334 research outputs found
Structure and kinematics of edge-on galaxy discs -- V. The dynamics of the stellar discs
In earlier papers in this series we determined the intrinsic stellar disc
kinematics of fifteen intermediate to late type edge-on spiral galaxies using a
dynamical modeling technique. From the photometry we find that intrinsically
more flattened discs tend to have a lower face-on central surface brightness
and a larger dynamica mass-to-light ratio. This observation suggests that at a
constant maximum rotational velocity lower surface brightness discs have
smaller vertical stellar velocity dispersions.Although the individual
uncertainties are large, we find from the dynamical modeling that at least
twelve discs are submaximal. The average disc contributes 534 percent to
the observed rotation at 2.2 disc scalelengths, with a 1 scatter of 15
percent. This percentage becomes somewhat lower when effects of finite disc
flattening and gravity by the dark halo and the gas are taken into account.
Since boxy and peanut-shaped bulges are probably associated with bars, the
result suggests that at 2.2 the submaximal nature of discs is
independent of barredness. The possibility remains that very high surface
brightness discs are maximal.We confirm that the radial stellar disc velocity
dispersion is related to the galaxy maximum rotational velocity. The scatter in
this relation appears to correlate with the disc
flattening, face-on central surface brightness and dynamical mass-to-light
ratio. Low surface brightness discs tend to be more flattened and have smaller
stellar velocity dispersions. The findings are consistent with the observed
correlation between disc flattening and dynamical mass-to-light ratio.Comment: Accepted for publication by Mon. Not. R.A.
The dark matter halo shape of edge-on disk galaxies - II. Modelling the HI observations: methods
This is the second paper of a series in which we attempt to put constraints
on the flattening of dark halos in disk galaxies. For this purpose, we observe
the HI in edge-on galaxies, where it is in principle possible to measure the
force field in the halo vertically and radially from gas layer flaring and
rotation curve decomposition respectively. To calculate the force fields, we
need to analyse the observed XV diagrams to accurately measure all three
functions that describe the planar kinematics and distribution of a galaxy: the
radial HI surface density, the rotation curve and the HI velocity dispersion.
In this paper, we discuss the improvements and limitations of the methods
previously used to measure these HI properties. We extend the constant velocity
dispersion method to include determination of the HI velocity dispersion as a
function of galactocentric radius and perform extensive tests on the quality of
the fits. We will apply this 'radial decomposition XV modelling method' to our
HI observations of 8 HI-rich, late-type, edge-on galaxies in the third paper of
this series.Comment: Accepted for publication by Astronomy & Astrophysics. For a higher
resolution version see
http://www.astro.rug.nl/~vdkruit/jea3/homepage/12566.pd
Very Luminous Carbon Stars in the Outer Disk of the Triangulum Spiral Galaxy
Stars with masses in the range from about 1.3 to 3.5 Mo pass through an
evolutionary stage where they become carbon stars. In this stage, which lasts a
few Myr, these stars are extremely luminous pulsating giants. They are so
luminous in the near-infrared that just a few of them can double the integrated
luminosity of intermediate-age (0.6 to 2 Gyr) Magellanic Cloud clusters at 2.2
microns. Astronomers routinely use such near-infrared observations to minimize
the effects of dust extinction, but it is precisely in this band that carbon
stars can contribute hugely. The actual contribution of carbon stars to the
outer disk light of evolving spiral galaxies has not previously been
morphologically investigated. Here we report new and very deep near-IR images
of the Triangulum spiral galaxy M33=NGC 598, delineating spectacular arcs of
carbon stars in its outer regions. It is these arcs which dominate the
near-infrared m=2 Fourier spectra of M33. We present near-infrared photometry
with the Hale 5-m reflector, and propose that the arcs are the signature of
accretion of low metallicity gas in the outer disk of M33.Comment: 4 pages, 4 figures. Revised version submitted to A&A Letter
Structure and kinematics of edge-on galaxy discs - I. Observations of the stellar kinematics
We present deep optical long-slit spectra of 17 edge-on spiral galaxies of
intermediate to late morphological type, mostly parallel to their major axes
and in a few cases parallel to the minor axes.The line-of-sight stellar
kinematics are obtained from the stellar absorption lines using the improvedc
ross-correlation technique. In general, the stellar kinematics are regular and
can be traced well into the disc-dominated region. The mean stellar velocity
curves are far from solid-body, indicating that the effect of dust extinction
is not large. The line-of-sight stellar disc velocity dispersion correlates
with the galaxy maximum rotational velocity, but detailed modeling is necessary
to establish whether this represents a physical relation. In four spirals with
a boxy- or peanut-shaped bulge we are able to detect asymmetric velocity
distributions, having a common signature with projected radius in the mean
line-of-sight velocity and the and curves. In two cases this
kinematic asymmetry probably represents the `figure-of-eight' pattern
synonymous of a barred potential. We emphasize, however, that the signatures
seen in the and curves may also be due to the disc seen in
projection.Comment: Accepted for publication by Mon. Not. R.A.
The dark matter halo shape of edge-on disk galaxies - I. HI observations
This is the first paper of a series in which we will attempt to put
constraints on the flattening of dark halos in disk galaxies. We observe for
this purpose the HI in edge-on galaxies, where it is in principle possible to
measure the force field in the halo vertically and radially from gas layer
flaring and rotation curve decomposition respectively. In this paper, we define
a sample of 8 HI-rich late-type galaxies suitable for this purpose and present
the HI observations.Comment: Accepted for publication by Astronomy & Astrophysics. For a higher
resolution version see
http://www.astro.rug.nl/~vdkruit/jea3/homepage/12565.pd
Kinematics and dynamics of the "superthin" edge-on disk galaxy IC 5249
We present spectroscopic observations of the stellar motions in the disk of
the superthin edge-on spiral galaxy IC 5249 and re-analyse synthesis
observations of the HI. We find that the HI rotation curve rises initially to
about 90-100 km/s, but contrary to the conclusion of Abe et al. (1999) flattens
well before the edge of the optical disk. Over most part of the optical disk we
have been able to establish that the (tangential) stellar velocity dispersion
is 25-30 km/s. From earlier surface photometry we adopt a value for the radial
scalelength of the disk of 7 +/- 1 kpc, a vertical scaleheight of 0.65 +/- 0.05
kpc and a disk truncation radius of 17 +/- 1 kpc. The very thin appearance of
IC 5249 on the sky is the result of a combination of a low (face-on) surface
brightness, a long scalelength and a a sharp truncation at only about 2.5
scalelengths. From various arguments we derive the stellar velocity dispersions
at a position one radial scalelength as sigma_R about 35 km/s, sigma_{theta}
about 30 km/s and sigma_z about 20 km/s. This is comparable to the values for
the disk of our Galaxy in the solar neighborhood.Comment: 11 pages and 8 figures. Accepted for Astronomy and Astrophysics
(September 2001
Identifying the gene(s) that allow tigriopus californicus to survive under thermal stress
The copepod species, Tigriopus californicus, is one of the most thermally adaptable species in the biosphere. They have been found in tide pools from the coast of Alaska down to the coast of Southern California. However, as all other organisms have limits, the T. californicus are only able to tolerate temperatures up to 34ÂșC. By comparing gene expression between specimens exposed to high temperatures and those expressed to optimal temperatures, we identified the genes responsible for conferring tolerance to increasing temperatures. After testing gene expression between copepods at 20ÂșC and at 34ÂșC, we have determined that both the hsp70 gene and the toll-like receptors of the T. californicus play a role in tolerance to temperature variance.LâespĂšce copĂ©pode, Tigriopus californicus, est une des espĂšces les plus thermiquement adaptables de la biosphĂšre. On les trouve dans les bĂąches depuis la cĂŽte de lâAlaska jusquâĂ la cĂŽte sud de la Californie. Toutefois, comme tous les autres organÂŹismes, les Tigriopus californicus ont des limites et ne peuvent pas tolĂ©rer des tempĂ©ratures supĂ©rieures Ă 34oC. En comparant lâexpression gĂ©nĂ©tique entre les spĂ©cimens exposĂ©s Ă des tempĂ©ratures Ă©levĂ©es et ceux exposĂ©s Ă des tempĂ©ratures optimales, nous avons identifiĂ© les gĂšnes responsables de la tolĂ©rance Ă des tempĂ©ratures en hausse. AprĂšs avoir testĂ© lâexpression gĂ©nĂ©tique entre les copĂ©podes Ă 20oC et Ă 34oC, nous avons dĂ©terminĂ© que le gĂšne hsp70 et les rĂ©cepteurs de type Toll du T. californicus jouent tous deux un rĂŽle dans la tolĂ©rance aux variations de tempĂ©rature
The outer disks of galaxies: "To be or not to be truncated?"
We have in recent years come to view the outer parts of galaxies as having
vital clues about their formation and evolution. Here, we would like to briefly
present our results from a complete sample of nearby, late-type, spiral
galaxies, using data from the SDSS survey, especially focused on the stellar
light distribution in the outer disk. Our study shows that only the minority of
late-type galaxies show a classical, exponential Freeman Type I profile down to
the noise limit, whereas the majority exhibit either downbending (stellar
truncation as introduced 1979 by Piet van der Kruit) or upbending profiles.Comment: LaTeX, 6 pages. To appear in the proceedings of the "Island
Universes: Structure and Evolution of Disk Galaxies" conference held in
Terschelling, Netherlands, July 2005, ed. R. de Jong (Springer: Dordrecht
Gravitational stability and dynamical overheating of stellar disks of galaxies
We use the marginal stability condition for galactic disks and the stellar
velocity dispersion data published by different authors to place upper limits
on the disk local surface density at two radial scalelengths .
Extrapolating these estimates, we constrain the total mass of the disks and
compare these estimates to those based on the photometry and color of stellar
populations. The comparison reveals that the stellar disks of most of spiral
galaxies in our sample cannot be substantially overheated and are therefore
unlikely to have experienced a significant merging event in their history. The
same conclusion applies to some, but not all of the S0 galaxies we consider.
However, a substantial part of the early type galaxies do show the stellar
velocity dispersion well in excess of the gravitational stability threshold
suggesting a major merger event in the past. We find dynamically overheated
disks among both seemingly isolated galaxies and those forming pairs. The ratio
of the marginal stability disk mass estimate to the total galaxy mass within
four radial scalelengths remains within a range of 0.4---0.8. We see no
evidence for a noticeable running of this ratio with either the morphological
type or color index.Comment: 25 pages, 5 figures, accepted to Astronomy Letter
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