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Observed abundances of elements heavier than helium may require a continuous infall of gas with metallicity around 0.1 times the solar value. In the distant Universe, low-metallicity hydrogen clouds are sometimes observed near galaxies. A metallicity of 0.09 times solar is reported for a massive cloud that is falling into the disk of the Milky Way.

Early results are reported from the SAURON survey of the kinematics and stellar populations of a representative sample of nearby E, S0 and Sa galaxies. The survey is aimed at determining the intrinsic shape of the galaxies, their orbital structure, the mass-to-light ratio as a function of radius, the age and metallicity of the stellar populations, and the frequency of kinematically decoupled cores and nuclear black holes. The construction of the representative sample is described, and its properties are illustrated. A comparison with long-slit spectroscopic data establishes that the SAURON measurements are comparable to, or better than, the highest-quality determinations. Comparisons are presented for NGC 3384 and 4365, where stellar velocities and velocity dispersions are determined to a precision of 6 km s[sup -1], and the h[sub 3] and h[sub 4] parameters of the line-of-sight velocity distribution to a precision of better than 0.02. Extraction of accurate gas emission-line intensities, velocities and linewidths from the data cubes is illustrated for NGC 5813. Comparisons with published line strengths for NGC 3384 and 5813 reveal uncertainties of ≲0.1 Å on the measurements of the Hβ, Mg b and Fe5270 indices. Integral-field mapping uniquely connects measurements of the kinematics and stellar populations to the galaxy morphology. The maps presented here illustrate the rich stellar kinematics, gaseous kinematics, and line-strength distributions of early-type galaxies. The results include the discovery of a thin, edge-on, disc in NGC 3623, confirm the axisymmetric shape of the central region of M32, illustrate the LINER nucleus and surrounding counter-rotating star-forming ring in NGC 7742, and suggest a uniform stellar population in the decoupled core galaxy NGC 5813. [ABSTRACT FROM AUTHOR]

A new stellar library at the near-IR spectral region developed for the empirical calibration of the Ca ii triplet and stellar population synthesis modelling is presented. The library covers the range λλ8348–9020 at 1.5-Å (FWHM) spectral resolution, and consists of 706 stars spanning a wide range in atmospheric parameters. We have defined a new set of near-IR indices, CaT*, CaT and PaT, which mostly overcome the limitations of previous definitions, the former being specially suited for the measurement of the Ca ii triplet strength corrected for the contamination from Paschen lines. We also present a comparative study of the new and the previous Ca indices, as well as the corresponding transformations between the different systems. A thorough analysis of the sources of index errors and the procedure to calculate them is given. Finally, index and error measurements for the whole stellar library are provided together with the final spectra. [ABSTRACT FROM AUTHOR]

We present a homogeneous set of stellar atmospheric parameters (T[sub eff], log g, [Fe/H]) for a sample of about 700 field and cluster stars which constitute a new stellar library in the near-IR developed for stellar population synthesis in this spectral region (λ8350–9020). Having compiled the available atmospheric data in the literature for field stars, we have found systematic deviations between the atmospheric parameters from different bibliographic references. The Soubiran, Katz & Cayrel sample of stars with very well determined fundamental parameters has been taken as our standard reference system, and other papers have been calibrated and bootstrapped against it. The obtained transformations are provided in this paper. Once most of the data sets were on the same system, final parameters were derived by performing error weighted means. Atmospheric parameters for cluster stars have also been revised and updated according to recent metallicity scales and colour–temperature relations. [ABSTRACT FROM AUTHOR]

We present subarcsecond-resolution, ground-based, near-infrared images of the central regions of a sample of 12 barred galaxies with circumnuclear star formation activity, which is organized in ring-like regions typically 1 kpc in diameter. We also present Hubble Space Telescope near-infrared images of 10 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 seven out of 10 HST images, star formation in the nuclear ring is clearly visible as a large number of small emitting regions, organized into spiral arm fragments, which are accompanied by dust lanes. Near-infrared 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. [ABSTRACT FROM AUTHOR]

Optical observations of a statistically complete sample of edge-on disc-dominated galaxies are used to study the intrinsic vertical colour gradients in the galactic discs, in order to constrain the effects of population gradients, residual dust extinction and gradients in the metal abundance of the galaxies. For the majority of our sample galaxies, the colours and colour gradients in the range 1.0h[sub z]⩽|z|⩽3.0h[sub z] most likely reflect the intrinsic galactic properties (where h[sub z] is the vertical scaleheight). It appears that the intrinsic vertical colour gradients are either non-existent, or small and relatively constant as a function of position along the major axes of the galaxies. On average, the earlier-type galaxies exhibit smaller vertical (B-I) gradients than the later types; 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 to be (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 probably 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. [ABSTRACT FROM AUTHOR]

Integral field spectroscopy has been obtained for the nuclear regions of three 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 multilenslet 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 disc 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 disc are consistent with the centres of other early-type galaxies, and not with large discs, like the disc of our Galaxy, where [Mg/Fe] ∼0. We confirm with this observation a recent result of Worthey: that Mg/Fe is determined only by the central kinetic energy, or escape velocity, of the stars, and not by the formation time-scale of the stars. A stellar population analysis using the models of Vazdekis et al. shows that our observed Hγ agrees well with what is predicted based on the other lines. Given the fact that Hβ is often contaminated by emission lines, we confirm the statement of Worthey & Ottaviani, Kuntschner & Davies and others that if one tries to measure ages of galaxies, Hγ is a much better index to use than Hβ. 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 α element. Finally, by combining the results of this paper with those of Vazdekis et al., we find that the line-strength gradients in the three galaxies are primarily caused by variations in metallicity. [ABSTRACT FROM AUTHOR]

We present optical and near-infrared colour maps of the central regions of bulges of S0 and spiral galaxies obtained with WFPC2 and NICMOS on the Hubble Space Telescope (HST). By combined use of HST and ground-based data, the colour information spans a region from a few tens of pc to a few kpc. In almost all galaxies, the colour profiles in the central 100–200 pc become more rapidly redder. We attribute the high central colour indices to a central concentration of dust. We infer an average extinction at the centre of A[sub V]=0.6–1.0 mag. Several objects show central dust rings or discs at subkpc scales similar to those found by others in giant ellipticals. For galactic bulges of types S0 to Sb, the tightness of the B-I versus I-H relation suggests that the age spread among bulges of early-type galaxies is small, at most 2 Gyr. Colours at 1R[sub eff], where we expect extinction to be negligible, are similar to those of elliptical galaxies in the Coma cluster, suggesting that these bulges formed at the same time as the bright galaxies in Coma. Furthermore, the galaxy ages are found to be independent of their environment. As it is likely that Coma was formed at redshift z>3, our bulges, which are in groups and in the field, must also have been formed at this epoch. Bulges of early-type spirals cannot be formed by secular evolution of bars at recent epochs, because such bulges would be much younger. There are three galaxies of type Sbc and later; their bulges are younger and could perhaps arise from secular evolution of transient bars. Our results are in good agreement with semi-analytic predictions, which also predict that bulges, in clusters and in the field, are as old as giant ellipticals in clusters. [ABSTRACT FROM AUTHOR]

We compare two methods of distance determination to spiral galaxies using optical/near-infrared (NIR) observations, the (I-K) versus M[sub 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°); by avoiding contamination by dust the scatter in the CM relation is significantly reduced, compared with similar galaxy samples published previously. The CM relation can be used to determine distances to field spiral galaxies with M[sub K]>-25.5, to at least M[sub 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 made 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 with 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 of the order of 25 per cent. 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 ∼15 per cent. However, one of the main advantages of the use of the NIR CM relation is that we need only photometric data to obtain distance estimates; use of the TFR requires additional kinematic data, although it can be used to significantly greater distances. [ABSTRACT FROM AUTHOR]