Robert Kenneth McMahan

Spatial learning and memory at defined points of the estrous cycle : Effects on performance of a hippocampal-dependent task

Learning based on hippocampal-dependent spatial navigation in female rats was assessed at identified points in the estrous cycle corresponding to low (estrus) and high (proestrus) circulating estrogen. With background training in water-maze procedures, rats learned the location of an escape platform in the maze in a single session of 8 training trials. A strong spatial bias for the escape platform was also evident in a probe trial used to assess retention of learning 30 min after the training session. This entire protocol was completed in less than an hour. The performance of the estrus and proestrus rats was indistinguishable on all behavioral measures, irrespective of the stage of estrous cycle during the task. These results indicate that rapid learning and retention for spatial information over a relatively short interval may be preserved despite morphological alterations in hippocampal dendritic spine density in the normally cycling female rat.

A re-examination of the role of basal forebrain cholinergic neurons in spatial working memory

The basal forebrain cholinergic system, which innervates widespread cortical and limbic structures, has traditionally been considered important for learning and memory. The use of an immunotoxin, 192 IgG-saporin, has brought this functional designation into question; selective immunolesions of basal forebrain cholinergic neurons have failed to reproduce a number of behavioral deficits that were observed with less selective lesion methods. Recent reports, however, have indicated that a mild impairment is observed in rats on a spatial working memory task after 192 IgG-saporin lesions of the rostral groups of cholinergic neurons located in the medial septal area (MSA). Those studies used a lesion protocol in which a single large volume injection of the immunotoxin was made into the MSA. In the current study, multiple small injections were made at the locations of cholinergic neurons in the MSA, producing a cholinergic depletion comparable to that reported in the earlier studies where deficits were observed. In the current study, however, rats with cholinergic lesions had no impairment in the spatial working memory task, even when delays ranging from 60 s to 8 h were imposed within a trial. The current report indicates that selective removal of cholinergic neurons in the basal forebrain may not be sufficient to produce a deficit in spatial working memory.

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

ABSTRA C T 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 zero-point 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 a 20 km s ˇ1 , Dj=j a 9:1 per cent, DMgb=Mgb a 7:2 per cent and DMg2 a 0:015 mag. Comparison of our measurements with published data sets shows no systematic errors in the redshifts or velocity dispersions, and only small zero-point corrections to bring our linestrengths on to 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 highquality 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.

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

We investigate the variation in the zero-point of the Mg‐j relation between clusters. We find that it is consistent with the number of galaxies observed per cluster and the intrinsic scatter between galaxies in the global Mg‐j relation. We find no significant correlation between the Mg‐j zero-point and the cluster velocity dispersion, X-ray luminosity or X-ray temperature over a wide range in cluster mass. These results provide constraints for models of the formation of elliptical galaxies. However, the Mg‐j relation on its own does not place strong limits on systematic errors in Fundamental Plane (FP) distance estimates resulting from stellar population differences between clusters. We compare the intrinsic scatter in the Mg‐j and Fundamental Plane relations with stellar population models in order to constrain the dispersion in ages, metallicities and M=L ratios for early-type galaxies at fixed velocity dispersion. We find that variations in age or metallicity alone cannot explain the measured intrinsic scatter in both Mg‐j and the FP. We derive the joint constraints on the dispersion in age and metallicity implied by the scatter in the Mg‐j and FP relations for a simple Gaussian model. We find upper limits on the dispersions in age and metallicity at fixed velocity dispersion of 32 per cent in dt=t and 38 per cent in dZ=Z if the variations in age and metallicity are uncorrelated; only strongly anticorrelated variations lead to significantly higher upper limits. The joint distribution of residuals from the Mg‐j 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 anticorrelated (dt=t < 40 per cent, dZ=Z < 50 per cent and r < ˇ0:5), with younger galaxies being more metal-rich.

The Peculiar Motions of Early-type Galaxies in Two Distant Regions. IV. The Photometric Fitting Procedure

The EFAR project is a study of 736 candidate early-type galaxies in 84 clusters lying in two regions toward Hercules-Corona Borealis and Perseus-Cetus at distances cz ? 6000-15,000 km s-1. In this paper we describe a new method of galaxy photometry adopted to derive the photometric parameters of the EFAR galaxies. The algorithm fits the circularized surface brightness profiles as the sum of two seeing-convolved components, an R1/4 and an exponential law. This approach allows us to fit the large variety of luminosity profiles displayed by the EFAR galaxies homogeneously and to derive (for at least a subset of these) bulge and disk parameters. Multiple exposures of the same objects are optimally combined and an optional sky-fitting procedure has been developed to correct for sky-subtraction errors. Extensive Monte Carlo simulations are analyzed to test the performance of the algorithm and estimate the size of random and systematic errors. Random errors are small, provided that the global signal-to-noise ratio of the fitted profiles is larger than ? 300. Systematic errors can result from (1) errors in the sky subtraction, (2) the limited radial extent of the fitted profiles, (3) the lack of resolution due to seeing convolution and pixel sampling, (4) the use of circularized profiles for very flattened objects seen edge-on, and (5) a poor match of the fitting functions to the object profiles. Large systematic errors are generated by the widely used simple R1/4 law to fit luminosity profiles when a disk component, as small as 20% of the total light, is present. The size of the systematic errors cannot be determined from the shape of the ?2 function near its minimum because extrapolation is involved. Rather, we must estimate them by a set of quality parameters, calibrated against our simulations, which take into account the amount of extrapolation involved to derive the total magnitudes, the size of the sky correction, the average surface brightness of the galaxy relative to the sky, the radial extent of the profile, its signal-to-noise ratio, the seeing value, and the reduced ?2 of the fit. We formulate a combined quality parameter Q, which indicates the expected precision of the fits. Errors in total magnitudes MTOT less than 0.05 mag and in half-luminosity radii Re less than 10% are expected if Q = 1, and less than 0.15 mag and 25% if Q = 2; 89% of the EFAR galaxies have fits with Q = 1 or Q = 2. The errors on the combined fundamental plane quantity FP = log Re-0.3SBe, where SBe is the average effective surface brightness, are smaller than 0.03 even if Q = 3. Thus, systematic errors on MTOT and Re only have a marginal effect on the distance estimates that involve FP. We show that the sequence of R1/n profiles, recently used to fit the luminosity profiles of elliptical galaxies, is equivalent (for n ? 8) to a subsample of R1/4 and exponential profiles, with appropriate scale lengths and disk-to-bulge ratios. This suggests that the variety of luminosity profiles shown by early-type galaxies may be due to the presence of a disk component.

Structural properties of discs and bulges of early-type galaxies

We have used the EFAR sample of galaxies to investigate the light distributions of early-type galaxies. We decompose the two-dimensional 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 if we assume that all galaxies can have a spheroidal and a disc component, then the brightest, bulge-dominated elliptical galaxies have a fairly broad distribution in the Sersic profile shape parameter nB, with a median of approximately 3.7 and with σ ∼ 0.9. Other galaxies have smaller nB values. This means that spheroids are in general less concentrated than the de Vaucouleurs R 1/4 -law profile, which has n B = 4. While the result of our light decomposition is robust, we cannot prove without kinematic information that these components are spheroids and discs, in the usual sense of pressure- and rotation-supported stellar systems. However, we show that the distribution of disc inclination angles is consistent with a random orientation if we take our selection effects into account. 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 nB 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 the luminosity dimension and a lognormal 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, but extending to brighter magnitudes; at fainter luminosities the scale size distribution of elliptical galaxies peaks at distinctly smaller sizes than the size distribution of spiral galaxies; and (5) bulge components of early-type galaxies are typically a factor of 1.5-2.5 smaller than the discs of spiral galaxies with a slight luminosity dependence, while disc components of early-type galaxies are typically twice as large as the discs of spiral galaxies at all luminosities. Ke yw ords: galaxies: elliptical and lenticular, cD - galaxies: fundamental parameters - galax- ies: statistics - galaxies: structure.

The Peculiar Motions of Early-Type Galaxies in Two Distant Regions. I. Cluster and Galaxy Selection

The EFAR project is a study of 736 candidate elliptical galaxies in 84 clusters lying in two regions towards Hercules-Corona Borealis and Perseus-Pisces-Cetus at distances cz = 6000-15000 km/s. In this paper (the first of a series) we present an introduction to the EFAR project and describe in detail the selection of the clusters and galaxies in our sample. Fundamental data for the galaxies and clusters are given, including accurate new positions for each galaxy and redshifts for each cluster. The galaxy selection functions are determined using diameters measured from Schmidt sky survey images for 2185 galaxies in the cluster fields. Future papers in this series will present the spectroscopic and photometric observations of this sample, investigate the properties of the fundamental plane for ellipticals, and determine the large-scale peculiar velocity fields in these two regions of the universe.

The EFAR Project: Monte Carlo Testing of the Fundamental Plane Distance Estimator

The EFAR project is a long-term study of 736 candidate early-type galaxies in 84 clusters lying in two directions towards Hercules-Corona Borealis and PerseusPisces-Cetus at distances 6000–15000 km/s. In the following we discuss the goals of the project and the properties of the photometric and spectroscopic database. We present a new method, based on maximum likelihood, to determine the parameters of the Fundamental Plane and describe the distribution of galaxies in it. The algorithm takes into account the effects of errors and selection and is superior to least-squares procedures.