We present stellar kinematics of 22 nearby early-type galaxies (ETGs), based on two-dimensional (2D) absorption line stellar spectroscopy out to ~2-4R sub(e) (effective radii), as part of the ongoing ...SLUGGS Survey. The galaxies span a factor of 20 in intrinsic luminosity, as well as a full range of environment and ETG morphology. Our data consist of good velocity resolution (sigma sub(inst) ~ 25 km s super(-1)) integrated stellar-light spectra extracted from the individual slitlets of custom made Keck/DEIMOS slitmasks. We extract stellar kinematics measurements (V, sigma, h sub(3) and h sub(4)) for each galaxy. Combining with literature values from smaller radii, we present 2D spatially resolved maps of the large-scale kinematic structure in each galaxy. We find that the kinematic homogeneity found inside 1 R sub(e) often breaks down at larger radii, where a variety of kinematic behaviors are observed. While central slow rotators remain slowly rotating in their halos, central fast rotators show more diversity, ranging from rapidly increasing to rapidly declining specific angular momentum profiles in the outer regions. There are indications that the outer trends depend on morphological type, raising questions about the proposed unification of the elliptical and lenticular (S0) galaxy families in the ATLAS super(3D) survey. Several galaxies in our sample show multiple lines of evidence for distinct disk components embedded in more slowly rotating spheroids, and we suggest a joint photometric-kinematic approach for robust bulge-disk decomposition. Our observational results appear generally consistent with a picture of two-phase (in-situ plus accretion) galaxy formation.
We present a study of the dynamical properties of 125 compact stellar systems (CSSs) in the nearby giant elliptical galaxy NGC 5128, using high-resolution spectra (R approx = 26,000) obtained with ...Very Large Telescope/FLAMES. Our results provide evidence for a new type of star cluster, based on the CSS dynamical mass scaling relations. All radial velocity (vr) and line-of-sight velocity dispersion (sigma sub(los)) measurements are performed with the penalized pixel fitting (ppxf) technique, which provided sigma sub(ppxf) estimates for 115 targets. The sigma sub(ppxf) estimates are corrected to the 2D projected half-light radii, sigma sub(1/2), as well as the cluster cores, sigma sub(0), accounting for observational/aperture effects and are combined with structural parameters, from high spatial resolution imaging, in order to derive total dynamical masses (scriptM sub(dyn)) for 112 members of NGC 5128's star cluster system. In total, 89 CSSs have dynamical masses measured for the first time along with the corresponding dynamical mass-to-light ratios (ProQuest: Formulae and/or non-USASCII text omitted). We find two distinct sequences in the (ProQuest: Formulae and/or non-USASCII text omitted) plane, which are well approximated by power laws of the forms (ProQuest: Formulae and/or non-USASCII text omitted) and (ProQuest: Formulae and/or non-USASCII text omitted). The shallower sequence corresponds to the very bright tail of the globular cluster luminosity function (GCLF), while the steeper relation appears to be populated by a distinct group of objects that require significant dark gravitating components such as central massive black holes and/or exotically concentrated dark matter distributions. This result would suggest that the formation and evolution of these CSSs are markedly different from the "classical" globular clusters in NGC 5128 and the Local Group, despite the fact that these clusters have luminosities similar to the GCLF turnover magnitude. We include a thorough discussion of myriad factors potentially influencing our measurements.
We use multipointing Hubble Space Telescope Advanced Camera for Surveys and wide field Subaru Suprime-Cam imaging to study the globular cluster system of the L* elliptical galaxy NGC 4278. We have ...also obtained a handful of new globular cluster spectra with the Keck Deep Imaging Multi-Object Spectrograph. We determine the globular cluster surface density profile and use it to calculate the total number of globular clusters, finding the system to be slightly more populous than average for galaxies of its luminosity. We find clear evidence for bimodality in the globular cluster colour distribution and for a colour-magnitude relation in the blue subpopulation (a 'blue tilt'). We also find negative radial colour gradients in both colour subpopulations of equal strength which are similar in strength to those reported in other galaxies. The sizes of NGC 4278's globular clusters decrease with redder colours and increase with galactocentric radius. The ratio of the sizes of blue to red globular clusters is independent of galactocentric radius demonstrating that internal effects are responsible for the size difference with colour.
NGC 5128, a giant elliptical galaxy only ~4 Mpc away, is the dominant member of a galaxy group of over 80 probable members. The Centaurus group provides an excellent sample for a kinematic comparison ...between the halo of NGC 5128 and its surrounding satellite galaxies. A new study, presented here, shows no kinematic difference in rotation amplitude, rotation axis, or velocity dispersion between the halo of NGC 5128, determined from over ~340 of its globular clusters, and those of the Centaurus group as a whole. These results suggest NGC 5128 could be behaving in part as the inner component to the galaxy group, and could have begun as a large initial seed galaxy, gradually built up by minor mergers and satellite accretions, consistent with simple cold dark matter models. The masses and mass-to-light ratios in the B band, corrected for projection effects, are determined to be (1.3 ± 0.5) X 1012 M and 52 ± 22 M L for NGC 5128 out to a galactocentric radius of 45 kpc and (9.2 ± 3.0) X 1012 M and 153 ± 50 M L for the Centaurus group, consistent with previous studies.
We present new integrated light spectroscopy of globular clusters (GCs) in NGC 5128, a nearby giant elliptical galaxy less than 4 Mpc away, in order to measure radial velocities and derive ages, ...metallicities, and alpha-element abundance ratios. Using the Gemini South 8 meter telescope with the instrument Gemini Multi-Object Spectrograph, we obtained spectroscopy in the range of ~3400-5700 A for 72 GCs with a signal-to-noise ratio greater than 30 A-1; and we have also discovered 35 new GCs within NGC 5128 from our radial velocity measurements. We measured and compared the Lick indices from Hdelta A through Fe5406 with the single stellar population models of Thomas et al. in order to derive age, metallicity, and alpha/Fe values. We also measure Lick indices for 41 Milky Way GCs from Puzia et al. and Schiavon et al. with the same methodology for direct comparison. Our results show that 68% of the NGC 5128 GCs have old ages ( > 8 Gyr), 14% have intermediate ages (5-8 Gyr), and 18% have young ages ( < 5 Gyr). However, when we look at the metallicity of the GCs as a function of age, we find 92% of metal-poor GCs and 56% of metal-rich GCs in NGC 5128 have ages > 8 Gyr, indicating that the majority of both metallicity subpopulations of GCs formed earlier, with a significant population of young and metal-rich GCs forming later. Our metallicity distribution function generated directly from spectroscopic Lick indices is clearly bimodal, as is the color distribution of the same set of GCs. Thus, the metallicity bimodality is real and not an artifact of the color to metallicity conversion. However, the metallicity distribution function obtained from comparison with the single stellar population models is consistent with a unimodal, bimodal, or multimodal shape. The alpha/Fe values are supersolar with a mean value of 0.14 +/- 0.04, indicating a fast formation timescale. However, the GCs in NGC 5128 are not as alpha/Fe enhanced as the Milky Way GCs also examined in this study. Our measured indices also indicate that the GCs in NGC 5128 may have a slight overabundance in nitrogen and a wider range of calcium strength compared to the Milky Way GCs. Our results support a rapid, early formation of the GC system in NGC 5128, with subsequent major accretion and/or GC and star-forming events in more recent times.
Using deep Hubble Space Telescope imaging, color-magnitude diagrams are constructed for the globular clusters 47 Tuc and NGC 6397. As expected, because of its lower metal abundance, the main sequence ...of NGC 6397 lies well to the blue of that of 47 Tuc. A comparison of the white dwarf cooling sequences of the two clusters, however, demonstrates that these sequences are indistinguishable over most of their loci-a consequence of the settling out of heavy elements in the dense white dwarf atmosphere and the near equality of their masses. Lower quality data on M4 continues this trend to a third cluster whose metallicity is intermediate between these two. While the path of the white dwarfs in the color-magnitude diagram is nearly identical in 47 Tuc and NGC 6397, the numbers of white dwarfs along the path are not. This results from the relatively rapid relaxation in NGC 6397 compared to 47 Tuc and provides a cautionary note that simply counting objects in star clusters in random locations as a method of testing stellar evolutionary theory is likely dangerous unless dynamical considerations are included.
New radial velocity measurements for previously known and newly confirmed globular clusters (GCs) in the nearby massive galaxy NGC 5128 are presented. We have obtained spectroscopy from ...LDSS-2/Magellan, VIMOS/Very Large Telescope, and HYDRA/Cerro Tololo Inter-American Observatory from which we have measured the radial velocities of 218 known, and identified 155 new, GCs. The current sample of confirmed GCs in NGC 5128 is now 605 with 563 of these having radial velocity measurements, the second largest kinematic database for any galaxy. We have performed a new kinematic analysis of the GC system that extends out to 45' in galactocentric radius. We have examined the systemic velocity, projected rotation amplitude and axis, and the projected velocity dispersion of the GCs as functions of galactocentric distance and metallicity. Our results indicate that the metal-poor GCs have a very mild rotation signature of 26 ? 15 km s--1. The metal-rich GCs are rotating with a higher, though still small signature of 43 ? 15 km s--1 around the isophotal major axis of NGC 5128 within 15'. Their velocity dispersions are consistent within the uncertainties and the profiles appear flat or declining within 20'. We note the small sample of metal-rich GCs with ages less than 5 Gyr in the literature appear to have different kinematic properties than the old, metal-rich GC subpopulation. The mass and mass-to-light ratios have also been estimated using the GCs as tracer particles for NGC 5128. Out to a distance of 20', we have obtained a mass of (5.9 ? 2.0) X 1011 M and a mass-to-light ratio in the B band of 16 M /L B. Combined with the previous work on the ages and metallicities of its GCs, as well as properties of its stellar halo, our findings suggest NGC 5128 formed via hierarchical merging over other methods of formation, such as major merging at late times.
We investigate the shallow increase in globular cluster half-light radii with projected galactocentric distance R
gc observed in the giant galaxies M87, NGC 1399, and NGC 5128. To model the trend in ...each galaxy, we explore the effects of orbital anisotropy and tidally underfilling clusters. While a strong degeneracy exists between the two parameters, we use kinematic studies to help constrain the distance R
β beyond which cluster orbits become anisotropic, as well as the distance R
fα beyond which clusters are tidally underfilling. For M87 we find R
β > 27 kpc and 20 < R
fα < 40 kpc and for NGC 1399 R
β > 13 kpc and 10 < R
fα < 30 kpc. The connection of R
fα with each galaxy's mass profile indicates the relationship between size and R
gc may be imposed at formation, with only inner clusters being tidally affected. The best-fitting models suggest the dynamical histories of brightest cluster galaxies yield similar present-day distributions of cluster properties. For NGC 5128, the central giant in a small galaxy group, we find R
β > 5 kpc and R
fα > 30 kpc. While we cannot rule out a dependence on R
gc, NGC 5128 is well fitted by a tidally filling cluster population with an isotropic distribution of orbits, suggesting it may have formed via an initial fast accretion phase. Perturbations from the surrounding environment may also affect a galaxy's orbital anisotropy profile, as outer clusters in M87 and NGC 1399 have primarily radial orbits while outer NGC 5128 clusters remain isotropic.
In Hubble Space Telescope (HST) Cycle 17, we imaged the well-known globular star cluster 47 Tucanae for 121 orbits using the Wide Field Channel of the Advanced Camera for Surveys (ACS) and both the ...UV/visible (UVIS) and IR channels of the newly installed Wide Field Camera 3 (WFC3) instrument (GO-11677, PI: H. Richer). This unique data set was obtained to address many scientific questions that demand a very deep, panchromatic, and panoramic view of the cluster's stellar populations. In total, the program obtained over 0.75 Ms of imaging exposure time with the three HST cameras, over a time span of 9 months in 2010. The primary ACS field was imaged in the two broadband filters F606W and F814W, at 13 orientations, for all 121 orbits. The parallel WFC3 imaging provides a panchromatic (0.4-1.7 Delta *mm) and contiguous imaging swath over a 250? azimuthal range at impact radii of 6.5-17.9 pc in 47 Tuc. This imaging totals over 60 arcmin2 in area and utilizes the F390W and F606W broadband filters on WFC3/UVIS and the F110W and F160W broadband filters on WFC3/IR. In this paper, we describe the observational design of the new survey and one of the methods used to analyze all of the imaging data. This analysis combines over 700 full-frame images taken with the three HST cameras into a handful of ultra-deep, well-sampled combined images in each of the six filters. We discuss in detail the methods used to calculate accurate transformations that provide optimal alignment of the input images, the methods used to perform sky background offsets in the input stack and the flagging of deviant pixels, and the balance reached between the input-pixel drop size onto an output supersampled pixel grid. Careful photometric, morphological, and astrometric measurements are performed on the stacks using iterative PSF-fitting techniques, and reveal unprecedented color-magnitude diagrams of the cluster extending to >30th magnitude in the optical, 29th magnitude in the UV, and 27th magnitude in the IR. The data set provides a characterization of the complete stellar populations of 47 Tuc, extending from the faintest hydrogen-burning dwarfs through the main-sequence and giant branches down to very cool white dwarf remnants in the cluster. The imaging also provides the deepest probe of the stellar populations of the background Small Magellanic Cloud galaxy, resolving low-mass main-sequence dwarfs with M 0.2 M .
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