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Stokholm MG, Iranzo A, Ostergaard K, et al., 2020, Cholinergic denervation in patients with idiopathic rapid eye movement sleep behaviour disorder, EUROPEAN JOURNAL OF NEUROLOGY, Vol: 27, Pages: 644-652, ISSN: 1351-5101
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- Citations: 21
Nicholas R, Brooks D, Owen D, 2020, Letter to the Editor re: Confirmation of Specific Binding of the 18-kDa Translocator Protein (TSPO) Radioligand [<SUP>18</SUP>F]GE-180: a Blocking Study Using XBD173 in Multiple Sclerosis Normal Appearing White and Grey Matter In Response, MOLECULAR IMAGING AND BIOLOGY, Vol: 22, Pages: 13-14, ISSN: 1536-1632
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- Citations: 3
Hansen AK, Parbo P, Ismail R, et al., 2020, Tau tangles in Parkinson's disease: A 2-year follow-up flortaucipir PET study., Journal of Parkinsons Disease, Vol: 10, Pages: 161-171, ISSN: 1877-718X
BACKGROUND: Flortaucipir PET, a marker of tau tangles, has shown lower than expected cortical uptake in Parkinson's disease (PD), than would be predicted from neuropathologic estimates of Alzheimer's disease co-pathology. Instead, the most characteristic finding of flortaucipir imaging in PD is decreased uptake in the substantia nigra, reflecting reduction in its "off-target" binding to neuromelanin. We have previously reported these observations in cross-sectional studies. OBJECTIVE: Here, we present two-year follow-up data of cortical and nigral flortaucipir uptake in PD patients. METHODS: Seventeen PD patients received repeat flortaucipir PET two years after baseline. We interrogated vertex-based group-wise cortical tracer binding (SUVRs) with a cerebellar reference using the general linear model while mean substantia nigra SUVRs were compared with volumes of interest group comparisons and voxel-wise group analyses using ANOVA. Finally, we performed linear regressions of tau load with changes in MoCA and UPDRS motor scores. RESULTS: We found no significant changes in substantia nigra or cortex flortaucipir uptake in Parkinson's disease patients over two years and no association with changes in cognitive symptoms. Signal reduction in the medial substantia nigra trended towards an association with worsening of motor symptoms. CONCLUSION: No significant increase in tau tangles occurred after a two-year follow-up of Parkinson's disease patients using flortaucipir PET.
Parbo P, Madsen LS, Ismail R, et al., 2020, Low plasma neurofilament light levels associated with raised cortical microglial activation suggest inflammation acts to protect prodromal Alzheimer's disease, ALZHEIMERS RESEARCH & THERAPY, Vol: 12
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- Citations: 18
Mansur A, Rabiner EA, Comley RA, et al., 2020, Characterization of 3 PET tracers for Quantification of Mitochondrial and Synaptic function in Healthy Human Brain: 18F-BCPP-EF, 11C-SA-4503, 11C-UCB-J, Journal of Nuclear Medicine, Vol: 61, Pages: 96-103, ISSN: 1535-5667
Mitochondrial complex 1 (MC1) is involved in maintaining brain bioenergetics, the sigma 1 receptor (σ1R) responds to neuronal stress and synaptic vesicle protein 2A (SV2A) reflects synaptic integrity. Expression of each of these proteins is altered in neurodegenerative diseases. Here we characterise the kinetic behaviour of three positron emission tomography (PET) radioligands 18F-BCPP-EF, 11C-SA-4503 and 11CUCB- J, for the measurement of MC1, σ1R and SV2A, respectively, and determine appropriate analysis workflows for their application in future studies of the in vivo molecular pathology of these diseases. Methods: Twelve human subjects underwent dynamic PET scans including associated arterial blood sampling with each radioligand. A range of kinetic models were investigated to identify an optimal kinetic analysis method for each radioligand and a suitable acquisition duration. Results: All three radioligands readily entered the brain and yielded heterogeneous uptake consistent with the known distribution of the targets. The optimal models determined for the regional estimates of volume of distribution (VT) were multilinear analysis 1 (MA1) and the 2-tissue compartment (2TC) model for 18F-BCPP-EF, MA1 for 11C-SA- 4503, and both MA1 and the 1-tissue compartment (1TC) model for 11C-UCB-J. Acquisition times of 70, 80 and 60 minutes for 18F-BCPP-EF, 11C-SA-4503, 11C-UCB-J, respectively, provided good estimates of regional VT values. An effect of age was observed on 18F-BCPP-EF and 11C-UCB-J signal in the caudate. Conclusion: These ligands can be assessed for their potential to stratify patients or monitor the progression of molecular neuropathology in neurodegenerative diseases.
Yu Z, Martini P, Davis TM, et al., 2020, Quasar Accretion Disk Sizes from Continuum Reverberation Mapping in the DES Standard-star Fields, Astrophysical Journal, Supplement Series, Vol: 246, ISSN: 0067-0049
Measurements of the physical properties of accretion disks in active galactic nuclei are important for better understanding the growth and evolution of supermassive black holes. We present the accretion disk sizes of 22 quasars from continuum reverberation mapping with data from the Dark Energy Survey (DES) standard-star fields and the supernova C fields. We construct continuum light curves with the griz photometry that span five seasons of DES observations. These data sample the time variability of the quasars with a cadence as short as 1 day, which corresponds to a rest-frame cadence that is a factor of a few higher than most previous work. We derive time lags between bands with both JAVELIN and the interpolated cross-correlation function method and fit for accretion disk sizes using the JAVELIN thin-disk model. These new measurements include disks around black holes with masses as small as ∼107 M o˙, which have equivalent sizes at 2500 Å as small as ∼0.1 lt-day in the rest frame. We find that most objects have accretion disk sizes consistent with the prediction of the standard thin-disk model when we take disk variability into account. We have also simulated the expected yield of accretion disk measurements under various observational scenarios for the Large Synoptic Survey Telescope Deep Drilling Fields. We find that the number of disk measurements would increase significantly if the default cadence is changed from 3 days to 2 days or 1 day.
Nielsen RB, Parbo P, Ismail R, et al., 2020, Impaired perfusion and capillary dysfunction in prodromal Alzheimer's disease, ALZHEIMER'S & DEMENTIA: DIAGNOSIS, ASSESSMENT & DISEASE MONITORING, Vol: 12
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- Citations: 21
Perani D, Iaccarino L, Jacobs AH, et al., 2019, Application of advanced brain positron emission tomography-based molecular imaging for a biological framework in neurodegenerative proteinopathies., Alzheimers Dement (Amst), Vol: 11, Pages: 327-332, ISSN: 2352-8729
Introduction: A rapid transition from a clinical-based classification to a pathology-based classification of neurodegenerative conditions, largely promoted by the increasing availability of imaging biomarkers, is emerging. The Framework for Innovative Multi-tracer molecular Brain Imaging, funded by the EU Joint Program - Neurodegenerative Disease Research 2016 "Working Groups for Harmonisation and Alignment in Brain Imaging Methods for Neurodegeneration," aimed at providing a roadmap for the applications of established and new molecular imaging techniques in dementia. Methods: We consider current and future implications of adopting a pathology-based framework for the use and development of positron emission tomography techniques. Results: This approach will enhance efforts to understand the multifactorial etiology of Alzheimer's disease and other dementias. Discussion: The availability of pathology biomarkers will soon transform clinical and research practice. Crucially, a comprehensive understanding of strengths and caveats of these techniques will promote an informed use to take full advantage of these tools.
Stuart S, Lawson RA, Yarnall AJ, et al., 2019, Pro-Saccades Predict Cognitive Decline in Parkinson's Disease: ICICLE-PD, MOVEMENT DISORDERS, Vol: 34, Pages: 1690-1698, ISSN: 0885-3185
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- Citations: 15
Metaxas A, Thygesen C, Kempf SJ, et al., 2019, Ageing and amyloidosis underlie the molecular and pathological alterations of tau in a mouse model of familial Alzheimer's disease, SCIENTIFIC REPORTS, Vol: 9, ISSN: 2045-2322
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- Citations: 16
Schubert JJ, Veronese M, Marchitelli L, et al., 2019, Dynamic 11C-PiB PET shows cerebrospinal fluid flow alterations in Alzheimer's disease and multiple sclerosis, Journal of Nuclear Medicine, Vol: 60, Pages: 1452-1460, ISSN: 1535-5667
Cerebrospinal fluid (CSF) plays an important role in the clearance of solutes and maintenance of brain homeostasis. 11C-PiB PET was recently proposed as a tool for detection of CSF clearance alterations in Alzheimer's disease. The current study seeks to investigate the magnitude of 11C-PiB PET signal in the lateral ventricles of an independent group of Alzheimer's and mild cognitive impairment subjects. We have also evaluated multiple sclerosis as a model of disease with CSF clearance alterations without amyloid-beta tissue accumulation. Methods: A set of Alzheimer's and mild cognitive impairment subjects and a set of multiple sclerosis subjects with matched healthy controls underwent MRI and dynamic 11C-PiB PET. Manual lateral ventricle regions of interest were generated from MRI data. PET data was analysed using a simplified reference tissue model with cerebellum or a supervised reference region, for the Alzheimer's and multiple sclerosis datasets, respectively. Magnitude of 11C-PiB signal in the lateral ventricles was calculated as area under curve from 35 to 80 minutes and standard uptake value ratio (SUVR) from 50 to 70 minutes. Compartmental modelling analysis was performed on a separate dataset containing Alzheimer's and matched healthy control data with an arterial input function to further understand the kinetics of the lateral ventricular 11C-PiB signal. Results: Analysis of variance revealed significant group differences in lateral ventricular SUVR across the Alzheimer's, mild cognitive impairment, and healthy control groups (P = 0.004). Additional pairwise comparisons revealed significantly lower lateral ventricular SUVR in Alzheimer's compared to healthy controls (p<0.001) and mild cognitive impairment (P = 0.029). Lateral ventricular SUVR was also significantly lower in multiple sclerosis compared to healthy controls (P = 0.008). Compartmental modelling analysis revealed significantly lower uptake rates of 11C-PiB signal from blood (P = 0.005) and b
Sridharan S, Raffel J, Nandoskar A, et al., 2019, Confirmation of specific binding of the 18 kDa translocator protein (TSPO) radioligand [18F]GE-180: a blocking study using XBD173 in multiple sclerosis normal appearing white and grey matter, Molecular Imaging and Biology, Vol: 21, Pages: 935-944, ISSN: 1536-1632
Purpose: Positron emission tomography (PET) ligands exhibit different levels of non-displaceable binding in vivo. In the case of ligands for the 18 kDa translocator protein (TSPO), the component of non-displaceable binding for the most widely used radiotracer, [11C]-(R)-PK11195, is relatively high compared to that for newer TSPO ligands. Non-displaceable binding is not often quantified in humans in vivo, partially due to a lack of available ligands that are known to be safe with which to displace binding to the target receptor. Recently, however, a technique has been developed to quantify the non-displaceable binding of TSPO tracers in vivo, by blocking the receptor with the TSPO ligand XBD173 and comparing the total volume of distribution ( ) pre and post-blockade. Here, we used an occupancy plot to quantify the non-displaceable binding ( ) of the TSPO PET tracers [18F]GE-180 and [11C]PBR28 in cohorts of people with multiple sclerosis (MS). We also compared plots of subjects carrying both high and mixed binding affinity polymorphisms of TSPO to estimate while potentially avoiding the need for receptor blockade.Procedures: Twelve people with multiple sclerosis (MS) and high (HAB) or mixed (MAB) affinity binding for TSPO underwent baseline MRI and 90-minute dynamic [18F]GE-180 PET (n=6; 3 HAB and 3 MAB) or [11C]PBR28 PET (n=6; 3 HAB, 3 MAB). Either one week later ([18F]GE-180) or the same afternoon ([11C]PBR28), participants had repeat PET following a 90mg dose of XBD173. PET images were co-registered with T1 MR volumetric images and regions of interest (ROIs) were defined using the 83-region Hammers atlas. Arterial blood sampling was used to generate plasma input functions for the two-tissue compartment model to quantify . The non-displaceable fraction of the total volume of distribution ( ) was calculated using two independent methods: the occupancy plot (by modelling the differences in signal post XBD173), and the polymorphism plot (by modelling the differences in
Horsager J, Knudsen K, Andersen K, et al., 2019, "Brain-first" vs. "body-first" Parkinson's disease is determined by RBD-status - a multi-modality imaging study, International Congress of Parkinson's Disease and Movement Disorders, Publisher: WILEY, Pages: S796-S796, ISSN: 0885-3185
Eskildsen S, Iranzo A, Stokholm M, et al., 2019, Occurrence of brain capillary dysfunction in patients with REM sleep behavior disorder, International Congress of Parkinson's Disease and Movement Disorders, Publisher: WILEY, Pages: S786-S787, ISSN: 0885-3185
Staer K, Iranzo A, Stokholm M, et al., 2019, Cortical cholinergic dysfunction correlates with microglial activation in the Substantia Innominata in patients with REM sleep behavior disorder, International Congress of Parkinson's Disease and Movement Disorders, Publisher: WILEY, Pages: S830-S830, ISSN: 0885-3185
Paquini J, Durcan R, Wiblin L, et al., 2019, Clinical implications of early caudate dysfunction in Parkinson's disease, Journal of Neurology, Neurosurgery and Psychiatry, Vol: 90, Pages: 1098-1104, ISSN: 1468-330X
Objective Although not typical of Parkinson’s disease (PD), caudate dopaminergic dysfunction can occur in early stages of the disease. However, its frequency and longitudinal implications in large cohorts of recently diagnosed patients remain to be established. We investigated the occurrence of caudate dopaminergic dysfunction in the very early phases of PD (<2 years from diagnosis) using 123I-FP-CIT single photon emission CT and determined whether it was associated with the presence or subsequent development of cognitive impairment, depression, sleep and gait problems.Methods Patients with PD and healthy controls were identified from the Parkinson’s Progression Markers Initiative (PPMI) database. We defined a clinically significant caudate dysfunction as 123I-FP-CIT binding <–2 SDs compared with the controls’ mean and categorised three groups accordingly (no reduction, unilateral reduction, bilateral reduction). All statistical analyses were adjusted for mean putamen binding.Results At baseline, 51.6% of 397 patients had normal caudate dopamine transporter binding, 26.0% had unilateral caudate involvement, 22.4% had bilaterally impaired caudate.Compared with those with a baseline normal caudate function, at the4-year follow-up patients with a baseline bilateral caudate involvement showed a higher frequency of cognitive impairment (p<0.001) and depression (p<0.001), and worse cognitive (p<0.001), depression (<0.05) and gait (<0.001) ratings. Significant caudate involvement was observed in 83.9% of the population after 4 years (unilateral 22.5%, bilateral 61.4%).Conclusions Early significant caudate dopaminergic denervation was found in half of the cases in the PPMI series. Baseline bilateral caudate involvement was associated with increased risk of developing cognitive impairment, depression and gait problems over the next 4 years.
Marshall JL, Hansen T, Simon JD, et al., 2019, Chemical Abundance Analysis of Tucana III, the Second r-process Enhanced Ultra-faint Dwarf Galaxy This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile., Astrophysical Journal, Vol: 882, ISSN: 0004-637X
We present a chemical abundance analysis of four additional confirmed member stars of Tucana III, a Milky Way satellite galaxy candidate in the process of being tidally disrupted as it is accreted by the Galaxy. Two of these stars are centrally located in the core of the galaxy while the other two stars are located in the eastern and western tidal tails. The four stars have chemical abundance patterns consistent with the one previously studied star in Tucana III: They are moderately enhanced in r-process elements, i.e., they have dex. The non-neutron-capture elements generally follow trends seen in other dwarf galaxies, including a metallicity range of 0.44 dex and the expected trend in -elements, i.e., the lower metallicity stars have higher Ca and Ti abundances. Overall, the chemical abundance patterns of these stars suggest that Tucana III was an ultra-faint dwarf galaxy, and not a globular cluster, before being tidally disturbed. As is the case for the one other galaxy dominated by r-process enhanced stars, Reticulum II, Tucana III's stellar chemical abundances are consistent with pollution from ejecta produced by a binary neutron star merger, although a different r-process element or dilution gas mass is required to explain the abundances in these two galaxies if a neutron star merger is the sole source of r-process enhancement.
Mollenhauer B, Caspell-Garcia CJ, Coffey CS, et al., 2019, Longitudinal analyses of cerebrospinal fluid α-Synuclein in prodromal and early Parkinson's disease, MOVEMENT DISORDERS, Vol: 34, Pages: 1354-1364, ISSN: 0885-3185
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- Citations: 72
Zhang Y, Miller CJ, Rooney P, et al., 2019, Galaxies in X-ray selected clusters and groups in Dark Energy Survey data - II. Hierarchical Bayesian modelling of the red-sequence galaxy luminosity function, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 488, Pages: 1-17, ISSN: 0035-8711
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- Citations: 7
Wang MY, De Boer T, Pieres A, et al., 2019, The Morphology and Structure of Stellar Populations in the Fornax Dwarf Spheroidal Galaxy from Dark Energy Survey Data, Astrophysical Journal, Vol: 881, ISSN: 0004-637X
Using deep wide-field photometry 3 yr data (Y3) from the Dark Energy Survey (DES), we present a panoramic study of the Fornax dwarf spheroidal galaxy. The data presented here - a small subset of the full survey - uniformly cover a region of 25 deg2 centered on the galaxy to a depth of g ∼ 23.5. We use these data to study the structural properties of Fornax, overall stellar population, and its member stars in different evolutionary phases. We also search for possible signs of tidal disturbance. Fornax is found to be significantly more spatially extended than what early studies suggested. No statistically significant distortions or signs of tidal disturbances were found down to a surface brightness limit of ∼32.1 mag arcsec-2. However, there are hints of shell-like features located ∼20′-40′ from the center of Fornax that may be stellar debris from past merger events. We also find that intermediate-age and young main-sequence populations show different orientation at the galaxy center and have many substructures. The deep DES Y3 data allow us to characterize the age of those young stellar substructures with great accuracy, both those previously known and those newly identified as possible overdensities in this work, on the basis of their color-magnitude diagram morphology. We find that the youngest overdensities are all found on the eastern side of Fornax, where the Fornax field population itself is slightly younger than in the west. In summary, the high-quality DES Y3 data reveal that Fornax has many rich structures and provide insights into its complex formation history.
Perani D, Iaccarino L, Lammertsma AA, et al., 2019, A new perspective for advanced positron emission tomography-based molecular imaging in neurodegenerative proteinopathies, ALZHEIMERS & DEMENTIA, Vol: 15, Pages: 1081-1103, ISSN: 1552-5260
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- Citations: 11
Dani M, Wood M, Mizoguchi R, et al., 2019, Tau Aggregation Correlates with Amyloid Deposition in Both Mild Cognitive Impairment and Alzheimer's Disease Subjects, JOURNAL OF ALZHEIMERS DISEASE, Vol: 70, Pages: 453-463, ISSN: 1387-2877
Venkataraman A, Mansur A, Lewis Y, et al., 2019, Evaluation of mitochondrial and synaptic function in Alzheimer’s disease (AD): a [18F]BCPP-EF, [11C]SA4503 and [11C]UCB-J PET study, Journal of Cerebral Blood Flow and Metabolism, Vol: 39, Pages: 121-122, ISSN: 1559-7016
ObjectivesMitochondrial deficits leading to synaptic dysfunction have been hypothesised in the pathophysiology of neurodegenerative disease, with Aβ/tau impairing mitochondrial function in AD. To date a combined evaluation of human mitochondrial and synaptic function has not been performed directly in vivo. We describe the pilot results of MINDMAPS-AD, a study within the MINDMAPS1 programme aiming to evaluate mitochondrial and synaptic function in the brain of patients with MCI/AD. MINDMAPS-AD uses the novel radioligands [18F]BCPP-EF, [11C]SA4503 and [11C]UCB-J, to compare the regional density of mitochondrial complex I (MC1), the sigma 1 receptor (s1R) and synaptic vesicular protein 2A (SV2A) respectively.MethodsSix participants with a range of AD related pathologies, EMCI (n = 2), LMCI (n = 2), and AD (n = 2), were enrolled into the study. Participants fulfilled NIA-AA criteria and were amyloid-beta +ve confirmed by [18F]Florbetaben PET. All participants underwent three PET scans with [18F]BCPP-EF, [11C]SA4503 and [11C]UCB-J. Arterial blood samples were collected and a metabolite corrected arterial plasma input function was estimated to derive regional volumes of distribution (VT). These data were compared to six age/sex matched cognitively normal (CN) healthy subjects recruited for ongoing studies within the MINDMAPS programme. Regions of interest (ROIs) were defined on individual subject MR images using an anatomical atlas and included: frontal cortex, hippocampus, amygdala, anterior cingulate, posterior cingulate, thalamus, temporal cortex, parietal cortex, caudate, putamen, and occipital lobe. Regional target density was evaluated using the VT, as well as VT corrected for the plasma free fraction of the radioligand (fP; VT/fp), and the regional VT ratio versus the VT in the centrum semiovale, a white matter region expected to have low levels of the targets evaluated (DVR). Comparison of regional target density and
Nielsen RB, Parbo P, Ismail R, et al., 2019, Impaired perfusion and capillary distribution of blood in mild cognitive impairment: Relation to oxygenation and amyloid load, 29th International Symposium on Cerebral Blood Flow, Metabolism and Function / 14th International Conference on Quantification of Brain Function with PET (BRAIN and BRAIN Pet), Publisher: SAGE PUBLICATIONS INC, Pages: 147-147, ISSN: 0271-678X
Venkataraman AV, Mansur A, Huiban M, et al., 2019, Evaluation of mitochondrial and synaptic function in Alzheimer's disease (AD): a [<SUP>18</SUP>F]BCPP-EF, [<SUP>11</SUP>C]SA4503 and [<SUP>11</SUP>C]UCB-J PET study, 29th International Symposium on Cerebral Blood Flow, Metabolism and Function / 14th International Conference on Quantification of Brain Function with PET (BRAIN and BRAIN Pet), Publisher: SAGE PUBLICATIONS INC, Pages: 121-122, ISSN: 0271-678X
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- Citations: 1
Durcan R, Wiblin L, Lawson RA, et al., 2019, Prevalence and duration of non-motor symptoms in prodromal Parkinson's disease, EUROPEAN JOURNAL OF NEUROLOGY, Vol: 26, Pages: 979-985, ISSN: 1351-5101
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- Citations: 53
Ismail R, Parbo P, Hansen KV, et al., 2019, Abnormal amyloid load in mild cognitive impairment: the effect of reducing the PiB-PET threshold, Journal of Neuroimaging, Vol: 29, Pages: 499-505, ISSN: 1051-2284
BACKGROUND AND PURPOSE: In vivo detection of β-amyloid (Aβ) plaques in Alzheimer's disease (AD) is now possible with 11 C-PiB positron emission tomography (PET). Conventionally, a cortical:cerebellar PiB uptake ratio threshold of 1.4-1.5 has been used to categorize at-risk subjects as "amyloid-positive" and "amyloid-negative." It has been suggested that this threshold is too conservative and may miss early amyloid pathology. We investigated the relationship between conventional and lower baseline 11 C-PiB PET thresholds for raised amyloid load and the subsequent clinical and radiological progression of mild cognitive impairment (MCI) cases longitudinally. METHODS: We serially determined the cortical amyloid load with 11 C-PiB PET of 44 MCI subjects over 2 years and compared findings with those for 12 healthy controls (HC) and 5 AD cases. RESULTS: Twenty-four subjects were classified as normal at baseline with mean cortical PiB standard uptake value ratios (SUVR) between 1.2 and 1.5. Their cognitive status remained stable over time. Three of these cases increased their amyloid load above a threshold of 1.5 over 2 years. Twenty-seven "raised amyloid" MCI cases with baseline cortical SUVRs above 1.5, showed deteriorating cognition. Note that 50% of these cases converted clinically to AD during the follow-up period. CONCLUSION: Use of a PiB SUVR threshold of >1.5 for raised amyloid missed 14.3% of MCI cases who likely had Thal stage 1 or 2 pathology and showed a progressive amyloid increase over 2 years. Lowering the threshold for abnormality to 1.3 abolished all false negatives but resulted in 75% of HCs being falsely diagnosed as raised amyloid subjects.
Cerri D, Albaugh D, Katz B, et al., 2019, Poster Viewing Sessions PA00-A01 to PA00-A49, JOURNAL OF CEREBRAL BLOOD FLOW AND METABOLISM, Vol: 39, Pages: 1-2, ISSN: 0271-678X
Soares-Santos M, Palmese A, Hartley W, et al., 2019, First Measurement of the Hubble Constant from a Dark Standard Siren using the Dark Energy Survey Galaxies and the LIGO/Virgo Binary-Black-hole Merger GW170814, ASTROPHYSICAL JOURNAL LETTERS, Vol: 876, ISSN: 2041-8205
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- Citations: 119
Wang MY, Koposov S, Drlica-Wagner A, et al., 2019, Rediscovery of the Sixth Star Cluster in the Fornax Dwarf Spheroidal Galaxy, Astrophysical Journal Letters, Vol: 875, ISSN: 2041-8205
Since first noticed by Shapley in 1939, a faint object coincident with the Fornax dwarf spheroidal has long been discussed as a possible sixth globular cluster (GC) system. However, debate has continued over whether this overdensity is a statistical artifact or a blended galaxy group. In this Letter we demonstrate, using deep DECam imaging data, that this object is well resolved into stars and is a bona fide star cluster. The stellar overdensity of this cluster is statistically significant at the level of ∼6-6.7σ in several different photometric catalogs including Gaia. Therefore, it is highly unlikely to be caused by random fluctuation. We show that Fornax 6 is a star cluster with a peculiarly low surface brightness and irregular shape, which may indicate a strong tidal influence from its host galaxy. The Hess diagram of Fornax 6 is largely consistent with that of Fornax field stars, but it appears to be slightly bluer. However, it is still likely more metal-rich than most of the GCs in the system. Faint clusters like Fornax 6 that orbit and potentially get disrupted in the centers of dwarf galaxies can prove crucial for constraining the dark matter distribution in Milky Way satellites.
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