Distant early-type galaxies: tracers of the galaxy mass assembly evolution

We review the most recent observational results on the formation and evolution of early-type galaxies and their mass assembly by focusing on: the existence, properties and role of distant old, massive, passive systems to z~2, the stellar mass function evolution, the ``downsizing'' scenario, and the high-z precursors of massive early-type galaxies.Comment: 8 pages, 7 figures; invited review at the Workshop on "AGN and galaxy evolution", Specola Vaticana, Castel Gandolfo, Italy, 3-6 October 200

Redshift-space distortions of galaxies, clusters and AGN: testing how the accuracy of growth rate measurements depends on scales and sample selections

Redshift-space clustering anisotropies caused by cosmic peculiar velocities provide a powerful probe to test the gravity theory on large scales. However, to extract unbiased physical constraints, the clustering pattern has to be modelled accurately, taking into account the effects of non-linear dynamics at small scales, and properly describing the link between the selected cosmic tracers and the underlying dark matter field. We use a large hydrodynamic simulation to investigate how the systematic error on the linear growth rate, $f$, caused by model uncertainties, depends on sample selections and comoving scales. Specifically, we measure the redshift-space two-point correlation function of mock samples of galaxies, galaxy clusters and Active Galactic Nuclei, extracted from the Magneticum simulation, in the redshift range 0.2 < z < 2, and adopting different sample selections. We estimate $f\sigma_8$ by modelling both the monopole and the full two-dimensional anisotropic clustering, using the dispersion model. We find that the systematic error on $f\sigma_8$ depends significantly on the range of scales considered for the fit. If the latter is kept fixed, the error depends on both redshift and sample selection, due to the scale-dependent impact of non-linearities, if not properly modelled. On the other hand, we show that it is possible to get unbiased constraints on $f\sigma_8$ provided that the analysis is restricted to a proper range of scales, that depends non trivially on the properties of the sample. This can have a strong impact on multiple tracers analyses, and when combining catalogues selected at different redshifts.Comment: 17 pages, 14 figures. Accepted for publication in Astronomy & Astrophysic

Dust in high-z radio-loud AGN

We present continuum observations of a small sample of high-redshift, radio-loud AGN (radio galaxies and quasars) aimed at the detection of thermal emission from dust. Seven AGN were observed with IRAM and SEST at 1.25mm; two of them, the radio galaxies 1243+036 ($z \sim 3.6$) and MG1019+0535 ($z \sim 2.8$) were also observed at 0.8mm with the JCMT submillimetre telescope. Additional VLA observations were obtained in order to derive the spectral shape of the synchrotron radiation of MG1019+0535 at high radio frequencies. MG1019+0535 and TX0211$-$122 were expected to contain a large amount of dust based on their depleted Ly$\alpha$ emission. The observations suggest a clear 1.25-mm flux density excess over the synchrotron radiation spectrum of MG1019+0535, suggesting the presence of thermal emission from dust in this radio galaxy, whereas the observations of TX0211$-$122 were not sensitive enough to meaningfully constrain its dust content. On the other hand, our observations of 1243+036 provide a stringent upper limit on the total dust mass of $<10^8$ M$_{\odot}$. Finally, we find that the spectra of the radio-loud quasars in our sample ($2 < z < 4.5$) steepen between rest-frame radio and the far-infrared. We discuss the main implications of our results, concentrating on the dusty radio galaxy, MG1019+0535.Comment: 11 pages, A&A LaTeX, 4 figure

A methodology to select galaxies just after the quenching of star formation

We propose a new methodology aimed at finding star-forming galaxies in the phase which immediately follows the star-formation (SF) quenching, based on the use of high- to low-ionization emission line ratios. These ratios rapidly disappear after the SF halt, due to the softening of the UV ionizing radiation. We focus on [O III] $\lambda$5007/H$\alpha$ and [Ne III] $\lambda$3869/[O II] $\lambda$3727, studying them with simulations obtained with the CLOUDY photoionization code. If a sharp quenching is assumed, we find that the two ratios are very sensitive tracers as they drop by a factor $\sim$ 10 within $\sim$ 10 Myr from the interruption of the SF; instead, if a smoother and slower SF decline is assumed (i.e. an exponentially declining star-formation history with $e$-folding time $\tau=$ 200 Myr), they decrease by a factor $\sim$ 2 within $\sim$ 80 Myr. We mitigate the ionization -- metallicity degeneracy affecting our methodology using pairs of emission line ratios separately related to metallicity and ionization, adopting the [N II] $\lambda$6584/[O II] $\lambda$3727 ratio as metallicity diagnostic. Using a Sloan Digital Sky Survey galaxy sample, we identify 10 examples among the most extreme quenching candidates within the [O III] $\lambda$5007/H$\alpha$ vs. [N II] $\lambda$6584/[O II] $\lambda$3727 plane, characterized by low [O III] $\lambda$5007/H$\alpha$, faint [Ne III] $\lambda$3869, and by blue dust-corrected spectra and $(u-r)$ colours, as expected if the SF quenching has occurred in the very recent past. Our results also suggest that the observed fractions of quenching candidates can be used to constrain the quenching mechanism at work and its time-scales.Comment: Accepted for publication in MNRAS; 19 pages, 21 figures, 1 tabl

Reconstructing the galaxy density field with photometric redshifts: II. Environment-dependent galaxy evolution since z≃3z \simeq 3

Although extensively investigated, the role of the environment in galaxy formation is still not well understood. In this context, the Galaxy Stellar Mass Function (GSMF) is a powerful tool to understand how environment relates to galaxy mass assembly and the quenching of star-formation. In this work, we make use of the high-precision photometric redshifts of the UltraVISTA Survey to study the GSMF in different environments up to $z \sim 3$, on physical scales from 0.3 to 2 Mpc, down to masses of $M \sim 10^{10} M_{\odot}$. We witness the appearance of environmental signatures for both quiescent and star-forming galaxies. We find that the shape of the GSMF of quiescent galaxies is different in high- and low-density environments up to $z \sim 2$ with the high-mass end ($M \gtrsim 10^{11} M_{\odot}$) being enhanced in high-density environments. On the contrary, for star-forming galaxies a difference between the GSMF in high- and low density environments is present for masses $M \lesssim 10^{11} M_{\odot}$. Star-forming galaxies in this mass range appear to be more frequent in low-density environments up to $z < 1.5$. Differences in the shape of the GSMF are not visible anymore at $z > 2$. Our results, in terms of general trends in the shape of the GSMF, are in agreement with a scenario in which galaxies are quenched when they enter hot gas-dominated massive haloes which are preferentially in high-density environments.Comment: 18 pages, 10 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Odors, words and objects

The paper focuses on concepts and words referring to odors and to objects that have an odor. We argue that odors are an interesting object of study since they are evanescent, and since odor words do not refer to concrete and manipulable objects, but to scents evoked by objects. A second reason why odors are interesting is that some languages, as the Western ones, lack a specific odor lexicon, comparable in richness and variety to the color lexicon, and that performance on odors naming is typically worse than performance in color naming. In this work we discuss three main issues. First, we illustrate literature showing that, even if odor words do not have concrete referents, many languages encode them quite easily: the case of odors suggests that word meaning cannot be exhausted by the relationship with a referent, and highlights the importance of the social sharing of meaning. Second, we have discussed the peculiar status of odor concepts and words. Given their ambiguous status, their simple existence poses problems both to theories according to which concrete and abstract concepts do not differ, and to theories according to which they represent a dichotomy. Finally, we present an experiment in which we show that names of objects evoke their smell, and that these smells evoke approach and avoidance movements, in line with theories according to which words are grounded in both sensorial and motor systems

The search for Population III stars

Population III stars, the first generation of stars formed from primordial Big Bang material with a top-heavy IMF, should contribute substantially to the Universe reionization and they are crucial for understanding the early metal enrichment of galaxies. Therefore it is very important that these objects, foreseen by theories, are detected by observations. However PopIII stars, searched through the HeII 1640A line signature, have remained elusive. We report about the search for the HeII line in a galaxy at z=6.5, which is a very promising candidate. Unfortunately we are not yet able to show the results of this search. However we call attention to the possible detection of PopIII stars in a lensed HII dwarf galaxy at z=3.4, which appeared in the literature some years ago, but has been overlooked.Comment: Contribution for the Proceedings of the IAU Symposium No. 255 on "Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies