296 research outputs found
The high mass end of the Tully-Fisher relation
We study the location of massive disk galaxies on the Tully-Fisher relation.
Using a combination of K-band photometry and high-quality rotation curves, we
show that in traditional formulations of the TF relation (using the width of
the global HI profile or the maximum rotation velocity), galaxies with rotation
velocities larger than 200 km/s lie systematically to the right of the relation
defined by less massive systems, causing a characteristic `kink' in the
relations. Massive, early-type disk galaxies in particular have a large offset,
up to 1.5 magnitudes, from the main relation defined by less massive and
later-type spirals.
The presence of a change in slope at the high-mass end of the Tully-Fisher
relation has important consequences for the use of the Tully-Fisher relation as
a tool for estimating distances to galaxies or for probing galaxy evolution. In
particular, the luminosity evolution of massive galaxies since z = 1 may have
been significantly larger than estimated in several recent studies.
We also show that many of the galaxies with the largest offsets have
declining rotation curves and that the change in slope largely disappears when
we use the asymptotic rotation velocity as kinematic parameter. The remaining
deviations from linearity can be removed when we simultaneously use the total
baryonic mass (stars + gas) instead of the optical or near-infrared luminosity.
Our results strengthen the view that the Tully-Fisher relation fundamentally
links the mass of dark matter haloes with the total baryonic mass embedded in
them.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
Exploring Disk Galaxy Dynamics Using IFU Data
In order to test the basic equations believed to dictate the dynamics of disk
galaxies, we present and analyze deep two-dimensional spectral data obtained
using the PPAK integral field unit for the early-type spiral systems NGC 2273,
NGC 2985, NGC 3898 and NGC 5533. We describe the care needed to obtain and
process such data to a point where reliable kinematic measurements can be
obtained from these observations, and a new more optimal method for deriving
the rotational motion and velocity dispersions in such disk systems. The data
from NGC 2273 and NGC 2985 show systematic variations in velocity dispersion
with azimuth, as one would expect if the shapes of their velocity ellipsoids
are significantly anisotropic, while the hotter disks in NGC 3898 and NGC 5533
appear to have fairly isotropic velocity dispersions. Correcting the rotational
motion for asymmetric drift using the derived velocity dispersions reproduces
the rotation curves inferred from emission lines reasonably well, implying that
this correction is quite robust, and that the use of the asymmetric drift
equation is valid. NGC 2985 is sufficiently close to face on for the data,
combined with the asymmetric drift equation, to determine all three components
of the velocity ellipsoid. The principal axes of this velocity ellipsoid are
found to be in the ratio sigma_z:sigma_phi:sigma_R ~ 0.7:0.7:1, which shows
unequivocally that this disk distribution function respects a third integral of
motion. The ratio is also consistent with the predictions of epicyclic theory,
giving some confidence in the application of this approximation to even fairly
early-type disk galaxies.Comment: 15 pages, 7 figures, accepted for publication in MNRA
Effect of Aromatic Oil on Phase Dynamics of S-SBR/BR Blends fro Passenger Car Tire Treads
Even though S-SBR/BR blends are commonly used for passenger car tire treads, little is known about the phase dynamics arising from the local morphological heterogeneities. The present study aims at developing the understanding of: (i) the influence of aromatic oil on the dynamics of the individual phases in S-SBR/BR (50/50) blend, and (ii) the partition of the aromatic oil in either phase.\ud
S-SBR/BR (50/50) blends with varying concentrations of aromatic oil (0/10/20 phr) were studied. Conventional techniques for the determination of Tg (glass transition temperature or α-relaxation process), such as Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) were of limited use for fulfilling the goal of the present study. Therefore, Broadband Dielectric Spectroscopy (BDS), a more sensitive technique to study the α-relaxation process was employed. It was possible to de-convolute the dielectric loss (ε") peak of the vulcanized blends into two super-positioned relaxation processes, α' and α (in increasing order of frequency), which were attributed to the S-SBR and BR phases, respectively. The distinct effective Tg’s (Tgeff) of the S-SBR and BR phases varied with the amount of aromatic oil added. Tgeff of the BR phase was close to the Tg of virgin BR, whereas Tgeff of the S-SBR phase was close to the blend average Tg. This is in accordance with the model for phase dynamics of miscible blends by Lodge and McLeish (2000). With this a deeper insight into the dynamic heterogeneity of traditional S-SBR/BR (50/50) blends is obtained
Testing the nature of S0 galaxies using planetary nebula kinematics in NGC 1023
We investigate the manner in which lenticular galaxies are formed by studying
their stellar kinematics: an S0 formed from a fading spiral galaxy should
display similar cold outer disc kinematics to its progenitor, while an S0
formed in a minor merger should be more dominated by random motions. In a pilot
study to attempt to distinguish between these scenarios, we have measured the
planetary nebula (PN) kinematics of the nearby S0 system NGC 1023. Using the
Planetary Nebula Spectrograph, we have detected and measured the line-of-sight
velocities of 204 candidate PNe in the field of this galaxy. Out to
intermediate radii, the system displays the kinematics of a normal
rotationally-supported disc system. After correction of its rotational
velocities for asymmetric drift, the galaxy lies just below the spiral galaxy
Tully-Fisher relation, as one would expect for a fading system. However, at
larger radii the kinematics undergo a gradual but major transition to random
motion with little rotation. This transition does not seem to reflect a change
in the viewing geometry or the presence of a distinct halo component, since the
number counts of PNe follow the same simple exponential decline as the stellar
continuum with the same projected disc ellipticity out to large radii. The
galaxy's small companion, NGC 1023A, does not seem to be large enough to have
caused the observed modification either. This combination of properties would
seem to indicate a complex evolutionary history in either the transition to
form an S0 or in the past life of the spiral galaxy from which the S0 formed.
More data sets of this type from both spirals and S0s are needed in order to
definitively determine the relationship between these types of system.Comment: Accepted for publication in MNRAS. Version with full resolution
figure 1 can be found at
http://www.nottingham.ac.uk/~ppzmrm/N1023_PNS.accepted.pd
Dark-Matter Content of Early-Type Galaxies with Planetary Nebulae
We examine the dark matter properties of nearby early-type galaxies using
planetary nebulae (PNe) as mass probes. We have designed a specialised
instrument, the Planetary Nebula Spectrograph (PN.S) operating at the William
Herschel telescope, with the purpose of measuring PN velocities with best
efficiency. The primary scientific objective of this custom-built instrument is
the study of the PN kinematics in 12 ordinary round galaxies. Preliminary
results showing a dearth of dark matter in ordinary galaxies (Romanowsky et al.
2003) are now confirmed by the first complete PN.S datasets. On the other hand
early-type galaxies with a "regular" dark matter content are starting to be
observed among the brighter PN.S target sample, thus confirming a correlation
between the global dark-to-luminous mass virial ratio (f_DM=M_DM/M_star) and
the galaxy luminosity and mass.Comment: 5 pages, 2 figures. To appear in the proceedings of the IAU Symposium
244 "Dark Galaxies and Lost Baryons", Cardiff 25-29 June 2007, eds. J.I.
Davies & M.J. Disne
The Link between the Baryonic Mass Distribution and the Rotation Curve Shape
The observed rotation curves of disc galaxies, ranging from late-type dwarf
galaxies to early-type spirals, can be fit remarkably well simply by scaling up
the contributions of the stellar and HI discs. This `baryonic scaling model'
can explain the full breadth of observed rotation curves with only two free
parameters. For a small fraction of galaxies, in particular early-type spiral
galaxies, HI scaling appears to fail in the outer parts, possibly due to
observational effects or ionization of the HI. The overall success of the
baryonic scaling model suggests that the well-known global coupling between the
baryonic mass of a galaxy and its rotation velocity (known as the baryonic
Tully-Fisher relation), applies at a more local level as well, and it seems to
imply a link between the baryonic mass distribution and the distribution of
total mass (including dark matter).Comment: 10 pages, accepted for publication in MNRA
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