Long‐slit spectra have been obtained with the Keck telescope for a sample of 11 early‐type galaxies covering a wide range in luminosity and hence mass. Rotation velocity and velocity dispersions, together with 19 Lick line‐strength gradients have been measured, to, on average, two effective radii. Stellar population models taking into account the effect of the non‐solar chemical composition have been used to derive ages, metallicities and α/Fe abundances along the radius. We find that line‐strength gradients are due mainly to variations of the total metallicity with the radius. One galaxy out of 11 shows very strong age gradients, with a young central component, while the age gradient for the rest of the sample is very shallow or consistent with zero. We also find small variations in the [α/Fe] ratio with radius. Contrary to what is expected in simple collapse models, galaxies show both positive and negative [α/Fe] profiles. This rules out a solely inside‐out, or outside‐in, formation mechanism for all early‐type galaxies. We do not find a correlation between the metallicity and the [α/Fe] gradients, and the local metallicity is not correlated with the local velocity dispersion for all the galaxies of our sample, which rules out scenarios where the delay in the onset of the galactic winds is the only mechanism producing the metallicity gradients. We found that metallicity gradients are correlated with the shape of the isophotes and the central mean age and metallicity of the galaxies, for galaxies younger than ∼10 Gyr. We show that the correlation between the gradients and the central values is not due to the correlation of the errors and indicates that the same process that shaped the gradient, also modified the structural parameters of the galaxies and triggered star formation in their centres. This strongly supports the merger scenario for the formation of these systems, where the degree of dissipation during those mergers increases as the mass of the progenitor galaxies decreases. Finally, we also find a dichotomy in the plane grad [α/Fe]–[α/Fe] between galaxies with velocity dispersions below and above ∼200 km s−1, which requires confirmation with larger samples.

???The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.15686.xWe present the largest, most homogeneous catalogue of merging galaxies in the nearby Universe obtained through the Galaxy Zoo project ??? an interface on the World Wide Web enabling large-scale morphological classification of galaxies through visual inspection of images from the Sloan Digital Sky Survey (SDSS). The method converts a set of visually inspected classifications for each galaxy into a single parameter (the 'weighted-merger-vote fraction,'fm) which describes our confidence that the system is part of an ongoing merger. We describe how fm is used to create a catalogue of 3003 visually selected pairs of merging galaxies from the SDSS in the redshift range 0.005 < z < 0.1 . We use our merger sample and values of fm applied to the SDSS Main Galaxy Spectral sample to estimate that the fraction of volume-limited (Mr < ???20.55) major mergers (1/3 < M*1/M*2 < 3) in the nearby Universe is 1???3 ??C per cent, where C??? 1.5 is a correction factor for spectroscopic incompleteness. Having visually classified the morphologies of the constituent galaxies in our mergers, we find that the spiral-to-elliptical ratio of galaxies in mergers is higher by a factor of ???2 relative to the global population. In a companion paper, we examine the internal properties of these merging galaxies and conclude that this high spiral-to-elliptical ratio in mergers is due to a longer time-scale over which mergers with spirals are detectable compared to mergers with ellipticals

-A comparative analysis is performed between high-quality integrated spectral indices of 30 globular clusters in M31, 20 Milky Way globular clusters, and a sample of field and cluster elliptical galaxies. We find that the Lick CN indices in the M31 and Galactic clusters are enhanced relative to the bulges of the Milky Way, M31, and elliptical spheroids, in agreement with Burstein et al. Although not particularly evident in the Lick CN indices, the near-UV cyanogen feature (λ3883) is strongly enhanced with respect to the Galactic globulars at metallicities, -1.5<[Fe/H]<-0.3. Carbon shows signs of varying amongst these two groups. For [Fe/H]>-0.8, we observe no systematic differences in the Hδ, Hγ, or Hβ indices between the M31 and Galactic globulars, in contrast to previous studies. The elliptical galaxy sample lies offset from the loci of the globular clusters in the both the Cyanogen-[MgFe], and Balmer-line-[MgFe] planes. Six of the M31 clusters appear young, and are projected onto the M31 disk. Population synthesis models suggest that these are metal-rich clusters with ages 100-800 Myr, metallicities -0.20 ≤ [Fe/H] ≤ 0.35, and masses 0.7 ∼ 7.0 × 10 4 M ⊙ . Two other young clusters are Hubble V in NGC 205, observed as a template, and an older (∼3 Gyr) cluster some 7 kpc away from the plane of the disk. The six clusters projected onto the disk show signs of rotation similar to the HI gas in M31, and three clusters exhibit thin disk kinematics (Morrison et al.). Dynamical mass estimates and detailed structural parameters are required for these objects to determine whether they are massive open clusters or globular clusters. If they are the latter, our findings suggest globular clusters may trace the build up of galaxy disks. In either case, we conclude that these clusters are part of a young, metal-rich disk cluster system in M31, possibly as young as 1 Gyr old.Subject headings: globular clusters: general -galaxies: individual: M31 -galaxies: individual 4 In principle, this actually provides an overestimation since we also include the intrinsic uncertainties within the P02 data. However, the quadrature subtraction of these uncertainties in some cases leads to an uncertainty of zero.

We present a newly observed relation between galaxy mass and radial metallicity gradients of earlytype galaxies. Our sample of 51 early-type galaxies encompasses a comprehensive mass range from dwarf to brightest cluster galaxies. The metallicity gradients are measured out to one effective radius by comparing nearly all of the Lick absorption-line indices to recent models of single stellar populations. The relation shows very different behavior at low and high masses, with a sharp transition being seen at a mass of ∼ 3.5 × 10 10 M ⊙ (velocity dispersion of ∼ 140 km s −1 , M B ∼ −19). Low-mass galaxies form a tight relation with mass, such that metallicity gradients become shallower with decreasing mass and positive at the very low-mass end. Above the mass transition point several massive galaxies have steeper gradients, but a clear downturn is visible marked by a broad scatter. The results are interpreted in comparison with competing model predictions. We find that an early star-forming collapse could have acted as the main mechanism for the formation of low-mass galaxies, with star formation efficiency increasing with galactic mass. The high-mass downturn could be a consequence of merging and the observed larger scatter a natural result of different merger properties. These results suggest that galaxies above the mass threshold of ∼ 3.5 × 10 10 M ⊙ might have formed initially by mergers of gas-rich disk galaxies and then subsequently evolved via dry merger events. The varying efficiency of the dissipative merger-induced starburst and feedback processes have shaped the radial metallicity gradients in these high-mass systems.

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