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We report the discovery of an ultra-compact dwarf (UCD) associated with the Sombrero galaxy (M104). This is the closest massive UCD known and the first spectroscopically verified massive UCD which is located in a low-density environment. The object, we name SUCD1, was identified in Hubble Space Telescope ( HST)/Advanced Camera for Surveys (ACS) imaging and confirmed to be associated with the Sombrero galaxy by its recession velocity obtained from Keck spectra. The light profile is well fitted by a Wilson model. We measure a half-light size of , an absolute magnitude of and an internal velocity dispersion of . Such values are typical of UCDs. From Lick spectral indices we measure a luminosity-weighted central age of , [Fe/H] of and of . The lack of colour gradients suggests these values are representative of the entire UCD. The derived stellar and virial masses are the same, within errors, at . Thus, we find no strong evidence for dark matter or the need to invoke a non-standard initial mass function. We also report arguably the first X-ray detection of a bona fide UCD, which we attribute to the presence of low-mass X-ray binaries. The X-ray luminosity of is consistent with the values observed for globular clusters (GCs) of the same metallicity. Overall, we find SUCD1 has properties similar to other known UCDs and massive GCs. [ABSTRACT FROM AUTHOR]

A common feature of hierarchical galaxy formation models is the process of ‘inverse’ morphological transformation: a bulge dominated galaxy accretes a gas disc, dramatically reducing the system's bulge-to-disc mass ratio. During their formation, present-day galaxies may execute many such cycles across the Hubble diagram. A good candidate for such a ‘hermaphrodite’ galaxy is NGC 3108: a dust-lane early-type galaxy which has a large amount of H i gas distributed in a large-scale disc. We present narrow-band Hα and R-band imaging, and compare the results with the H i distribution from the literature. The emission is in two components: a nuclear bar and an extended disc component which coincides with the H i distribution. This suggests that a stellar disc is currently being formed out of the H i gas. The spatial distributions of the Hα and H i emission and the H ii regions are consistent with a barred spiral structure, extending some 20 kpc in radius. We measure an extinction-corrected star formation rate (SFR) of . The luminosity function of the H ii regions is similar to other spiral galaxies, with a power-law index of −2.1, suggesting that the star formation mechanism is similar to other spiral galaxies. We measured the current disc mass and find that it is too massive to have been formed by the current SFR over the last few Gyr. It is likely that the SFR in NGC 3108 was higher in the past. With the current SFR, the disc in NGC 3108 will grow to be in stellar mass within the next 5.5 Gyr. While this is substantial, the disc will be insignificant compared with the large bulge mass: the final stellar mass disc-to-bulge ratio will be ∼0.02. NGC 3108 will fail to transform into anything resembling a spiral without a boost in the SFR and additional supply of gas. [ABSTRACT FROM AUTHOR]

We present a possible star formation and chemical evolutionary history for two early-type galaxies NGC 1407 and NGC 1400. They are the two brightest galaxies of the NGC 1407 (or Eridanus-A) group, one of the 60 groups studied as part of the Group Evolution Multi-wavelength Study. Our analysis is based on new high signal-to-noise ratio spatially resolved integrated spectra obtained at the ESO 3.6-m telescope, out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. Using Lick/IDS indices, we estimate luminosity-weighted ages, metallicities and α-element abundance ratios. Colour radial distributions from HST/ACS and Subaru Suprime-Cam multiband wide-field imaging are compared to colours predicted from spectroscopically determined ages and metallicities using single stellar population (SSP) models. The galaxies formed over half of their mass in a single short-lived burst of star formation at redshift z≥ 5. This likely involved an outside–in mechanism with supernova-driven galactic winds, as suggested by the flatness of the α-element radial profiles and the strong negative metallicity gradients. Our results support the predictions of the revised version of the monolithic collapse model for galaxy formation and evolution. We speculate that, since formation, the galaxies have evolved quiescently and that we are witnessing the first infall of NGC 1400 in the group. [ABSTRACT FROM AUTHOR]

Here we present new measurements of effective radii, surface brightnesses and internal velocity dispersions for 23 isolated early-type galaxies. The photometric properties are derived from new multicolour imaging of ten galaxies, whereas the central kinematics for seven galaxies are taken from forthcoming work by Hau&Forbes. These are supplemented with data from the literature. We reproduce the colour–magnitude and Kormendy relations and strengthen the result of the recent work of Reda et al. that isolated galaxies follow the same photometric relations as galaxies in high-density environments. We also find that some isolated galaxies reveal fine structure indicative of a recent merger, while others appear undisturbed. We examine the Fundamental Plane both in the traditionalspace and also inκ space. Most isolated galaxies follow the same Fundamental Plane tilt and scatter for galaxies in high-density environments. However, a few galaxies notably deviate from the Plane in the sense of having smallerM/ Lratios. This can be understood in terms of their younger stellar populations, which are presumably induced by a gaseous merger. Overall, isolated galaxies have similar properties to those in groups and clusters with a slight enhancement in the frequency of recent mergers/interactions. [ABSTRACT FROM AUTHOR]

Hickson compact groups (HCGs) constitute an interesting extreme in the range of environments in which galaxies are located, as the space density of galaxies in these small groups are otherwise only found in the centres of much larger clusters. The work presented here uses Lick indices to make a comparison of ages and chemical compositions of galaxies in HCGs with those in other environments (clusters, loose groups and the field). The metallicity and relative abundance of ‘α-elements’ show strong correlations with galaxy age and central velocity dispersion, with similar trends found in all environments. However, we show that the previously reported correlation between α-element abundance ratios and velocity dispersion disappears when a full account is taken of the abundance ratio pattern in the calibration stars. This correlation is thus found to be an artefact of incomplete calibration to the Lick system. Variations are seen in the ranges and average values of age, metallicity and α-element abundance ratios for galaxies in different environments. Age distributions support the hierarchical formation prediction that field galaxies are on average younger than their cluster counterparts. However, the ages of HCG galaxies are shown to be more similar to those of cluster galaxies than those in the field, contrary to the expectations of current hierarchical models. A trend for lower velocity dispersion galaxies to be younger was also seen. This is again inconsistent with hierarchical collapse models, but is qualitatively consistent with the latest N-body smoothed particle hydrodynamics models based on monolithic collapse in which star formation continues for many Gyr in low-mass haloes. [ABSTRACT FROM AUTHOR]