arXiv subjects

J. J. Kavelaars

Publications and source records attributed to J. J. Kavelaars.

77 records · Page 5Linked to original sources

arXiv2005

The CFEPS Kuiper Belt Survey: Strategy and Pre-survey Results

We present the data acquisition strategy and characterization procedures for the Canada-France Ecliptic Plane Survey (CFEPS), a sub-component of the Canada-France-Hawaii Telescope Legacy Survey. The survey began in early 2003 and as of summer 2005 has covered 430 square degrees of sky within a few degrees of the ecliptic. Moving objects beyond the orbit of Uranus are detected to a magnitude limit of $m_R$=23 -- 24 (depending on the image quality). To track as large a sample as possible and avoid introducing followup bias, we have developed a multi-epoch observing strategy that is spread over several years. We present the evolution of the uncertainties in ephemeris position and orbital elements as the objects progress through the epochs. We then present a small 10-object sample that was tracked in this manner as part of a preliminary survey starting a year before the main CFEPS project. We describe the CFEPS survey simulator, to be released in 2006, which allows theoretical models of the Kuiper Belt to be compared with the survey discoveries since CFEPS has a well-documented pointing history with characterized detection efficiencies as a function of magnitude and rate of motion on the sky. Using the pre-survey objects we illustrate the usage of the simulator in modeling the classical Kuiper Belt.

astro-ph↗

arXiv2005

Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters

We present new (B,I) photometry for the globular cluster systems in eight Brightest Cluster Galaxies (BCGs), obtained with the ACS/WFC camera on the Hubble Space Telescope. In the very rich cluster systems that reside within these giant galaxies, we find that all have strongly bimodal color distributions All the BCGs show population gradients, with much higher relative numbers of red clusters within 5 kpc of their centers, consistent with their having formed at later times than the blue, metal-poor population. A striking new feature of the color distributions emerging from our data is that for the brightest clusters (M_I < -10.5) the color distribution becomes broad and less obviously bimodal. we suggest that it may be a characteristic of many BCGs. Furthermore, the blue (metal-poor) clusters become progressively redder with increasing luminosity, following a mass/metallicity scaling relation Z ~ M^0.55. We argue that these GCS characteristics are consistent with a hierarchical-merging formation picture in which the metal-poor clusters formed in protogalactic clouds or dense starburst complexes with gas masses in the range 10^7 - 10^10 M_Sun, but where the more massive clusters on average formed in bigger clouds with deeper potential wells where more pre-enrichment could occur.

astro-ph↗

arXiv1999

The Globular Cluster Systems in the Coma Ellipticals. II: Metallicity Distribution and Radial Structure in NGC 4874, and Implications for Galaxy Formation

Deep HST/WFPC2 (V,I) photometry is used to investigate the globular cluster system (GCS) in NGC 4874, the central cD galaxy of the Coma cluster. The luminosity function of the clusters displays its normal Gaussian-like shape and turnover level. Other features of the system are surprising: the GCS is (a) spatially extended, with core radius r_c = 22 kpc, (b) entirely metal-poor (a narrow, unimodal metallicity distribution with mean [Fe/H] = -1.5), and (c) modestly populated, with specific frequency S_N = 3.7 +- 0.5. We suggest on the basis of some simple models that as much as half of this galaxy might have accreted from low-mass satellites, but no single one of the three classic modes of galaxy formation (accretion, disk mergers, in situ formation) can supply a fully satisfactory formation picture. Even when they are used in combination, strong challenges to these models remain. The principal anomaly in this GCS is essentially the complete lack of metal-rich clusters. If these were present in normal (M87-like) numbers in addition to the metal-poor ones that are already there, then the GCS in total would more closely resemble what we see in many other giant E galaxies.

astro-ph↗

arXiv1999

The Globular Cluster Systems in the Coma Ellipticals. I: The Luminosity Function in NGC 4874, and Implications for Hubble's Constant

We have used deep HST/WFPC2 images in V (F606W) and I (F814W) to measure the luminosity distribution of the globular clusters in NGC 4874, the central cD galaxy of the Coma cluster. We find the ``turnover'' point of the globular cluster luminosity function (GCLF) to lie at V = 27.88 +/- 0.12, while the overall GCLF shape matches the standard Gaussian-like form with dispersion SIGMA_V = 1.49 +/- 0.12. We use the GCLF as a standard candle by matching the turnover points in NGC 4874 and another Coma elliptical, IC 4051, with those of the giant ellipticals in the Virgo cluster (M87 and five others). The result is (m-M)_(Coma - Virgo) = 4.06 +/- 0.11 magnitudes, which converts to a Coma distance d = 102 Mpc if the Virgo distance modulus is (m-M)_0 = 30.99 +/- 0.04. The Hubble constant which emerges from our GCLF measurement is then H0 = (69 +/- 9) km/s/Mpc. We confirm this H0 value with a novel presentation of the ``Hubble diagram'' for GCLFs in giant E galaxies. Measurements of additional GCLFs in the Coma ellipticals, as well as calibrating galaxies in Virgo and Fornax, have excellent potential to refine this result in the near future.

astro-ph↗

arXiv1996

Kinematics and Metallicities of Globular Clusters in M104

We have obtained spectra for globular cluster candidates in M104 with LDSS-2 on the William Herschel Telescope, confirming 34 objects as M104 globular clusters. We find a cluster velocity dispersion of $\sim$ 260 km/sec, and the Projected Mass Estimator gives a mass of 5.0 (3.5,6.7) $\times 10^{11}$ M$_\odot$ for M104 within a projected radius of $\sim 330^{''}$ (14 kpc for D=8.55 Mpc). Our best estimate for the mass-to-light ratio is M/L$_{V_T}$= 16$^{+5.5}_{-5.0}$ within the same radius. Considering all of the possible sources of uncertainty, we find a lower limit of M/L_V= 5.3, which is larger than the M/L$_V$ found from rotation curve analyses inside 180$^{''}$. We thus conclude that the mass-to-light ratio increases with radius, or in other words that M104 possesses a dark matter halo. There is a marginal detection of rotation in the M104 cluster system at the 92.5% confidence level; larger samples will be needed to investigate this possibility. Interestingly, the M104 globular cluster and planetary nebulae (PNe) kinematics are roughly consistent inside $\sim 100^{''}$. Finally, we find a mean cluster metallicity of [Fe/H] = $-$0.70 $\pm$ 0.3, which is more typical of clusters in gE/cD galaxies than it is of clusters in other spirals.

astro-ph↗