B. Lanzoni

The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge

Globular star clusters are compact and massive stellar systems old enough to have witnessed the entire history of our Galaxy, the Milky Way. Although recent results suggest that their formation may have been more complex than previously thought, they still are the best approximation to a stellar population formed over a relatively short timescale (less than 1 Gyr) and with virtually no dispersion in the iron content. Indeed, only one cluster-like system (ω Centauri) in the Galactic halo is known to have multiple stellar populations with a significant spread in iron abundance and age. Similar findings in the Galactic bulge have been hampered by the obscuration arising from thick and varying layers of interstellar dust. Here we report that Terzan 5, a globular-cluster-like system in the Galactic bulge, has two stellar populations with different iron contents and ages. Terzan 5 could be the surviving remnant of one of the primordial building blocks that are thought to merge and form galaxy bulges.

The tilt of the fundamental plane of elliptical galaxies — I. Exploring dynamical and structural effects

In this paper we explore several structural and dynamical effects on the projected velocity dispersion as possible causes of the fundamental plane (FP) tilt of elliptical galaxies. Specifically, we determine the size of the systematic trend along the FP in the orbital radial anisotropy, in the dark matter (DM) content and distribution relative to the bright matter, and in the shape of the light profile that would be needed to produce the tilt, under the assumption of a constant stellar mass to light ratio. Spherical, non rotating, two--components models are constructed, where the light profiles resemble the

The evolution of early-type galaxies at z ∼ 1 from the K20 survey

R^{1/4}

Two distinct sequences of blue straggler stars in the globular cluster M 30

law. For the investigated models anisotropy cannot play a major role in causing the tilt, while a systematic increase in the DM content and/or concentration may formally produce it. Also a suitable variation of the shape of the light profile can produce the desired effect, and there may be some observational hints supporting this possibility. However, fine tuning is always required in order to produce the tilt, while preserving the {\it tightness} of the galaxies distribution about the FP.

Dynamical age differences among coeval star clusters as revealed by blue stragglers

We have performed VLT spectroscopy of an almost complete sample of 18 early-type galaxies with

The radial distribution of blue straggler stars and the nature of their progenitors

0.88\leq z\leq 1.3

The peculiar horizontal branch of NGC 2808

plus two at

The Importance of Dry and Wet Merging on the Formation and Evolution of Elliptical Galaxies

z=0.67

Discovery of Carbon/Oxygen-depleted Blue Straggler Stars in 47 Tucanae: The Chemical Signature of a Mass Transfer Formation Process*

, selected from the K20 survey, and derived the velocity dispersion for 15+2 of them. By combining these data with HST and VLT images, we study the Fundamental Plane (FP), the Faber–Jackson and the Kormendy relations at

Another Nonsegregated Blue Straggler Population in a Globular Cluster: the Case of NGC 2419*

z \sim 1