14899076
On star formation in primordial protoglobular clouds.
Using a new physical model for star formation (Padoan 1995) we have tested the possibility that globular clusters (GCs) are formed from primordial mass fluctuations, whose mass scale (10 8 - 10 9 M⊙) is selected out of a CDM spectrum by the mechanism of non-equilibrium formation of H2.
17439585
Protogalactic starbursts at high redshift
We have computed the evolving ultraviolet-millimeter spectral energy distribution (SED) produced by protogalactic starbursts at high redshift, incorporating the chemical evolution of the interstellar medium in a consistent manner. Dust extinction is calculated in a novel way that is not based on empirical calibrations of extinction curves, but rather on the lifetime of molecular clouds which delays the emergence of each successive generation of stars at ultraviolet wavelengths by typically 15 Myr. The predicted rest-frame far-infrared-to-millimeter-wave emission includes the calculation of molecular emission-line luminosities (12CO and O2 among other molecules) consistent with the evolving chemical abundances. Here we present details of this new model along with the results of comparing its predictions with several high-redshift observables, namely, the ultraviolet SEDs of Lyman limit galaxies, the high-redshift radio galaxies 4C 41.17 and 8C 1435, the SCUBA submillimeter survey of the Hubble Deep Field (HDF), and the SEDs of intermediate-redshift elliptical galaxies. With our new reddening method, we are able to fit the spectrum of the Lyman limit galaxy 1512-cB58, and we find an extinction of about 1.9 mag at 1600 A. This extinction applies to starbursts with spectral slope α in the range 0 α 1.5. The model also predicts that most Lyman limit galaxies should have a value of α inside that range, as is observed. The 850 μm flux density of a typical Lyman limit galaxy is expected to be only 0.5 mJy, and therefore the optical counterparts of the most luminous submillimeter sources in the HDF (or any other currently feasible submillimeter survey) are unlikely to be Lyman break galaxies. The passive evolution of our starburst model is also compared with Keck observations of the reddest known elliptical galaxy at z ~ 1.5 and with the SED of a typical nearby elliptical galaxy. The SED of the high-redshift elliptical is nicely matched by the starburst model with an age of 4 Gyr and the SED of the nearby elliptical galaxy with an age of 13 Gyr.
15852494
Luminosity-metallicity relation for stars on the lower main sequence
We present a comparison of the predictions of stellar models with the luminosity of the lower main sequence (5.5 < MV < 7.3) using K dwarfs in the Hipparcos catalogue. The parallaxes of our comparison stars are known to better than 15 per cent and metallicities have been recently determined from photometry. A major advantage of our comparison is that distances in our sample are known with good accuracy, while tests that involve open and globular clusters are constrained by potentially inaccurate distances. We show that the luminosity of
119108970
Constraining the expansion rate of the Universe using low-redshift ellipticals as cosmic chronometers
We present a new methodology to determine the expansion history of the Universe analyzing the spectral properties of early-type galaxies (ETG), based on the study of the redshift dependence of the 4000 A break. In this paper we describe the method, explore its robustness using theoretical synthetic stellar population models, and apply it using a SDSS sample of ~ 14 000 ETGs. Our motivation to look for a new technique has been to minimize the dependence of the cosmic chronometer method on systematic errors. In particular, as a test of our method, we derive the value of the Hubble constant H0 = 72.6 ±2.9(stat)±2.3(syst) km Mpc-1s-1 (68% confidence), which is not only fully compatible with the value derived from the Hubble key project, but also with a comparable error budget. Using the SDSS, we also derive, assuming w = constant, a value for the dark energy equation of state parameter w = -1 ±0.2(stat)±0.3(syst). Given the fact that the SDSS ETG sample only reaches z ~ 0.3, this result shows the potential of the method. In future papers we will present results using the high-redshift universe, to yield a determination of H(z) up to z ~ 1.
119278213
The stellar evolution of luminous red galaxies, and its dependence on colour, redshift, luminosity and modelling
We present a series of colour-evolution models for luminous red galaxies (LRGs) in the seventh spectroscopic data release of the Sloan Digital Sky Survey (SDSS), computed using the full-spectrum fitting code vespa on high signal-to-noise ratio stacked spectra. The colour-evolution models are computed as a function of colour, luminosity and redshift, and we do not a priori assume that LRGs constitute a uniform population of galaxies in terms of stellar evolution. By computing star formation histories from the fossil record, the measured stellar evolution of the galaxies is decoupled from the survey’s selection function, which also evolves with redshift. We present these evolutionary models computed using three different sets of stellar population synthesis (SPS) codes. We show that the traditional fiducial model of purely passive stellar evolution of LRGs is broadly correct, but it is not sufficient to explain the full-spectral signature. We also find that higher-order corrections to this model are dependent on the SPS used, particularly when calculating the amount of recent star formation. The amount of young stars can be non-negligible in some cases, and has important implications for the interpretation of the number density of LRGs within the selection box as a function of redshift. Dust extinction, however, is more robust to the SPS modelling: extinction increases with decreasing luminosity, increasing redshift and increasing r − i colour. We are making the colour-evolution tracks publicly available at http://www.icg.port.ac.uk/~tojeiror/lrg_evolution/.
55296191
Fundamental physics from astronomical observations
Astronomy is a peculiar science, as one does not do experiments, it simply observes the sky. The amount of information contained in the sky is finite, thus one can wonder if observations can extract all such information, and if so, what can be learned about fundamental physics. It turns out we already have one example where all information in the sky has been extracted. This is the case of the Planck satellite and the temperature of the cosmic microwave background. This satellite has performed a cosmic variance limited observation of the full sky; nobody ever will need to repeat it. Unfortunately, we have not reached the same status with other interesting probes, such as the polarization of the cosmic microwave background and the angular postions and redshifts of galaxies. However, it is not farfetched to think that at the end of this century we will have extracted all information in the sky at most wavelengths of the electromagnetic spectrum. In any event, even today, we have already obtained significant constraints on fundamental physics using astronomical observations. Here I will describe what our current robust limits are on the mass of neutrinos, how we can discover if they are Majorana or Dirac and what can be said about the nature of dark matter. Most of the material has been presented elsewhere [1, 2, 3] and I refer the interested reader to those papers for full details.
122591819
Experimental test of the PCAC-hypothesis in charged current neutrino and antineutrino interactions on protons
Data obtained with the bubble chamber BEBC at CERN are used for the first significant test of Adler's prediction for the neutrino and antineutrino-proton scattering cross sections at vanishing four-momentum transfer squaredQ2. An Extended Vector Meson Dominance Model (EVDM) is applied to extrapolate Adler's prediction to experimentally accessible values ofQ2. The data show good agreement with Adler's prediction forQ2→0 thus confirming the PCAC hypothesis in the kinematical region of high leptonic energy transfer ν>2 GeV. The good agreement of the data with the theoretical predictions also at higherQ2, where the EVDM terms are dominant, also supports this model. However, an EVDM calculation without PCAC is clearly ruled out by the data.
122721907
Into the mix
The challenge to measure the quantum-mechanical mixing between particle and antiparticle states for a particular type of meson is at last being met — but as yet, alas, reveals no exotic physics.
178487761
The ganga user interface for physics analysis and distributed resources
117156652
Properties of Quark and Gluon Jets — a LEP Mini Review
Recent results on the structure of and differences between quark and gluon jets from the four LEP experiments are reviewed.