238 research outputs found
"L'effetto di un singolo lumicino o di una singola voce lontana". Dall'"Autunno del Medioevo" a "Prima che faccia luce"
Riflessione sullo status dell'Autunno del Medioevo" come opera di storiografia globale e world literature. Analisi delle traduzioni e ritraduzioni dell'opera, in particolare in Italia, dove finalmente si fa luce sulla figura del primo traduttore Bernardo Jasink. Evoluzione del pensiero storiografico di Huizinga negli anni Trenta e ricezione in Italia
On elimination of quantifiers in some non-classical mathematical theories
Elimination of quantifiers is shown to fail dramatically for a group of
well-known mathematical theories (classically enjoying the property) against a
wide range of relevant logical backgrounds. Furthermore, it is suggested that
only by moving to more extensional underlying logics can we get the property
back
Spanish foreign words in Dutch: period 2000-2013
The purpose of this research is to look into the recent influence of the Spanish
language, both European and from the center and south of America (with approx-
imately 400 million native speakers altogether), on the Dutch language (24 million
speakers). Spanish foreign words will be analyzed according to the European his-
torical-cultural method, that is, they will be dealt with within a historical frame, in
this case from the year 2000 until 2013. By creating a corpus of Spanish foreign
words, I will try to clarify which semantic fields have been the most influential on
Dutch nowadays. From this division into semantic fields, it will be possible to
understand what kind of vocabulary has had the strongest impact and which has
been the degree of contact during the first thirteen years of the 21st century
The web of the Giant: spectroscopic confirmation of a Large Scale Structure around the z=6.31 quasar SDSS J1030+0524
We report on the spectroscopic confirmation of a large scale structure around
the luminous, z=6.31 QSO SDSS~J1030+0524, that is powered by a billion solar
mass black hole. The structure is populated by at least six members, four Lyman
Break Galaxies (LBGs) and two Lyman Alpha Emitters (LAEs). The four LBGs have
been identified among a sample of 21 i-band dropouts with z{AB}<25.5 selected
up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their
redshifts have been determined through up to 8hr-long multi-object
spectroscopic observations at 8-10m class telescopes. The two LAEs have been
identified in a 6hr VLT/MUSE observation centered on the QSO. The redshifts of
the six galaxies cover the range 6.129-6.355. Assuming that peculiar velocities
are negligible, this range corresponds to radial separations of +/-5 physical
Mpc from the QSO, that is comparable to the projected scale of the observed LBG
distribution on the sky. We conservatively estimate that this structure is
significant at >3.5 sigma level, and that the level of the galaxy overdensity
is at least 1.5-2 within the large volume sampled (~780 physical Mpc^3). The
spectral properties of the six member galaxies (Lyalpha strength and UV
luminosity) are similar to those of field galaxies at similar redshifts. This
is the first spectroscopic identification of a galaxy overdensity around a
super-massive black hole in the first billion years of the Universe. Our
finding lends support to the idea that the most distant and massive black holes
form and grow within massive (>10^{12} Msun) dark matter halos in large scale
structures, and that the absence of earlier detections of such systems was
likely due to observational limitations.Comment: 8 pages including Appendix, 5 figures, accepted as a letter on
Astronomy & Astrophysics. v2: minor changes in Table 1 caption and Figs. 2 &
3 label
X-ray properties and obscured fraction of AGN in the J1030 Chandra field
The 500ks Chandra ACIS-I observation of the field around the quasar
SDSS J1030+0524 is currently the 5th deepest extragalactic X-ray survey. The
rich multi-band coverage of the field allowed for an effective identification
and redshift determination of the X-ray source counterparts: to date a catalog
of 243 extragalactic X-ray sources with either a spectroscopic or photometric
redshift estimate in the range is available over a 355 arcmin
area. Given its depth and the multi-band information, this catalog is an
excellent resource to investigate X-ray spectral properties of distant Active
Galactic Nuclei (AGN) and derive the redshift evolution of their obscuration.
We performed a thorough X-ray spectral analysis for each object in the sample,
measuring its nuclear column density and intrinsic (de-absorbed)
2-10 keV rest-frame luminosity, . Whenever possible, we also used the
presence of the Fe K emission line to improve the photometric redshift
estimates. We measured the fractions of AGN hidden by column densities in
excess of and cm ( and ,
respectively) as a function of and redshift, and corrected for
selection effects to recover the intrinsic obscured fractions. At ,
we found and , respectively, in broad
agreement with the results from other X-ray surveys. No significant variations
with X-ray luminosity were found within the limited luminosity range probed by
our sample (log). When focusing on luminous AGN with
log to maximize the sample completeness up to large
cosmological distances, we did not observe any significant change in
or over the redshift range . Nonetheless, the obscured
fractions we measure are significantly higher than ...Comment: A&A, in pres
LBT-MODS spectroscopy of high-redshift candidates in the Chandra J1030 field. A newly discovered z2.8 large scale structure
We present the results of a spectroscopic campaign with the Multi-Object
Double Spectrograph (MODS) instrument mounted on the Large Binocular Telescope
(LBT), aimed at obtaining a spectroscopic redshift for seven Chandra J1030
sources with a photometric redshift >=2.7 and optical magnitude
r_AB=[24.5-26.5]. We obtained a spectroscopic redshift for five out of seven
targets: all of them have z_spec>=2.5, thus probing the reliability of the
Chandra J1030 photometric redshifts. The spectroscopic campaign led to the
serendipitous discovery of a z~2.78 large scale structure (LSS) in the J1030
field: the structure contains four X-ray sources (three of which were targeted
in the LBT-MODS campaign) and two non-X-ray detected galaxies for which a
VLT-MUSE spectrum was already available. The X-ray members of the LSS are
hosted in galaxies that are significantly more massive
(log(M_*/M_sun)=[10.0-11.1]) than those hosting the two MUSE-detected sources
(log(M_*/M_sun)<10). Both observations and simulations show that massive
galaxies, and particularly objects having log(M_*/M_sun)>10, are among the best
tracers of large scale structures and filaments in the cosmic web.
Consequently, our result can explain why X-ray-detected AGN have also been
shown to be efficient tracers of large scale structures.Comment: 16 pages, 9 Figures. Accepted for publication in Astronomy and
Astrophysic
The deep Chandra survey in the SDSS J1030+0524 field
We present the X-ray source catalog for the ∼479 ks Chandra exposure of the SDSS J1030+0524 field, which is centered on a region that shows the best evidence to date of an overdensity around a z > 6 quasar, and also includes a galaxy overdensity around a Compton-thick Fanaroff-Riley type II (FRII) radio galaxy at z = 1.7. Using wavdetect for initial source detection and ACIS Extract for source photometry and significance assessment, we create preliminary catalogs of sources that are detected in the full (0.5-7.0 keV), soft (0.5-2.0 keV), and hard (2-7 keV) bands, respectively. We produce X-ray simulations that mirror our Chandra observation to filter our preliminary catalogs and achieve a completeness level of > 91% and a reliability level of ∼95% in each band. The catalogs in the three bands are then matched into a final main catalog of 256 unique sources. Among them, 244, 193, and 208 are detected in the full, soft, and hard bands, respectively. The Chandra observation covers a total area of 335 arcmin2 and reaches flux limits over the central few square arcmins of ∼3 × 10-16, 6 × 10-17, and 2 × 10-16 erg cm-2 s-1 in the full, soft, and hard bands, respectively This makes J1030 field the fifth deepest extragalactic X-ray survey to date. The field is part of the Multiwavelength Survey by Yale-Chile (MUSYC), and is also covered by optical imaging data from the Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT), near-infrared imaging data from the Canada France Hawaii Telescope WIRCam (CFHT/WIRCam), and Spitzer IRAC. Thanks to its dense multi-wavelength coverage, J1030 represents a legacy field for the study of large-scale structures around distant accreting supermassive black holes. Using a likelihood ratio analysis, we associate multi-band (r, z, J, and 4.5  μm) counterparts for 252 (98.4%) of the 256 Chandra sources, with an estimated reliability of 95%. Finally, we compute the cumulative number of sources in each X-ray band, finding that they are in general agreement with the results from the Chandra Deep Fields.We acknowledge the referee for a prompt and constructive report. We acknowledge financial contribution from the agreement ASI-INAF n. 2017-14-H.O. We thank P. Broos for providing great support for the analysis of our simulations with AE, and H. M. Günther for the support provided for using MARX. We also thank B. Luo for providing us the log(N)–log(S) of the 7Ms CDF-S. FV acknowledges financial support from CONICYT and CASSACA through the Fourth call for tenders of the CAS-CONICYT Fund, and CONICYT grants Basal-CATA AFB-170002. DM and MA acknowledge support by grant number NNX16AN49G issued through the NASA Astrophysics Data Analysis Program (ADAP). Further support was provided by the Faculty Research Fund (FRF) of Tufts University
Multi-Wavelength Study of a Proto-BCG at z = 1.7
In this work we performed a spectral energy distribution (SED) analysis in
the optical/infrared band of the host galaxy of a proto-brightest cluster
galaxy (BCG, NVSS J103023+052426) in a proto-cluster at z = 1.7. We found that
it features a vigorous star formation rate (SFR) of 570
/yr and a stellar mass of ; the high corresponding specific SFR = classifies this object as a starburst galaxy that will
deplete its molecular gas reservoir in yr. Thus, this
system represents a rare example of a proto-BCG caught during the short phase
of its major stellar mass assembly. Moreover, we investigated the nature of the
host galaxy emission at 3.3 mm. We found that it originates from the cold dust
in the interstellar medium, even though a minor non-thermal AGN contribution
cannot be completely ruled out. Finally, we studied the polarized emission of
the lobes at 1.4 GHz. We unveiled a patchy structure where the polarization
fraction increases in the regions in which the total intensity shows a bending
morphology; in addition, the magnetic field orientation follows the direction
of the bendings. We interpret these features as possible indications of an
interaction with the intracluster medium. This strengthens the hypothesis of
positive AGN feedback, as inferred in previous studies of this object on the
basis of X-ray/mm/radio analysis. In this scenario, the proto-BCG heats the
surrounding medium and possibly enhances the SFR in nearby galaxies
AGN populations in GOODS-N through eMERGE ultra-deep JVLA observations
Multi-wavelength studies of deep radio fields show a composite population of star-forming galaxies, radio-quiet and radio-loud AGNs, with the formers dominating at the lowest flux densities (In my talk I will report about the e-MERLIN Galaxy Evolution Survey (eMERGE, PI: Muxlow), a legacy project which aims at undertaking a spatially-resolved study of AGN and star formation processes up to high redshift in a 30 arcmin diameter field in the GOODS-N region, through ultra-deep (sub-microJy rms), sub-arcsec (50-500 mas) imaging at 1.4 and 5 GHz, using combined JVLA and eMERLIN observations. I will focus on the 5 GHz JVLA mosaic observations and catalogue of GOODS-N (94 sources), in the framework of the eMERGE project, and on the study of a larger sample of GOODS-N galaxies (300 objects) selected at 1.4 GHz to constrain the presence of AGN cores in moderate-to-high redshift (1<z<5) galaxies, via radio spectra-morphological analysis with the additional help of multi-wavelength information
Redshift identification of X-ray-selected active galactic nuclei in the J1030 field: searching for large-scale structures and high-redshift sources
We publicly release the spectroscopic and photometric redshift catalog of the sources detected with Chandra in the field of the z = 6.3 quasar SDSS J1030+0525. This is currently the fifth-deepest extragalactic X-ray field, and reaches a 0.5 2 keV flux limit of f0:5-2 = 6 × 10-17 erg s-1 cm-2. Using two independent methods, we measure a photometric redshift for 243 objects, while 123 (51%) sources also have a spectroscopic redshift, 110 of which come from an INAF-Large Binocular Telescope (LBT) Strategic Program.We use the spectroscopic redshifts to determine the quality of the photometric ones, and find it to be in agreement with that of other X-ray surveys which used a similar number of photometric data points. In particular, we measure a sample normalized median absolute deviation of NMAD = 1.48 × median(||zphot - zspec||/(1 + zspec)) = 0.065. We use these new spectroscopic and photometric redshifts to study the properties of the Chandra J1030 field.We observe several peaks in our spectroscopic redshift distribution between z = 0.15 and z = 1.5, and find that the sources in each peak are often distributed across the whole Chandra field of view. This confirms that X-ray-selected AGNs can efficiently track large-scale structures over physical scales of several megaparsecs. Finally, we computed the Chandra J1030 z > 3 number counts: while the spectroscopic completeness of our sample is limited at high redshift, our results point towards a potential source excess at z ≥ 4, which we plan to either confirm or reject in the near future with dedicated spectroscopic campaigns
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