234 research outputs found
The central parsecs of active galactic nuclei: challenges to the torus
Type 2 AGN are by definition nuclei in which the broad-line region and
continuum light are hidden at optical/UV wavelengths by dust. Via accurate
registration of infrared (IR) Very Large Telescope adaptive optics images with
optical \textit{Hubble Space Telescope} images we unambiguously identify the
precise location of the nucleus of a sample of nearby, type 2 AGN. Dust
extinction maps of the central few kpc of these galaxies are constructed from
optical-IR colour images, which allow tracing the dust morphology at scales of
few pc. In almost all cases, the IR nucleus is shifted by several tens of pc
from the optical peak and its location is behind a dust filament, prompting to
this being a major, if not the only, cause of the nucleus obscuration. These
nuclear dust lanes have extinctions mag, sufficient to at least
hide the low-luminosity AGN class, and in some cases are observed to connect
with kpc-scale dust structures, suggesting that these are the nuclear fueling
channels. A precise location of the ionised gas H and
[\textsc{Si\,vii}] 2.48 m coronal emission lines relative to those of the
IR nucleus and dust is determined. The H peak emission is often shifted
from the nucleus location and its sometimes conical morphology appears not to
be caused by a nuclear --torus-- collimation but to be strictly defined by the
morphology of the nuclear dust lanes. Conversely, [\textsc{Si\,vii}] 2.48
m emission, less subjected to dust extinction, reflects the truly, rather
isotropic, distribution of the ionised gas. All together, the precise location
of the dust, ionised gas and nucleus is found compelling enough to cast doubts
on the universality of the pc-scale torus and supports its vanishing in
low-luminosity AGN. Finally, we provide the most accurate position of the NGC
1068 nucleus, located at the South vertex of cloud B.Comment: 23 pages, 10 figures, accepted for publication in MNRA
Starbursts and black hole masses in X-shaped radio galaxies: Signatures of a merger event?
We present new spectroscopic identifications of 12 X-shaped radio galaxies
and use the spectral data to derive starburst histories and masses of the
nuclear supermassive black holes in these galaxies. The observations were done
with the 2.1-m telescope of the Observatorio Astron\'omico Nacional at San
Pedro M\'artir, M\'exico. The new spectroscopic results extend the sample of
X-shaped radio galaxies studied with optical spectroscopy. We show that the
combined sample of the X-shaped radio galaxies has statistically higher
black-hole masses and older episodes of star formation than a control sample of
canonical double-lobed radio sources with similar redshifts and luminosities.
The data reveal enhanced star-formation activity in the X-shaped sample on the
timescales expected in galactic mergers. We discuss the results obtained in the
framework of the merger scenario.Comment: 9 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
The environment of AGN dwarf galaxies at z0.7 from the VIPERS survey
Dwarf galaxies are ideal laboratories to study the relationship between the
environment and AGN activity. However, the type of environments in which dwarf
galaxies hosting AGN reside is still unclear and limited to low-redshift
studies (z < 0.5). We use the VIMOS Public Extragalactic Redshift Survey
(VIPERS) to investigate, for the first time, their environments at 0.5 < z <
0.9. We select a sample of 12,942 low-mass
() galaxies and use the emission-line
diagnostic diagram to identify AGN. We characterise their local environments as
the galaxy density contrast, , derived from the fifth nearest neighbour
method. Our work demonstrates that AGN and non-AGN dwarf galaxies reside in
similar environments at intermediate redshift suggesting that the environment
is not an important factor in triggering AGN activity already since z = 0.9.
Dwarf galaxies show a strong preference for low-density environments,
independently of whether they host an AGN or not. Their properties do not
change when moving to denser environments, suggesting that dwarf galaxies are
not gas-enriched due to environmental effects. Moreover, AGN presence does not
alter host properties supporting the scenario that AGN feedback does not impact
the star formation of the host. Lastly, AGN are found to host over-massive
black holes. This is the first study of dwarf galaxies hosting AGN at z > 0.5.
The next generation of deep surveys will reveal whether or not such lack of
environmental trends is common also for faint higher-redshift dwarf galaxy
populations.Comment: Accepted for publication in MNRAS, 19 pages, 14 figure
Radio Emission From a 10.3 Black Hole in UHZ1
The recent discovery of a 4 10 M black hole (BH) in
UHZ1 at 10.3, just 450 Myr after the big bang, suggests that the seeds of
the first quasars may have been direct-collapse black holes (DCBHs) from the
collapse of supermassive primordial stars at 20. This object was
identified in James Webb Space Telescope (JWST) NIRcam and Chandra X-ray data,
but recent studies suggest that radio emission from such a BH should also be
visible to the Square Kilometer Array (SKA) and the next-generation Very Large
Array (ngVLA). Here, we present estimates of radio flux for UHZ1 from 0.1 - 10
GHz, and find that SKA and ngVLA could detect it with integration times of 10 -
100 hr and just 1 - 10 hr, respectively. It may be possible to see this object
with VLA now with longer integration times. The detection of radio emission
from UHZ1 would be a first test of exciting new synergies between near infrared
(NIR) and radio observatories that could open the era of 5 - 15 quasar
astronomy in the coming decade.Comment: 5 pages, 2 figures, submitted to Ap
Radio Emission from the First Quasars at 6-15
Nearly 300 quasars have now been found at 6, including nine at 7.
They are thought to form from the collapse of supermassive primordial stars to
10 - 10 M black holes at 20 - 25, which then rapidly
grow in the low-shear environments of rare, massive halos fed by strong
accretion flows. Sensitive new radio telescopes such as the Next-Generation
Very Large Array (ngVLA) and the Square Kilometer Array (SKA) could probe the
evolution of these objects at much earlier times. Here, we estimate radio flux
from the first quasars at 6 - 15 at 0.5 - 12.5 GHz. We find that SKA
and ngVLA could detect a quasar like ULAS J1120+0641, a 1.35 10
M black hole at 7.1, at much earlier stages of evolution, 14 - 15, with 100 hr integration times in targeted searches. The advent
of these new observatories, together with the James Webb Space Telescope
(JWST), Euclid, and the Roman Space Telescope (RST), will inaugurate the era of
15 quasar astronomy in the coming decade.Comment: 5 pages, 3 figures, accepted by MNRAS Letter
Cosmic evolution of supermassive black holes: A view into the next two decades
Astro2020 Science White Paper: et al.The discoveries made over the past 20 years by Chandra and XMM-Newton surveys in conjunction with multiwavelength imaging and spectroscopic data available in the same fields have significantly changed the view of the supermassive black hole (SMBH) and galaxy connection. These discoveries have opened up several exciting questions that are beyond the capabilities of current X-ray telescopes and will need to be addressed by observatories in the next two decades. As new observatories peer into the early Universe, we will begin to understand the physics and demographics of SMBH infancy (at z > 6) and investigate the influence of their accretion on the formation of the first galaxies (§ 2.1). We will also be able to understand the accretion and evolution over the cosmic history (at z ∼1–6) of the full population of black holes in galaxies, including low accretion rate, heavily obscured AGNs at luminosities beyond the reach of current X-ray surveys (§2.2 and §2.3), enabling us to resolve the connection between SMBH growth and their environment
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