Compact Elliptical Research Articles

Globular Cluster Systems of Massive Compact Elliptical Galaxies in the Local Universe: Evidence for Relic Red Nuggets?

Abstract Nearby massive compact elliptical galaxies (MCEGs) are strong candidates for relic galaxies (i.e., local analogs of red nuggets at high redshifts). It is expected that the globular cluster (GC) systems of relic galaxies are dominated by red (metal-rich) GCs. NGC 1277 is known as a unique example of such a galaxy in the previous study. In this study, we search for GCs in 12 nearby MCEGs at distances of ≲100 Mpc from the Hubble Space Telescope/Wide Field Camera 3 F814W(I 814)/F160W(H 160) archival images. We find that most of these MCEGs host a rich population of GCs with a color range of . The fractions of their red GCs range from f RGC = 0.2 to 0.7 with a mean of f RGC = 0.48 ± 0.14. We divide the MCEG sample into two groups: one in clusters and the other in groups/fields. The mean red GC fraction of the cluster MCEGs is 0.60 ± 0.06, which is 0.2 larger than the value of the group/field MCEGs, 0.40 ± 0.10. The value for the cluster MCEGs is ∼0.3 larger than the mean value of giant early-type galaxies with similar stellar mass in the Virgo Cluster (f RGC = 0.33 ± 0.13). Our results show that most of the MCEGs in our sample are indeed relic galaxies. This further implies that a majority of the red GCs in MCEGs are formed early in massive galaxies and that most MCEGs in the local universe have rarely undergone mergers after they became red nuggets about 10 Gyr ago.

The formation of compact dwarf ellipticals through merging star clusters

Abstract In the past decades, extended old stellar clusters have been observed. These extended objects cover a large range in masses, from extended clusters or faint fuzzies to ultracompact dwarf galaxies. It has been demonstrated that these extended objects can be the result of the merging of star clusters in cluster complexes (small regions in which dozens to hundreds of star clusters form). This formation channel is called the ‘Merging Star Cluster Scenario’. This work tries to explain the formation of compact ellipticals in the same theoretical framework. Compact ellipticals are a comparatively rare class of spheroidal galaxies, possessing very small effective radii and high central surface brightnesses. With the use of numerical simulations we show that the merging star cluster scenario, adopted for higher masses, as found with those galaxies, can reproduce all major characteristics and the dynamics of these objects. This opens up a new formation channel to explain the existence of compact elliptical galaxies.

M32 Analogs? A Population of Massive Ultra-compact Dwarf and Compact Elliptical Galaxies in Intermediate-redshift Clusters

Abstract We report the discovery of relatively massive, M32-like ultra compact dwarf (UCD) and compact elliptical (CE) galaxy candidates in massive galaxy clusters imaged by the Cluster Lensing And Supernova survey with Hubble (CLASH) survey. Examining the nearly unresolved objects in the survey, we identify a sample of compact objects concentrated around the cluster central galaxies with colors similar to cluster red sequence galaxies. Their colors and magnitudes suggest stellar masses around . More than half of these galaxies have half-light radii smaller than 200 pc, falling into the category of massive UCDs and CEs, with properties similar to M32. The properties are consistent with a tidal stripping origin, but we cannot rule out the possibility that they are early-formed compact objects trapped in massive dark matter halos. The 17 CLASH clusters studied in this work on average contain 2.7 of these objects in their central 0.3 Mpc and 0.6 in their central 50 kpc. Our study demonstrates the possibility of statistically characterizing UCDs/CEs with a large set of uniform imaging survey data.

Discovery of an isolated compact elliptical galaxy in the field

We present the discovery of an isolated compact elliptical (cE) galaxy, found during a search of SDSS DR7 for cEs, and for which we obtained WHT/ACAM imaging. It is ~900 kpc distant from its nearest neighbour, has an effective r-band radius of ~500 pc and a B-band mean surface brightness within its effective radius of 19.75 mag/arcsec. Serendipitous deep SuprimeCam imaging shows that there is no underlying disk. Its isolated position suggests that there is an alternative channel to the stripping scenario for the formation of compact ellipticals. We also report analysis of recent deeper imaging of the previous candidate free-flying cE, which shows that it is, in fact, a normal dwarf elliptical (dE). Hence the new cE reported here is the first confirmed isolated compact elliptical to be found in the field.

Efficiency of a Compact Elliptical Planar Ultra-Wideband Antenna Based on Conductive Polymers

A planar antenna for ultra-wideband (UWB) applications covering the 3.1–10.6 GHz range has been designed as a test bed for efficiency measurements of antennas manufactured using polymer conductors. Two types of conductive polymers, PEDOT and PPy (polypyrrole), with very different thicknesses and conductivities have been selected as conductors for the radiating elements. A comparison between measured radiation patterns of the conductive polymers and a copper reference antenna allows to estimate the conductor losses of the two types of conductive polymers. For a 158 μm thick PPy polymer, an efficiency of almost 80% can be observed over the whole UWB spectrum. For a 7 μm thick PEDOT layer, an average efficiency of 26.6% demonstrates, considering the room for improvement, the potential of this type of versatile materials as flexible printable alternative to conductive metallic paints. The paper demonstrates that, even though the PEDOT conductivity is an order of magnitude larger than that of PPy, the thicker PPy layer leads to much higher efficiency over the whole UWB frequency range. This result highlights that high efficiency can be achieved not only through high conductivity, but also through a sufficiently thick layer of conductive polymers.

SDSS J124155.33+114003.7 – a missing link between compact elliptical and ultracompact dwarf galaxies

Abstract We report the discovery of a compact object (Re= 32 pc, MB=−12.34 mag) at a projected distance of 9 kpc from Messier 59, a giant elliptical in the Virgo cluster. Using HST imaging and SDSS spectroscopy, both available in the Virtual Observatory, we find that this object has a blue core containing one-quarter of the light, and a redder n= 1 Sérsic envelope, as well as luminosity-weighted age of 9.3 ± 1.4 Gyr, a metallicity of −0.03 ± 0.04 dex and a velocity dispersion of 48 ± 5 km s−1. While ultracompact dwarf galaxies (UCDs) in the face-on view of the Fundamental Plane are found to form a sequence connecting the highest-luminosity globular clusters with the lowest-luminosity dwarf ellipticals, the compact object near M59 lies in between this UCD sequence and the positions of compact ellipticals. Its stellar age, metallicity, and effective surface brightness are similar to low-luminosity ellipticals and lenticulars, suggesting that SDSS J124155.33+114003.7 is a result of the tidal stripping of such an object.

Compact Elliptical Monopole Antenna With Impedance Bandwidth in Excess of 21:1

A compact CPW-fed monopole antenna composed of an elliptical monopole patch and a coplanar trapeziform ground plane is introduced. The simulated and experimental results demonstrate that this antenna achieves a ratio impedance bandwidth of 21.6:1 for VSWR les 2, and exhibits a nearly omnidirectional radiation pattern, while its area is only about 0.19 lambda1 times 0.16 lambda1 where lambda1 is the wavelength of the lowest operating frequency. By comparing with various designs, it is shown that its bandwidth broadening comes from three factors: the optimum elliptical monopole shape, a trapeziform ground plane and a tapered CPW feeder.

Discovery of a new M 32-like “Compact Elliptical” galaxy in the halo of the Abell 496 cD galaxy

Aims: ``Compact ellipticals'' are so rare that a search for M32 analogs is needed to ensure the very existence of this class. Methods: We report here the discovery of A496cE, a M32 twin in the cluster Abell 496, located in the halo of the central cD. Results: Based on CFHT and HST imaging we show that the light profile of A496cE requires a two component fit: a Sersic bulge and an exponential disc. The spectrum of A496cE obtained with the ESO-VLT FLAMES/Giraffe spectrograph can be fit by a stellar synthesis spectrum dominated by old stars, with high values of [Mg/Fe] and velocity dispersion. Conclusions: The capture of A496cE by the cD galaxy and tidal stripping of most of its disc are briefly discussed.

Discovery of two M 32 twins in Abell 1689

The M 31 satellite galaxy M 32 has long been considered an object of unique properties, being the most extreme example of the very rare compact elliptical galaxy class. Here we present the spectroscopic discovery of two M 32 twins in the massive galaxy cluster Abell 1689. As these objects are so rare, this is an important step towards a better understanding of the nature of compact galaxies. The two M 32 twins had first been detected within our photometric search for ultra compact dwarf galaxy (UCDs) candidates in A1689 (Mieske et al. 2004b, AJ, 128, 1529) with the Advanced Camera for Surveys (ACS). Their luminosities (M V ≃ -17 mag) are very similar to M 32 and their surface brightness profiles are consistent with that of M 32 projected to A1689's distance. From our ACS imaging we detect several fainter compact galaxy candidates with luminosities intermediate between M 32 and the Fornax UCDs. If spectroscopically confirmed as cluster members, this would almost close the gap in the mag-μ plane between the region of UCDs and the compact ellipticals, implying a sequence of faint compact galaxies well separated from that of dwarf ellipticals.

Evidence for an Outer Disk in the Prototype “Compact Elliptical” Galaxy M32

M32 is the prototype for the relatively rare class of galaxies referred to as compact ellipticals. It has been suggested that M32 may be a tidally disturbed r1/4 elliptical galaxy or the remnant bulge of a disk-stripped early-type spiral galaxy. This Letter reveals that the surface brightness profile, the velocity dispersion measurements, and the estimated supermassive black hole mass in M32 are inconsistent with the galaxy having, and probably ever having had, an r1/4 light profile. Instead, the radial surface brightness distribution of M32 resembles an almost perfect (bulge+exponential disk) profile; this is accompanied by a marked increase in the ellipticity profile and an associated change in the position angle profile where the "disk" starts to dominate. Compelling evidence that this bulge/disk interpretation is accurate comes from the best-fitting r1/n bulge model, which has a Sérsic index of n = 1.5, in agreement with the recently discovered relation between a bulge's Sérsic index and the mass of a bulge's supermassive black hole. An index of n ≥ 4 would also be inconsistent with the stellar velocity dispersion of M32. The bulge-to-disk size ratio re/h equals 0.20, and the logarithm of the bulge-to-disk luminosity ratio log(B/D) equals 0.22, typical of Sϕ galaxies. The effective radius of the bulge is 27'' (~100 pc), while the scale length of the disk is less well determined: owing to possible tidal stripping of the outer profile beyond 220''-250'', the scale length may be as large as 1.3 kpc. M32 is a relatively face-on, nucleated dwarf galaxy with a low surface brightness disk and a high surface brightness bulge. This finding brings into question the very existence of the compact elliptical class of galaxies.

Stellar Populations in Dwarf Elliptical Galaxies

We present the results of a spectroscopic study in which we have measured line-strength indices in a sample of 5 dwarf and 2 compact elliptical galaxies (mostly from Virgo). Some conclusions about the stellar populations in dwarf E's are derived by comparing the sample with classical E galaxies. In the adjacent figure, we plot in the Hβ-[MgFe] plane the central indices of our sample of dwarf and compact E's together with data from González (1993, PhD Thesis). The grid represents the predictions of single-burst stellar population models from Worthey (1994, ApJS, 95, 107). The main conclusion is that, whilst the central regions of giant, intermediate and compact ellipticals span, according to stellar population models, a wide range in mean stellar ages, bright dwarf ellipticals are found to be old, compatible with a ∼ 10 Gyr old stellar population. This means that the dichotomy found in the Fundamental Plane between dwarf ellipticals and the gE-iE-cE sequence (Bender, Burstein & Faber 1992, ApJ, 399, 462) is also observed in the stellar populations.

On the formation of Compact ellipticals

A model for the formation of compact elliptical galaxies as satellites of massive galaxies is presented. It is assumed that compact ellipticals formed through a starburst and the subsequent violent collapse of the stellar system. Numerical N-body experiments show that one can understand the peculiar structure of compacts if they were produced as a result of the relaxation of initially cold stellar systems which were disturbed by the tidal field of a bright galaxy. The observed differences between compact ellipticals and low-mass giant ellipticals might therefore result from the fact that the compacts formed within the potential well of another galaxy whereas the giant ellipticals evolved as isolated systems

Compact Elliptical Galaxies

We summarize our present knowledge on low-mass high-surface brightness elliptical objects near massive galaxies that are often called M32-type or compact elliptical galaxies. The origin of the low mass of these objects is a controversial matter: is it intrinsic to their formation or produced, as classically believed, by tidal stripping from the massive neighbor? We present new observational data allowing to define better the characteristics of these objects and a simple theoretical model whose consequences support the idea that the precursors of compact ellipticals are related to the low-mass end of the luminosity function of elliptical galaxies.