511 research outputs found
High-angle-of-attack stability characteristics of a 3-surface fighter configuration
A wind tunnel investigation was conducted to study the low speed, high angle of attack stability characteristics of a three surface fighter concept based on the F-15 configuration. Static force data were measured over angle of attack and side-slip ranges of 0 to 85 and -10 and 10 deg, respectively. A force oscillation technique was used to obtain dynamic derivatives at angles of attack from 0 to 60 deg. The tests were conducted for several canard deflections and with the canards removed to investigate the effects of the close coupled canard on the high angle of attack stability characteristics of the configuration. A fuselage strake was developed which significantly improved static lateral directional stability characteristics at high angles of attack while also increasing the maximum lift of the configuration
The Tully–Fisher relation from SDSS-MaNGA: physical causes of scatter and variation at different radii
The stellar mass Tully–Fisher relation (STFR) and its scatter encode valuable information about the processes shaping galaxy evolution across cosmic time. However, we are still missing a proper quantification of the STFR slope and scatter dependence on the baryonic tracer used to quantify rotational velocity, on the velocity measurement radius and on galaxy integrated properties. We present a catalogue of stellar and ionized gas (traced by H emission) kinematic measurements for a sample of galaxies drawn from the MaNGA Galaxy Survey, providing an ideal tool for galaxy formation model calibration and for comparison with high-redshift studies. We compute the STFRs for stellar and gas rotation at 1, 1.3 and 2 effective radii (Re). The relations for both baryonic components become shallower at 2Re compared to 1Re and 1.3Re. We report a steeper STFR for the stars in the inner parts (≤1.3Re) compared to the gas. At 2Re, the relations for the two components are consistent. When accounting for covariances with integrated v/σ, scatter in the stellar and gas STFRs shows no strong correlation with: optical morphology, star formation rate surface density, tidal interaction strength or gas accretion signatures. Our results suggest that the STFR scatter is driven by an increase in stellar/gas dispersional support, from either external (mergers) or internal (feedback) processes. No correlation between STFR scatter and environment is found. Nearby Universe galaxies have their stars and gas in statistically different states of dynamical equilibrium in the inner parts (≤1.3Re), while at 2Re the two components are dynamically coupled
QSO clustering and the AAT 2dF redshift survey
We review previous results on the clustering and environments of QSOs. We
show that the correlation length for QSOs derived from existing surveys is
r~5/h Mpc, similar to the observed correlation length for field galaxies at the
present epoch. The galaxy environment for z<1 radio-quiet QSOs is also
consistent with field galaxies. The evolution of the QSO correlation length
with redshift is currently uncertain, largely due to the small numbers of QSOs
(~2000) in surveys suitable for clustering analysis. We report on intial
progress with the AAT 2dF QSO redshift survey, which, once completed will
comprise almost 30000 QSOs. With over 1000 QSOs already observed, it is already
the largest single homogeneous QSO survey. We discuss prospects for deriving
limits on cosmological parameters from this survey, and on the evolution of
large-scale structure in the Universe.Comment: Invited talk at RS meeting on 'Large Scale Structure in the Universe'
held at the Royal Society on 25-26 March 1998 14 pages, 11 figre
The SAMI Galaxy Survey: Unveiling the nature of kinematically offset active galactic nuclei
We have observed two kinematically offset active galactic nuclei (AGN), whose
ionised gas is at a different line-of-sight velocity to their host galaxies,
with the SAMI integral field spectrograph (IFS). One of the galaxies shows gas
kinematics very different to the stellar kinematics, indicating a recent merger
or accretion event. We demonstrate that the star formation associated with this
event was triggered within the last 100 Myr. The other galaxy shows simple disc
rotation in both gas and stellar kinematics, aligned with each other, but in
the central region has signatures of an outflow driven by the AGN. Other than
the outflow, neither galaxy shows any discontinuity in the ionised gas
kinematics at the galaxy's centre. We conclude that in these two cases there is
no direct evidence of the AGN being in a supermassive black hole binary system.
Our study demonstrates that selecting kinematically offset AGN from
single-fibre spectroscopy provides, by definition, samples of kinematically
peculiar objects, but IFS or other data are required to determine their true
nature.Comment: MNRAS accepted. 14 pages, 11 figure
The SAMI Galaxy Survey: Gas Streaming and Dynamical M/L in Rotationally Supported Systems
Line-of-sight velocities of gas and stars can constrain dark matter (DM)
within rotationally supported galaxies if they trace circular orbits
extensively. Photometric asymmetries may signify non-circular motions,
requiring spectra with dense spatial coverage. Our integral-field spectroscopy
of 178 galaxies spanned the mass range of the SAMI Galaxy Survey. We derived
circular speed curves (CSCs) of gas and stars from non-parametric Diskfit fits
out to . For 12/14 with measured H I profiles, ionized gas and H I
maximum velocities agreed. We fitted mass-follows-light models to 163 galaxies
by approximating the radial starlight profile as nested, very flattened mass
homeoids viewed as a S\'ersic form. Fitting broad-band SEDs to SDSS images gave
median stellar mass/light 1.7 assuming a Kroupa IMF vs. 2.6 dynamically.
Two-thirds of the dynamical mass/light measures were consistent with
star+remnant IMFs. One-fifth required upscaled starlight to fit, hence
comparable mass of unobserved baryons and/or DM distributed similarly across
the SAMI aperture that came to dominate motions as the starlight CSC declined
rapidly. The rest had mass distributed differently from starlight. Subtracting
fits of S\'ersic profiles to 13 VIKING Z-band images revealed residual weak
bars. Near the bar PA, we assessed m = 2 streaming velocities, and found
deviations usually <30 km/s from the CSC; three showed no deviation. Thus,
asymmetries rarely influenced our CSCs despite co-located shock-indicating,
emission-line flux ratios in more than 2/3.Comment: 21 pages, 15 figures. Accepted to 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
The SAMI Galaxy Survey: Asymmetry in Gas Kinematics and its links to Stellar Mass and Star Formation
We study the properties of kinematically disturbed galaxies in the SAMI
Galaxy Survey using a quantitative criterion, based on kinemetry (Krajnovic et
al.). The approach, similar to the application of kinemetry by Shapiro et al.
uses ionised gas kinematics, probed by H{\alpha} emission. By this method
23+/-7% of our 360-galaxy sub-sample of the SAMI Galaxy Survey are
kinematically asymmetric. Visual classifications agree with our kinemetric
results for 90% of asymmetric and 95% of normal galaxies. We find stellar mass
and kinematic asymmetry are inversely correlated and that kinematic asymmetry
is both more frequent and stronger in low-mass galaxies. This builds on
previous studies that found high fractions of kinematic asymmetry in low mass
galaxies using a variety of different methods. Concentration of star forma-
tion and kinematic disturbance are found to be correlated, confirming results
found in previous work. This effect is stronger for high mass galaxies (log(M*)
> 10) and indicates that kinematic disturbance is linked to centrally
concentrated star formation. Comparison of the inner (within 0.5Re) and outer
H{\alpha} equivalent widths of asymmetric and normal galaxies shows a small but
significant increase in inner equivalent width for asymmetric galaxies.Comment: 29 pages, 21 figure
The SAMI Galaxy Survey: The Low-Redshift Stellar Mass Tully-Fisher Relation
We investigate the Tully-Fisher Relation (TFR) for a morphologically and
kine- matically diverse sample of galaxies from the SAMI Galaxy Survey using 2
dimensional spatially resolved Halpha velocity maps and find a well defined
relation across the stellar mass range of 8.0 < log(M*) < 11.5. We use an
adaptation of kinemetry to parametrise the kinematic Halpha asymmetry of all
galaxies in the sample, and find a correlation between scatter (i.e. residuals
off the TFR) and asymmetry. This effect is pronounced at low stellar mass,
corresponding to the inverse relationship between stellar mass and kinematic
asymmetry found in previous work. For galaxies with log(M*) < 9.5, 25 +/- 3%
are scattered below the root mean square (RMS) of the TFR, whereas for galaxies
with log(M*) > 9.5 the fraction is 10 +/- 1% We use 'simulated slits' to
directly compare our results with those from long slit spectroscopy and find
that aligning slits with the photometric, rather than the kinematic, position
angle, increases global scatter below the TFR. Further, kinematic asymmetry is
correlated with misalignment between the photometric and kinematic position
angles. This work demonstrates the value of 2D spatially resolved kinematics
for accurate TFR studies; integral field spectroscopy reduces the
underestimation of rotation velocity that can occur from slit positioning off
the kinematic axis
Measuring large-scale structure with quasars in narrow-band filter surveys
We show that a large-area imaging survey using narrow-band filters could
detect quasars in sufficiently high number densities, and with more than
sufficient accuracy in their photometric redshifts, to turn them into suitable
tracers of large-scale structure. If a narrow-band optical survey can detect
objects as faint as i=23, it could reach volumetric number densities as high as
10^{-4} h^3 Mpc^{-3} (comoving) at z~1.5 . Such a catalog would lead to
precision measurements of the power spectrum up to z~3-4. We also show that it
is possible to employ quasars to measure baryon acoustic oscillations at high
redshifts, where the uncertainties from redshift distortions and nonlinearities
are much smaller than at z<1. As a concrete example we study the future impact
of J-PAS, which is a narrow-band imaging survey in the optical over 1/5 of the
unobscured sky with 42 filters of ~100 A full-width at half-maximum. We show
that J-PAS will be able to take advantage of the broad emission lines of
quasars to deliver excellent photometric redshifts, \sigma_{z}~0.002(1+z), for
millions of objects.Comment: Matches version published in MNRAS (2012
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