431 research outputs found
Polarized Broad-Line Emission from Low-Luminosity Active Galactic Nuclei
In order to determine whether unified models of active galactic nuclei apply
to low-luminosity objects, we have undertaken a spectropolarimetric survey of
of LINERs and Seyfert nuclei at the Keck Observatory. The 14 objects observed
have a median H-alpha luminosity of 8x10^{39} erg/s, well below the typical
value of ~10^{41} erg/s for Markarian Seyfert nuclei. Polarized broad H-alpha
emission is detected in three LINERs: NGC 315, NGC 1052, and NGC 4261. Each of
these is an elliptical galaxy with a double-sided radio jet, and the
emission-line polarization in each case is oriented roughly perpendicular to
the jet axis, as expected for the obscuring torus model. NGC 4261 and NGC 315
are known to contain dusty circumnuclear disks, which may be the outer
extensions of the obscuring tori. The detection of polarized broad-line
emission suggests that these objects are nearby, low-luminosity analogs of
obscured quasars residing in narrow-line radio galaxies. The nuclear continuum
of the low-luminosity Seyfert 1 galaxy NGC 4395 is polarized at p = 0.67%,
possibly the result of an electron scattering region near the nucleus.
Continuum polarization is detected in other objects, with a median level of p =
0.36% over 5100-6100 A, but in most cases this is likely to be the result of
transmission through foreground dust. The lack of significant broad-line
polarization in most type 1 LINERs is consistent with the hypothesis that we
view the broad-line regions of these objects directly, rather than in scattered
light.Comment: 28 pages, including 3 tables and 16 figures. Uses the emulateapj
latex style file. Accepted for publication in The Astrophysical Journa
Dephasing model for spatially extended atomic states in cyclotronlike resonances
In recent work, the formation of ring-shaped electron distributions for hydrogen atoms in resonant static magnetic-laser fields has exclusively been associated with the impact of relativity. In this note we will generalize this statement and show that the nonlinearity associated with the nuclear binding force can trigger similarly shaped steady-state charge clouds in atoms under suitable conditions. The dephasing model, based on modeling the quantum-mechanical state by a classical ensemble of quasiparticles evolving with slightly different cyclotron periods, can recover features, in the two lowest-order resonances as well as the Coulomb-field-induced charge distributions
Searching for galaxy clusters in the Kilo-Degree Survey
In this paper, we present the tools used to search for galaxy clusters in the
Kilo Degree Survey (KiDS), and our first results. The cluster detection is
based on an implementation of the optimal filtering technique that enables us
to identify clusters as over-densities in the distribution of galaxies using
their positions on the sky, magnitudes, and photometric redshifts. The
contamination and completeness of the cluster catalog are derived using mock
catalogs based on the data themselves. The optimal signal to noise threshold
for the cluster detection is obtained by randomizing the galaxy positions and
selecting the value that produces a contamination of less than 20%. Starting
from a subset of clusters detected with high significance at low redshifts, we
shift them to higher redshifts to estimate the completeness as a function of
redshift: the average completeness is ~ 85%. An estimate of the mass of the
clusters is derived using the richness as a proxy. We obtained 1858 candidate
clusters with redshift 0 < z_c < 0.7 and mass 13.5 < log(M500/Msun) < 15 in an
area of 114 sq. degrees (KiDS ESO-DR2). A comparison with publicly available
Sloan Digital Sky Survey (SDSS)-based cluster catalogs shows that we match more
than 50% of the clusters (77% in the case of the redMaPPer catalog). We also
cross-matched our cluster catalog with the Abell clusters, and clusters found
by XMM and in the Planck-SZ survey; however, only a small number of them lie
inside the KiDS area currently available.Comment: 13 pages, 15 figures. Accepted for publication on Astronomy &
Astrophysic
A weak lensing analysis of the Abell 383 cluster
In this paper we use deep CFHT and SUBARU archival images of the
Abell 383 cluster (z=0.187) to estimate its mass by weak lensing. To this end,
we first use simulated images to check the accuracy provided by our KSB
pipeline. Such simulations include both the STEP 1 and 2 simulations, and more
realistic simulations of the distortion of galaxy shapes by a cluster with a
Navarro-Frenk-White (NFW) profile. From such simulations we estimate the effect
of noise on shear measurement and derive the correction terms. The R-band image
is used to derive the mass by fitting the observed tangential shear profile
with a NFW mass profile. Photometric redshifts are computed from the uBVRIz
catalogs. Different methods for the foreground/background galaxy selection are
implemented, namely selection by magnitude, color and photometric redshifts,
and results are compared. In particular, we developed a semi-automatic
algorithm to select the foreground galaxies in the color-color diagram, based
on observed colors. Using color selection or photometric redshifts improves the
correction of dilution from foreground galaxies: this leads to higher signals
in the inner parts of the cluster. We obtain a cluster mass that is ~ 20%
higher than previous estimates, and is more consistent the mass expected from
X--ray data. The R-band luminosity function of the cluster is finally computed.Comment: 11 pages, 12 figures. Accepted for publication on Astronomy &
Astrophysic
The XMM-LSS survey: The XMDS/VVDS 4 sigma catalogue
We present a first catalogue of X-ray sources resulting from the central area
of the XMM-LSS (Large Scale Structure survey). We describe the reduction
procedures and the database tools we developed and used to derive a well
defined catalogue of X-ray sources. The present catalogue is limited to a
sub-sample of 286 sources detected at 4 sigma in the 1 deg^2 area covered by
the photometric VVDS (VIRMOS VLT Deep Survey), which allows us to provide
optical and radio identifications. We also discuss the X-ray properties of a
larger X-ray sample of 536 sources detected at > 4 sigma in the full 3 deg^2
area of the XMM Medium Deep Survey (XMDS) independently of the optical
identification. We also derive the logN-logS relationship for a sample of more
than one thousand sources that we discuss in the context of other surveys at
similar fluxes.Comment: 15+6 pages, 12 figures, accepted for publication in Astronomy &
Astrophysics The online catalogue announced in the paper will be accessible
in about 2 weeks due to technical reasons Fig. 2 replaced with a low
resolution on
A weak lensing analysis of the PLCK G100.2-30.4 cluster
We present a mass estimate of the Planck-discovered cluster PLCK G100.2-30.4,
derived from a weak lensing analysis of deep SUBARU griz images. We perform a
careful selection of the background galaxies using the multi-band imaging data,
and undertake the weak lensing analysis on the deep (1hr) r-band image. The
shape measurement is based on the KSB algorithm; we adopt the PSFex software to
model the Point Spread Function (PSF) across the field and correct for this in
the shape measurement. The weak lensing analysis is validated through extensive
image simulations. We compare the resulting weak lensing mass profile and total
mass estimate to those obtained from our re-analysis of XMM-Newton
observations, derived under the hypothesis of hydrostatic equilibrium. The
total integrated mass profiles are in remarkably good agreement, agreeing
within 1 across their common radial range. A mass is derived for the cluster from our weak lensing
analysis. Comparing this value to that obtained from our reanalysis of
XMM-Newton data, we obtain a bias factor of (1-b) = 0.8 0.1. This is
compatible within 1 with the value of (1-b) obtained by Planck
Collaboration XXIV from their calibration of the bias factor using
newly-available weak lensing reconstructed masses.Comment: 11 pages, 12 figures, accepted for publication on Astronomy &
Astrophysics; updates in affiliation
Comparing the use and content of antenatal care in adolescent and older first-time mothers in 13 countries of west Africa: a cross-sectional analysis of Demographic and Health Surveys
Background
West Africa has the highest proportion of married adolescents, and the highest adolescent childbirth rate and maternal death rate in sub-Saharan Africa. However, few studies have focused on the type and quality of health care accessed by pregnant young women in countries in this subregion.
Methods
We obtained data from Demographic and Health Surveys done between 2010 and 2014, to compare the use, timing, source, and components of antenatal care between adolescent and older first-time mothers in 13 west African countries. The sample included primiparous women who were aged 15â49 years with a livebirth in the 5-year survey recall period, and women were assigned to one of three groups on the basis of age at the time of childbirth: adolescent (10â19 years), young adults (20â24 years), or adults (25 years or older). We calculated the percentage of women who: attended at least one antenatal care visit, completed at least one visit during the first trimester of pregnancy, attended four or more appointments in antenatal care, and received four components of antenatal care (blood pressure measurement, urine tests, blood tests, and information on complications), as well as the sector where the women received care. We primarily report the comparison between adolescents and young adults.
Findings
In 2016, we acquired data from the Demographic Health Surveys from 13 west African countries between 2010 and 2014 on primiparous women. The study sample was 19â211 women, of whom 10â025 (52%) were adolescents, 6099 (32%) were young adults, and 3087 (16%) were adults. Overall, 17â386 (91%) of 19â211 first-time mothers made use of antenatal care facilities on at least one occasion. 3597 (41%) of 8741 adolescents compared with 8202 (47%) of all 17â386 women began the use of antenatal care during the first trimester. Across west Africa, 5430 (62%) of 8741 adolescents had four or more antenatal care visits compared with 4067 (71%) of 5717 young adults and 2358 (81%) of 2928 adults. Of those who had four or more visits to antenatal care, 2779 (51%) of 5430 adolescents received all the antenatal care components examined compared with 2488 (61%) of 4067 young adults and 1600 (68%) of 2358 adults. Although most women received antenatal care in the public sector, in nine of the 13 countries, the proportion of women that used the private sector was higher in older mothers.
Interpretation
Although a large percentage of west African adolescents use some antenatal care for their first birth, they seek care later, make fewer visits during pregnancy, and receive fewer components of care than older first-time mothers. Governments must ensure the pregnancy care accessed by adolescent mothers is of high quality and tailored to meet their needs
SUDARE-VOICE variability-selection of Active Galaxies in the Chandra Deep Field South and the SERVS/SWIRE region
One of the most peculiar characteristics of Active Galactic Nuclei (AGN) is
their variability over all wavelengths. This property has been used in the past
to select AGN samples and is foreseen to be one of the detection techniques
applied in future multi-epoch surveys, complementing photometric and
spectroscopic methods.
In this paper, we aim to construct and characterise an AGN sample using a
multi-epoch dataset in the r band from the SUDARE-VOICE survey.
Our work makes use of the VST monitoring program of an area surrounding the
Chandra Deep Field South to select variable sources. We use data spanning a six
month period over an area of 2 square degrees, to identify AGN based on their
photometric variability.
The selected sample includes 175 AGN candidates with magnitude r < 23 mag. We
distinguish different classes of variable sources through their lightcurves, as
well as X-ray, spectroscopic, SED, optical and IR information overlapping with
our survey.
We find that 12% of the sample (21/175) is represented by SN. Of the
remaining sources, 4% (6/154) are stars, while 66% (102/154) are likely AGNs
based on the available diagnostics. We estimate an upper limit to the
contamination of the variability selected AGN sample of about 34%, but we point
out that restricting the analysis to the sources with available
multi-wavelength ancillary information, the purity of our sample is close to
80% (102 AGN out of 128 non-SN sources with multi-wavelength diagnostics). Our
work thus confirms the efficiency of the variability selection method in
agreement with our previous work on the COSMOS field; in addition we show that
the variability approach is roughly consistent with the infrared selection.Comment: Published in A & A, 15 pages, 6 figure
Crustal distribution in the central Gulf of Mexico from an integrated geophysical analysis
This study addresses the question of the crustal composition in the central part of the northern Gulf of Mexico (GOM) â the region of the major disagreement between published tectonic models. The location of the Ocean-Continental Boundary (OCB) for different tectonic models varies within 140 km (87 mi) in the study area. I have developed a 2D model integrating the seismic reflection and refraction data with potential fields (gravity and magnetics) along the profile through the debated region. Two alternative OCB locations were tested. The preferred model suggests the OCB position near the Sigsbee Escarpment, which is in agreement with the result of Eddy, 2014 and with the findings of the LithoSPAN experiment (Makris et al, 2015). However, the model with an alternative OCB location (further to the north of the Sigsbee Escarpment) may also satisfy the observed gravity and magnetic fields, although the crust in the oceanic domain is thicker than normal. Since the potential fields do not offer the unique answer, the other geophysical data should be examined, such as the Vp/Vs ratio. This parameter was analyzed for the LithoSPAN (Makris et al., 2015) and allowed distinguishing between continental and oceanic domains; it was also examined for GUMBO 3 and 4 (Duncan, 2013). However, the values of Vs derived during retraction experiment for GUMBO 2 are not publically available at this time
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