We report the results of [O III] λ5007 surveys for planetary nebulae (PNe) in six galaxies: NGC 2403, NGC 3115, NGC 3351, NGC 3627, NGC 4258, and NGC 5866. Using on-band/off-band [O III] λ5007 images, as well as images taken in Hα, we identify samples of PNe in these galaxies and derive their distances using the planetary nebula luminosity function (PNLF). We then combine these measurements with previous data to compare the PNLF, Cepheid, and surface brightness fluctuation (SBF) distance scales. We use a sample of 13 galaxies to show that the absolute magnitude of the PNLF cutoff is fainter in small, low-metallicity systems, but the trend is well modeled by the theoretical relation of Dopita, Jacoby, & Vassiliadis (1992). When this metallicity dependence is removed, the scatter between the Cepheid and PNLF distances becomes consistent with the internal errors of the methods and independent of any obvious galaxy parameter. We then use these data to recalibrate the zero point of the PNLF distance scale. We use a sample of 28 galaxies to show that the scatter between the PNLF and SBF distance measurements agrees with that predicted from the techniques' internal errors, and that there is no systematic trend between the distance residuals and stellar population. However, we also find that the PNLF and SBF methods have a significant scale offset: Cepheid-calibrated PNLF distances are, on average, ∼ 0.3 mag smaller than Cepheid-calibrated SBF distances. We discuss the possible causes of this offset, and suggest that internal extinction in the bulges of the SBF calibration galaxies is the principle cause of the discrepancy. If this hypothesis is correct, then the SBF-based Hubble Constant must be increased by ∼ 7%. We also use our distance to NGC 4258 to argue that the short distance scale to the LMC is correct, and and that the global Hubble Constant inferred from the HST Key Project should be increased by 8 ± 3% to H 0 = 78 ± 7 km s −1 Mpc −1 .

The Next Generation Virgo Cluster Survey (NGVS) is a program that uses the 1 deg 2 MegaCam instrument on the Canada-France-Hawaii Telescope to carry out a comprehensive optical imaging survey of the Virgo cluster, from its core to its virial radius-covering a total area of 104 deg 2-in the u * griz bandpasses. Thanks to a dedicated data acquisition strategy and processing pipeline, the NGVS reaches a point-source depth of g ≈ 25.9 mag (10σ) and a surface brightness limit of μ g ∼ 29 mag arcsec −2 (2σ above the mean sky level), thus superseding all previous optical studies of this benchmark galaxy cluster. In this paper, we give an overview of the technical aspects of the survey, such as areal coverage, field placement, choice of filters, limiting magnitudes, observing strategies, data processing and calibration pipelines, survey timeline, and data products. We also describe the primary scientific topics of the NGVS, which include: the galaxy luminosity and mass functions; the color-magnitude relation; galaxy scaling relations; compact stellar systems; galactic nuclei; the extragalactic distance scale; the large-scale environment of the cluster and its relationship to the Local Supercluster; diffuse light and the intracluster medium; galaxy interactions and evolutionary processes; and extragalactic star clusters. In addition, we describe a number of ancillary programs dealing with "foreground" and "background" science topics, including the study of highinclination trans-Neptunian objects; the structure of the Galactic halo in the direction of the Virgo Overdensity and Sagittarius Stream; the measurement of cosmic shear, galaxy-galaxy, and cluster lensing; and the identification of distant galaxy clusters, and strong-lensing events.

We report the discovery of three large (R 29 1 ) extremely low surface brightness (µ V,0 ≈ 27.0) galaxies identified using our deep, wide-field imaging of the Virgo Cluster from the Burrell Schmidt telescope. Complementary data from the Next Generation Virgo Cluster Survey do not resolve red giant branch stars in these objects down to i = 24, yielding a lower distance limit of 2.5 Mpc. At the Virgo distance, these objects have half-light radii 3-10 kpc and luminosities L V = 2 − 9 × 10 7 L . These galaxies are comparable in size but lower in surface brightness than the large ultradiffuse LSB galaxies recently identified in the Coma cluster, and are located well within Virgo's virial radius; two are projected directly on the cluster core. One object appears to be a nucleated LSB in the process of being tidally stripped to form a new Virgo ultracompact dwarf galaxy. The others show no sign of tidal disruption, despite the fact that such objects should be most vulnerable to tidal destruction in the cluster environment. The relative proximity of Virgo makes these objects amenable to detailed studies of their structural properties and resolved stellar populations. They thus provide an important new window onto the connection between cluster environment and galaxy evolution at the extremes.

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 (NGVS), a large imaging survey covering Virgo's primary subclusters (Virgo A=M87 and Virgo B=M49) out to their virial radii. Using the g o , (g − i ) o color-magnitude diagram of unresolved and marginally resolved sources within the NGVS, we have constructed 2-D maps of the (irregular) GC distribution over 100 square degrees to a depth of g o =24. We present the clearest evidence to date showing the difference in concentration between red and blue GCs over the full extent of the cluster, where the red (more metal-rich) GCs are largely located around the massive early-type galaxies in Virgo, while the blue (metal-poor) GCs have a much more extended spatial distribution, with significant populations still present beyond 83' (∼ 215 kpc) along the major axes of both M49 and M87. A comparison of our GC maps to the diffuse light in the outermost regions of M49 and M87 show remarkable agreement in the shape, ellipticity, and boxiness of both luminous systems. We also 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 that of the locations of Virgo galaxies and the X-ray intracluster gas, and find generally good agreement between these various baryonic structures. We calculate the Virgo cluster contains a total population of N GC = 67, 300 ± 14, 400, of which 35% are located in M87 and M49 alone. For the first time, we compute a cluster-wide specific frequency S N,CL = 2.8 ± 0.7, after correcting for Virgo's diffuse light. We also find a GC-to-baryonic mass fraction b = 5.7 ± 1.1 × 10 −4 and a GC-to-total cluster mass formation efficiency t = 2.9±0.5×10 −5 , the latter values slightly lower than, but consistent with, those derived for individual galactic halos. Taken as a whole, our results show that the production of the complex structures in the unrelaxed Virgo cluster core (including the production of the diffuse intracluster light) is an ongoing and continuing process.

We have conducted a wide-field CCD-mosaic study of the resolved red-giant branch (RGB) stars of M31, in a field located 20 kpc from the nucleus along the SE minor axis. In our (I, V-I) color-magnitude diagram, RGB stars in the top three magnitudes of the M31 halo are strongly present. Photometry of a more distant control field to subtract field contamination is used to derive the `cleaned' luminosity function and metallicity distribution function (MDF) of the M31 halo field. From the color distribution of the foreground Milky Way halo stars, we find a reddening E(V-I)= 0.10 +/- 0.02 for this field, and from the luminosity of the RGB tip, we determine a distance modulus (m-M)_o = 24.47 +/- 0.12 (= 783 +/- 43 kpc). The MDF is derived from interpolation within an extensive new grid of RGB models (Vandenberg et al. 2000). The MDF is dominated by a moderately high-metallicity population ([m/H]~ -0.5) found previously in more interior M31 halo/bulge fields, and is much more metal-rich than the [m/H]~ -1.5 level in the Milky Way halo. A significant (~30% - 40%, depending on AGB star contribution) metal-poor population is also present. To first order, the shape of the MDF resembles that predicted by a simple, single-component model of chemical evolution starting from primordial gas with an effective yield y=0.0055. It strongly resembles the MDF recently found for the outer halo of the giant elliptical NGC 5128 (Harris et al. 2000), though NGC 5128 has an even lower fraction of low-metallicity stars. Intriguingly, in both NGC 5128 and M31, the metallicity distribution of the globular clusters in M31 does not match the halo stars; the clusters are far more heavily weighted to metal-poor objects. We suggest similarities in the formation and early evolution of massive, spheroidal stellar systems.Comment: to appear in the Astronomical Journal; 43 pages, including 15 figure

We report the results of a photometric and spectroscopic survey for planetary nebulae (PNe) in the Local Group spiral galaxy M33. We use our sample of 152 PNe to derive an [O III] planetary nebula luminosity function (PNLF) distance of (m-M)_0 = 24.86^+0.07-0.11 (0.94^+0.03-0.05 Mpc). Although this value is ~ 15% larger than the galaxy's Cepheid distance, the discrepancy likely arises from differing assumptions about the system's internal extinction. Our photometry (which extends >3 mag down the PNLF), also reveals that the faint-end of M33's PN luminosity function is non-monotonic, with an inflection point ~2 mag below the PNLF cutoff. We argue that this feature is due to the galaxy's large population of high core-mass planetaries, and that its amplitude may eventually be useful as a diagnostic for studies of stellar populations. Fiber-coupled spectroscopy of 140 of the PN candidates confirms that M33's PN population rotates along with the old disk, with a small asymmetric drift of \~ 10km/s. Remarkably, the population's line-of-sight velocity dispersion varies little over ~4 optical disk scale lengths, with sigma_{rad}~20km/s. We show that this is due to a combination of factors, including a decline in the radial component of the velocity ellipsoid at small galactocentric radii, and a gradient in the ratio of the vertical to radial velocity dispersion. We use our data to show that the mass scale length of M33's disk is ~2.3 times larger than that of the system's IR luminosity and that the disk's V-band mass-to-light ratio changes from M/L_V ~0.3 in the galaxy's inner regions to M/L_V ~2.0 at ~9 kpc. Models in which the dark matter is distributed in the plane of the galaxy are excluded by our data. (abridged)Comment: 45 pages, including 12 figures (some with reduced resolution); accepted for publication in the Astrophysical Journa

We have used the WFPC2 camera of the Hubble Space Telescope to obtain deep F814W images of a blank field in the Virgo Cluster located 41 arcmin northwest of M87. We perform star counts in that field, and in another Virgo field observed by Ferguson, Tanvir & von Hippel (1998), and show that, when compared to the Hubble Deep Field North and South, the Virgo Cluster contains an excess of objects with magnitudes I > 27. We attribute this excess to a population of intracluster red-giant branch (IC-RGB) stars. By modeling the luminosity function of these stars, we show that the tip of the Virgo RGB is at I = 27.31 +0.27/-0.17 and that the cluster contains a small, but significant, excess of stars that are up to ~1 mag brighter than this tip. If this luminous component is due entirely to stars on the asymptotic giant branch (AGB), it implies an age for the population of > 2 Gyr; if foreground RGB stars contribute to the luminous tail, then the derived age for the stars is older still. The luminosity function also suggests that most of the intracluster stars are moderately metal-rich (-0.8 < [Fe/H] <-0.2), a result consistent with that expected from stars that have been tidally stripped from intermediate luminosity galaxies. Additionally, a comparison with the planetary nebulae in our field also supports this view, although the existence of a more metal-poor population (from stripped dwarfs) cannot be ruled out. Our derived average surface brightness, mu_I = 27.9 +0.3/-0.5 mag/arcsec^2 for Virgo's diffuse component suggests that intracluster stars contribute 10% to 20% of the cluster's total I-band luminosity.Comment: 21 pages, 8 figures included, accepted for publication in the Astrophysical Journa

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 cluster's 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 cluster's known dynamical youth.