$ $4214 has LINER emission. Among the ellipticals, only in NGC$ $6958 did we detect ionized gas, whose spectra is typical of LINERs.

We present results of a CCD optical imaging survey of the dust content in 22 early-type luminous galaxies, selected from the RC3 Catalog. A large fraction (75%) of the observed galaxies show significant amounts of dust. The morphology and size of the dust distribution of the observed galaxies follows very closely that of the ionized gas. For each galaxy, we have used broad band Vand Rfilters imaging to build colour maps and determine the AVand ARextinction maps. We have found typical AVvalues of 0.026 and ARof 0.023 and have derived $(V-R)$values in the range 0.49-0.68. The AVvalues together with an assumption of the dust grain size and composition enable us to estimate the dust masses. We have studied the correlations between the mass of dust and the Hα, IR and $L_{\mathrm{B}}$luminosities. Finally, we investigate the possible mechanisms responsible for the dust emission.

We analyse the UV properties of early-type galaxies from their UV spectra in the IUE library, including both normal and active nuclei. We co-added the spectra, and hence the objects into groups of similar spectral properties in the UV, also taking into account their properties in the visible/near-infrared ranges. Although, owing to the presence of a residual fixed pattern noise, IUE data cannot be improved by co-addition as expected for spectra containing only random noise, this procedure still provided spectra of higher signal/noise ratio than in previous studies, often based on individual spectra and therefrom derived colour indices. Thanks to the co-adding procedure, information on spectral features can now be assessed. The red stellar population groups exhibit a far-UV flux at different levels. The higher ones denote the presence of the UV turnup, which possibly exhibits absorption features, at least as detected through the IUE aperture. As to the blue stellar population groups and/or AGNs, we have carried out simple syntheses with UV star cluster templates and galaxy spectra in order to infer the properties such as burst ages and contamination by an active nucleus. It has been possible to derive information on the extinction law affecting some internally reddened galaxies; there are cases where the presence of the $\lambda2200$Å absorption feature suggests a reddening law similar to the Galactic one, and others without the $\lambda2200$Å  feature, suggesting that it is rather an SMC type law which applies, then.

Radial colour gradients in the globular clusters NGC 2808, NGC 1851, NGC 5139, NGC 5139, NGC 6388, NGC 6441, NGC 6541, NGC 6723, and NGC 7099 were searched byB-V and DDO photoelectric photometry, using a set of circular diaphragms. Two of the observed globular clusters, NGC 5139 (?Cen) and NGC 7099 (M30), showedB-V and C(45–48) colour gradients; the colour C(42–45) is essentially constant in these clusters, which means that the physical reason for those gradients cannot be attributed to chemical composition variations, since C(42–45) is a good metal abundance indicator.B-V colours in the external regions of NGC 5139 and NGC 7099 were obtained by synthesizing the observed HR diagrams of these clusters. The ages and the relaxation times for NGC 5139 and NGC 7099 indicate that mass segregation must have taken place in both clusters, which is probably related to the observed colour gradients.

Morphology and elliptically averaged luminosity profiles have been derived from CCD surface photometry of thirteen seyfert galaxies. ApparentV andI magnitudes,V-I colour index, as well as absolute Mv and MI magnitudes have been calculatedV andI luminosity profiles of Mk 10, Mk 79, Mk 358, Mk 618, Mk 352, and Mk 110, are adjusted by the usual model bulge plus disk with structural parameters comparable to those observed in normal spirals. The averaged luminosity profiles of Mk 50, Mk 124, Mk 348, and 3C227 are fitted byr-1/4 law with structural parameters similar to those observed in ellipticals and red compact galaxies. Mk 42 and NGC 985 show disturbed luminosity profiles.

We study the gas abundance in Seyfert 2 and LINER nuclei using optical emission-line data for a sample of 177 galaxies obtained from the literature. On the basis of photoionization model results it is shown that the range presented by the emission-line ratios [S II]/H? and [N II]/H? can only be reproduced by a range in sulfur and nitrogen abundances from half-solar to five times solar. The abundances of these two elements seem to be correlated. It is also shown that, if the apertures are small enough, the observed [S II]/H? values indicate overabundance of sulfur for most Seyfert 2 and LINER nuclei. A similar result has been previously found for nitrogen.

CCD frames in the B, V, R, and I passbands were obtained for the nearly edge-on spiral galaxy NGC 6835. The frames were analyzed to derive standard geometric and photometric parameters as well as luminosity and color distributions. The analysis of the luminosity profiles shows the existence of a flattened bulge and an exponential disk. The face-on parameters of the disk were obtained from a fit of an exponential disk seen edge-on to the observed data. The distribution of color indices along the major axis shows a pronounced blue gradient toward the nucleus, which we interpreted as a region of recent stellar formation.

Photometric, morphological and spectral grounds suggest that the peculiar nuclei regions of NGC 1097, 1672, 2997, 5236, and 7552 are composed basically of a normal nucleus surrounded by several large but otherwise normal (Te~8000 K,Ne~1000/cm3) H II regions. The stellar components are also normal although in some cases (NGC 1097, 1672, 1808 and 7552) there is a larger contribution of late type stars.

Spectral types, stellar population, and an estimation of metal abundances [Fe/H] were obtained for a sample of G and K peculiar stars from a list of Stock and Wroblewski and of metal-deficient stars from a list of Bond using DDO photometry.