493 research outputs found
Three-dimensional modelling of edge-on disk galaxies
We present detailed three-dimensional modelling of the stellar luminosity
distribution for the disks of 31 relatively nearby (<= 110 Mpc) edge-on spiral
galaxies. In contrast to most of the standard methods available in the
literature we take into account the full three-dimensional information of the
disk. We minimize the difference between the observed 2D-image and an image of
our 3D-disk model integrated along the line of sight. Thereby we specify the
inclination, the fitting function for the z-distribution of the disk, and the
best values for the structural parameters such as scalelength, scaleheight,
central surface brightness, and a disk cut-off radius. From a comparison of two
independently developed methods we conclude, that the discrepancies e.g. for
the scaleheights and scalelengths are of the order of ~10%. These differences
are not due to the individual method itself, but rather to the selected fitting
region, which masks the bulge component, the dust lane, or present foreground
stars. Other serious limitations are small but appreciable intrinsic deviations
of real disks compared to the simple input model. In this paper we describe the
methods and present contour plots as well as radial profiles for all galaxies
without previously published surface photometry. Resulting parameters are given
for the complete sample.Comment: LaTeX, 25 pages, 28 figures higher quality figures available at
http://www.astro.ruhr-uni-bochum.de/astro/publications/pub2000.htm
Outer edges of face-on spiral galaxies
We present deep optical imaging of three face-on disk galaxies together with
a detailed description of the reduction and calibration methods used, in order
to measure the intrinsic shape of their outer stellar edges. Whereas it is now
well accepted that disks of spiral galaxies are not infinite exponential beyond
galactocentric distances of about 3-5 radial scalelengths, the genuine
structure of the truncation region is not yet well known. Our data
quantitatively establish a smooth truncation behaviour of the radial surface
brightness profiles and is best described by a two-slope model, characterised
by an inner and outer exponential scalelength separated at a relatively well
defined break radius. This result disagrees with the frequently assumed sharply
truncated nature of the radial surface brightness profiles and implies the
presence of stars and even star-formation beyond the break radius. In addition,
we do not find a strong influence of a nearby companion on the ratio of the
break radius to the radial scalelength. Our results denote new observational
constraints for the search of the physical explanation for these smooth disk
truncations.Comment: LaTeX, 10 pages, 17 figures, accepted to be published in A&A, minor
changes to the quality of figure
Radial distribution of gas and dust in spiral galaxies: The case of Mâ99 (NGCâ4254) and Mâ100 (NGCâ4321)
By combining Herschel-SPIRE data with archival Spitzer, Hâiâ, and CO maps, we investigate the spatial distribution of gas and dust in the two famous grand-design spirals Mâ99 and Mâ100 in the Virgo cluster. Thanks to the unique resolution and sensitivity of the Herschel-SPIRE photometer, we are for the first time able to measure the distribution and extent of cool, submillimetre (submm)-emitting dust inside and beyond the optical radius. We compare this with the radial variation in both the gas mass and the metallicity. Although we adopt a model-independent, phenomenological approach, our analysis provides important insights. We find the dust extending to at least the optical radius of the galaxy and showing breaks in its radial profiles at similar positions as the stellar distribution. The colour indices f350/f500 and f250/f350 decrease radially consistent with the temperature decreasing with radius. We also find evidence of an increasing gas to dust ratio with radius in the outer regions of both galaxies
Are truncated stellar disks linked to the molecular gas density?
We know that the slope of the radial, stellar light distribution in galaxies
is well described by an exponential decline and this distribution is often
truncated at a break radius (). We don't have a clear understanding for
the origin of these outer truncations and several hypotheses have been proposed
to explain them. We want to test the various theories with direct observations
of the cold molecular gas for a few truncated galaxies in comparison with the
non-truncated ones. The answer to the existence of a possible link between
truncated stellar disks and the molecular gas density cannot be obtained from
CO maps in the literature, because so far there are no galaxies with a clear
truncation observed in CO at high resolution.Comment: 3 pages, 6 figures, to appear in Astrophysics and Space Science
(Apss), special issue of "Science with ALMA: a new era for Astrophysics"
conference, ed. Dr. Bachille
Evidence for a Large Stellar Bar in the LSB Galaxy UGC 7321
Late-type spiral galaxies are thought to be the dynamically simplest type of
disk galaxies and our understanding of their properties plays a key role in the
galaxy formation and evolution scenarios. The low surface brightness (LSB)
galaxy UGC 7321, a nearby, isolated, ``superthin'' edge-on galaxy, is an ideal
object to study those purely disk dominated bulge-less galaxies. Although late
type spirals are believed to exhibit the simplest possible structure, even
prior observations showed deviations from a pure single component exponential
disk in the case of UGC 7321. We present for the first time photometric
evidence for peanut-shaped outer isophotes from a deep optical (R-band) image
of UGC 7321. Observations and dynamical modeling suggest that
boxy/peanut-shaped (b/p) bulges in general form through the buckling
instability in bars of the parent galaxy disks. Together with recent HI
observations supporting the presence of a stellar bar in UGC 7321 this could be
the earliest known case of the buckling process during the evolutionary life of
a LSB galaxy, whereby material in the disk-bar has started to be pumped up
above the disk, but a genuine bulge has not yet formed.Comment: LaTeX, 6 pages, 4 figures, accepted to be published in A&
The extent of dust in NGC 891 from Herschel/SPIRE images
We analyse Herschel/SPIRE images of the edge-on spiral galaxy NGC 891 at 250,
350 and 500 micron. Using a 3D radiative transfer model we confirm that the
dust has a radial fall-off similar to the stellar disk. The dust disk shows a
break at about 12 kpc from the center, where the profile becomes steeper.
Beyond this break, emission can be traced up to 90% of the optical disk in the
NE side. On the SW, we confirm dust emission associated with the extended,
asymmetric HI disk, previously detected by the Infrared Space Observatory
(ISO). This emission is marginally consistent with the large diffuse dust disk
inferred from radiative transfer fits to optical images. No excess emission is
found above the plane beyond that of the thin, unresolved, disk.Comment: Letter accepted for publication in A&A; final version after
shortening and language editin
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