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Timothy D Brandt - One of the best experts on this subject based on the ideXlab platform.
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constraints on macho dark matter from compact Stellar Systems in ultra faint dwarf galaxies
2017Co-Authors: Timothy D BrandtAbstract:I show that a recently discovered star cluster near the center of the ultra-faint dwarf galaxy Eridanus II provides strong constraints on massive compact halo objects (MACHOs) of >~5 M_sun as the main component of dark matter. MACHO dark matter will dynamically heat the cluster, driving it to larger sizes and higher velocity dispersions until it dissolves into its host galaxy. The stars in compact ultra-faint dwarf galaxies themselves will be subject to the same dynamical heating; the survival of at least ten such galaxies places independent limits on MACHO dark matter of masses >~10 M_sun. Both Eri II's cluster and the compact ultra-faint dwarfs are characterized by Stellar masses of just a few thousand M_sun and half-light radii of 13 pc (for the cluster) and ~30 pc (for the ultra-faint dwarfs). These Systems close the ~20--100 M_sun window of allowed MACHO dark matter and combine with existing constraints from microlensing, wide binaries, and disk kinematics to rule out dark matter composed entirely of MACHOs from ~10$^{-7}$ M_sun up to arbitrarily high masses.
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constraints on macho dark matter from compact Stellar Systems in ultra faint dwarf galaxies
2016Co-Authors: Timothy D BrandtAbstract:I show that a recently discovered star cluster near the center of the ultra-faint dwarf galaxy Eridanus II provides strong constraints on massive compact halo objects (MACHOs) of &5 M⊙ as the main component of dark matter. MACHO dark matter will dynamically heat the cluster, driving it to larger sizes and higher velocity dispersions until it dissolves into its host galaxy. The stars in compact ultra-faint dwarf galaxies themselves will be subject to the same dynamical heating; the survival of at least ten such galaxies places independent limits on MACHO dark matter of masses &10 M⊙. Both Eri II’s cluster and the compact ultra-faint dwarfs are characterized by Stellar masses of just a few thousand M⊙ and half-light radii of 13 pc (for the cluster) and ∼30 pc (for the ultra-faint dwarfs). These Systems close the ∼20–100 M⊙ window of allowed MACHO dark matter and combine with existing constraints from microlensing, wide binaries, and disk kinematics to rule out dark matter composed entirely of MACHOs from ∼10 −7 M⊙ up to arbitrarily high masses. Subject headings:
Avon Huxor - One of the best experts on this subject based on the ideXlab platform.
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the aimss project iii the Stellar populations of compact Stellar Systems
2016Co-Authors: Joachin Janz, Duncan A Forbes, Aaron J Romanowsky, Mark A Norris, Avon Huxor, Matthias J Frank, Carlos Gabriel EscuderoAbstract:In recent years, a growing zoo of compact Stellar Systems (CSSs) have been found whose physical properties (mass, size, velocity dispersion) place them between classical globular clusters (GCs) and true galaxies, leading to debates about their nature. Here we present results using a so far underutilised discriminant, their Stellar population properties. Based on new spectroscopy from 8-10m telescopes, we derive ages, metallicities, and [\alpha/Fe] of 29 CSSs. These range from GCs with sizes of merely a few parsec to compact ellipticals larger than M32. Together with a literature compilation, this provides a panoramic view of the Stellar population characteristics of early-type Systems. We find that the CSSs are predominantly more metal rich than typical galaxies at the same Stellar mass. At high mass, the compact ellipticals (cEs) depart from the mass-metallicity relation of massive early-type galaxies, which forms a continuous sequence with dwarf galaxies. At lower mass, the metallicity distribution of ultra-compact dwarfs (UCDs) changes at a few times $10^7$ M$_{\odot}$, which roughly coincides with the mass where luminosity function arguments previously suggested the GC population ends. The highest metallicities in CSSs are paralleled only by those of dwarf galaxy nuclei and the central parts of massive early types. These findings can be interpreted as CSSs previously being more massive and undergoing tidal interactions to obtain their current mass and compact size. Such an interpretation is supported by CSSs with direct evidence for tidal stripping, and by an examination of the CSS internal escape velocities.
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the aimss project i bridging the star cluster galaxy divide
2014Co-Authors: Duncan A Forbes, Jean P Brodie, Aaron J Romanowsky, Mark A Norris, Sheila J Kannappan, F R Faifer, Avon HuxorAbstract:We describe the structural and kinematic properties of the first compact Stellar Systems discovered by the Archive of Intermediate Mass Stellar Systems project. These spectroscopically confirmed objects have sizes (∼6 < Re [pc] < 500) and masses (∼2 × 106 < M*/M⊙ < 6 × 109) spanning the range of massive globular clusters, ultracompact dwarfs (UCDs) and compact elliptical galaxies (cEs), completely filling the gap between star clusters and galaxies. Several objects are close analogues to the prototypical cE, M32. These objects, which are more massive than previously discovered UCDs of the same size, further call into question the existence of a tight mass–size trend for compact Stellar Systems, while simultaneously strengthening the case for a universal ‘zone of avoidance’ for dynamically hot Stellar Systems in the mass–size plane. Overall, we argue that there are two classes of compact Stellar Systems (1) massive star clusters and (2) a population closely related to galaxies. Our data provide indications for a further division of the galaxy-type UCD/cE population into two groups, one population that we associate with objects formed by the stripping of nucleated dwarf galaxies, and a second population that formed through the stripping of bulged galaxies or are lower mass analogues of classical ellipticals. We find compact Stellar Systems around galaxies in low- to high-density environments, demonstrating that the physical processes responsible for forming them do not only operate in the densest clusters.
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the hst acs coma cluster survey v compact Stellar Systems in the coma cluster
2009Co-Authors: James Price, Avon Huxor, S Phillipps, Neil Trentham, Henry C Ferguson, Ronald O Marzke, A E Hornschemeier, Paul Goudfrooij, Derek Hammer, R B TullyAbstract:The Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) Coma Cluster Treasury Survey is a deep two-passband imaging survey of the nearest very rich cluster of galaxies, covering a range of galaxy density environments. The imaging is complemented by a recent wide field redshift survey of the cluster conducted with Hectospec on the 6.5-m Monolithic Mirror Telescope (MMT). Among the many scientific applications for these data is the search for compact galaxies. In this paper, we present the discovery of seven compact (but quite luminous) Stellar Systems, ranging from M32-like galaxies down to ultra-compact dwarfs (UCDs)/dwarf to globular transition objects (DGTOs). We find that all seven compact galaxies require a two-component fit to their light profile and have measured velocity dispersions that exceed those expected for typical early-type galaxies at their luminosity. From our structural parameter analysis, we conclude that three of the samples should be classified as compact ellipticals or M32-like galaxies, and the remaining four being less extreme Systems. The three compact ellipticals are all found to have old luminosity weighted ages (≳12 Gyr), intermediate metallicities (−0.6 < [Fe/H] < −0.1) and high [Mg/Fe] (≳0.25). Our findings support a tidal stripping scenario as the formation mode of compact galaxies covering the luminosity range studied here. We speculate that at least two early-type morphologies may serve as the progenitor of compact galaxies in clusters.
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the hst acs coma cluster survey v compact Stellar Systems in the coma cluster
2009Co-Authors: James Price, Avon Huxor, S Phillipps, Neil Trentham, Henry C Ferguson, Ronald O Marzke, A E Hornschemeier, Paul Goudfrooij, Derek Hammer, R B TullyAbstract:The HST ACS Coma Cluster Treasury Survey is a deep two passband imaging survey of the nearest very rich cluster of galaxies, covering a range of galaxy density environments. The imaging is complemented by a recent wide field redshift survey of the cluster conducted with Hectospec on the 6.5m MMT. Among the many scientific applications for this data are the search for compact galaxies. In this paper, we present the discovery of seven compact (but quite luminous) Stellar Systems, ranging from M32-like galaxies down to ultra-compact dwarfs (UCDs)/dwarf to globular transition objects (DGTOs). We find that all seven compact galaxies require a two-component fit to their light profile and have measured velocity dispersions that exceed those expected for typical early-type galaxies at their luminosity. From our structural parameter analysis we conclude that three of the sample should be classified as compact ellipticals or M32-like galaxies, the remaining four being less extreme Systems. The three compact ellipticals are all found to have old luminosity weighted ages (> 12 Gyr), intermediate metallicities (-0.6 0.25). Our findings support a tidal stripping scenario as the formation mode of compact galaxies covering the luminosity range studied here. We speculate that at least two early-type morphologies may serve as the progenitor of compact galaxies in clusters.
R B Tully - One of the best experts on this subject based on the ideXlab platform.
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the hst acs coma cluster survey v compact Stellar Systems in the coma cluster
2009Co-Authors: James Price, Avon Huxor, S Phillipps, Neil Trentham, Henry C Ferguson, Ronald O Marzke, A E Hornschemeier, Paul Goudfrooij, Derek Hammer, R B TullyAbstract:The Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) Coma Cluster Treasury Survey is a deep two-passband imaging survey of the nearest very rich cluster of galaxies, covering a range of galaxy density environments. The imaging is complemented by a recent wide field redshift survey of the cluster conducted with Hectospec on the 6.5-m Monolithic Mirror Telescope (MMT). Among the many scientific applications for these data is the search for compact galaxies. In this paper, we present the discovery of seven compact (but quite luminous) Stellar Systems, ranging from M32-like galaxies down to ultra-compact dwarfs (UCDs)/dwarf to globular transition objects (DGTOs). We find that all seven compact galaxies require a two-component fit to their light profile and have measured velocity dispersions that exceed those expected for typical early-type galaxies at their luminosity. From our structural parameter analysis, we conclude that three of the samples should be classified as compact ellipticals or M32-like galaxies, and the remaining four being less extreme Systems. The three compact ellipticals are all found to have old luminosity weighted ages (≳12 Gyr), intermediate metallicities (−0.6 < [Fe/H] < −0.1) and high [Mg/Fe] (≳0.25). Our findings support a tidal stripping scenario as the formation mode of compact galaxies covering the luminosity range studied here. We speculate that at least two early-type morphologies may serve as the progenitor of compact galaxies in clusters.
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the hst acs coma cluster survey v compact Stellar Systems in the coma cluster
2009Co-Authors: James Price, Avon Huxor, S Phillipps, Neil Trentham, Henry C Ferguson, Ronald O Marzke, A E Hornschemeier, Paul Goudfrooij, Derek Hammer, R B TullyAbstract:The HST ACS Coma Cluster Treasury Survey is a deep two passband imaging survey of the nearest very rich cluster of galaxies, covering a range of galaxy density environments. The imaging is complemented by a recent wide field redshift survey of the cluster conducted with Hectospec on the 6.5m MMT. Among the many scientific applications for this data are the search for compact galaxies. In this paper, we present the discovery of seven compact (but quite luminous) Stellar Systems, ranging from M32-like galaxies down to ultra-compact dwarfs (UCDs)/dwarf to globular transition objects (DGTOs). We find that all seven compact galaxies require a two-component fit to their light profile and have measured velocity dispersions that exceed those expected for typical early-type galaxies at their luminosity. From our structural parameter analysis we conclude that three of the sample should be classified as compact ellipticals or M32-like galaxies, the remaining four being less extreme Systems. The three compact ellipticals are all found to have old luminosity weighted ages (> 12 Gyr), intermediate metallicities (-0.6 0.25). Our findings support a tidal stripping scenario as the formation mode of compact galaxies covering the luminosity range studied here. We speculate that at least two early-type morphologies may serve as the progenitor of compact galaxies in clusters.
Aaron J Romanowsky - One of the best experts on this subject based on the ideXlab platform.
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initial mass function variability or not among low velocity dispersion compact Stellar Systems
2017Co-Authors: Alexa Villaume, Jean P Brodie, Charlie Conroy, Aaron J Romanowsky, Pieter G Van DokkumAbstract:Analyses of strong gravitational lenses, galaxy-scale kinematics, and absorption line Stellar population synthesis (SPS) have all concluded that the Stellar initial mass function (IMF) varies within the massive early-type galaxy (ETG) population. However, the physical mechanism that drives variation in the IMF is an outstanding question. Here we use new SPS models to consider a diverse set of compact, low-velocity dispersion Stellar Systems: globular clusters (GCs), an ultra-compact dwarf (UCD), and the compact elliptical (cE) galaxy M32. We compare our results to massive ETGs and available dynamical measurements. We find that the GCs have Stellar mass-to-light ratios (M/L) that are either consistent with a Kroupa IMF or are slightly bottom-light while the UCD and cE have mildly elevated M/L. The separation in derived IMFs for Systems with similar metallicities and abundance patterns indicates that our SPS models can distinguish abundance and IMF effects. Variation among the sample in this paper is only $\sim 50\%$ in normalized M/L compared to the $\sim 4\times$ among the ETG sample. This suggests that metallicity is not the sole driver of IMF variability and additional parameters need to be considered.
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the aimss project iii the Stellar populations of compact Stellar Systems
2016Co-Authors: Joachin Janz, Duncan A Forbes, Aaron J Romanowsky, Mark A Norris, Avon Huxor, Matthias J Frank, Carlos Gabriel EscuderoAbstract:In recent years, a growing zoo of compact Stellar Systems (CSSs) have been found whose physical properties (mass, size, velocity dispersion) place them between classical globular clusters (GCs) and true galaxies, leading to debates about their nature. Here we present results using a so far underutilised discriminant, their Stellar population properties. Based on new spectroscopy from 8-10m telescopes, we derive ages, metallicities, and [\alpha/Fe] of 29 CSSs. These range from GCs with sizes of merely a few parsec to compact ellipticals larger than M32. Together with a literature compilation, this provides a panoramic view of the Stellar population characteristics of early-type Systems. We find that the CSSs are predominantly more metal rich than typical galaxies at the same Stellar mass. At high mass, the compact ellipticals (cEs) depart from the mass-metallicity relation of massive early-type galaxies, which forms a continuous sequence with dwarf galaxies. At lower mass, the metallicity distribution of ultra-compact dwarfs (UCDs) changes at a few times $10^7$ M$_{\odot}$, which roughly coincides with the mass where luminosity function arguments previously suggested the GC population ends. The highest metallicities in CSSs are paralleled only by those of dwarf galaxy nuclei and the central parts of massive early types. These findings can be interpreted as CSSs previously being more massive and undergoing tidal interactions to obtain their current mass and compact size. Such an interpretation is supported by CSSs with direct evidence for tidal stripping, and by an examination of the CSS internal escape velocities.
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hiding in plain sight record breaking compact Stellar Systems in the sloan digital sky survey
2015Co-Authors: Michael Alexander Sandoval, Jean P Brodie, Charlie Conroy, Aaron J Romanowsky, Jay Strader, Jieun Choi, Zachary G Jennings, Caroline FosterAbstract:Motivated by the recent, serendipitous discovery of the densest known galaxy, M60-UCD1, we present two initial findings from a follow-up search, using the Sloan Digital Sky Survey, Subaru/Suprime-Cam, and Hubble Space Telescope imaging, and SOuthern Astrophysical Research (SOAR)/Goodman spectroscopy. The first object discovered, M59-UCD3, has a similar size to M60-UCD1 (half-light radius of rh ~ 20 pc) but is 40% more luminous (MV ~ −14.6), making it the new densest-known galaxy. The second, M85-HCC1, has a size like a typical globular cluster (GC; rh ~ 1.8 pc) but is much more luminous (MV ~ −12.5). This hypercompact cluster is by far the densest confirmed free-floating Stellar system, and is equivalent to the densest known nuclear star clusters. From spectroscopy, we find that both objects are relatively young (~9 and ~3 Gyr, respectively), with metal-abundances that resemble those of galaxy centers. Their host galaxies show clear signs of large-scale disturbances, and we conclude that these dense objects are the remnant nuclei of recently accreted galaxies. M59-UCD3 is an ideal target for follow-up with high-resolution imaging and spectroscopy to search for an overweight central supermassive black hole as was discovered in M60-UCD1. These findings also emphasize the potential value of ultra-compact dwarfs and massive GCs as tracers of the assembly histories of galaxies.
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the aimss project i bridging the star cluster galaxy divide
2014Co-Authors: Duncan A Forbes, Jean P Brodie, Aaron J Romanowsky, Mark A Norris, Sheila J Kannappan, F R Faifer, Avon HuxorAbstract:We describe the structural and kinematic properties of the first compact Stellar Systems discovered by the Archive of Intermediate Mass Stellar Systems project. These spectroscopically confirmed objects have sizes (∼6 < Re [pc] < 500) and masses (∼2 × 106 < M*/M⊙ < 6 × 109) spanning the range of massive globular clusters, ultracompact dwarfs (UCDs) and compact elliptical galaxies (cEs), completely filling the gap between star clusters and galaxies. Several objects are close analogues to the prototypical cE, M32. These objects, which are more massive than previously discovered UCDs of the same size, further call into question the existence of a tight mass–size trend for compact Stellar Systems, while simultaneously strengthening the case for a universal ‘zone of avoidance’ for dynamically hot Stellar Systems in the mass–size plane. Overall, we argue that there are two classes of compact Stellar Systems (1) massive star clusters and (2) a population closely related to galaxies. Our data provide indications for a further division of the galaxy-type UCD/cE population into two groups, one population that we associate with objects formed by the stripping of nucleated dwarf galaxies, and a second population that formed through the stripping of bulged galaxies or are lower mass analogues of classical ellipticals. We find compact Stellar Systems around galaxies in low- to high-density environments, demonstrating that the physical processes responsible for forming them do not only operate in the densest clusters.
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the relationships among compact Stellar Systems a fresh view of ultracompact dwarfs
2011Co-Authors: Jean P Brodie, Aaron J Romanowsky, Jay Strader, Duncan A ForbesAbstract:We use a combined imaging and spectroscopic survey of the nearby central cluster galaxy, M87, to assemble a sample of 34 confirmed ultracompact dwarfs (UCDs) with half-light radii of 210 pc measured from Hubble Space Telescope images. This doubles the existing sample in M87, making it the largest such sample for any galaxy, while extending the detection of UCDs to unprecedentedly low luminosities (MV =− 9). With this expanded sample, we find no correlation between size and luminosity, in contrast to previous suggestions, and no general correlation between size and galactocentric distance. We explore the relationships between UCDs, less luminous extended clusters (including faint fuzzies), globular clusters (GCs), as well as early-type galaxies and their nuclei, assembling an extensive new catalog of sizes and luminosities for Stellar Systems. Most of the M87 UCDs follow a tight color–magnitude relation, offset from the metal-poor GCs. This, along with kinematical differences, demonstrates that most UCDs are a distinct population from normal GCs, and not simply a continuation to larger sizes and higher luminosities. The UCD color–magnitude trend couples closely with that for Virgo dwarf elliptical nuclei. We conclude that the M87 UCDs are predominantly stripped nuclei. The brightest and reddest UCDs may be the remnant nuclei of more massive galaxies while a subset of the faintest UCDs may be tidally limited and related to more compact star clusters. In the broader context of galaxy assembly, blue UCDs may trace halo build-up by accretion of low-mass satellites, while red UCDs may be markers of metal-rich bulge formation in larger galaxies.
Paul Goudfrooij - One of the best experts on this subject based on the ideXlab platform.
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compact Stellar Systems in the polar ring galaxies ngc 4650a and ngc 3808b clues to polar disk formation
2016Co-Authors: Yasna Ordenesbriceno, Paul Goudfrooij, Iskren Y Georgiev, Thomas H Puzia, Magda ArnaboldiAbstract:Polar ring galaxies (PRGs) are composed of two kinematically distinct and nearly orthogonal components, a host galaxy (HG) and a polar ring/disk (PR). The HG usually contains an older Stellar population than the PR. The suggested formation channel of PRGs is still poorly constrained. Suggested options are merger, gas accretion, tidal interaction, or a combination of both. To constrain the formation scenario of PRGs, we study the compact Stellar Systems (CSSs) in two PRGs at different evolutionary stages: NGC 4650A with well-defined PR, and NGC 3808B, which is in the process of PR formation. We use archival HST/WFPC2 imaging. PSF-fitting techniques, and color selection criteria are used to select cluster candidates. Photometric analysis of the CSSs was performed to determine their ages and masses using Stellar population models at a fixed metallicity. Both PRGs contain young CSSs ($< 1$ Gyr) with masses of up to 5$\times$10$^6$M$_\odot$, mostly located in the PR and along the tidal debris. The most massive CSSs may be progenitors of metal-rich globular clusters or ultra compact dwarf (UCD) galaxies. We identify one such young UCD candidate, NGC 3808 B-8, and measure its size of $r_{\rm eff}=25.23^{+1.43}_{-2.01}$ pc. We reconstruct the star formation history of the two PRGs and find strong peaks in the star formation rate (SFR $\simeq$ 200M$_\odot$/yr) in NGC 3808B, while NGC 4650A shows milder (declining) star formation (SFR $<$ 10M$_\odot$/yr). This difference may support different evolutionary paths between these PRGs. The spatial distribution, masses, and peak star formation epoch of the clusters in NGC 3808 suggest for a tidally triggered star formation. Incompleteness at old ages prevents us from probing the SFR at earlier epochs of NGC 4650A, where we observe the fading tail of CSS formation. This also impedes us from testing the formation scenarios of this PRG.
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the hst acs coma cluster survey v compact Stellar Systems in the coma cluster
2009Co-Authors: James Price, Avon Huxor, S Phillipps, Neil Trentham, Henry C Ferguson, Ronald O Marzke, A E Hornschemeier, Paul Goudfrooij, Derek Hammer, R B TullyAbstract:The Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) Coma Cluster Treasury Survey is a deep two-passband imaging survey of the nearest very rich cluster of galaxies, covering a range of galaxy density environments. The imaging is complemented by a recent wide field redshift survey of the cluster conducted with Hectospec on the 6.5-m Monolithic Mirror Telescope (MMT). Among the many scientific applications for these data is the search for compact galaxies. In this paper, we present the discovery of seven compact (but quite luminous) Stellar Systems, ranging from M32-like galaxies down to ultra-compact dwarfs (UCDs)/dwarf to globular transition objects (DGTOs). We find that all seven compact galaxies require a two-component fit to their light profile and have measured velocity dispersions that exceed those expected for typical early-type galaxies at their luminosity. From our structural parameter analysis, we conclude that three of the samples should be classified as compact ellipticals or M32-like galaxies, and the remaining four being less extreme Systems. The three compact ellipticals are all found to have old luminosity weighted ages (≳12 Gyr), intermediate metallicities (−0.6 < [Fe/H] < −0.1) and high [Mg/Fe] (≳0.25). Our findings support a tidal stripping scenario as the formation mode of compact galaxies covering the luminosity range studied here. We speculate that at least two early-type morphologies may serve as the progenitor of compact galaxies in clusters.
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the hst acs coma cluster survey v compact Stellar Systems in the coma cluster
2009Co-Authors: James Price, Avon Huxor, S Phillipps, Neil Trentham, Henry C Ferguson, Ronald O Marzke, A E Hornschemeier, Paul Goudfrooij, Derek Hammer, R B TullyAbstract:The HST ACS Coma Cluster Treasury Survey is a deep two passband imaging survey of the nearest very rich cluster of galaxies, covering a range of galaxy density environments. The imaging is complemented by a recent wide field redshift survey of the cluster conducted with Hectospec on the 6.5m MMT. Among the many scientific applications for this data are the search for compact galaxies. In this paper, we present the discovery of seven compact (but quite luminous) Stellar Systems, ranging from M32-like galaxies down to ultra-compact dwarfs (UCDs)/dwarf to globular transition objects (DGTOs). We find that all seven compact galaxies require a two-component fit to their light profile and have measured velocity dispersions that exceed those expected for typical early-type galaxies at their luminosity. From our structural parameter analysis we conclude that three of the sample should be classified as compact ellipticals or M32-like galaxies, the remaining four being less extreme Systems. The three compact ellipticals are all found to have old luminosity weighted ages (> 12 Gyr), intermediate metallicities (-0.6 0.25). Our findings support a tidal stripping scenario as the formation mode of compact galaxies covering the luminosity range studied here. We speculate that at least two early-type morphologies may serve as the progenitor of compact galaxies in clusters.
