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Register a new userIntracluster Planetary Nebulae in the Virgo Cluster III: Luminosity of the Intracluster Light and Tests of the Spatial Distribution
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Intracluster planetary nebulae are a useful tracer of the evolution of galaxies and galaxy clusters. We analyze our catalog of 318 intracluster planetary nebulae candidates found in 0.89 square degrees of the Virgo cluster. We give additional evidence for the great depth of the Virgo clusters intracluster stellar population, which implies that the bulk of the intracluster stars come from late-type galaxies and dwarfs. We also provide evidence that the intracluster stars are clustered on the sky on arcminute scales, in agreement with tidal-stripping scenarios of intracluster star production. Although significant systematic uncertainties exist, we find that the average fraction of intracluster starlight in the Virgo is 15.8% +/- 3.0% (statistical) +/- 5.0% (systematic), and may be higher if the intracluster stars have a large spatial line-of-sight depth. We find that the intracluster star density changes little with radius or projected density over the range surveyed. These results, along with other intracluster star observations, imply that intracluster star production in Virgo is ongoing and consistent with the clusters known dynamical youth.
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We briefly describe the properties of the confirmed spectroscopic sample of intracluster planetary nebulae recently discovered in the Virgo cluster. We find 23 bonafide intracluster planetary nebulae and 8 high redshift (z ~ 3.1) Lyalpha emitters identified by their broad asymmetric emission line.
We compare the distribution of diffuse intracluster light detected in the Virgo Cluster via broadband imaging with that inferred from searches for intracluster planetary nebulae (IPNe). We find a rough correspondence on large scales (~ 100 kpc) between the two, but with very large scatter (~ 1.3 mag/arcsec^2). On smaller scales (1 -- 10 kpc), the presence or absence of correlation is clearly dependent on the underlying surface brightness. On these scales, we find a correlation in regions of higher surface brightness (mu_V < ~27) which are dominated by the halos of large galaxies such as M87, M86, and M84. In those cases, we are likely tracing PNe associated with galaxies rather than true IPNe. In true intracluster fields, at lower surface brightness, the correlation between luminosity and IPN candidates is much weaker. While a correlation between broadband light and IPNe is expected based on stellar populations, a variety of statistical, physical, and methodological effects can act to wash out this correlation and explain the lack of a strong correlation at lower surface brightness found here. [abridged]
The intracluster light (ICL) is a faint diffuse stellar component in clusters made of stars not bound to individual galaxies. We have carried out a large scale study of this component in the nearby Virgo cluster. The diffuse light is traced using planetary nebulae (PNe). The PNe are detected in the on-band image due to their strong emission in the [OIII] 5007 line, but disappear in the off-band image. The contribution of Ly-alpha emitters at z=3.14 are corrected statistically using blank field surveys. We have surveyed a total area of 3.3 square degrees in the Virgo cluster with eleven fields located at different radial distances. Those fields located at smaller radii than 80 arcmin from the cluster center contain most of the detected diffuse light. In this central region of the cluster, the ICL has a surface brightness in the range 28.8 - 30 mag per sqarsec in the B band, it is not uniformly distributed, and represents about 7% of the total galaxy light in this area. At distances larger than 80 arcmin the ICL is confined to single fields and individual sub-structures, e.g. in the Virgo sub-clump B, the M60/M59 group. For several fields at 2 and 3 degrees from the Virgo cluster center we set only upper limits. These results indicate that the ICL is not homogeneously distributed in the Virgo core, and it is concentrated in the high density regions of the Virgo cluster, e.g. the cluster core and other sub-structures. Outside these regions, the ICL is confined within areas of 100 kpc in size, where tidal effects may be at work. These observational results link the formation of the ICL with the formation history of the most luminous cluster galaxies.
[OIII] lambda 5007AA emission lines of 16 intracluster planetary nebulae candidates in the Coma cluster were detected with a Multi-Slit Imaging Spectroscopy (MSIS) technique using FOCAS on the Subaru telescope. The identification of these faint emission sources as PNe is supported by (i) their point-like flux distribution in both space and wavelength, with tight limits on the continuum flux; (ii) the identification of the second [OIII] lambda 4959 line in the only object at high enough velocity that this line too falls into the filter bandpass; (iii) emission line fluxes consistent with PNe at 100 Mpc distance, in the range 2.8 x 10^{-19} - 1.7 x 10^{-18} erg/s/cm^2; and (iv) a narrow velocity distribution approximately centered on the systemic velocity of the Coma cluster. Comparing with the velocities of galaxies in our field, we conclude that the great majority of these candidates would be intracluster PNe, free floating in the Coma cluster core. Their velocity dispersion is ~760 km/s, and their mean velocity is lower than that of the galaxies. The velocity distribution suggests that the intracluster stellar population has different dynamics from the galaxies in the Coma cluster core.
Radial velocities of 40 intracluster planetary nebulae (ICPNe) in the Virgo cluster were obtained with the new multi-fiber FLAMES spectrograph on UT2 at VLT. For the first time, the lambda 4959 AA line of the [OIII] doublet is seen in a large fraction (50%) of ICPNe spectra, and a large fraction of the photometric candidates with m(5007) <= 27.2 is spectroscopically confirmed. ICPNe with the velocity dispersion of the Virgo cluster are found in our CORE field 1 deg from M87. These may have originated from tidal mass loss of smaller galaxies in the M87 subcluster halo. In a field 0.25 deg from M87, we see an extended stellar halo of M87 in approximate dynamical equilibrium, but with few ICPNe. Finally, in a field near M84/M86, the ICPNe velocities are highly correlated with the galaxy velocities, showing that any well-mixed intracluster population is yet to form. Overall, the measured velocity distributions confirm the non-uniform dynamical structure and on-going assembly of the Virgo cluster.(Based on data collected with the FLAMES spectrograph at the UT2 of the VLT at Cerro Paranal, Chile, operated by ESO, during observing run 71.B-0147(A))
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