Stephen E. Zepf's research while affiliated with Michigan State University and other places
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Publications (255)
The globular cluster ultraluminous X-ray source, RZ2109, is a complex and unique system which has been detected at X-ray, ultra-violet, and optical wavelengths. Based on almost 20 years of Chandra and XMM-Newton observations, the X-ray luminosity exhibits order-of-magnitude variability, with the peak flux lasting on the order of a few hours. We per...
We use multiband archival Hubble Space Telescope (HST) observations to measure the photometric and structural parameters of the M81 globular cluster (GC) that hosts the fast radio burst FRB 20200120E. Our best-fitting King model has an effective radius r h = 3.06 pc with a moderate King model concentration of c = 53, and an inferred core radius of...
Utilising archival Chandra X-ray Observatory data and Hubble Space Telescope globular cluster catalogues, we probe the time-domain properties of the low mass X-ray binary population in the elliptical galaxy NGC 4261. Of the 98 unique X-ray sources identified in this study, 62 sources are within the optical field of view and, of those, 33% are align...
Utilising archival Chandra X-ray Observatory data and Hubble Space Telescope globular cluster catalogues, we probe the time-domain properties of the low mass X-ray binary population in the elliptical galaxy NGC 4261. Of the 98 unique X-ray sources identified in this study, 62 sources are within the optical field of view and, of those, 33% are align...
Ultraluminous X-ray Sources (ULXs) in globular clusters are low mass X-ray binaries that achieve high X-ray luminosities through a currently uncertain accretion mechanism. Using archival Chandra and Hubble Space Telescope observations, we perform a volume-limited search ($\lesssim$ 70 Mpc) of 21 of the most massive ($>10^{11.5} M_\odot$) early-type...
Ultraluminous X-ray Sources (ULXs) in globular clusters are low mass X-ray binaries that achieve high X-ray luminosities through a currently uncertain accretion mechanism. Using archival Chandra and Hubble Space Telescope (HST) observations, we perform a volume-limited search (≲ 70 Mpc) of 21 of the most massive (>1011.5M⊙) early-type galaxies to i...
NGC 4472 is home to five ultraluminous X-ray sources hosted by globular clusters. These sources have been suggested as good black hole candidates in extragalactic globular clusters− a highly sought after population that may provide observational information regarding the progenitors of merging black hole binaries. In this body of work, we present X...
We investigate archival Hubble Space Telescope ACS/SBC F140LP observations of NGC 1399 to search for evidence of multiple stellar populations in extragalactic globular clusters. Enhanced FUV populations are thought to be indicators of He-enhanced second generation populations in globular clusters, specifically extreme/blue horizontal branch stars....
NGC 4472 is home to five ultraluminous X-ray sources hosted by globular clusters. These sources have been suggested as good black hole candidates in extragalactic globular clusters$-$ a highly sought after population that may provide observational information regarding the progenitors of merging black hole binaries. In this body of work, we present...
We investigate archival Hubble Space Telescope ACS/SBC F140LP observations of NGC~1399 to search for evidence of multiple stellar populations in extragalactic globular clusters. Enhanced FUV populations are thought to be indicators of He-enhanced second generation populations in globular clusters, specifically extreme/blue horizontal branch stars....
Globular clusters (GCs) have been at the heart of many longstanding questions in many sub-fields of astronomy and, as such, systematic identification of GCs in external galaxies has immense impacts. In this study, we take advantage of M87’s well-studied GC system to implement supervised machine learning (ML) classification algorithms — specifically...
Globular clusters (GCs) have been at the heart of many longstanding questions in many sub-fields of astronomy and, as such, systematic identification of GCs in external galaxies has immense impacts. In this study, we take advantage of M87's well-studied GC system to implement supervised machine learning (ML) classification algorithms - specifically...
We investigate a sample of seven edge-on spiral galaxies using Chandra observations. Edge-on spiral galaxies allow us to clearly separate source associated with their star-forming regions versus the outer edges of the system; offering a clear advantage over other systems. We uncover a number of X-ray point sources across these galaxies, and after e...
We investigate a sample of seven edge-on spiral galaxies using Chandra observations. Edge-on spiral galaxies allow us to clearly separate source associated with their star-forming regions versus the outer edges of the system; offering a clear advantage over other systems. We uncover a number of X-ray point sources across these galaxies, and after e...
We have identified three ultraluminous X-ray sources (ULXs) hosted by globular clusters (GCs) within NGC 1316’s stellar system. These discoveries bring the total number of known ULXs in GCs up to 20. We find that the X-ray spectra of the three new sources do not deviate from the established pattern of spectral behaviour of the other known GC ULXs....
We have identified three ultraluminous X-ray sources (ULXs) hosted by globular clusters (GCs) within NGC 1316's stellar system. These discoveries bring the total number of known ULXs in GCs up to 20. We find that the X-ray spectra of the three new sources do not deviate from the established pattern of spectral behaviour of the other known GC ULXs....
We have identified seven ultraluminous X-ray sources (ULXs) that are coincident with globular cluster candidates (GC) associated with M87. ULXs in the old GC environment represent a new population of ULXs, and ones likely to be black holes. In this study, we perform detailed X-ray spectroscopic follow-up to seven GC ULXs across a wealth of archival...
We have identified seven ultraluminous X-ray sources (ULXs) which are coincident with globular cluster candidates (GCs) associated with M87. ULXs in the old GC environment represent a new population of ULXs, and ones likely to be black holes. In this study we perform detailed X-ray spectroscopic followup to seven GC ULXs across a wealth of archival...
RZ2109 is the first of several extragalactic globular clusters shown to host an ultraluminous X-ray source. RZ2109 is particularly notable because optical spectroscopy shows it has broad, luminous [O iii] λλ4959,5007 emission, while also having no detectable hydrogen emission. The X-ray and optical characteristics of the source in RZ2109 make it a...
RZ2109 is the first of several extragalactic globular clusters shown to host an ultraluminous X-ray source. RZ2109 is particularly notable because optical spectroscopy shows it has broad, luminous [OIII] 4959,5007 emission, while also having no detectable hydrogen emission. The X-ray and optical characteristics of the source in RZ2109 make it a goo...
We present an unprecedented, deep study of the primordial low-mass X-ray binary population in an isolated, lower metallicity environment. We perform follow-up observations of previously identified X-ray binary candidates in the Sculptor Dwarf Galaxy by combining a second Chandra observation with Spitzer and Gemini photometry, as well as Gemini spec...
We report the discovery of the transient ultraluminous X-ray source (ULX) CXOU J122602.3+125951 (hereafter M86 tULX-1), located 3′52″ (19 kpc) north-west of the centre of the giant elliptical galaxy M86 (NGC 4406) in the Virgo Cluster. The spectrum of M86 tULX-1 can be fit by a power law plus multicolour disc model with a |$1.0^{+0.8}_{-2.6}$| inde...
We present an unprecedented, deep study of the primordial low-mass X-ray binary population in an isolated, lower-metallicity environment. We perform followup observations of previously-identified X-ray binary candidates in the Sculptor Dwarf Galaxy by combining a second Chandra observation with Spitzer and Gemini photometry, as well as Gemini spect...
A number of ultraluminous X-ray sources (ULXs) are physically associated with extragalactic globular clusters (GCs). We undertake a systematic X-ray analysis of eight of the brightest of these sources. We fit the spectra of the GC ULXs to single power law and single disk models. We find that the data never require that any of the sources change bet...
A number of ultraluminous X-ray sources (ULXs) are physically associated with extragalactic globular clusters (GCs). We undertake a systematic X-ray analysis of eight of the brightest of these sources. We fit the spectra of the GC ULXs to single power law and single disk models. We find that the data never require that any of the sources change bet...
We present high spatial resolution, far ultraviolet (FUV) F140LP observations of 12 massive globular clusters inM31 obtained using the ACS/SBC on the Hubble Space Telescope (HST). These observations resolve the cluster profiles to scales similar to their core radii and enable the study of the spatial distribution of blue and extreme horizontal bran...
We report the discovery of the transient ultraluminous X-ray source (ULX) CXOU J122602.3+125951 (hereafter M86 tULX-1), located 3'52" (19 kpc) northwest of the centre of the giant elliptical galaxy M86 (NGC 4406) in the Virgo Cluster. The spectrum of M86 tULX-1 can be fit by a power-law plus multicolour-disc model with a 1.0 [+0.8 -2.6] index and a...
We present high spatial resolution, far ultraviolet (FUV) F140LP observations of 12 massive globular clusters in M 31 obtained using the ACS/SBC on the Hubble Space Telescope (HST). These observations resolve the cluster profiles to scales similar to their core radii and enable the study of the spatial distribution of blue and extreme horizontal br...
We present the results of long-term monitoring of the X-ray emission from the ultraluminous X-ray source XMMU J122939.9+075333 in the extragalactic globular cluster RZ2109. The combination of the high X-ray luminosity, short-term X-ray variability, X-ray spectrum, and optical emission suggests that this system is likely an accreting black hole in a...
We present the results of long-term monitoring of the X-ray emission from the ultraluminous X-ray source XMMUJ122939.9+075333 in the extragalactic globular cluster RZ2109. The combination of the high X-ray luminosity, short term X-ray variability, X-ray spectrum, and optical emission suggest that this system is likely an accreting black hole in a g...
We present new Chandra observations of the outer halo of the giant elliptical galaxy NGC 4472 (M49) in the Virgo Cluster. The data extend to 130 kpc (28'), and have a combined exposure time of 150 ks. After identifying optical counterparts using the Next Generation Virgo Cluster Survey to remove background active galactic nuclei and globular cluste...
We have derived ages and metallicities from co-added spectra of 131 globular clusters (GCs) associated with the giant Virgo elliptical NGC 4472. ¿From their metal-line indices, we find that our sample of GCs span a metallicity range of approximately −1.6 ≤ [Fe/H] ≤ 0 dex. The SSP models of Worthey (1994; W94) predict that the metal-poor population...
We present constraints on variations in the initial mass function (IMF) of nine local early-type galaxies based on their low-mass X-ray binary (LMXB) populations. Comprised of accreting black holes and neutron stars, these LMXBs can be used to constrain the important high-mass end of the IMF. We consider LMXB populations beyond the cores of the gal...
We present constraints on variations in the initial mass function (IMF) of nine local early-type galaxies based on their low mass X-ray binary (LMXB) populations. Comprised of accreting black holes and neutron stars, these LMXBs can be used to constrain the important high mass end of the IMF. We consider the LMXB populations beyond the cores of the...
We present the X-ray point source population of NGC 7457 based on 124 ks of Chandra observations. Previous deep Chandra observations of low mass X-ray binaries (LMXBs) in early-type galaxies have typically targeted the large populations of massive galaxies. NGC 7457 is a nearby, early-type galaxy with a stellar luminosity of $1.7\times10^{10} L_{K\...
The stellar initial mass function (IMF), which is often assumed to be universal across unresolved stellar populations, has recently been suggested to be "bottom-heavy" for massive ellipticals. In these galaxies, the prevalence of gravity-sensitive absorption lines (e.g. Na I and Ca II) in their near-IR spectra implies an excess of low-mass ($m <= 0...
We investigate the integrated far-ultraviolet (FUV) emission from globular clusters. We present new FUV photometry of M~87's clusters based on archival HST WFPC2 F170W observations. We use these data to test the reliability of published photometry based on HST STIS FUV-MAMA observations, which are now known to suffer from significant red-leak. We g...
We present the X-ray luminosity function (XLF) of low mass X-ray binaries
(LMXBs) in the globular clusters (GCs) and fields of seven early-types
galaxies. These galaxies are selected to have both deep Chandra observations,
which allow their LMXB populations to be observed to X-ray luminosities of
$10^{37}-10^{38}$ erg/s, and HST optical mosaics whi...
We present new wide-field photometry and spectroscopy of the globular
clusters (GCs) around NGC 4649 (M60), the third brightest galaxy in the Virgo
cluster. Imaging of NGC 4649 was assembled from a recently-obtained HST/ACS
mosaic, and new Subaru/Suprime-Cam and archival CFHT/MegaCam data. About 1200
sources were followed up spectroscopically using...
We study the effects of the external tidal field on the violent relaxation
phase of star clusters dynamical evolution, with particular attention to the
kinematical properties of the equilibrium configurations emerging at the end of
this phase.We show that star clusters undergoing the process of violent
relaxation in the tidal field of their host ga...
We present a study of the faint-end of the X-ray Luminosity Function of Low
Mass X-ray binaries in the Globular Cluster system of the cD galaxy NGC 1399 by
performing a stacking experiment on 618 X-ray undetected GCs, in order to
verify the presence of faint LMXBs and to constrain the faint-end slope of the
GC-LMXBs XLF below the individual detecti...
We have obtained radial velocity measurements for 51 new globular clusters
around the Sombrero galaxy. These measurements were obtained using
spectroscopic observations from the AAOmega spectrograph on the
Anglo-Australian Telescope and the Hydra spectrograph at WIYN. Combined with
our own past measurements and velocity measurements obtained from t...
We present an analysis of optical spectra from the globular cluster RZ2109 in
NGC4472, which hosts the first unambiguous globular cluster black hole. We use
these spectra to determine the elemental composition of the emission line
system associated with this source, and to constrain the age and metallicity of
the host globular cluster. For the emis...
A number of recent studies have proposed that the stellar initial mass
function (IMF) of early type galaxies varies systematically as a function of
galaxy mass, with higher mass galaxies having steeper IMFs. These steeper IMFs
have more low-mass stars relative to the number of high mass stars, and
therefore naturally result in proportionally fewer...
We present a optical spectra from an ongoing monitoring program of black
hole hosting globular RZ2109 located in the Virgo elliptical NGC4472.
The collected low ( 400) to moderate ( 2000) resolution spectra span a 5
year period from 2007-2013. The cluster's spectra display extremely
broad [O III]4959,5007 lines with widths of ~3000 km/s and a notew...
Using spectra from the Hydra spectrograph on the 3.5m WIYN telescope and
from the AAOmega spectrograph on the 3.9m Anglo-Australian Telescope, we
have measured heliocentric radial velocities for >50 globular
clusters in the Sombrero Galaxy (M104). We combine these new
measurements with those from previous studies to construct and analyze a
total sa...
We present an investigation of potential signatures of the formation of multiple stellar populations in recently formed extragalactic star clusters. All of the Galactic globular clusters for which good samples of individual stellar abundances are available show evidence for multiple populations. This appears to require that multiple episodes of sta...
In this paper we continue the study of the GC system of NGC 3923 first
presented in Norris et al. (2008MNRAS.385...40N). To the 29 NGC 3923 GC
velocities previously determined from MOS we add an additional 50 GC
velocities measured using a combination of MOS and Nod-and-Shuffle
(N&S) observations.
(1 data file).
In recent years spectroscopic and photometric observations have
established the presence of distinct stellar populations in the Milky
Way's globular clusters. The identification of these multiple stellar
populations within individual globular clusters has challenged our
fundamental understanding of cluster formation. Observations of
relatively newl...
We present optical HST/STIS spectroscopy of RZ 2109, a globular cluster in
the elliptical galaxy NGC 4472. This globular cluster is notable for hosting an
ultraluminous X-ray source as well as associated strong and broad [OIII] 4959,
5007 emission. We show that the HST/STIS spectroscopy spatially resolves the
[OIII] emission in RZ 2109. While we ar...
Star formation plays a central role in the evolution of galaxies and of the
Universe as a whole. Studies of star-forming regions in the local universe have
shown that star formation typically occurs in a clustered fashion. Building a
coherent picture of how star clusters form and evolve is therefore critical to
our overall understanding of the star...
We report the spectral and temporal variability properties of 18 candidate
transient and potential transient (TC and PTC) sources detected in deep
multi-epoch Chandra observation of the nearby elliptical galaxies, NGC 3379,
NGC 4278 and NGC 4697. Only one source can be identified with a background
counterpart, leaving 17 TCs + PTCs in the galaxies....
![Figure 1. NGC 4472 GC luminosities in the [O iii] 5007 emission line as...](profile/Mark-Peacock-2/publication/224849065/figure/fig2/AS:342261192773633@1458612835567/NGC4472-GC-luminosities-in-the-Oiii-5007-emission-line-as-measured-with-respect-to-the_Q320.jpg)
We have searched for [O III] 5007 emission in high-resolution spectroscopic data from FLAMES/GIRAFFE Very Large Telescope observations of 174 massive globular clusters (GCs) in NGC 4472. No planetary nebulae (PNe) are observed in these clusters, constraining the number of PNe per bolometric luminosity, α < 0.8 × 10–7 PN/L
☉. This is significantly l...
Deep images of 10 early-type galaxies in low-density environments have been obtained with the Advanced Camera for Surveys
(ACS) aboard the Hubble Space Telescope. The global properties of the globular cluster (GC) systems of the galaxies have been derived in order to investigate the
role of the environment in galaxy formation and evolution. Using t...
The images presented here were taken using GMOS in imaging mode on both
the Gemini South and Gemini North telescopes.
(3 data files).
There are no known black hole X-ray sources in Galactic globular
clusters. This could either be due to the small number of Galactic
globular clusters combined with a very low formation rate or a very long
duty cycle for globular cluster black hole X-ray sources, or a true
absence of black holes in globular clusters. Advances in X-ray and
optical ob...
We present a multi-facility study of the optical spectrum of the
extragalactic globular cluster RZ2109, which hosts a bright black hole X-ray
source. The optical spectrum of RZ2109 shows strong and very broad [O
III]\lambda \lambda 4959,5007 emission in addition to the stellar absorption
lines typical of a globular cluster. We use observations over...
We present a wide-field study of the globular cluster (GC)/low-mass X-ray binary (LMXB) connection in the giant elliptical NGC 1399. The large field of view of the Advanced Camera for Surveys/WFC, combined with Hubble Space Telescope and Chandra high resolution, allow us to constrain the LMXB formation scenarios in elliptical galaxies. We confirm t...
![Figure 4. Spectra of 12 Gyr SSPs with [Fe/H] = +0.00 produced from the...](profile/Mark-Peacock-2/publication/51892092/figure/fig2/AS:340049011986437@1458085410214/Spectra-of-12-Gyr-SSPs-with-Fe-H-000-produced-from-the-models-of-M05-red_Q320.jpg)
Accurate stellar population synthesis models are vital in understanding the
properties and formation histories of galaxies. In order to calibrate and test
the reliability of these models, they are often compared with observations of
star clusters. However, relatively little work has compared these models in the
ugriz filters, despite the recent wid...
We present a wide field study of the Globular Clusters/Low Mass X-ray Binary
(LMXB) connection in the giant elliptical NGC1399. The large FOV of the
ACS/WFC, combined with the HST and Chandra high resolution, allow us to
constrain the LMXB formation scenarios in elliptical galaxies. We confirm that
NGC1399 has the highest LMXB fraction in GCs of al...
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...
We proposed in the most recent Chandra round for a 20 kilosecond
observation of the globular cluster RZ2109 in NGC 4472, along with a
Gemini spectrum of 7.2 hours in duration. This proposal is for banding
of the Gemini time awarded by the Chandra TAC. This globular cluster
hosts the first black hole X-ray source to be umambiguosly identified in
a g...
The globular cluster RZ2109 located in NGC4472 was the first unambiguous identification of a black hole x-ray source in a globular cluster. Optical spectroscopy of RZ2109 display 3000 km s-1 [O III]lambdalambda4959,5007 line along with the stellar spectra of the host globular cluster. Notably, the observed spectrum lacks measurable emission from an...
Globular clusters are the smallest gravitationally bound stellar systems in the universe. There has long been an interest in detecting black holes in globular clusters and studying its implications. Accreting X-ray luminous systems can provide some of the most direct evidence of black holes in globular clusters. We present the results of our ongoin...
Whether there are black holes in globular clusters and what the
properties of any such black holes might be remained unclear for many
years. Advances in both X-ray and optical/near-infrared work have
enabled searches for black hole X-ray sources to be extended to
extragalactic globular clusters. We combined X-ray and optical
observations to identif...
We report a detailed spectral analysis of the population of low-mass X-ray binaries (LMXBs) detected in the elliptical galaxy NGC~4278 with Chandra. Seven luminous sources were studied individually, four in globular clusters (GCs), and three in the stellar field. The range of (0.3-8 keV) $L_X$ for these sources suggests that they may be black hole...
We present the results of new X-ray observations of XMMU 122939.7+075333, the black hole (BH) in the globular cluster RZ 2109
in the Virgo cluster galaxy NGC 4472. A combination of non-detections and marginal detections in several recent Swift and Chandra observations show that the source has varied by at least a factor of 20 in the past 6 yr, and...
We discuss CXOU 1229410+075744, a new black hole candidate in a globular cluster in the elliptical galaxy NGC 4472. By comparing
two Chandra observations of the galaxy, we find a source that varies by at least a factor of 4, and has a peak luminosity of at least
2 × 1039 erg s−1. As such, the source varies by significantly more than the Eddington l...
We have discovered an accreting black hole (BH) in a spectroscopically confirmed globular cluster (GC) in NGC 1399 through monitoring of its X-ray activity. The source, with a peak luminosity of L_x=2x10^39 ergs/s, reveals an order of magnitude change in the count rate within ~10 ks in a Chandra observation. The BH resides in a metal-rich [Fe/H]~0....
We present a wide field study of the Globular Clusters/Low Mass X-ray
Binaries connection in the cD elliptical NGC1399, combining HST/ACS and Chandra
high resolution data. We find evidence that LMXB formation likelihood is
influenced by GCs structural parameters, in addition to the well known effects
of mass and metallicity, independently from gala...
We present an updated catalogue of M31 globular clusters (GCs) based on images from the Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope and from the Sloan Digital Sky Survey (SDSS). Our catalogue includes new, self-consistent ugriz and K-band photometry of these clusters. We discuss the difficulty of obtaining accurate photometry...
We investigate low mass X-ray binaries (LMXBs) in the M31 globular cluster (GC) system using data from the 2XMMi catalogue. These X-ray data are based on all publicly available XMM-Newton observations of the galaxy. This new survey provides the most complete and homogeneous X-ray survey of M31's GCs to date, covering >80% of the confirmed old clust...
From a deep multi-epoch Chandra observation of the elliptical galaxy NGC 3379 we report the spectral properties of eight luminous LMXBs (L
X >1.2 × 1038 erg s–1). We also present a set of spectral simulations, produced to aid the interpretation of low-count single-component spectral modeling. These simulations demonstrate that it is possible to inf...
A key observational result that can constrain the nature of Low-Mass
X-ray Binaries (LMXBs) is their time variability. From theory it has
been suggested that transient behavior is expected from luminous
(LX>1037 erg/s) LMXBs if these sources have evolved from
native X-ray binaries in the stellar field, whereas GC-LMXBs are only
expected to display...
Globular clusters, which are found in large numbers around all types of galaxies, are the closest analogues to simple stellar systems. It is now well established mainly on the basis of optical observations that the cluster systems of most nearby galaxies have bimodal metallicity distributions. This has led to interesting discussions about the galax...
We present radial velocities for 393 globular clusters around the Virgo elliptical galaxy NGC 4472. The velocities were primarily obtained with the VLT and FLAMES, and are notable for their very small uncertainties, typically less than 10 km/s. We use this large dataset to constrain the mass profile of NGC 4472 over a large range of radii. The resu...
The six separate Chandra observations of NGC 4278 have been carried out over a two-year baseline, with the first of these, a 37ks pointing, being performed in 2005 February. This observation has been followed by five deeper pointings, all carried out between 2006 March and 2007 February, resulting in a total exposure time of 471ks. (11 data files).
We present an updated catalogue of M31 globular clusters (GCs) based on images from the Wide Field CAMera (WFCAM) on the UK Infrared Telescope and from the Sloan Digital Sky Survey (SDSS). Our catalogue includes new, self-consistent ugriz and K-band photometry of these clusters. We discuss the difficulty of obtaining accurate photometry of clusters...
(abridged) We present a statistical study of the low-mass X-ray binary (LMXB) populations of three nearby, old elliptical galaxies: NGC 3379, NGC 4278, and NGC 4697. With a cumulative ~1 Ms Chandra ACIS observing time, we detect 90-170 LMXBs within the D25 ellipse of each galaxy. Cross-correlating Chandra X-ray sources and HST optical sources, we i...
The five separate Chandra observations of NGC 3379 have been carried out over a 6yr baseline, with the first of these, a 30ks pointing, performed in 2001 February. This observation was followed by four deeper pointings, all carried out between 2006 January and 2007 January, resulting in a total exposure time of 337ks. (8 data files).
Large extra dimensions have been proposed as a possible solution to the hierarchy problem in physics. One of the suggested models, the RS2 braneworld model, makes a prediction that black holes evaporate by Hawking radiation on a short timescale that depends on the black hole mass and on the asymptotic radius of curvature of the extra dimensions. Th...
To investigate the properties of the GCs in M31, we obtained K-band photometry using the Wide Field CAMera (WFCAM) on the United Kingdom Infrared Telescope (UKIRT) under the service program USERV1652. Our observations were taken on the nights of 2005 November 30 and 2007 August 06 with seeing of 0.85-1.00 and 0.6-0.8arcsec, respectively. (1 data fi...
We present the properties of the discrete X-ray sources detected in our monitoring program of the globular cluster (GC) rich elliptical galaxy, NGC 4278, observed with Chandra ACIS-S in six separate pointings, resulting in a co-added exposure of 458 ks. From this deep observation, 236 sources have been detected within the region overlapped by all o...
We study the luminosity function of galaxies in Hickson groups using our recent redshift survey of galaxies in and around 17 of these groups. We find that the galaxies in these regions have a luminosity function with M*=-19.5+5 log h and α=-1.0, where M* and α are the usual parameters in the standard Schechter form of the luminosity function and th...
We propose a physically motivated and self-consistent prescription for the modeling of transient neutron star (NS) low-mass X-ray binary (LMXB) properties, such as duty cycle (DC), outburst duration and recurrence time. We apply this prescription to the population synthesis (PS) models of field LMXBs presented by Fragos et al. (2008), and compare t...
We have identified 1057 globular cluster candidates in a WFPC2 image of the inner region of M87. The globular cluster luminosity function (GCLF) can be well fitted by a Gaussian profile with a mean value of m0V=23.67±0.07 mag and σ=1.39±0.06 mag. The GCLF in five radial bins is found to be statistically the same at all points, showing no clear evid...
In an attempt to use Cepheid variables to determine the distance to the Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space Telescope for 9 epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (totalling six orbits) in the F814W filter. This galaxy has been suggested to lie within the "Cen 30" portio...
We report the results of N-body simulations of the early evolution of globular clusters and show how the kinematical properties of clusters emerging at the end of the violent relaxation are affected by the motion of a cluster in its host galaxy and by the host galaxy tidal field. In particular, we discuss the properties and the origin of the intern...
The formation and evolution of early-type galaxies is still under debate. In order to assign the underlying formation scenario to a given galaxy we need to know the age structure of the stellar content. Globular clusters are widely used to probe the evolutionary history of their host galaxies. Representing simple stellar populations almost perfectl...
We present new ultraviolet photometry of the jet in M87 obtained from Hubble Space Telescope (HST) WFPC2 imaging. We combine these ultraviolet data with previously published photometry for the knots of the jet in radio, optical, and X-ray and fit three theoretical synchrotron models to the full data set. The synchrotron models consistently overpred...
We present near-infrared photometry of the globular cluster systems of the early-type galaxies NGC 4472, NGC 4594, NGC 3585, and NGC 5813. We combine these near-infrared data, obtained with PANIC at the Magellan Baade 6.5 m telescope, with archival optical HST and FORS/VLT data, and use the optical to near-infrared colors to constrain the ages and...
We present the discovery of [O III] λ5007 emission associated with the black hole X-ray binary recently identified in a globular cluster in the Virgo elliptical galaxy NGC 4472. This object is the first confirmed black hole X-ray binary in a globular cluster. The identification of [O III] λ5007 emission from the black hole hosting globular cluster...
We present new Hubble Space Telescope (HST) NIC3, near-infrared H-band photometry of globular clusters (GCs) around NGC 4365 and NGC 1399 in combination with archival HST WFPC2 and ACS optical data. We find that NGC 4365 has a number of globular clusters with bluer optical colors than expected for their red optical-to-near-infrared colors and an ol...
In a previous paper we reported a Hubble Space Telescope (HST) Cepheid distance to the galaxy NGC 4258 obtained using the calibrations and methods then standard for the Key Project. Here we reevaluate the Cepheid distance using the recently revised Key Project procedures. These revisions alter the zero points and slopes of the Cepheid period-lumino...
We present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXBs) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code, assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that h...
We present the luminosity function to very faint magnitudes for the globular clusters in M87, based on a 30 orbit Hubble Space Telescope (HST) WFPC2 imaging program. The very deep images and corresponding improved false source rejection allow us to probe the mass function further beyond the turnover than has been done before. We compare our luminos...
We present the properties of the discrete X-ray sources detected in our monitoring program of the 'typical' elliptical galaxy, NGC 3379, observed with Chandra ACIS-S in five separate pointings, resulting in a co-added exposure of 324 ks. From this deep observation, 132 sources have been detected within the region overlapped by all observations, 98...
We report recent Chandra observations of the ULX in the elliptical galaxy NGC 3379 that clearly detect two flux variability cycles. Comparing these data with the Chandra observation of ~5 years ago, we measure a flux modulation with a period of ~12.6 hr. Moreover, we find that the emission undergoes a correlated spectral modulation, becoming softer...
We investigate the relationship between low-mass X-ray binaries (LMXBs) and globular clusters (GCs) using United Kingdom Infrared
Telescope (UKIRT) observations of M31 and existing Chandra, XMM–Newton and ROSAT catalogues. By fitting King models to these data, we have estimated the structural parameters and stellar collision rates
of 239 of its GCs...
Citations
... Globular clusters are also intimately linked with high-energy astrophysical events: novae (Kato et al. 2013;Doyle et al. 2019), supernovae (Voss & Nelemans 2012;Washabaugh & Bregman 2013), fast radio bursts (Kirsten et al. 2022) and many X-ray binaries, including ultraluminous X-ray sources (ULXs) (Maccarone et al. 2007). The remnant population of globular clusters can shine light on understanding the progenitors of transients, including gravitational wave events (Dage et al. 2020;Athukoralalage et al. 2023). Due to their relatively simple stellar populations, it is easier to measure the age and metallicity of a star cluster than field starlight, allowing the progenitor of a transient to be constrained. ...
... As a classification problem, selection of star clusters is well suited to machine learning techniques. Recent experiments with machine learning selection of clusters on either images (Pérez et al. 2021;Thilker et al. 2022) or photometric catalogs (Barbisan et al. 2022;Mohammadi et al. 2022) show promise. Samples of star clusters, foreground stars and background galaxies from space based imaging (HST or JWST) can be used to train and validate classification techniques with Rubin data; other efforts (photometric redshift pipelines from the LSST Galaxies collaboration, star-galaxy separation techniques from SMWLV collaboration) may also prove useful. ...
... Not only ultraluminous pulsars exhibit variability amplitudes of several orders of magnitude among ULXs. At present, about two dozen ULX transients are known (Sivakoff et al. 2008 ;Middleton et al. 2012 ;Pintore et al. 2018 ;Earnshaw et al. 2019 ;Liu et al. 2019 ;Brightman et al. 2020 ;Earnshaw et al. 2020 ;Dage et al. 2021 ;Walton et al. 2021 ), most of which are less luminous sources that only briefly reach luminosities of 2 × 10 39 erg s -1 during outbursts. In connection with the possible residence of NGC 5474 X-1 in an old stellar cluster, of particular interest are three ULX transients that were reported to likely be associated with an old population: M83 ULX-1 (Soria et al. 2012(Soria et al. , 2015, M86 tULX-1 (van Haaften et al. 2019 ), and 2SXPS J235825.7-323609 ...
... Observationally, there were many X-ray survey campaigns that aimed to search for new ULXs in nearby galaxies. Some of the most recent examples are the surveys with spectral and temporal analysis of ULXs in NGC 2276, NGC 891, and NGC 1316(Dage et al. 2021Earley et al. 2021;Singha & Devi 2021). In addition, detailed spectral and temporal analyses for individual systems also give insights into the emission mechanisms in ULXs (e.g., NGC 55 ULX1, M82 ULX, and NGC 5408 X-1; Kaaret et al. 2006;Strohmayer 2009;Jithesh 2022). ...
... The optical counterpart was not identified, mainly because the galaxy is relatively distant (16.83 Mpc), so the type of the donor is not constrained. The old age of this object was suspected based on the fact that it is located in a giant elliptical galaxy in an area without young stars (van Haaften et al. 2019 ). There is some possibility that these two objects are background/foreground sources; ho we ver, their spectra look quite usual for ULXs (van Haaften et al. 2019 ;Brightman et al. 2023 ). ...
... To date, there have been no dynamically confirmed black hole XRBs identified in any globular cluster, although over the past two decades, a handful of candidates have been identified in Galactic and extragalactic globular clusters (e.g., see Maccarone et al. 2007;Strader et al. 2012;Chomiuk et al. 2013;Miller-Jones et al. 2015;Shishkovsky et al. 2018;Dage et al. 2019Dage et al. , 2020. All the Galactic candidates among these have been identified in quiescent/faint states (L X ≤ 10 34 erg s −1 ) and none have so far shown bright (L X ≥ 10 35 erg s −1 ) outbursts. ...
... Globular clusters are also intimately linked with high-energy astrophysical events: novae (Kato et al. 2013;Doyle et al. 2019), supernovae (Voss & Nelemans 2012;Washabaugh & Bregman 2013), fast radio bursts (Kirsten et al. 2022) and many X-ray binaries, including ultraluminous X-ray sources (ULXs) (Maccarone et al. 2007). The remnant population of globular clusters can shine light on understanding the progenitors of transients, including gravitational wave events (Dage et al. 2020;Athukoralalage et al. 2023). Due to their relatively simple stellar populations, it is easier to measure the age and metallicity of a star cluster than field starlight, allowing the progenitor of a transient to be constrained. ...
... The aim of the Chandra observations was to detect bright XRBs in this galaxy and five candidates were reported (Maccarone et al. 2005). Arnason et al. (2019) performed a multi-wavelength study using Spitzer and Gemini telescopes for thirteen bright X-ray sources in the field of Sculptor dSph including those five sources, which have been suggested as candidates for low-mass X-ray binaries (LMXBs) in the study of Maccarone et al. (2005). The study of Arnason et al. (2019) did not confirm any source as a member of Sculptor dSph. ...
... (SN); kcdage@msu.edu (KCD) Irwin et al. 2010 ;Shih et al. 2010 ;Maccarone et al. 2011 ;Roberts et al. 2012 ;Dage et al. 2019aDage et al. , b , 2020Dage et al. , 2021. ...
... While many mechanisms have been suggested to explain the presence of multiple stellar populations in globular clusters (see Peacock et al. 2018 and references therein for a summary of many of the proposed scenarios), there is currently no one theory that can explain all of the observational signatures (Bastian & Lardo 2018 ). Clusters with second generation stars are thought to have undergone multiple star formation episodes; ho we ver, the source of the gas is unknown. ...
