31 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
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
SDSS surface photometry of M 31 with absorption corrections
The objective of this work is to obtain an extinction-corrected distribution
of optical surface brightness and colour indices of the large nearby galaxy M
31 using homogeneous observational data and a model for intrinsic extinction.
We process the Sloan Digital Sky Survey (SDSS) images in ugriz passbands and
construct corresponding mosaic images, taking special care of subtracting the
varying sky background. We apply the galactic model developed in Tempel et al.
(2010) and far-infrared imaging to correct the photometry for intrinsic dust
effects.
We obtain observed and dust-corrected distributions of the surface brightness
of M 31 and a map of line-of-sight extinctions inside the galaxy. Our
extinction model suggests that either M 31 is intrinsically non-symmetric along
the minor axis or the dust properties differ from those of the Milky Way.
Assuming the latter case, we present the surface brightness distributions and
integral photometry for the Sloan filters as well as the standard UBVRI system.
We find the following intrinsic integral colour indices for M 31: (U-B)_0=0.35;
(B-V)_0=0.86; (V-R)_0=0.63; (R-I)_0=0.53; the total intrinsic
absorption-corrected luminosities of M 31 in the B and the V filters are 4.10
and 3.24 mag, respectively.Comment: 6 pages, 8 figures, accepted for publication in A&A. The
high-resolution zoomable colour image of M 31 can be seen at
http://www.aai.ee/~elmo/m31
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 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&