1,294 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
Asymmetric Drift and the Stellar Velocity Ellipsoid
We present the decomposition of the stellar velocity ellipsoid using stellar
velocity dispersions within a 40 deg wedge about the major-axis (sigma_maj),
the epicycle approximation, and the asymmetric drift equation. Thus, we employ
no fitted forms for sigma_maj and escape interpolation errors resulting from
comparisons of the major and minor axes. We apply the theoretical construction
of the method to integral field data taken for NGC 3949 and NGC 3982. We derive
the vertical-to-radial velocity dispersion ratio (sigma_z / sigma_R) and find
(1) our decomposition method is accurate and reasonable, (2) NGC 3982 appears
to be rather typical of an Sb type galaxy with sigma_z / sigma_R = 0.73
(+0.13/-0.11) despite its high surface brightness and small size, and (3) NGC
3949 has a hot disk with sigma_z / sigma_R = 1.18 (+0.36/-0.28).Comment: 4 pages including 3 figures, to appear in "Island Universes:
Structure and Evolution of Disk Galaxies", Terschelling, Netherlands, July
3-8, 200
The Kinematics in the Core of the Low Surface Brightness Galaxy DDO 39
We present a high resolution, SparsePak two-dimensional velocity field for
the center of the low surface brightness (LSB) galaxy DDO 39. These data are a
significant improvement on previous HI or Halpha long slit data, yet the inner
rotation curve is still uncertain due to significant noncircular and random
motions. These intrinsic uncertainties, probably present in other LSB galaxies
too, result in a wide range of inner slopes being consistent with the data,
including those expected in cold dark matter (CDM) simulations. The halo
concentration parameter provides a more useful test of cosmological models than
the inner slope as it is more tightly constrained by observations. DDO 39's
concentration parameter is consistent with, but on the low end of the
distribution predicted by CDM.Comment: 4 pages, accepted for publication in ApJ Letter
WIYN Integral-Field Kinematics of Disk Galaxies
We have completed a new fiber array, SparsePak, optimized for low-surface-brightness studies of extended sources on the WIYN telescope. We are now using this array as a measuring engine of velocity and velocity-dispersion fields of stars and ionized gas in disk galaxies from high to low surface-brightness. Here we present commissioning data on the velocity ellipsoids, surface densities and mass-to-light ratios in two blue, high surface-brightness, yet small disks. If our preliminary results survive further observation and more sophisticated analysis, then NGC 3949 has sigma_z/sigma_R >> 1, implying strong vertical heating, while NGC 3982's disk is substantially sub-maximal. These galaxies are strikingly unlike the Milky Way, and yet would be seen more easily at high redshift
WSRT Ultra-Deep Neutral Hydrogen Imaging of Galaxy Clusters at z=0.2, a Pilot Survey of Abell 963 and Abell 2192
A pilot study with the powerful new backend of the Westerbork Synthesis Radio
Telescope (WSRT) of two galaxy clusters at z=0.2 has revealed neutral hydrogen
emission from 42 galaxies. The WSRT probes a total combined volume of 3.4x10^4
Mpc^3 at resolutions of 54x86 kpc^2 and 19.7 km/s, surveying both clusters and
the large scale structure in which they are embedded. In Abell 963, a
dynamically relaxed, lensing Butcher-Oemler cluster with a high blue fraction,
most of the gas-rich galaxies are located between 1 and 3 Mpc in projection,
northeast from the cluster core. Their velocities are slightly redshifted with
respect to the cluster, and this is likely a background group. None of the blue
galaxies in the core of Abell 963 are detected in HI, although they have
similar colors and luminosities as the HI detected galaxies in the cluster
outskirts and field. Abell 2192 is less massive and more diffuse. Here, the
gas-rich galaxies are more uniformly distributed. The detected HI masses range
from 5x10^9 to 4x10^10 Msun. Some galaxies are spatially resolved, providing
rudimentary rotation curves useful for detailed kinematic studies of galaxies
in various environments. This is a pilot for ultra-deep integrations down to HI
masses of 8x10^8 Msun, providing a complete survey of the gas content of
galaxies at z=0.2, probing environments ranging from cluster cores to voids.Comment: 5 pages, 6 figures + 1 Plate, accepted for publication in the
Astrophysical Journal Letter
From gas to galaxies
The unsurpassed sensitivity and resolution of the Square Kilometer Array
(SKA) will make it possible for the first time to probe the continuum emission
of normal star forming galaxies out to the edges of the universe. This opens
the possibility for routinely using the radio continuum emission from galaxies
for cosmological research as it offers an independent probe of the evolution of
the star formation density in the universe. In addition it offers the
possibility to detect the first star forming objects and massive black holes.
In deep surveys SKA will be able to detect HI in emission out to redshifts of
and hence be able to trace the conversion of gas into stars
over an era where considerable evolution is taking place. Such surveys will be
able to uniquely determine the respective importance of merging and accreting
gas flows for galaxy formation over this redshift range (i.e. out to when the
universe was only one third its present age). It is obvious that only SKA will
able to see literally where and how gas is turned into stars.
These and other aspects of SKA imaging of galaxies will be discussed.Comment: To be published in New Astronomy Reviews, Elsevier, Amsterdam as part
of "Science with the Square Kilometre Array", eds. C. Carilli and S.
Rawlings. 18 pages + 13 figures; high resolution version and other chapters
of "Science with the Square Kilometre Array" available at
http://www.skatelescope.org/pages/science_gen.ht
Star Formation and Tidal Encounters with the Low Surface Brightness Galaxy UGC 12695 and Companions
We present VLA H I observations of the low surface brightness galaxy UGC
12695 and its two companions, UGC 12687 and a newly discovered dwarf galaxy
2333+1234. UGC 12695 shows solid body rotation but has a very lopsided
morphology of the H I disk, with the majority of the H I lying in the southern
arm of the galaxy. The H I column density distribution of this very blue, LSB
galaxy coincides in detail with its light distribution. Comparing the H I
column density of UGC 12695 with the empirical (but not well understood) value
of Sigma_c = 10E21 atoms/cm^2 found in, i.e., Skillman's 1986 paper shows the
star formation to be a local affair, occurring only in those regions where the
column density is above this star formation threshold. The low surface
brightness nature of this galaxy could thus be attributed to an insufficient
gas surface density, inhibiting star formation on a more global scale.
Significantly, though, the Toomre criterion places a much lower critical
density on the galaxy (+/-10E20 atoms/cm^2), which is shown by the galaxy's low
SFR to not be applicable.
Within a projected distance of 300kpc/30kms of UGC 12695 lie two companion
galaxies - UGC 12687, a high surface brightness barred spiral galaxy, and
2333+1234, a dwarf galaxy discovered during this investigation. The close
proximity of the three galaxies, combined with UGC 12695's extremely blue color
and regions of localized starburst and UGC 12687's UV excess bring to mind
mutually induced star formation through tidal activity.Comment: 14 pages, 8 figures (2 color), To be published in A.J., May 2000
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