NOAO fundamental plane survey II: Age and metallicity along the red sequence from line-strength data

We present spectroscopic line-strength data for 4097 red-sequence galaxies in 93 low-redshift galaxy clusters and use these to investigate variations in average stellar populations as a function of galaxy mass. Our analysis includes an improved treatment of nebular emission contamination, which affects 10% of the sample galaxies. Using the stellar population models of D. Thomas and collaborators, we simultaneously fit 12 observed line-strength relations in terms of common underlying trends of age, [Z/H] (total metallicity), and [/Fe] (-element enhancement). We find that the observed line-strength relations can be explained only if higher mass red-sequence galaxies are, on average, older, more metal-rich, and more -enhanced than lower mass galaxies. Quantitatively, the scaling relations are age0.59±0.13, Z/H0.53±0.08, and /Fe0.31±0.06, where the errors reflect the range obtained using different subsets of indices. Our conclusions are not strongly dependent on which Balmer lines are used as age indicators. The derived age- relation is such that if the largest (400 km s-1) galaxies formed their stars 13 Gyr ago, then the mean age of low-mass (50 km s-1) objects is only 4 Gyr. The data also suggest a large spread in age at the low-mass end of the red sequence, with 68% of the galaxies having ages between 2 and 8 Gyr. We conclude that although the stars in giant red galaxies in clusters formed early, most of the galaxies at the faint end joined the red sequence only at recent epochs. This "downsizing" trend is in good qualitative agreement with observations of the red sequence at higher redshifts but is not predicted by semianalytic models of galaxy formation

Fitting the integrated Spectral Energy Distributions of Galaxies

Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting, with a special emphasis on describing the interplay between the quality of the available data, the quality of the available models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties. We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift, stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details ofdust properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The present review will be made available on an interactive, moderated web page (sedfitting.org), where the community can access and change the text. The intention is to expand the text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics & Space Scienc

The Norma Cluster (ACO 3627): I. A Dynamical Analysis of the Most Massive Cluster in the Great Attractor

A detailed dynamical analysis of the nearby rich Norma cluster (ACO 3627) is presented. From radial velocities of 296 cluster members, we find a mean velocity of 4871 +/- 54 km/s and a velocity dispersion of 925 km/s. The mean velocity of the E/S0 population (4979 +/- 85 km/s) is offset with respect to that of the S/Irr population (4812 +/- 70 km/s) by `Delta' v = 164 km/s in the cluster rest frame. This offset increases towards the core of the cluster. The E/S0 population is free of any detectable substructure and appears relaxed. Its shape is clearly elongated with a position angle that is aligned along the dominant large-scale structures in this region, the so-called Norma wall. The central cD galaxy has a very large peculiar velocity of 561 km/s which is most probably related to an ongoing merger at the core of the cluster. The spiral/irregular galaxies reveal a large amount of substructure; two dynamically distinct subgroups within the overall spiral-population have been identified, located along the Norma wall elongation. The dynamical mass of the Norma cluster within its Abell radius is 1 - 1.1 x 10^15 h^-1_73 M_Sun. One of the cluster members, the spiral galaxy WKK 6176 which recently was observed to have a 70 kpc X-ray tail, reveals numerous striking low-brightness filaments pointing away from the cluster centre suggesting strong interaction with the intracluster medium.Comment: Sumbitted to MNRAS. 13 pages, 11 figures. Figures 6 and 10 reduced in resolution. Original available on reques

The Norma cluster (ACO 3627) - III. The distance and peculiar velocity via the near-infrared Ks-band Fundamental Plane

While Norma (ACO 3627) is the richest cluster in the Great Attractor (GA) region, its role in the local dynamics is poorly understood. The Norma cluster has a mean redshift (zCMB) of 0.0165 and has been proposed as the ‘core’ of the GA. We have used the Ks-band Fundamental Plane (FP) to measure Norma cluster's distance with respect to the Coma cluster. We report FP photometry parameters (effective radii and surface brightnesses), derived from ESO New Technology Telescope Son of ISAAC images, and velocity dispersions, from Anglo-Australian Telescope 2dF spectroscopy, for 31 early-type galaxies in the cluster. For the Coma cluster we use Two Micron All Sky Survey images and Sloan Digital Sky Survey velocity dispersion measurements for 121 early-type galaxies to generate the calibrating FP data set. For the combined Norma–Coma sample we measure FP coefficients of a = 1.465 ± 0.059 and b = 0.326 ± 0.020. We find an rms scatter, in log σ, of ∼0.08 dex which corresponds to a distance uncertainty of ∼28 per cent per galaxy. The zero-point offset between Norma's and Coma's FPs is 0.154 ± 0.014 dex. Assuming that the Coma cluster is at rest with respect to the cosmic microwave background frame and zCMB(Coma) = 0.0240, we derive a distance to the Norma cluster of 5026 ± 160 km s−1, and the derived peculiar velocity is −72 ± 170 km s−1, i.e. consistent with zero. This is lower than previously reported positive peculiar velocities for clusters/groups/galaxies in the GA region and hence the Norma cluster may indeed represent the GA's ‘core’

Early-type galaxies in the NOAO Fundamental Plane Survey

We review the NOAO Fundamental Plane Survey of nearby X-ray luminous galaxy clusters and present some preliminary results from early data.Peer reviewed: YesNRC publication: Ye

Clustering in the Great Attractor Region

A large part of the Great Attractor (GA) region is hidden by the Milky Way. However, the mapping of structures in this region (clusters as well as voids) is important for the understanding of this massive overdensity and its dynamics. We discuss our observing program of the Norma cluster (ACO 3627), a rich cluster at the core of the GA, as well as first results from an I-band survey centered on PKS 1343−601, a strong, but heavily obscured radio continuum source that might constitute the center of yet another rich cluster in the GA region

NOAO fundamental plane survey. I. Survey design, redshifts, and velocity dispersion data

We introduce the NOAO Fundamental Plane Survey (NFPS), a wide-field imaging/spectroscopic study of rich, low-redshift galaxy clusters. The survey targets X-rayselected clusters at 0.010 < z < 0.067, distributed over the whole sky, with imaging and spectroscopic observations obtained for 93 clusters. This data set will be used in investigations of galaxy properties in the cluster environment and of large-scale velocity fields through the fundamental plane. In this paper, we present details of the cluster sample construction and the strategies employed to select early-type galaxy samples for spectroscopy. Details of the spectroscopic observations are reported. From observations of 5479 red galaxies, we present redshift measurements for 5388 objects and internal velocity dispersions for 4131. The velocity dispersions have a median estimated error 7%. The NFPS has 15% overlap with previously published velocity dispersion data sets. Comparisons to these external catalogs are presented and indicate typical external errors of 8%