817 research outputs found
Spitzer 70 Micron Source Counts in GOODS-North
We present ultradeep Spitzer 70 μm observations of GOODS-North (Great Observatories Origins Deep Survey). For the first time, the turnover in the 70 μm Euclidean-normalized differential source counts is observed. We derive source counts down to a flux density of 1.2 mJy. From the measured source counts and fluctuation analysis, we estimate a power-law approximation of the faint 70 μm source counts of dN/dS ∝ S^−1.6, consistent with that observed for the faint 24 μm sources. An extrapolation of the 70 μm source counts to zero flux density implies a total extragalactic background light (EBL) of 7.4 ± 1.9 nW m^−2 sr^−1. The source counts above 1.2 mJy account for about 60% of the estimated EBL. From fluctuation analysis, we derive a photometric confusion level of σc = 0.30 ± 0.15 mJy (q = 5) for the Spitzer 70 μm band
The evolution of galaxy star formation activity in massive halos
There is now a large consensus that the current epoch of the Cosmic Star
Formation History (CSFH) is dominated by low mass galaxies while the most
active phase at 1<z<2 is dominated by more massive galaxies, which undergo a
faster evolution. Massive galaxies tend to inhabit very massive halos such as
galaxy groups and clusters. We aim to understand whether the observed "galaxy
downsizing" could be interpreted as a "halo downsizing", whereas the most
massive halos, and their galaxy populations, evolve more rapidly than the halos
of lower mass. Thus, we study the contribution to the CSFH of galaxies
inhabiting group-sized halos. This is done through the study of the evolution
of the Infra-Red (IR) luminosity function of group galaxies from redshift 0 to
~1.6. We use a sample of 39 X-ray selected groups in the Extended Chandra Deep
Field South (ECDFS), the Chandra Deep Field North (CDFN), and the COSMOS field,
where the deepest available mid- and far-IR surveys have been conducted with
Spitzer MIPS and Hersche PACS. Groups at low redshift lack the brightest,
rarest, and most star forming IR-emitting galaxies observed in the field. Their
IR-emitting galaxies contribute <10% of the comoving volume density of the
whole IR galaxy population in the local Universe. At redshift >~1, the most
IR-luminous galaxies (LIRGs and ULIRGs) are preferentially located in groups,
and this is consistent with a reversal of the star-formation rate vs .density
anti-correlation observed in the nearby Universe. At these redshifts, group
galaxies contribute 60-80% of the CSFH, i.e. much more than at lower redshifts.
Below z~1, the comoving number and SFR densities of IR-emitting galaxies in
groups decline significantly faster than those of all IR-emitting galaxies. Our
results are consistent with a "halo downsizing" scenario and highlight the
significant role of "environment" quenching in shaping the CSFH.Comment: 14 pages, 10 figures, accepted for publication by A&
Segregation Effects According to the Evolutionary Stage of Galaxy Groups
We study segregation phenomena in 57 groups selected from the 2PIGG catalog
of galaxy groups. The sample corresponds to those systems located in areas of
at least 80% redshift coverage out to 10 times the radius of the groups. The
dynamical state of the galaxy systems was determined after studying their
velocity distributions. We have used the Anderson-Darling test to distinguish
relaxed and non-relaxed systems. This analysis indicates that 84% of groups
have galaxy velocities consistent with the normal distribution, while 16% of
them have more complex underlying distributions. Properties of the member
galaxies are investigated taking into account this classification. Our results
indicate that galaxies in Gaussian groups are significantly more evolved than
galaxies in non-relaxed systems out to distances of about 4R200, presenting
signficantly redder (B-R) color. We also find evidence that galaxies with M_R <
-21.5 in Gaussian groups are closer to the condition of energy equipartition.Comment: 5 pages, 4 figures, accepted for publication in the MNRAS Letter
Role of the (Mn)superoxide dismutase of Enterococcus faecalis in the in vitro interaction with microglia
Enterococcus faecalis is a significant human pathogen worldwide and is responsible for severenosocomial and community-acquired infections. Although enterococcal meningitis is rare,mortality is considerable, reaching 21 %. Nevertheless, the pathogenetic mechanisms of thisinfection remain poorly understood, even though the ability of E. faecalis to avoid or survivephagocytic attack in vivo may be very important during the infection process. We previouslyshowed that the manganese-cofactored superoxide dismutase (MnSOD) SodA of E. faecalis wasimplicated in oxidative stress responses and, interestingly, in the survival within mouse peritonealmacrophages using an in vivo\u2013in vitro infection model. In the present study, we investigated therole of MnSOD in the interaction of E. faecalis with microglia, the brain-resident macrophages. Byusing an in vitro infection model, murine microglial cells were challenged in parallel with the wildtypestrain JH2-2 and its isogenic sodA deletion mutant. While both strains were phagocytosedby microglia efficiently and to a similar extent, the DsodA mutant was found to be significantlymore susceptible to microglial killing than JH2-2, as assessed by the antimicrobial protectionassay. In addition, a significantly higher percentage of acidic DsodA-containing phagosomes wasfound and these also underwent enhanced maturation as determined by the expression ofendolysosomal markers. In conclusion, these results show that the MnSOD of E. faecaliscontributes to survival of the bacterium in microglial cells by influencing their antimicrobial activity,and this could even be important for intracellular killing in neutrophils and thus for E. faecalispathogenesis
Tyrosinase Inhibitor Activity of Coumarin-Resveratrol Hybrids
In the present work we report on the contribution of the coumarin moiety to
tyrosinase inhibition. Coumarin-resveratrol hybrids 1-8 have been resynthesized to
investigate the structure-activity relationships and the IC50 values of these compounds
were measured. The results showed that these compounds exhibited tyrosinase inhibitory
activity. Compound 3-(3’,4’,5’-trihydroxyphenyl)-6,8-dihydroxycoumarin (8) is the most
potent compound (0.27 mM), more so than umbelliferone (0.42 mM), used as reference
compound. The kinetic studies revealed that compound 8 caused non-competitive
tyrosinase inhibition
The role of massive halos in the Star Formation History of the Universe
The most striking feature of the Cosmic Star Formation History (CSFH) of the
Universe is a dramatic drop of the star formation (SF) activity, since z~1. In
this work we investigate if the very same process of assembly and growth of
structures is one of the major drivers of the observed decline. We study the
contribution to the CSFH of galaxies in halos of different masses. This is done
by studying the total SFR-halo mass-redshift plane from redshift 0 to redshift
z~1.6 in a sample of 57 groups and clusters by using the deepest available mid-
and far-infrared surveys conducted with Spitzer MIPS and Herschel PACS and
SPIRE. Our results show that low mass groups provide a 60-80% contribution to
the CSFH at z~1. Such contribution declines faster than the CSFH in the last 8
billion years to less than 10% at z<0.3, where the overall SF activity is
sustained by lower mass halos. More massive systems provide only a marginal
contribution (<10%) at any epoch. A simplified abundance matching method shows
that the large contribution of low mass groups at z~1 is due to a large
fraction (>50%) of very massive, highly star forming Main Sequence galaxies.
Below z~1 a quenching process must take place in massive halos to cause the
observed faster suppression of their SF activity. Such process must be a slow
one though, as most of the models implementing a rapid quenching of the SF
activity in accreting satellites significantly underpredicts the observed SF
level in massive halos at any redshift. Starvation or the transition from cold
to hot accretion would provide a quenching timescale of 1 Gyrs more consistent
with the observations. Our results suggest a scenario in which, due to the
structure formation process, more and more galaxies experience the group
environment and, thus, the associated quenching process. This leads to the
progressive suppression of their SF activity shaping the CSFH below z~1.Comment: 18 pages, 21 figures, accepted for publication by A&
Automatic Extraction of Dermatological Parameters from Nevi Using an Inexpensive Smartphone Microscope: A Proof of Concept
The evolution of smartphone technology has made their use more common in dermatological applications. Here we studied the feasibility of using an inexpensive smartphone microscope for the extraction of dermatological parameters and compared the results obtained with a portable dermoscope, commonly used in clinical practice. Forty-two skin lesions were imaged with both devices and visually analyzed by an expert dermatologist. The presence of a reticular pattern was observed in 22 dermoscopic images, but only in 10 smartphone images. The proposed paradigm segments the image and extracts texture features which are used to train and validate a neural network to classify the presence of a reticular pattern. Using 5-fold cross-validation, an accuracy of 100% and 95% was obtained with the dermoscopic and smartphone images, respectively. This approach can be useful for general practitioners and as a triage tool for skin lesion analysis
Reversal or no reversal: the evolution of the star formation rate-density relation up to z~1.6
We investigate the evolution of the star formation rate (SFR)-density
relation in the Extended Chandra Deep Field South (ECDFS) and the Great
Observatories Origin Deep Survey (GOODS) fields up to z~1.6. In addition to the
"traditional method", in which the environment is defined according to a
statistical measurement of the local galaxy density, we use a "dynamical"
approach, where galaxies are classified according to three different
environment regimes: group, "filament-like", and field. Both methods show no
evidence of a SFR-density reversal. Moreover, group galaxies show a mean SFR
lower than other environments up to z~1, while at earlier epochs group and
field galaxies exhibit consistent levels of star formation (SF) activity. We
find that processes related to a massive dark matter halo must be dominant in
the suppression of the SF below z~1, with respect to purely density-related
processes. We confirm this finding by studying the distribution of galaxies in
different environments with respect to the so-called Main Sequence (MS) of
star-forming galaxies. Galaxies in both group and "filament-like" environments
preferentially lie below the MS up to z~1, with group galaxies exhibiting lower
levels of star-forming activity at a given mass. At z>1, the star-forming
galaxies in groups reside on the MS. Groups exhibit the highest fraction of
quiescent galaxies up to z~1, after which group, "filament-like", and field
environments have a similar mix of galaxy types. We conclude that groups are
the most efficient locus for star-formation quenching. Thus, a fundamental
difference exists between bound and unbound objects, or between dark matter
haloes of different masses.Comment: Accepted for publication in MNRA
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