Raymond E. White

Handedness in the human fetus

The developmental origins of behavioural asymmetries, in particular handedness, have aroused considerable interest and debate. Until now such behavioural asymmetries have only been reported after birth. Here we report the existence of handedness before birth, expressed in terms of thumb-sucking by the fetus. Ultrasound observations of fetuses from 15 weeks to term revealed a marked bias for sucking the thumb of the right hand. This preference appears to be maintained throughout pregnancy, is unrelated to fetal position in utero but correlates with head position preference in the supine newborn. The findings indicate that handedness is present prior to birth and the implications of this for the development of laterality are discussed.

Steady state cooling flow models for normal elliptical galaxies

An extensive grid of steady state cooling flow models for the hot gas in elliptical galaxies is calculated. The effects of allowing inflow of surrounding gas and varying the supernova heating rate, the mass distribution of the galaxy, the rate of stellar mass loss, and the outer boundary pressure are studied. The X-ray luminosities, spectra, and surface brightness profiles of the galaxies are computed. In all of the models, the gas density varies approximately as r exp -3/2. In the models with heavy halos, the X-ray and optical surface brightnesses are nearly proportional to one another within individual galaxies, and the temperature profiles are roughly isothermal. 48 references.

Prevalence and Properties of Dark Matter in Elliptical Galaxies

Given the recently deduced relationship between X-ray temperatures and stellar velocity dispersions (the T-σ relation) in an optically complete sample of elliptical galaxies (see recent work of Davis & White), we demonstrate that L>L* elliptical galaxies contain substantial amounts of dark matter in general. We present constraints on the dark matter scale length and on the dark-to-luminous mass ratio within the optical half-light radius and within the entire galaxy. For example, we find that minimum values of dark matter core radii scale as rdm>4(LV/3L*)3/4 h-180 kpc and that the minimum dark matter mass fraction is 20% within one optical effective radius re and is 39%-85% within 6re, depending on the stellar density profile and observed value of βspec. We also confirm the prediction of Davis & White that the dark matter is characterized by velocity dispersions that are greater than those of the luminous stars: σ2dm≈1.4-2σ2*. The T-σ relation implies a nearly constant mass-to-light ratio within six half-light radii: M/LV≈25 h80 M☉/LV☉. This conflicts with the simplest extension of cold dark matter theories of large-scale structure formation to galactic scales; we consider several modifications that can better account for the observed T-σ relation.

Axial ratios and orientations for 100 Galactic globular star clusters

The non-spherical appearance of globular clusters was first noted by Pease and Shapley (1917) and discussed in some detail by Shapley (1930) who analyzed cluster shapes determined from star counts made by Helen Sawyer on the Franklin-Adams star charts. This classic work has provided most of the data set used in all subsequent discussions of cluster shapes. A number of studies reporting cluster shapes have appeared in the years since we began this project, the most recent of which include Geyer, Hopp and Nelles (1983), Frenk and Fall (1982), and Kadla et al. (1976, 1977).

ROSAT Temperatures and Abundances for a Complete Sample of Elliptical Galaxies

We determine X-ray temperatures and abundances for elliptical galaxies drawn from a complete, optically selected sample. The optical magnitude-limited sample consists of 43 galaxies, complete to a (corrected) B magnitude of m -->0B = 11.36. Of these, 30 have enough X-ray spectral counts to allow temperature determinations. We find that the temperatures of the X-ray-emitting gas in these elliptical galaxies are correlated with the central stellar velocity dispersions: T σ1.45; this is a shallower trend than the simple thermal relation T σ2. The diffuse gas is substantially hotter than the kinetic temperature of the luminous stars, since kT > μmpσ2 for all galaxies with measurable temperatures. This strongly indicates that dark matter halos are characterized by velocity dispersions that exceed those of the luminous stars. We see no evidence of emission from X-ray binaries becoming progressively more dominant in lower luminosity elliptical galaxies. We find that so-called supersoft sources adhere to the observed kT-σ relation, so they are no softer than expected for their velocity dispersions. We also find that interstellar medium temperatures and abundances are correlated, with the gas in hotter systems being more enriched than in cooler galaxies. However, no correlation is found between gaseous abundances and stellar abundances, as inferred from Mg2 indices.

The metal abundance and specific energy of intracluster gas

The hot gas in the cores of rich galaxy clusters is metal-rich with nearly solar abundances of metals. It is not clear whether the metals were shed from galaxies via protogalactic winds or via ram-pressure stripping. It has been suggested that if metals were injected via centrally concentrated stripping, the overall abundances could be much less than those observed in cluster cores, diminishing the degree of stellar processing required. The observed energetics of intracluster gas can be used to deduce the metal injection mechanism, which in turn may allow the global metal abundance uncertainty to be resolved in the absence of spatially resolved X-ray spectra. Existing X-ray spectral and surface brightness data for galaxy clusters indicate that the gas in cool clusters has substantially greater specific energy than could have been gained through cluster collapse. Supernovae-driven protogalactic winds can provide this extra energy, while ram-pressure stripping cannot. Such protogalactic winds will distribute metals fairly homogeneously. Much processing of gas through stars is then required, with protogalaxies losing perhaps one-half of their initial luminous mass in metal-rich winds. Furthermore, the oxygen-to-iron ratio observed in two clusters indicates that the bulk of the iron in cluster gas was produced by Type II supernovae, not Type I supernovae, as is usually supposed.

X-Ray Binaries and Globular Clusters in Elliptical Galaxies

The X-ray emission from normal elliptical galaxies has two major components: soft (kT ? 0.2-1 keV) emission from diffuse gas and harder (kT ? 6 keV) emission from populations of accreting (low mass) stellar X-ray binaries. If the low-mass X-ray binary (LMXB) population is intimately tied to the field stellar population in a galaxy, its aggregate X-ray luminosity is expected to be simply proportional to the optical luminosity of the galaxy. However, recent ASCA and Chandra X-ray observations show that the global luminosities of LMXB components in elliptical galaxies exhibit significant scatter (a factor of ~4) at a given optical luminosity. This scatter may reflect a range of evolutionary stages among X-ray binary populations in elliptical galaxies of different ages. If so, the ratio of the global LMXB X-ray luminosity to the galactic optical luminosity, LLMXB/Lopt, may in principle be used to determine when the bulk of stars were formed in individual elliptical galaxies. To test this we compare variations in LLMXB/Lopt for LMXB populations in elliptical galaxies to optically derived estimates of stellar ages in the same galaxies. We find no correlation, which suggests that variations in LLMXB/Lopt are not a good age indicator for elliptical galaxies. Alternatively, LMXBs may be formed primarily in globular clusters (through stellar tidal interactions) rather than comprise a subset of the primordial binary star population in a galactic stellar field. Since elliptical galaxies exhibit a wide range of globular cluster populations for a given galactic luminosity, this may induce a dispersion in the LMXB populations of elliptical galaxies with similar optical luminosities. Indeed, we find that LLMXB/Lopt ratios for LMXB populations are strongly correlated with the specific globular cluster frequencies in elliptical galaxies. This suggests that most LMXBs were formed in globular clusters. If so, Chandra observations of central dominant galaxies with unusually large globular cluster populations should find proportionally excessive numbers of LMXBs.

Evidence for environmental effects on early-type galaxy X-ray halos

Possible causes for the large dispersion in the X-ray luminosities (Lx) of early-type galaxies are discussed. It is shown that early-type galaxies with relatively low values of Lx for a given optical luminosity L(B) have about 50 percent more neighbors than galaxies with relatively high Lx, suggesting that low-Lx galaxies tend to be in denser environments. It is concluded that the large dispersion in X-ray luminosity, for a given L(B) might be caused either by ram-pressure stripping of the gaseous halos or by mergers. 53 refs.

Seeing Galaxies through Thick and Thin. II. Direct Measures of Extinction in Spiral Disks through Spectroscopy of Overlapping Galaxies

We use slit spectroscopy of overlapping pairs of galaxies to directly determine the extinction in disks of foreground spiral galaxies. The Doppler shifts of pair members are determined via cross-correlation, and their relative correlation amplitudes are used to separate their contributions to the combined spectra in regions of overlap. This spectroscopic approach is less subject to stringent symmetry constraints than our previous, purely photometric analyses. Extinctions of foreground members were obtained for six of the candidates in our sample of 18 mostly spiral/spiral pairs, when the signal-to-noise-ratio and velocity differences were suitable. In agreement with our previous imaging results, we find that the extinction in interarm regions is very modest, typically AB ~ 0.1 mag (corrected to face-on), while spiral arms exhibit higher extinctions of ~0.3 mag.

Star formation in X-ray cluster cooling flows

The basic equations for X-ray cluster cooling flows, including the effects of star formation, are derived. It is confirmed that cooling flows are thermally unstable, and it is found that the fastest-growing linear perturbations in the flow are radial, comoving, and isobaric. A local approximation for the star formation rate is developed which allows analytic solutions to be found for both isobaric and gravity-dominated cooling flows. These solutions are used to show how star formation reduces the gas density, thereby lowering the cooling rate, which raises the gas temperature relative to the non-star-forming case. The analytic solutions are also used to estimate the spatial distribution of newly formed stars. It is found that star formation must proceed at a nearly maximal rate if isothermal mass profiles are to result. 47 references.