We use the Atlas3D sample to perform a study of the intrinsic shapes of early-type galaxies, taking advantage of the available combined photometric and kinematic data. Based on our ellipticity measurements from the Sloan Digital Sky Survey Data Relea
se 7, and additional imaging from the Isaac Newton Telescope, we first invert the shape distribution of fast and slow rotators under the assumption of axisymmetry. The so-obtained intrinsic shape distribution for the fast rotators can be described with a Gaussian with a mean flattening of q=0.25 and standard deviation sigma_q = 0.14, and an additional tail towards rounder shapes. The slow rotators are much rounder, and are well described with a Gaussian with mean q = 0.63 and sigma_q =0.09. We then checked that our results were consistent when applying a different and independent method to obtain intrinsic shape distributions, by fitting the observed ellipticity distributions directly using Gaussian parametrisations for the intrinsic axis ratios. Although both fast and slow rotators are identified as early-type galaxies in morphological studies, and in many previous shape studies are therefore grouped together, their shape distributions are significantly different, hinting at different formation scenarios. The intrinsic shape distribution of the fast rotators shows similarities with the spiral galaxy population. Including the observed kinematic misalignment in our intrinsic shape study shows that the fast rotators are predominantly axisymmetric, with only very little room for triaxiality. For the slow rotators though there are very strong indications that they are (mildly) triaxial.
Recent deep Hubble Space Telescope WFC3 imaging suggests that a majority of compact quiescent massive galaxies at z~2 may contain disks. To investigate this claim, we have compared the ellipticity distribution of 31 carefully selected high-redshift m
assive quiescent compact galaxies to a set of mass-selected ellipticity and Sersic index distributions obtained from 2D structural fits to ~40,000$ nearby galaxies from the Sloan Digital Sky Survey. A Kolmogorov-Smirnov test shows that the distribution of ellipticities for the high-redshift galaxies is consistent with the ellipticity distribution of a similarly chosen sample of massive early-type galaxies. However the distribution of Sersic indices for the high-redshift sample is inconsistent with that of local early-type galaxies, and instead resembles that of local disk-dominated populations. The mismatch between the properties of high-redshift compact galaxies and those of both local early-type and disk-dominated systems leads us to conclude that the basic structures of high-redshift compact galaxies probably do not closely resemble those of any single local galaxy population. Any galaxy population analog to the high-redshift compact galaxies that exists at the current epoch is either a mix of different types of galaxies, or possibly a unique class of objects on their own.
We report observations of Lyman Alpha Blob 1 (LAB1) in the SSA 22 protocluster region (z=3.09) with the integral-field spectrograph SAURON. We increased the signal-to-noise in the spectra by more than a factor three compared to our previous observati
ons. This allows us to probe the structure of the LAB system in detail, examining its structure in the spatial and wavelength dimensions. We find that the emission from the system comes largely from five distinct blobs. Two of the emission regions are associated with Lyman Break Galaxies, while a third appears to be associated with a heavily obscured submillimeter galaxy. The fourth and fifth components do not appear to be associated with any galaxy despite the deep imaging that is available in this field. If we interpret wavelength shifts in the line centroid as velocity structure in the underlying gas, many of these emission systems show evidence of velocity shear. It remains difficult to distinguish between an underlying rotation of the gas and an outflow driven by the central object. We have examined all of the line profiles for evidence of strong absorption features. While several systems are better fitted by the inclusion of a weak absorption component, we do not see evidence for a large-scale coherent absorption feature such as that seen in LAB2.
We use the integral-field spectrograph SAURON to measure the stellar line-of-sight velocity distribution and absorption line strengths out to four effective radii (Re) in the early-type galaxies NGC 3379 and NGC 821. With our newly developed observin
g technique we can now probe these faint regions in galaxies that were previously not accessible with traditional long-slit spectroscopy. We make optimal use of the large field-of-view and high throughput of the spectrograph: by adding the signal of all ~1400 lenslets into one spectrum, we obtain sufficient signal-to-noise in a few hours of observing time to reliably measure the absorption line kinematics and line strengths out to large radius. We find that the line strength gradients previously observed within 1 Re remain constant out to at least 4 Re, which puts constraints on the merger histories of these galaxies. The stellar halo populations are old and metal-poor. By constructing orbit-based Schwarzschild dynamical models we find that dark matter is necessary to explain the observed kinematics in NGC 3379 and NGC 821, with 30 - 50 per cent of the total matter being dark within 4 Re. The radial anisotropy in our best-fit halo models is less than in our models without halo, due to differences in orbital structure. The halo also has an effect on the Mgb - Vesc relation: its slope is steeper when a dark matter halo is added to the model.
We describe a new technique to measure stellar kinematics and line-strengths at large radii in nearby galaxies. Using the integral-field spectrograph SAURON as a photon-collector, we obtain spectra out to four effective radii (Re) in the early-type g
alaxy NGC 3379. By fitting orbit-based models to the extracted stellar velocity profile, we find that ~40% of the total mass within 5 Re is dark. The measured absorption line-strengths reveal a radial gradient with constant slope out to 4 Re.
We present HI observations of the elliptical galaxy NGC 2974, obtained with the Very Large Array. These observations reveal that the previously detected HI disc in this galaxy (Kim et al. 1988) is in fact a ring. By studying the harmonic expansion of
the velocity field along the ring, we constrain the elongation of the halo and find that the underlying gravitational potential is consistent with an axisymmetric shape. We construct mass models of NGC 2974 by combining the HI rotation curve with the central kinematics of the ionised gas, obtained with the integral-field spectrograph SAURON. We introduce a new way of correcting the observed velocities of the ionised gas for asymmetric drift, and hereby disentangle the random motions of the gas caused by gravitational interaction from those caused by turbulence. To reproduce the observed flat rotation curve of the HI gas, we need to include a dark halo in our mass models. A pseudo-isothermal sphere provides the best model to fit our data, but we also tested an NFW halo and Modified Newtonian Dynamics (MOND), which fit the data marginally worse. The mass-to-light ratio M/L_I increases in NGC 2974 from 4.3 (M/L_I)sun at one effective radius to 8.5 (M/L_I)sun at 5 Re. This increase of M/L already suggests the presence of dark matter: we find that within 5 Re at least 55 per cent of the total mass is dark.
