204 research outputs found
The SAMI Galaxy Survey: Satellite galaxies undergo little structural change during their quenching phase
At fixed stellar mass, satellite galaxies show higher passive fractions than
centrals, suggesting that environment is directly quenching their star
formation. Here, we investigate whether satellite quenching is accompanied by
changes in stellar spin (quantified by the ratio of the rotational to
dispersion velocity V/) for a sample of massive (10
M) satellite galaxies extracted from the SAMI Galaxy Survey. These
systems are carefully matched to a control sample of main sequence, high
central galaxies. As expected, at fixed stellar mass and
ellipticity, satellites have lower star formation rate (SFR) and spin than the
control centrals. However, most of the difference is in SFR, whereas the spin
decreases significantly only for satellites that have already reached the red
sequence. We perform a similar analysis for galaxies in the EAGLE
hydro-dynamical simulation and recover differences in both SFR and spin similar
to those observed in SAMI. However, when EAGLE satellites are matched to their
`true' central progenitors, the change in spin is further reduced and galaxies
mainly show a decrease in SFR during their satellite phase. The difference in
spin observed between satellites and centrals at 0 is primarily due to
the fact that satellites do not grow their angular momentum as fast as centrals
after accreting into bigger halos, not to a reduction of due to
environmental effects. Our findings highlight the effect of progenitor bias in
our understanding of galaxy transformation and they suggest that satellites
undergo little structural change before and during their quenching phase.Comment: 11 pages, 7 figures. Accepted for publication in MNRA
The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry
In order to determine the causes of kinematic asymmetry in the H gas
in the SAMI Galaxy Survey sample, we investigate the comparative influences of
environment and intrinsic properties of galaxies on perturbation. We use
spatially resolved H velocity fields from the SAMI Galaxy Survey to
quantify kinematic asymmetry () in nearby galaxies and
environmental and stellar mass data from the GAMA survey.
{We find that local environment, measured as distance to nearest neighbour,
is inversely correlated with kinematic asymmetry for galaxies with
, but there is no significant correlation for
galaxies with . Moreover, low mass galaxies
() have greater kinematic asymmetry at all
separations, suggesting a different physical source of asymmetry is important
in low mass galaxies.}
We propose that secular effects derived from gas fraction and gas mass may be
the primary causes of asymmetry in low mass galaxies. High gas fraction is
linked to high (where is H velocity
dispersion and the rotation velocity), which is strongly correlated with
, and galaxies with have offset
from the rest of the sample. Further,
asymmetry as a fraction of dispersion decreases for galaxies with
. Gas mass and asymmetry are also inversely correlated
in our sample. We propose that low gas masses in dwarf galaxies may lead to
asymmetric distribution of gas clouds, leading to increased relative
turbulence.Comment: 15 pages, 20 figure
Quantitative Study of Guide-Field Effects on Hall Reconnection in a Laboratory Plasma
The effect of guide field on magnetic reconnection is quantitatively studied by systematically varying an applied guide field in the Magnetic Reconnection Experiment (MRX). The quadrupole field, a signature of two-fluid reconnection at zero guide field, is significantly altered by a finite guide field. It is shown that the reconnection rate is significantly reduced with increasing guide field, and this dependence is explained by a combination of local and global physics: locally, the in-plane Hall currents are reduced, while globally guide field compression produces an increased pressure both within and downstream of the reconnection region. _________________________________________________
The SAMI Galaxy Survey: Towards a unified dynamical scaling relation for galaxies of all types
We take advantage of the first data from the Sydney-AAO Multi-object Integral
field (SAMI) Galaxy Survey to investigate the relation between the kinematics
of gas and stars, and stellar mass in a comprehensive sample of nearby
galaxies. We find that all 235 objects in our sample, regardless of their
morphology, lie on a tight relation linking stellar mass () to internal
velocity quantified by the parameter, which combines the contribution
of both dispersion () and rotational velocity () to the
dynamical support of a galaxy (). Our
results are independent of the baryonic component from which and
are estimated, as the of stars and gas agree remarkably
well. This represents a significant improvement compared to the canonical
vs. and vs. relations. Not only is no sample
pruning necessary, but also stellar and gas kinematics can be used
simultaneously, as the effect of asymmetric drift is taken into account once
and are combined. Our findings illustrate how the
combination of dispersion and rotational velocities for both gas and stars can
provide us with a single dynamical scaling relation valid for galaxies of all
morphologies across at least the stellar mass range
8.511. Such relation appears to be more general and at
least as tight as any other dynamical scaling relation, representing a unique
tool for investigating the link between galaxy kinematics and baryonic content,
and a less biased comparison with theoretical models.Comment: 6 pages, 4 figures. Accepted for publication in ApJ Letter
A comparison of vestibular and auditory phenotypes in inbred mouse strains
The purposes of this research were to quantify gravity receptor function in inbred mouse strains and compare vestibular and auditory function for strain- and age-matched animals. Vestibular evoked potentials (VsEPs) were collected for 19 inbred strains at ages from 35 to 389 days old. On average, C57BL/6J (35 to 190 days), BALB/cByJ, C3H/HeSnJ, CBA/J, and young LP/J mice had VsEP thresholds comparable to normal. Elevated VsEP thresholds were found for elderly C57BL/ 6J, NOD.NONH2kb, BUB/BnJ, A/J, DBA/2J, NOD/LtJ, A/WySnJ, MRL/MpJ, A/HeJ, CAST/Ei, SJL/J, elderly LP/J, and CE/J. These results suggest that otolithic function varies among inbred strains and several strains displayed gravity receptor deficits by 90 days old. Auditory brainstem response (ABR) thresholds were compared to VsEP thresholds for 14 age-matched strains. C57BL/6J mice (up to 190 days) showed normal VsEPs with normal to mildly elevated ABR thresholds. Four strains (BUB/BnJ, NOD/LtJ, A/J, elderly LP/J) had significant hearing loss and elevated VsEP thresholds. Four strains (DBA/2J, A/WySnJ, NOD. NONH2kb, A/HeJ) had elevated VsEP thresholds (including absent VsEPs) with mild to moderate elevations in ABR thresholds. Three strains (MRL/MpJ, Ce/J, SJL/J) had significant vestibular loss with no concomitant hearing loss. These results suggest that functional change in one sensory system does not obligate change in the other. We hypothesize that genes responsible for early onset hearing loss may affect otolithic function, yet the time course of functional change may vary. In addition, some genetic mutations may produce primarily gravity receptor deficits. Potential genes responsible for selective gravity receptor impairment demonstrated herein remain to be identified. Originally published in Brain Research 1091(1), 2006
The role of neutrophils in the upper and lower respiratory tract during influenza virus infection of mice
BACKGROUND: Neutrophils have been shown to play a role in host defence against highly virulent and mouse-adapted strains of influenza virus, however it is not clear if an effective neutrophil response is an important factor moderating disease severity during infection with other virus strains. In this study, we have examined the role of neutrophils during infection of mice with influenza virus strain HKx31, a virus strain of the H3N2 subtype and of moderate virulence for mice, to determine the role of neutrophils in the early phase of infection and in clearance of influenza virus from the respiratory tract during the later phase of infection. METHODS: The anti-Gr-1 monoclonal antibody (mAb) RB6-8C5 was used to (i) identify neutrophils in the upper (nasal tissues) and lower (lung) respiratory tract of uninfected and influenza virus-infected mice, and (ii) deplete neutrophils prior to and during influenza virus infection of mice. RESULTS: Neutrophils were rapidly recruited to the upper and lower airways following influenza virus infection. We demonstrated that use of mAb RB6-8C5 to deplete C57BL/6 (B6) mice of neutrophils is complicated by the ability of this mAb to bind directly to virus-specific CD8+ T cells. Thus, we investigated the role of neutrophils in both the early and later phases of infection using CD8+ T cell-deficient B6.TAP-/- mice. Infection of B6.TAP-/- mice with a low dose of influenza virus did not induce clinical disease in control animals, however RB6-8C5 treatment led to profound weight loss, severe clinical disease and enhanced virus replication throughout the respiratory tract. CONCLUSION: Neutrophils play a critical role in limiting influenza virus replication during the early and later phases of infection. Furthermore, a virus strain of moderate virulence can induce severe clinical disease in the absence of an effective neutrophil response
The SAMI Galaxy Survey: Spatially resolving the environmental quenching of star formation in GAMA galaxies
We use data from the Sydney-AAO Multi-Object Integral Field Spectrograph (SAMI) Galaxy Survey and the Galaxy And Mass Assembly (GAMA) survey to investigate the spatially-resolved signatures of the environmental quenching of star formation in galaxies. Using dust-corrected measurements of the distribution of Hα emission we measure the radial profiles of star formation in a sample of 201 star-forming galaxies covering three orders of magnitude in stellar mass (M∗M∗; 108.1-1010.95 M⊙) and in 5th nearest neighbour local environment density (Σ5; 10−1.3- 102.1 Mpc−2). We show that star formation rate gradients in galaxies are steeper in dense (log10(Σ5/Mpc2) > 0.5) environments by 0.58 ± 0.29 dex re−1 in galaxies with stellar masses in the range 1010 1.0). These lines of evidence strongly suggest that with increasing local environment density the star formation in galaxies is suppressed, and that this starts in their outskirts such that quenching occurs in an outside-in fashion in dense environments and is not instantaneous
The SAMI Galaxy Survey: Cubism and covariance, putting round pegs into square holes
We present a methodology for the regularization and combination of sparse sampled and irregularly gridded observations from fibre-optic multiobject integral field spectroscopy. The approach minimizes interpolation and retains image resolution on combining subpixel dithered data. We discuss the methodology in the context of the Sydney-AAO multiobject integral field spectrograph (SAMI) Galaxy Survey underway at the Anglo-Australian Telescope. The SAMI instrument uses 13 fibre bundles to perform high-multiplex integral field spectroscopy across a 1° diameter field of view. The SAMI Galaxy Survey is targeting ~3000 galaxies drawn from the full range of galaxy environments. We demonstrate the subcritical sampling of the seeing and incomplete fill factor for the integral field bundles results in only a 10 per cent degradation in the final image resolution recovered. We also implement a new methodology for tracking covariance between elements of the resulting data cubes which retains 90 per cent of the covariance information while incurring only a modest increase in the survey data volume
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