The Star Formation History of Ellipticals from the Fossil Evidence

Mid-infrared observations (3.6 - 24 microns) of normal giant elliptical galaxies with the Spitzer space telescope are consistent with pure populations of very old stars with no evidence of younger stars. Most of the stars in giant elliptical galaxies are old but the mean stellar age determined from Balmer absorption in optical spectra can appear much younger due to a small admixture of younger stars. The mean stellar age can also be determined from the spectral energy distrib...

Major progress has been achieved in recent years in mapping the properties of passively-evolving, early-type galaxies (ETG) from the local universe all the way to redshift ~2. Here, age and metallicity estimates for local cluster and field ETGs are reviewed as based on color-magnitude, color-sigma, and fundamental plane relations, as well as on spectral-line indices diagnostics. The results of applying the same tools at high redshifts are then discussed, and their consistency...

How elliptical galaxy dynamics relate to galaxy structure, stellar populations, spiral galaxies and environment are reviewed. The evidence assembled shows that most, if not all, galaxies originally classified as gE contain disks within them. Taken together, the existing evidence are most consistent with the gravitational, hierarchical, clustering, merging (HCM) concept that all galaxies, including gE, are formed from the combination of much smaller galaxies. Within the HCM pi...

Massive galaxies, such as nearby ellipticals, have relatively low number densities, yet they host the majority of the stellar mass in the universe. Understanding their origin is a central problem of galaxy formation. Age dating of stellar populations found in modern ellipticals, and observations of star formation in high redshift galaxies, allow us to determine roughly when these systems formed. These age diagnostics however do not tell us what triggered star formation, or ho...

The last decade of research on elliptical galaxies has produced a wealth of new information concerning both their detailed structure and their global scaling relations. We review the old and new results about isophote shapes and subcomponents (Sect. 1), scaling relations of global parameters and redshift evolution (Sect. 2), and the ages, metallicities (Sect. 3) and abundance ratios (Sect. 4). Finally, we confront the observations with hierarchical formation scenarios of elli...

I review recent progress in exploring the formation times of spheroidal stellar populations (elliptical galaxies and large spiral bulges) using spectrophotometric techniques. A quickly growing body of evidence shows that although massive spheroids can form at early times, there are strong environmental dependencies, and major transitions in star formation histories and even morphologies are detectable to surprisingly small redshifts (z ~ 0.2). These features are consistent wi...

I will present recent theoretical results on the formation and the high redshift assembly of spheroids. These findings have been obtained by utilising different and complementary techniques: chemodynamical models offer great insight in the radial abundance gradients in the stars; while state semi-analytic codes implementing a detailed treatment of the chemical evolution allow an exploration of the role of the galactic mass in shaping many observed relations. The results will ...

Small amounts of star formation in elliptical galaxies are suggested by several results: surprisingly young ages from optical line indices, cooling X-ray gas, and mid-IR dust emission. Such star formation has previously been difficult to directly detect, but using UV Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging, we have identified individual young stars and star clusters in four nearby ellipticals. This technique is orders of magnitude more sensitive than o...

We present optical VLT spectroscopy of 16 dwarf elliptical galaxies (or dEs) comparable in mass to NGC 205, and belonging to the Fornax cluster and to nearby groups of galaxies. Using ULySS and STECKMAP, we derive radial profiles of the SSP-equivalent ages, metallicities and star-formation histories. The old stellar population of the dEs, which dominates their mass, is likely coeval with that of massive ellipticals or bulges, but the star formation efficiency is lower. Import...

We present near-IR spectroscopy of three Extremely Red Objects (EROs) using the OHS/CISCO spectrograph at Subaru telescope. One target exhibits a strong emission line which we identify as H-alpha at z = 1.34. Using new and existing ground-based optical and near-IR imaging, and archival HST imaging, we argue that this target is essentially an elliptical galaxy, with an old stellar population of around 4E11 solar masses, but having a dust-enshrouded star-forming component with ...