30 research outputs found
Photometric redshift galaxies as tracers of the filamentary network
Galaxy filaments are the dominant feature in the overall structure of the
cosmic web. The study of the filamentary web is an important aspect in
understanding galaxy evolution and the evolution of matter in the Universe. A
map of the filamentary structure is an adequate probe of the web. We propose
that photometric redshift galaxies are significantly positively associated with
the filamentary structure detected from the spatial distribution of
spectroscopic redshift galaxies. The catalogues of spectroscopic and
photometric galaxies are seen as point-process realisations in a sphere, and
the catalogue of filamentary spines is proposed to be a realisation of a random
set in a sphere. The positive association between these sets was studied using
a bivariate function, which is a summary statistics studying clustering. A
quotient was built to estimate the distance distribution of the filamentary
spine to galaxies in comparison to the distance distribution of the filamentary
spine to random points in dimensional Euclidean space. This measure gives a
physical distance scale to the distances between filamentary spines and the
studied sets of galaxies. The bivariate function shows a statistically
significant clustering effect in between filamentary spines and photometric
redshift galaxies. The quotient confirms the previous result that smaller
distances exist with higher probability between the photometric galaxies and
filaments. The trend of smaller distances between the objects grows stronger at
higher redshift. Additionally, the quotient for photometric galaxies gives
a rough estimate for the filamentary spine width of about ~Mpc. Photometric
redshift galaxies are positively associated with filamentary spines detected
from the spatial distribution of spectroscopic galaxies.Comment: Accepted to Astronomy & Astrophysics. 13 pages and 9 figure
Spiral arms and disc stability in the Andromeda galaxy
Aims: Density waves are often considered as the triggering mechanism of star
formation in spiral galaxies. Our aim is to study relations between different
star formation tracers (stellar UV and near-IR radiation and emission from HI,
CO and cold dust) in the spiral arms of M31, to calculate stability conditions
in the galaxy disc and to draw conclusions about possible star formation
triggering mechanisms.
Methods: We select fourteen spiral arm segments from the de-projected data
maps and compare emission distributions along the cross sections of the
segments in different datasets to each other, in order to detect spatial
offsets between young stellar populations and the star forming medium. By using
the disc stability condition as a function of perturbation wavelength and
distance from the galaxy centre we calculate the effective disc stability
parameters and the least stable wavelengths at different distances. For this we
utilise a mass distribution model of M31 with four disc components (old and
young stellar discs, cold and warm gaseous discs) embedded within the external
potential of the bulge, the stellar halo and the dark matter halo. Each
component is considered to have a realistic finite thickness.
Results: No systematic offsets between the observed UV and CO/far-IR emission
across the spiral segments are detected. The calculated effective stability
parameter has a minimal value Q_{eff} ~ 1.8 at galactocentric distances 12 - 13
kpc. The least stable wavelengths are rather long, with the minimal values
starting from ~ 3 kpc at distances R > 11 kpc.
Conclusions: The classical density wave theory is not a realistic explanation
for the spiral structure of M31. Instead, external causes should be considered,
e.g. interactions with massive gas clouds or dwarf companions of M31.Comment: 12 pages, 8 figures, Astron & Astrophys accepte
The bivariate J-function to analyse positive association between galaxies and galaxy filaments
International audienceThe compelling and intrinsic network of galaxies builds up a complex structure for the Universe. In this work positive association between long bridging structures named galaxy filaments and a photometric redshift galaxy dataset is under investigation. Possible positive association is studied by the use of a bivariate J-function.Le réseau de filaments formé par la position des galaxies est une des structures les plus fascinantes dans notre Univers. Dans cet article, nous étudions des possibles associations entre le réseau de filaments déjà détecté et des nouvelles observations. Ces observations trÚs récentes sont obtenues à partir des mesures du décalage vers le rouge photométrique. L'utilisation de la fonction J-bivariée tend à indiquer une association positive entre les filaments existants et les nouvelles observations
NikotiinisÔltuvuse ravi bupropiooniga kroonilise bronhiidiga haigetel
Sigareti suitsetamisest loobumisel vĂ”ib krooniline bronhiit kaduda ja kopsu funktsiooni kiire halvenemine peatuda. Ainult oma tahtejĂ”uga Ă”nnestub pĂŒsiv loobumine saavutada vĂ€hem kui 6%-l. Bupropioon SR oma noradrenergilise ja dopaminergilise toimega on aidanud efektiivselt suitsetamisest loobumisel. Uuringu eesmĂ€rk oli hinnata bupropiooni efektiivsust, ohutust ja talutavust kroonilise bronhiidiga isikutel. Bupropioon SR osutus tĂ”husaks ja hĂ€sti talutavaks abivahendiks suitsetamisest loobumisel krooniliste bronhiidihaigete hulgas, pĂ”hjustades sarnast kĂ”rvaltoimete esinemist vĂ”rreldes ĂŒldrahvastiku uuringutega. Isikud, kes ei lĂ”petanud suitsetamist, vĂ€hendasid oluliselt suitsetatud sigarettide arvu raviperioodi vĂ€ltel.
Eesti Arst 2006; 85 (6): 354â36
Quantifying torque from the Milky Way bar using Gaia DR2
We determine the mass of the Milky Way bar and the torque it causes, using
Gaia DR2, by applying the orbital arc method. Based on this, we have found that
the gravitational acceleration is not directed towards the centre of our Galaxy
but a few degrees away from it. We propose that the tangential acceleration
component is caused by the bar of the Galaxy. Calculations based on our model
suggest that the torque experienced by the region around the Sun is per solar mass. The mass estimate for the bar is . Using greatly improved data from Gaia DR2, we
have computed the acceleration field to great accuracy by adapting the oPDF
method (Han et al. 2016) locally and used the phase space coordinates of stars within a distance of 0.5 kpc from the Sun. In the orbital
arc method, the first step is to guess an acceleration field and then
reconstruct the stellar orbits using this acceleration for all the stars within
a specified region. Next, the stars are redistributed along orbits to check if
the overall phase space distribution has changed. We repeat this process until
we find an acceleration field that results in a new phase space distribution
that is the same as the one that we started with; we have then recovered the
true underlying acceleration.Comment: 12 pages, 6 figures, accepted to MNRA
The role of stochastic and smooth processes in regulating galaxy quenching
Galaxies can be classified as passive ellipticals or star-forming discs.
Ellipticals dominate at the high end of the mass range, and therefore there
must be a mechanism responsible for the quenching of star-forming galaxies.
This could either be due to the secular processes linked to the mass and star
formation of galaxies or to external processes linked to the surrounding
environment. In this paper, we analytically model the processes that govern
galaxy evolution and quantify their contribution. We have specifically studied
the effects of mass quenching, gas stripping, and mergers on galaxy quenching.
To achieve this, we first assumed a set of differential equations that describe
the processes that shape galaxy evolution. We then modelled the parameters of
these equations by maximising likelihood. These equations describe the
evolution of galaxies individually, but the parameters of the equations are
constrained by matching the extrapolated intermediate-redshift galaxies with
the low-redshift galaxy population. In this study, we modelled the processes
that change star formation and stellar mass in massive galaxies from the GAMA
survey between z~0.4 and the present. We identified and quantified the
contributions from mass quenching, gas stripping, and mergers to galaxy
quenching. The quenching timescale is on average 1.2 Gyr and a closer look
reveals support for the slow-then-rapid quenching scenario. The major merging
rate of galaxies is about once per 10~Gyr, while the rate of ram pressure
stripping is significantly higher. In galaxies with decreasing star formation,
we show that star formation is lost to fast quenching mechanisms such as ram
pressure stripping and is countered by mergers, at a rate of about 41%
Gyr and to mass quenching 49% Gyr. (abridged)Comment: 12 pages, 10 figures, accepted to A&