121 research outputs found
How cold is Dark Matter? Constraints from Milky Way Satellites
We test the luminosity function of Milky Way satellites as a constraint for
the nature of Dark Matter particles. We perform dissipationless high-resolution
N-body simulations of the evolution of Galaxy-sized halo in the standard Cold
Dark Matter (CDM) model and in four Warm Dark Matter (WDM) scenarios, with a
different choice for the WDM particle mass (m_w). We then combine the results
of the numerical simulations with semi-analytic models for galaxy formation, to
infer the properties of the satellite population. Quite surprisingly we find
that even WDM models with relatively low m_w values (2-5 keV) are able to
reproduce the observed abundance of ultra faint (Mv<-9) dwarf galaxies, as well
as the observed relation between Luminosity and mass within 300 pc. Our results
suggest a lower limit of 1 keV for thermal warm dark matter, in broad agreement
with previous results from other astrophysical observations like Lyman-alpha
forest and gravitational lensing.Comment: 6 pages, 5 figures. Introduction improved, references added. Accepted
for publication on MNRAS Letter
Dust properties of Lyman break galaxies at
We explore from a statistical point of view the far-infrared (far-IR) and
sub-millimeter (sub-mm) properties of a large sample of LBGs (22,000) at z~3 in
the COSMOS field. The large number of galaxies allows us to split it in several
bins as a function of UV luminosity, UV slope, and stellar mass to better
sample their variety. We perform stacking analysis in PACS (100 and 160 um),
SPIRE (250, 350 and 500 um) and AzTEC (1.1 mm) images. Our stacking procedure
corrects the biases induced by galaxy clustering and incompleteness of our
input catalogue in dense regions. We obtain the full IR spectral energy
distributions (SED) of subsamples of LBGs and derive the mean IR luminosity as
a function of UV luminosity, UV slope, and stellar mass. The average IRX is
roughly constant over the UV luminosity range, with a mean of 7.9 (1.8 mag).
However, it is correlated with UV slope, and stellar mass. We investigate using
a statistically-controlled stacking analysis as a function of (stellar mass, UV
slope) the dispersion of the IRX-UVslope and IRX-M* plane. Our results enable
us to study the average relation between star-formation rate (SFR) and stellar
mass, and we show that our LBG sample lies on the main sequence of star
formation at z~3.Comment: Accepted to A&A, 17 Pages, 14 Figures, 2 Table
Star Formation Rates from [C II] 158 μm and Mid-infrared Emission Lines for Starbursts and Active Galactic Nuclei
A summary is presented for 130 galaxies observed with the Herschel Photodetector Array Camera and Spectrometer instrument to measure fluxes for the [C II] 158 μm emission line. Sources cover a wide range of active galactic nucleus to starburst classifications, as derived from polycyclic aromatic hydrocarbon strength measured with the Spitzer Infrared Spectrograph. Redshifts from [C II] and line to continuum strengths (equivalent width (EW) of [C II]) are given for the full sample, which includes 18 new [C II] flux measures. Calibration of L([C II)]) as a star formation rate (SFR) indicator is determined by comparing [C II] luminosities with mid-infrared [Ne II] and [Ne III] emission line luminosities; this gives the same result as determining SFR using bolometric luminosities of reradiating dust from starbursts: log SFR = log L([C II)]) - 7.0, for SFR in M ⊙ yr-1 and L([C II]) in L ⊙. We conclude that L([C II]) can be used to measure SFR in any source to a precision of ~50%, even if total source luminosities are dominated by an active galactic nucleus (AGN) component. The line to continuum ratio at 158 μm, EW([C II]), is not significantly greater for starbursts (median EW([C II]) = 1.0 μm) compared to composites and AGNs (median EW([C II]) = 0.7 μm), showing that the far-infrared continuum at 158 μm scales with [C II] regardless of classification. This indicates that the continuum at 158 μm also arises primarily from the starburst component within any source, giving log SFR = log νL ν(158 μm) - 42.8 for SFR in M ⊙ yr-1 and νL ν(158 μm) in erg s-1
A quiescent galaxy at the position of the long GRB 050219A
Long-duration gamma-ray bursts (LGRBs) are produced by the collapse of very
massive stars. Due to the short lifetime of their progenitors, LGRBs pinpoint
star-forming galaxies. We present here a multi-band search for the host galaxy
of the long dark GRB 050219A within the enhanced Swift/XRT error circle. We
used spectroscopic observations acquired with VLT/X-shooter to determine the
redshift and star-formation rate of the putative host galaxy. We compared the
results with the optical/IR spectral energy distribution obtained with
different facilities. Surprisingly, the host galaxy is a old and quiescent
early-type galaxy at z = 0.211 characterised by an unprecedentedly low specific
star-formation rate. It is the first LGRB host to be also an early-type
post-starburst galaxy. This is further evidence that GRBs can explode in all
kind of galaxies, with the only requirement being an episode of star-formation.Comment: 11 pages, 10 figures, 3 tables; accepted for publication in Astronomy
& Astrophysic
The complex physics of dusty star-forming galaxies at high redshifts as revealed by Herschel and Spitzer
We combine far-infrared photometry from Herschel (PEP/HerMES) with deep mid-infrared spectroscopy from
Spitzer to investigate the nature and the mass assembly history of a sample of 31 luminous and ultraluminous
infrared galaxies ((U)LIRGs) at z ∼ 1 and 2 selected in GOODS-S with 24μm fluxes between 0.2 and 0.5 mJy.We
model the data with a self-consistent physical model (GRASIL) which includes a state-of-the-art treatment of dust
extinction and reprocessing. We find that all of our galaxies appear to require massive populations of old (>1 Gyr)
stars and, at the same time, to host a moderate ongoing activity of star formation (SFR 100M yr−1). The bulk of
the stars appear to have been formed a few Gyr before the observation in essentially all cases. Only five galaxies of
the sample require a recent starburst superimposed on a quiescent star formation history.We also find discrepancies
between our results and those based on optical-only spectral energy distribution (SED) fitting for the same objects;
by fitting their observed SEDs with our physical model we find higher extinctions (by ΔAV ∼ 0.81 and 1.14)
and higher stellar masses (by Δlog(M ) ∼ 0.16 and 0.36 dex) for z ∼ 1 and z ∼ 2 (U)LIRGs, respectively. The
stellar mass difference is larger for the most dust-obscured objects. We also find lower SFRs than those computed
from LIR using the Kennicutt relation due to the significant contribution to the dust heating by intermediate-age
stellar populations through “cirrus” emission (∼73% and ∼66% of the total LIR for z ∼ 1 and z ∼ 2 (U)LIRGs,
respectively).Department of HE and Training approved lis
Directional control of weakly localized Raman from a random network of fractal nanowires
Disordered optical media are an emerging class of materials capable of
strongly scattering light. Their study is relevant to investigate transport
phenomena and for applications in imaging, sensing and energy storage. While
such materials can be used to generate coherent light, their directional
emission is typically hampered by their very multiple scattering nature. Here,
we tune the out-of-plane directionality of coherent Raman light scattered by a
fractal network of silicon nanowires. By visualizing Rayleigh scattering,
photoluminescence and weakly localized Raman light from the random network of
nanowires via real-space microscopy and Fourier imaging, we gain insight on the
light transport mechanisms responsible for the material's inelastic coherent
signal and for its directionality. The possibility of visualizing and
manipulating directional coherent light in such networks of nanowires opens
venues for fundamental studies of light propagation in disordered media as well
as for the development of next generation optical devices based on disordered
structures, inclusive of sensors, light sources and optical switches
The Herschel Multi-tiered Extragalactic Survey: HerMES
The Herschel Multi-tiered Extragalactic Survey, HerMES, is a legacy program
designed to map a set of nested fields totalling ~380 deg^2. Fields range in
size from 0.01 to ~20 deg^2, using Herschel-SPIRE (at 250, 350 and 500 \mu m),
and Herschel-PACS (at 100 and 160 \mu m), with an additional wider component of
270 deg^2 with SPIRE alone. These bands cover the peak of the redshifted
thermal spectral energy distribution from interstellar dust and thus capture
the re-processed optical and ultra-violet radiation from star formation that
has been absorbed by dust, and are critical for forming a complete
multi-wavelength understanding of galaxy formation and evolution.
The survey will detect of order 100,000 galaxies at 5\sigma in some of the
best studied fields in the sky. Additionally, HerMES is closely coordinated
with the PACS Evolutionary Probe survey. Making maximum use of the full
spectrum of ancillary data, from radio to X-ray wavelengths, it is designed to:
facilitate redshift determination; rapidly identify unusual objects; and
understand the relationships between thermal emission from dust and other
processes. Scientific questions HerMES will be used to answer include: the
total infrared emission of galaxies; the evolution of the luminosity function;
the clustering properties of dusty galaxies; and the properties of populations
of galaxies which lie below the confusion limit through lensing and statistical
techniques.
This paper defines the survey observations and data products, outlines the
primary scientific goals of the HerMES team, and reviews some of the early
results.Comment: 23 pages, 17 figures, 9 Tables, MNRAS accepte
HELP: the Herschel Extragalactic Legacy Project
We present the Herschel Extragalactic Legacy Project (HELP). This project collates, curates, homogenises, and creates derived data products for most of the premium multi-wavelength extragalactic data sets. The sky boundaries for the first data release cover 1270 deg2 defined by the Herschel SPIRE extragalactic survey fields; notably the Herschel Multi-tiered Extragalactic Survey (HerMES) and the Herschel Atlas survey (H-ATLAS). Here, we describe the motivation and principal elements in the design of the project. Guiding principles are transparent or “open” methodologies with care for reproducibility and identification of provenance. A key element of the design focuses around the homogenisation of calibration, meta data and the provision of information required to define the selection of the data for statistical analysis. We apply probabilistic methods that extract information directly from the images at long wavelengths, exploiting the prior information available at shorter wavelengths and providing full posterior distributions rather than maximum likelihood estimates and associated uncertainties as in traditional catalogues. With this project definition paper we provide full access to the first data release of HELP; Data Release 1 (DR1), including a monolithic map of the largest SPIRE extragalactic field at 385 deg2 and 18 million measurements of PACS and SPIRE fluxes. We also provide tools to access and analyse the full HELP database. This new data set includes far-infrared photometry, photometric redshifts, and derived physical properties estimated from modelling the spectral energy distributions over the full HELP sky. All the software and data presented is publicly available
Luminosity function and radial distribution of Milky Way Satellites in a LCDM Universe
We study the luminosity function and the radial distribution of satellite
galaxies within Milky Way sized haloes as predicted in Cold Dark Matter based
models of galaxy formation, making use of numerical N-body techniques as well
as three different semi-analytic model (SAMs) galaxy formation codes. We
extract merger trees from very high-resolution dissipationless simulations of
four Galaxy-sized DM haloes, and use these as common input for the
semi-analytic models. We present a detailed comparison of our predictions with
the observational data recently obtained on the Milky Way satellite luminosity
function (LF). We find that semi-analytic models with rather standard
astrophysical ingredients are able to reproduce the observed luminosity
function over six orders of magnitude in luminosity, down to magnitudes as
faint as M_V=-2. We also perform a comparison with the actual observed number
of satellites as a function of luminosity, by applying the selection criteria
of the SDSS survey to our simulations instead of correcting the observations
for incompleteness. Using this approach we again find good agreement for both
the luminosity and radial distributions of MW satellites. We investigate which
physical processes in our models are responsible for shaping the predicted
satellite LF, and find that tidal destruction, suppression of gas infall by a
photo-ionizing background, and supernova feedback all make important
contributions. We conclude that the number and luminosity of Milky Way
satellites can be naturally accounted for within the (Lambda) Cold Dark Matter
paradigm, and this should no longer be considered a problem.Comment: 16 pages, 15 figures, paper shortened, statistical analysis improved,
new title, accepted for publication in MNRA
Differences in clinical presentation of primary open-angle glaucoma between African and European populations
Purpose: Primary open-angle glaucoma (POAG) has been reported to occur more frequently in Africans, and to follow a more severe course compared to Europeans. We aimed to describe characteristics of POAG presentation and treatment across three ethnic groups from Africa and one from Europe. Methods: We ascertained 151 POAG patients from South African Coloured (SAC) and 94 South African Black (SAB) ethnicity from a university hospital in South Africa. In Tanzania, 310 patients were recruited from a university hospital and a referral hospital. In the Netherlands, 241 patients of European ancestry were included. All patients were over 35 years old and had undergone an extensive ophthalmic examination. Patients were diagnosed according to the ISGEO criteria. A biogeographic ancestry analysis was performed to estimate the proportion of genetic African ancestry (GAA). Results: The biogeographic ancestry analysis showed that the median proportion of GAA was 97.6% in Tanzanian, 100% in SAB, 34.2% in SAC and 1.5% in Dutch participants. Clinical characteristics at presentation for Tanzanians, SAB, SAC and Dutch participants, respectively: mean age: 63, 57, 66, 70 years (p < 0.001); visual acuity in the worse eye: 1.78, 1.78, 0.3, 0.3 LogMAR (p < 0.001); maximum intraocular pressure of both eyes: 36, 34, 29, 29 mmHg (panova < 0.001); maximum vertical cup to disc ratio (VCDR) of both eyes: 0.90, 0.90, 0.84, 0.83 (p < 0.001); mean central corneal thickness: 506, 487, 511, 528 μm (p < 0.001). Fourteen percent of Tanzanian patients presented with blindness (<3/60 Snellen) in the better eye in contrast to only 1% in the Dutch. Conclusion: In this multi-ethnic comparative study, Sub-Saharan Africans present at a younger age with lower visual acuity, higher IOP, larger VCDR, than SAC and Dutch participants. This indicates the more progressive and destructive course in Sub-Saharan Africans
- …