26 research outputs found
Correlation function: biasing and fractal properties of the cosmic web
We calculated spatial correlation functions of galaxies, , structure
functions, , gradient functions, , and fractal dimension functions, , using dark
matter particles of the biased cold dark matter (CDM) simulation,
observed galaxies of the Sloan Digital Sky Survey (SDSS), and simulated
galaxies of the Millennium and EAGLE simulations. We analysed how these
functions describe fractal and biasing properties of the cosmic web. The
correlation functions of the biased CDM model samples at small
distances (particle and galaxy separations), ~\Mpc, describe the
distribution of matter inside dark matter (DM) halos. In real and simulated
galaxy samples, only the brightest galaxies in clusters are visible, and the
transition from clusters to filaments occurs at a distance ~\Mpc. Real and simulated galaxies of low luminosity, , have
almost identical correlation lengths and amplitudes, indicating that dwarf
galaxies are satellites of brighter galaxies, and do not form a smooth
population in voids. The combination of several physical processes (e.g. the
formation of halos along the caustics of particle trajectories and the phase
synchronisation of density perturbations on various scales) transforms the
initial random density field to the current highly non-random density field.
Galaxy formation is suppressed in voids, which increases the amplitudes of
correlation functions and power spectra of galaxies, and increases the
large-scale bias parameter. The combined evidence leads to the large-scale bias
parameter of galaxies the value . We find
for the correlation length of
galaxies.Comment: 15 pages, 10 figures, 5 tables. The revised version is accepted by
Astronomy & Astrophysic
An EAGLE view of the missing baryons
Context. A significant fraction of the predicted baryons remain undetected in the local Universe. We adopted the common assumption that a large fraction of the missing baryons correspond to the hot (log T(K) = 5.5–7) phase of the warm-hot intergalactic medium (WHIM). We base our missing baryons search on the scenario whereby the WHIM has been heated up via accretion shocks and galactic outflows, and it is concentrated towards the filaments of the cosmic web.
Aims. Our aim is to improve the observational search for the poorly detected hot WHIM.
Methods. We detected the filamentary structure within the EAGLE hydrodynamical simulation by applying the Bisous formalism to the galaxy distribution. To test the reliability of our results, we used the MMF/NEXUS+ classification of the large-scale environment of the dark matter component in EAGLE. We then studied the spatio-thermal distribution of the hot baryons within the extracted filaments.
Results. While the filaments occupy only ≈5% of the full simulation volume, the diffuse hot intergalactic medium in filaments amounts to ≈23%−25% of the total baryon budget, or ≈79%−87% of all the hot WHIM. The optimal filament sample, with a missing baryon mass fraction of ≈82%, is obtained by selecting Bisous filaments with a high galaxy luminosity density. For these filaments, we derived analytic formulae for the radial gas density and temperature profiles, consistent with recent Planck Sunyaev-Zeldovich and cosmic microwave background lensing observations within the central r ≈ 1 Mpc.
Conclusions. Results from the EAGLE simulation suggest that the missing baryons are strongly concentrated towards the filament axes. Since the filament finding methods used here are applicable to galaxy surveys, a large fraction of the missing baryons can be localised by focusing the observational efforts on the central ∼1 Mpc regions of the filaments. To optimise the observational signal, it is beneficial to focus on the filaments with the highest galaxy luminosity densities detected in the optical data
An EAGLE view of the missing baryons
Context. A significant fraction of the predicted baryons remain undetected in the local Universe. We adopted the common assumption that a large fraction of the missing baryons correspond to the hot (log T(K) = 5.5–7) phase of the warm-hot intergalactic medium (WHIM). We base our missing baryons search on the scenario whereby the WHIM has been heated up via accretion shocks and galactic outflows, and it is concentrated towards the filaments of the cosmic web.Aims. Our aim is to improve the observational search for the poorly detected hot WHIM.Methods. We detected the filamentary structure within the EAGLE hydrodynamical simulation by applying the Bisous formalism to the galaxy distribution. To test the reliability of our results, we used the MMF/NEXUS+ classification of the large-scale environment of the dark matter component in EAGLE. We then studied the spatio-thermal distribution of the hot baryons within the extracted filaments.Results. While the filaments occupy only ≈5% of the full simulation volume, the diffuse hot intergalactic medium in filaments amounts to ≈23%−25% of the total baryon budget, or ≈79%−87% of all the hot WHIM. The optimal filament sample, with a missing baryon mass fraction of ≈82%, is obtained by selecting Bisous filaments with a high galaxy luminosity density. For these filaments, we derived analytic formulae for the radial gas density and temperature profiles, consistent with recent Planck Sunyaev-Zeldovich and cosmic microwave background lensing observations within the central r ≈ 1 Mpc.Conclusions. Results from the EAGLE simulation suggest that the missing baryons are strongly concentrated towards the filament axes. Since the filament finding methods used here are applicable to galaxy surveys, a large fraction of the missing baryons can be localised by focusing the observational efforts on the central ∼1 Mpc regions of the filaments. To optimise the observational signal, it is beneficial to focus on the filaments with the highest galaxy luminosity densities detected in the optical data.</p
A pulsation analysis of K2 observations of the subdwarf B star PG 1142-037 during Campaign 1 : A subsynchronously rotating ellipsoidal variable
We report a new subdwarf B pulsator, PG 1142-037, discovered during the first full-length campaign of K2, the two-gyro mission of the Kepler space telescope. 14 periodicities have been detected between 0.9 and 2.5 hr with amplitudes below 0.35 parts-per-thousand. We have been able to associate all of the pulsations with low-degree, 1Peer reviewe
The Astropy Problem
The Astropy Project (http://astropy.org) is, in its own words, "a community
effort to develop a single core package for Astronomy in Python and foster
interoperability between Python astronomy packages." For five years this
project has been managed, written, and operated as a grassroots,
self-organized, almost entirely volunteer effort while the software is used by
the majority of the astronomical community. Despite this, the project has
always been and remains to this day effectively unfunded. Further, contributors
receive little or no formal recognition for creating and supporting what is now
critical software. This paper explores the problem in detail, outlines possible
solutions to correct this, and presents a few suggestions on how to address the
sustainability of general purpose astronomical software
Costs and benefits of automation for astronomical facilities
The Observatorio Astrof\'isico de Javalambre (OAJ{\dag}1) in Spain is a young
astronomical facility, conceived and developed from the beginning as a fully
automated observatory with the main goal of optimizing the processes in the
scientific and general operation of the Observatory. The OAJ has been
particularly conceived for carrying out large sky surveys with two
unprecedented telescopes of unusually large fields of view (FoV): the JST/T250,
a 2.55m telescope of 3deg field of view, and the JAST/T80, an 83cm telescope of
2deg field of view. The most immediate objective of the two telescopes for the
next years is carrying out two unique photometric surveys of several thousands
square degrees, J-PAS{\dag}2 and J-PLUS{\dag}3, each of them with a wide range
of scientific applications, like e.g. large structure cosmology and Dark
Energy, galaxy evolution, supernovae, Milky Way structure, exoplanets, among
many others. To do that, JST and JAST are equipped with panoramic cameras under
development within the J-PAS collaboration, JPCam and T80Cam respectively,
which make use of large format (~ 10k x 10k) CCDs covering the entire focal
plane. This paper describes in detail, from operations point of view, a
comparison between the detailed cost of the global automation of the
Observatory and the standard automation cost for astronomical facilities, in
reference to the total investment and highlighting all benefits obtained from
this approach and difficulties encountered. The paper also describes the
engineering development of the overall facilities and infrastructures for the
fully automated observatory and a global overview of current status,
pinpointing lessons learned in order to boost observatory operations
performance, achieving scientific targets, maintaining quality requirements,
but also minimizing operation cost and human resources.Comment: Global Observatory Control System GOC
A pulsation analysis of K2 observations of the subdwarf B star PG 1142-037 during Campaign 1: A subsynchronously rotating ellipsoidal variable
Contains fulltext :
157925.pdf (preprint version ) (Open Access