9,120 research outputs found
The evolution of the colour-magnitude relation and of the star formation activity in galaxy clusters since z~0.8
We present recent results on the evolution of the colour-magnitude relation
and of the star formation activity in galaxy clusters since z~0.8. Results are
based on the ESO Distant Cluster Survey (EDisCS) - an ESO large programme aimed
at the study of cluster structure and cluster galaxy evolution over a
significant fraction of cosmic time - and are discussed in the framework of the
current standard paradigm of structure formation.Comment: 8 pages, 5 figure, to appear in ASP Conference Series (Proceedings of
the 1st Subaru International Conference "Panoramic Views of Galaxy Formation
and Evolution", held in Japan, 10-15 December 2007
On the scatter in the relation between stellar mass and halo mass: random or halo formation time dependent?
The empirical HOD model of Wang et al. 2006 fits, by construction, both the
stellar mass function and correlation function of galaxies in the local
Universe. In contrast, the semi-analytical models of De Lucia & Blazoit 2007
(DLB07) and Guo et al. 2011 (Guo11), built on the same dark matter halo merger
trees than the empirical model, still have difficulties in reproducing these
observational data simultaneously. We compare the relations between the stellar
mass of galaxies and their host halo mass in the three models, and find that
they are different. When the relations are rescaled to have the same median
values and the same scatter as in Wang et al., the rescaled DLB07 model can fit
both the measured galaxy stellar mass function and the correlation function
measured in different galaxy stellar mass bins. In contrast, the rescaled Guo11
model still over-predicts the clustering of low-mass galaxies. This indicates
that the detail of how galaxies populate the scatter in the stellar mass --
halo mass relation does play an important role in determining the correlation
functions of galaxies. While the stellar mass of galaxies in the Wang et al.
model depends only on halo mass and is randomly distributed within the scatter,
galaxy stellar mass depends also on the halo formation time in semi-analytical
models. At fixed value of infall mass, galaxies that lie above the median
stellar mass -- halo mass relation reside in haloes that formed earlier, while
galaxies that lie below the median relation reside in haloes that formed later.
This effect is much stronger in Guo11 than in DLB07, which explains the
over-clustering of low mass galaxies in Guo11. Our results illustrate that the
assumption of random scatter in the relation between stellar and halo mass as
employed by current HOD and abundance matching models may be problematic in
case a significant assembly bias exists in the real Universe.Comment: 10 pages, 6 figures, published in MNRA
Radiative feedback and cosmic molecular gas: the role of different radiative sources
We present results from multifrequency radiative hydrodynamical chemistry
simulations addressing primordial star formation and related stellar feedback
from various populations of stars, stellar energy distributions (SEDs) and
initial mass functions. Spectra for massive stars, intermediate-mass stars and
regular solar-like stars are adopted over a grid of 150 frequency bins and
consistently coupled with hydrodynamics, heavy-element pollution and
non-equilibrium species calculations. Powerful massive population III stars are
found to be able to largely ionize H and, subsequently, He and He, causing
an inversion of the equation of state and a boost of the Jeans masses in the
early intergalactic medium. Radiative effects on star formation rates are
between a factor of a few and 1 dex, depending on the SED. Radiative processes
are responsible for gas heating and photoevaporation, although emission from
soft SEDs has minor impacts. These findings have implications for cosmic gas
preheating, primordial direct-collapse black holes, the build-up of "cosmic
fossils" such as low-mass dwarf galaxies, the role of AGNi during reionization,
the early formation of extended disks and angular-momentum catastrophe.Comment: 19 pages on MNRA
Unions of slices are not slices
Many approaches to slicing rely upon the 'fact' that the union of two static slices is a valid slice. It is known that static slices constructed using program dependence graph algorithms are valid slices (Reps and Yang, 1988). However, this is not true for other forms of slicing. For example, it has been established that the union of two dynamic slices is not necessarily a valid dynamic slice (Hall, 1995). In this paper this result is extended to show that the union of two static slices is not necessarily a valid slice, based on Weiser's definition of a (static) slice. We also analyse the properties that make the union of different forms of slices a valid slice
The millimeter and submillimeter laboratory spectrum of methyl formate in its ground symmetric torsional state
Over 200 rotational lines of methyl formate in its ground (v-t = 0), symmetric (A) torsional state have been measured in the frequency range 140-550 GHz. Analysis of these and lower frequency transitions permits accurate prediction (≤0.1 MHz) of over 10,000 transitions at frequencies below 600 GHz with angular momentum J ≤ 50. The measured spectral lines have permitted identification of over 100 new methyl formate lines in Orion
The laboratory millimeter-wave spectrum of methyl formate in its ground torsional E state
Over 250 rotational transitions of the internal rotor methyl formate (HCOOCH_3) in its ground v_t = 0 degenerate (E) torsional substate have been measured in the millimeter-wave spectral region. These data and a number of E-state lines identified by several other workers have been analyzed using an extension of the classical principal-axis method in the high barrier limit. The resulting rotational constants allow accurate prediction of the v_t = 0 E substate methyl formate spectrum below 300 GHz between states with angular momentum J ≤ 30 and rotational energy E_(rot)≤ 350cm^(-1). The calculated transition frequencies for the E state, when combined with the results of the previous analysis of the ground-symmetric, nondegenerate state, account for over 200 of the emission lines observed toward Orion in a recent survey of the 215-265 GHz band
Improving geophysics education for schools in the museum of Osservatorio Vesuviano - INGV
The Osservatorio Vesuviano, section of the Istituto Nazionale di Geofisica e Vulcanologia
(INGV), is the oldest vulcanological observatory worldwide, dating back
to 1841. Its outreach activities pursued two main goals: dissemination of scientific
knowledge about volcanoes and eruption forecasting, and the increase of the volcanic
risk awareness among people living in high risk active volcanoes such as Vesuvius
and Campi Flegrei
A topological approach to neural complexity
Considerable efforts in modern statistical physics is devoted to the study of
networked systems. One of the most important example of them is the brain,
which creates and continuously develops complex networks of correlated
dynamics. An important quantity which captures fundamental aspects of brain
network organization is the neural complexity C(X)introduced by Tononi et al.
This work addresses the dependence of this measure on the topological features
of a network in the case of gaussian stationary process. Both anlytical and
numerical results show that the degree of complexity has a clear and simple
meaning from a topological point of view. Moreover the analytical result offers
a straightforward algorithm to compute the complexity than the standard one.Comment: 6 pages, 4 figure
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