Stochastic contribution to the growth factor in the LCDM model

We study the effect of noise on the evolution of the growth factor of density perturbations in the context of the LCDM model. Stochasticity is introduced as a Wiener process amplified by an intensity parameter alpha. By comparing the evolution of deterministic and stochastic cases for different values of alpha we estimate the intensity level necessary to make noise relevant for cosmological tests based on large-scale structure data. Our results indicate that the presence of random forces underlying the fluid description can lead to significant deviations from the nonstochastic solution at late times for alpha>0.001.Comment: 6 pages, 1 figur

Stable isotopic analysis of atmospheric methane by infrared spectroscopy by use of diode laser difference-frequency generation

An infrared absorption spectrometer has been constructed to measure the stable isotopic composition of atmospheric methane samples. The spectrometer employs periodically poled lithium niobate to generate 15 μW of tunable difference-frequency radiation from two near-infrared diode lasers that probe the ν3 rotational-vibrational band of methane at 3.4 μm. To enhance the signal, methane is extracted from 25 l of air by use of a cryogenic chromatographic column and is expanded into the multipass cell for analysis. A measurement precision of 12‰ is demonstrated for both δ13C and δD

The XMM spectral catalog of SDSS optically selected Seyfert 2 galaxies

We present an X-ray spectroscopic study of optically selected (SDSS) Seyfert 2 (Sy2) galaxies. The goal is to study the obscuration of Sy2 galaxies beyond the local universe, using good quality X-ray spectra in combination with high S/N optical spectra for their robust classification. We analyzed all available XMM-Newton archival observations of narrow emission line galaxies that meet the above criteria in the redshift range 0.05<z<0.35. We initially selected narrow line AGN using the SDSS optical spectra and the BPT classification diagram. We further modeled and removed the stellar continuum, and we analyzed the residual emission line spectrum to exclude any possible intermediate-type Seyferts. Our final catalog comprises 31 Sy2 galaxies with median redshift z~0.1. X-ray spectroscopy is performed using the available X-ray spectra from the 3XMM and the XMMFITCAT catalogs. Implementing various indicators of obscuration, we find seven (~23%) Compton-thick AGN. The X-ray spectroscopic Compton-thick classification agrees with other commonly used diagnostics, such as the X-ray to mid-IR luminosity ratio and the X-ray to [OIII] luminosity ratio. Most importantly, we find four (~13%) unobscured Sy2 galaxies, at odds with the simplest unification model. Their accretion rates are significantly lower than the rest of our Sy2 sample, in agreement with previous studies that predict the absence of the broad line region below a certain Eddington ratio threshold.Comment: 12 pages, 6 figures, accepted for publication in A&

Molecular gas in AzTEC/C159: a star-forming disk galaxy 1.3 Gyr after the Big Bang

We studied the molecular gas properties of AzTEC/C159, a star-forming disk galaxy at z = 4.567, in order to better constrain the nature of the high-redshift end of the submillimeter-selected galaxy (SMG) population. We secured ^(12)CO molecular line detections for the J = 2 →1 and J = 5 →4 transitions using the Karl G. Jansky Very Large Array (VLA) and the NOrthern Extended Millimeter Array (NOEMA) interferometer. The broad (FWHM ~ 750 km s^(−1)) and tentative double-peaked profiles of the two ^(12)CO lines are consistent with an extended molecular gas reservoir, which is distributed in a rotating disk, as previously revealed from [CII] 158 μm line observations. Based on the 12CO(2 →1) emission line, we derived L′_(CO)=(3.4±0.6)×10^(10) K km s^(−1) pc^2, which yields a molecular gas mass of M_(H2)(α_(CO)/4.3)=(1.5±0.3)×10^(11) M⊙ and unveils a gas-rich system with μ_(gas)(α_(CO)/4.3)≡M_(H2)/M⋆=3.3±0.7. The extreme star formation efficiency of AzTEC/C159, parametrized by the ratio L_(IR)/L′_(CO)=(216±80) L⊙ (K km s^(−1) pc^2)^(−1), is comparable to merger-driven starbursts such as local ultra-luminous infrared galaxies and SMGs. Likewise, the ^(12)CO(5 →4)/CO(2 →1) line brightness temperature ratio of r_(52)= 0.55 ± 0.15 is consistent with high-excitation conditions as observed in SMGs. Based on mass budget considerations, we constrained the value for the L′_(CO) – H_2 mass conversion factor in AzTEC/C159, that is, α_(CO)=3.9_(−1.3)^(+2.7) M⊙ K^(−1) km^(−1) s pc^(−2), which is consistent with a self-gravitating molecular gas distribution as observed in local star-forming disk galaxies. Cold gas streams from cosmological filaments might be fueling a gravitationally unstable gas-rich disk in AzTEC/C159, which breaks into giant clumps and forms stars as efficiently as in merger-driven systems and generates high gas excitation. These results support the evolutionary connection between AzTEC/C159-like systems and massive quiescent disk galaxies at z ~ 2

The quality of designs by shape grammar systems and architects: a comparative test on refurbishing Lisbon’s Rabo-de-Bacalhau apartments

This paper compares the quality of designs generated by shape grammar systems with designs created by professional architects. It describes an experiment in which evaluators ranked the quality of preliminary designs for refurbishing Lisbon's rabo-de-bacalhau apartments. The result showed that the design quality of the grammar solutions for the task was similar to that of the designs by professional architects. Thus, this paper argues that shape grammars can be used as stand-alone design systems in architecture. The practical value is that shape grammar systems become alternative means of taking up design challenges that currently require too much effort by architects to be economically feasible, such as refurbishing all of Lisbon's rabo-de-bacalhau apartments.info:eu-repo/semantics/acceptedVersio