99 research outputs found
Application of the MST clustering to the high energy gamma-ray sky. I - New possible detection of high-energy gamma-ray emission associated with BL Lac objects
In this paper we show an application of the Minimum Spanning Tree (MST)
clustering method to the high-energy gamma-ray sky observed at energies higher
than 10 GeV in 6.3 years by the Fermi-Large Area Telescope. We report the
detection of 19 new high-energy gamma-ray clusters with good selection
parameters whose centroid coordinates were found matching the positions of
known BL Lac objects in the 5th Edition of the Roma-BZCAT catalogue. A brief
summary of the properties of these sources is presented.Comment: 11 pages, 7 figures. Accepted for publication in Astrophysics & Space
Scienc
An ALMA view of 11 dusty star-forming galaxies at the peak of cosmic star formation history
We present the ALMA view of 11 main-sequence dusty star-forming galaxies (DSFGs) (sub-)millimetre selected in the Great Observatories Origins Survey South (GOODS-S) field and spectroscopically confirmed to be at the peak of cosmic star formation history (z ∼2). Our study combines the analysis of galaxy spectral energy distribution with ALMA continuum and CO spectral emission by using ALMA Science Archive products at the highest spatial resolution currently available for our sample (Δθ 1 arcsec). We include galaxy multiband images and photometry (in the optical, radio, and X-rays) to investigate the interlink between dusty, gaseous, and stellar components and the eventual presence of AGN. We use multiband sizes and morphologies to gain an insight on the processes that lead galaxy evolution, e.g. gas condensation, star formation, AGN feedback. The 11 DSFGs are very compact in the (sub-)millimetre (median rALMA = 1.15 kpc), while the optical emission extends to larger radii (median rH/rALMA = 2.05). CO lines reveal the presence of a rotating disc of molecular gas, but we cannot exclude the presence of interactions and/or molecular outflows. Images at higher (spectral and spatial) resolution are needed to disentangle from the possible scenarios. Most of the galaxies are caught in the compaction phase, when gas cools and falls into galaxy centre, fuelling the dusty burst of star formation and the growing nucleus. We expect these DSFGs to be the high-z star-forming counterparts of massive quiescent galaxies. Some features of CO emission in three galaxies are suggestive of forthcoming/ongoing AGN feedback, which is thought to trigger the morphological transition from star-forming discs to early-type galaxies
The Way of Water: ALMA resolves H2O emission lines in a strongly lensed dusty star-forming galaxy at z 3.1
We report ALMA high-resolution observations of water emission lines
), ,
, in the strongly lensed galaxy
HATLASJ113526.2-01460 at redshift z 3.1. From the lensing-reconstructed
maps of water emission and line profiles, we infer the general physical
properties of the ISM in the molecular clouds where the lines arise. We find
that the water vapor lines , are mainly excited by FIR pumping from dust radiation in a
warm and dense environment, with dust temperatures ranging from 70 K to K, as suggested by the line ratios. The
line instead, is excited by a complex interplay between FIR pumping and
collisional excitation in the dense core of the star-forming region. This
scenario is also supported by the detection of the medium-level excitation of
CO resulting in the line emission CO (J=8-7). Thanks to the unprecedented high
resolution offered by the combination of ALMA capabilities and gravitational
lensing, we discern the different phases of the ISM and locate the hot
molecular clouds into a physical scale of 500 pc. We discuss the
possibility of J1135 hosting an AGN in its accretion phase. Finally, we
determine the relation between the water emission lines and the total IR
luminosity of J1135, as well as the SFR as a function of water emission
intensities, comparing the outcomes to local and high- galactic samples from
the literature.Comment: 23 pages, 13 figures, to be published in Astrophysical Journa
A deep 1.4 GHz survey of the J1030 equatorial field: a new window on radio source populations across cosmic time
We present deep L-Band observations of the equatorial field centered on the
z=6.3 SDSS QSO, reaching a 1 sigma sensitivity of ~2.5 uJy at the center of the
field. We extracted a catalog of 1489 radio sources down to a flux density of
~12.5 uJy (5 sigma) over a field of view of ~ 30' diameter. We derived the
source counts accounting for catalog reliability and completeness, and compared
them with others available in the literature. Our source counts are among the
deepest available so far, and, overall, are consistent with recent counts'
determinations and models. We detected for the first time in the radio band the
SDSS J1030+0524 QSO (26 +/- 5 uJy). We derived its optical radio loudness R_O =
0.62 +/- 0.12, which makes it the most radio quiet AGN at z >~ 6 discovered so
far and detected at radio wavelengths. We unveiled extended diffuse radio
emission associated with the lobes of a bright FRII radio galaxy located close
to the center of the J1030 field, which is likely to become the future BCG of a
protocluster at z=1.7. The lobes' complex morphology, coupled with the presence
of X-ray diffuse emission detected around the FRII galaxy lobes, may point
toward an interaction between the radio jets and the external medium. We also
investigated the relation between radio and X-ray luminosity for a sample of
243 X-ray-selected objects obtained from 500 ks Chandra observations of the
same field, and spanning a wide redshift range (0 ~< z ~< 3). Focused on
sources with a spectroscopic redshift and classification, we found that sources
hosted by ETG and AGN follow Log(L_R)/Log(L_X) linear correlations with slopes
of ~0.6 and ~0.8, respectively. This is interpreted as a likely signature of
different efficiency in the accretion process. Finally, we found that most of
these sources (>~87%) show a radio-to-X-ray radio loudness R_X < -3.5,
classifying these objects as radio quiet.Comment: 18 pages, 15 figures, 5 table. Accepted for publication in A&
Supermassive Black Holes at High Redshift are Expected to be Obscured by their Massive Host Galaxies' Inter Stellar Medium
We combine results from deep ALMA observations of massive
() galaxies at different redshifts to show that the
column density of their inter stellar medium (ISM) rapidly increases towards
early cosmic epochs. Our analysis includes objects from the ASPECS and ALPINE
large programs, as well as individual observations of QSO hosts. When
accounting for non-detections and correcting for selection effects, we find
that the median surface density of the ISM of the massive galaxy population
evolves as . This means that the ISM column density towards
the nucleus of a galaxy is typically times larger than locally,
and it may reach values as high as Compton-thick at . Remarkably,
the median ISM column density is of the same order of what is measured from
X-ray observations of large AGN samples already at .
We develop a simple analytic model for the spatial distribution of ISM clouds
within galaxies, and estimate the total covering factor towards active nuclei
when obscuration by ISM clouds on the host scale is added to that of pc-scale
circumnuclear material (the so-called 'torus'). The model includes clouds with
a distribution of sizes, masses, and surface densities, and also allows for an
evolution of the characteristic cloud surface density with redshift,
. We show that, for , such a model
successfully reproduces the increase of the obscured AGN fraction with redshift
that is commonly observed in deep X-ray surveys, both when different absorption
thresholds and AGN luminosities are considered.
Our results suggest that 80-90\% of supermassive black holes in the early
Universe () are hidden to our view, primarily by the ISM in their hosts.
[abridged]Comment: 22 pages, 15 figures, accepted for publication in A&
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
An ALMA view of 11 dusty star-forming galaxies at the peak of cosmic star formation history
We present the ALMA view of 11 main-sequence dusty star-forming galaxies (DSFGs) (sub-)millimetre selected in the Great Observatories Origins Survey South (GOODS-S) field and spectroscopically confirmed to be at the peak of cosmic star formation history (z ~ 2). Our study combines the analysis of galaxy spectral energy distribution with ALMA continuum and CO spectral emission by using ALMA Science Archive products at the highest spatial resolution currently available for our sample (Δθ ≲ 1 arcsec). We include galaxy multiband images and photometry (in the optical, radio, and X-rays) to investigate the interlink between dusty, gaseous, and stellar components and the eventual presence of AGN. We use multiband sizes and morphologies to gain an insight on the processes that lead galaxy evolution, e.g. gas condensation, star formation, AGN feedback. The 11 DSFGs are very compact in the (sub-)millimetre (median rALMA = 1.15 kpc), while the optical emission extends to larger radii (median rH/rALMA = 2.05). CO lines reveal the presence of a rotating disc of molecular gas, but we cannot exclude the presence of interactions and/or molecular outflows. Images at higher (spectral and spatial) resolution are needed to disentangle from the possible scenarios. Most of the galaxies are caught in the compaction phase, when gas cools and falls into galaxy centre, fuelling the dusty burst of star formation and the growing nucleus. We expect these DSFGs to be the high-z star-forming counterparts of massive quiescent galaxies. Some features of CO emission in three galaxies are suggestive of forthcoming/ongoing AGN feedback, which is thought to trigger the morphological transition from star-forming discs to early-type galaxies
- …