583 research outputs found
Deep Luminosity Functions and Colour-Magnitude Relations for Cluster Galaxies at 0.2 < z < 0.6
We derive deep band luminosity functions and colour-magnitude diagrams
from HST imaging for eleven clusters observed at various stages of
merging, and a comparison sample of five more relaxed clusters at similar
redshifts. The characteristic magnitude evolves passively out to ,
while the faint end slope of the luminosity function is at all
redshifts. Cluster galaxies must have been completely assembled down to out to . We observe tight colour-magnitude relations over a
luminosity range of up to 8 magnitudes, consistent with the passive evolution
of ancient stellar populations. This is found in all clusters, irrespective of
their dynamical status (involved in a collision or not, or even within
subclusters for the same object) and suggests that environment does not have a
strong influence on galaxy properties. A red sequence luminosity function can
be followed to the limits of our photometry: we see no evidence of a weakening
of the red sequence to . The blue galaxy fraction rises with redshift,
especially at fainter absolute magnitudes. We observe bright blue galaxies in
clusters at that are not encountered locally. Surface brightness
selection effects preferentially influence the detectability of faint red
galaxies, accounting for claims of evolution at the faint end.Comment: 21 pages. A series of figures for individual clusters (the full
sample) will be made available on the MNRAS website. Accepted by MNRA
Morphological evolution in situ: Disk-dominated cluster red sequences at z ~ 1.25
We have carried out a joint photometric and structural analysis of red
sequence galaxies in four clusters at a mean redshift of z ~ 1.25 using optical
and near-IR HST imaging reaching to at least 3 magnitudes fainter than .
As expected, the photometry and overall galaxy sizes imply purely passive
evolution of stellar populations in red sequence cluster galaxies. However, the
morphologies of red sequence cluster galaxies at these redshifts show
significant differences to those of local counterparts. Apart from the most
massive galaxies, the high redshift red sequence galaxies are significantly
diskier than their low redshift analogues. These galaxies also show significant
colour gradients, again not present in their low redshift equivalents, most
straightforwardly explained by radial age gradients. A clear implication of
these findings is that red sequence cluster galaxies originally arrive on the
sequence as disk-dominated galaxies whose disks subsequently fade or evolve
secularly to end up as high S\'ersic index early-type galaxies (classical S0s
or possibly ellipticals) at lower redshift. The apparent lack of growth seen in
a comparison of high and low redshift red sequence galaxies implies that any
evolution is internal and is unlikely to involve significant mergers. While
significant star formation may have ended at high redshift, the cluster red
sequence population continues to evolve (morphologically) for several Gyrs
thereafter.Comment: Accepted by MNRA
The K-selected Butcher-Oemler Effect
[abridged] We investigate the Butcher-Oemler effect in a sample of K-selected
galaxies in 33 clusters at 0.15 < z < 0.92. We attempt to duplicate the
original Butcher-Oemler analysis as closely as possible given the
characteristics of our data. We find that the infrared selected blue fractions
are lower than those measured in the optical and that the trend with redshift
is much weaker. Comparison with optical data in clusters in common with Butcher
& Oemler (1984) shows that infrared selection is the primary difference between
our study and optically selected samples. We suggest that the Butcher-Oemler
effect is in large part due to a population of star-forming low mass galaxies
which will evolve into dwarf galaxies. These early results point to the need
for larger and deeper infrared samples of cluster galaxies to address this
issueComment: 37 pages, 19 figures, ApJ accepted (vol 598 n1
Scaling relations of the colour-detected cluster RzCS 052 at z=1.016 and of some other high redshift clusters
We report on the discovery of the z=1.016 cluster RzCS 052 using a modified
red sequence method, followup spectroscopy and X-ray imaging. This cluster has
a velocity dispersion of 710+-150 km/s, a virial mass of 4.0e14 Msol (based on
21 spectroscopically confirmed members) and an X-ray luminosity of (0.68+-
0.47)e44 ergs/s in the [1-4] keV band. This optically selected cluster appears
to be of richness class 3 and to follow the known L_X-sigma_v relation for high
redshift X-ray selected clusters. Using these data, we find that the halo
occupation number for this cluster is only marginally consistent with what
expected assuming a self-similar evolution of cluster scaling relations,
suggesting perhaps a break of them at z~1. We also rule out a strong galaxy
merging activity between z=1 and today. Finally, we present a Bayesian approach
to measuring cluster velocity dispersions and X-ray luminosities in the
presence of a background: we critically reanalyze recent claims for X-ray
underluminous clusters using these techniques and find that the clusters can be
accommodated within the existing L_X -sigma_v relation.Comment: MNRAS, in pres
Evolution of the UV upturn in cluster galaxies:Abell 1689
We have measured the strength of the UV upturn for red sequence galaxies in
the Abell~1689 cluster at , reaching to or below the level and
therefore probing the general evolution of the upturn phenomenon. We find that
the range of UV upturn strengths in the population as a whole has not declined
over the past 2.2 Gyrs. This is consistent with a model where hot horizontal
branch stars, produced by a Helium-enriched population, provide the required UV
flux. Based on local counterparts, this interpretation of the result implies
Helium abundances of at least 1.5 times the primordial value for this HB
population, along with high formation and assembly redshifts for the galaxies
and at least a subset of their stellar populations.Comment: MNRAS, in pres
Anthropic pressures on Nature 2000 Sites: recommendations and monitoring criteria for the pollution emergency response activities within the Orbetello lagoon
L’elevato valore naturalistico e socioeconomico
di un Sito Natura 2000 richiede che tutte le
attività antropiche che si svolgono al suo interno
(es. pesca, turismo, trasporti, attività industriali,
etc.) siano gestite in maniera tale da non pregiudicare
le specie e gli habitat per i quali l’area è
stata designata. Molti di questi Siti sono ambienti
di transizione, ovvero zone che costituiscono il
passaggio naturale tra terra e mare. La loro
posizione di interfaccia tra questi due ambienti li
rende ecosistemi unici e biologicamente molto
produttivi, sede di meccanismi di regolazione dei processi interattivi della biosfera nelle due
fasi, terrestre e marina. In alcuni Siti la presenza
di attività antropiche diffuse e prolungate nel
tempo ha portato al riscontro di stati di
contaminazione elevata, fino all’inclusione di
queste zone, o parti di esse, tra i Siti di bonifica
di Interesse Nazionale (SIN). Il presente lavoro
descrive le linee di indirizzo e le attività di
monitoraggio da attuare per la salvaguardia della
salute pubblica e dell’ambiente nel corso degli
interventi di messa in sicurezza di emergenza
predisposti nell’area lagunare antistante l’area
industriale Ex Sitoco, all’interno della perimetrazione
del SIN di Orbetello, incluso in un Sito di
Importanza Comunitaria. Le matrici ambientali
potenzialmente a rischio a causa dell’esecuzione
di tali interventi sono: acqua, sedimento,
biocenosi acquatiche, avifauna, uomo.
È altresì importante valutare gli effetti che le
ipotetiche modifiche su microscala, apportate a
livello di ogni matrice, potrebbero causare nel
lungo periodo su macroscala.The high naturalistic and socio-economic value
of Natura 2000 sites requires that all human
activities performed within their borders (e.g.
fishing, tourism, transports, industrial activities)
are regulated. Indeed, the site management
should assure the effective safeguard of all
species and habitats of European interest
included in the protected area. A lot of such
sites are located in transitional environments,
that are areas characterised by a natural
progression from the terrestrial to the water
environments. Such environments include
unique and very productive habitats, and they
represent the regulation mechanisms of the
interactive processes of the terrestrial and
marine biosphere. In some sites, the presence
of human activities that are distributed both in
space and time has led to high levels of contamination,
that in some cases even required their
inclusion in Reclamation Sites of National
Interest (SIN). The present study describes the
planning and monitoring activities to be
performed in order to safeguard human and
environment health during the actions of MISE in the lagoonal area in front of the industrial area
Ex Sitoco, within the borders of the Orbetello
SIN, included in a SCI. The environmental
parameters that are potentially at risk due to
such activities are: water, sediment, water
biocenosis, birds, humans. Furthermore, it is
important to evaluate the effects that potential
variations at the microscale level may cause at
the macroscale level
Dim galaxies and outer halos of galaxies missed by 2MASS ? The near-infrared luminosity function and density
By using high-resolution and deep Ks band observations of early-type galaxies
of the nearby Universe and of a cluster at z=0.3 we show that the two
luminosity functions (LFs) of the local universe derived from 2MASS data miss a
fair fraction of the flux of the galaxies (more than 20 to 30%) and a whole
population of galaxies of central brightness fainter than the isophote used for
detection, but bright enough to be included in the published LFs. In
particular, the fraction of lost flux increases as the galaxy surface
brightness become fainter. Therefore, the so far derived LF slopes and
characteristic luminosity as well as luminosity density are underestimated.
Other published near-infrared LFs miss flux in general, including the LF of the
distant field computed in a 3 arcsec aperture.Comment: A&A in pres
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