701 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.
Structure and kinematics of edge-on galaxy discs -- IV. The kinematics of the stellar discs
The stellar disc kinematics in a sample of fifteen intermediate- to late-type
edge-on spiral galaxies are studied using a dynamical modeling technique. The
sample covers a substantial range in maximum rotation velocity and deprojected
face-on surface brightness and contains seven spirals with either a boxy- or
peanut-shaped bulge. Dynamical models of the stellar discs are constructed
using the disc structure from -band surface photometry and rotation curves
observed in the gas. The differences in the line-of-sight stellar kinematics
between the models and absorption line spectroscopy are minimized using a
least-squares approach. The modeling constrains the disc surface density and
stellar radial velocity dispersion at a fiducial radius through the free
parameter , where
is the ratio of vertical and radial velocity
dispersion and the disc mass-to-light ratio. For thirteen spirals a
transparent model provides a good match to the mean line-of-sight stellar
velocity dispersion. Models that include a realistic radiative transfer
prescription confirm that the effect of dust on the observable stellar
kinematics is small at the observed slit positions. We discuss possible sources
of systematic error and conclude that most of these are likely to be small. The
exception is the neglect of the dark halo gravity, which has probably caused an
overestimate of the surface density in the case of low surface brightness
discs.Comment: Accepted for publication by the Monthly Notices of the R.A.
Structure and kinematics of edge-on galaxy discs -- III. The rotation curves in the gas
A technique is introduced for deriving the gaseous rotation curves of edge-on
spiral galaxies. The entire major axis position-velocity (XV) diagram is
modeled with a set of rings in a least-squares sense, allowing for the effects
of beam-smearing and line-of-sight projection. The feasibility of the technique
is demonstrated by applying it to good quality HI XV diagrams of eight edge-on
spirals. For seven additional spirals the XV diagrams are of insufficient
quality, and the HI rotational velocities derived earlier using the
envelope-tracing method are retained. The HI results are augmented with the
optical emission line (HII) kinematics to arrive at estimates of the full
rotation curves. A detailed comparison of the HI and HII kinematics shows that
the discs in our sample are sufficiently transparent at the heights above the
plane where we have taken our optical spectra to derive the stellar kinematics.
In several of these spirals the HII is mainly confined to spiral arms and does
not extend out to the edge of the HI layer, which may have caused the HII
velocity profiles to be significantly narrower than those of the HI.
This paper has been accepted by MNRAS and is available in pdf-format at the
following URL: http://www.astro.rug.nl/vdkruit/jea3/homepage/paperIII.pdfComment: Accepted for publication in MNRA
Structure and kinematics of edge-on galaxy discs -- II. Observations of the neutral hydrogen
We present Australia Telescope Compact Array (ATCA) and Westerbork Synthesis
Radio Telescope (WSRT) HI observations of 15 edge-on spiral galaxies of
intermediate to late morphological type. The global properties and the
distribution and kinematics of the HI gas are analysed and discussed. We
determine the rotation curves using the envelope-tracing method. For 10 spiral
galaxies with a stellar disc truncation we find an average ratio of the HI
radius to the truncation radius of the stellar disc of 1.1 +/- 0.2 (1 sigma).
This paper has been accepted by MNRAS and is available in pdf-format at the
following URL: http://www.astro.rug.nl/vdkruit/jea3/homepage/paperII.pdfComment: Accepted for oublication in MNRA
Structure, mass and stability of galactic disks
In this review I concentrate on three areas related to structure of disks in
spiral galaxies. First I will review the work on structure, kinematics and
dynamics of stellar disks. Next I will review the progress in the area of
flaring of HI layers. These subjects are relevant for the presence of dark
matter and lead to the conclusion that disk are in general not `maximal', have
lower M/L ratios than previously suspected and are locally stable w.r.t.
Toomre's Q criterion for local stability. I will end with a few words on
`truncations' in stellar disks.Comment: Invited review at "Galaxies and their Masks" for Ken Freeman's 70-th
birthday, Sossusvlei, Namibia, April 2010. A version with high-res. figures
is available at
http://www.astro.rug.nl/~vdkruit/jea3/homepage/Namibiachapter.pd
NGC 3310, a galaxy merger?
The HI structure and kinematics of the peculiar starburst galaxy NGC 3310
(Arp 217, UGC 5786) are discussed. New evidence bearing on the origin of the
starburst is presented. The bulk of HI coincides with the bright optical disk
and shows differential rotation. Its velocity dispersion is, however, unusually
large for a spiral galaxy (up to 40 km/s), suggesting that the disk is highly
perturbed as already indicated by optical emission line spectroscopy. There
are, in addition, two prominent HI tails, one extending to the north-west and
the other, somewhat patchy, to the south. These HI tails, the perturbed
kinematics and the peculiar optical morphology strongly suggest a recent merger
between two gas-rich galaxies. This seems to have been a major merger in which
most of the gas in the inner parts has been preserved in neutral atomic form
and either one of the progenitor disks has survived or a new disk has formed.Comment: 10 pages, 11 figures, accepted for publication in A&
A faint red stellar halo around an edge-on disc galaxy in the Hubble Ultra Deep Field
We analyse the detailed structure of a highly-inclined (i>~80 degrees) disc
galaxy which lies within the Hubble Ultra Deep Field (UDF). The unprecedented
depth of the UDF data allow disc and extraplanar emission to be reliably traced
to surface brightness levels of mu_{V,i,z}~29-30 mag/arcsec^2 (corresponding to
rest-frame equivalents of mu_{g,r,i}~28-29 mag/arcsec^2) in this redshift
z=0.32 system. We detect excess emission above the disc which is characterised
by a moderately-flattened (b/a~0.6) power-law (I proportional to R^(-2.6)). The
structure and colour of this component are very similar to the stellar halo
detected in an SDSS stacking analysis of local disc galaxies (Zibetti, White
and Brinkmann 2004) and lend support to the idea that we have detected a
stellar halo in this distant system. Although the peculiar colours of the halo
are difficult to understand in terms of normal stellar populations, the
consistency found between the UDF and SDSS analyses suggests that they cannot
be easily discounted.Comment: 5 pages, 5 figures, accepted for publication in MNRAS Letters. Figure
1 substantially degraded, full resolution version available at
http://www.mpa-garching.mpg.de/~zibetti/UDFhalo.pd
A possible radio supernova in the outer part of NGC 3310
As part of an on-going radio supernova monitoring program, we have discovered
a variable, compact steep spectrum radio source ~65 arcsec (~4 kpc) from the
centre of the starburst galaxy NGC 3310. If the source is at the distance of
NGC 3310, then its 5 GHz luminosity is ~3 x 10^{19} WHz^-1. The source
luminosity, together with its variability characteristics, compact structure
(<17 mas) and its association with a group of HII regions, leads us to propose
that it is a previously uncatalogued type II radio supernova. A search of
archival data also shows an associated X-ray source with a luminosity similar
to known radio supernova.Comment: 5 pages, 3 figures. Accepted by MNRA
Equilibrium Disk-Bulge-Halo Models for the Milky Way and Andromeda Galaxies
We describe a new set of self-consistent, equilibrium disk galaxy models that
incorporate an exponential disk, a Hernquist model bulge, an NFW halo and a
central supermassive black hole. The models are derived from explicit
distribution functions for each component and the large number of parameters
permit detailed modeling of actual galaxies. We present techniques that use
structural and kinematic data such as radial surface brightness profiles,
rotation curves and bulge velocity dispersion profiles to find the best-fit
models for the Milky Way and M31. Through N-body realizations of these models
we explore their stability against the formation of bars. The models permit the
study of a wide range of dynamical phenomenon with a high degree of realism.Comment: 58 pages, 20 figures, submitted to the Astrophysical Journa
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