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Articles 1 - 16 of 16
Full-Text Articles in Physical Sciences and Mathematics
New Constraints On Early-Type Galaxy Assembly From Spectroscopic Metallicities Of Globular Clusters In M87, Alexa Villaume, Aaron Romanowsky, Jean Brodie, Jay Strader
New Constraints On Early-Type Galaxy Assembly From Spectroscopic Metallicities Of Globular Clusters In M87, Alexa Villaume, Aaron Romanowsky, Jean Brodie, Jay Strader
Faculty Publications
The observed characteristics of globular cluster (GC) systems, such as metallicity distributions, are commonly used to place constraints on galaxy formation models. However, obtaining reliable metallicity values is particularly difficult because of our limited means to obtain high quality spectroscopy of extragalactic GCs. Often, "color–metallicity relations" are invoked to convert easier-to-obtain photometric measurements into metallicities, but there is no consensus on what form these relations should take. In this paper we make use of multiple photometric data sets and iron metallicity values derived from applying full-spectrum stellar population synthesis models to deep Keck/LRIS spectra of 177 GCs centrally located around …
Upper Limits On The Presence Of Central Massive Black Holes In Two Ultra-Compact Dwarf Galaxies In Centaurus A, Karina Voggel, Anil Seth, Nadine Neumayer, Steffen Mieske, Igor Chilingarian, Christopher Ahn, Holger Baumgardt, Michael Hilker, Dieu Nguyen, Aaron J. Romanowsky, Jonelle Walsh, Mark Den Brok, Jay Strader
Upper Limits On The Presence Of Central Massive Black Holes In Two Ultra-Compact Dwarf Galaxies In Centaurus A, Karina Voggel, Anil Seth, Nadine Neumayer, Steffen Mieske, Igor Chilingarian, Christopher Ahn, Holger Baumgardt, Michael Hilker, Dieu Nguyen, Aaron J. Romanowsky, Jonelle Walsh, Mark Den Brok, Jay Strader
Faculty Publications
The recent discovery of massive black holes (BHs) in the centers of high-mass ultra-compact dwarf galaxies (UCDs) suggests that at least some are the stripped nuclear star clusters of dwarf galaxies. We present the first study that investigates whether such massive BHs, and therefore stripped nuclei, also exist in low-mass (M < 107 M ⊙) UCDs. We constrain the BH masses of two UCDs located in Centaurus A (UCD 320 and UCD 330) using Jeans modeling of the resolved stellar kinematics from adaptive optics data obtained with the SINFONI integral field spectrograph at the Very Large Telescope (VLT/SINFONI). No massive BHs …
Initial Mass Function Variability (Or Not) Among Low-Velocity Dispersion, Compact Stellar Systems, Alexa Villaume, Jean Brodie, Charlie Conroy, Aaron Romanowsky, Pieter Van Dokkum
Initial Mass Function Variability (Or Not) Among Low-Velocity Dispersion, Compact Stellar Systems, Alexa Villaume, Jean Brodie, Charlie Conroy, Aaron Romanowsky, Pieter Van Dokkum
Faculty Publications
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 …
The Sluggs Survey: A Catalog Of Over 4000 Globular Cluster Radial Velocities In 27 Nearby Early-Type Galaxies, Duncan Forbes, Adebusola Alabi, Jean Brodie, Aaron Romanowsky, Jay Strader, Caroline Foster, Christopher Usher, Lee Spitler, Sabine Bellstedt, Nicola Pastorello, Alexa Villaume, Asher Wasserman, Vincenzo Pota
The Sluggs Survey: A Catalog Of Over 4000 Globular Cluster Radial Velocities In 27 Nearby Early-Type Galaxies, Duncan Forbes, Adebusola Alabi, Jean Brodie, Aaron Romanowsky, Jay Strader, Caroline Foster, Christopher Usher, Lee Spitler, Sabine Bellstedt, Nicola Pastorello, Alexa Villaume, Asher Wasserman, Vincenzo Pota
Faculty Publications
No abstract provided.
The Sluggs Survey: Globular Clusters And The Dark Matter Content Of Early-Type Galaxies, Duncan Forbes, Adebusola Alabi, Aaron Romanowsky, Jean Brodie, Jay Strader, Christopher Usher, Vincenzo Pota
The Sluggs Survey: Globular Clusters And The Dark Matter Content Of Early-Type Galaxies, Duncan Forbes, Adebusola Alabi, Aaron Romanowsky, Jean Brodie, Jay Strader, Christopher Usher, Vincenzo Pota
Faculty Publications
No abstract provided.
Erratum: The Sluggs Survey: The Globular Cluster Systems Of Three Early-Type Galaxies Using Wide-Field Imaging, Sreeja Kartha, Duncan Forbes, Lee Spitler, Aaron Romanowsky, Jacob Arnold, Jean Brodie
Erratum: The Sluggs Survey: The Globular Cluster Systems Of Three Early-Type Galaxies Using Wide-Field Imaging, Sreeja Kartha, Duncan Forbes, Lee Spitler, Aaron Romanowsky, Jacob Arnold, Jean Brodie
Faculty Publications
The paper ‘The SLUGGS survey: the globular cluster systems of three early-type galaxies using wide-field imaging’ was published in Monthly Notices of the Royal Astronomical Society, 437, 273 – 292 (2014).
An Overmassive Dark Halo Around An Ultra-Diffuse Galaxy In The Virgo Cluster, Michael Beasley, Aaron Romanowsky, Vincenzo Pota, Ignacio Navarro, David Martinez-Delgado, Fabian Neyer, Aaron Deich
An Overmassive Dark Halo Around An Ultra-Diffuse Galaxy In The Virgo Cluster, Michael Beasley, Aaron Romanowsky, Vincenzo Pota, Ignacio Navarro, David Martinez-Delgado, Fabian Neyer, Aaron Deich
Faculty Publications
No abstract provided.
Star Clusters In M31. Vii. Global Kinematics And Metallicity Subpopulations Of The Globular Clusters, Nelson Caldwell, Aaron Romanowsky
Star Clusters In M31. Vii. Global Kinematics And Metallicity Subpopulations Of The Globular Clusters, Nelson Caldwell, Aaron Romanowsky
Faculty Publications
We carry out a joint spatial–kinematical–metallicity analysis of globular clusters (GCs) around the Andromeda Galaxy (M31), using a homogeneous, high-quality spectroscopic data set. In particular, we remove the contaminating young clusters that have plagued many previous analyses. We find that the clusters can be divided into three major metallicity groups based on their radial distributions: (1) an inner metal-rich group ([Fe/H] > -0.4); (2) a group with intermediate metallicity (with median [Fe/H] = −1); and (3) a metal-poor group, with [Fe/H] < -1.5. The metal-rich group has kinematics and spatial properties like those of the disk of M31, while the two more metal-poor groups show mild prograde rotation overall, with larger dispersions—in contrast to previous claims of stronger rotation. The metal-poor GCs are the least concentrated group; such clusters occur five times less frequently in the central bulge than do clusters of higher metallicity. Despite some well-known differences between the M31 and Milky Way GC systems, our revised analysis points to remarkable similarities in their chemodynamical properties, which could help elucidate the different formation stages of galaxies and their GCs. In particular, the M31 results motivate further exploration of a metal-rich GC formation mode in situ, within high-redshift, clumpy galactic disks.
The Sluggs Survey: Globular Cluster Kinematics In A ‘Double Sigma’ Galaxy – Ngc 4473, Adebusola Alabi, Caroline Foster, Duncan Forbes, Aaron Romanowsky, Nicola Pastorello, Jean Brodie, Lee Spitler, Jay Strader, Christopher Usher
The Sluggs Survey: Globular Cluster Kinematics In A ‘Double Sigma’ Galaxy – Ngc 4473, Adebusola Alabi, Caroline Foster, Duncan Forbes, Aaron Romanowsky, Nicola Pastorello, Jean Brodie, Lee Spitler, Jay Strader, Christopher Usher
Faculty Publications
NGC 4473 is a so-called double sigma (2σ) galaxy, i.e. a galaxy with rare, double peaks in its 2D stellar velocity dispersion. Here, we present the globular cluster (GC) kinematics in NGC 4473 out to ∼10Re (effective radii) using data from combined Hubble Space Telescope/Advanced Camera for Surveys and Subaru/Suprime-Cam imaging and Keck/Deep Imaging Multi-Object Spectrograph. We find that the 2σ nature of NGC 4473 persists up to 3Re, though it becomes misaligned to the photometric major axis. We also observe a significant offset between the stellar and GC rotation amplitudes. This offset can be understood as a co-addition of …
The Sluggs Survey: Inferring The Formation Epochs Of Metal-Poor And Metal-Rich Globular Clusters, Duncan Forbes, Nicola Pastorello, Aaron Romanowsky, Christopher Usher, Jean Brodie, Jay Strader
The Sluggs Survey: Inferring The Formation Epochs Of Metal-Poor And Metal-Rich Globular Clusters, Duncan Forbes, Nicola Pastorello, Aaron Romanowsky, Christopher Usher, Jean Brodie, Jay Strader
Faculty Publications
We present a novel, observationally-based framework for the formation epochs and sites of globular clusters (GCs) in a cosmological context. Measuring directly the mean ages of the metal-poor and metal-rich GC subpopulations in our own Galaxy, and in other galaxies, is observationally challenging. Here we apply an alternative approach utilizing the property that the galaxy mass–metallicity relation is a strong function of redshift (or look-back age) but is relatively insensitive to galaxy mass for massive galaxies. Assuming that GCs follow galaxy mass–metallicity relations that evolve with redshift, one can estimate the mean formation epochs of the two GC subpopulations by …
The Sluggs Survey: Combining Stellar And Globular Cluster Metallicities In The Outer Regions Of Early-Type Galaxies, Nicola Pastorello, Duncan Forbes, Christopher Usher, Jean Brodie, Aaron Romanowsky, Jay Strader, Lee Spitler, Adebusola Alabi, Caroline Foster, Zachary Jennings, Sreeja Kartha, Vincenzo Pota
The Sluggs Survey: Combining Stellar And Globular Cluster Metallicities In The Outer Regions Of Early-Type Galaxies, Nicola Pastorello, Duncan Forbes, Christopher Usher, Jean Brodie, Aaron Romanowsky, Jay Strader, Lee Spitler, Adebusola Alabi, Caroline Foster, Zachary Jennings, Sreeja Kartha, Vincenzo Pota
Faculty Publications
The outer halo regions of early-type galaxies carry key information about their past accretion history. However, spectroscopically probing the stellar component at such galactocentric radii is still challenging. Using the DEep Imaging Multi-Object Spectrograph on the Keck, we have been able to measure the metallicities of the stellar and globular cluster components in 12 early-type galaxies out to more than 10Re. We find similar metallicity gradients for the metal-poor and metal-rich globular cluster subpopulations, suggesting a common formation process for the two subpopulations. This is in conflict with most current theoretical predictions, where the metal-poor globular clusters are thought to …
How Elevated Is The Dynamical-To-Stellar Mass Ratio Of The Ultracompact Dwarf S999?, Joachim Janz, Duncan Forbes, Mark Norris, Jay Strader, Samantha Penny, Martina Fagioli, Aaron Romanowsky
How Elevated Is The Dynamical-To-Stellar Mass Ratio Of The Ultracompact Dwarf S999?, Joachim Janz, Duncan Forbes, Mark Norris, Jay Strader, Samantha Penny, Martina Fagioli, Aaron Romanowsky
Faculty Publications
No abstract provided.
Vegas-Sss. A Vst Early-Type Galaxy Survey: Analysis Of Small Stellar Systems: Testing The Methodology On The Globular Cluster System In Ngc 3115⋆, Michele Cantiello, Massimo Capaccioli, Nicola Napolitano, Aniello Grado, Luca Limatola, Maurizio Paolillo, Enrica Iodice, Aaron Romanowsky, Duncan Forbes, Gabriella Raimondo, Marilena Spavone, Francesco La Barbera, Thomas Puzia, Pietro Schipani
Vegas-Sss. A Vst Early-Type Galaxy Survey: Analysis Of Small Stellar Systems: Testing The Methodology On The Globular Cluster System In Ngc 3115⋆, Michele Cantiello, Massimo Capaccioli, Nicola Napolitano, Aniello Grado, Luca Limatola, Maurizio Paolillo, Enrica Iodice, Aaron Romanowsky, Duncan Forbes, Gabriella Raimondo, Marilena Spavone, Francesco La Barbera, Thomas Puzia, Pietro Schipani
Faculty Publications
We present a study of globular clusters (GCs) and other small stellar systems (SSSs) in the field of NGC 3115, observed as part of the ongoing wide-field imaging survey VEGAS, carried out with the 2.6 m VST telescope. We used deep g and i observations of NGC 3115, a well-studied lenticular galaxy that is covered excellently well in the scientific literature. This is fundamental to test the methodologies, verify the results, and probe the capabilities of the VEGAS-SSS. Leveraging the large field of view of the VST allowed us to accurately study the distribution and properties of SSSs as a …
The Sluggs Survey: Globular Cluster Stellar Population Trends From Weak Absorption Lines In Stacked Spectra, Christopher Usher, Duncan Forbes, Jean Brodie, Aaron Romanowsky, Jay Strader, Charlie Conroy, Caroline Foster, Nicola Pastorello, Vincenzo Pota, Jacob Arnold
The Sluggs Survey: Globular Cluster Stellar Population Trends From Weak Absorption Lines In Stacked Spectra, Christopher Usher, Duncan Forbes, Jean Brodie, Aaron Romanowsky, Jay Strader, Charlie Conroy, Caroline Foster, Nicola Pastorello, Vincenzo Pota, Jacob Arnold
Faculty Publications
As part of the SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey, we stack 1137 Keck DEIMOS (Deep Imaging Multi-Object Spectrograph) spectra of globular clusters from 10 galaxies to study their stellar populations in detail. The stacked spectra have median signal-to-noise ratios of ∼90 Å−1. Besides the calcium triplet, we study weaker sodium, magnesium, titanium and iron lines as well as the Hα and higher order Paschen hydrogen lines. In general, the stacked spectra are consistent with old ages and a Milky Way-like initial mass function. However, we see different metal line index strengths at fixed colour and magnitude, and …
Ngc 3628-Ucd1: A Possible Ω Cen Analog Embedded In A Stellar Stream, Zachary Jennings, Aaron Romanowsky, Jean Brodie, Joachim Janz, Mark Norris, Duncan Forbes, David Martinez-Delgado, Martina Fagioli, Samantha Penny
Ngc 3628-Ucd1: A Possible Ω Cen Analog Embedded In A Stellar Stream, Zachary Jennings, Aaron Romanowsky, Jean Brodie, Joachim Janz, Mark Norris, Duncan Forbes, David Martinez-Delgado, Martina Fagioli, Samantha Penny
Faculty Publications
No abstract provided.
Hiding In Plain Sight: Record-Breaking Compact Stellar Systems In The Sloan Digital Sky Survey, Michael Sandoval, Richard Vo, Aaron Romanowsky, Jay Strader, Jieun Choi, Zachary Jennings, Charlie Conroy, Jean Brodie, Caroline Foster, Alexa Villaume, Mark Norris, Joachim Janz, Duncan Forbes
Hiding In Plain Sight: Record-Breaking Compact Stellar Systems In The Sloan Digital Sky Survey, Michael Sandoval, Richard Vo, Aaron Romanowsky, Jay Strader, Jieun Choi, Zachary Jennings, Charlie Conroy, Jean Brodie, Caroline Foster, Alexa Villaume, Mark Norris, Joachim Janz, Duncan Forbes
Faculty Publications
No abstract provided.