ALBERT

Description: We study the distribution of projected ellipticity n () for galaxies in a sample of 20 rich (Richness ≥ 2) nearby ( z 〈 0.1) clusters of galaxies. We find no evidence of differences in n (), although the nearest cluster in the sample (the Coma Cluster) is the largest outlier ( P (same) 〈 0.05). We then study n () within the clusters, and find that increases with projected cluster-centric radius R (hereafter the -R relation). This trend is preserved at fixed magnitude, showing that this relation exists over and above the trend of more luminous galaxies to be both rounder and more common in the centres of clusters. The -R relation is particularly strong in the subsample of intrinsically flattened galaxies ( 〉 0.4), therefore it is not a consequence of the increasing fraction of round slow rotator galaxies near cluster centers. Furthermore, the -R relation persists for just smooth flattened galaxies and for galaxies with de Vaucouleurs-like light profiles, suggesting that the variation of the spiral fraction with radius is not the underlying cause of the trend. We interpret our findings in light of the classification of early type galaxies (ETGs) as fast and slow rotators. We conclude that the observed trend of decreasing towards the centres of clusters is evidence for physical effects in clusters causing fast rotator ETGs to have a lower average intrinsic ellipticity near the centres of rich clusters.

Description: We present a study into the capabilities of integrated and spatially resolved integral field spectroscopy of galaxies at z  = 2–4 with the future HARMONI spectrograph for the European Extremely Large Telescope (E-ELT) using the simulation pipeline, hsim . We focus particularly on the instrument's capabilities in stellar absorption line integral field spectroscopy, which will allow us to study the stellar kinematics and stellar population characteristics. Such measurements for star-forming and passive galaxies around the peak star formation era will provide a critical insight into the star formation, quenching and mass assembly history of high- z , and thus present-day galaxies. First, we perform a signal-to-noise study for passive galaxies at a range of stellar masses for z  = 2–4, assuming different light profiles; for this population, we estimate that integrated stellar absorption line spectroscopy with HARMONI will be limited to galaxies with M * 10 10.7  M . Secondly, we use hsim to perform a mock observation of a typical star-forming 10 10  M galaxy at z  = 3 generated from the high-resolution cosmological simulation nutfb . We demonstrate that the input stellar kinematics of the simulated galaxy can be accurately recovered from the integrated spectrum in a 15-h observation, using common analysis tools. Whilst spatially resolved spectroscopy is likely to remain out of reach for this particular galaxy, we estimate HARMONI's performance limits in this regime from our findings. This study demonstrates how instrument simulators such as hsim can be used to quantify instrument performance and study observational biases on kinematics retrieval; and shows the potential of making observational predictions from cosmological simulation output data.

Description: We analyse the sizes, colour gradients and resolved stellar mass distributions for 36 massive and passive galaxies in the cluster XMMUJ2235-2557 at z  = 1.39 using optical and near-infrared Hubble Space Telescope ( HST ) imaging. We derive light-weighted Sérsic fits in five HST bands ( i 775 , z 850 , Y 105 , J 125 , H 160 ), and find that the size decreases by ~20 per cent going from i 775 to H 160 band, consistent with recent studies. We then generate spatially resolved stellar mass maps using an empirical relationship between $M_{{\ast }}/L_{H_{160}}$ and ( z 850  –  H 160 ) and use these to derive mass-weighted Sérsic fits: the mass-weighted sizes are ~41 per cent smaller than their rest-frame r -band counterparts compared with an average of ~12 per cent at z  ~ 0. We attribute this evolution to the evolution in the $M_{{\ast }}/L_{H_{160}}$ and colour gradient. Indeed, as expected, the ratio of mass-weighted to light-weighted size is correlated with the M * / L gradient, but is also mildly correlated with the mass surface density and mass-weighted size. The colour gradients ( z  –  H ) are mostly negative, with a median value of ~0.45 mag dex –1 , twice the local value. The evolution is caused by an evolution in age gradients along the semimajor axis ( a ), with age  = dlog ( age )/dlog ( a ) ~– 0.33, while the survival of weaker colour gradients in old, local galaxies implies that metallicity gradients are also required, with Z  = dlog ( Z )/dlog ( a ) ~– 0.2. This is consistent with recent observational evidence for the inside–out growth of passive galaxies at high redshift, and favours a gradual mass growth mechanism, such as minor mergers.

Description: Using the Oxford Short Wavelength Integral Field specTrograph, we investigate radial variations of several initial mass function (IMF) dependent absorption features in M31 and M32. We obtain high signal-to-noise spectra at six pointings along the major axis of M31 out to ~700 arcsec (2.7 kpc) and a single pointing of the central 10 pc for M32. In M31 the sodium Na i 8190 index shows a flat equivalent width profile at ~0.4 Å through the majority of the bulge, with a strong gradient up to 0.8 Å in the central 10 arcsec (38 pc); the Wing–Ford FeH 9916 index is measured to be constant at 0.4 Å for all radii; and calcium triplet CaT 8498, 8542, 8662 shows a gradual increase through the bulge towards the centre. M32 displays flat profiles for all three indices, with FeH at ~0.5 Å, very high CaT at ~0.8 Å and low Na i at ~0.1 Å. We analyse these data using stellar population models. We find that M31 is well described on all scales by a Chabrier IMF, with a gradient in sodium enhancement of [Na/Fe] ~ +0.3 dex in the outer bulge, rising within the central 10 arcsec to perhaps [Na/Fe] ~ +1.0 dex in the nuclear region. We find M32 is described by a Chabrier IMF and young stellar age in line with other studies. Models show that CaT is much more sensitive to metallicity and [α/Fe] than to IMF. We note that the centres of M31 and M32 have very high stellar densities and yet we measure Chabrier IMFs in these regions.

Description: We present the SAMI Pilot Survey, consisting of integral field spectroscopy of 106 galaxies across three galaxy clusters, Abell 85, Abell 168 and Abell 2399. The galaxies were selected by absolute magnitude to have M r 〈 –20.25 mag. The survey, using the Sydney-AAO Multi-object Integral field spectrograph (SAMI), comprises observations of galaxies of all morphological types with 75 per cent of the sample being early-type galaxies (ETGs) and 25 per cent being late-type galaxies (LTGs). Stellar velocity and velocity dispersion maps are derived for all 106 galaxies in the sample. The R parameter, a proxy for the specific stellar angular momentum, is calculated for each galaxy in the sample. We find a trend between R and galaxy concentration such that LTGs are less concentrated higher angular momentum systems, with the fast-rotating ETGs (FRs) more concentrated and lower in angular momentum. This suggests that some dynamical processes are involved in transforming LTGs to FRs, though a significant overlap between the R distributions of these classes of galaxies implies that this is just one piece of a more complicated picture. We measure the kinematic misalignment angle, , for the ETGs in the sample, to probe the intrinsic shapes of the galaxies. We find the majority of FRs (83 per cent) to be aligned, consistent with them being oblate spheroids (i.e. discs). The slow rotating ETGs (SRs), on the other hand, are significantly more likely to show kinematic misalignment (only 38 per cent are aligned). This confirms previous results that SRs are likely to be mildly triaxial systems.

Description: In light of recent findings from the kinematic morphology–density relation, we investigate whether the same trends exist in the original morphology–density relation, using the same data as Dressler. In addition to Dressler's canonical relations, we find that further refinements are possible when considering the average local projected density of galaxies in a cluster. First, the distribution of ellipticals in a cluster depends on the relative local density of galaxies in that cluster: equivalent rises in the elliptical fraction occur at higher local densities for clusters with higher average local densities. This is not true for the late-type fraction, where the variation with local density within a cluster is independent of the average local density of galaxies in that cluster, and is as Dressler originally found. Furthermore, the overall ratio of ellipticals to early types in a cluster does not depend on the average density of galaxies in that cluster (unlike the ratio of lenticulars to disc systems), and is fixed at around 30 per cent. In the paradigm of fast and slow rotators, we show that such an elliptical fraction in the early type population is consistent with a slow rotator fraction of 15 per cent in the early type population, using the statistics of the ATLAS 3D survey. We also find the scatter in the overall ratio of ellipticals to early types is greatest for clusters with lower average densities, such that clusters with the highest elliptical fractions have the lowest average local densities. Finally, we show that average local projected density correlates well with global projected density, but the latter has difficulty in accurately characterizing the density of irregular cluster morphologies.

Description: We present hsim : a dedicated pipeline for simulating observations with the High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI) on the European Extremely Large Telescope. hsim takes high spectral and spatial resolution input data cubes, encoding physical descriptions of astrophysical sources, and generates mock observed data cubes. The simulations incorporate detailed models of the sky, telescope and instrument to produce realistic mock data. Further, we employ a new method of incorporating the strongly wavelength-dependent adaptive optics point spread functions. hsim provides a step beyond traditional exposure time calculators and allows us to both predict the feasibility of a given observing programme with HARMONI and perform instrument design trade-offs. In this paper, we concentrate on quantitative measures of the feasibility of planned observations. We give a detailed description of hsim and present two studies: estimates of point source sensitivities along with simulations of star-forming emission-line galaxies at z ~ 2–3. We show that HARMONI will provide exquisite resolved spectroscopy of these objects on sub-kpc scales, probing and deriving properties of individual star-forming regions.

Description: We present integral field spectroscopy of 10 early-type galaxies in the nearby, low-mass, Fornax cluster, from which we derive spatially resolved stellar kinematics. Based on the morphologies of their stellar velocity maps we classify 2/10 galaxies as slow rotators, with the remaining eight galaxies fast rotators. Supplementing our integral field observations with morphological and kinematic data from the literature, we analyse the ‘kinematic’ type of all 30 galaxies in the Fornax cluster brighter than M K  = –21.5 mag ( M * ~ 6 10 9 M ). Our sample's slow rotator fraction within one virial radius is $7^{+4}_{-6}$  per cent. $13^{+8}_{-6}$  per cent of the early-type galaxies are slow rotators, consistent with the observed fraction in other galaxy aggregates. The fraction of slow rotators in Fornax varies with cluster-centric radius, rising to 16 $^{+11}_{-8}$  per cent of all kinematic types within the central 0.2 virial radii, from 0 per cent in the cluster outskirts. We find that, even in mass-matched samples of slow and fast rotators, slow rotators are found preferentially at higher projected environmental density than fast rotators. This demonstrates that dynamical friction alone cannot be responsible for the differing distributions of slow and fast rotators. For dynamical friction to play a significant role, slow rotators must reside in higher mass sub-haloes than fast rotators and/or form in the centres of groups before being accreted on to the cluster.

Description: We examine the kinematic morphology of early-type galaxies (ETGs) in three galaxy clusters Abell 85, 168 and 2399. Using data from the Sydney-AAO Multi-object Integral field spectrograph we measure spatially resolved kinematics for 79 ETGs in these clusters. We calculate R , a proxy for the projected specific stellar angular momentum, for each galaxy and classify the 79 ETGs in our samples as fast or slow rotators. We calculate the fraction of slow rotators in the ETG populations ( f SR ) of the clusters to be 0.21 ± 0.08, 0.08 ± 0.08 and 0.12 ± 0.06 for Abell 85, 168 and 2399, respectively, with an overall fraction of 0.15 ± 0.04. These numbers are broadly consistent with the values found in the literature, confirming recent work asserting that the fraction of slow rotators in the ETG population is constant across many orders of magnitude in global environment. We examine the distribution of kinematic classes in each cluster as a function of environment using the projected density of galaxies: the kinematic morphology–density relation. We find that in Abell 85 f SR increases in higher density regions but in Abell 168 and 2399 this trend is not seen. We examine the differences between the individual clusters to explain this. In addition, we find slow rotators on the outskirts of two of the clusters studied, Abell 85 and 2399. These galaxies reside in intermediate to low density regions and have clearly not formed at the centre of a cluster environment. We hypothesize that they formed at the centres of groups and are falling into the clusters for the first time.