401 research outputs found
The WISSH quasars Project: II. Giant star nurseries in hyper-luminous quasars
Studying the coupling between the energy output produced by the central
quasar and the host galaxy is fundamental to fully understand galaxy evolution.
Quasar feedback is indeed supposed to dramatically affect the galaxy properties
by depositing large amounts of energy and momentum into the ISM. In order to
gain further insights on this process, we study the SEDs of sources at the
brightest end of the quasar luminosity function, for which the feedback
mechanism is supposed to be at its maximum. We model the rest-frame UV-to-FIR
SEDs of 16 WISE-SDSS Selected Hyper-luminous (WISSH) quasars at 1.8 < z < 4.6
disentangling the different emission components and deriving physical
parameters of both the nuclear component and the host galaxy. We also use a
radiative transfer code to account for the contribution of the quasar-related
emission to the FIR fluxes. Most SEDs are well described by a standard
combination of accretion disk+torus and cold dust emission. However, about 30%
of them require an additional emission component in the NIR, with temperatures
peaking at 750K, which indicates the presence of a hotter dust component in
these powerful quasars. We measure extreme values of both AGN bolometric
luminosity (LBOL > 10^47 erg/s) and SFR (up to 2000 Msun/yr). A new relation
between quasar and star-formation luminosity is derived (LSF propto
LQSO^(0.73)) by combining several Herschel-detected quasar samples from z=0 to
4. Future observations will be crucial to measure the molecular gas content in
these systems, probe the impact between quasar-driven outflows and on-going
star-formation, and reveal the presence of merger signatures in their host
galaxies.Comment: 19 pages, 12 figures; Accepted for publication in Astronomy &
Astrophysics on June 13, 201
A NWB-based dataset and processing pipeline of human single-neuron activity during a declarative memory task
A challenge for data sharing in systems neuroscience is the multitude of different data formats used. Neurodata Without Borders: Neurophysiology 2.0 (NWB:N) has emerged as a standardized data format for the storage of cellular-level data together with meta-data, stimulus information, and behavior. A key next step to facilitate NWB:N adoption is to provide easy to use processing pipelines to import/export data from/to NWB:N. Here, we present a NWB-formatted dataset of 1863 single neurons recorded from the medial temporal lobes of 59 human subjects undergoing intracranial monitoring while they performed a recognition memory task. We provide code to analyze and export/import stimuli, behavior, and electrophysiological recordings to/from NWB in both MATLAB and Python. The data files are NWB:N compliant, which affords interoperability between programming languages and operating systems. This combined data and code release is a case study for how to utilize NWB:N for human single-neuron recordings and enables easy re-use of this hard-to-obtain data for both teaching and research on the mechanisms of human memory
BLAST Observations of the South Ecliptic Pole field: Number Counts and Source Catalogs
We present results from a survey carried out by the Balloon-borne Large
Aperture Submillimeter Telescope (BLAST) on a 9 deg^2 field near the South
Ecliptic Pole at 250, 350 and 500 {\mu}m. The median 1{\sigma} depths of the
maps are 36.0, 26.4 and 18.4 mJy, respectively. We apply a statistical method
to estimate submillimeter galaxy number counts and find that they are in
agreement with other measurements made with the same instrument and with the
more recent results from Herschel/SPIRE. Thanks to the large field observed,
the new measurements give additional constraints on the bright end of the
counts. We identify 132, 89 and 61 sources with S/N>4 at 250, 350, 500 {\mu}m,
respectively and provide a multi-wavelength combined catalog of 232 sources
with a significance >4{\sigma} in at least one BLAST band. The new BLAST maps
and catalogs are available publicly at http://blastexperiment.info.Comment: 25 pages, 6 figures, 4 tables, Accepted by ApJS. Maps and catalogs
available at http://blastexperiment.info
Herschel-ATLAS/GAMA: A difference between star formation rates in strong-line and weak-line radio galaxies
We have constructed a sample of radio-loud objects with optical spectroscopy from the Galaxy and Mass Assembly (GAMA) project over the Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS) Phase 1 fields. Classifying the radio sources in terms of their optical spectra, we find that strong-emission-line sources ('high-excitation radio galaxies') have, on average, a factor of ~4 higher 250-μm Herschel luminosity than weak-line ('lowexcitation') radio galaxies and are also more luminous than magnitude-matched radio-quiet galaxies at the same redshift. Using all five H-ATLAS bands, we show that this difference in luminosity between the emission-line classes arises mostly from a difference in the average dust temperature; strong-emission-line sources tend to have comparable dust masses to, but higher dust temperatures than, radio galaxies with weak emission lines. We interpret this as showing that radio galaxies with strong nuclear emission lines are much more likely to be associated with star formation in their host galaxy, although there is certainly not a one-to-one relationship between star formation and strong-line active galactic nuclei (AGN) activity. The strong-line sources are estimated to have star formation rates at least a factor of 3-4 higher than those in the weak-line objects. Our conclusion is consistent with earlier work, generally carried out using much smaller samples, and reinforces the general picture of high-excitation radio galaxies as being located in lower-mass, less evolved host galaxies than their low-excitation counterparts.Peer reviewe
The hyperluminous Compton-Thick z ∼ 2 quasar nucleus of the hot DOG W1835+4355 observed by NuSTAR
We present a 155ks NuSTAR observation of the hot dust-obscured
galaxy (hot DOG) W1835+4355. We extracted spectra from the two NuSTAR detectors
and analyzed them jointly with the archival XMM PN and MOS spectra. We
performed a spectroscopic analysis based on both phenomenological and
physically motivated models employing toroidal and spherical geometry for the
obscurer. In all the modelings, the source exhibits a Compton-thick column
density cm, a 2-10 keV luminosity
erg s , and a prominent soft excess
( % of the primary radiative output), which translates into a
luminosity erg s. We modeled the spectral energy
distribution from 1.6 to 850 using a clumpy two-phase dusty torus model
plus a modified blackbody to account for emission powered by star formation in
the far-infrared. We employed several geometrical configurations consistent
with those applied in the X-ray analysis. In all cases we obtained a bolometric
luminosity erg s, which confirms
the hyperluminous nature of this active galactic nucleus. Finally, we estimate
a prodigious star formation rate of 3000 , which is
consistent with the rates inferred for hyperluminous type I
quasars. The heavily obscured nature, together with , the ratio of
X-ray to mid-infrared luminosity, the rest-frame optical morphology, and the
host star formation rate are indicative of its evolutionary stage. We can
interpret this as a late-stage merger event in the transitional,
dust-enshrouded, evolutionary phase eventually leading to an optically bright
AGN.ERC
STF
Far-infrared spectroscopy of a lensed starburst: a blind redshift from Herschel
We report the redshift of HATLAS J132427.0+284452 (hereafter HATLAS J132427),
a gravitationally lensed starburst galaxy, the first determined 'blind' by the
Herschel Space Observatory. This is achieved via the detection of [C II]
consistent with z = 1.68 in a far-infrared spectrum taken with the SPIRE
Fourier Transform Spectrometer. We demonstrate that the [C II] redshift is
secure via detections of CO J = 2 - 1 and 3 - 2 using the Combined Array for
Research in Millimeter-wave Astronomy and the Institut de Radioastronomie
Millimetrique's Plateau de Bure Interferometer. The intrinsic properties appear
typical of high-redshift starbursts despite the high lensing-amplified fluxes,
proving the ability of the FTS to probe this population with the aid of
lensing. The blind detection of [C II] demonstrates the potential of the SAFARI
imaging spectrometer, proposed for the much more sensitive SPICA mission, to
determine redshifts of multiple dusty galaxies simultaneously without the
benefit of lensing.Comment: 6 pages, 5 figures, accepted for publication in MNRAS as a Lette
Is GRB 050904 at z=6.3 absorbed by dust?
Claim of dust extinction for this GRB has been debated in the past. We
suggest that the discrepant results occur primarily because most of previous
studies have not simultaneously investigated the X-ray to near-IR spectral
energy distribution of this GRB. The difficulty with this burst is that the
X-ray afterglow is dominated by strong flares at early times and is poorly
monitored at late times. In addition, the Z band photometry, which is the most
sensitive to dust extinction, has been found to be affected by strong
systematics. In this paper we carefully re-analyze the Swift/XRT afterglow
observations of this GRB, using extensive past studies of X-ray flare
properties when computing the X-ray afterglow flux level and exploiting the
recent reanalysis of the optical (UV rest frame) data of the same GRB. We
extract the X-ray to optical/near-IR afterglow SED for the three epochs where
the best spectral coverage is available: 0.47, 1.25, and 3.4 days after the
trigger. A spectral power-law model has been fitted to the extracted SEDs. We
discuss that no spectral breaks or chromatic temporal breaks are expected in
the epochs of interest. To fit any UV rest-frame dust absorption, we tested the
Small Magellanic Cloud (SMC) extinction curve, the mean extinction curve (MEC)
found for a sample of QSO at and its corresponding attenuation curve, as
well as a starburst attenuation curve, and the extinction curve consistent with
a supernova dust origin (SN-type). The SMC extinction curve and the SN-type one
provide good fit to the data at all epochs, with an average amount of dust
absorption at of mag.
These results indicate that the primeval galaxy at hosting this GRB
has already enriched its ISM with dust.Comment: 8 pages, 3 figures, accepted for publication in Astronomy and
Astrophysics; figure 1 has been degraded, full resolution version at
http://dl.dropbox.com/u/1670579/fig01.p
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