4,234 research outputs found
Deep Spectroscopy in the Field of 3C 212
We present the results of longslit and multiaperture spectroscopy of faint
galaxies in the field of the z=1.049 quasar 3C212. We show that an apparently
aligned optical feature beyond the NW radio lobe has a redshift z=0.928, and a
similarly aligned feature just beyond the SE radio lobe has a redshift z=1.053,
quite close to that of the quasar. While the NW optical component is extremely
well aligned with the radio jet and has a morphology that is very similar to
that of the radio lobe lying 3" interior to it, the fact that we find three
other field galaxies with closely similar redshifts indicates that it is most
likely a member of an intervening group rather than an unusual example of true
alignment with the radio structure. In addition, we have found two galaxies
(besides the one near the SE radio lobe) having redshifts close to that of
3C212. We have firm or probable redshifts for 66 out of 82 galaxies we have
observed in this field. Comparison with the redshift distribution of faint
field galaxies indicates that a large fraction of the remaining 16 galaxies are
likely to be at redshifts >1.4. There are at least two low-redshift dwarf
starburst galaxies showing low metal abundance and high ionization in our
sample; such galaxies are likely to be relatively common in very faint samples,
and, under certain conditions, they could be confused with high-redshift
objects.Comment: 15 pages, 4 figures, one of which is a separate JPEG plate. To be
published in the April 1998 issue of The Astronomical Journa
Oxygen Gas Abundances at 0.4<z<1.5: Implications for the Chemical Evolution History of Galaxies
We report VLT-ISAAC and Keck-NIRSPEC near-infrared spectroscopy for a sample
of 30 0.47<z<0.92 CFRS galaxies and five [OII]-selected, M_B,AB<-21.5, z~1.4
galaxies. We have measured Halpha and [NII] line fluxes for the CFRS galaxies
which have [OII], Hbeta and [OIII] line fluxes available from optical
spectroscopy. For the z~1.4 objects we measured Hbeta and [OIII] emission line
fluxes from J-band spectra, and Halpha line fluxes plus upper limits for [NII]
fluxes from H-band spectra. We derive the extinction and oxygen abundances for
the sample using a method based on a set of ionisation parameter and oxygen
abundance diagnostics, simultaneously fitting the [OII], Hbeta, [OIII], Halpha
and [NII] line fluxes. Our most salient conclusions are: a) the source of gas
ionisation in the 30 CFRS and in all z~1.4 galaxies is not due to AGN activity;
b) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have
substantially lower metallicities than local galaxies with similar luminosities
and star formation rates; c) comparison with a chemical evolution model
indicates that these low metallicity galaxies are unlikely to be the
progenitors of metal-poor dwarf galaxies at z~0, but more likely the
progenitors of massive spirals; d) the z~1.4 galaxies are characterized by the
high [OIII]/[OII] line ratios, low extinction and low metallicity that are
typical of lower luminosity CADIS galaxies at 0.4<z<0.7, and of more luminous
Lyman Break Galaxies at z~3.1, but not seen in CFRS galaxies at 0.4<z<1.0; e)
the properties of the z~1.4 galaxies suggest that the period of rapid chemical
evolution takes place progressively in lower mass systems as the universe ages,
and thus provides further support for a downsizing picture of galaxy formation,
at least from z~1.4 to today.Comment: Proceedings contribution for "The Fabulous Destiny of Galaxies;
Bridging Past and Present", Marseille, 200
High-Resolution K' Imaging of the z = 1.786 Radio Galaxy 3C 294
We have obtained imaging in the K' band (~I-band rest frame) of the z=1.786
radio galaxy 3C 294 with the 36-element curvature-sensing adaptive optics
system Hokupa`a and the Canada-France-Hawaii Telescope. At a resolution of <
\~0."15, the galaxy is seen as a group of small but resolved knots distributed
over a roughly triangular region ~1."4 across. The interpretation of the
structure depends on the location of the nucleus, as indicated by the compact
radio core. Its position is uncertain by > ~0."5 (2-sigma) because of
uncertainties in the optical astrometry, but our best estimate places it at or
near the southern apex of the distribution. If this location is correct, the
most likely interpretation is that of a hidden quasar nucleus illuminating
dusty infalling dwarf-galaxy-like clumps having characteristic sizes of ~1.5
kpc.Comment: 8 pages. One figure in gif format. Postscript version including fig.
(240 kb) available at http://www.ifa.hawaii.edu/~canaguby/preprints.html To
appear in ApJ. Letter
Developing a questionnaire to assess community severance, walkability, and wellbeing: results from the Street Mobility Project in London
This working paper describes the development of the survey questionnaire component of the toolkit designed to measure community severance, and assess its potential associations with transport and health. We discuss the cognitive testing and piloting of the questionnaire in two contrasting case study areas in inner London, and present results from the survey data
A Companion Galaxy to the Post-Starburst Quasar UN J1025-0040
UN J1025-0040 is a quasar at z = 0.6344 that shows an extremely bright post
starburst population of age ~ 400 Myr (Brotherton et al. 1999). Images of UN
J1025-0040 show a nearly stellar object 4.2 arcseconds SSW of the quasar. We
present imaging and spectroscopy that confirm that this object is a companion
galaxy at redshift z = 0.6341. We estimate an age of ~ 800 Myr for the dominant
stellar population in the companion. The companion appears to be interacting
with the quasar host galaxy, and this interaction may have triggered both the
starburst and the quasar activity in UN J1025-0040.Comment: 8 pages plus 4 figures (2 postscript, 2 jpg). Postscript version
available at http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
the January 2000 issue of A
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