257 research outputs found
The HELLAS2XMM survey. IX. Spectroscopic identification of super-EROs hosting AGNs
We present VLT near-IR spectroscopic observations of three X-ray sources
characterized by extremely high X-ray-to-optical ratios (X/O>40), extremely red
colors (6.3<R-K<7.4, i.e. EROs) and bright infrared magnitudes (17.6<K<18.3).
These objects are very faint in the optical, making their spectroscopic
identification extremely challenging. Instead, our near-IR spectroscopic
observations have been successful in identifying the redshift of two of them
(z=2.08 and z=1.35), and tentatively even of the third one (z=2.13). When
combined with the X-ray properties, our results clearly indicate that all these
objects host obscured QSOs (4e44 < L(2-10keV) < 1.5e45 erg/s, 2e22 < N_H < 4e23
cm-2) at high redshift. The only object with unresolved morphology in the K
band shows broad Halpha emission, but not broad Hbeta, implying a type 1.9 AGN
classification. The other two objects are resolved and dominated by the host
galaxy light in the K band, and appear relatively quiescent: one of them has a
LINER-like emission line spectrum and the other presents only a single, weak
emission line which we tentatively identify with Halpha. The galaxy
luminosities for the latter two objects are an order of magnitude brighter than
typical local L* galaxies and the derived stellar masses are well in excess of
10^11 Msun. For these objects we estimate black hole masses higher than 10^9
Msun and we infer that they are radiating at Eddington ratios L/L_Edd < 0.1. We
discuss the implications of these findings for the coevolution of galaxies and
black hole growth. Our results provide further support that X-ray sources with
high X/O ratios and very red colors tend to host obscured QSO in very massive
galaxies at high redshift.Comment: 7 pages, 5 figures, accepted for publication in A&
Noninvasive Ultrasound Monitoring of Embryonic and Fetal Development in Chinchilla lanigera to Predict Gestational Age: Preliminary Evaluation of This Species as a Novel Animal Model of Human Pregnancy
Ultrasound is a noninvasive routine method that allows real-time monitoring of fetal development in utero to determine gestational age and to detect congenital anomalies and multiple pregnancies. To date, the developmental biology of Chinchilla lanigera has not yet been characterized. This species has been found to undergo placentation, long gestation, and fetal dimensions similar to those in humans. The aim of this study was to assess the use of high-frequency ultrasound (HFUS) and clinical ultrasound (US) to predict gestational age in chinchillas and evaluate the possibility of this species as a new animal model for the study of human pregnancy. In this study, 35 pregnant females and a total of 74 embryos and fetuses were monitored. Ultrasound examination was feasible in almost all chinchilla subjects. It was possible to monitor the chinchilla embryo with HFUS from embryonic day (E) 15 to 60 and with US from E15 to E115 due to fetus dimensions. The placenta could be visualized and measured with HFUS from E15, but not with US until E30. From E30, the heartbeat became detectable and it was possible to measure fetal biometrics. In the late stages of pregnancy, stomach, eyes, and lenses became visible. Our study demonstrated the importance of employing both techniques while monitoring embryonic and fetal development to obtain an overall and detailed view of all structures and to recognize any malformation at an early stage. Pregnancy in chinchillas can be confirmed as early as the 15th day postmating, and sonographic changes and gestational age are well correlated. The quantitative measurements of fetal and placental growth performed in this study could be useful in setting up a database for comparison with human fetal ultrasounds. We speculate that, in the future, the chinchilla could be used as an animal model for the study of US in human pregnancy
The Richness and Beauty of the Physics of Cosmological Recombination: The Contributions from Helium
The physical ingredients to describe the epoch of cosmological recombination
are amazingly simple and well-understood. This fact allows us to take into
account a very large variety of processes, still finding potentially measurable
consequences. In this contribution we highlight some of the detailed physics
that were recently studied in connection with cosmological hydrogen and helium
recombination. The impact of these considerations is two-fold: (i) the
associated release of photons during this epoch leads to interesting and unique
deviations of the Cosmic Microwave Background (CMB) energy spectrum from a
perfect blackbody, which, in particular at decimeter wavelength, may become
observable in the near future. Despite the fact that the abundance of helium is
rather small, it also contributes a sizeable amount of photons to the full
recombination spectrum, which, because of differences in the dynamics of the
helium recombinations and the non-trivial superposition of all components, lead
to additional distinct spectral features. Observing the spectral distortions
from the epochs of hydrogen and helium recombination, in principle would
provide an additional way to determine some of the key parameters of the
Universe (e.g. the specific entropy, the CMB monopole temperature and the
pre-stellar abundance of helium), not suffering from limitations set by cosmic
variance. Also it permits us to confront our detailed understanding of the
recombination process with direct observational evidence. (ii) with the advent
of high precision CMB data, e.g. as will be available using the Planck Surveyor
or CMBpol, a very accurate theoretical understanding of the ionization history
of the Universe becomes necessary for the interpretation of the CMB temperature
and polarization anisotropies. (abridged)Comment: 16 pages, 11 figures, proceedings of the conference: "A Century of
Cosmology: Past, Present and Future
A revision of the X-ray absorption nature of the BALQSOs
Broad absorption line quasars (BALQSOs) are key objects for studying the
structure and emission/absorption properties of AGN. However, despite their
fundamental importance, the properties of BALQSOs are still not well
understood. In order to investigate the X-ray nature of these sources, as well
as the correlations between X-ray and rest-frame UV properties, we compile a
large sample of 88 BALQSOs observed by XMM-Newton. We performed a full X-ray
spectral analysis on a sample of 39 sources with higher X-ray spectral quality,
and an approximate HR analysis on the remaining sources. Using available
optical spectra, we calculate the BALnicity index and investigate the
dependence between this optical parameter and different X-ray properties.
Using the neutral absorption model, we found that 36% of our BALQSOs have NH
< 5x10^21 cm^-2, lower than the expected X-ray absorption for such objects.
However, when we used a physically-motivated model for the X-ray absorption in
BALQSOs, i.e. ionized absorption, \sim 90% of the objects are absorbed. The
absorption properties also suggest that LoBALs may be physically different
objects from HiBALs. In addition, we report on a correlation between the
ionized absorption column density and BAL parameters. There is evidence (at 98%
level) that the amount of X-ray absorption is correlated with the strength of
high-ionization UV absorption. This correlation, not previously reported, can
be naturally understood in virtually all BALQSO models, as driven by the total
amount of gas mass flowing towards the observer.Comment: Accepted by A&A. 12 pages, 8 figures. Added references and corrected
typo
The HELLAS2XMM survey. X. The bolometric output of luminous obscured quasars: The Spitzer perspective
Aims: We aim at estimating the spectral energy distributions (SEDs) and the
physical parameters related to the black holes harbored in eight high
X-ray-to-optical (F_X/F_R>10) obscured quasars at z>0.9 selected in the 2--10
keV band from the HELLAS2XMM survey.
Methods: We use IRAC and MIPS 24 micron observations, along with optical and
Ks-band photometry, to obtain the SEDs of the sources. The observed SEDs are
modeled using a combination of an elliptical template and torus emission (using
the phenomenological templates of Silva et al. 2004) for six sources associated
with passive galaxies; for two point-like sources, the empirical SEDs of red
quasars are adopted. The bolometric luminosities and the M_BH-L_K relation are
used to provide an estimate of the masses and Eddington ratios of the black
holes residing in these AGN.
Results: All of our sources are detected in the IRAC and MIPS (at 24 micron)
bands. The SED modeling described above is in good agreement with the observed
near- and mid-infrared data. The derived bolometric luminosities are in the
range ~10^45-10^47 erg s^-1, and the median 2--10 keV bolometric correction is
~25, consistent with the widely adopted value derived by Elvis et al. (1994).
For the objects with elliptical-like profiles in the K_s band, we derive high
stellar masses (0.8-6.2)X10^11 Mo, black hole masses in the range
(0.2-2.5)X10^9 Mo, and Eddington ratios L/L_Edd<0.1, suggesting a low-accretion
phase.Comment: 12 pages, 6 figures, A&A accepted. Typo corrected in the titl
The HELLAS2XMM survey: IV. Optical identifications and the evolution of the accretion luminosity in the Universe
We present results from the photometric and spectroscopic identification of
122 X-ray sources recently discovered by XMM-Newton in the 2-10 keV band (the
HELLAS2XMM 1dF sample). Their flux cover the range 8E-15-4E-13 cgs and the
total area surveyed is 0.9 deg2. About 20% of the hard X-ray selected sources
have an X-ray to optical flux ratio (X/O) ten times or more higher than that of
optically selected AGN. Unlike the faint sources found in the ultra-deep
Chandra and XMM-Newton surveys, which reach X-ray (and optical) fluxes more
than one order of magnitude lower than the HELLAS2XMM survey sources, many of
the extreme X/O sources in our sample have R<=25 and are therefore accessible
to optical spectroscopy. We report the identification of 13 sources with
X/O>10: 8 are narrow line QSO (i.e. QSO2), four are broad line QSO. We use a
combined sample of 317 hard X-ray selected sources (HELLAS2XMM 1dF, CDFN 1Msec,
SSA13 and Lockman Hole flux limited samples), 221 with measured z, to evaluate
the cosmological evolution of the hard X-ray source's number and luminosity
densities. Looking backward in time, the low luminosity sources (logL(2-10keV)
= 43-44 erg/s) increase in number at a rate different than the high luminosity
sources (logL(2-10keV)>44.5 erg/s), reaching a maximum around z=1 and then
levelling off beyond z=2. This translates into an accretion driven luminosity
density which is dominated by sources with logL(2-10keV) < 44.5 erg/s up to at
least z=1, while the contribution of the same sources and of those with
logL(2-10keV)>44.5 erg/s appear to be comparable between z=2 and 4.Comment: v2, minor changes, A&A in pres
The HELLAS2XMM survey. XIII. Multi-component analysis of the spectral energy distribution of obscured AGN
We combine near-to-mid-IR Spitzer data with shorter wavelength observations
(optical to X-rays) to get insights on the properties of a sample of luminous,
obscured Active Galactic Nuclei (AGN). We aim at modeling their broad-band
Spectral Energy Distributions (SEDs) in order to estimate the main parameters
related to the dusty torus. The sample comprises 16 obscured high-redshift
(0.9<z<2.1) xray luminous quasars (L_2-10 ~ 10^44 erg s-1) selected from the
HELLAS2XMM survey. The SEDs are described by a multi-component model including
a stellar component, an AGN component and a starburst. The majority (~80%) of
the sources show moderate optical depth (tau_9.7um<3) and the derived column
densities N_H are consistent with the xray inferred values (10^22 <N_H< 3x10^23
cm-2) for most of the objects, confirming that the sources are moderately
obscured Compton-thin AGN. Accretion luminosities in the range 5x10^44 < Lbol <
4x10^46 erg s-1 are inferred. We compare model luminosities with those obtained
by integrating the observed SED, finding that the latter are lower by a factor
of ~2 in the median. The discrepancy can be as high as an order of magnitude
for models with high optical depth (tau_9.7um=10). The ratio between the
luminosities obtained by the fitting procedure and from the observed SED
suggest that, at least for Type~2 AGN, observed bolometric luminosities are
likely to underestimate intrinsic ones and the effect is more severe for highly
obscured sources. Bolometric corrections from the hard X-ray band are computed
and have a median value of k_2-10kev ~ 20. The obscured AGN in our sample are
characterized by relatively low Eddington ratios (median lambda_Edd~0.08). On
average, they are consistent with the Eddington ratio increasing at increasing
bolometric correction (e.g. Vasudevan & Fabiam 2009).Comment: 16 pages, 10 figures. Accepted for pubblication in Astronomy and
Astrophysics
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