3,742 research outputs found
Galaxy pairs align with galactic filaments
Context. Gravitational collapse theory and numerical simulations suggest that
the velocity field within large-scale galaxy filaments is dominated by motions
along the filaments.
Aims. Our aim is to check whether observational data reveal any preferred
orientation of galaxy pairs with respect to the underlying filaments as a
result of the expectedly anisotropic velocity field.
Methods. We use galaxy pairs and galaxy filaments identified from the Sloan
Digital Sky Survey data. For filament extraction, we use the Bisous model that
is based the marked point process technique. During the filament detection, we
use the centre point of each pair instead of the positions of galaxies to avoid
a built-in influence of pair orientation on the filament construction. For
pairs lying within filaments (3012 cases), we calculate the angle between the
line connecting galaxies of each pair and their host filament. To avoid
redshift-space distortions, the angle is measured in the plain of the sky.
Results. The alignment analysis shows that the orientation of galaxy pairs
correlates strongly with their host filaments. The alignment signal is stronger
for loose pairs, with at least 25% excess of aligned pairs compared to a random
distribution. The alignment of galaxy pairs and filaments measured from the
observational data is in good concordance with the alignment in the Millennium
simulation and thus provides support to the {\Lambda}CDM formalism.Comment: 5 pages, 4 figures, accepted for publication in A&A Letter
How does the grouping scheme affect the Wiener Filter reconstruction of the local Universe?
High quality reconstructions of the three dimensional velocity and density
fields of the local Universe are essential to study the local Large Scale
Structure. In this paper, the Wiener Filter reconstruction technique is applied
to galaxy radial peculiar velocity catalogs to understand how the Hubble
constant (H0) value and the grouping scheme affect the reconstructions. While
H0 is used to derive radial peculiar velocities from galaxy distance
measurements and total velocities, the grouping scheme serves the purpose of
removing non linear motions. Two different grouping schemes (based on the
literature and a systematic algorithm) as well as five H0 values ranging from
72 to 76 km/s/Mpc are selected. The Wiener Filter is applied to the resulting
catalogs. Whatever grouping scheme is used, the larger H0 is, the larger the
infall onto the local Volume is. However, this conclusion has to be strongly
mitigated: a bias minimization scheme applied to the catalogs after grouping
suppresses this effect. At fixed H0, reconstructions obtained with catalogs
grouped with the different schemes exhibit structures at the proper location in
both cases but the latter are more contrasted in the less aggressive scheme
case: having more constraints permits an infall from both sides onto the
structures to reinforce their overdensity. Such findings highlight the
importance of a balance between grouping to suppress non linear motions and
preserving constraints to produce an infall onto structures expected to be
large overdensities. Such an observation is promising to perform constrained
simulations of the local Universe including its massive clusters.Comment: Accepted for publication in MNRAS, 10 pages, 6 figures, 3 table
Double gamma-ray lines from unassociated Fermi-LAT sources revisited
We search for the presence of double gamma-ray line from unassociated
Fermi-LAT sources including detailed Monte Carlo simulations to study its
global statistical significance. Applying the Su & Finkbeiner selection
criteria for high-energy photons we obtain a similar excess over the power-law
background from 12 unassociated sources. However, the Fermi-LAT energy
resolution and the present low statistics does not allow to distinguish a
double peak from a single one with any meaningful statistical significance. We
study the statistical significance of the fit to data with Monte Carlo
simulations and show that the fit agrees almost perfectly with the expectations
from random scan over the sky. We conclude that the claimed high-energy
gamma-ray excess over the power-law background from unassociated sources is
nothing but an artifact of the applied selection criteria and no preference to
any excess can be claimed with the present statistics.Comment: 3 pages, 1 figur
Dust-corrected surface photometry of M 31 from the Spitzer far infrared observations
We create a model for recovering the intrinsic, absorption-corrected surface
brightness distribution of a galaxy and apply the model to the M31.
We construct a galactic model as a superposition of axially symmetric stellar
components and a dust disc to analyse the intrinsic absorption efects. Dust
column density is assumed to be proportional to the far-infrared flux of the
galaxy. Along each line of sight, the observed far-infrared spectral energy
distribution is approximated with modified black body functions considering
dust components with different temperatures, allowing to determine the
temperatures and relative column densities of the dust components.
We apply the model to the nearby galaxy M31 using the Spitzer Space Telescope
far-infrared observations for mapping dust distribution and temperature. A warm
and a cold dust component are distinguished. The temperature of the warm dust
in M31 varies between 56 and 60 K and is highest in the spiral arms; the
temperature of the cold component is mostly 15-19 K and rises up to about 25 K
at the centre of the galaxy. The intensity-weighted mean temperature of the
dust decreases from T ~32 K at the centre to T ~20 K at R ~7 kpc and outwards.
We also calculate the intrinsic UBVRIL surface brightness distributions and the
spatial luminosity distribution. The intrinsic dust extinction in the V-colour
rises from 0.25 mag at the centre to 0.4-0.5 mag at R = 6-13 kpc and decreases
smoothly thereafter. The calculated total extinction-corrected luminosity of
M31 is L_B = (3.64 pm 0.15) 10^10L_sun, corresponding to an absolute luminosity
M_B = (-20.89 pm 0.04) mag. Of the total B-luminosity, 20% (0.24 mag) is
obscured from us by the dust inside M31. The intrinsic shape of the bulge is
slightly prolate in our best-fit model.Comment: 13 pages, 14 figures, accepted for publication in A&
From voids to filaments: environmental transformations of galaxies in the SDSS
We investigate the impact of filament and void environments on galaxies,
looking for residual effects beyond the known relations with environment
density. We quantified the host environment of galaxies as the distance to the
spine of the nearest filament, and compared various galaxy properties within 12
bins of this distance. We considered galaxies up to 10 Mpc from
filaments, i.e. deep inside voids. The filaments were defined by a point
process (the Bisous model) from the Sloan Digital Sky Survey data release 10.
In order to remove the dependence of galaxy properties on the environment
density and redshift, we applied weighting to normalise the corresponding
distributions of galaxy populations in each bin. After the normalisation with
respect to environment density and redshift, several residual dependencies of
galaxy properties still remain. Most notable is the trend of morphology
transformations, resulting in a higher elliptical-to-spiral ratio while moving
from voids towards filament spines, bringing along a corresponding increase in
the colour index and a decrease in star formation rate. After separating
elliptical and spiral subsamples, some of the colour index and star formation
rate evolution still remains. The mentioned trends are characteristic only for
galaxies brighter than about mag. Unlike some other recent
studies, we do not witness an increase in the galaxy stellar mass while
approaching filaments. The detected transformations can be explained by an
increase in the galaxy-galaxy merger rate and/or the cut-off of extragalactic
gas supplies (starvation) near and inside filaments. Unlike voids, large-scale
galaxy filaments are not a mere density enhancement, but have their own
specific impact on the constituent galaxies, reducing the star formation rate
and raising the chances of elliptical morphology also at a fixed environment
density level.Comment: 4 pages, 3 figures, Astronomy & Astrophysics letters accepte
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