424 research outputs found
The Diffuse Supernova Neutrino Background is detectable in Super-Kamiokande
The Diffuse Supernova Neutrino Background (DSNB) provides an immediate
opportunity to study the emission of MeV thermal neutrinos from core-collapse
supernovae. The DSNB is a powerful probe of stellar and neutrino physics,
provided that the core-collapse rate is large enough and that its uncertainty
is small enough. To assess the important physics enabled by the DSNB, we start
with the cosmic star formation history of Hopkins & Beacom (2006) and confirm
its normalization and evolution by cross-checks with the supernova rate,
extragalactic background light, and stellar mass density. We find a sufficient
core-collapse rate with small uncertainties that translate into a variation of
+/- 40% in the DSNB event spectrum. Considering thermal neutrino spectra with
effective temperatures between 4-6 MeV, the predicted DSNB is within a factor
4-2 below the upper limit obtained by Super-Kamiokande in 2003. Furthermore,
detection prospects would be dramatically improved with a gadolinium-enhanced
Super-Kamiokande: the backgrounds would be significantly reduced, the fluxes
and uncertainties converge at the lower threshold energy, and the predicted
event rate is 1.2-5.6 events /yr in the energy range 10-26 MeV. These results
demonstrate the imminent detection of the DSNB by Super-Kamiokande and its
exciting prospects for studying stellar and neutrino physics.Comment: 14 pages, 5 figures, 4 tables, some added discussions, accepted for
publication in Physical Review
The Far-Infrared Background Correlation with CMB Lensing
The intervening large--scale structure distorts cosmic microwave background
(CMB) anisotropies via gravitational lensing. The same large--scale structure,
traced by dusty star--forming galaxies, also induces anisotropies in the
far--infrared background (FIRB). We investigate the resulting inter--dependence
of the FIRB and CMB with a halo model for the FIRB. In particular, we calculate
the cross--correlation between the lensing potential and the FIRB. The lensing
potential can be quadratically estimated from CMB temperature and/or
polarization maps. We show that the cross--correlation can be measured with
high signal--to--noise with data from the Planck Surveyor. We discuss how such
a measurement can be used to understand the nature of FIRB sources and their
relation to the distribution of dark matter.Comment: 9 pages, 5 figures, submitted to Ap
The infrared luminosity function of galaxies at redshifts z=1 and z~2 in the GOODS fields
We present the rest-frame 8 micron luminosity function (LF) at redshifts z=1
and ~2, computed from Spitzer 24 micron-selected galaxies in the GOODS fields
over an area of 291 sq. arcmin. Using classification criteria based on X-ray
data and IRAC colours, we identify the AGN in our sample. The rest-frame 8
micron LF for star-forming galaxies at redshifts z=1 and ~2 have the same shape
as at z~0, but with a strong positive luminosity evolution. The number density
of star-forming galaxies with log_{10}(nu L_nu(8 micron))>11 increases by a
factor >250 from redshift z~0 to 1, and is basically the same at z=1 and ~2.
The resulting rest-frame 8 micron luminosity densities associated with star
formation at z=1 and ~2 are more than four and two times larger than at z~0,
respectively. We also compute the total rest-frame 8 micron LF for star-forming
galaxies and AGN at z~2 and show that AGN dominate its bright end, which is
well-described by a power-law. Using a new calibration based on Spitzer
star-forming galaxies at 0<z<0.6 and validated at higher redshifts through
stacking analysis, we compute the bolometric infrared (IR) LF for star-forming
galaxies at z=1 and ~2. We find that the respective bolometric IR luminosity
densities are (1.2+/-0.2) x 10^9 and (6.6^{+1.2}_{-1.0}) x 10^8 L_sun Mpc^{-3},
in agreement with previous studies within the error bars. At z~2, around 90% of
the IR luminosity density associated with star formation is produced by
luminous and ultraluminous IR galaxies (LIRG and ULIRG), with the two
populations contributing in roughly similar amounts. Finally, we discuss the
consistency of our findings with other existing observational results on galaxy
evolution.Comment: Accepted for publication in the ApJ. 33 pages, 15 figures. Uses
emulateap
Observational evidence for the presence of PAHs in distant Luminous Infrared Galaxies using ISO and Spitzer
We present ISOCAM 15 micron and MIPS 24 micron photometry of a sample of 16
distant Luminous Infrared Galaxies (LIRGs) characterized by a median luminosity
L(IR) 2x10^11 Lsol and redshift z = 0.7 (distributed from z = 0.1 to 1.2).
While some sources display 24/15 micron flux ratios also consistent with a
featureless continuum dominating their mid-infrared (MIR) spectral energy
distributions (SEDs), the presence of prominent emission features such as the
Polycyclic Aromatic Hydrocarbons is clearly required to explain the observed
colors for more than half of the sample. As a result, a general good agreement
is observed between the data and predictions from the local starburst-dominated
SEDs that have been used so far to constrain IR galaxy evolution. This is
consistent with the star-forming nature of LIRGs derived from previous works,
even though our approach cannot rule out the dominance of an AGN in some cases.
Our study also supports the possibility of tracing the total IR luminosity of
distant galaxies (up to z ~ 1) from their MIR emission.Comment: 4 pages, 3 figures, Astronomy & Astrophysics Letters (in press
Response of stream ecosystem structure to heavy metal pollution: context-dependency of top-down control by fish
The stress-gradient hypothesis predicts that biotic interactions within food webs are context dependent, since environmental stressors can attenuate consumer-prey interactions. Yet, how heavy metal pollution influences the impacts of predatory fish on ecosystem structure is unknown. This study was conducted in the Osor stream (Spain), which features a metal (mainly Zn) pollution gradient. We aimed to determine how the responses of benthic communities to the presence and absence of predatory fish interact with environmental stress and to test whether the top-down control of top predators is context dependent. To address these questions, periphyton biomass and macroinvertebrate densities were determined throughout an exclosure/enclosure mesocosm experiment using the Mediterranean barbel (Barbus meridionalis) as a top predator. The monitoring study showed that metal accumulation in periphyton and macroinvertebrates reflected patterns observed in water. The mesocosm study showed that fish predation effects on larval chironomids were not context-dependent and that periphyton biomass was markedly lower in the presence of fish regardless of metal pollution levels. This strong top-down control on periphytic algae was attributed to the foraging behaviour of fish causing bioturbation. In contrast, the top predator removal revealed grazer-periphyton interactions, which were mediated by heavy metal pollution. That is, periphyton benefitted from a lower grazing pressure in the metal-polluted sites. Together, our results suggest that the top-down control by fishes depends more on functional traits (e.g. feeding behaviour) than on feeding guild, and demonstrate the capacity of top predators to modify anthropogenic stressor effects on stream food-web structure.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This research was supported by the Spanish Ministry of Science, Innovation and Universities (projects CGL2013-43822-R and CGL2016-80820-R, AEI/FEDER/EU) and the Government of Catalonia (ref. 2017 SGR 548 and CERCA Programme). F. Rubio-Gracia and M. Argudo benefitted from a predoctoral fellowship from the University of Girona (IFUdG2017) and the Agency for Management of University and Research Grants (AGAUR) of the Government of Catalonia (2016 FI-B 00284), respectively
Properties of mm galaxies: Constraints from K-band blank fields
We have used the IRAM Plateau de Bure mm interferometer to locate with
subarcsecond accuracy the dust emission of three of the brightest 1.2mm sources
in the NTT Deep Field (NDF) selected from our 1.2mm MAMBO survey at the IRAM
30m telescope. We combine these results with deep B to K imaging and VLA
interferometry. Strikingly, none of the three accurately located mm galaxies
MMJ120546-0741.5, MMJ120539-0745.4, and MMJ120517-0743.1 has a K-band
counterpart down to the faint limit of K>21.9. This implies that these three
galaxies are either extremely obscured and/or are at very high redshifts
(z>~4). We combine our results with literature data for 11 more (sub)mm
galaxies that are identified with similar reliability. In terms of their K-band
properties, the sample divides into three roughly equal groups: (i) undetected
to K~22, (ii) detected in the near-infrared but not the optical and (iii)
detected in the optical with the possibility of optical follow-up spectroscopy.
We find a trend in this sample between near-infrared to submm and submm to
radio spectral indices, which in comparison to spectral energy distributions
(SEDs) of low redshift infrared luminous galaxies suggests that the most
plausible primary factor causing the extreme near-infrared faintness of our
objects is their high redshift. We show that the near-infrared to radio SEDs of
the sample are inconsistent with SEDs that resemble local far-infrared cool
galaxies with moderate luminosities, which were proposed in some models of the
submm sky. We briefly discuss the implications of the results for our
understanding of galaxy formation.Comment: aastex, 5 figures. Accepted by Ap
An 850 Micron SCUBA Survey of the HDF-N GOODS Region
The Hubble Deep Field-North (HDF-N) is one of the best studied extragalactic
fields, and ultra-deep optical, radio, X-ray, and mid-infrared wide-field
images are available for this area. Here we present an 850 um survey around the
HDF-N, covering most of the area imaged by the Advanced Camera for Surveys as a
part of the Great Observatories Origins Deep Survey. Our map has 0.4-4 mJy
sensitivities (1 sigma) over an area ~110 arcmin^2 and there are 45 sources
detected at >3 sigma. After correcting the effects of noise, confusion,
incompleteness, and the Eddington bias using Monte Carlo simulations, we find
that the detected 850 m sources with fluxes greater than 2 mJy have a
surface density of 3200^+1900_-1000 deg^-2 and account for about 24% to 34% of
the far-infrared extragalactic background light. Using the deep radio
interferometric image and the deep X-ray image, we are able to accurately
locate ~60% of the bright submillimeter (submm) sources. In addition, by
assuming the Arp 220 spectral energy distribution in the submm and radio, we
estimate millimetric redshifts for the radio detected submm sources, and
redshift lower limits for the ones not detected in the radio. Using the
millimetric redshifts of the radio identified sources and spectroscopic and
optical photometric redshifts for galaxies around the submm positions, we find
a median redshift of 2.0 for 11 possibly identified sources, or a lower limit
of 2.4 for the median redshift of our 4 sigma sample.Comment: 27 pages, 8 figures, ApJ accepte
Interferometric detections of GOODS 850-5 at 1 mm and 1.4 GHz
We have obtained a position (at sub-arcsecond accuracy) of the submillimeter
bright source GOODS 850-5 (also known as GN10) in the GOODS North field using
the IRAM Plateau de Bure interferometer at 1.25 mm wavelengths (MM
J123633+6214.1, flux density: S(1.25 mm)=5.0+-1.0 mJy). This source has no
optical counterpart in deep ACS imaging down to a limiting magnitude of
i(775)=28.4 mag and its position is coincident with the position found in
recent sub-millimeter mapping obtained at the SMA (Wang et al. 2007). Using
deep VLA imaging at 20 cm, we find a radio source (S(20 cm)=32.7+-4.3 microJy)
at the same position that is significantly brighter than reported in Wang et
al. The source is detected by Spitzer in IRAC as well as at 24 microns. We
apply different photometric redshift estimators using measurements of the
dusty, mid/far-infrared part of the SED and derive a redshift z~4. Given our
detection in the millimeter and radio we consider a significantly higher
redshift (e.g., z~6 Wang et al. 2007) unlikely. MM J123633+6214.1 alias GOODS
850-5 nevertheless constitutes a bright representative of the high-redshift
tail of the submillimeter galaxy population that may contribute a significant
fraction to the (sub)millimeter background.Comment: Accepted for publication by ApJL (12 pages, 1 figure). The resolution
of figure 1 has been degraded. A higher quality pdf version of this paper is
available at http://www.mpia-hd.mpg.de/homes/dannerb
FIRBACK Source Counts and Cosmological Implications
FIRBACK is a one of the deepest surveys performed at 170 microns with ISOPHOT
onboard ISO, and is aimed at the study of cosmic far infrared background
sources. About 300 galaxies are detected in an area of four square degrees, and
source counts present a strong slope of 2.2 on an integral "logN-logS" plot,
which cannot be due to cosmological evolution if no K-correction is present.
The resolved sources account for less than 10% of the Cosmic Infrared
Background at 170 microns. In order to understand the nature of the sources
contributing to the CIB, and to explain deep source counts at other
wavelengths, we have developed a phenomenological model, which constrains in a
simple way the luminosity function evolution with redshift, and fits all the
existing deep source counts from the mid-infrared to the submillimetre range.
Images, materials and papers available on the FIRBACK web:
http://wwwfirback.ias.u-psud.fr wwwfirback.ias.u-psud.frComment: proceedings of "ISO Surveys of a Dusty Universe", eds. D. Lemke, M.
Stickel, K. Wilke, Ringberg, 8-12 Nov 1999, to appear in Springer 'Lecture
Notes of Physics'. 8 pages, 7 eps figures, .sty include
Mitochondrial dynamicsâfusion, fission, movement, and mitophagyâin neurodegenerative diseases
Neurons are metabolically active cells with high energy demands at locations distant from the cell body. As a result, these cells are particularly dependent on mitochondrial function, as reflected by the observation that diseases of mitochondrial dysfunction often have a neurodegenerative component. Recent discoveries have highlighted that neurons are reliant particularly on the dynamic properties of mitochondria. Mitochondria are dynamic organelles by several criteria. They engage in repeated cycles of fusion and fission, which serve to intermix the lipids and contents of a population of mitochondria. In addition, mitochondria are actively recruited to subcellular sites, such as the axonal and dendritic processes of neurons. Finally, the quality of a mitochondrial population is maintained through mitophagy, a form of autophagy in which defective mitochondria are selectively degraded. We review the general features of mitochondrial dynamics, incorporating recent findings on mitochondrial fusion, fission, transport and mitophagy. Defects in these key features are associated with neurodegenerative disease. Charcot-Marie-Tooth type 2A, a peripheral neuropathy, and dominant optic atrophy, an inherited optic neuropathy, result from a primary deficiency of mitochondrial fusion. Moreover, several major neurodegenerative diseasesâincluding Parkinson's, Alzheimer's and Huntington's diseaseâinvolve disruption of mitochondrial dynamics. Remarkably, in several disease models, the manipulation of mitochondrial fusion or fission can partially rescue disease phenotypes. We review how mitochondrial dynamics is altered in these neurodegenerative diseases and discuss the reciprocal interactions between mitochondrial fusion, fission, transport and mitophagy
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