4,858 research outputs found
Active Galactic Nuclei and their Role in Galaxy Evolution: The Infrared Perspective
The remarkable progress made in infrared (IR) astronomical instruments over
the last 10-15 years has radically changed our vision of the extragalactic IR
sky, and overall understanding of galaxy evolution. In particular, this has
been the case for the study of active galactic nuclei (AGN), for which IR
observations provide a wealth of complementary information that cannot be
derived from data in other wavelength regimes. In this review, I summarize the
unique contribution that IR astronomy has recently made to our understanding of
AGN and their role in galaxy evolution, including both physical studies of AGN
at IR wavelengths, and the search for AGN among IR galaxies in general.
Finally, I identify and discuss key open issues that it should be possible to
address with forthcoming IR telescopes.Comment: 34 pages, 13 figures. Invited review article, in press at the
International Journal of Modern Physics
The role of HST in the study of near- and mid-infrared-selected galaxies
Because of their unique quality, Hubble Space Telescope (HST) data have
played an important complementary role in studies of infrared (IR) galaxies
conducted with major facilities, as VLT or Spitzer, and will be as well very
valuable for future telescopes as Herschel and ALMA. I review here some of the
most recent works led by European astronomers on IR galaxies, and discuss the
role that HST has had in the study of different IR galaxy populations. I
particularly focus the analysis on the GOODS fields, where the multiwavelength
data and unique HST coverage have enabled to jointly put constraints on the
evolution of star formation activity and stellar-mass growth with cosmic time.Comment: To appear in the proceedings of the 41st ESLAB Symposium "The impact
of HST on European Astronomy". 4 pages, 1 figur
Microbiome-gut-brain axis and toll-like receptors in parkinson\u2019s disease
Parkinson’s disease (PD) is a progressively debilitating neurodegenerative disease characterized by α-synucleinopathy, which involves all districts of the brain-gut axis, including the central, autonomic and enteric nervous systems. The highly bidirectional communication between the brain and the gut is markedly influenced by the microbiome through integrated immunological, neuroendocrine and neurological processes. The gut microbiota and its relevant metabolites interact with the host via a series of biochemical and functional inputs, thereby affecting host homeostasis and health. Indeed, a dysregulated microbiota-gut-brain axis in PD might lie at the basis of gastrointestinal dysfunctions which predominantly emerge many years prior to the diagnosis, corroborating the theory that the pathological process is spread from the gut to the brain. Toll-like receptors (TLRs) play a crucial role in innate immunity by recognizing conserved motifs primarily found in microorganisms and a dysregulation in their signaling may be implicated in α-synucleinopathy, such as PD. An overstimulation of the innate immune system due to gut dysbiosis and/or small intestinal bacterial overgrowth, together with higher intestinal barrier permeability, may provoke local and systemic inflammation as well as enteric neuroglial activation, ultimately triggering the development of alpha-synuclein pathology. In this review, we provide the current knowledge regarding the relationship between the microbiota-gut–brain axis and TLRs in PD. A better understanding of the dialogue sustained by the microbiota-gut-brain axis and innate immunity via TLR signaling should bring interesting insights in the pathophysiology of PD and provide novel dietary and/or therapeutic measures aimed at shaping the gut microbiota composition, improving the intestinal epithelial barrier function and balancing the innate immune response in PD patients, in order to influence the early phases of the following neurodegenerative cascade
Analysis of the SFR - M* plane at z<3: single fitting versus multi-Gaussian decomposition
The analysis of galaxies on the star formation rate - stellar mass (SFR-M*)
plane is a powerful diagnostic for galaxy evolution at different cosmic times.
We consider a sample of 24463 galaxies from the CANDELS/GOODS-S survey to
conduct a detailed analysis of the SFR-M* relation at redshifts 0.53 over more than three dex in stellar mass. To obtain SFR estimates, we
utilise mid- and far-IR photometry when available, and rest-UV fluxes for all
the other galaxies. We perform our analysis in different redshift bins, with
two different methods: 1) a linear regression fitting of all star-forming
galaxies, defined as those with specific star formation rates , similarly to what is typically done in the
literature; 2) a multi-Gaussian decomposition to identify the galaxy main
sequence (MS), the starburst sequence and the quenched galaxy cloud. We find
that the MS slope becomes flatter when higher stellar mass cuts are adopted,
and that the apparent slope change observed at high masses depends on the SFR
estimation method. In addition, the multi-Gaussian decomposition reveals the
presence of a starburst population which increases towards low stellar masses
and high redshifts. We find that starbursts make up ~5% of all galaxies at
z=0.5-1.0, while they account for ~16% of galaxies at 23 with
log8.25-11.25. We conclude that the dissection of the SFR-M* in
multiple components over a wide range of stellar masses is necessary to
understand the importance of the different modes of star formation through
cosmic time.Comment: 15 pages, 12 figures, 1 table. Accepted for publication in A&A, after
addressing referee report. Main changes with respect to v1: two new
appendixes to investigate the impact of redshift outliers and to test a
two-Gaussian component fit to the sSFR distribution. No conclusion change
The role of the LIRG and ULIRG phases in the evolution of Ks-selected galaxies
We investigate the role of the luminous infrared galaxy (LIRG) and
ultra-luminous infrared galaxy (ULIRG) phases in the evolution of Ks-selected
galaxies and, in particular, Extremely Red Galaxies (ERGs). With this aim, we
compare the properties of a sample of 2905 Ks<21.5 (Vega mag) galaxies in the
GOODS/CDFS with the sub-sample of those 696 sources which are detected at 24
microns. We find that LIRGs constitute 30% of the galaxies with stellar mass
M>1x10^{11} Msun assembled at redshift z=0.5. A minimum of 65% of the galaxies
with M>2.5x10^{11} Msun at z~2-3 are ULIRGs at those redshifts. 60% of the
ULIRGs in our sample have the characteristic colours of ERGs. Conversely, 40%
of the ERGs with stellar mass M>1.3x10^{11} Msun at 1.5<z<2.0 and a minimum of
52% of those with the same mass cut at 2.0<z<3.0 are ULIRGs. The average
optical/near-IR properties of the massive ERGs at similar redshifts that are
identified with ULIRGs and that are not have basically no difference,
suggesting that both populations contain the same kind of objects in different
phases of their lives.
LIRGs and ULIRGs have an important role in galaxy evolution and mass
assembly, and, although they are only able to trace a fraction of the massive
(M>1x10^{11} Msun) galaxies present in the Universe at a given time, this
fraction becomes very significant (>50%) at redshifts z>~2.Comment: Accepted for publication in A&A. 9 pages, 6 figure
Organ Donation: A Comparison of Altruistic and Market-Based Systems
One of the most heavily regulated aspects of the Health Care industry is the organ donation system (“Legislation and Policy”). Regulations in this area ensure the quality of the organs and morality of the process through which they were procured. This system, however, is failing in at least one sense; the number of patients requiring organ transplants is increasing, but the number of donors remains stagnant (Gordon, Patel, Sohn, Hippen, Sherman , 2014). Due to the lack of available transplant organs, a debate has been sparked on whether the United States government should allow for the purchasing of these organs
The stellar mass function of the most massive galaxies at 3<=z<5 in the UKIDSS Ultra Deep Survey
We have analysed a sample of 1292 4.5 micron-selected galaxies at z>=3, over
0.6 square degrees of the UKIRT Infrared Deep Survey (UKIDSS) Ultra Deep Survey
(UDS). Using photometry from the U band through 4.5 microns, we have obtained
photometric redshifts and derived stellar masses for our sources. Only two of
our galaxies potentially lie at z>5. We have studied the galaxy stellar mass
function at 3<=z<5, based on the 1213 galaxies in our catalogue with [4.5]<=
24.0. We find that: i) the number density of M > 10^11 Msun galaxies increased
by a factor > 10 between z=5 and 3, indicating that the assembly rate of these
galaxies proceeded > 20 times faster at these redshifts than at 0<z<2; ii) the
Schechter function slope alpha is significantly steeper than that displayed by
the local stellar mass function, which is both a consequence of the steeper
faint end and the absence of a pure exponential decline at the high-mass end;
iii) the evolution of the comoving stellar mass density from z=0 to 5 can be
modelled as log10 (rho_M) =-(0.05 +/- 0.09) z^2 - (0.22 -/+ 0.32) z + 8.69. At
3 10^11 Msun galaxies would be missed by optical
surveys with R<27 or z<26. Thus, our study demonstrates the importance of deep
mid-IR surveys over large areas to perform a complete census of massive
galaxies at high z and trace the early stages of massive galaxy assembly.Comment: 16 pages, 15 figures, 2 tables. Accepted for publication in MNRA
Cyclic homology for bornological coarse spaces
Funding Information: Open Access funding provided by Projekt DEAL. This work formed part of the author’s PhD thesis at Regensburg University. It is a pleasure to again acknowledge Ulrich Bunke, this work would not exist without him. The author also thanks Clara Löh, Denis-Charles Cisinski and Alexander Engel for helpful discussions, and the anonymous referees for constructive comments and recommendations. The author has been supported by the DFG Research Training Group GRK 1692 “Curvature, Cycles, and Cohomology” and by the DFG SFB 1085 “Higher Invariants”. Publisher Copyright: © 2020, The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Peer reviewedPublisher PD
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