11,290 research outputs found
The stellar content of the Local Group dwarf galaxy Phoenix
We present new deep ground-based photometry of the Local Group dwarf
galaxy Phoenix. Our results confirm that this galaxy is mainly dominated by red
stars, with some blue plume stars indicating recent (100 Myr old) star
formation in the central part of the galaxy. We have performed an analysis of
the structural parameters of Phoenix based on an ESO/SRC scanned plate, in
order to search for differentiated component. The results were then used to
obtain the color-magnitude diagrams for three different regions of Phoenix in
order to study the variation of the properties of its stellar population. The
young population located in the central component of Phoenix shows a clear
asymmetry in its distribution, that could indicate a propagation of star
formation across the central component. The HI cloud found at 6 arcmin
Southwest by Young & Lo (1997) could have been involved in this process.
We also find the presence of a substantial intermediate-age population in the
central region of Phoenix that would be less abundant or absent in its outer
regions. This result is also consistent with the gradient found in the number
of horizontal branch stars, whose frequency relative to red giant branch stars
increases towards the outer part of the galaxy. These results, together with
those of our morphological study, suggest the existence of an old, metal-poor
population with a spheroidal distribution surrounding the younger inner
component of Phoenix. This two-component structure may resemble the halo-disk
structure observed in spirals, although more data, in particular on kinematics,
are necessary to confirm this.Comment: 46 pages, 21 figures, 9 Tables, to be published in AJ, August 9
Stellar Populations in the Andromeda V Dwarf Spheroidal Galaxy
Using archival imaging from the Wide Field Planetary Camera 2 aboard the
Hubble Space Telescope, we investigate the stellar populations of the Local
Group dwarf spheroidal Andromeda V - a companion satellite galaxy of M31. The
color-magnitude diagram (CMD) extends from above the first ascent red giant
branch (RGB) tip to approximately one magnitude below the horizontal branch
(HB). The steep well-defined RGB is indicative of a metal-poor system while the
HB is populated predominantly redward of the RR Lyrae instability strip.
Utilizing Galactic globular cluster fiducial sequences as a reference, we
calculate a mean metallicity of [Fe/H] = -2.20 +/- 0.15 and a distance of
(m-M)0 = 24.57 +/- 0.04 after adopting a reddening of E(B-V) = 0.16. This metal
abundance places And V squarely in the absolute magnitude - metallicity diagram
for dwarf spheroidal galaxies. In addition, if we attribute the entire
error-corrected color spread of the RGB stars to an abundance spread, we
estimate a range of ~0.5 dex in the metallicities of And V stars. Our analysis
of the variable star population of And V reveals the presence of 28 potential
variables. Of these, at least 10 are almost certainly RR Lyrae stars based on
their time sequence photometry.Comment: 4 pages, 6 figures Accepted to the Astronomical Journa
DGSAT: Dwarf Galaxy Survey with Amateur Telescopes II. A catalogue of isolated nearby edge-on disk galaxies and the discovery of new low surface brightness systems
The connection between the bulge mass or bulge luminosity in disk galaxies
and the number, spatial and phase space distribution of associated dwarf
galaxies is a discriminator between cosmological simulations related to galaxy
formation in cold dark matter and generalized gravity models. Here, a nearby
sample of isolated Milky Way class edge-on galaxies is introduced, to
facilitate observational campaigns to detect the associated families of dwarf
galaxies at low surface brightness. Three galaxy pairs with at least one of the
targets being edge-on are also introduced. About 60% of the catalogued isolated
galaxies contain bulges of different size, while the remaining objects appear
to be bulge-less. Deep images of NGC 3669 (small bulge, with NGC 3625 at the
edge of the image) and NGC 7814 (prominent bulge), obtained with a 0.4-m
aperture, are also presented, resulting in the discovery of two new dwarf
galaxy candidates, NGC3669-DGSAT-3 and NGC7814-DGSAT-7. Eleven additional low
surface brightness galaxies are identified, previously notified with low
quality measurement flags in the Sloan Digital Sky Survey (SDSS). Integrated
magnitudes, surface brightnesses, effective radii, Sersic indices, axis ratios,
and projected distances to their putative major hosts are displayed. At least
one of the galaxies, NGC3625-DGSAT-4, belongs with a surface brightness of
approximately 26 mag per arcsec^2 and effective radius >1.5 kpc to the class of
ultra-diffuse galaxies (UDGs). NGC3669-DGSAT-3, the galaxy with lowest surface
brightness in our sample, may also be an UDG.Comment: 12 pages including 6 figures, 4 tables, a brief appendix, accepted
for publication in Astronomy & Astrophysics (A&A). Paper slightly modified
after A&A language editing, updating very few references and correcting a
small typo at the start of the Appendi
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