1,178 research outputs found
An X-ray Survey in SA 57 with XMM-Newton
The maximum number density of Active Galactic Nuclei (AGNs), as deduced from
X-ray studies, occurs at z<~1, with lower luminosity objects peaking at smaller
redshifts. Optical studies lead to a different evolutionary behaviour, with a
number density peaking at z~2 independently of the intrinsic luminosity, but
this result is limited to active nuclei brighter than the host galaxy. A
selection based on optical variability can detect low luminosity AGNs (LLAGNs),
where the host galaxy light prevents the identification by non-stellar colours.
We want to collect X-ray data in a field where it exists an optically-selected
sample of "variable galaxies'', i.e. variable objects with diffuse appearance,
to investigate the X-ray and optical properties of the population of AGNs,
particularly of low luminosity ones, where the host galaxy is visible. We
observed a field of 0.2 deg^2 in the Selected Area 57, for 67ks with
XMM-Newton. We detected X-ray sources, and we correlated the list with a
photographic survey of SA 57, complete to B_J~23 and with available
spectroscopic data. We obtained a catalogue of 140 X-ray sources to limiting
fluxes 5x10^-16, 2x10^-15 erg/cm^2/s in the 0.5-2 keV and 2-10 keV
respectively, 98 of which are identified in the optical bands. The X-ray
detection of part of the variability-selected candidates confirms their AGN
nature. Diffuse variable objects populate the low luminosity side of the
sample. Only 25/44 optically-selected QSOs are detected in X-rays. 15% of all
QSOs in the field have X/O<0.1.Comment: 13 pages, 6 figures, 4 tables, A&A in pres
Evidence for T Tauri-like emission in the EXor V1118 Ori from near-IR and X-ray data
We present a near-IR study of the EXor variable V1118 Ori, performed by
following a slightly declining phase after a recent outburst. In particular,
the near-IR (0.8 - 2.3 micron) spectrum, obtained for the first time, shows a
large variety of emission features of the HI and HeI recombination and CO
overtone. By comparing the observed spectrum with a wind model, a mass loss
rate value is derived along with other parameters whose values are typical of
an accreting T Tauri star. In addition, we have used X-ray data from the XMM
archive, taken in two different epochs during the declining phase monitored in
IR. X-ray emission (in the range 0.5 - 10 keV) permits to derive several
parameters which confirm the T Tauri nature of the source. In the near-IR the
object maintains a low visual extinction during all the activity phases,
confirming that variable extinction does not contribute to brightness
variations. The lack of both a significant amount of circumstellar material and
any evidence of IR cooling from collimated jet/outflow driven by the source,
indicates that, at least this member of the EXor class, is in a late stage of
the Pre-Main Sequence evolution. In the X-ray regime, an evident fading is
present, detected in the post-outburst phase, that cannot be reconciled with
the presence of any absorbing material. This circumstance, combined with the
persistence (in the pre- and post-outburst phases) of a temperature component
at about 10 MK, suggests that accretion has some influence in regulating the
coronal activity
The Nustar Extragalactic Surveys: Overview and Catalog from the Cosmos Field
To provide the census of the sources contributing to the X-ray background peak above 10 keV, NuSTAR is performing extragalactic surveys using a three-tier wedding cake approach. We present the NuSTAR survey of the COSMOS field, the medium sensitivity and medium area tier, covering 1.7 deg2 and overlapping with both Chandra and XMM-Newton data. This survey consists of 121 observations for a total exposure of ~3 Ms. To fully exploit these data, we developed a new detection strategy, carefully tested through extensive simulations. The survey sensitivity at 20% completeness is 5.9, 2.9 and 6.4 x 10^-14 erg/cm2/s in the 3-24 keV, 3-8 keV and 8-24 keV bands, respectively. By combining detections in 3 bands, we have a sample of 91 NuSTAR sources with 10^42 -10^45.5 erg/s luminosities and redshift z=0.04-2.5. Thirty two sources are detected in the 8-24 keV band with fluxes ~100 times fainter than sources detected by Swift-BAT. Of the 91 detections, all but four are associated with a Chandra and/or XMM-Newton point-like counterpart. One source is associated with an extended lower energy X-ray source. We present the X-ray (hardness ratio and luminosity) and optical-to-X-ray properties. The observed fraction of candidate Compton-thick AGN measured from the hardness ratio is between 13-20%. We discuss the spectral properties of NuSTAR J100259+0220.6 (ID 330) at z=0.044, with the highest hardness ratio in the entire sample. The measured column density exceeds 10^24 /cm2, implying the source is Compton-thick. This source was not previously recognized as such without the \u3e10 keV data
The multi-phase winds of Markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow
We present the best sensitivity and angular resolution maps of the molecular
disk and outflow of Mrk 231, as traced by CO observations obtained with
IRAM/PdBI, and we analyze archival Chandra and NuSTAR observations. We
constrain the physical properties of both the molecular disk and outflow, the
presence of a highly-ionized ultra-fast nuclear wind, and their connection. The
molecular outflow has a size of ~1 kpc, and extends in all directions around
the nucleus, being more prominent along the south-west to north-east direction,
suggesting a wide-angle biconical geometry. The maximum projected velocity of
the outflow is nearly constant out to ~1 kpc, thus implying that the density of
the outflowing material decreases from the nucleus outwards as . This
suggests that either a large part of the gas leaves the flow during its
expansion or that the bulk of the outflow has not yet reached out to ~1 kpc,
thus implying a limit on its age of ~1 Myr. We find and erg s.
Remarkably, our analysis of the X-ray data reveals a nuclear ultra-fast outflow
(UFO) with velocity -20000 km s, , and momentum load .We find as predicted for outflows undergoing an energy
conserving expansion. This suggests that most of the UFO kinetic energy is
transferred to mechanical energy of the kpc-scale outflow, strongly supporting
that the energy released during accretion of matter onto super-massive black
holes is the ultimate driver of giant massive outflows. We estimate a momentum
boost . The ratios and agree
with the requirements of the most popular models of AGN feedback.Comment: 16 pages, 17 figures. Accepted for publication in A&
AGN counts at 15um. XMM observations of the ELAIS-S1-5 sample
Context: The counts of galaxies and AGN in the mid infra-red (MIR) bands are
important instruments for studying their cosmological evolution. However, the
classic spectral line ratios techniques can become misleading when trying to
properly separate AGN from starbursts or even from apparently normal galaxies.
Aims: We use X-ray band observations to discriminate AGN activity in
previously classified MIR-selected starburst galaxies and to derive updated
AGN1 and (Compton thin) AGN2 counts at 15 um.
Methods: XMM observations of the ELAIS-S1 15um sample down to flux limits
~2x10^-15 erg cm^-2 s^-1 (2-10 keV band) were used. We classified as AGN all
those MIR sources with a unabsorbed 2-10 keV X-ray luminosity higher that
~10^42 erg/s.
Results: We find that at least about 13(+/-6) per cent of the previously
classified starburst galaxies harbor an AGN. According to these figures, we
provide an updated estimate of the counts of AGN1 and (Compton thin) AGN2 at 15
um. It turns out that at least 24% of the extragalactic sources brighter than
0.6 my at 15 um are AGN (~13% contribution to the extragalactic background
produced at fluxes brighter than 0.6 mJy).Comment: Accepted for publication on A&
Unveiling obscured accretion in the Chandra Deep Field South
A large population of heavily obscured, Compton Thick AGNs is predicted by
models of galaxy formation, models of Cosmic X-ray Background and by the
``relic'' super-massive black-hole mass function measured from local bulges.
However, so far only a handful of Compton thick AGNs have been possibly
detected using even the deepest Chandra and XMM surveys. Compton-thick AGNs can
be recovered thanks to the reprocessing of the AGN UV emission in the infrared
by selecting sources with AGN luminosity's in the mid-infrared and faint
near-infrared and optical emission. To this purpose, we make use of deep HST,
VLT, Spitzer and Chandra data on the Chandra Deep Field South to constrain the
number of Compton thick AGN in this field. We show that sources with high
24m to optical flux ratios and red colors form a distinct source
population, and that their infrared luminosity is dominated by AGN emission.
Analysis of the X-ray properties of these extreme sources shows that most of
them (80) are indeed likely to be highly obscured, Compton thick AGNs.
The number of infrared selected, Compton thick AGNs with 5.8m luminosity
higher than erg s turns out to be similar to that of X-ray
selected, unobscured and moderately obscured AGNs with 2-10 keV luminosity
higher than erg s in the redshift bin 1.2-2.6. This ``factor
of 2'' source population is exactly what it is needed to solve the
discrepancies between model predictions and X-ray AGN selection.Comment: Revised version, to be published by The Astrophysical Journa
Preclinical discovery and development of fingolimod for the treatment of multiple sclerosis
ABSTRACTIntroduction: Fingolimod, the first oral disease-modifying treatment (DMT) in multiple sclerosis (MS), is a sphingosine 1-phosphate receptor (S1PR) ligand. Approved in 2010, fingolimod has ..
The XMM-Newton survey of the ELAIS-S1 field II: optical identifications and multiwavelength catalogue of X-ray sources
We present optical identifications and a multi-band catalogue of a sample of
478 X-ray sources in the XMM and Chandra surveys of the central 0.6 deg^2 of
the ELAIS-S1 field. The optical/infrared counterpart of each X-ray source was
identified using R and IRAC 3.6 um bands. This method was complemented by the
precise positions obtained through Chandra observations. Approximately 94% of
the counterparts are detected in the R band, while the remaining are blank
fields in the optical down to R~24.5, but have a near-infrared counterpart
detected by IRAC within 6 arcsec from the XMM centroid. The multi-band
catalogue contains photometry in ten photometric bands (B to the MIPS 24 um).
We determined redshift and classification for 237 sources (~50% of the sample)
brighter than R=24. We classified 47% of the sources with spectroscopic
redshift as broad-line active galactic nuclei (BL AGNs) with z=0.1-3.5, while
sources without broad-lines are about 46% of the spectroscopic sample and are
found up to z=2.6. We identified 11 type 2 QSOs among the sources with X/O>8,
with z=0.9-2.6, high 2-10 keV luminosity (log(L2-10keV)>=43.8 erg/s) and hard
X-ray colors suggesting large absorbing columns at the rest frame (logN_H up to
23.6 cm^-2). BL AGNs show on average blue optical-to-near-infrared colors,
softer X-ray colors and X-ray-to-optical colors typical of optically selected
AGNs. Conversely, narrow-line sources show redder optical colors, harder X-ray
flux ratio and span a wider range of X-ray-to-optical colors. On average the
SEDs of high-luminosity BL AGNs resemble the power-law typical of unobscured
AGNs. The SEDs of NOT BL AGNs are dominated by the galaxy emission in the
optical/near-infrared, and show a rise in the mid-infrared which suggests the
presence of an obscured active nucleus.Comment: 15 pages, A&A accepted, affiliations correcte
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