18 research outputs found
The Clustering of K\sim 20 Galaxies on 17 Radio Galaxy Fields
We investigate the angular correlation function, , of the
galaxi es detected in the K-band on 17 fields (101.5 square arcmin in total),
each containing a radio galaxy. There is a significant detection of
galaxy clustering at limits, with an amplitude higher than expected
from simple models which fit the faint galaxy clustering in the blue and red
passbands, but consistent with a pure luminosity evolution model i f clustering
is stable and early-type galaxies have a steeper correlation function than
spirals. We do not detect a significant cross-correlation between the radio
galaxies and the other galaxies on these fields, obtaining upper limits
consistent with a mean clustering environment of Abell class 0 for
radio galaxies, similar to that observed for radio galaxies at . At
, the number of galaxy-galaxy pairs of 2--3 arcsec separations
exceeds the random expectation by a factor of . This excess
suggests at least a tripling of the local merger rate at .Comment: 13 pages, 3 tables, 7 postscript figures, TEX, submitted to MNRA
Multi-Object Near-IR H-alpha Spectroscopy of z~1 star-forming galaxies in the HDF-N
We present preliminary results from a programme to obtain multi-object
near-infrared spectroscopy of galaxies at redshifts . We are using
the instrument CIRPASS (the Cambridge Infra-Red PAnoramic Survey Spectrograph),
in multi-object mode, to survey H-alpha in galaxies at . We aim to
address the true star formation history of the universe at this epoch:
potentially the peak period of star formation activity. H-alpha is the same
star formation measure used at low redshift, and hence we can trace star
formation without the systematic uncertainties of using different calibrators
in different redshift bins, or the extreme dust extinction in the rest-UV.
CIRPASS has been successfully demonstrated in multi-object mode on the AAT and
WHT. Here we present preliminary results from one of our fields, the Hubble
Deep Field North, observed with the WHT. With 150 fibres deployed over an
unvignetted field of arcmin, we have several detections of H-alpha from
star forming galaxies at and present spectra of the seven brightest
of these. By pre-selecting galaxies with redshifts such that H-alpha will
appear between the OH sky lines, we can detect star formation rates of ( in 3-hours, ,
). It appears that star formation rates inferred from
H-alpha are, on average, a factor of more than two higher than those based on
the UV continuum alone.Comment: 6 pages, 3 figures, accepted for publication in MNRAS Letter
The Angular Correlation Function of K=19.5 Galaxies and the Detection of a Cluster at z=0.775
On five K-band Omega camera images, covering a total of 162.2 sq. arcmin to
K=19.5, we investigate (i) the clustering environment of 5 radio galaxies at
0.7<z<0.8 and (ii) the galaxy angular correlation function. We detect a cluster
of estimated Abell richness class 1 or 2, centred on the radio galaxy 5C6.75 at
z=0.775. Of the other radio galaxies, two appear to be in less rich groups or
structures, and two in field environments. The mean clustering environment of
all 5 is similar to that of radio galaxies at more moderate redshifts of
0.35<z<0.55. The angular correlation function of the galaxies, at limits
K=18.5--20.0, is most consistent with a luminosity evolution model in which
E/S0 galaxies are much more clustered than spirals (r_0=8.4 compared to 4.2 1/h
Mpc) and clustering is approximately stable (epsilon=0), although the
clustering may exceed the stable model at the highest (z>1.5) redshifts. We
also find a significant excess of 1.5--5.0 arcsec separation pairs of galaxies
compared to the expectation from the inward extrapolation of omega(theta). To
K=19.5, we estimate that 11.0\pm 3.4 per cent of galaxies are in close pairs in
excess of omega(theta). This can be explained if the local rate of galaxy
mergers and interactions increases with redshift as with
.Comment: 14 pages, latex, 8 figures, submitted to MNRA
Should we take patients to hospital in cardiac arrest?
We present deep diffraction-limited far-infrared (FIR) strip maps of a sample of 63 galaxies later than S0 and brighter than BT 16.8, selected from the Virgo Cluster Catalogue of Binggeli, Sandage & Tammann (1985). The ISOPHOT instrument on board the Infrared Space Observatory was used to achieve sensitivities typically an order of magnitude deeper than IRAS in the 60 and 100”m bands and to reach the confusion limit at 170”m. The averaged 3Ï upper limits for integrated flux densities of point sources at 60, 100 and 170”m are 43, 33 and 58mJy, respectively. 54 galaxies (85.7%) are detected at least at one wavelength, and 40 galaxies (63.5%) are detected at all three wavelengths. The highest detection rate (85.7%) is in the 170”m band. In many cases the galaxie