923 research outputs found
A 610-MHz survey of the ELAIS-N1 field with the Giant Metrewave Radio Telescope - Observations, data analysis and source catalogue
Observations of the ELAIS-N1 field taken at 610 MHz with the Giant Metrewave
Radio Telescope are presented. Nineteen pointings were observed, covering a
total area of 9 square degrees with a resolution of 6" x 5", PA +45 deg. Four
of the pointings were deep observations with an rms of 40 microJy before
primary beam correction, with the remaining fifteen pointings having an rms of
70 microJy. The techniques used for data reduction and production of a
mosaicked image of the region are described, and the final mosaic is presented,
along with a catalogue of 2500 sources detected above 6 sigma. This work
complements the large amount of optical and infrared data already available on
the region. We calculate 610-MHz source counts down to 270 microJy, and find
further evidence for the turnover in differential number counts below 1 mJy,
previously seen at both 610 MHz and 1.4 GHz.Comment: 12 pages, 18 figures, two tables. Table 1 can be found in full via
http://www.mrao.cam.ac.uk/surveys/ . Accepted for publication in MNRA
WINGS: a WIde-field nearby Galaxy-cluster survey III. Deep near-infrared photometry of 28 nearby clusters
Context. This is the third paper of a series devoted to the WIde-field Nearby
Galaxy-cluster Survey (WINGS).WINGS is a long term project aimed at gathering
wide-field, multiband imaging and spectroscopy of galaxies in a complete sample
of 77 X-ray selected nearby clusters (0.04<z<0.07) located far from the
galactic plane (b>20deg). The main goal of this project is to establish a local
reference sample for evolutionary studies of galaxies and galaxy clusters.
Aims. This paper presents the near-infrared (J,K) photometric catalogs of 28
clusters of the WINGS sample and describes the procedures followed to construct
them. Methods. The raw data has been reduced at CASU and special care has been
devoted to the final coadding, drizzling technique, astrometric solution and
magnitude calibration for the WFCAM pipeline processed data. We have
constructed the photometric catalogs based on the final calibrated coadded
mosaics (0.79 deg2) in J (19 clusters) and K (27 clusters) bands. A customized
interactive pipeline has been used to clean the catalogs and to make mock
images for photometric errors and completeness estimates. Results. We provide
deep near-infrared photometric catalogs (90% complete in detection rate at
total magnitudes J =20.5, K =19.4, and in classification rate at J = 19.5 and K
= 18.5), giving positions, geometrical parameters, total and aperture
magnitudes for all detected sources. For each field we classify the detected
sources as stars, galaxies and objects of "unknown" nature.Comment: Published by A&A501.851 - 15 pages, 3 tables, 13 figures. Catalogs
will be available via CDS and http://web.oapd.inaf.it/wing
Properties of dusty tori in active galactic nuclei - II. Type 2 AGN
(abridged) This paper is the second part of a work investigating the
properties of dusty tori in AGN by means of multi-component SED fitting. It
focuses on low luminosity, low redshift (z < 0.25) AGN selected among emission
line galaxies as well as X-ray, radio and mid-infrared selected type 2 AGN
samples from the literature. The available multi-band photometry covers the
spectral range from the u-band up to 160 um. The observed SED of each object is
fit to a set of multi-component models comprising a stellar component, a high
optical depth torus and cold emission from a starburst (SB). The contribution
of the various components (stars, torus, SB) is reflected in the position of
the objects on the IRAC colour diagram. The comparison of type 1 (as derived
from Hatziminaoglou et al. 2008) and type 2 AGN properties is broadly
consistent with the Unified Scheme. The estimated ratio between type 2 and type
1 objects is about 2-2.5:1. The AGN accretion-to-infrared luminosity ratio is
an indicator of the obscuration of the AGN since it scales down with the
covering factor. We find evidence supporting the receding torus paradigm, with
the estimated fraction of obscured AGN decreasing with increasing optical
luminosity over four orders of magnitude. The average star formation rates are
of ~ 10, 40 and 115 Mo/yr for the low-z, type 2 and quasar samples,
respectively; but this might simply reflect observational biases, as our
quasars are one to two orders of magnitude more luminous than the type 2 AGN.
For the majority of objects with 70 and/or 160 um detections an SB component
was needed in order to reproduce the data points, implying that the
far-infrared emission in AGN arises mostly from star formation; moreover, the
SB-to-AGN luminosity ratio shows a slight trend with increasing luminosity.Comment: 20 pages, 23 figures, accepted for publication in MNRAS; full
versions of tables 1-4 and Figs. 5, 14 and 15 only available as online
materia
Obscured and powerful AGN and starburst activities at z~3.5
We report the discovery of two sources at z=3.867 and z=3.427 that exhibit
powerful starburst and AGN activities. They benefit from data from radio to X
rays from the CFHTLS-D1/SWIRE/XMDS surveys. Follow-up optical and near-infrared
spectroscopy, and millimeter IRAM/MAMBO observations are also available. We
performed an analysis of their spectral energy distributions to understand the
origin of their emission and constrain their luminosities. A comparison with
other composite systems at similar redshifts from the literature is also
presented. The AGN and starburst bolometric luminosities are ~10^13 Lsun. The
AGN emission dominates at X ray, optical, mid-infrared wavelengths, and
probably in the radio. The starburst emission dominates in the far-infrared.
The estimated star formation rates range from 500 to 3000Msun/yr. The AGN
near-infrared and X ray emissions are heavily obscured in both sources with an
estimated dust extinction Av>4, and Compton-thick gas column densities. The two
sources are the most obscured and most luminous AGNs detected at millimeter
wavelengths currently known. The sources presented in this work are heavily
obscured QSOs, but their properties are not fully explained by the standard AGN
unification model. In one source, the ultraviolet and optical spectra suggest
the presence of outflowing gas and shocks, and both sources show emission from
hot dust, most likely in the vicinity of the nucleus. Evidence of moderate
AGN-driven radio activity is found in both sources. The two sources lie on the
local M_BH-M_bulge relation. To remain on this relation, their star formation
rate has to decrease. Our results support evolutionary models that invoke radio
feedback as star formation quenching mechanism, and suggest that such a
mechanism might play a major role also in powerful AGNs.Comment: Accepted for publication in Astronomy & Astrophysics (12 pages; 6
figures); replaced version includes minor language editing and revised
reference
Revised SWIRE photometric redshifts
We have revised the Spitzer Wide-Area Infrared Extragalactic survey (SWIRE) Photometric
Redshift Catalogue to take account of new optical photometry in several of the SWIRE areas,
and incorporating Two Micron All Sky Survey (2MASS) and UKIRT Infrared Deep Sky
Survey (UKIDSS) near-infrared data. Aperture matching is an important issue for combining
near-infrared and optical data, and we have explored a number of methods of doing this.
The increased number of photometric bands available for the redshift solution results in
improvements both in the rms error and, especially, in the outlier rate.
We have also found that incorporating the dust torus emission into the quasi-stellar object
(QSO) templates improves the performance for QSO redshift estimation. Our revised redshift
catalogue contains over 1 million extragalactic objects, of which 26 288 are QSOs.Web of Scienc
Tracing the cosmic growth of supermassive black holes to z~3 with Herschel
We study a sample of Herschel selected galaxies within the Great Observatories Origins Deep Survey-South and the Cosmic Evolution Survey fields in the framework of the Photodetector Array Camera and Spectrometer (PACS) Evolutionary Probe project. Starting from the rich multiwavelength photometric data sets available in both fields, we perform a broad-band spectral energy distribution decomposition to disentangle the possible active galactic nucleus (AGN) contribution from that related to the host galaxy. We find that 37 per cent of the Herschel-selected sample shows signatures of nuclear activity at the 99 per cent confidence level. The probability of revealing AGN activity increases for bright (L 1â1000 > 10 11 L ? ) star-forming galaxies at z > 0.3, becoming about 80 per cent for the brightest (L 1â1000 > 10 12 L ? )
Infrared (IR) galaxies at zâ„1. Finally, we reconstruct the AGN bolometric luminosity function and the supermassive black hole growth rate across cosmic time up to z ⌠3 from a far-IR perspective. This work shows general agreement with most of the panchromatic estimates from the literature, with the global black hole growth peaking at z ⌠2 and reproducing the observed local black hole mass density with consistent values of the radiative efficiency Erad (âŒ0.07)
Witchcraft and the Somerset idyll : The depiction of folk belief in Walter Raymondâs novels
The work of Walter Raymond (1852-1931) is now largely forgotten. Yet his Somerset novels, complemented by his ethnographic writings, contain depictions of local witchcraft belief that are worthy of study in literary and historical contexts. They raise issues regarding the fictional depiction of rural life and tradition, and the value of fiction as a folkloric and historical sourcePeer reviewe
Disk, merger, or outflow ? Molecular gas kinematics in two powerful obscured QSOs at z>3.4
We report on the detection of bright CO(4-3) line emission in two powerful,
obscured quasars discovered in the SWIRE survey, SW022513 and SW022550 at
z>3.4. We analyze the line strength and profile to determine the gas mass,
dynamical mass and the gas dynamics for both galaxies. In SW022513 we may have
found the first evidence for a molecular, AGN-driven wind in the early
Universe. The line profile in SW022513 is broad (FWHM = 1000 km/s) and
blueshifted by -200 km/s relative to systemic (where the systemic velocity is
estimated from the narrow components of ionized gas lines, as is commonly done
for AGN at low and high redshifts). SW022550 has a more regular, double-peaked
profile, which is marginally spatially resolved in our data, consistent with
either a merger or an extended disk. The molecular gas masses, 4x10^10 Msun,
are large and account for <30% of the stellar mass, making these obscured QSOs
as gas rich as other powerful CO emitting galaxies at high redshift, i.e.,
submillimeter galaxies. Our sources exhibit relatively lower star-formation
efficiencies compared to other dusty, powerful starburst galaxies at high
redshift. We speculate that this could be a consequence of the AGN perturbing
the molecular gas.Comment: Accepted for publication in A&
Mid-infrared spectroscopy of infrared-luminous galaxies at z~0.5-3
We present results on low-resolution mid-infrared (MIR) spectra of 70
infrared-luminous galaxies obtained with the Infrared Spectrograph (IRS)
onboard Spitzer. We selected sources from the European Large Area Infrared
Survey (ELAIS) with S15 > 0.8 mJy and photometric or spectroscopic z > 1. About
half of the sample are QSOs in the optical, while the remaining sources are
galaxies, comprising both obscured AGN and starbursts. We classify the spectra
using well-known infrared diagnostics, as well as a new one that we propose,
into three types of source: those dominated by an unobscured AGN (QSOs),
obscured AGN, and starburst-dominated sources. Starbursts concentrate at z ~
0.6-1.0 favored by the shift of the 7.7-micron PAH band into the selection 15
micron band, while AGN spread over the 0.5 < z < 3.1 range. Star formation
rates (SFR) are estimated for individual sources from the luminosity of the PAH
features. An estimate of the average PAH luminosity in QSOs and obscured AGN is
obtained from the composite spectrum of all sources with reliable redshifts.
The estimated mean SFR in the QSOs is 50-100 Mo yr^-1, but the implied FIR
luminosity is 3-10 times lower than that obtained from stacking analysis of the
FIR photometry, suggesting destruction of the PAH carriers by energetic photons
from the AGN. The SFR estimated in obscured AGN is 2-3 times higher than in
QSOs of similar MIR luminosity. This discrepancy might not be due to luminosity
effects or selection bias alone, but could instead indicate a connection
between obscuration and star formation. However, the observed correlation
between silicate absorption and the slope of the near- to mid-infrared spectrum
is compatible with the obscuration of the AGN emission in these sources being
produced in a dust torus.Comment: 32 pages, 24 figures, 15 tables, accepted for publication in MNRA
Extragalactic Background Light Inferred from AEGIS Galaxy SED-type Fractions
The extragalactic background light (EBL) is of fundamental importance both
for understanding the entire process of galaxy evolution and for gamma-ray
astronomy, but the overall spectrum of the EBL between 0.1-1000 microns has
never been determined directly from galaxy spectral energy distribution (SED)
observations over a wide redshift range. The evolving, overall spectrum of the
EBL is derived here utilizing a novel method based on observations only. This
is achieved from the observed evolution of the rest-frame K-band galaxy
luminosity function up to redshift 4 (Cirasuolo et al. 2010), combined with a
determination of galaxy SED-type fractions. These are based on fitting SWIRE
templates to a multiwavelength sample of about 6000 galaxies in the redshift
range from 0.2 to 1 from the All-wavelength Extended Groth Strip International
Survey (AEGIS). The changing fractions of quiescent galaxies, star-forming
galaxies, starburst galaxies and AGN galaxies in that redshift range are
estimated, and two alternative extrapolations of SED-types to higher redshifts
are considered. This allows calculation of the evolution of the luminosity
densities from the UV to the IR, the evolving star formation rate density of
the universe, the evolving contribution to the bolometric EBL from the
different galaxy populations including AGN galaxies and the buildup of the EBL.
Our EBL calculations are compared with those from a semi-analytic model, from
another observationally-based model and observational data. The EBL
uncertainties in our modeling based directly on the data are quantified, and
their consequences for attenuation of very high energy gamma-rays due to pair
production on the EBL are discussed. It is concluded that the EBL is well
constrained from the UV to the mid-IR, but independent efforts from infrared
and gamma-ray astronomy are needed in order to reduce the uncertainties in the
far-IR.Comment: 25 pages, 18 figures, 4 tables; accepted for publication in MNRAS on
September 3, 2010. Online material available at http://side.iaa.es/EB
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