Spectroscopy Of Globular Clusters Research Articles

Dark Matter in Ultra-diffuse Galaxies in the Virgo Cluster from Their Globular Cluster Populations

Abstract We present Keck/DEIMOS spectroscopy of globular clusters (GCs) around the ultra-diffuse galaxies (UDGs) VLSB−B, VLSB−D, and VCC615 located in the central regions of the Virgo cluster. We spectroscopically identify 4, 12, and 7 GC satellites of these UDGs, respectively. We find that the three UDGs have systemic velocities (V sys) consistent with being in the Virgo cluster, and that they span a wide range of velocity dispersions, from ∼16 to ∼47 km s−1, and high dynamical mass-to-light ratios within the radius that contains half the number of GCs ( , , , respectively). VLSB−D shows possible evidence for rotation along the stellar major axis and its V sys is consistent with that of the massive galaxy M84 and the center of the Virgo cluster itself. These findings, in addition to having a dynamically and spatially (∼1 kpc) off-centered nucleus and being extremely elongated, suggest that VLSB−D could be tidally perturbed. On the contrary, VLSB−B and VCC615 show no signs of tidal deformation. Whereas the dynamics of VLSB−D suggest that it has a less massive dark matter halo than expected for its stellar mass, VLSB−B and VCC615 are consistent with a ∼1012 M ⊙ dark matter halo. Although our samples of galaxies and GCs are small, these results suggest that UDGs may be a diverse population, with their low surface brightnesses being the result of very early formation, tidal disruption, or a combination of the two.

LBT/MODS spectroscopy of globular clusters in the irregular galaxy NGC 4449

We present intermediate-resolution (R$\sim$1000) spectra in the $\sim$3500-10,000 A range of 14 globular clusters in the magellanic irregular galaxy NGC 4449 acquired with the Multi Object Double Spectrograph on the Large Binocular Telescope. We derived Lick indices in the optical and the CaII-triplet index in the near-infrared in order to infer the clusters' stellar population properties. The inferred cluster ages are typically older than $\sim$9 Gyr, although ages are derived with large uncertainties. The clusters exhibit intermediate metallicities, in the range $-1.2\lesssim$[Fe/H]$\lesssim-0.7$, and typically sub-solar [$\alpha/Fe$] ratios, with a peak at $\sim-0.4$. These properties suggest that i) during the first few Gyrs NGC 4449 formed stars slowly and inefficiently, with galactic winds having possibly contributed to the expulsion of the $\alpha$-elements, and ii) globular clusters in NGC 4449 formed relatively "late", from a medium already enriched in the products of type Ia supernovae. The majority of clusters appear also under-abundant in CN compared to Milky Way halo globular clusters, perhaps because of the lack of a conspicuous N-enriched, second-generation of stars like that observed in Galactic globular clusters. Using the cluster velocities, we infer the dynamical mass of NGC 4449 inside 2.88 kpc to be M($<$2.88 kpc)=$3.15^{+3.16}_{-0.75} \times 10^9~M_\odot$. We also report the serendipitous discovery of a planetary nebula within one of the targeted clusters, a rather rare event.

Spectroscopy of globular clusters in the low-luminosity spiral galaxy NGC 45

Context. Extragalactic globular clusters have been studied in elliptical galaxies and in a few luminous spiral galaxies, but little is known about globular clusters in low-luminosity spirals.

Globular Clusters in Early-Type Galaxies with GMOS

AbstractWe 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 color distribution, with the fraction of blue/red clusters increasing with galacto-centric 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.

Spectroscopy of Globular Clusters in NGC 4472

?????Optical multislit spectra have been obtained for 47 globular clusters surrounding the brightest Virgo elliptical galaxy, NGC 4472 (M49). Including data from the literature, we analyze velocities for a total sample of 57 clusters and present the first tentative evidence for kinematic differences between the red and blue cluster populations that make up the bimodal color distribution of this galaxy. The redder clusters are more centrally concentrated and have a velocity dispersion of 240 km s-1, compared with 320 km s-1 for the blue clusters. The origin of this difference appears to be a larger component of systematic rotation in the blue cluster system. The larger rotation in the more extended blue cluster system is indicative of efficient angular momentum transport, as provided by galaxy mergers. Masses estimated from the globular cluster velocities are consistent with the mass distribution estimated from X-ray data and indicate that the M/LB rises to 50 (M/L)? at 2.5Re.

Spectroscopy of globular clusters in M87 and M49

Optical multislit spectra of globular clusters in two giant elliptical galaxies in the Virgo Cluster indicate average metal abundances of one-sixth and one-tenth solar composition for M49 and M87, respectively. These estimates are based on the strength of Mg lines. Taken together with observations of globular clusters in dwarf ellipticals this suggests a direct relation between mean metallicity of the cluster system and the luminosity of the parent galaxy which is an interesting constraint on theories of cluster formation during the protogalactic epoch. Rotation is evident in both globular cluster systems. The line-of-sight velocity dispersions of clusters in the two galaxies are estimated to be 340 + or - 50 km/s (M49) and 386 + or - 42 km/s (M87). Although sparsely sampled, the velocity dispersion profiles of the cluster systems are flat, suggesting the existence of an isothermal halo of dark matter in these ellipticals. 37 refs.

Spectroscopy of Globular Clusters in the Remote Halo

Spectra from 3800 to 5200 Å with a resolution of 4.5 Å/mm have been obtained for from 4 to 10 stars in each of the remote globular clusters Palomar 1, Eridarm s, NGC 2419, Palomar 3, Palomar 4, Palomar 5, Palomar 14 and Palomar 13. For comparison purposes the moderately distant clusters NGC 1904, NGC 4U7.NGC 5024, NGC 5053, NGC 5466 and NGC 5634 were also observed, along with the nearby globulare M 3, M 5, M 13, M 92, M 71 and M 15. In a1l cases spectra of stars in each cluster were recorded simultaneously, using an aperture plate with the KPNO 4 m telescope, R-C spectrograph, Simmons camera and baked IIIaJ plates. Sky spectra were also obtained at the same time.

IUE observations of globular clusters and blue horizontal branch stars

This paper presents a review of ultraviolet photometry and spectroscopy of globular clusters and blue horizontal branch stars. Current observations with IUE are placed within the framework of earlier photometric studies carried out by OAO and ANS. In order to provide basic information on the nature of the horizontal branch star, whose light dominates in the ultraviolet, observations of field horizontal branch stars as well as individual stars in globular clusters are discussed. Finally the IUE observations of globular clusters in the Magellanic Clouds are examined, since they provide a sequence spanning the age range from 7 × 106 years to 1010 years.