1,538 research outputs found
Comparison of bar strengths in optical and near-infrared for the OSUBSGS sample
We use a gravitational bar torque method to compare bar strengths (the
maximum tangential force normalized by radial force) in B and H-band images of
152 galaxies from the Ohio State University Bright Spiral Galaxy Survey. Our
main motivation is to check how much the difference in the rest-frame
wavelength could affect comparisons of bar strengths in low and high redshift
observations. Between these two bands we find an average bar strength ratio
Q_B/H= 1.25 which factor is nearly independent of the morphological type. We
show that Q_B/H > 1 is mostly due to reduced bulge dilution of radial forces in
the B-band. The bar torque method needs an estimate for the vertical scale
height of the galaxy, based on the radial scale length of the disk and the
galaxy's morphological type. Since these two might not always be possible to
determine at high redshifts in a reliable manner, we also checked that similar
results are obtained with vertical scale heights estimated from the radii
corresponding to the K-band surface brightness of 20 mag/arcsec^2. Also, we
made a simple test of the usability of the bar torque method at high redshifts
by checking the effects of image degradation (nearest neighbour sampling
without any adjustment of noise levels): we found that the estimated bar
strengths varied by +/- 10% at most as long as the total extent of the bar was
at least 10 pixels. Overall, we show that the gravitational bar torque method
should provide a proficient tool for quantifying bar strengths also at high
redshifts.Comment: 15 pages, 9 figures, 1 table, accepted to MNRA
Influence of galaxy stellar mass and observed wavelength on disc breaks in SG, NIRS0S, and SDSS data
Breaks in the surface brightness profiles in the outer regions of galactic
discs are thought to have formed by various internal and external processes,
and by studying the breaks we aim to better understand what processes are
responsible for the evolution of the outer discs. We use a large well-defined
sample to study how common the breaks are, and whether their properties depend
on galaxy stellar mass or observed wavelength. We study radial surface
brightness profiles of 753 galaxies, obtained from the images of
the Spitzer Survey of Stellar Structure in Galaxies (SG), and the
-band data from the Near InfraRed S0-Sa galaxy Survey (NIRS0S), covering a
wide range of galaxy morphologies and stellar masses. Optical SDSS or Liverpool
telescope data was used for 480 of these galaxies. We find that in low-mass
galaxies the single exponential discs (Type I) are most common, and that their
fraction decreases with increasing galaxy stellar mass. The fraction of
down-bending (Type II) discs increases with stellar mass, possibly due to more
common occurrence of bar resonance structures. The up-bending (Type III) discs
are also more common in massive galaxies. The observed wavelength affects the
scalelength of the disc of every profile type. Especially the scalelength of
the inner disc of Type II profiles increases from infrared to u-band on average
by a factor of . Consistent with the previous studies, we find that
Type II outer disc scalelengths () in late-type and low-mass galaxies are
shorter in bluer wavelengths, possibly due to stellar radial migration
populating the outer discs with old stars. In Type III discs are larger
in the u-band, hinting to the presence of young stellar population in the outer
disc. While the observed wavelength affects the disc parameters, it does not
significantly affect the profile type in our sample. (Abridged)Comment: 22 pages, 16 figures. Accepted for publication in Astronomy &
Astrophysic
Decreased Frequency of Strong Bars in S0 Galaxies: Evidence for Secular Evolution?
Using data from the Near-Infrared S0 Survey (NIRS0S) of nearby, early-type
galaxies, we examine the distribution of bar strengths in S0 galaxies as
compared to S0/a and Sa galaxies, and as compared to previously published bar
strength data for Ohio State University Bright Spiral Galaxy Survey (OSUBSGS)
spiral galaxies. Bar strengths based on the gravitational torque method are
derived from 2.2 micron Ks-band images for a statistical sample of 138 (98 S0,
40 S0/a,Sa) galaxies having a mean total blue magnitude <= 12.5 and
generally inclined less than 65 degrees. We find that S0 galaxies have weaker
bars on average than spiral galaxies in general, even compared to their closest
spiral counterparts, S0/a and Sa galaxies. The differences are significant and
cannot be due entirely to uncertainties in the assumed vertical scale-heights
or in the assumption of constant mass-to-light ratios. Part of the difference
is likely due simply to the dilution of the bar torques by the higher mass
bulges seen in S0s. If spiral galaxies accrete external gas, as advocated by
Bournaud & Combes, then the fewer strong bars found among S0s imply a lack of
gas accretion according to this theory. If S0s are stripped former spirals, or
else are evolved from former spirals due to internal secular dynamical
processes which deplete the gas as well as grow the bulges, then the weaker
bars and the prevalence of lenses in S0 galaxies could further indicate that
bar evolution continues to proceed during and even after gas depletionComment: Accepted for publication in the Astrophysical Journal, September 2010
issue (LaTex, 29 pages + 3 figures, uses aastex.cls
On the nature of the barlens component in barred galaxies: what do boxy/peanut bulges look like when viewed face-on?
Barred galaxies have interesting morphological features whose presence and
properties set constraints on galactic evolution. Here we examine barlenses,
i.e. lens-like components whose extent along the bar major axis is shorter than
that of the bar and whose outline is oval or circular. We identify and analyse
barlenses in -body plus SPH simulations, compare them extensively with those
from the NIRS0S (Near-IR S0 galaxy survey) and the SG samples (Spitzer
Survey of Stellar Structure in Galaxies) and find very good agreement. We
observe barlenses in our simulations from different viewing angles. This
reveals that barlenses are the vertically thick part of the bar seen face-on,
i.e. a barlens seen edge-on is a boxy/peanut/X bulge. In morphological studies,
and in the absence of kinematics or photometry, a barlens, or part of it, may
be mistaken for a classical bulge. Thus the true importance of classical
bulges, both in numbers and mass, is smaller than currently assumed, which has
implications for galaxy formation studies. Finally, using the shape of the
isodensity curves, we propose a rule of thumb for measuring the barlens extent
along the bar major axis of moderately inclined galaxies, thus providing an
estimate of which part of the bar is thicker.Comment: 21 pages, 11 figures, revised version as published in MNRA
Catalogue of the morphological features in the Spitzer Survey of Stellar Structure in Galaxies (SG)
A catalogue of the morphological features for the complete Spitzer Survey of
Stellar Structure in Galaxies (SG), including 2352 nearby galaxies, is
presented. The measurements are made using 3.6 m images, largely tracing
the old stellar population; at this wavelength the effects of dust are also
minimal. The measured features are the sizes, ellipticities, and orientations
of bars, rings, ringlenses, and lenses. Measured in a similar manner are also
barlenses (lens-like structures embedded in the bars), which are not lenses in
the usual sense, being rather the more face-on counterparts of the boxy/peanut
structures in the edge-on view. In addition, pitch angles of spiral arm
segments are measured for those galaxies where they can be reliably traced.
More than one pitch angle may appear for a single galaxy. All measurements are
made in a human-supervised manner so that attention is paid to each galaxy. We
used isophotal analysis, unsharp masking, and fitting ellipses to measured
structures. We find that the sizes of the inner rings and lenses normalized to
barlength correlate with the galaxy mass: the normalized sizes increase toward
the less massive galaxies; it has been suggested that this is related to the
larger dark matter content in the bar region in these systems. Bars in the low
mass galaxies are also less concentrated, likely to be connected to the mass
cut-off in the appearance of the nuclear rings and lenses. We also show
observational evidence that barlenses indeed form part of the bar, and that a
large fraction of the inner lenses in the non-barred galaxies could be former
barlenses in which the thin outer bar component has dissolved.Comment: 17 pages, 12 figures, accepted for publication in A&
The function of the endocannabinoid system and glial cells in vivo in patients with first episode psychosis
Psychoses are relatively common and often severely debilitating mental disorders with a multifactorial etiological background involving both psychosocial and biological factors. Previously reported associations between the endocannabinoid and immune systems, and psychotic disorders, suggest that they are involved in the etiology of psychosis.
Healthy individuals were studied with the selective type 1 endocannabinoid receptor (CB1R) radiotracer [18F]FMPEP-d2, and positron emission tomography (PET), for possible demographic confounders. Radiotracer synthesis and the compound’s behaviour in blood and brain tissues, were in line with reports from previous validation studies. Females had lower availabilities of CB1R than males in 17 discrete brain regions.
Separate samples of male patients with first-episode psychosis (FEP) were then studied concurrently in Turku and London, using the CB1R radiotracers [18F]FMPEP-d2 and [11C]MEPPEP respectively. Lower CB1R availability was seen in FEP as compared to healthy controls. The availability of CB1R was also inversely associated with the symptomatology of the psychoses.
Translocator protein (TSPO) expression has been postulated to represent glial cell and mitochondrial functions, both of which are influenced by endocannabinoid signalling. Another sample of male and female patients with first episode psychoses was studied using PET with the selective TSPO radiotracer [11C]PBR28. Male and female FEP subjects showed globally lower availability of brain TSPO in comparison to healthy controls. Two concurrent samples of FEP individuals showed persistent elevations of the chemokine CCL22 when compared to population controls. A subgroup of patients with the highest levels of CCL22 also had aberrant levels of other cyto- and chemokines.
These results indicate that the immune and brain endocannabinoid systems have become dysregulated in early psychosis. Aberrant glial cell function and/or disturbances in cell metabolism are indicated by the lower availability of TSPO.Endokannabinoidijärjestelmän ja gliasolujen toiminta ensipsykooseissa
Psykoosit ovat verrattain yleisiä, vakavia mielenterveyshäiriöitä, joiden syntyyn vaikuttaa sekä psykososiaaliset että biologiset tekijät. Endokannabinoidi- ja immuunijärjestelmien yhteydet psykooseihin, sekä dopamiinijärjestelmän toimintaan, viittaavat näiden järjestelmien toimivan osana psykoosien etiologiaa.
Terveiden koehenkilöiden aivojen endokannabinoidijärjestelmän toimintaa tutkittiin tyypin 1 endokannabinoidireseptorin (CB1R) merkkiaineella [18F]FMPEPd2, ja positroniemissiotomografialla (PET), mahdollisten sekoittavien tekijöiden tunnistamiseksi. Merkkiaineen tuotannon laatua kuvaavat tunnusluvut, sekä merkkiaineen käyttäytyminen veressä ja aivokudoksessa, vastasivat aiempien validointitutkimusten tuloksia. Naiskoehenkilöillä oli alhaisemmat [18F]FMPEP-d2:n jakautumistilavuudet 17 aivoalueella verrattuna miehiin.
Miespuolisten ensipsykoosipotilaiden aivojen endokannabinoidijärjestelmän toimintaa tutkittiin erikseen Turussa ja Lontoossa PET:lla vastaavasti CB1R merkkiaineilla [18F]FMPEP-d2 ja [11C]MEPPEP. Molempien otosten ensipsykoosipotilailla oli alhaisemmat merkkiaineiden jakautumistilavuudet verrattuna terveisiin koehenkilöihin. Merkkiaineen sitoutumiselle vapaat CB1R:t olivat lisäksi käänteisesti yhteydessä psykoosioireiden vaikeusasteeseen.
Aivojen tukisolujen ja näiden mitokondrioiden toimintaan vaikuttavat sekä endokannabinoidiviestintä, että translokaattoriproteiinin (TSPO) toiminta. Ensipsykoosipotilailla oli kauttaaltaan alhaisemmat TSPO PET merkkiaineen [11C]PBR28 jakautumistilavuudet verrattuna terveisiin verrokkihenkilöihin. Ensipsykoosipotilaiden kemokiini CCL22:n pitoisuudet olivat verrokkien pitoisuuksia korkeammat. Korkeimpia CCL22:n pitoisuuksia omaavien potilaiden immuuniviestintä poikkesi muista verrokki- ja potilastutkittavista laaja-alaisesti.
Nämä tulokset osoittavat, että immuuni- ja endokannabinoidijärjestelmät toimivat poikkeavasti ensipsykooseissa. TSPO:n poikkeava toiminta viittaa siihen, että aivojen tukisolut ja/tai solujen aineenvaihdunta häiriintyvät psykooseissa
On the Role of Minor Galaxy Mergers in the Formation of Active Galactic Nuclei
The large scale (~ 100 kpc) environments of Seyfert galaxies are not
significantly different from those of non-Seyfert galaxies. In the context of
the interaction model of the formation of active galactic nuclei (AGN), it has
been proposed that AGN form via "minor mergers" of large disk galaxies with
smaller companions. We test this hypothesis by comparing the nuclear spectra of
105 bright nearby galaxies with measurements of their R or r band morphological
asymmetries at three successive radii. We find no significant differences in
these asymmetries between the 13 Seyfert galaxies in the sample and galaxies
having other nuclear spectral types (absorption, H II-region like, LINER), nor
is there strong qualitative evidence that such mergers have occured among any
of the Seyferts or LINERs. Thus either any minor mergers began > 1 Gyr ago and
are essentially complete, or they did not occur at all, and AGN form
independently of any type of interaction. Support for the latter interpretation
is provided by the growing evidence that supermassive black holes exist in the
cores of most elliptical and early-type spiral galaxies, which in turn suggests
that nuclear activity represents a normal phase in the evolution of the bulges
of massive galaxies. Galaxy mergers may increase the luminosity of Seyfert
nuclei to the level of QSOs, which could explain why the latter objects appear
to be found in rich environments and in interacting systems.Comment: 13 pages, 2 figures, to appear in Astrophysical Journal Letter
Kinematics and dynamics of the M51-type galaxy pair NGC 3893/96 (KPG 302)
We study the kinematics and dynamics of the M51-type interacting galaxy pair
KPG 302 (NGC 3893/96). We analyse the distribution of the dark matter (DM) halo
of the main galaxy in order to explore possible differences between DM halos of
"isolated" galaxies and those of galaxies belonging to a pair. The velocity
field of each galaxy was obtained using scanning Fabry-Perot interferometry. A
two-dimensional kinematic and dynamical analysis of each galaxy and the pair as
a whole is done emphasizing the contribution of circular and non-circular
velocities. Non-circular motions can be traced on the rotation curves of each
galaxy allowing us to differentiate between motions associated to particular
features and motions that reflect the global mass distribution of the galaxy.
For the main galaxy of the pair, NGC 3893, optical kinematic information is
complemented with HI observations from the literature to build a
multi-wavelength rotation curve. We try to fit this curve with a
mass-distribution model using different DM halos. We find that the
multi-wavelength rotation curve of NGC 3893, "cleaned" from the effect of
non-circular motions, cannot be fitted neither by a pseudo-isothermal nor by a
NFW DM halo.Comment: Accepted for publication in A&A. 11 pages, 9 figures and 2 table
- …