1119742
Old massive ellipticals and S0 in the Hubble deep field vanish from view at z > 1.3: Possible solutions of the enigma
We have investigated the properties of a bright K-band selected sample of early-type galaxies in the Hubble Deep Field, as representative of the field galaxy population. This dataset, based on public archives from HST and from deep observations at Hawaii and Kitt-Peak, is unique as for the morphological information on faint high-z sources, and for complete photometric and spectroscopic coverage. The majority of bright early-type galaxies in this field are found at redshifts z ≤ 1.3 to share common properties with those of high-z cluster samples, as for the age and mass of the dominant stellar population – which are found to be as old as 3-5 Gyr and as massive as 10 M⊙ already at z ≃ 1. The bright end of the E/S0 population is already in place by that cosmic epoch, with space densities, masses and luminosities consistent with those of the local field population. There is no evidence of a steepening of the mass function from z=0 to z=1, as inferred by some authors from analyses of optically-selected samples and favoured by hierarchical clustering models forming most of the E/S0s at z 1.3, which would be expected as clearly detectable above the flux limits, given the aged properties of the lower redshift counterparts. So, something hide them at high redshifts. Merging could be an explanation, but it would require that already formed and old stellar systems would assemble on short timescales of Dipartimento di Astronomia, Vicolo Osservatorio 5, I-35122, Padova, Italy. E-mail: Franceschini@astrpd.pd.astro.it International School for Advanced Studies, Via Beirut, I34014 Trieste, Italy Osservatorio Astronomico, Vicolo dell’Osservatorio 5, I35122 Padova, Italy.
16695624
Far infrared and radio emission in dusty starburst galaxies
We revisit the nature of the far infrared (FIR)/radio correlation by means of the most recent models of star forming galaxies, focusing in particular on the case of obscured starbursts. We model the IR emission with our population synthesis code, GRASIL (Silva et al. 1998). For the radio emission, we revisit the simple model of Condon & Yin (1990). We find that a tight FIR/radio correlation is natural when the synchrotron mechanism dominates over the inverse Compton, and the electron cooling time is shorter than the fading time of the supernova (SN) rate. Observations indicate that both these conditions are met in star forming galaxies, from normal spirals to obscured starbursts. However, since the radio non-thermal (NT) emission is delayed, deviations are expected both in the early phases of a starburst, when the radio thermal component dominates, and in the post-starburst phase, when the bulk of the NT component originates from less massive stars. We show that this delay allows the analysis of obscured starbursts with a time resolution of a few tens of Myrs, unreachable with other star formation (SF) indicators. We suggest a strategy to complement the analysis of the deviations from the FIR/radio correlation with the radio slope (q-radio slope diagram) to obtain characteristic parameters of the burst, e.g. its intensity, age and fading time scale. The analysis of a sample of compact ULIRGs shows that they are intense but transient starbursts, to which one should not apply usual SF indicators devised for constant SF rates. We also discuss the possibility of using the q-radio slope diagram to assess the presence of obscured AGN. A firm prediction of the models is an apparent radio excess during the post-starburst phase, which seems to be typical of a class of star forming galaxies in rich cluster cores. Finally we discuss how deviations from the correlation, due to the evolutionary status of the starburst, aect the technique of photometric redshift determination widely used for high-z sources.
19031056
Panchromatic models of galaxies: GRASIL
We present here a model for simulating the panchromatic spectral energy distribution of galaxies, which aims to be a complete tool to study the complex multi‐wavelength picture of the universe. The model take into account all important components that concur to the SED of galaxies at wavelengths from X‐rays to the radio. We review the modeling of each component and provide several applications, interpreting observations of galaxy of different types at all the wavelengths.
15082408
Extragalactic source contributions to arcminute-scale Cosmic Microwave Background anisotropies
The possible contributions of the various classes of extragalactic sources (including, in addition to the canonical radio sources, GHz Peaked Spectrum sources, advection-dominated sources, starburst galaxies, high-redshift proto-spheroidal galaxies) to the arcminute scale fluctuations measured by the CBI, BIMA, and ACBAR experiments are discussed. At 30 GHz, fluctuations due to radio sources undetected by ancillary low-frequency surveys may be higher than estimated by the CBI and BIMA groups. High-redshift dusty galaxies, whose fluctuations may be strongly enhanced by the effect of clustering, could contribute to the BIMA excess signal, and dominate at 150 GHz (the ACBAR frequency). Moreover, in the present data situation, the dust emission of these high-redshift sources set an unavoidable limit to the detection of primordial CMB anisotropies at high multipoles, even at frequencies as low as $\simeq $30 GHz. It is concluded that the possibility that the excess power at high multipoles is dominated by unsubtracted extragalactic sources cannot be ruled out. On the other hand, there is room for a contribution from the Sunyaev-Zeldovich effect within clusters of galaxies, with a density fluctuation amplitude parameter $\sigma_8$ consistent with the values preferred by current data.
6720121
A Physical Model for the Coevolution of QSOs and Their Spheroidal Hosts
We present a physically motivated model for the early coevolution of massive spheroidal galaxies and active nuclei at their centers. Within dark matter halos, forming at the rate predicted by the canonical hierarchical clustering scenario, the gas evolution is controlled by gravity, radiative cooling, and heating by feedback from supernovae and from the growing active nucleus. Supernova heating is increasingly effective with decreasing binding energy in slowing down the star formation and in driving gas outflows. The more massive protogalaxies virializing at earlier times are thus the sites of the faster star formation. The correspondingly higher radiation drag fastens the angular momentum loss by the gas, resulting in a larger accretion rate onto the central black hole. In turn, the kinetic energy carried by outflows driven by active nuclei can unbind the residual gas, thus halting both the star formation and the black hole growth, in a time again shorter for larger halos. For the most massive galaxies the gas unbinding time is short enough for the bulk of the star formation to be completed before Type Ia supernovae can substantially increase the Fe abundance of the interstellar medium, thus accounting for the α-enhancement seen in the largest galaxies. The feedback from supernovae and from the active nucleus also determines the relationship between the black hole mass and the mass, or the velocity dispersion, of the host galaxy, as well as the black hole mass function. In both cases the model predictions are in excellent agreement with the observational data. Coupling the model with GRASIL (Silva et al. 1998), the code computing in a self-consistent way the chemical and spectrophotometric evolution of galaxies over a very wide wavelength interval, we have obtained predictions in excellent agreement with observations for a number of observables that proved to be extremely challenging for all the current semianalytic models, including the submillimeter counts and the corresponding redshift distributions, and the epoch-dependent K-band luminosity function of spheroidal galaxies.
210001150
Bridging the cosmic infrared background to the X-ray background
116437401
COMPASS RESULTS ON GLUON POLARISATION FROM HIGH PT HADRON PAIRS
AbstractOne of the goals of the COMPASS experiment is the determination of the gluonpolarisation ∆G/G, for a deep understanding of the spin structure of the nucleon.In DIS the gluon polarisation can be measured via the Photon-Gluon-Fusion (PGF)process, identiﬁed by open charm production or by selecting high p T hadron pairsin the ﬁnal state. The data used for this work were collected by the COMPASSexperiment during the years 2002-2004, using a 160 GeV naturally polarised positivemuon beam scattering on a polarised nucleon target. A new preliminary result of thegluon polarisation ∆G/G from high p T hadron pairs in events with Q 2 > 1 (GeV/c) 2 is presented. In order to extract ∆G/G, this analysis takes into account the leadingprocess γq contribution together with the PGF and QCD Compton processes. Anew weighted method based on a neural network approach is used. A preliminary∆G/G result for events from quasi-real photoproduction (Q 2 < 1 (GeV/c) 2 ) is alsopresented. 1 Introduction
117242696
Measurement of The Gluon Polarisation Through High $p_T$ Hadron Production in COMPASS
One of the missing keys in the present understanding of the spin structure of the nucleon is the contribution from the gluons: the so called gluon polarisation. This quantity can be determined in DIS through the Photon-Gluon Fusion (PGF) process, in which two analysis methods may be used: (i) identifying open charm events or (ii) selecting events with high pT hadrons. The data used in the present work were collected by the COMPASS Experiment, where a naturally polarised muon beam of 160 GeV, impinging on a polarised nucleon fixed target, is used. The results for the gluon polarisation from high pT are presented. The gluon polarisation result for high pT hadrons is divided, for the first time, into three independent xG bins at leading order (LO). A new weighted method based on a neural network approach is used.
125350297
COMPASS results on gluon polarisation