2,162 research outputs found
A New Galaxy in the Local Group: the Antlia Dwarf Galaxy
We report the discovery of new member of the Local Group in the constellation
of Antlia. Optically the system appears to be a typical dwarf spheroidal galaxy
of type dE3.5 with no apparent young blue stars or unusual features. A
color-magnitude diagram in I, V-I shows the tip of the red giant branch, giving
a distance modulus of 25.3 +/- 0.2 (1.15 Mpc +/- 0.1) and a metallicity of -1.6
+/- 0.3. Although Antlia is in a relatively isolated part of the Local Group it
is only 1.2 degrees away on the sky from the Local Group dwarf NGC3109, and may
be an associated system.Comment: AJ in press, 15 pages, 7 figures, figure 2 in b/w for space saving,
full postscript version available at
http://www.ast.cam.ac.uk/~gkth/antlia-pp.htm
Visual Search for Galaxies near the Northern Crossing of the Supergalactic plane by the Milky Way
We have visually examined twelve Palomar red Plates for galaxies at low
Galactic latitude b, where the Supergalactic Plane (SGP) is crossed by the
Galactic Plane (GP), at Galactic longitude l ~135 degrees. The catalogue
consists of 2575 galaxy candidates, of which 462 have major axis diameters d >=
0.8 arc min (uncorrected for extinction). Galaxy candidates can be identified
down to |b| ~ 0 degrees. One of our galaxy candidates (J24 = Dwingeloo 1) has
recently been discovered independently in 21cm by Kraan-Korteweg et al. (1994)
as a nearby galaxy. Comparisons with the structures seen in the IRAS and UGC
catalogues are made. We compare the success rate of identifying galaxies using
the IRAS Point Source Catalogue under different colour selection criteria. The
criteria that require both the 60 micron and 100 micron fluxes to be of high
quality, have the highest probability of selecting a galaxy (with d >= 0.6 arc
min), but at the expense of selecting a smaller number of galaxies in total.Comment: uuencoded compressed postscript, without figures. The figures are
available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm
An Observational Limit on the Dwarf Galaxy Population of the Local Group
We present the results of an all-sky, deep optical survey for faint Local
Group dwarf galaxies. Candidate objects were selected from the second Palomar
survey (POSS-II) and ESO/SRC survey plates and follow-up observations performed
to determine whether they were indeed overlooked members of the Local Group.
Only two galaxies (Antlia and Cetus) were discovered this way out of 206
candidates. Based on internal and external comparisons, we estimate that our
visual survey is more than 77% complete for objects larger than one arc minute
in size and with a surface brightness greater than an extremely faint limit
over the 72% of the sky not obstructed by the Milky Way. Our limit of
sensitivity cannot be calculated exactly, but is certainly fainter than 25
magnitudes per square arc second in R, probably 25.5 and possibly approaching
26. We conclude that there are at most one or two Local Group dwarf galaxies
fitting our observational criteria still undiscovered in the clear part of the
sky, and a roughly a dozen hidden behind the Milky Way. Our work places the
"missing satellite problem" on a firm quantitative observational basis. We
present detailed data on all our candidates, including surface brightness
measurements.Comment: 58 pages in AJ manuscript format; some figures at slightly reduced
quality; accepted by the Astronomical Journa
The puzzlingly large Ca II triplet absorption in dwarf elliptical galaxies
We present central CaT, PaT, and CaT* indices for a sample of fifteen dwarf
elliptical galaxies (dEs). Twelve of these have CaT* ~ 7 A and extend the
negative correlation between the CaT* index and central velocity dispersion
sigma, which was derived for bright ellipticals (Es), down to 20 < sigma < 55
km/s. For five dEs we have independent age and metallicity estimates. Four of
these have CaT* ~ 7 A, much higher than expected from their low metallicities
(-1.5 < [Z/H] < -0.5). The observed anti-correlation of CaT* as a function of
sigma or Z is in flagrant disagreement with theory. We discuss some of the
amendments that have been proposed to bring the theoretical predictions into
agreement with the observed CaT*-values of bright Es and how they can be
extended to incorporate also the observed CaT*-values of dEs. Moreover, 3 dEs
in our sample have CaT* ~ 5 A, as would be expected for metal-poor stellar
systems. Any theory for dE evolution will have to be able to explain the
co-existence of low-CaT* and high-CaT* dEs at a given mean metallicity. This
could be the first direct evidence that the dE population is not homogeneous,
and that different evolutionary paths led to morphologically and kinematically
similar but chemically distinct objects.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Novelty Induces Behavioural And Glucocorticoid Responses In A Songbird Artificially Selected For Divergent Personalities
Stress physiology is thought to contribute to individual differences in behaviour. In part this reflects the fact that canonical personality measures consist of responses to challenges, including novel objects and environments. Exposure to novelty is typically assumed to induce a moderate increase in glucocorticoids (CORT), although this has rarely been tested. We tested this assumption using great tits, Parus major, selected for divergent personalities (bold-fast and shy-slow explorers), predicting that the shy birds would exhibit higher CORT following exposure to a novel object. We also scored behavioural responses to the novel object, predicting that bold birds would more frequently approach the novel object and exhibit more abnormal repetitive behaviours. We found that the presence of a novel object did induce a moderate CORT response, but selection lines did not differ in the magnitude of this response. Furthermore, although both selection lines showed a robust CORT elevation to a subsequent restraint stressor, the CORT response was stronger in bold birds and this effect was specific to novel object exposure. Shy birds showed a strong positive phenotypic correlation between CORT concentrations following the novel object exposure and the subsequent restraint stress. Behaviourally, the selection lines differed in their response during novel object exposure: as predicted, bold birds more frequently approached the novel object and shy birds more strongly decreased overall locomotion during the novel object trial, but birds from both selection lines showed significant and similar frequencies of abnormal repetitive behaviours during novel object exposure. Our findings support the hypothesis that personality emerges as a result of correlated selection on behaviour and underlying endocrine mechanisms and suggest that the relationship between endocrine stress physiology and personality is context dependent
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Local entanglement and confinement transitions in the random transverse-field Ising model on the pyrochlore lattice
We use numerical linked cluster expansions (NLC) and exact diagonalization to study confinement transitions out of the quantum spin liquid phase in the pyrochlore-lattice Ising antiferromagnet with random transverse fields. We calculate entanglement entropies associated with local regions defined by single tetrahedron to observe these transitions. The randomness-induced confinement transition is marked by a sharp reduction in the local entanglement and a concomitant increase in Ising correlations. In NLC, it is studied through the destruction of loop resonances due to random transverse-fields. The confining phase is characterized by a distribution of local entanglement entropies, which persists to large random fields
Observational evidence for a connection between supermassive black holes and dark matter haloes
We present new velocity dispersion measurements of sample of 12 spiral
galaxies for which extended rotation curves are available. These data are used
to refine a recently discovered correlation between the circular velocity and
the central velocity dispersion of spiral galaxies. We find a slightly steeper
slope for our larger sample, we confirm the negligible intrinsic scatter on
this correlation, and we find a striking agreement with a corresponding
relation for elliptical galaxies. We combine this correlation with the
well-known MBH-sigma relation to obtain a tight correlation between the
circular velocities of galaxies and the masses of the supermassive black holes
they host. This correlation is the observational evidence for an intimate link
between dark matter haloes and supermassive black holes. Apart from being an
important ingredient for theoretical models of galaxy formation and evolution,
the relation between MBH and circular velocity can serve as a practical tool to
estimate black hole masses in spiral galaxies.Comment: 5 pages, 2 figures, accepted for publication in MNRAS pink page
Echinostoma caprom' infection in non-pregnant female BALB/c and Swiss T.O. mice: effect on feed intake, liveweight, and serum pregnancy-associated murine protein-l and corticosterone
The effect of experimental infection with the intestinal ti'einatode. Echinosloma caprani, on feed intake, liyeweight and serum pregnaney-associated murine protein-l (PAMP-1) and corticosteronc was investigated in non-pregnant female BALB/cand Swiss T.O. mice. Twenty-five metacereariae were given by oral gavage on day 0 of which 19.6 % were recovered at post monem on day 46 in the BALB/c mice and 22.0 % in the Swiss T.O. mice. Oral praziquantel treatment (50 mg/kg) on day 39 reduced the recovery of tlnkes from previously-infected mice by 85.4% and 100% in BALB/e and Swiss T 0 mice respectively. The food consumption in the infected Swiss T.0. mice was significantly increased compared to the infected-treated and the controls. In the BALB/c mice the food intake in the infected and infectedtreated animals was significantly increased compared with the controls, The liveweight gain during the experiment in the BALB/e control mice was significantly higher than in the infectedtreated groups. In the Swiss T.0. mice the infected animals gained more weight than the controls and the infected- treated animals. E. caproni was associated with a significant reduction in PAMP-l concentrations in both strains of mice, even in animals from which the majority of flukes had been removed by praziquantel-treatment. There was no significant correlation between the magnitude of the parasite burden and serum PAMP~1 values. Corticosterone values were unaffected by either mouse strain, E. capromi infection or anthelmintie treatment. These results suggest that the previously reported adverse effect of E. capromi on early pregnancy in mice may be caused by parasiteiinduced effects occurring prior to fertilisation
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