272,022 research outputs found
Fossil groups in the Millennium simulation. From the brightest to the faintest galaxies during the past 8 Gyr
We investigate the evolution of bright and faint galaxies in fossil and
non-fossil groups. We used mock galaxies constructed based on the Millennium
run simulation II. We identified fossil groups at redshift zero according to
two different selection criteria, and then built reliable control samples of
non-fossil groups that reproduce the fossil virial mass and assembly time
distributions. The faint galaxies were defined as having r-band absolute
magnitudes in the range [-16,-11]. We analysed the properties of the bright and
faint galaxies in fossil and non-fossil groups during the past 8 Gyr. We
observed that the brightest galaxy in fossil groups is typically brighter and
more massive than their counterparts in control groups. Fossil groups developed
their large magnitude gap between the brightest galaxies around 3.5 Gyr ago.
The brightest galaxy stellar masses of all groups show a notorious increment at
that time. By analysing the behaviour of the magnitude gap between the first
and the second, third, and fourth ranked galaxies, we found that at earlier
times, fossil groups comprised two large brightest galaxies with similar
magnitudes surrounded by much fainter galaxies, while in control groups these
magnitude gaps were never as large as in fossils. At early times, fossil groups
in the faint population were denser than non-fossil groups, then this trend
reversed, and finally they became similar at the present day. The mean number
of faint galaxies in non-fossil systems increases in an almost constant rate
towards later times, while this number in fossil groups reaches a plateau at
that lasts Gyr, and then starts growing again more rapidly.
The formation of fossil groups is defined at the very beginning of the groups
according to their galaxy luminosity sampling, which could be determined by
their merging rate at early times.Comment: 10 pages, 6 figures, 1 table. Accepted for publication in Astronomy &
Astrophysic
Dental tissue proportions in fossil orangutans from mainland Asia and Indonesia
Orangutans (Pongo) are the only great ape genus with a substantial Pleistocene and Holocene fossil record, demonstrating a much larger geographic range than extant populations. In addition to having an extensive fossil record, Pongo shows several convergent morphological similarities with Homo, including a trend of dental reduction during the past million years. While studies have documented variation in dental tissue proportions among species of Homo, little is known about variation in enamel thickness within fossil orangutans. Here we assess dental tissue proportions, including conventional enamel thickness indices, in a large sample of fossil orangutan postcanine teeth from mainland Asia and Indonesia. We find few differences between regions, except for significantly lower average enamel thickness (AET) values in Indonesian mandibular first molars. Differences between fossil and extant orangutans are more marked, with fossil Pongo showing higher AET in most postcanine teeth. These differences are significant for maxillary and mandibular first molars. Fossil orangutans show higher AET than extant Pongo due to greater enamel cap areas, which exceed increases in enamel-dentine junction length (due to geometric scaling of areas and lengths for the AET index calculation). We also find greater dentine areas in fossil orangutans, but relative enamel thickness indices do not differ between fossil and extant taxa. When changes in dental tissue proportions between fossil and extant orangutans are compared with fossil and recent Homo sapiens, Pongo appears to show isometric reduction in enamel and dentine, while crown reduction in H. sapiens appears to be due to preferential loss of dentine. Disparate selective pressures or developmental constraints may underlie these patterns. Finally, the finding of moderately thick molar enamel in fossil orangutans may represent an additional convergent dental similarity with Homo erectus, complicating attempts to distinguish these taxa in mixed Asian faunas
Fossil Groups Origins III. Characterization of the sample and observational properties of fossil systems
(Abridged) Fossil systems are group- or cluster-sized objects whose
luminosity is dominated by a very massive central galaxy. In the current cold
dark matter scenario, these objects formed hierarchically at an early epoch of
the Universe and then slowly evolved until present day. That is the reason why
they are called {\it fossils}. We started an extensive observational program to
characterize a sample of 34 fossil group candidates spanning a broad range of
physical properties. Deep band images were taken for each candidate and
optical spectroscopic observations were obtained for 1200 galaxies. This
new dataset was completed with SDSS DR7 archival data to obtain robust cluster
membership and global properties of each fossil group candidate. For each
system, we recomputed the magnitude gaps between the two brightest galaxies
() and the first and fourth ranked galaxies ()
within 0.5 . We consider fossil systems those with mag or mag within the errors. We find
that 15 candidates turned out to be fossil systems. Their observational
properties agree with those of non-fossil systems. Both follow the same
correlations, but fossils are always extreme cases. In particular, they host
the brightest central galaxies and the fraction of total galaxy light enclosed
in the central galaxy is larger in fossil than in non-fossil systems. Finally,
we confirm the existence of genuine fossil clusters. Combining our results with
others in the literature, we favor the merging scenario in which fossil systems
formed due to mergers of galaxies. The large magnitude gap is a
consequence of the extreme merger ratio within fossil systems and therefore it
is an evolutionary effect. Moreover, we suggest that at least one candidate in
our sample could represent a transitional fossil stage.Comment: 14 pages, 11 figures, accepted for publication in A&
Fossil group origins - VI. Global X-ray scaling relations of fossil galaxy clusters
We present the first pointed X-ray observations of 10 candidate fossil galaxy
groups and clusters. With these Suzaku observations, we determine global
temperatures and bolometric X-ray luminosities of the intracluster medium (ICM)
out to for six systems in our sample. The remaining four systems show
signs of significant contamination from non-ICM sources. For the six objects
with successfully determined properties, we measure global
temperatures in the range ,
bolometric X-ray luminosities of , and estimate masses,
as derived from , of .
Fossil cluster scaling relations are constructed for a sample that combines our
Suzaku observed fossils with fossils in the literature. Using measurements of
global X-ray luminosity, temperature, optical luminosity, and velocity
dispersion, scaling relations for the fossil sample are then compared with a
control sample of non-fossil systems. We find the fits of our fossil cluster
scaling relations are consistent with the relations for normal groups and
clusters, indicating fossil clusters have global ICM X-ray properties similar
to those of comparable mass non-fossil systems.Comment: 17 pages, 7 figures, 8 tables. Accepted for publication in MNRA
Evolution of the galaxy luminosity function in progenitors of fossil groups
Using the semi-analytic models based on the Millennium simulation, we trace
back the evolution of the luminosity function of galaxies residing in
progenitors of groups classified by the magnitude gap at redshift zero. We
determine the luminosity function of galaxies within , and for galaxy groups/clusters. The bright end of the galaxy
luminosity function of fossil groups shows a significant evolution with
redshift, with changes in by 1-2 mag between and
(for the central ), suggesting that the formation of the most
luminous galaxy in a fossil group has had a significant impact on the
galaxies e.g. it is formed as a result of multiple mergers of the
galaxies within the last Gyr. In contrast, the slope of the faint end,
, of the luminosity function shows no considerable redshift evolution
and the number of dwarf galaxies in the fossil groups exhibits no evolution,
unlike in non-fossil groups where it grows by towards low
redshifts. In agreement with previous studies, we also show that fossil groups
accumulate most of their halo mass earlier than non-fossil groups. Selecting
the fossils at a redshift of 1 and tracing them to a redshift 0, we show that
of the fossil groups () will lose their large magnitude gaps. However, about
of fossil clusters () will retain their large
gaps.Comment: Accepted for publication in A&A. 13 pages, 15 figure
Are fossil groups a challenge of the Cold Dark Matter paradigm?
We study six groups and clusters of galaxies suggested in the literature to
be `fossil' systems (i.e. to have luminous diffuse X-ray emission and a
magnitude gap of at least 2 mag-R between the first and the second ranked
member within half of the virial radius), each having good quality X-ray data
and SDSS spectroscopic or photometric coverage out to the virial radius. The
poor cluster AWM4 is clearly established as a fossil system, and we confirm the
fossil nature of four other systems (RXJ1331.5+1108, RXJ1340.6+4018,
RXJ1256.0+2556 and RXJ1416.4+2315), while the cluster RXJ1552.2+2013 is
disqualified as fossil system. For all systems we present the luminosity
functions within 0.5 and 1 virial radius that are consistent, within the
uncertainties, with the universal luminosity function of clusters. For the five
bona fide fossil systems, having a mass range 2x10^13-3x10^14 M_Sun, we compute
accurate cumulative substructure distribution functions (CSDFs) and compare
them with the CSDFs of observed and simulated groups/clusters available in the
literature. We demonstrate that the CSDFs of fossil systems are consistent with
those of normal observed clusters and do not lack any substructure with respect
to simulated galaxy systems in the cosmological LambdaCDM framework. In
particular, this holds for the archetype fossil group RXJ1340.6+4018 as well,
contrary to earlier claims.Comment: Accepted for publication on MNRAS. Minor changes in sections 2.1 and
6. 13 pages, 4 eps figure
Implications of "peak oil" for atmospheric CO2 and climate
Unconstrained CO2 emission from fossil fuel burning has been the dominant
cause of observed anthropogenic global warming. The amounts of "proven" and
potential fossil fuel reserves are uncertain and debated. Regardless of the
true values, society has flexibility in the degree to which it chooses to
exploit these reserves, especially unconventional fossil fuels and those
located in extreme or pristine environments. If conventional oil production
peaks within the next few decades, it may have a large effect on future
atmospheric CO2 and climate change, depending upon subsequent energy choices.
Assuming that proven oil and gas reserves do not greatly exceed estimates of
the Energy Information Administration, and recent trends are toward lower
estimates, we show that it is feasible to keep atmospheric CO2 from exceeding
about 450 ppm by 2100, provided that emissions from coal, unconventional fossil
fuels, and land use are constrained. Coal-fired power plants without
sequestration must be phased out before mid-century to achieve this CO2 limit.
It is also important to "stretch" conventional oil reserves via energy
conservation and efficiency, thus averting strong pressures to extract liquid
fuels from coal or unconventional fossil fuels while clean technologies are
being developed for the era "beyond fossil fuels". We argue that a rising price
on carbon emissions is needed to discourage conversion of the vast fossil
resources into usable reserves, and to keep CO2 beneath the 450 ppm ceiling.Comment: (22 pages, 7 figures; final version accepted by Global Biogeochemical
Cycles
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