260 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
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
The metallicity-luminosity relation at medium redshift based on faint CADIS emission line galaxies
The emission line survey within the Calar Alto Deep Imaging Survey (CADIS)
detects galaxies with very low continuum brightness by using an imaging
Fabry-Perot interferometer. With spectroscopic follow-up observations of
MB>~-19 CADIS galaxies using FORS2 at the VLT and DOLORES at TNG we obtained
oxygen abundances of 5 galaxies at z~0.4 and 10 galaxies at z~0.64. Combining
these measurements with published oxygen abundances of galaxies with MB<~-19 we
find evidence that a metallicity-luminosity relation exists at medium redshift,
but it is displaced to lower abundances and higher luminosities compared to the
metallicity-luminosity relation in the local universe. Comparing the observed
metallicities and luminosities of galaxies at z<3 with Pegase2 chemical
evolution models we have found a favoured scenario in which the metallicity of
galaxies increases by a factor of ~2 between z~0.7 and today, and their
luminosity decreases by ~0.5-0.9mag.Comment: Accepted for publication in A&A; 12 pages, 9 figure
Photometric Mapping with ISOPHOT using the "P32" Astronomical Observation Template
The ``P32'' Astronomical Observation Template (AOT) provided a means to map
large areas of sky (up to 45 x 45 arcmin) in the far-infrared (FIR) at high
redundancy and with sampling close to the Nyquist limit using the ISOPHOT C100
(3 x 3) and C200 (2 x 2) detector arrays on board the Infrared Space
Observatory (ISO). However, the transient response behaviour of the Ga:Ge
detectors, if uncorrected, can lead to severe systematic photometric errors and
distortions of source morphology on maps. We describe the basic concepts of an
algorithm which can successfully correct for transient response artifacts in
P32 observations. Examples are given to demonstrate the photometric and imaging
performance of ISOPHOT P32 observations of point and extended sources corrected
using the algorithm. For extended sources we give the integrated flux densities
of the nearby galaxies NGC6946, M51 and M101 and an image of M101 at 100
micron.Comment: 15 pages, 16 figures, published in A&A 410, 107
Progressive Star Bursts and High Velocities in the Infrared Luminous, Colliding Galaxy Arp 118
In this paper we demonstrate for the first time the connection between the
spatial and temporal progression of star formation and the changing locations
of the very dense regions in the gas of a massive disk galaxy (NGC 1144) in the
aftermath of its collision with a massive elliptical (NGC 1143). These two
galaxies form the combined object Arp 118, a collisional ring galaxy system.
The results of 3D, time-dependent, numerical simulations of the behavior of the
gas, stars, and dark matter of a disk galaxy and the stars and dark matter in
an elliptical during a collision are compared with multiwavelength observations
of Arp 118. The collision that took place approximately 22 Myr ago generated a
strong, non-linear density wave in the stars and gas in the disk of NGC 1144,
causing the gas to became clumped on a large scale. This wave produced a series
of superstarclusters along arcs and rings that emanate from the central point
of impact in the disk. The locations of these star forming regions match those
of the regions of increased gas density predicted the time sequence of models.
The models also predict the large velocity gradients observed across the disk
of NGC 1144. These are due to the rapid radial outflow of gas coupled to large
azimuthal velocities in the expanding ring, caused by the impact of the massive
intruder.Comment: 12 pages in document, and 8 figures (figures are separate from the
document's file); Submitted to Astrophysical Journal Letter
Distant galaxy clusters in the COSMOS field found by HIROCS
We present the first high-redshift galaxy cluster candidate sample from the
HIROCS survey found in the COSMOS field. It results from a combination of
public COSMOS with proprietary H-band data on a 0.66 square degree part of the
COSMOS field and comprises 12 candidates in the redshift range 1.23 < z < 1.55.
We find an increasing fraction of blue cluster members with increasing
redshift. Many of the blue and even some of the reddest member galaxies exhibit
disturbed morphologies as well as signs of interaction.Comment: 5 pages, 5 figures, in print format, accepted for publication by A&A
Letter
The HI and Ionized Gas Disk of the Seyfert Galaxy NGC 1144 = Arp 118: A Violently Interacting Galaxy with Peculiar Kinematics
We present observations of the distribution and kinematics of neutral and
ionized gas in NGC 1144, a galaxy that forms part of the Arp 118 system.
Ionized gas is present over a huge spread in velocity (1100 km/s) in the disk
of NGC 1144, but HI emission is detected over only 1/3 of this velocity range,
in an area that corresponds to the NW half of the disk. In the nuclear region
of NGC 1144, a jump in velocity in the ionized gas component of 600 km/s is
observed. Faint, narrow HI absorption lines are also detected against radio
sources in the SE part of the disk of NGC 1144, which includes regions of
massive star formation and a Seyfert nucleus. The peculiar HI distribution,
which is concentrated in the NW disk, seems to be the inverse of the molecular
distribution which is concentrated in the SE disk. Although this may partly be
the result of the destruction of HI clouds in the SE disk, there is
circumstantial evidence that the entire HI emission spectrum of NGC 1144 is
affected by a deep nuclear absorption line covering a range of 600 km/s, and is
likely blueshifted with respect to the nucleus. In this picture, a high
column-density HI stream is associated with the nuclear ionized gas velocity
discontinuity, and the absorption effectively masks any HI emission that would
be present in the SE disk of NGC 1144.Comment: manuscript, arp118.ps: 28 pages; 1 Table: arp118.tab1.ps; 16 Figures:
arp118.fig1-16.ps; Accepted to Ap
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