David Schade

Hubble Space Telescope imaging of the CFRS and LDSS redshift surveys - IV. Influence of mergers in the evolution of faint field galaxies from z~1

ABSTRA C T Hubble Space Telescope images of a sample of 285 galaxies with measured redshifts from the Canada‐France Redshift Survey (CFRS) and Autofib‐Low Dispersion Spectrograph Survey (LDSS) redshift surveys are analysed to derive the evolution of the merger fraction out to redshifts z , 1. We have performed visual and machine-based merger identifications, as well as counts of bright pairs of galaxies with magnitude differences dm # 1:5 mag. We find that the pair fraction increases with redshift, with up to ,20 per cent of the galaxies being in physical pairs at z , 0:75‐1. We derive a merger fraction varying with redshift as /O1a zU 3:2^0:6 , after correction for line-of-sight contamination, in excellent agreement with the merger fraction derived from the visual classification of mergers for which ma 3:4 ^ 0:6. After correcting for seeing effects on the ground-based selection of survey galaxies, we conclude that the pair fraction evolves as/O1a zU 2:7^0:6 . This implies that an average L* galaxy will have undergone 0.8‐1.8 merger events from za 1t oza 0, with 0.5 to 1.2 merger events occuring in a 2-Gyr time-span at around z , 0:9. This result is consistent with predictions from semi-analytical models of galaxy formation. From the simple coaddition of the observed luminosities of the galaxies in pairs, physical mergers are computed to lead to a brightening of 0.5 mag for each pair on average, and a boost in star formation rate of a factor of 2, as derived from the average [O ii] equivalent widths. Mergers of galaxies are therefore contributing significantly to the evolution of both the luminosity function and luminosity density of the Universe out to z , 1.

The Dependence of Cluster Galaxy Star Formation Rates on the Global Environment

A comparison of star formation properties as a function of environment is made from the spectra of identically selected cluster and field galaxies in the CNOC 1 redshift survey of over 2000 galaxies in the fields of 15 X-ray luminous clusters at 0.18 r=-17.5+5log

Evolution of Galactic Disks in Clusters and the Field at 0.1 < z < 0.6 in the CNOC Survey

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Internal Kinematics of Blue Canada-France Redshift Survey Galaxies at z ~ 0.6*

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Discovery of a New Quadruple Lens HST 1411+5211* **

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High Resolution Imaging of Faint Blue Galaxies

-->h is found to vary from 0.17 ± 0.02 h-2 M☉ yr-1 at R200 (1.5-2 h-1 Mpc) to 0.00 ± 0.01 in the cluster center, and it is always less than the mean star formation rate of field galaxies, which is 0.39 ± 0.01 h-2 M☉ yr-1. It is demonstrated that this significant difference is not exclusively a result of the difference in morphological type, as parameterized by the B/T value, by correcting for the B/T-radius relation. The distribution of [O II] equivalent widths among cluster galaxies is skewed toward lower values relative to the distribution for field galaxies of comparable physical size, B/T, and redshift, with a statistical significance of more than 99%. The cluster environment affects not only the morphological mix of the galaxy population but also suppresses the star formation rate within those galaxies, relative to morphologically similar galaxies in the field.

The CNOC2 field galaxy redshift survey

Two-dimensional surface photometry is presented for a sample of 351 late-type galaxies with 0.12 < z < 0.65. These objects are drawn from the Canadian Network for Observational Cosmology (CNOC) cluster survey and are either spectroscopically confirmed members of clusters at z = 0.23 (64 galaxies), 0.43 (45), and 0.55 (36) or field galaxies with similar redshifts. Galaxies in the rich cluster Abell 2256 at z = 0.06 were also analyzed with the same methods to provide a local reference point. At redshifts of (0.23, 0.43, 0.55) the disk surface brightness in cluster late-type galaxies is higher in the B band by Δμ0(B) = (-0.58 ± 0.12, -1.22 ± 0.17, -0.97 ± 0.2) mag, respectively, relative to the Freeman (1970) constant surface brightness relation; whereas disks in cluster galaxies at z = 0.06 are consistent with that relation. Field galaxies show a progressive disk brightening with redshift that is consistent with that seen in the cluster population. Taken together with similar measurements of early-type galaxies, these results suggest that the evolution of the field and cluster galaxy populations are similar, although we emphasize that our sample of cluster galaxies is dominated by objects at large distances (up to 3 Mpc) from the dense cluster core, so that the implications of these findings with respect to the Butcher-Oemler effect and the morphology-density relation will not be clear until an analysis of galaxy properties as a function of clustercentric distance is completed.

Evolution of Cluster and Field Elliptical Galaxies at 0.2 < [ITAL]z[/ITAL] < 0.6 in the CNOC Cluster Survey

We present the results of a study of the internal kinematics of luminous star-forming galaxies in the 0 0.45 have sizes (from Hubble Space Telescope images) and velocity widths σv (from emission lines) similar to those of typical local irregular galaxies. This is consistent with their morphologies and rest-frame colors; however, these galaxies are as bright as the brightest local irregular galaxies and roughly 2 mag brighter than the typical irregular galaxies known nearby. We conclude that the increase in the number density of luminous blue galaxies at z ≥ 0.5 is mainly due to a population of small and unusually bright late-type galaxies.

The space density of low-redshift active galactic nuclei

Gravitational lensing is an important tool for probing the mass distribution of galaxies. In this Letter, we report the discovery of a new quadruple lens HST 1411+5211 found in archived Wide-Field Planetary Camera 2 images of the galaxy cluster CL 140933+5226. If the galaxy is a cluster member, then its redshift is z=0.46. The images of the source appear unresolved in the Wide-Field Camera, implying that the source is a quasar. We have modeled the lens as both a single galaxy and a galaxy plus a cluster. The latter model yields excellent fits to the image positions along with reasonable parameters for the galaxy and cluster, making HST 1411+5211 a likely gravitational lens. Determination of the source redshift and confirmation of the lens redshift would allow us to put strong constraints on the mass distribution of the lensing galaxy.

Shape of the Galactic Orbits in the CNOC1 Clusters

We have used HRCam on the CFHT to obtain subarcsec images of 26 galaxies with z=0.1-0.7 from the redshift survey of Colless et al. The 17 galaxies of the primary sample have enhanced star formation indicated by [O II] equivalent widths greater than 20 A, while the nine galaxies of the comparison sample have equivalent widths of less than 10 A. By fitting exponential discs or r 1/4 bulges to B, V and I images, we derive scalelengths for the blue and red stellar populations and so establish the location of the star formation (in the nucleus or the disc) for each galaxy. We have also searched for nearby faint companions in order to determine whether the star formation might be linked to tidal interactions or mergers