The Fundamental Plane for early-type galaxies: dependence on the magnitude range

Studying three samples of early-type galaxies, which include approximately 8800 galaxies and cover a relatively ample magnitude range  (〈Δ M 〉∼ 5.5 mag)  , we find that the coefficients as well as the intrinsic dispersion of the Fundamental Plane depend on the width and brightness of the magnitude range within which the galaxies are distributed. We analyse this dependence, and the results show that it is due to the fact that the distribution of galaxies in the space defined by the variables     depends on the luminosity.     

New clues to the evolution of dwarf early-type galaxies

Surface photometry of 18 Virgo cluster dwarf elliptical (dE) and dwarf lenticular (dS0) galaxies, made by Gavazzi et al. in the H band (1.65 μm) and in the B band (0.44 μm), shows that the ratio of the effective radii of these stellar systems in the B and H bands,   r _{e B} / r _{e H}   , ranges between 0.7 and 2.2. In particular, dwarf ellipticals and lenticulars with a red total colour index   B - H   (i.e. with  3.2< B - H <4)  have equal effective radii in these two passbands. By contrast, blue (i.e. with  2.5< B - H <3.1)  dEs and dS0s have B -band effective radii about 50 per cent larger than the H -band ones, on average. Consistently, strong negative gradients in   B - H   along the galactocentric radius are found to be associated with blue total colours. This trend is not found in a sample of 29 giant E and S0 galaxies of the Coma cluster with analogous data available in the literature. These early-type giants span a broad range in    r _{e B} / r _{e H}    (0.2–2.2)  , with a mean   r _{e B} / r _{e H} ∼1.1  , but a narrow range in (red) colour  (3.3< B - H <4.2)  . In these stellar systems, colour gradients are usually interpreted as arising either from age/metallicity gradients along the radial coordinate or from dust attenuation, whatever the total colour of the system is. Assuming each of these three distinct interpretations of the origin of colour gradients, we discuss the origin of the association of strong negative colour gradients with blue colours found in the early-type dwarfs under study, in relation with current scenarios of formation and evolution of dE and dS0 galaxies.     

Strong size evolution of the most massive galaxies since z∼ 2

Using the combined capabilities of the large near-infrared Palomar/DEEP-2 survey, and the superb resolution of the Advanced Camera for Surveys HST camera, we explore the size evolution of 831 very massive galaxies  ( M _⋆≥ 10¹¹ h ⁻²₇₀ M_⊙)  since   z ∼ 2  . We split our sample according to their light concentration using the Sérsic index n . At a given stellar mass, both low  ( n < 2.5)  and high  ( n > 2.5)  concentrated objects were much smaller in the past than their local massive counterparts. This evolution is particularly strong for the highly concentrated (spheroid like) objects. At   z ∼ 1.5  , massive spheroid-like objects were a factor of 4 (±0.4) smaller (i.e. almost two orders of magnitudes denser) than those we see today. These small sized, high-mass galaxies do not exist in the nearby Universe, suggesting that this population merged with other galaxies over several billion years to form the largest galaxies we see today.     

The colour–magnitude relation for galaxies in the Coma cluster

We present a new photometric catalogue of the Coma galaxy cluster in the Johnson U and V bands. We cover an area of 3360 arcmin² of sky, to a depth of     in a 13-arcsec diameter aperture, and produce magnitudes for ∼1400 extended objects in metric apertures from 8.8- to 26-arcsec diameters. The mean internal rms scatter in the photometry is 0.014 mag in V , and 0.026 mag in U , for     .
We place new limits on the levels of scatter in the colour–magnitude relation (CMR) in the Coma cluster, and investigate how the slope and scatter of the CMR depend on galaxy morphology, luminosity and position within the cluster. As expected, the lowest levels of scatter are found in the elliptical galaxies, while the late-type galaxies have the highest numbers of galaxies bluewards of the CMR. We investigate whether the slope of the CMR is an artefact of colour gradients within galaxies, and show that it persists when the colours are measured within a diameter that scales with galaxy size. Looking at the environmental dependence of the CMR, we find a trend of systematically bluer galaxy colours with increasing projected radius from the centre of the cluster. Surprisingly, this is accompanied by a decreased scatter of the CMR. We investigate whether this gradient could be caused by dust in the cluster potential, however the reddening required would produce too large a scatter in the colours of the central galaxies. The gradient appears to be better reproduced by a gradient in the mean galactic ages with projected radius.     

Luminous early-type field galaxies at z∼0.4– I. Observations and redshift catalogue of 581 galaxies

We have compiled a sample of ∼ 9600 bright, i ≤18.95 , red, b _J− r >2 , candidate galaxies in an area of 220 deg². These are luminous, L > L * , field early-type galaxies with redshifts 0.3≲ z ≲0.6 . We present a redshift catalogue of a subsample of 581 targets. The galaxies were selected according to their broad-band b _J ri colours from United Kingdom Schmidt Telescope plates, and have a surface density on the sky of only ∼ 50 deg⁻². Such luminous field galaxies are virtually absent from published redshift surveys and the catalogue provides a large sample of the most luminous normal galaxies, at cosmological distances. The statistical properties of the galaxy spectra, including absorption-line and emission-line measures, are presented and a composite spectrum constructed. The nature of the sample, combined with the relatively bright apparent magnitudes, makes the galaxies suitable targets for several key investigations in galaxy evolution and cosmology.