1,391 research outputs found
The dark and baryonic matter content of low surface brightness disk galaxies
We present mass models of a sample of 19 low surface brightness (LSB)
galaxies and compare the properties of their constituent mass components with
those of a sample of high surface brightness (HSB) galaxies.We find that LSB
galaxies are dark matter dominated. Their halo parameters are only slightly
affected by assumptions on stellar mass-to-light ratios. Comparing LSB and HSB
galaxies we find that mass models derived using the maximum disk hypothesis
result in the disks of LSB galaxies having systematically higher stellar
mass-to-light ratios than HSB galaxies of similar rotation velocity. This is
inconsistent with all other available evidence on the evolution of LSB
galaxies. We argue therefore that the maximum disk hypothesis does not provide
a representative description of the LSB galaxies and their evolution. Mass
models with stellar mass-to-light ratios determined by the colors and stellar
velocity dispersions of galactic disks imply that LSB galaxies have dark matter
halos that are more extended and less dense than those of HSB galaxies. Surface
brightness is thus related to the halo properties. LSB galaxies are slowly
evolving, low density and dark matter dominated galaxies.Comment: 23 pages Latex, 12 postscript figures, uses mn.sty. Accepted for
publication in MNRA
Testing Modified Newtonian Dynamics with Low Surface Brightness Galaxies --Rotation curve fits-
We present MOND (Modified Newtonian Dynamics) fits to 15 rotation curves of
LSB galaxies. Good fits are readily found, although for a few galaxies minor
adjustments to the inclination are needed. Reasonable values for the stellar
mass-to-light ratios are found, as well as an approximately constant value for
the total (gas and stars) mass-to-light ratio. We show that the LSB galaxies
investigated here lie on the one, unique Tully-Fisher relation, as predicted by
MOND. The scatter on the Tully-Fisher relation can be completely explained by
the observed scatter in the total mass-to-light ratio. We address the question
of whether MOND can fit any arbitrary rotation curve by constructing a
plausible fake model galaxy. While MOND is unable to fit this hypothetical
galaxy, a normal dark halo fit is readily found, showing that dark matter fits
are much less selective in producing fits. The good fits to rotation curves of
LSB galaxies support MOND, especially as these are galaxies with large mass
discrepancies deep in the MOND regime.Comment: Accepted for publication in Astrophysical Journal 14 page
The baryonic Tully-Fisher relation and its implication for dark matter halos
The baryonic Tully-Fisher relation (BTF) is a fundamental relation between
baryonic mass and maximum rotation velocity. It can be used to estimate
distances, as well as to constrain the properties of dark matter and its
relation with the visible matter. In this paper, we explore if extremely
low-mass dwarf galaxies follow the same BTF relation as high-mass galaxies. We
quantify the scatter in the BTF relation and use this to constrain the allowed
elongations of dark matter halo potentials. We obtained HI synthesis data of 11
dwarf galaxies and derive several independent estimates for the maximum
rotation velocity. Constructing a BTF relation using data from the literature
for the high-mass end, and galaxies with detected rotation from our sample for
the low-mass end results in a BTF with a scatter of 0.33 mag. This scatter
constrains the ellipticities of the potentials in the plane of the disks of the
galaxies to an upper limit of 0-0.06 indicating that dwarf galaxies are at most
only mildly tri-axial. Our results indicate that the BTF relation is a
fundamental relation which all rotationally dominated galaxies seem to follow.Comment: Accepted for publication in A&
The Stellar Populations of Low Surface Brightness Galaxies
Near-infrared (NIR) K' images of a sample of five low surface brightness disc
galaxies (LSBGs) were combined with optical data, with the aim of constraining
their star formation histories. Both red and blue LSBGs were imaged to enable
comparison of their stellar populations. For both types of galaxy strong colour
gradients were found, consistent with mean stellar age gradients. Very low
stellar metallicities were ruled out on the basis of metallicity-sensitive
optical-NIR colours. These five galaxies suggest that red and blue LSBGs have
very different star formation histories and represent two independent routes to
low B band surface brightness. Blue LSBGs are well described by models with
low, roughly constant star formation rates, whereas red LSBGs are better
described by a `faded disc' scenario.Comment: 5 pages LaTeX; 2 embedded figures; MNRAS Letters, Accepte
Low Surface Brightness Galaxies around the HDF-S: II. Distances and volume densities
With this study we aim at the spectroscopic verification of a photometrically
selected sample of Low Surface Brightness (LSB) galaxy candidates in a field
around the Hubble Deep Field-South (HDF-S). The sample helps to extend the
parameter space for LSB galaxies to lower central surface brightnesses and to
provide better estimates on the volume densities of these objects. To derive
redshifts for the LSB candidates, long-slit spectra were obtained covering a
spectral range from 3400{\AA} to 7500{\AA}. The observations have been obtained
using the ESO 3.6m telescope, equipped with the EFOSC2 spectrograph. From the
measured radial velocities, distances could be estimated. With this distance
information, it is possible to differentiate between true LSB galaxies and
higher redshift High Surface Brightness (HSB) galaxies which may contaminate
the sample. A correction for the surface brightnesses can then be applied,
accounting for the cosmological dimming effect (``Tolman Dimming''). We show
that ~70% of the LSB candidates, selected based on their location in the
color-color space, are real LSB galaxies. Their position in the color-color
diagrams, therefore, indicate that the LSB galaxies have a different stellar
population mix resulting from a different star formation history compared to
HSBs. Our LSB galaxy sample consists only of large disk galaxies with
scale-length between 2.5kpc and 7.3kpc. We confirm the flat central surface
brightness distribution of previous surveys and extend this distribution down
to central surface brightnesses of 27 B mag arcsec^-2.Comment: 12 pages, 20 figures, accepted by A&
The Baryon Content of Cosmic Structures
We make an inventory of the baryonic and gravitating mass in structures
ranging from the smallest galaxies to rich clusters of galaxies. We find that
the fraction of baryons converted to stars reaches a maximum between M500 =
1E12 and 1E13 Msun, suggesting that star formation is most efficient in bright
galaxies in groups. The fraction of baryons detected in all forms deviates
monotonically from the cosmic baryon fraction as a function of mass. On the
largest scales of clusters, most of the expected baryons are detected, while in
the smallest dwarf galaxies, fewer than 1% are detected. Where these missing
baryons reside is unclear.Comment: ApJ Letters, in pres
Low surface brightness galaxies
A program to investigate the properties of low surface brightness (LSB) galaxies involving surface photometry in U, B, V, R, I, and H-alpha, HI imaging with the Westerbork Synthesis Radio Telescope (WSRT) and the very large array (VLA) and spectrophotometry of H2 regions in LSB galaxies is underway. The goal is to verify the idea that LSB galaxies have low star formation rates because the local gas density falls below the critical density for star formation, and to study the stellar population and abundances in LSB galaxies. Such information should help understanding the evolutionary history of LSB galaxies. Some preliminary results are reported
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