63 research outputs found
The space density of z>4 blazars
High redshift blazars are an important class of Active Galactic Nuclei (AGN)
that can provide an independent estimate of the supermassive black-hole mass
function in high redshift radio-loud AGN without the bias due to absorption
along the line-of-sight. Using the Cosmic Lens All Sky Survey (CLASS) we built
a complete radio flux-limited sample of high redshift (z>4) blazars suitable
for statistical studies. By combining dedicated optical observations and the
SDSS spectroscopic database, we obtained a sample of 26 blazar candidates with
a spectroscopic redshift above 4. On the basis of their radio spectrum we
distinguish between blazars and QSO with a Gigahertz Peaked Spectrum (GPS) like
spectrum. Out of the 18 confirmed blazars 14 constitute a completely
identified, flux-limited sample down to a magnitude of 21 (AB). Using this
complete sample we derive a space density of blazars with 4<z<5.5 of rho=0.13
(+0.05,-0.03) Gpc^-3. This is the first actual estimate of the blazar space
density in this range of redshift. This value is in good agreement with the
extrapolation of the luminosity function and cosmological evolution based on a
sample of flat-spectrum radio quasars selected at lower redshifts and it is
consistent with a cosmological evolution peaking at z2 similar to
radio-quiet QSO. We do not confirm, instead, the presence of a peak at z~4 in
the space density evolution, recently suggested using an X-ray selected sample
of blazars. It is possible that this extreme peak of the evolution is present
only among the most luminous blazars.Comment: 14 pages, accepted for publication on MNRAS
(https://doi.org/10.1093/mnras/sty3526
A near-infrared study of the multi-phase outflow in the type-2 quasar J1509+0434
Based on new near-infrared spectroscopic data from the instrument EMIR on the 10.4 m Gran Telescopio Canarias (GTC) we report the presence of an ionized and warm molecular outflow in the luminous type-2 quasar J150904.22+043441.8 (z = 0.1118). The ionized outflow is faster than its molecular counterpart, although the outflow sizes that we derive for them are consistent within the errors (1.34±0.18 kpc and 1.46±0.20 kpc respectively). We use these radii, the broad emission-line luminosities and in the case of the ionized outflow, the density calculated from the trans-auroral [OII] and [SII] lines, to derive mass outflow rates and kinetic coupling efficiencies. Whilst the ionized and warm molecular outflows represent a small fraction of the AGN power (≤0.033% and 0.0001% of Lbol respectively), the total molecular outflow, whose mass is estimated from an assumed warm-to-cold gas mass ratio of 6× 10−5, has a kinetic coupling efficiency of ∼1.7%Lbol. Despite the large uncertainty, this molecular outflow represents a significant fraction of Lbol and it could potentially have a significant impact on the host galaxy. In addition, the quasar spectrum reveals bright and patchy narrow Paα emission extending out to 4″ (8 kpc) South-East and North-West from the active nucleus.Includes Horizon 202
Testing the blast-wave AGN feedback scenario in MCG-03-58-007
We report the first Atacama large millimeter/submillimeter array observations
of MCG-03-58-007, a local (, this work) AGN
(), hosting a powerful X-ray ultra-fast
() outflow (UFO). The CO(1-0) line emission is observed across
kpc scales with a resolution of . About 78\% of the
CO(1-0) luminosity traces a galaxy-size rotating disk. However, after
subtracting the emission due to such rotating disk, we detect with a S/N=20 a
residual emission in the central kpc. Such residuals may trace a low
velocity () outflow. We compare the momentum rate
and kinetic power of such putative molecular outflow with that of the X-ray UFO
and find and
. This result is at odds with the
energy-conserving scenario suggested by the large momentum boosts measured in
some other molecular outflows. An alternative interpretation of the residual CO
emission would be a compact rotating structure, distinct from the main disk,
which would be a factor of more extended and massive than typical
circumnuclear disks revealed in Seyferts. However, in both scenarios, our
results rule out the hypothesis of a momentum-boosted molecular outflow in this
AGN, despite the presence of a powerful X-ray UFO. [Abridged]Comment: Accepted for publication in MNRAS. 13 pages, 11 figure
The hidden circumgalactic medium
The cycling of baryons in and out of galaxies is what ultimately drives
galaxy formation and evolution. The circumgalactic medium (CGM) represents the
interface between the interstellar medium and the cosmic web, hence its
properties are directly shaped by the baryon cycle. Although traditionally the
CGM is thought to consist of warm and hot gas, recent breakthroughs are
presenting a new scenario according to which an important fraction of its mass
may reside in the cold atomic and molecular phase. This would represent fuel
that is readily available for star formation, with crucial implications for
feeding and feedback processes in galaxies. However, such cold CGM, especially
in local galaxies where its projected size on sky is expected to be of several
arcminutes, cannot be imaged by ALMA due to interferometric spatial scale
filtering of large-scale structures. We show that the only way to probe the
multiphase CGM including its coldest component is through a large (e.g. 50-m)
single dish (sub-)mm telescope.Comment: Science white paper submitted to the Astro2020 Decadal Surve
High resolution modeling of [CII], [CI], [OIII] and CO line emission from the ISM and CGM of a star forming galaxy at z ~ 6.5
The circumgalactic medium (CGM) is a crucial component of galaxy evolution,
but thus far its physical properties are highly unconstrained. As of yet, no
cosmological simulation has reached convergence when it comes to constraining
the cold and dense gas fraction of the CGM. Such components are also
challenging to observe, and require sub-millimeter instruments with a high
sensitivity to extended, diffuse emission, like the proposed Atacama Large
Aperture Sub-millimetre telescope (AtLAST). We present a state-of-the-art
theoretical effort at modeling the [CII], [CI](1-0), [CI](2-1), CO(3-2), and
[OIII] line emissions of galaxies. We use the high-resolution cosmological
zoom-in simulation Ponos, representing a star forming galaxy system at z = 6.5
(), undergoing a major merger. We adopt different
modeling approaches based on the photoionisation code Cloudy. Our fiducial
model uses radiative transfer post-processing with RamsesRT and Krome to create
realistic FUV radiation fields, which we compare to sub-grid modeling
approaches adopted in the literature. We find significant differences in the
luminosity and in the contribution of different gas phases and galaxy
components between the different modeling approaches. [CII] is the least
model-dependant gas tracer, while [CI](1-0) and CO(3-2) are very
model-sensitive. In all models, we find a significant contribution to the
emission of [CII] (up to 10%) and [OIII] (up to 20%) from the CGM.
[CII] and [OIII] trace different regions of the CGM: [CII] arises from an
accreting filament and from tidal tails, while [OIII] traces a puffy halo
surrounding the main disc, probably linked to SN feedback. We discuss our
results in the context of current and future sub-mm observations with ALMA and
AtLAST.Comment: Submitted for publication to A&A. 25 pages, 17 figures. Abstract
summarised for arXiv submissio
The Atacama Large Aperture Submillimetre Telescope (AtLAST)
The coldest and densest structures of gas and dust in the Universe have
unique spectral signatures across the (sub-)millimetre bands (~GHz). The current generation of single dish facilities has given a
glimpse of the potential for discovery, while sub-mm interferometers have
presented a high resolution view into the finer details of known targets or in
small-area deep fields. However, significant advances in our understanding of
such cold and dense structures are now hampered by the limited sensitivity and
angular resolution of our sub-mm view of the Universe at larger scales.
In this context, we present the case for a new transformational astronomical
facility in the 2030s, the Atacama Large Aperture Submillimetre Telescope
(AtLAST). AtLAST is a concept for a 50-m-class single dish telescope, with a
high throughput provided by a 2~deg - diameter Field of View, located on a
high, dry site in the Atacama with good atmospheric transmission up to ~THz, and fully powered by renewable energy.
We envision AtLAST as a facility operated by an international partnership
with a suite of instruments to deliver the transformative science that cannot
be achieved with current or in-construction observatories. As an 50m-diameter
telescope with a full complement of advanced instrumentation, including highly
multiplexed high-resolution spectrometers, continuum cameras and integral field
units, AtLAST will have mapping speeds hundreds of times greater than current
or planned large aperture ( 12m) facilities. By reaching confusion limits
below L in the distant Universe, resolving low-mass protostellar cores at
the distance of the Galactic Centre, and directly mapping both the cold and the
hot (the Sunyaev-Zeldovich effect) circumgalactic medium of galaxies, AtLAST
will enable a fundamentally new understanding of the sub-mm Universe.Comment: 20 pages, 5 figures, to be submitted to SPIE Astronomical telescopes
& Instruments 2020, Ground-based and Airborne Telescopes VIII (conference
11445, abstract 290
Progress in the Design of the Atacama Large Aperture Submillimeter Telescope
The Atacama Large Aperture Submillimeter Telescope (AtLAST) aims to be the
premier next generation large diameter (50 meter) single dish observatory
capable of observations across the millimeter/submillimeter spectrum, from
30~GHz to 1~THz. AtLAST will be sited in Chile at approximately 5100 meters
above sea level, high in the Atacama Desert near Llano de Chajnantor. The novel
rocking-chair telescope design allows for a unprecedentedly wide field of view
(FoV) of 1-2 diameter, a large receiver cabin housing six major
instruments, and high structural stability during fast scanning operations (up
to per second in azimuth). Here we describe the current status
of, and expected outcomes for, the antenna design study, which will be
completed in 2024.Comment: Accepted for the URSI GASS 2023, Sapporo, Japan, 19-26 August 2023. 4
pages, 3 figure
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