2,177 research outputs found
Star formation activity of intermediate redshift cluster galaxies out to the infall regions
We present a spectroscopic analysis of two galaxy clusters out to ~4Mpc at
z~0.2. The two clusters VMF73 and VMF74 identified by Vikhlinin et al. (1998)
were observed with MOSCA at the Calar Alto 3.5m telescope. Both clusters lie in
the ROSAT PSPC field R285 and were selected from the X-ray Dark Cluster Survey
(Gilbank et al. 2004) that provides optical V- and I-band data. VMF73 and VMF74
are located at respective redshifts of z=0.25 and z=0.18 with velocity
dispersions of 671 km/s and 442 km/s, respectively. The spectroscopic
observations reach out to ~2.5 virial radii. Line strength measurements of the
emission lines H_alpha and [OII]3727 are used to assess the star formation
activity of cluster galaxies which show radial and density dependences. The
mean and median of both line strength distributions as well as the fraction of
star forming galaxies increase with increasing clustercentric distance and
decreasing local galaxy density. Except for two galaxies with strong H_alpha
and [OII] emission, all of the cluster galaxies are normal star forming or
passive galaxies. Our results are consistent with other studies that show the
truncation in star formation occurs far from the cluster centre.Comment: 15 pages, 12 figures. A&A in pres
One health approach to food safety in pork production chain
With the increase in worldwide demand for meat, fast-growing species with efficient feed conversion rates – such as pigs – are likely to account for a major share in the growth in the livestock subsector. Commercial pig production has intensified significantly in recent decades. In developing countries, half of the current pig population is still kept in traditional small-scale subsistence-driven production systems in which pigs provide much more than meat playing a role as a financial safety net, providing additional cash for school fees, medical treatment or small investments beside being part of cultural traditions
A composite K-band Luminosity Function for Cluster Galaxies
We present a composite K-band luminosity function for 10 clusters at low
redshift, where member galaxies are identified from an existing spectroscopic
survey (the 2dF galaxy redshift survey). Our kinematically selected K-band
luminosity function is well fitted by a Schechter function with and over . This is very
similar to the 2dF field value and suggests that the integrated mass accretion
history of galaxies does not vary strongly with environmentComment: 3 pages, 1 figure, Astronomische Nachrichten (JENAM 2008 Symposium 6
The evolution of cluster dwarfs
We summarize the results from analyzing six clusters of galaxies at 0.14 < z
< 0.40 observed with the Hubble Space Telescope Advanced Camera for Surveys. We
derive deep composite luminosity functions in B,g,V,r,i and z down to an
absolute magnitude of -14 +5 log h mag. The luminosity functions are fitted by
a single Schechter function with M^*=-19.8,-20.9,-21.9, -22.0,-21.7 and -22.3 i
B,g,V.r,i,z respectively and alpha=-1.3 for all bands. The data suggest that
the red sequence dominates the luminosity function down to more than 6 mag.
below L*, the dwarf spheroidal regime. Hence, at least at z=0.3 the red
sequence is well established and galaxies down to dwarf spheroidals are fully
assembled within these clusters. We do not detect the faint-end upturn (M >
-16) that is observed in lower redshift clusters. If this is real, the
faint-end population has originated since z = 0.3.Comment: To be published in Astronomische Nachrichten, proceeding of JENAM
2008 Symposium 6. Includes an.cls classfil
The role of E+A and post-starburst galaxies – II. Spectral energy distributions and comparison with observations
‘The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.15036.xIn a previous paper, we have shown that the classical definition of E+A galaxies excludes a significant number of post-starburst galaxies. We suggested that analysing broad-band spectral energy distributions (SEDs) is a more comprehensive method to select and distinguish post-starburst galaxies than the classical definition of measuring equivalent widths of (Hδ) and [O ii] lines. In this paper, we will carefully investigate this new method and evaluate it by comparing our model grid of post-starburst galaxies to observed E+A galaxies from the MORPHS catalogue. In the first part, we investigate the UV-optical-NIR (near-infrared) SEDs of a large variety in terms of progenitor galaxies, burst strengths and time-scales of post-starburst models and compare them to undisturbed spiral, S0 and E galaxies as well as to galaxies in their starburst phase. In the second part, we compare our post-starburst models with the observed E+A galaxies in terms of Lick indices, luminosities and colours. We then use the new method of comparing the model SEDs with SEDs of the observed E+A galaxies. We find that the post-starburst models can be distinguished from undisturbed spiral, S0 and E galaxies and galaxies in their starburst phase on the basis of their SEDs. It is even possible to distinguish most of the different post-starbursts by their SEDs. From the comparison with observations, we find that all observed E+A galaxies from the MORPHS catalogue can be matched by our models. However, only models with short decline time-scales for the star formation rate are possible scenarios for the observed E+A galaxies in agreement with our results from the first paper.Peer reviewe
The IR Luminosity Functions of Rich Clusters
We present MIPS observations of the cluster A3266. About 100 spectroscopic
cluster members have been detected at 24 micron. The IR luminosity function in
A3266 is very similar to that in the Coma cluster down to the detection limit
L_IR~10^43 ergs/s, suggesting a universal form of the bright end IR LF for
local rich clusters with M~10^15 M_sun. The shape of the bright end of the
A3266-Coma composite IR LF is not significantly different from that of nearby
field galaxies, but the fraction of IR-bright galaxies (SFR > 0.2M_sun/yr) in
both clusters increases with cluster-centric radius. The decrease of the blue
galaxy fraction toward the high density cores only accounts for part of the
trend; the fraction of red galaxies with moderate SFRs (0.2 < SFR < 1 M_sun/yr)
also decreases with increasing galaxy density. These results suggest that for
the IR bright galaxies, nearby rich clusters are distinguished from the field
by a lower star-forming galaxy fraction, but not by a change in L*_IR. The
composite IR LF of Coma and A3266 shows strong evolution when compared with the
composite IR LF of two z~0.8 clusters, MS 1054 and RX J0152, with L*_IR \propto
(1+z)^{3.2+/-0.7},Phi*_IR \propto (1+z)^{1.7+/-1.0}. This L*_IR evolution is
indistinguishable from that in the field, and the Phi*_IR evolution is
stronger, but still consistent with that in the field. The similarity of the
evolution of bright-end IR LF in very different cluster and field environments
suggests either this evolution is driven by the mechanism that works in both
environments, or clusters continually replenish their star-forming galaxies
from the field, yielding an evolution in the IR LF that is similar to the
field. The mass-normalized integrated star formation rates (SFRs) of clusters
within 0.5R_200 also evolve strongly with redshift, as (1+z)^5.3.Comment: 15 pages, 8 figures, 1 table, accepted by Ap
A snapshot on galaxy evolution occurring in the Great Wall: the role of Nurture at z=0
With the aim of quantifying the contribution of the environment on the
evolution of galaxies at z=0 we have used the DR7 catalogue of the Sloan
Digital Sky Survey (SDSS) to reconstruct the 3-D distribution of 4132 galaxies
in 420 square degrees of the Coma supercluster, containing two rich clusters
(Coma and A1367), several groups, and many filamentary structures belonging to
the "Great Wall", at the approximate distance of 100 Mpc. At this distance the
galaxy census is complete to Mi=-17.5 mag, i.e. approx 4 mag fainter than M*.
The morphological classification of galaxies into early- (ellipticals) and
late-types (spirals) was carried out by inspection of individual SDSS images
and spectra. The density around each galaxies was determined in cylinders of 1
Mpc radius and 1000 km s^-1 half length. The color-luminosity relation was
derived for galaxies in bins morphological type and in four thresholds of
galaxy density-contrast, ranging from delta{1,1000} <= 0 (UL = the cosmic web);
0 < delta{1,1000} <= 4 (L = the loose groups); 4 < delta{1,1000} <= 20 (H = the
large groups and the cluster's outskirts) and delta{1,1000} > 20 (UH = the
cluster's cores). The fraction of early-type galaxies increases with the log of
the over-density. A well defined "red sequence" composed of early-type galaxies
exists in all environments at high luminosity, but it lacks of low luminosity
(dwarf) galaxies in the lowest density environment. Conversely low luminosity
isolated galaxies are predominantly of late-type. In other words the low
luminosity end of the distribution is dominated by red dE galaxies in clusters
and groups and by dwarf blue amorphous systems in the lowest density regions.
At z=0 we find evidence for strong evolution induced by the environment
(Nurture). Transformations take place mostly at low luminosity when star
forming dwarf galaxies inhabiting low density environments migrate into
amorphous passive dwarf ellipticals in their infall into denser regions. The
mechanism involves suppression of the star formation due to gas stripping,
without significant mass growth, as proposed by Boselli et al. (2008a). This
process is more efficient and fast in ambients of increasing density. In the
highest density environments (around clusters) the truncation of the star
formation happens fast enough (few 100 Myr) to produce the signature of
post-star-burst in galaxy spectra. PSB galaxies, that are in fact found
significantly clustered around the largest dynamical units, represent the
remnants of star forming isolated galaxies that had their star formation
violently suppressed during their infall in clusters in the last 0.5-1.5 Gyrs,
and the progenitors of future dEs.Comment: 14 pages, 14 figures, Astronomy and Astrophysics, in pres
A Robust AFPTAS for Online Bin Packing with Polynomial Migration
In this paper we develop general LP and ILP techniques to find an approximate
solution with improved objective value close to an existing solution. The task
of improving an approximate solution is closely related to a classical theorem
of Cook et al. in the sensitivity analysis for LPs and ILPs. This result is
often applied in designing robust algorithms for online problems. We apply our
new techniques to the online bin packing problem, where it is allowed to
reassign a certain number of items, measured by the migration factor. The
migration factor is defined by the total size of reassigned items divided by
the size of the arriving item. We obtain a robust asymptotic fully polynomial
time approximation scheme (AFPTAS) for the online bin packing problem with
migration factor bounded by a polynomial in . This answers
an open question stated by Epstein and Levin in the affirmative. As a byproduct
we prove an approximate variant of the sensitivity theorem by Cook at el. for
linear programs
Galaxy interactions II: High density environments
With the aim to assess the role of dense environments in galaxy interactions,
properties we present an analysis of close galaxy pairs in groups and clusters,
obtained from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7). We
identified pairs that reside in groups by cross-correlating the total galaxy
pair catalogue with the SDSS-DR7 group catalogue from Zapata et al. (2009). We
classify pair galaxies according to the intensity of interaction. We analysed
the effect of high density environments on different classes of galaxy-galaxy
interactions and we have also studied the impact of the group global
environment on pair galaxies. We find that galaxy pairs are more concentrated
towards the group centres with respect to the other group galaxy members, and
disturbed pairs show a preference to contain the brightest galaxy in the
groups. The color-magnitude relation exhibits significant differences between
pair galaxies and the control sample, consisting in color tails with a clear
excess of extremely blue and red galaxies for merging systems. In addition,
pair galaxies show a significant excess of young stellar populations with
respect to galaxies in the control sample; this finding suggests that, in dense
environments, strong interactions produce an important effect in modifying
galaxy properties. We find that the fraction of star forming galaxies decreases
toward the group centre; however, galaxy pairs show a more efficient star
formation activity than galaxies without a close companion. We have also found
that pair galaxies prefer groups with low density global environments with
respect to galaxies of the corresponding control sample. Blue, young stellar
population galaxies prefer groups within low density global environments.Comment: 10 pages, 11 figures, accepted for publication in A&
The Age of Ellipticals and the Color-Magnitude Relation
Using new narrowband color observations of early-type galaxies in clusters,
we reconstruct the color-magnitude relation (CMR) with a higher degree of
accuracy than previous work. We then use the spectroscopically determined ages
and metallicities from three samples (Trager et al 2008, Thomas et al 2005,
Gallazzi et al 2006), combined with multi-metallicity SED models, to compare
predicted colors for galaxies with young ages (less than 8 Gyr) with the known
CMR. We find that the CMR cannot by reproduced by the spectroscopically
determined ages and metallicities in any of the samples despite the high
internal accuracies to the spectroscopic indices. In contrast, using only the
index to determine [Fe/H], and assuming a mean age of 12 Gyr for a
galaxy's stellar population, we derive colors that exactly match not only the
color zeropoint of the CMR but also its slope. We consider the source of young
age estimates, the H index, and examine the conflict between red
continuum colors and large H values in galaxy spectra. We conclude that
our current understanding of stellar populations is insufficient to correctly
interpret H values and that the sum of our galaxy observations supports
an old and monolithic scenario of galaxy formation. This result has a
devastating impact on every study that has used the H index to calculate
galaxy age, as the use of the H versus MgFe diagram will result in
incorrectly deduced young ages.Comment: 29 pages, 9 figures. This version deviates from the version accepted
by Ap
- …