arXiv subjects

Gary Wegner

Publications and source records attributed to Gary Wegner.

At least 19 recordsLinked to original sources

arXiv2019

Metal Abundances and Star-Formation Rates of Emission-Line Galaxies in and around the Bootes Void

We explore the possible dependencies of galaxy metal abundance and star-formation rate (SFR) on local environment, focusing on the volume of space in and around the Bootes Void. Our sample of star-forming galaxies comes from the second catalog of the H-alpha-selected KPNO International Spectroscopic Survey (KISS) which overlaps the void. This sample represents a statistically complete, line-flux-limited ensemble of 820 star-forming galaxies, all of which possess metallicity and SFR estimates. We carry out two distinct analyses of the KISS galaxies: one which probes the properties of the entire sample as a function of local density, and a second which details the properties of 33 KISS star-forming galaxies located within the Bootes Void. In both cases we find no evidence that either the metallicity of the KISS galaxies or their SFRs depend on the environments within which the galaxies are located. Our global analysis does show weak trends for decreasing stellar mass, decreasing metallicity, and decreasing SFRs with decreasing local densities. However, we argue that the metallicity and SFR trends are artifacts of the stellar mass - local density trend. In particular, the change in metallicity with density is precisely what one would predict from the mass-metallicity relation given the observed drop in stellar mass with decreasing metallicity. Likewise, the SFR trend with density disappears when one instead considers the mass-normalized specific SFR. The KISS galaxies dwelling in the Bootes Void are found to have nearly identical metallicity and SFR properties to a matched comparison sample, despite the fact that the former are located in density environments that are, on average, more than 16 times lower.

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arXiv2008

Ages and Metallicities of Early-Type Void Galaxies from Line Strength Measurements

We present spectroscopic observations of 26 galaxies of type E and S0, based on their blue morphologies, located in voids by the study of Grogin & Geller (1999). Measurements of redshift, velocity dispersion, and four Lick line indices, Mgb, Fe5270, Fe5335, and Hbeta with their errors are given for all of these galaxies, along with Hbeta, [OIII], Halpha, and [NII] emission line strengths for a subset of these objects. These sources are brighter than M star for low density regions and tend to be bluer than their counterpart early-type objects in high density regions. Using the models of Thomas et al. (2003) gives metal abundances and ages with a median alpha enhancement, [alpha/Fe] = +0.13, and median metals abundance, [Z/H] = +0.22, values comparable to those found for E and S0 galaxies in clusters, but with a wider spread in [Z/H] towards low values. If the emission line subsample is interpreted as younger, the proportion of young objects is higher than for early-types in higher density regions. There is a significant incidence of sources in the sample with emission lines in their spectra (46% with Hbeta and [OIII] and 69% with Halpha or [NII]) as well as shells and rings in their morphologies (19%). The diagnostic log[NII/Halpha], log[OIII/Hbeta] diagram places 10 of 12 emission line galaxies in or near the star forming and liner region and two among the Seyferts. The Halpha fluxes indicate star formation rates of 0.2 to 1.0 Msun per yr. The percentage of these early-type void galaxies undergoing star formation appears to be higher compared to their cluster counterparts and the range of ages wider.

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arXiv2005

The Oxford-Dartmouth Thirty Degree Survey II: Clustering of Bright Lyman Break Galaxies - Strong Luminosity Dependent Bias at z=4

We present measurements of the clustering properties of bright ($L>L_{*}$) z$\sim$4 Lyman Break Galaxies (LBGs) selected from the Oxford-Dartmouth Thirty Degree Survey (ODT). We describe techniques used to select and evaluate our candidates and calculate the angular correlation function which we find best fitted by a power law, $ω(θ)=A_{w}θ^{-β}$ with $A_{w}=15.4$ (with $θ$ in arcseconds), using a constrained slope of $β=0.8$. Using a redshift distribution consistent with photometric models, we deproject this correlation function and find a comoving $r_{0}=11.4_{-1.9}^{+1.7}$ h$_{100}^{-1}$ Mpc in a $Ω_m=0.3$ flat $Λ$ cosmology for $i_{AB}\leq24.5$. This corresponds to a linear bias value of $b=8.1_{-2.6}^{+2.0}$ (assuming $σ_{8}=0.9$). These data show a significantly larger $r_{0}$ and $b$ than previous studies at $z\sim4$. We interpret this as evidence that the brightest LBGs have a larger bias than fainter ones, indicating a strong luminosity dependence for the measured bias of an LBG sample. Comparing this against recent results in the literature at fainter (sub-$L_{*}$) limiting magnitudes, and with simple models describing the relationship between LBGs and dark matter haloes, we discuss the implications on the implied environments and nature of LBGs. It seems that the brightest LBGs (in contrast with the majority sub-$L_{*}$ population), have clustering properties, and host dark matter halo masses, that are consistent with them being progenitors of the most massive galaxies today.

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arXiv2004

Structural properties of discs and bulges of early-type galaxies

We have used the EFAR sample of galaxies to study the light distributions of early-type galaxies. We decompose the 2D light distribution of the galaxies in a flattened spheroidal component with a Sersic radial light profile and an inclined disc component with an exponential light profile. We show that the brightest, bulge dominated elliptical galaxies have a fairly broad distribution in the Sersic profile shape parameter n_B, with a median of about 3.7 and a sigma of ~0.9. Other galaxies have smaller n_B values, meaning that spheroids are in general less concentrated than the n_B=4 de Vaucouleurs-law profile. The results of our light decompositions are robust, even though without kinematic information we cannot prove that the spheroids and discs are really pressure- and rotation-supported stellar systems. If we assume that the detected spheroids and discs are indeed separate components, we can draw the following conclusions: 1) the spheroid and disc scale sizes are correlated; 2) bulge-to-total luminosity ratios, bulge effective radii, and bulge n_B values are all positively correlated; 3) the bivariate space density distribution of elliptical galaxies in the (luminosity, scale size)-plane is well described by a Schechter luminosity function in and a log-normal scale-size distribution at a given luminosity; 4) at the brightest luminosities, the scale size distribution of elliptical galaxies is similar to those of bright spiral galaxies; at fainter luminosities the elliptical scale size distribution peaks at distinctly smaller sizes than the spiral galaxy distribution; and 5) bulge components of early-type galaxies are typically a factor 1.5 to 2.5 smaller than the disks of spiral galaxies, while disc components of early-type galaxies are typically twice as large as the discs of spiral galaxies. [abridged]

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arXiv2004

The Oxford-Dartmouth Thirty Degree Survey I: Observations and Calibration of a Wide-Field Multi-Band Survey

The Oxford Dartmouth Thirty Degree Survey (ODTS) is a deep, wide, multi-band imaging survey designed to cover a total of 30 square degrees in BVRi'Z, with a subset of U and K band data, in four separate fields of 5-10 deg^2 centred at 00:18:24 +34:52, 09:09:45 +40:50, 13:40:00 +02:30 and 16:39:30 +45:24. Observations have been made using the Wide Field Camera on the 2.5-m Isaac Newton Telescope in La Palma to average limiting depths (5 sigma Vega, aperture magnitudes) of U=24.8, B=25.6, V=25.0, R=24.6, and i'=23.5, with observations taken in ideal conditions reaching the target depths of U=25.3, B=26.2, V=25.7, R=25.4, and i'=24.6. The INT Z band data was found to be severely effected by fringing and, consequently, is now being obtained at the MDM observatory in Arizona. A complementary K-band survey has also been carried out at MDM, reaching an average depth of K_{5σ}~18.5. At present, approximately 23 deg^2 of the ODTS have been observed, with 3.5 deg^2 of the K band survey completed. This paper details the survey goals, field selection, observation strategy and data reduction procedure, focusing on the photometric calibration and catalogue construction. Preliminary photometric redshifts have been obtained for a subsample of the objects with R <= 23. These results are presented alongside a brief description of the photometric redshift determination technique used. The median redshift of the survey is estimated to be z~0.7 from a combination of the ODTS photometric redshifts and comparison with the redshift distributions of other surveys. Finally, galaxy number counts for the ODTS are presented which are found to be in excellent agreement with previous studies.

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arXiv2003

An estimate of Ω_m without priors

Using mean relative peculiar velocity measurements for pairs of galaxies, we estimate the cosmological density parameter $Ω_m$ and the amplitude of density fluctuations $σ_8$. Our results suggest that our statistic is a robust and reproducible measure of the mean pairwise velocity and thereby the $Ω_m$ parameter. We get $Ω_m = 0.30^{+0.17}_{-0.07}$ and $σ_8 = 1.13^{+0.22}_{-0.23}$. These estimates do not depend on prior assumptions on the adiabaticity of the initial density fluctuations, the ionization history, or the values of other cosmological parameters.

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arXiv2000

The Peculiar Motions of Early-Type Galaxies in Two Distant Regions VI: The Maximum Likelihood Gaussian Algorithm

The EFAR project is designed to measure the properties and peculiar motions of early-type galaxies in two distant regions. Here we describe the maximum likelihood algorithm we developed to investigate the correlations between the parameters of the EFAR database. One-, two-, and three-dimensional gaussian models are constructed to determine the mean value and intrinsic spread of the parameters, and the slopes and intrinsic parallel and orthogonal spread of the Mgb'-Mg2, Mg2-sigma, Mgb'-sigma relations, and the Fundamental Plane. In the latter case, the cluster peculiar velocities are also determined. We show that this method is superior to ``canonical'' approaches of least-squares type, which give biased slopes and biased peculiar velocities. We test the algorithm with Monte Carlo simulations of mock EFAR catalogues and derive the systematic and random errors on the estimated parameters. We find that random errors are always dominant. We estimate the influence of systematic errors due to the way clusters were selected and the hard limits and uncertainties in the selection function parameters for the galaxies. We explore the influence of uniform distributions in the Fundamental Plane parameters and the errors. We conclude that the mean peculiar motions of the EFAR clusters can be determined reliably. In particular, the placement of the two EFAR sample regions relative to the Lauer and Postman dipole allows us to strongly constrain the amplitude of the bulk motion in this direction.

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arXiv2000

The peculiar motions of early-type galaxies in two distant regions - VII. Peculiar velocities and bulk motions

We present peculiar velocities for 84 clusters of galaxies in two large volumes at distances between 6000 and 15000 km/s in the directions of Hercules-Corona Borealis and Perseus-Pisces-Cetus. These velocities are based on Fundamental Plane (FP) distance estimates for early-type galaxies in each cluster. We fit the FP using a maximum likelihood algorithm which accounts for both selection effects and measurement errors, and yields FP parameters with smaller bias and variance than other fitting procedures. We find a best-fit FP with coefficients consistent with the best existing determinations. We measure the bulk motions of the sample volumes using the 50 clusters with the best-determined peculiar velocities. We find the bulk motions in both regions are small, and consistent with zero at about the 5% level. The EFAR results are in agreement with the small bulk motions found by Dale et al. (1999) on similar scales, but are inconsistent with pure dipole motions having the large amplitudes found by Lauer & Postman (1994) and Hudson et al. (1999). The alignment of the EFAR sample with the Lauer & Postman dipole produces a strong rejection of a large-amplitude bulk motion in that direction, but the rejection of the Hudson et al. result is less certain because their dipole lies at a large angle to the main axis of the EFAR sample. We find the bulk motion of our sample is consistent with most cosmological models that approximately reproduce the shape and normalisation of the observed galaxy power spectrum. We conclude that existing measurements of large-scale bulk motions provide no significant evidence against standard models for the formation of structure.

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arXiv2000

Comparison of the ENEAR Peculiar Velocities with the PSCz Gravity Field

We present a comparison between the peculiar velocity field measured from the ENEAR all-sky $D_n-σ$ catalog and that derived from the galaxy distribution of the IRAS PSCz redshift survey. The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500km/s at 3000km/s. The general flow patterns in the filtered ENEAR and PSCz velocity fields agree well within 6000km/s, assuming a linear biasing relation between the mass and the PSCz galaxies. The comparison allows us to determine the parameter $β=Ω^{0.6}/b$, where $Ω$ is the cosmological density parameter and $b$ is the linear biasing factor. A likelihood analysis of the ENEAR and PSCz modes yields $β=0.5 +- 0.1$, in good agreement with values obtained from Tully-Fisher surveys.

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arXiv1999

EFAR peculiar velocities and bulk motions

The EFAR project has measured peculiar motions in two distant volumes of the universe using Fundamental Plane (FP) distances for 85 clusters with cz=6000-15000 km/s. The scatter in distance about the FP is observed to be 20% per galaxy for EFAR sample, resulting in peculiar velocities with a median precision of 1075 km/s for the 50 clusters with 3 or more galaxies. We find that there is no evidence for a large bulk flow within either of the two volumes sampled by the EFAR clusters. The measured bulk motion in both regions is small and consistent with zero. The Lauer and Postman (1994) bulk motion is ruled out at the 4-sigma level. There is no evidence supporting the SMAC (Hudson et al. 1999) or LP10K (Willick 1999) bulk motions, but the directionality of the EFAR sample would only allow a weak (2-sigma) detection at best.

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arXiv1999

Large-Scale Power Spectrum and Cosmological Parameters from SFI Peculiar Velocities

We estimate the power spectrum of mass density fluctuations from peculiar velocities of galaxies by applying an improved maximum-likelihood technique to the new all-sky SFI catalog. Parametric models are used for the power spectrum and the errors, and the free parameters are determined by assuming Gaussian velocity fields and errors and maximizing the probability of the data given the model. It has been applied to generalized CDM models with and without COBE normalization. The method has been carefully tested using artificial SFI catalogs. The most likely distance errors are found to be similar to the original error estimates in the SFI data. The general result that is not very sensitive to the prior model used is a relatively high amplitude of the power spectrum. For example, at k=0.1 h/Mpc we find P(k)Ω^{1.2}=(4.4+/-1.7)X10^3 (Mpc/h)^3. An integral over the power spectrum yields σ_8Ω^{0.6}=0.82+/-0.12. Model-dependent constraints on the cosmological parameters are obtained for families of CDM models. For example, for COBE-normalized ΛCDM models (scalar fluctuations only), the maximum-likelihood result can be approximated by Ωn^{2} h_{60}^{1.3} =0.58+/-0.11. The formal random errors quoted correspond to the 90% confidence level. The total uncertainty, including systematic errors associated with nonlinear effects, may be larger by a factor of ~2. These results are in agreement with an application of a similar method to other data (Mark III).

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arXiv1998

The peculiar motions of early-type galaxies in two distant regions - II. The spectroscopic data

We present the spectroscopic data for the galaxies studied in the EFAR project, which is designed to measure the properties and peculiar motions of early-type galaxies in two distant regions. We have obtained 1319 spectra of 714 early-type galaxies over 33 observing runs on 10 different telescopes. We describe the observations and data reductions used to measure redshifts, velocity dispersions and the Mgb and Mg2 Lick linestrength indices. Detailed simulations and intercomparison of the large number of repeat observations lead to reliable error estimates for all quantities. The measurements from different observing runs are calibrated to a common zeropoint or scale before being combined, yielding a total of 706 redshifts, 676 velocity dispersions, 676 Mgb linestrengths and 582 Mg2 linestrengths. The median estimated errors in the combined measurements are dcz=20 km/s, dsigma/sigma=9.1%, dMgb/Mgb=7.2% and dMg2=0.015 mag. Comparison of our measurements with published datasets shows no systematic errors in the redshifts or velocity dispersions and only small zeropoint corrections to bring our linestrengths onto the standard Lick system. We have assigned galaxies to physical clusters by examining the line-of-sight velocity distributions based on EFAR and ZCAT redshifts, together with the projected distributions on the sky. We derive mean redshifts and velocity dispersions for these clusters, which will be used in estimating distances and peculiar velocities and to test for trends in the galaxy population with cluster mass. The spectroscopic parameters presented here for 706 galaxies combine high quality data, uniform reduction and measurement procedures, and detailed error analysis. They form the largest single set of velocity dispersions and linestrengths for early-type galaxies published to date.

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arXiv1998

The peculiar motions of early-type galaxies in two distant regions - V. The Mg-sigma relation, age and metallicity

We examine the Mg-sigma relation for early-type galaxies in the EFAR sample and its dependence on cluster properties. A maximum likelihood fit gives global Mg-sigma relations of Mgb'=0.131log(sigma)-0.131 and Mg2=0.257log(sigma)-0.305, with intrinsic scatter of 0.016 mag in Mgb' and 0.023 mag in Mg2. The zeropoint for cD galaxies is higher than for E/S0 galaxies, implying cDs are older and/or more metal-rich than E/S0s with the same sigma. Mg-sigma zeropoint variations between clusters are consistent with the number of galaxies observed per cluster and the global intrinsic scatter in Mg-sigma. We find no significant correlation between the Mg-sigma zeropoint and the cluster velocity dispersion, X-ray luminosity or X-ray temperature over a wide range in cluster mass. We compare the intrinsic scatter in the Mg-sigma and Fundamental Plane (FP) relations with stellar population models to constrain the dispersion in ages, metallicities and M/L ratios for early-type galaxies at fixed sigma. Variations in age alone or metallicity alone cannot explain the measured intrinsic scatter in both Mg-sigma and the FP. We derive the joint constraints on the dispersion in age and metallicity implied by the scatter in the Mg-sigma and FP relations for a simple Gaussian model. We find upper limits on the dispersions at fixed sigma of 32% in dt/t and 38% in dZ/Z if variations in age and metallicity are uncorrelated; only strongly anti-correlated variations lead to significantly higher upper limits. The joint distribution of residuals from the Mg-sigma and FP relations is only marginally consistent with a model having no correlation between age and metallicity, and is better-matched by a model in which age and metallicity variations are moderately anti-correlated, with younger galaxies being more metal-rich. (Abridged)

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arXiv1998

Cluster vs. Field Elliptical Galaxies and Clues on their Formation

Using new observations for a sample of 931 early-type galaxies we investigate whether the \mg2--\so relation shows any dependence on the local environment. The galaxies have been assigned to three different environments depending on the local overdensity: clusters, groups, and field, having used our completeredshift database to guide the assignment of galaxies. It is found that cluster, group and field early-type galaxies follow almost identical \mg2--\so\ relations, with the largest \mg2 zero-point difference (clusters minus field) being only $0.007\pm 0.002$ mag. No correlation of the residuals is found with the morphological type or the bulge to disk ratio. Using stellar population models in a differential fashion, this small zero-point difference implies a luminosity-weighted age difference of only $\sim 1$ Gyr between the corresponding stellar populations, with field galaxies being younger. The mass-weighted age difference could be significantly smaller, if minor events of late star formation took place preferentially in field galaxies. We combine these results with the existing evidence for the bulk of stars in cluster early-type galaxies having formed at very high redshift, and conclude that the bulk of stars in galactic spheroids had to form at high redshifts ($z\gsim 3$), no matter whether such spheroids now reside in low or high density regions. The cosmological implications of these findings are briefly discussed.

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arXiv1998

A Photometric and Kinematic Study of AWM 7

We have measured redshifts and Kron-Cousins R-band magnitudes for a sample of galaxies in the poor cluster AWM 7. We have measured redshifts for 172 galaxies; 106 of these are cluster members. We determine the luminosity function from a photometric survey of the central 1.2 h^{-1} x 1.2 h^{-1} Mpc. The LF has a bump at the bright end and a faint-end slope of α= -1.37+-0.16, populated almost exclusively by absorption-line galaxies. The cluster velocity dispersion is lower in the core (\sim 530 km/s) than at the outskirts (\sim 680 km/s), consistent with the cooling flow seen in the X-ray. The cold core extends \sim 150 h^{-1} kpc from the cluster center. The Kron-Cousins R-band mass-to-light ratio of the system is 650+-170 h M_\odot/L_\odot, substantially lower than previous optical determinations, but consistent with most previous X-ray determinations. We adopt H_0 = 100 h km/s/Mpc throughout this paper; at the mean cluster redshift, (5247+-76 km/s), 1 h^{-1} Mpc subtends 65$\farcm$5.

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arXiv1997

The kinematically peculiar cores of the Coma cluster early -- type galaxies NGC 4816 and IC 4051

The Coma cluster is one of the richest known cluster of galaxies, spanning about 4 dex in density. Hence it is the ideal place to study the structure of galaxies as a function of environmental density in order to constrain the theories of galaxy formation and evolution. For a magnitude limited sample of 35 E and S0 galaxies we obtained long slit spectra to derive the rotation curves, the velocity dispersion profiles and the radial gradients of the Mg, Fe and H_beta line indices. Here we report on two early -- type galaxies which turned out to host the largest kinematically peculiar cores yet found in ``normal'' early -- type galaxies: NGC 4816 hosts a decoupled counter rotating core with a radial extension along the major axis of 2.7 kpc, while IC 4051 has a co-rotating peculiar core with a sizes of 3.4 kpc. We combine our data with HST photometry and show that both cores are flattened central stellar disks which contribute less than 1 % to the total V band light of the galaxies, but are nevertheless conspicuous (1 - 2 x 10**9 L_sun). The metallicity of the cores is 0.25 dex super solar and drops to solar and sub solar in the outer part of NGC 4816 and IC 4051, respectively. The mean stellar population in both central disks is old (8 - 12 Gyr) and highly overabundant in Mgb relative to (approximatly 0.5 dex). We discuss the evidence that these central disks formed via dissipational major merger events.

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arXiv1997

Spectroscopic Gradients in Early -- Type Galaxies and Implications on Galaxy Formation

The Coma cluster is the ideal place to study galaxy structure as a function of environmental density in order to constrain theories of galaxy formation and evolution. Here we present the spectroscopy of 35 early type Coma galaxies, which shows that the age spread of early type galaxies in the Coma cluster is large (15 Gyrs). In contrast to the field, the dominant stellar population in all (massive) Coma Es is older than 8 Gyr, while only S0s, which possess extended disks, can be as young as 2 Gyr. The old, most massive Es show a strong light element enhancement, probably due to a rather short star formation time scale and hence to a SNII -- dominated element enrichment. The lower mass S0s are much less enhanced in light elements, indicating a longer star formation time scale. The measured absorption line index gradients support the idea that early type galaxies formed in processes that include both stellar merging and gaseous dissipation.

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arXiv1997

Comparison of the SFI Peculiar Velocities with the IRAS 1.2 Jy Gravity Field

We present a comparison between the peculiar velocity fields measured from the SFI all-sky Sbc-Sc Tully-Fisher catalog and that derived from the \iras 1.2 Jy redshift survey galaxy distribution. The analysis is based on the expansion of these data in redshift space using smooth orthonormal functions and is performed using low and high resolution expansions, with an effective smoothing scale which increases almost linearly with redshift. The effective smoothing scales at 3000 \kms are 1500\kms and 1000\kms for the low and high resolution filters. The agreement between the high and low resolution SFI velocity maps is excellent. The general features in the filtered SFI and \iras velocity fields agree remarkably well within 6000\kms. This good agreement between the fields allows us to determine the parameter $β=Ω^{0.6}/b$, where $Ω$ is the cosmological density parameter and $b$ is the linear biasing factor. From a likelihood analysis on the SFI and \iras modes we find that $β=0.6\pm 0.1$ independently of the resolution of the modal expansion. For this value of $β$, the residual fields for the two filters show no systematic variations within 6000 \kms. Most remarkable is the lack of any coherent, redshift dependent dipole flow in the residual field.

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