Kris Blindert

SPECTROSCOPIC CONFIRMATION OF TWO MASSIVE RED-SEQUENCE-SELECTED GALAXY CLUSTERS AT z ∼ 1.2 IN THE SpARCS-NORTH CLUSTER SURVEY

The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a z ′ -passband imaging survey, consisting of deep (z ′ ≃ 24 AB) observations made from both hemispheres using the CFHT 3.6m and CTIO 4m telescopes. The survey was designed with the primary aim of detecting galaxy clusters at z > 1. In tandem with pre-existing 3.6µm observations from the Spitzer Space Telescope SWIRE Legacy Survey, SpARCS detects clusters using an infrared adaptation of the two-filter redsequence cluster technique. The total effective area of the SpARCS cluster survey is 41.9 deg 2 . In this paper, we provide an overview of the 13.6 deg 2 Southern CTIO/MOSAICII observations. The 28.3 deg 2 Northern CFHT/MegaCam observations are summarized in a companion paper by Muzzin et al. (2008a). In this paper, we also report spectroscopic confirmation of SpARCS J003550431224, a very rich galaxy cluster at z = 1.335, discovered in the ELAIS-S1 field. To date, this is the highest spectroscopically confirmed redshift for a galaxy cluster discovered using the red-sequence technique. Based on nine confirmed members, SpARCS J003550-431224 has a preliminary velocity dispersion of 1050 ±230 km s −1 . With its proven capability for efficient cluster detection,SpARCS is a demonstration that we have entered an era of large, homogeneously-selected z > 1 cluster surveys. Subject headings: surveys — cosmology: observations — galaxies: clusters: general — galaxies: highredshift — infrared: galaxies

The DDO IVC Distance Project: Survey Description and the Distance to G139.6+47.6

We present a detailed analysis of the distance determination for one intermediate-velocity cloud (IVC, G139.6+47.6) from the ongoing DDO IVC Distance Project. Stars along the line of sight to G139.6+47.6 are examined for the presence of sodium absorption attributable to the cloud, and the distance bracket is established by astrometric and spectroscopic parallax measurements of demonstrated foreground and background stars. We detail our strategy regarding target selection, observational setup, and analysis of the data, including a discussion of wavelength calibration and sky subtraction uncertainties. We find a distance estimate of 129 ± 10 pc for the lower limit and 257 pc for the upper limit. Given the high number of stars showing absorption due to this IVC, we also discuss the small-scale covering factor of the cloud and the likely significance of nondetections for subsequent observations of this and other similar IVCs. Distance measurements of the remaining targets in the DDO IVC project will be detailed in a companion paper.