159 research outputs found
The Local Environment of HII Galaxies
We address the question of whether violent star formation in HII galaxies is
induced by low mass companions by describing statistically their local
environment as estimated by the correlation function. We argue that even if low
mass companions were mainly intergalactic HI clouds, their optical counterparts
should be detectable at faint limits of the Automatic Plate Measuring Machine
scans. We then cross-correlate a large sample of HII galaxies with the APM
faint field galaxy catalogue. The preliminary results are all consistent with
HII galaxies being a randomly selected sample of normal faint field galaxy with
no extra clustering. This suggests that at least in these dwarf starburst
galaxies star formation is not triggered by tidal interactions and may have a
different origin.Comment: 4 pages, 2 Postscript figures, uses moriond.sty. To appear in ``Dwarf
Galaxies and Cosmology'', Eds. T.X. Thuan, C. Balkowski, V. Cayette, J. Tran
Than Van, Editions Frontieres (Gyf-sur-Yvette, France
The APM Galaxy Survey:- V. Catalogues of Galaxy Clusters
We describe the construction of catalogues of galaxy clusters from the APM
Galaxy survey using an automated algorithm based on Abell-like selection
criteria. We investigate the effects of varying several parameters in our
selection algorithm, including the magnitude range, and radius from the cluster
centre used to estimate the cluster richnesses. We quantify the accuracy of the
photometric distance estimates by comparing with measured redshifts, and we
investigate the stability and completeness of the resulting catalogues. We find
that the angular correlation functions for different cluster catalogues are in
good agreement with one another, and are also consistent with the observed
amplitude of the spatial correlation function of rich clusters.Comment: 14 pages, PostScript, including 15 figures, submitted to MNRAS. Also
available from ftp://ftp-astro.physics.ox.ac.uk/pub/gbd/papers/apm5.ps.g
Weak Gravitational Lensing by a Sample of X-ray Luminous Clusters of Galaxies -- III. Serendipitous Weak Lensing Detections of Dark and Luminous Mass Concentrations
In the course of a weak gravitational lensing survey of 39 clusters of
galaxies,covering a total sky area of ~1 square degree, we have serendipitously
discovered mass concentrations in the fields of A1705 and A1722 which are most
probably not associated with the main cluster target. By combining weak lensing
information with two-color galaxy photometry in fields centered on our sample
clusters, we identify a new cluster candidate at z~0.5 in the field of A1705.
This cluster candidate also displays strong lensing in the form of a giant
luminous arc. The new mass concentration in the field of A1722 also seems to be
associated with an optically luminous cluster of galaxies at z~0.5, but in this
case there is some evidence for additional structures along the line of sight
that may contribute to the lensing signal. A third cluster, A959, has a dark
sub-clump which shows interesting morphological evidence in the mass map for
being associated with the main cluster. This is the first case where there is
any significant evidence for a physical association between a dark sub-clump
(discovered from weak lensing) and a normal cluster. Analysis of archival X-ray
data shows that the three new mass concentrations are not firmly detected in
X-rays and that they are X-ray underluminous.Comment: 14 pages, 10 figures, version accepted by ApJ. See
http://www.nordita.dk/~dahle/paper3.ps.gz for a version with high-resolution
figures and Fig.5 in colo
Teacher Candidate Success on State Mandated Professional Tests: One Predictive Measure
This article presents a predictive model using teacher candidates\u27 Grade Point Average (GPA) and its relationship to candidate success on two professional state mandated teaching exams. The 196 subjects for the study were traditional undergraduate teacher education candidates at a major university in Virginia. Specifically, the majority of courses were presented in the face-to-face setting, with a few online courses available. Subject selection was based upon completion of the Virginia Communication Literacy Assessment (VCLA) and the Virginia Reading Assessment (VRA). Data were collected for three consecutive years. Analysis of the relationship between GPA and scores on the VRA and VCLA demonstrated a statistically significant relationship between (a) GPA and mean score on the VRA, and (b) GPA and mean score on the VCLA. These results indicate that better overall performance in the classroom, as measured by grade point average (GPA), produces a higher mean score on both professional assessments
The Ha Luminosity Function and Star Formation Rate at z\sim 0.2
We have measured the Ha+[N II] fluxes of the I-selected Canada-France
Redshift Survey (CFRS) galaxies lying at a redshift z below 0.3, and hence
derived the Ha luminosity function. The magnitude limits of the CFRS mean that
only the galaxies with M(B) > -21 mag were observed at these redshifts. We
obtained a total Ha luminosity density of at least 10^{39.44\pm 0.04}
erg/s/Mpc^{3} at a mean z=0.2 for galaxies with rest-fame EW(Ha+[N II]) > 10
Angs. This is twice the value found in the local universe by Gallego et al.
1995. Our Ha star formation rate, derived from Madau (1997) is higher than the
UV observations at same z, implying a UV dust extinction of about 1 mag. We
found a strong correlation between the Ha luminosity and the absolute magnitude
in the B-band: M(B(AB)) = 46.7 - 1.6 log L(Ha). This work will serve as a basis
of future studies of Ha luminosity distributions measured from
optically-selected spectroscopic surveys of the distant universe, and it will
provide a better understanding of the physical processes responsible for the
observed galaxy evolution.Comment: Accepted for publication in ApJ, 14 pages, LaTeX (macro aas2pp4.sty),
6 figure
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