1,414 research outputs found
Muons tomography applied to geosciences and volcanology
Imaging the inner part of large geological targets is an important issue in
geosciences with various applications. Dif- ferent approaches already exist
(e.g. gravimetry, electrical tomography) that give access to a wide range of
informations but with identified limitations or drawbacks (e.g. intrinsic
ambiguity of the inverse problem, time consuming deployment of sensors over
large distances). Here we present an alternative and complementary tomography
method based on the measurement of the cosmic muons flux attenuation through
the geological structures. We detail the basics of this muon tomography with a
special emphasis on the photo-active detectors.Comment: Invited talk at the 6th conference on New Developments In
Photodetection (NDIP'11), Lyon-France, July 4-8, 2011; Nuclear Instruments
and Methods in Physics Research Section A, 201
Massive galaxies at redshift 2 in cosmological hydrodynamic simulations
We study the properties of galaxies at z=2 in a Lambda cold dark matter
universe, using two different types of hydrodynamic simulation methods --
Eulerian TVD and smoothed particle hydrodynamics (SPH) -- and a
spectrophotometric analysis in the U_n, G, R filter set. The simulated galaxies
at z=2 satisfy the color-selection criteria proposed by Adelberger et al.
(2004) and Steidel et al. (2004) when we assume Calzetti extinction with
E(B-V)=0.15. We find that the number density of simulated galaxies brighter
than R<25.5 at z=2 is about 1e-2 h^3 Mpc^-3 for E(B-V)=0.15, which is roughly
twice that of the number density found by Erb et al. (2004) for the UV bright
sample. This suggests that roughly half of the massive galaxies with M*>10^{10}
Msun/h at z=2 are UV bright population, and the other half is bright in the
infra-red wavelengths. The most massive galaxies at z=2 have stellar masses >=
10^{11-12} Msun. They typically have been continuously forming stars with a
rate exceeding 30 Msun/yr over a few Gyrs from z=10 to z=2, together with
significant contribution by starbursts reaching up to 1000 Msun/yr which lie on
top of the continuous component. TVD simulations indicate a more sporadic star
formation history than the SPH simulations. Our results do not imply that
hierarchical galaxy formation fails to account for the observed massive
galaxies at z>=1. The global star formation rate density in our simulations
peaks at z>=5, a much higher redshift than predicted by the semianalytic
models. This star formation history suggests early build-up of the stellar mass
density, and predicts that 70 (50, 30)% of the total stellar mass at z=0 had
already been formed by z=1 (2, 3). Upcoming observations by Spitzer and Swift
might help to better constrain the star formation history at high redshift.Comment: 4 pages, Kluwer style files included. To appear in "Starbursts - from
30 Doradus to Lyman break galaxies" (IoA, Cambridge UK, Sep 2004; talk
summary), Astrophysics & Space Science Library, eds. de Grijs R., Gonzalez
Delgado R.M. (Kluwer: Dordrecht
Imaging the cool gas, dust, star formation, and AGN in the first galaxies
When, and how, did the first galaxies and supermassive black holes (SMBH)
form, and how did they reionization the Universe? First galaxy formation and
cosmic reionization are among the last frontiers in studies of cosmic structure
formation. We delineate the detailed astrophysical probes of early galaxy and
SMBH formation afforded by observations at centimeter through submillimeter
wavelengths. These observations include studies of the molecular gas (= the
fuel for star formation in galaxies), atomic fine structure lines (= the
dominant ISM gas coolant), thermal dust continuum emission (= an ideal star
formation rate estimator), and radio continuum emission from star formation and
relativistic jets. High resolution spectroscopic imaging can be used to study
galaxy dynamics and star formation on sub-kpc scales. These cm and mm
observations are the necessary compliment to near-IR observations, which probe
the stars and ionized gas, and X-ray observations, which reveal the AGN.
Together, a suite of revolutionary observatories planned for the next decade
from centimeter to X-ray wavelengths will provide the requisite panchromatic
view of the complex processes involved in the formation of the first generation
of galaxies and SMBHs, and cosmic reionization.Comment: 8 pages total. White paper submitted to the Astro 2010 Decadal Surve
The Galaxy Mass Function up to z=4 in the GOODS-MUSIC sample: into the epoch of formation of massive galaxies
The goal of this work is to measure the evolution of the Galaxy Stellar Mass
Function and of the resulting Stellar Mass Density up to redshift ~4, in order
to study the assembly of massive galaxies in the high redshift Universe. We
have used the GOODS-MUSIC catalog, containing ~3000 Ks-selected galaxies with
multi-wavelength coverage extending from the U band to the Spitzer 8 micron
band, of which 27% have spectroscopic redshifts and the remaining fraction have
accurate photometric redshifts. On this sample we have applied a standard
fitting procedure to measure stellar masses. We compute the Galaxy Stellar Mass
Function and the resulting Stellar Mass Density up to redshift ~4, taking into
proper account the biases and incompleteness effects. Within the well known
trend of global decline of the Stellar Mass Density with redshift, we show that
the decline of the more massive galaxies may be described by an exponential
timescale of ~6 Gyrs up to z~1.5, and proceeds much faster thereafter, with an
exponential timescale of ~0.6 Gyrs. We also show that there is some evidence
for a differential evolution of the Galaxy Stellar Mass Function, with low mass
galaxies evolving faster than more massive ones up to z~1-1.5 and that the
Galaxy Stellar Mass Function remains remarkably flat (i.e. with a slope close
to the local one) up to z~1-1.3. The observed behaviour of the Galaxy Stellar
Mass Function is consistent with a scenario where about 50% of present-day
massive galaxies formed at a vigorous rate in the epoch between redshift 4 and
1.5, followed by a milder evolution until the present-day epoch.Comment: accepted for publication in A&A. Uses aa.cls, 15 pages, 11 figures.
The observed mass functions are available in electronic form at
http://lbc.oa-roma.inaf.it/goods/massfunctio
Topology of structure in the Sloan Digital Sky Survey: model testing
We measure the three-dimensional topology of large-scale structure in the
Sloan Digital Sky Survey (SDSS). This allows the genus statistic to be measured
with unprecedented statistical accuracy. The sample size is now sufficiently
large to allow the topology to be an important tool for testing galaxy
formation models. For comparison, we make mock SDSS samples using several
state-of-the-art N-body simulations: the Millennium run of Springel et al.
(2005)(10 billion particles), Kim & Park (2006) CDM models (1.1 billion
particles), and Cen & Ostriker (2006) hydrodynamic code models (8.6 billion
cell hydro mesh). Each of these simulations uses a different method for
modeling galaxy formation. The SDSS data show a genus curve that is broadly
characteristic of that produced by Gaussian random phase initial conditions.
Thus the data strongly support the standard model of inflation where Gaussian
random phase initial conditions are produced by random quantum fluctuations in
the early universe. But on top of this general shape there are measurable
differences produced by non-linear gravitational effects (cf. Matsubara 1994),
and biasing connected with galaxy formation. The N-body simulations have been
tuned to reproduce the power spectrum and multiplicity function but not
topology, so topology is an acid test for these models. The data show a
``meatball'' shift (only partly due to the Sloan Great Wall of Galaxies; this
shift also appears in a sub-sample not containing the Wall) which differs at
the 2.5\sigma level from the results of the Millennium run and the Kim & Park
dark halo models, even including the effects of cosmic variance.Comment: 13 Apj pages, 7 figures High-resolution stereo graphic available at
http://www.astro.princeton.edu/~dclayh/stereo50.ep
Muon radiography and deformation analysis of the lava dome formed by the 1944 eruption of Usu, Hokkaido âContact between high-energy physics and volcano physicsâ
Lava domes are one of the conspicuous topographic features on volcanoes. The subsurface structure of the lava dome is important to discuss its formation mechanism. In the 1944 eruption of Volcano Usu, Hokkaido, a new lava dome was formed at its eastern foot. After the completion of the lava dome, various geophysical methods were applied to the dome to study its subsurface structure, but resulted in a rather ambiguous conclusion. Recently, from the results of the levelings, which were repeated during the eruption, âpseudo growth curvesâ of the lava dome were obtained. The curves suggest that the lava dome has a bulbous shape. In the present work, muon radiography, which previously proved effective in imaging the internal structure of Volcano Asama, has been applied to the Usu lava dome. The muon radiography measures the distribution of the âdensity lengthâ of volcanic bodies when detectors are arranged properly. The result obtained is consistent with the model deduced from the pseudo growth curves. The measurement appears to afford useful method to clarify the subsurface structure of volcanoes and its temporal changes, and in its turn to discuss volcanic processes. This is a point of contact between high-energy physics and volcano physics
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