arXiv subjects

David Schade

Publications and source records attributed to David Schade.

23 records · Page 2Linked to original sources

arXiv1996

Surface Brightness Evolution of Cluster Galaxies

Surface brightness evolution has been detected in elliptical galaxies (consistent with passive evolution models of old stellar populations) and in disk galaxies (presumably due to enhanced star-formation rates). The rates of evolution in clusters and the field are not measurably different. In addition to this similarity, the high-redshift populations in both environments exhibit a ``blue-excess'' population, increased rates of star formation, and high frequency of peculiar structure. Thus, there are several parallels between evolving cluster and field galaxies and the high-redshift cluster environment will be understood only by comparison with the field population at the same epoch.

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arXiv1996

Evolution of Cluster Ellipticals at 0.2 < z < 1.2 from Hubble Space Telescope Imaging

Two-dimensional surface photometry derived from Hubble Space Telescope imaging is presented for a sample of 225 early-type galaxies (assumed to be cluster members) in the fields of 9 clusters at redshifts $0.17 < z < 1.21$. The 94 luminous ellipticals ($M_{AB}(B)<-20$; selected by morphology alone with no reference to color) form tight sequences in the size-luminosity plane. The position of these sequences shifts, on average, with redshift so that an object of a given size at z=0.55 is brighter by $ΔM(B)=-0.57 \pm 0.13$ mag than its counterpart (measured with the same techniques) in nearby clusters. At z=0.9 the shift is $ΔM(B)=-0.96 \pm 0.22$ mag. If the relation between size and luminosity is universal so that the local cluster galaxies represent the evolutionary endpoints of those at high redshift, and if the size-luminosity relation is not modified by dynamical processes then this population of galaxies has undergone significant luminosity evolution since z=1 consistent with expectations based on models of passively evolving, old stellar populations.

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arXiv1996

The CANADA-FRANCE REDSHIFT SURVEY XI: Morphology of high-redshift field galaxies from high-resolution ground-based imaging

The 143 galaxies with secure redshifts (median z = 0.62) from the 1415+52 field of the Canada-France Redshift Survey have been imaged at CFHT with median seeing of 0.67 arcseconds. Structural parameters have been derived by fitting multi-component models, and the results confirm two phenomena seen in a smaller sample of galaxies imaged with HST. First, 11% of the galaxies lie off the normal locus of colour vs. bulge fraction. This class of objects ("blue-nucleated galaxies" or BNGs) was first identified using HST observations (Schade et al. 1995, Ap J, 451, L1), where it was shown that they are associated with peculiar or asymmetric structures and mergers/interactions. The observed frequency of BNGs in this sample is 14% for 0.5 < z < 1.2 and 6% at 0.2 < z < 0.5, but the true frequency is likely to be a factor ~2 higher after corrections are made for the effect of asymmetric/peculiar structures. Second, galaxy disks at 0.5 < z < 1.1 are found to have a mean rest-frame, inclination-corrected, central surface brightness of $μ_{AB}(B)=19.8 \pm 0.1$ mag arcsec$^{-2}$, about 1.6 mag brighter than the Freeman (1970) value. At low redshift, the mean surface brightness is consistent with the Freeman value. These results are consistent with the HST observations. With larger numbers of galaxies and therefore more statistical weight, they demonstrate the capabilities, and limits, of ground-based work in the study of galaxy morphology at high redshift.

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arXiv1995

The Canada-France Redshift Survey X: The Quasar Sample

Six objects with broad emission lines and redshifts from 0.48 to 2.07 were discovered among 736 extragalactic objects in the Canada-France Redshift Survey (CFRS). Although the luminosities of half of the objects are such that they are in the Seyfert regime (M_B > -23), all would be designated as quasars in traditional surveys. Since the only selection criterion was that 17.5 < I_{AB} < 22.5, or approximately B < 23 (assuming a continuum power-law slope of alpha = -0.5), these quasars represent an unbiased, flux-limited sample. Although uncertain, the implied surface density, 200^{+120}_{-80} deg^{-2} is the highest yet measured, and is in good agreement with extrapolations from other faint surveys and the evolving luminosity function models of Boyle (1991). The distributions of the continuum properties, emission-line strengths, etc., of the quasars do not differ significantly from those of quasars selected by other means, and therefore they would have been detected in most traditional surveys. Three of the quasars may be associated with clusters or large structures of galaxies at z > 1.

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arXiv1994

High-Resolution Imaging of Faint Blue Galaxies

We have used HRCam on the CFHT to obtain subarcsecond images of 26 galaxies with z=0.1--0.7. The primary sample of 17 galaxies have enhanced star formation indicated by [OII] equivalent widths greater than 20Å, while the comparison sample of 9 galaxies have equivalent widths less than 10Å. By fitting disks or bulges to BVI images we derive scalelengths for the blue and red stellar populations and locate the star-formation in each galaxy. These moderate-redshift galaxies generally have straightforward low-redshift analogues, in that their colours, sizes and luminosities are consistent with those of various types of z$\approx$0 galaxies. The star-forming objects have structures consistent with the full range of present-day disk galaxies, and absolute magnitudes M$^\ast$$-$1 to M$^\ast$+5. Some have star-formation concentrated in their nuclei but in most it occurs across the entire disk. We find companions at projected distances closer than 10 kpc for 30% of the star-forming galaxies, whereas none of the comparison sample have such close companions. This provides the first direct evidence linking interactions or mergers to the increased fraction of star-forming field galaxies at moderate redshifts.

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