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Register a new userThe Next Generation Virgo Cluster Survey. XVII. A Search for Planetary Nebulae in Virgo Cluster Globular Clusters
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The occurrence of planetary nebulae (PNe) in globular clusters (GCs) provides an excellent chance to study low-mass stellar evolution in a special (low-metallicity, high stellar density) environment. We report a systematic spectroscopic survey for the [O{sc iii}] 5007 emission line of PNe in 1469 Virgo GCs and 121 Virgo ultra-compact dwarfs (UCDs), mainly hosted in the giant elliptical galaxies M87, M49, M86, and M84. We detected zero PNe in our UCD sample and discovered one PN ($M_{5007} = -4.1$ mag) associated with an M87 GC. We used the [O{sc iii}] detection limit for each GC to estimate the luminosity-specific frequency of PNe, $alpha$, and measured $alpha$ in the Virgo cluster GCs to be $alpha sim 3.9_{-0.7}^{+5.2}times 10^{-8}mathrm{PN}/L_odot$. $alpha$ in Virgo GCs is among the lowest values reported in any environment, due in part to the large sample size, and is 5--6 times lower than that for the Galactic GCs. We suggest that $alpha$ decreases towards brighter and more massive clusters, sharing a similar trend as the binary fraction, and the discrepancy between the Virgo and Galactic GCs can be explained by the observational bias in extragalactic surveys toward brighter GCs. This low but non-zero efficiency in forming PNe may highlight the important role played by binary interactions in forming PNe in GCs. We argue that a future survey of less massive Virgo GCs will be able to determine whether PN production in Virgo GCs is governed by internal process (mass, density, binary fraction), or is largely regulated by external environment.
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Substructure in globular cluster (GC) populations around large galaxies is expected in galaxy formation scenarios that involve accretion or merger events, and it has been searched for using direct associations between GCs and structure in the diffuse galaxy light, or with GC kinematics. Here, we present a search for candidate substructures in the GC population around the Virgo cD galaxy M87 through the analysis of the spatial distribution of the GC colors.~The study is based on a sample of $sim!1800$ bright GCs with high-quality $u,g,r,i,z,K_s$ photometry, selected to ensure a low contamination by foreground stars or background galaxies.~The spectral energy distributions of the GCs are associated with formal estimates of age and metallicity, which are representative of its position in a 4-D color-space relative to standard single stellar population models.~Dividing the sample into broad bins based on the relative formal ages, we observe inhomogeneities which reveal signatures of GC substructures.~The most significant of these is a spatial overdensity of GCs with relatively young age labels, of diameter $sim!0.1$,deg ($sim!30,$kpc), located to the south of M87.~The significance of this detection is larger than about 5$sigma$ after accounting for estimates of random and systematic errors.~Surprisingly, no large Virgo galaxy is present in this area, that could potentially host these GCs.~But candidate substructures in the M87 halo with equally elusive hosts have been described based on kinematic studies in the past.~The number of GC spectra available around M87 is currently insufficient to clarify the nature of the new candidate substructure.
We report on a large-scale study of the distribution of globular clusters (GCs) throughout the Virgo cluster, based on photometry from the Next Generation Virgo Cluster Survey, a large imaging survey covering Virgos primary subclusters to their virial radii. Using the g, (g-i) color-magnitude diagram of unresolved and marginally-resolved sources, we constructed 2-D maps of the GC distribution. We present the clearest evidence to date showing the difference in concentration between red and blue GCs over the extent of the cluster, where the red (metal-rich) GCs are largely located around the massive early-type galaxies, whilst the blue (metal-poor) GCs have a more extended spatial distribution, with significant populations present beyond 83 (215 kpc) along the major axes of M49 and M87. The GC distribution around M87 and M49 shows remarkable agreement with the shape, ellipticity and boxiness of the diffuse light surrounding both galaxies. We find evidence for spatial enhancements of GCs surrounding M87 that may be indicative of recent interactions or an ongoing merger history. We compare the GC map to the locations of Virgo galaxies and the intracluster X-ray gas, and find good agreement between these baryonic structures. The Virgo cluster contains a total population of 67300$pm$14400 GCs, of which 35% are located in M87 and M49 alone. We compute a cluster-wide specific frequency S_N,CL=$2.8pm0.7$, including Virgos diffuse light. The GC-to-baryonic mass fraction is e_b=$5.7pm1.1times10^{-4} $and the GC-to-total cluster mass formation efficiency is e_t=$2.9pm0.5times10^{-5}$, values slightly lower than, but consistent with, those derived for individual galactic halos. Our results show that the production of the complex structures in the unrelaxed Virgo cluster core (including the diffuse intracluster light) is an ongoing process.(abridged)
Intra-cluster (IC) populations are expected to be a natural result of the hierarchical assembly of clusters, yet their low space densities make them difficult to detect and study. We present the first definitive kinematic detection of an IC population of globular clusters (GCs) in the Virgo cluster, around the central galaxy, M87. This study focuses on the Virgo core for which the combination of NGVS photometry and follow-up spectroscopy allows us to reject foreground star contamination and explore GC kinematics over the full Virgo dynamical range. The GC kinematics changes gradually with galactocentric distance, decreasing in mean velocity and increasing in velocity dispersion, eventually becoming indistinguishable from the kinematics of Virgo dwarf galaxies at $mathrm{R>320, kpc}$. By kinematically tagging M87 halo and intra-cluster GCs we find that 1) the M87 halo has a smaller fraction ($52pm3%$) of blue clusters with respect to the IC counterpart ($77pm10%$), 2) the $(g-r)_{0}$ vs $(i-z)_{0}$ color-color diagrams reveal a galaxy population that is redder than the IC population that may be due to a different composition in chemical abundance and progenitor mass, and 3) the ICGC distribution is shallower and more extended than the M87 GCs, yet still centrally concentrated. The ICGC specific frequency, $S_{N,mathrm{ICL}}=10.2pm4.8$, is consistent with what is observed for the population of quenched, low-mass galaxies within 1~Mpc from the clusters center. The IC population at Virgos center is thus consistent with being an accreted component from low-mass galaxies tidally stripped or disrupted through interactions, with a total mass of $mathrm{M_{ICL,tot}=10.8pm0.1times10^{11}M_{odot}}$.
We present a study of ultra compact dwarf (UCD) galaxies in the Virgo cluster based mainly on imaging from the Next Generation Virgo Cluster Survey (NGVS). Using $sim$100 deg$^{2}$ of $u^*giz$ imaging, we have identified more than 600 candidate UCDs, from the core of Virgo out to its virial radius. Candidates have been selected through a combination of magnitudes, ellipticities, colors, surface brightnesses, half-light radii and, when available, radial velocities. Candidates were also visually validated from deep NGVS images. Subsamples of varying completeness and purity have been defined to explore the properties of UCDs and compare to those of globular clusters and the nuclei of dwarf galaxies with the aim of delineating the nature and origins of UCDs. From a surface density map, we find the UCDs to be mostly concentrated within Virgos main subclusters, around its brightest galaxies. We identify several subsamples of UCDs -- i.e., the brightest, largest, and those with the most pronounced and/or asymmetric envelopes -- that could hold clues to the origin of UCDs and possible evolutionary links with dwarf nuclei. We find some evidence for such a connection from the existence of diffuse envelopes around some UCDs, and comparisons of radial distributions of UCDs and nucleated galaxies within the cluster.
We build a background cluster candidate catalog from the Next Generation Virgo Cluster Survey, using our detection algorithm RedGOLD. The NGVS covers 104$deg^2$ of the Virgo cluster in the $u^*,g,r,i,z$-bandpasses to a depth of $ g sim 25.7$~mag (5$sigma$). Part of the survey was not covered or has shallow observations in the $r$--band. We build two cluster catalogs: one using all bandpasses, for the fields with deep $r$--band observations ($sim 20 deg^2$), and the other using four bandpasses ($u^*,g,i,z$) for the entire NGVS area. Based on our previous CFHT-LS W1 studies, we estimate that both of our catalogs are $sim100%$($sim70%$) complete and $sim80%$ pure, at $zle 0.6$($zlesssim1$), for galaxy clusters with masses of $Mgtrsim10^{14} M_{odot}$. We show that when using four bandpasses, though the photometric redshift accuracy is lower, RedGOLD detects massive galaxy clusters up to $zsim 1$ with completeness and purity similar to the five-band case. This is achieved when taking into account the bias in the richness estimation, which is $sim40%$ lower at $0.5le z<0.6$ and $sim20%$ higher at $0.6<z< 0.8$, with respect to the five-band case. RedGOLD recovers all the X-ray clusters in the area with mass $M_{500} > 1.4 times 10^{14} rm M_{odot}$ and $0.08<z<0.5$. Because of our different cluster richness limits and the NGVS depth, our catalogs reach to lower masses than the published redMaPPer cluster catalog over the area, and we recover $sim 90-100%$ of its detections.
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