Mike Beasley | Instituto de Astrofisica de Canarias (original) (raw)

Papers by Mike Beasley

arXiv (Cornell University), Nov 22, 2000

We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), ... more We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), and ages and metallicities from co-added spectra of 131 GCs. We confirm our earlier finding that the metal-poor GCs have a significantly higher velocity dispersion than the metal-rich GCs, and we find little or no rotation in the metal-rich GCs. The velocity dispersion profile is consistent with isotropic orbits for the GCs and the NGC 4472 mass distribution inferred from X-ray data. Our sample of GCs spans a metallicity range of −1.6 ≤ [F e/H] ≤ 0 dex. The metal-poor and metal-rich GC populations are coeval within the errors, and all GCs older than 6 Gyr at 95% confidence. Our findings are consistent with a merger origin for NGC 4472, but other elliptical formation models cannot be ruled out.

Highlights of Astronomy, 2005

We present recent results from our long-term Gemini/GMOS study of globular clusters (GCs) in earl... more We present recent results from our long-term Gemini/GMOS study of globular clusters (GCs) in early-type galaxies. To date, we have obtained photometry and spectroscopy for GCs in NGCs 3379, 4649, 524, 7332, and IC 1459. We find a clear bimodality in the NGC 4649 GC colour distribution, with the fraction of blue/red clusters increasing with galactocentric radius. We derive ages and metallicities for 22 GCs in NGC 3379, finding that most of the clusters appear old (10−15 Gyr); however, there is a group of 4 metal-rich, younger clusters with ages of 2−6 Gyr. The NGC 3379 GC velocity dispersion decreases with radius, as does the inferred (local) mass-to-light ratio: there is no evidence for a dark matter halo in NGC 3379 based on our GC data.

Carolina Digital Repository (University of North Carolina at Chapel Hill), 2011

This paper presents deep high quality photometry of globular cluster (GC) systems belonging to fi... more This paper presents deep high quality photometry of globular cluster (GC) systems belonging to five early-type galaxies covering a range of mass and environment. Photometric data were obtained with the Gemini North and Gemini South telescopes in the filter passbands g ′ , r ′ , and i ′. The combination of these filters with good seeing conditions allows an excellent separation between GC candidates and unresolved field objects. In fact, our previously published spectroscopic data indicates a contamination level of only ∼10 percent in our sample of GC candidates. Bimodal GC colour distributions are found in all five galaxies. Most of the GC systems appear bimodal even in the (g ′-r ′) vs (r ′-i ′) plane. A population of resolved/marginally resolved GC and Ultra Compact Dwarf candidates was found in all the galaxies. A search for the so-called "blue tilt" in the colour-magnitude diagrams reveals that NGC 4649 clearly shows that phenomenon although no conclusive evidence was found for the other galaxies in the sample. This "blue tilt" translates into a mass-metallicity relation given by Z ∝ M 0.28±0.03. This dependence was found using a new empirical (g ′-i ′) vs [Z/H] relation which relies on an homogeneous sample of GC colours and metallicities. This paper also explores the radial trends in both colour and surface density for the blue (metal-poor) and red (metal-rich) GC subpopulations. As usual, the red GCs show a steeper radial distribution than the blue ones. Evidence of galactocentric colour gradients is found in some of the GC systems, being more significant for the two S0 galaxies in the sample. Red GC subpopulations show similar colours and gradients to the galaxy halo stars in their inner region. A GC mean colour-galaxy luminosity relation, consistent with [Z/H] ∝ L B 0.26±0.08 , is present for the red GCs. An estimate of the total GC populations and specific frequency S N values is presented for NGC 3115, NGC 3923 and NGC 4649.

arXiv (Cornell University), Aug 15, 2003

Our numerical simulations first demonstrate that the pressure of ISM in a major merger becomes so... more Our numerical simulations first demonstrate that the pressure of ISM in a major merger becomes so high ($>$ 10510^5105 rmkrmB\rm k_{\rm B}rmkrmB K rmcm−3\rm cm^{-3}rmcm−3) that GMCs in the merger can collapse to form globular clusters (GCs) within a few Myr. The star formation efficiency within a GMC in galaxy mergers can rise up from a few percent to sim\simsim 80 percent, depending on the shapes and the temperature of the GMC. This implosive GC formation due to external high pressure of warm/hot ISM can be more efficient in the tidal tails or the central regions of mergers. The developed clusters have King-like profile with the effective radius of a few pc. The structural, kinematical, and chemical properties of these GC systems can depend on orbital and chemical properties of major mergers.

Monthly Notices of the Royal Astronomical Society, Feb 1, 2000

We have obtained spectra for 103 published globular cluster candidates in the Sculptor group gala... more We have obtained spectra for 103 published globular cluster candidates in the Sculptor group galaxies NGC 253 and 55. On the basis of radial velocities and digitized plate images, 14 globular clusters are identified in NGC 253 and one probable globular cluster is identified in NGC 55. The majority of the objects in the sample appear to be background galaxies. We have obtained and analysed COSMOS plate scans of NGC 253 and 55 and use these along with the spectroscopically identified clusters to define new samples of globular cluster candidates in the two galaxies which should have reduced contamination.

NOAO Proposal, Feb 1, 2003

One of our most important probes for understanding galaxy formation and evolution are globular cl... more One of our most important probes for understanding galaxy formation and evolution are globular cluster (GC) systems. We are continuing our aggressive campaign to obtain spectroscopy for a large sample of GCs in galaxies with a variety of properties, in different environments, in order to understand their kinematics, ages and abundances. Kinematical results from this project will provide a detailed

Symposium - International Astronomical Union, 2005

We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), ... more We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), and ages and metallicities for 131 GCs. We confirm our earlier finding that the metal-poor GCs have a significantly higher velocity dispersion than the metal-rich GCs, and we find little or no rotation in the metal-rich GCs. The velocity dispersion profile is consistent with isotropic GC orbits and the mass distribution inferred from X-ray data. Our sample of GCs spans a metallicity range of −1.6 ≤ [Fe/H] ≤ 0 dex. The metal-poor and metal-rich GCs are coeval within the errors, and all GCs older than 6 Gyr at 95% confidence.

Globular clusters (GCs) play an essential role in understanding the star formation history of gal... more Globular clusters (GCs) play an essential role in understanding the star formation history of galaxies. At the same time GCs are the best candidates to check the reliability of single stellar population (SSP) models which have broad ranging applications. On the basis of a new empirical stellar library in the K band, new SSP model predictions suggest that CO and

I will present results for the formation of spiral galaxy globular cluster systems in the context... more I will present results for the formation of spiral galaxy globular cluster systems in the context of hierarchical merger models. In particular I will show that such models predict correlations between mean properties of the metal-rich clusters and the host spheroid which are observable. I will also discuss our recent work on including SNe type Ia and type II products

Monthly Notices of the Royal Astronomical Society, 2000

We have derived ages and metallicities from co-added spectra of 131 globular clusters associated ... more We have derived ages and metallicities from co-added spectra of 131 globular clusters associated with the giant elliptical galaxy NGC 4472. Based upon a calibration with Galactic globular clusters, we find that our sample of globular clusters in NGC 4472 span a metallicity range of approximately 21X6 # FeaH # 0 dexX There is evidence of a radial metallicity gradient in the globular cluster system which is steeper than that seen in the underlying starlight. Determination of the absolute ages of the globular clusters is uncertain, but formally, the metal-poor population of globular clusters has an age of 14X5^4 Gyr and the metal-rich population is 13X8^6 Gyr old. Monte Carlo simulations indicate that the globular cluster populations present in these data are older than 6 Gyr at the 95 per cent confidence level. We find that within the uncertainties, the globular clusters are old and coeval, implying that the bimodality seen in the broadband colours primarily reflects metallicity and not age differences.

Monthly Notices of the Royal Astronomical Society, 2011

In this paper, we present deep high-quality photometry of globular cluster systems (GCSs) belongi... more In this paper, we present deep high-quality photometry of globular cluster systems (GCSs) belonging to five early-type galaxies, covering a range of mass and environment. Photometric data were obtained with the Gemini North and Gemini South telescopes in the filter passbands g , r and i. The combination of these filters with good seeing conditions allows an excellent separation between globular cluster (GC) candidates and unresolved field objects. In fact, our previously published spectroscopic data indicate a contamination level of only ∼10 per cent in our sample of GC candidates. Bimodal GC colour distributions are found in all five galaxies. Most of the GCSs appear bimodal even in the (g − r) versus (r − i) plane. A population of resolved/marginally resolved GC and ultracompact dwarf candidates was found in all the galaxies. A search for the so-called 'blue tilt' in the colour-magnitude diagrams reveals that NGC 4649 clearly shows this phenomenon, although no conclusive evidence was found for the other galaxies in the sample. This 'blue tilt' translates into a mass-metallicity relation given by Z ∝ M 0.28 ±0.03. This dependence was found using a new empirical (g − i) versus [Z/H] relation, which relies on an homogeneous sample of GC colours and metallicities. In this paper, we also explore the radial trends in both colour and surface density for the blue (metal-poor) and red (metal-rich) GC subpopulations. As usual, the red GCs show a steeper radial distribution than the blue GCs. Evidence of galactocentric colour gradients is found in some of the GCSs, which is more significant for the two S0 galaxies in the sample. Red GC subpopulations show similar colours and gradients to the galaxy halo stars in their inner region. A GC mean colour-galaxy luminosity relation, consistent with [ Z/H ] ∝ L 0.26 ±0.08 B , is present for the red GCs. Estimates of the total GC populations and specific frequency S N values are presented for NGC 3115, 3923 and 4649.

Astronomy and Astrophysics, 2008

ABSTRACT We present the results of an ongoing spectroscopic survey of globular clusters around th... more ABSTRACT We present the results of an ongoing spectroscopic survey of globular clusters around the giant elliptical galaxy NGC 4472. We have obtained velocities for 144 globulars out to radii of 8' (40 kpc). We discuss dynamical evidence for dark matter in the galaxy from these data. These dynamical constraints are then compared to the mass distribution inferred from X-ray data. We also compare the kinematics of the metal-rich and metal-poor globular cluster populations previously identified through their colors. We find kinematic differences between the populations, confirming the physical distinction between cluster populations of different colors. In particular, the metal-poor cluster population has greater velocity dispersion than the metal-rich population. The metal-rich population also shows no evidence for rotation about any axis. This absence of rotation in the more spatially concentrated and enriched metal-rich population rules out proposed collapse scenarios which lead to the spin-up of this population. However, merger models are consistent with the observations as they provide a known mechanism for angular momentum transport. We also discuss ongoing work that will result in spectra of more clusters and at larger distances from the center of the galaxy.

One of our most important probes for understanding galaxy formation and evolution are globular cl... more One of our most important probes for understanding galaxy formation and evolution are globular cluster (GC) systems. We are continuing our aggressive campaign to obtain spectroscopy for a large sample of GCs in galaxies with a variety of properties, in different environments, in order to understand their kinematics, ages and abundances. Kinematical results from this project will provide a detailed

Globular clusters (GCs) provide crucial constraints on galaxy formation models and structure in t... more Globular clusters (GCs) provide crucial constraints on galaxy formation models and structure in the Universe, as well as the amount and distribution of galactic dark matter (DM). We request time to double the existing sample of GC velocities for the Virgo elliptical galaxy NGC 4649 from 120 to 250. This increased GC sample will allow the use of the most general possible 3-integral orbit-based models to determine simultaneously the NGC 4649 DM halo profile and the GC orbital anisotropy (for all GCs, and for metal-poor/rich GCs separately), providing an important check on the X-ray derived potential. Using a novel approach pioneered by this group, we will also extract kinematics for the stellar light of NGC 4649 beyond 4 effective radii from the same MOS exposures used in the GC investigation. This combined GC-stellar spectroscopic dataset will be a powerful probe of the DM content, GC orbital anisotropy, and angular momentum of NGC 4649.

arXiv (Cornell University), Oct 13, 2003

We present recent results from our long-term Gemini/GMOS study of globular clusters (GCs) in earl... more We present recent results from our long-term Gemini/GMOS study of globular clusters (GCs) in early-type galaxies. To date, we have obtained photometry and spectroscopy for GCs in NGCs 3379, 4649, 524, 7332, and IC 1459. We find a clear bimodality in the NGC 4649 GC colour distribution, with the fraction of blue/red clusters increasing with galactocentric radius. We derive ages and metallicities for 22 GCs in NGC 3379, finding that most of the clusters appear old (10−15 Gyr); however, there is a group of 4 metal-rich, younger clusters with ages of 2−6 Gyr. The NGC 3379 GC velocity dispersion decreases with radius, as does the inferred (local) mass-to-light ratio: there is no evidence for a dark matter halo in NGC 3379 based on our GC data.

arXiv (Cornell University), Nov 22, 2000

We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), ... more We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), and ages and metallicities from co-added spectra of 131 GCs. We confirm our earlier finding that the metal-poor GCs have a significantly higher velocity dispersion than the metal-rich GCs, and we find little or no rotation in the metal-rich GCs. The velocity dispersion profile is consistent with isotropic orbits for the GCs and the NGC 4472 mass distribution inferred from X-ray data. Our sample of GCs spans a metallicity range of −1.6 ≤ [F e/H] ≤ 0 dex. The metal-poor and metal-rich GC populations are coeval within the errors, and all GCs older than 6 Gyr at 95% confidence. Our findings are consistent with a merger origin for NGC 4472, but other elliptical formation models cannot be ruled out.

Highlights of Astronomy, 2005

We present recent results from our long-term Gemini/GMOS study of globular clusters (GCs) in earl... more We present recent results from our long-term Gemini/GMOS study of globular clusters (GCs) in early-type galaxies. To date, we have obtained photometry and spectroscopy for GCs in NGCs 3379, 4649, 524, 7332, and IC 1459. We find a clear bimodality in the NGC 4649 GC colour distribution, with the fraction of blue/red clusters increasing with galactocentric radius. We derive ages and metallicities for 22 GCs in NGC 3379, finding that most of the clusters appear old (10−15 Gyr); however, there is a group of 4 metal-rich, younger clusters with ages of 2−6 Gyr. The NGC 3379 GC velocity dispersion decreases with radius, as does the inferred (local) mass-to-light ratio: there is no evidence for a dark matter halo in NGC 3379 based on our GC data.

Carolina Digital Repository (University of North Carolina at Chapel Hill), 2011

This paper presents deep high quality photometry of globular cluster (GC) systems belonging to fi... more This paper presents deep high quality photometry of globular cluster (GC) systems belonging to five early-type galaxies covering a range of mass and environment. Photometric data were obtained with the Gemini North and Gemini South telescopes in the filter passbands g ′ , r ′ , and i ′. The combination of these filters with good seeing conditions allows an excellent separation between GC candidates and unresolved field objects. In fact, our previously published spectroscopic data indicates a contamination level of only ∼10 percent in our sample of GC candidates. Bimodal GC colour distributions are found in all five galaxies. Most of the GC systems appear bimodal even in the (g ′-r ′) vs (r ′-i ′) plane. A population of resolved/marginally resolved GC and Ultra Compact Dwarf candidates was found in all the galaxies. A search for the so-called "blue tilt" in the colour-magnitude diagrams reveals that NGC 4649 clearly shows that phenomenon although no conclusive evidence was found for the other galaxies in the sample. This "blue tilt" translates into a mass-metallicity relation given by Z ∝ M 0.28±0.03. This dependence was found using a new empirical (g ′-i ′) vs [Z/H] relation which relies on an homogeneous sample of GC colours and metallicities. This paper also explores the radial trends in both colour and surface density for the blue (metal-poor) and red (metal-rich) GC subpopulations. As usual, the red GCs show a steeper radial distribution than the blue ones. Evidence of galactocentric colour gradients is found in some of the GC systems, being more significant for the two S0 galaxies in the sample. Red GC subpopulations show similar colours and gradients to the galaxy halo stars in their inner region. A GC mean colour-galaxy luminosity relation, consistent with [Z/H] ∝ L B 0.26±0.08 , is present for the red GCs. An estimate of the total GC populations and specific frequency S N values is presented for NGC 3115, NGC 3923 and NGC 4649.

arXiv (Cornell University), Aug 15, 2003

Our numerical simulations first demonstrate that the pressure of ISM in a major merger becomes so... more Our numerical simulations first demonstrate that the pressure of ISM in a major merger becomes so high ($>$ 10510^5105 rmkrmB\rm k_{\rm B}rmkrmB K rmcm−3\rm cm^{-3}rmcm−3) that GMCs in the merger can collapse to form globular clusters (GCs) within a few Myr. The star formation efficiency within a GMC in galaxy mergers can rise up from a few percent to sim\simsim 80 percent, depending on the shapes and the temperature of the GMC. This implosive GC formation due to external high pressure of warm/hot ISM can be more efficient in the tidal tails or the central regions of mergers. The developed clusters have King-like profile with the effective radius of a few pc. The structural, kinematical, and chemical properties of these GC systems can depend on orbital and chemical properties of major mergers.

Monthly Notices of the Royal Astronomical Society, Feb 1, 2000

We have obtained spectra for 103 published globular cluster candidates in the Sculptor group gala... more We have obtained spectra for 103 published globular cluster candidates in the Sculptor group galaxies NGC 253 and 55. On the basis of radial velocities and digitized plate images, 14 globular clusters are identified in NGC 253 and one probable globular cluster is identified in NGC 55. The majority of the objects in the sample appear to be background galaxies. We have obtained and analysed COSMOS plate scans of NGC 253 and 55 and use these along with the spectroscopically identified clusters to define new samples of globular cluster candidates in the two galaxies which should have reduced contamination.

NOAO Proposal, Feb 1, 2003

One of our most important probes for understanding galaxy formation and evolution are globular cl... more One of our most important probes for understanding galaxy formation and evolution are globular cluster (GC) systems. We are continuing our aggressive campaign to obtain spectroscopy for a large sample of GCs in galaxies with a variety of properties, in different environments, in order to understand their kinematics, ages and abundances. Kinematical results from this project will provide a detailed

Symposium - International Astronomical Union, 2005

We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), ... more We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), and ages and metallicities for 131 GCs. We confirm our earlier finding that the metal-poor GCs have a significantly higher velocity dispersion than the metal-rich GCs, and we find little or no rotation in the metal-rich GCs. The velocity dispersion profile is consistent with isotropic GC orbits and the mass distribution inferred from X-ray data. Our sample of GCs spans a metallicity range of −1.6 ≤ [Fe/H] ≤ 0 dex. The metal-poor and metal-rich GCs are coeval within the errors, and all GCs older than 6 Gyr at 95% confidence.

Globular clusters (GCs) play an essential role in understanding the star formation history of gal... more Globular clusters (GCs) play an essential role in understanding the star formation history of galaxies. At the same time GCs are the best candidates to check the reliability of single stellar population (SSP) models which have broad ranging applications. On the basis of a new empirical stellar library in the K band, new SSP model predictions suggest that CO and

I will present results for the formation of spiral galaxy globular cluster systems in the context... more I will present results for the formation of spiral galaxy globular cluster systems in the context of hierarchical merger models. In particular I will show that such models predict correlations between mean properties of the metal-rich clusters and the host spheroid which are observable. I will also discuss our recent work on including SNe type Ia and type II products

Monthly Notices of the Royal Astronomical Society, 2000

We have derived ages and metallicities from co-added spectra of 131 globular clusters associated ... more We have derived ages and metallicities from co-added spectra of 131 globular clusters associated with the giant elliptical galaxy NGC 4472. Based upon a calibration with Galactic globular clusters, we find that our sample of globular clusters in NGC 4472 span a metallicity range of approximately 21X6 # FeaH # 0 dexX There is evidence of a radial metallicity gradient in the globular cluster system which is steeper than that seen in the underlying starlight. Determination of the absolute ages of the globular clusters is uncertain, but formally, the metal-poor population of globular clusters has an age of 14X5^4 Gyr and the metal-rich population is 13X8^6 Gyr old. Monte Carlo simulations indicate that the globular cluster populations present in these data are older than 6 Gyr at the 95 per cent confidence level. We find that within the uncertainties, the globular clusters are old and coeval, implying that the bimodality seen in the broadband colours primarily reflects metallicity and not age differences.

Monthly Notices of the Royal Astronomical Society, 2011

In this paper, we present deep high-quality photometry of globular cluster systems (GCSs) belongi... more In this paper, we present deep high-quality photometry of globular cluster systems (GCSs) belonging to five early-type galaxies, covering a range of mass and environment. Photometric data were obtained with the Gemini North and Gemini South telescopes in the filter passbands g , r and i. The combination of these filters with good seeing conditions allows an excellent separation between globular cluster (GC) candidates and unresolved field objects. In fact, our previously published spectroscopic data indicate a contamination level of only ∼10 per cent in our sample of GC candidates. Bimodal GC colour distributions are found in all five galaxies. Most of the GCSs appear bimodal even in the (g − r) versus (r − i) plane. A population of resolved/marginally resolved GC and ultracompact dwarf candidates was found in all the galaxies. A search for the so-called 'blue tilt' in the colour-magnitude diagrams reveals that NGC 4649 clearly shows this phenomenon, although no conclusive evidence was found for the other galaxies in the sample. This 'blue tilt' translates into a mass-metallicity relation given by Z ∝ M 0.28 ±0.03. This dependence was found using a new empirical (g − i) versus [Z/H] relation, which relies on an homogeneous sample of GC colours and metallicities. In this paper, we also explore the radial trends in both colour and surface density for the blue (metal-poor) and red (metal-rich) GC subpopulations. As usual, the red GCs show a steeper radial distribution than the blue GCs. Evidence of galactocentric colour gradients is found in some of the GCSs, which is more significant for the two S0 galaxies in the sample. Red GC subpopulations show similar colours and gradients to the galaxy halo stars in their inner region. A GC mean colour-galaxy luminosity relation, consistent with [ Z/H ] ∝ L 0.26 ±0.08 B , is present for the red GCs. Estimates of the total GC populations and specific frequency S N values are presented for NGC 3115, 3923 and 4649.

Astronomy and Astrophysics, 2008

ABSTRACT We present the results of an ongoing spectroscopic survey of globular clusters around th... more ABSTRACT We present the results of an ongoing spectroscopic survey of globular clusters around the giant elliptical galaxy NGC 4472. We have obtained velocities for 144 globulars out to radii of 8' (40 kpc). We discuss dynamical evidence for dark matter in the galaxy from these data. These dynamical constraints are then compared to the mass distribution inferred from X-ray data. We also compare the kinematics of the metal-rich and metal-poor globular cluster populations previously identified through their colors. We find kinematic differences between the populations, confirming the physical distinction between cluster populations of different colors. In particular, the metal-poor cluster population has greater velocity dispersion than the metal-rich population. The metal-rich population also shows no evidence for rotation about any axis. This absence of rotation in the more spatially concentrated and enriched metal-rich population rules out proposed collapse scenarios which lead to the spin-up of this population. However, merger models are consistent with the observations as they provide a known mechanism for angular momentum transport. We also discuss ongoing work that will result in spectra of more clusters and at larger distances from the center of the galaxy.

One of our most important probes for understanding galaxy formation and evolution are globular cl... more One of our most important probes for understanding galaxy formation and evolution are globular cluster (GC) systems. We are continuing our aggressive campaign to obtain spectroscopy for a large sample of GCs in galaxies with a variety of properties, in different environments, in order to understand their kinematics, ages and abundances. Kinematical results from this project will provide a detailed

Globular clusters (GCs) provide crucial constraints on galaxy formation models and structure in t... more Globular clusters (GCs) provide crucial constraints on galaxy formation models and structure in the Universe, as well as the amount and distribution of galactic dark matter (DM). We request time to double the existing sample of GC velocities for the Virgo elliptical galaxy NGC 4649 from 120 to 250. This increased GC sample will allow the use of the most general possible 3-integral orbit-based models to determine simultaneously the NGC 4649 DM halo profile and the GC orbital anisotropy (for all GCs, and for metal-poor/rich GCs separately), providing an important check on the X-ray derived potential. Using a novel approach pioneered by this group, we will also extract kinematics for the stellar light of NGC 4649 beyond 4 effective radii from the same MOS exposures used in the GC investigation. This combined GC-stellar spectroscopic dataset will be a powerful probe of the DM content, GC orbital anisotropy, and angular momentum of NGC 4649.

arXiv (Cornell University), Oct 13, 2003

We present recent results from our long-term Gemini/GMOS study of globular clusters (GCs) in earl... more We present recent results from our long-term Gemini/GMOS study of globular clusters (GCs) in early-type galaxies. To date, we have obtained photometry and spectroscopy for GCs in NGCs 3379, 4649, 524, 7332, and IC 1459. We find a clear bimodality in the NGC 4649 GC colour distribution, with the fraction of blue/red clusters increasing with galactocentric radius. We derive ages and metallicities for 22 GCs in NGC 3379, finding that most of the clusters appear old (10−15 Gyr); however, there is a group of 4 metal-rich, younger clusters with ages of 2−6 Gyr. The NGC 3379 GC velocity dispersion decreases with radius, as does the inferred (local) mass-to-light ratio: there is no evidence for a dark matter halo in NGC 3379 based on our GC data.