1,314 research outputs found
Chemical abundances in low surface brightness galaxies: Implications for their evolution
Low Surface Brightness (LSB) galaxies are an important but often neglected part of the galaxy content of the universe. Their importance stems both from the selection effects which cause them to be under-represented in galaxy catalogs, and from what they can tell us about the physical processes of galaxy evolution that has resulted in something other than the traditional Hubble sequence of spirals. An important constraint for any evolutionary model is the present day chemical abundances of LSB disks. Towards this end, spectra for a sample of 75 H 2 regions distributed in 20 LSB disks galaxies were obtained. Structurally, this sample is defined as having B(0) fainter than 23.0 mag arcsec(sup -2) and scale lengths that cluster either around 3 kpc or 10 kpc. In fact, structurally, these galaxies are very similar to the high surface brightness spirals which define the Hubble sequence. Thus, our sample galaxies are not dwarf galaxies but instead have masses comparable to or in excess of the Milky Way. The basic results from these observations are summarized
The new Milky Way satellites: alignment with the VPOS and predictions for proper motions and velocity dispersions
The evidence that stellar systems surrounding the Milky Way (MW) are
distributed in a Vast Polar Structure (VPOS) may be observationally biased by
satellites detected in surveys of the northern sky. The recent discoveries of
more than a dozen new systems in the southern hemisphere thus constitute a
critical test of the VPOS phenomenon. We report that the new objects are
located close to the original VPOS, with half of the sample having offsets less
than 20 kpc. The positions of the new satellite galaxy candidates are so well
aligned that the orientation of the revised best-fitting VPOS structure is
preserved to within 9 degrees and the VPOS flattening is almost unchanged (31
kpc height). Interestingly, the shortest distance of the VPOS plane from the MW
center is now only 2.5 kpc, indicating that the new discoveries balance out the
VPOS at the Galactic center. The vast majority of the MW satellites are thus
consistent with sharing a similar orbital plane as the Magellanic Clouds,
confirming a hypothesis proposed by Kunkel & Demers and Lynden-Bell almost 40
years ago. We predict the absolute proper motions of the new objects assuming
they orbit within the VPOS. Independent of the VPOS results we also predict the
velocity dispersions of the new systems under three distinct assumptions: that
they (i) are dark-matter-free star clusters obeying Newtonian dynamics, (ii)
are dwarf satellites lying on empirical scaling relations of galaxies in dark
matter halos, and (iii) obey MOND.Comment: 17 pages, 6 figures, 5 tables. Updated to match version accepted for
publication in MNRA
Radio Observations of AGN in Low Surface Brightness Galaxies
We present preliminary results of a study of the low frequency radio
continuum emission from the nuclei of Giant Low Surface Brightness (LSB)
galaxies. We have mapped the emission and searched for extended features such
as radio lobes/jets associated with AGN activity. LSB galaxies are poor in star
formation and generally less evolved compared to nearby bright spirals. This
paper presents low frequency observations of 3 galaxies; PGC 045080 at 1.4 GHz,
610 MHz, 325MHz, UGC 1922 at 610 MHz and UGC 6614 at 610 MHz. The observations
were done with the GMRT. Radio cores as well as extended structures were
detected and mapped in all three galaxies; the extended emission may be
assocated with jets/lobes associated with AGN activity. Our results indicate
that although these galaxies are optically dim, their nuclei can host AGN that
are bright in the radio domain.Comment: To appear in proceedings IAU Symp 244, 'Dark Galaxies and Lost
Baryons', June 2007, 2 pages including 1 figur
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