19 research outputs found
The Build-up of the Colour-Magnitude Relation as a Function of Environment
We discuss the environmental dependence of galaxy evolution based on deep
panoramic imaging of two distant clusters taken with Suprime-Cam as part of the
PISCES project. By combining with the SDSS data as a local counterpart for
comparison, we construct a large sample of galaxies that spans wide ranges in
environment, time, and stellar mass (or luminosity). We find that colours of
galaxies, especially those of faint galaxies (), change from blue
to red at a break density as we go to denser regions. Based on local and global
densities of galaxies, we classify three environments: field, groups, and
clusters. We show that the cluster colour-magnitude relation is already built
at . In contrast to this, the bright-end of the field colour-magnitude
relation has been vigorously built all the way down to the present-day and the
build-up at the faint-end has not started yet. A possible interpretation of
these results is that galaxies evolve in the 'down-sizing' fashion. That is,
massive galaxies complete their star formation first and the truncation of star
formation is propagated to smaller objects as time progresses. This trend is
likely to depend on environment since the build-up of the colour-magnitude
relation is delayed in lower-density environments. Therefore, we may suggest
that the evolution of galaxies took place earliest in massive galaxies and in
high density regions, and it is delayed in less massive galaxies and in lower
density regions.Comment: 23pages, 19 figures, accepted for publication in MNRA
Early galaxy formation and its large-scale effects
Galaxy formation is at the heart of our understanding of cosmic evolution. Although there is a consensus that galaxies emerged from the expanding matter background by gravitational instability of primordial fluctuations, a number of additional physical processes must be understood and implemented in theoretical models before these can be reliably used to interpret observations. In parallel, the astonishing recent progresses made in detecting galaxies that formed only a few hundreds of million years after the Big Bang is pushing the quest for more sophisticated and detailed studies of early structures. In this review, we combine the information gleaned from different theoretical models/studies to build a coherent picture of the Universe in its early stages which includes the physics of galaxy formation along with the impact that early structures had on large-scale processes as cosmic reionization and metal enrichment of the intergalactic medium
No excess of bright galaxies around the redshift 7.1 quasar ULAS J1120+0641
We present optical and near-infrared imaging of the field of the z=7.0842
quasar ULAS J112001.48+064124.3 taken with the Hubble Space Telescope. We use
these data to search for galaxies that may be physically associated with the
quasar, using the Lyman break technique, and find three such objects, although
the detection of one in Spitzer Space Telescope imaging strongly suggests it
lies at z~2. This is consistent with the field luminosity function and
indicates that there is no excess of >L* galaxies within 1 Mpc of the quasar. A
detection of the quasar shortward of the Ly-alpha line is consistent with the
previously observed evolution of the intergalactic medium at z>5.5.Comment: Accepted for publication in MNRAS, 8 page