699 research outputs found
A break in the high-redshift stellar mass Tully-Fisher relation
We investigate the stellar-mass Tully-Fisher relation (TFR) between the
stellar mass and the integrated gas velocity dispersion, quantified by the
kinematic estimator S_0.5 measured from strong emission lines in spectra of
galaxies at 0<z<5. We combine luminosity-selected galaxies (`high-luminosity
sample') with galaxies selected in other ways (`low-luminosity sample') to
cover a range in stellar mass that spans almost five orders of magnitude: 7.0 <
log M* < 11.5. We find that the logarithmic power-law slope and normalisation
of the TFR are independent of redshift out to z~3. The scatter in the TFR is
<0.5 dex such that the gas velocity dispersion can be used as a proxy for the
stellar mass of a galaxy independently of its redshift. At z>3 the scatter
increases and the existence of a correlation is not obvious. The
high-luminosity sample exhibits a flatter slope of 1.50.2 at z<3 compared
to the low-luminosity sample slope of 2.90.3, suggesting a turnover in the
TFR. The combined sample is well fit with a break in the TFR at a
characteristic stellar mass scale of M*~10 M, with no
significant evolution out to z~3. We demonstrate that a break in the TFR with a
steeper slope at the low-mass end is a natural consequence of galaxy models
with a mass-dependent stellar to halo-mass ratio.Comment: 12 pages, Accepted for publication in MNRA
Merging galaxies produce outliers from the Fundamental Metallicity Relation
From a large sample of local SDSS galaxies, we find that
the Fundamental Metallicity Relation (FMR) has an overabundance of outliers,
compared to what would be expected from a Gaussian distribution of residuals,
with significantly lower metallicities than predicted from their stellar mass
and star formation rate (SFR). This low-metallicity population has lower
stellar masses, bimodial specific SFRs with enhanced star formation within the
aperture and smaller half-light radii than the general sample, and is hence a
physically distinct population. We show that they are consistent with being
galaxies that are merging or have recently merged with a satellite galaxy. In
this scenario, low-metallicity gas flows in from large radii, diluting the
metallicity of star-forming regions and enhancing the specific SFR until the
inflowing gas is processed and the metallicity has recovered. We introduce a
simple model in which mergers with a mass ratio larger than a minimum dilute
the central galaxy's metallicity by an amount that is proportional to the
stellar mass ratio for a constant time, and show that it provides an excellent
fit to the distribution of FMR residuals. We find the dilution time-scale to be
Gyr, the average metallicity depression caused
by a 1:1 merger to be dex and the minimum
mass ratio merger that can be discerned from the intrinsic Gaussian scatter in
the FMR to be (these are
statistical errors only). From this we derive that the average metallicity
depression caused by a merger with mass ratio between 1:5 and 1:1 is 0.114 dex.Comment: 14 pages, 10 figures, published in MNRAS, updated to be essentially
identical to the published versio
Probing quasar sight lines in three dimensions
Strong damped Lyman alpha absorption (DLA) lines seen spectra of distant quasar are believed to arise when the sight line to the quasar goes trough the disc of a galaxy or a proto galaxy. Most of the neutral matter in the universe is contained in these clouds of neutral hydrogen that cause the absorption lines. Hence these DLAs are reservoirs for the formation of stars and galaxies throughout the universe. Despite intensive efforts over more than two decades only few galaxies responsible for the DLAs have been found. The problem is that the galaxies that harbour the neutral clouds are not necessarily bright, and selecting galaxies based on absorption lines could well select different types of galaxies than found in large surveys. If we are to understand how galaxies form out of neutral gas clouds it is essential to locate the galaxies in which DLAs reside ...thesi
The nature of damped HI absorbers probed by cosmological simulations: satellite accretion and outflows
We use state-of-the-art cosmological zoom simulations to explore the
distribution of neutral gas in and around galaxies that gives rise to high
column density \ion{H}{i} \mbox{Ly-} absorption (formally, sub-DLAs and
DLAs) in the spectra of background quasars. Previous cosmological hydrodynamic
simulations under-predict the mean projected separations of these
absorbers relative to the host, and invoke selection effects to bridge the gap
with observations. On the other hand, single lines of sight (LOS) in absorption
cannot uniquely constrain the galactic origin. Our simulations match all
observational data, with DLA and sub-DLA LOS existing over the entire probed
parameter space ([M/H], kpc) at all redshifts
(). We demonstrate how the existence of DLA LOS at kpc from a massive host galaxy require high numerical resolution, and
that these LOS are associated with dwarf satellites in the main halo, stripped
metal-rich gas and outflows. Separating the galaxy into interstellar
("\ion{H}{i} disc") and circumgalactic ("halo") components, we find that both
components significantly contribute to damped \ion{H}{i} absorption LOS. Above
the sub-DLA (DLA) limits, the disc and halo contribute with and
per cent, respectively. Our simulations confirm analytical
model-predictions of the DLA-distribution at . At high redshift
() sub-DLA and DLAs occupy similar spatial scales, but on average
separate by a factor of two by . On whether sub-DLA and DLA LOS
sample different stellar-mass galaxies, such a correlation can be driven by a
differential covering-fraction of sub-DLA to DLA LOS with stellar mass. This
preferentially selects sub-DLA LOS in more massive galaxies in the low-
universe.Comment: 12 pages, 5 figures, submitted to MNRAS 29/01/201
Vitaliseringspsykologi i neurorehabilitering
The article shows how a vitalising psychological approach can contribute to the area of neurorehabilitation for the purpose of understanding the psychological deficit position of the brain injured person. It is argued that a vitalising psychological understanding of the basic psychological needs in humans and their vitalising environments can contribute to the development of the holistic approach towards neurorehabilitation. Based on the premises in vitalising psychology, the discussion of the practical implications for this approach towards neurorehabilitationis contextualised within an integral framework that facilitates respect for complexity
On the mass-metallicity relation, velocity dispersion and gravitational well depth of GRB host galaxies
We analyze a sample of 16 absorption systems intrinsic to long duration GRB
host galaxies at for which the metallicities are known. We
compare the relation between the metallicity and cold gas velocity width for
this sample to that of the QSO-DLAs, and find complete agreement. We then
compare the redshift evolution of the mass-metallicity relation of our sample
to that of QSO-DLAs and find that also GRB hosts favour a late onset of this
evolution, around a redshift of . We compute predicted stellar
masses for the GRB host galaxies using the prescription determined from QSO-DLA
samples and compare the measured stellar masses for the four hosts where
stellar masses have been determined from SED fits. We find excellent agreement
and conclude that, on basis of all available data and tests, long duration
GRB-DLA hosts and intervening QSO-DLAs are consistent with being drawn from the
same underlying population. GRB host galaxies and QSO-DLAs are found to have
different impact parameter distributions and we briefly discuss how this may
affect statistical samples. The impact parameter distribution has two effects.
First any metallicity gradient will shift the measured metallicity away from
the metallicity in the centre of the galaxy, second the path of the sightline
through different parts of the potential well of the dark matter halo will
cause different velocity fields to be sampled. We report evidence suggesting
that this second effect may have been detected.Comment: 11 pages, 6 figures, 6 tables. Accepted for publication in MNRAS Main
Journal. For the definitive version visit http://mnras.oxfordjournals.org
A spectroscopic look at the gravitationally lensed type Ia SN 2016geu at z=0.409
The spectacular success of type Ia supernovae (SNe Ia) in SN-cosmology is
based on the assumption that their photometric and spectroscopic properties are
invariant with redshift. However, this fundamental assumption needs to be
tested with observations of high-z SNe Ia. To date, the majority of SNe Ia
observed at moderate to large redshifts (0.4 < z < 1.0) are faint, and the
resultant analyses are based on observations with modest signal-to-noise ratios
that impart a degree of ambiguity in their determined properties. In rare cases
however, the Universe offers a helping hand: to date a few SNe Ia have been
observed that have had their luminosities magnified by intervening galaxies and
galaxy clusters acting as gravitational lenses. In this paper we present
long-slit spectroscopy of the lensed SNe Ia 2016geu, which occurred at a
redshift of z=0.409, and was magnified by a factor of ~55 by a galaxy located
at z=0.216. We compared our spectra, which were obtained a couple weeks to a
couple months past peak light, with the spectroscopic properties of
well-observed, nearby SNe Ia, finding that SN 2016geu's properties are
commensurate with those of SNe Ia in the local universe. Based primarily on the
velocity and strength of the Si II 6355 absorption feature, we find that SN
2016geu can be classified as a high-velocity, high-velocity gradient and
"core-normal" SN Ia. The strength of various features (measured though their
pseudo-equivalent widths) argue against SN 2016geu being a faint, broad-lined,
cool or shallow-silicon SN Ia. We conclude that the spectroscopic properties of
SN 2016geu imply that it is a normal SN Ia, and when taking previous results by
other authors into consideration, there is very little, if any, evolution in
the observational properties of SNe Ia up to z~0.4. [Abridged]Comment: 12 pages, 5 figures, 4 tables. Submitted to MNRAS. Comments welcome
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