68 research outputs found
Jet-induced star formation in 3C 285 and Minkowski Object
How efficiently star formation proceeds in galaxies is still an open
question. Recent studies suggest that AGN can regulate the gas accretion and
thus slow down star formation (negative feedback). However, evidence of AGN
positive feedback has also been observed in a few radio galaxies (eg. Centaurus
A).
Here we present CO observations of 3C 285 and Minkowski Object (MO), which
are examples of jet-induced star formation. A spot (named 09.6) aligned with
the 3C 285 radio jet, at a projected distance of ~70 kpc from the galaxy
centre, shows star formation, detected in optical emission. MO is located along
the jet of NGC 541 and also shows star formation. To know the distribution of
molecular gas along the jets is a way to study the physical processes at play
in the AGN interaction with the intergalactic medium.
We observed CO lines in 3C 285, NGC 541, 09.6 and MO with the IRAM-30m
telescope. In the central galaxies, the spectra present a double-horn profile,
typical of a rotation pattern, from which we are able to estimate the molecular
gas density profile of the galaxy. The molecular gas appears to be in a compact
reservoir. In addition, no kinematic signature of a molecular outflow is
detected by the 30m-telescope.
Interestingly, 09.6 and MO are not detected in CO. The cold gas mass upper
limits are consistent with a star formation induced by the compression of dense
ambient material by the jet. The depletion time scales are of the order of and
even smaller than what is found in 3C 285, NGC 541 and local spiral galaxies
(10^9 yr). The molecular gas surface density in 09.6 follows a
Schmidt-Kennicutt law if the emitting region is very compact, while MO is found
to have a much higher SFE (very short depletion time). Higher sensitivity and
spatial resolution are necessary to detect CO in the spots of star formation,
and map the emission in these jet-induced star forming regions.Comment: 9 pages, 10 figures, submitted to A&
Structure formation in a colliding flow: The Herschel view of the Draco nebula
The Draco nebula is a high Galactic latitude interstellar cloud likely to
have been formed by the collision of a Galactic halo cloud entering the disk of
the Milky Way. Such conditions are ideal to study the formation of cold and
dense gas in colliding flows of warm gas. We present Herschel-SPIRE
observations that reveal the fragmented structure of the interface between the
infalling cloud and the Galactic layer. This front is characterized by a
Rayleigh-Taylor instability structure. From the determination of the typical
length of the periodic structure (2.2 pc) we estimated the gas kinematic
viscosity and the turbulence dissipation scale (0.1 pc) that is compatible with
that expected if ambipolar diffusion is the main mechanism of energy
dissipation in the WNM. The small-scale structures of the nebula are typical of
that seen in some molecular clouds. The gas density has a log-normal
distribution with an average value of cm. The size of the
structures is 0.1-0.2 pc but this estimate is limited by the resolution of the
observations. The mass ranges from 0.2 to 20 M and the distribution
of the more massive clumps follows a power law . We
identify a mass-size relation with the same exponent as that found in GMCs
() but only 15% of the mass of the cloud is in gravitationally
bound structures. We conclude that the increase of pressure in the collision is
strong enough to trigger the WNM-CNM transition caused by the interplay between
turbulence and thermal instability as self-gravity is not dominating the
dynamics.Comment: 16 pages, A&A, in pres
Evidence of galaxy interaction in the Narrow-line Seyfert 1 galaxy IRAS17020+4544 seen by NOEMA
The narrow-line Seyfert 1 galaxy IRAS17020+4544 is one of the few sources
where both an X-ray ultra-fast outflow and a molecular outflow were observed to
be consistent with energy conservation. However, IRAS17020+4544 is less massive
and has a much more modest active galactic nucleus (AGN) luminosity than the
other examples. Using recent CO(1-0) observations with the NOrthern Extended
Millimeter Array (NOEMA), we characterised the molecular gas content of the
host galaxy for the first time. We found that the molecular gas is distributed
into an apparent central disc of 1.1x10^9 Msun, and a northern extension
located up to 8 kpc from the centre with a molecular gas mass M_H2~10^8 Msun.
The molecular gas mass and the CO dynamics in the northern extension reveal
that IRAS 17020+4544 is not a standard spiral galaxy, instead it is interacting
with a dwarf object corresponding to the northern extension. This interaction
possibly triggers the high accretion rate onto the super massive black hole.
Within the main galaxy, which hosts the AGN, a simple analytical model predicts
that the molecular gas may lie in a ring, with less molecular gas in the
nuclear region. Such distribution may be the result of the AGN activity which
removes or photodissociates the molecular gas in the nuclear region (AGN
feedback). Finally, we have detected a molecular outflow of mass
M_H2=(0.7-1.2)x10^7 Msun in projection at the location of the northern galaxy,
with a similar velocity to that of the massive outflow reported in previous
millimeter data obtained by the Large Millimeter Telescope.Comment: Published in MNRAS, Volume 501, Issue 1, Pages 219-22
Formation and Evolution of Supermassive Black Holes
The correlation between the mass of supermassive black holes in galaxy nuclei
and the mass of the galaxy spheroids or bulges (or more precisely their central
velocity dispersion), suggests a common formation scenario for galaxies and
their central black holes. The growth of bulges and black holes can commonly
proceed through external gas accretion or hierarchical mergers, and are both
related to starbursts. Internal dynamical processes control and regulate the
rate of mass accretion. Self-regulation and feedback are the key of the
correlation. It is possible that the growth of one component, either BH or
bulge, takes over, breaking the correlation, as in Narrow Line Seyfert 1
objects. The formation of supermassive black holes can begin early in the
universe, from the collapse of Population III, and then through gas accretion.
The active black holes can then play a significant role in the re-ionization of
the universe. The nuclear activity is now frequently invoked as a feedback to
star formation in galaxies, and even more spectacularly in cooling flows. The
growth of SMBH is certainly there self-regulated. SMBHs perturb their local
environment, and the mergers of binary SMBHs help to heat and destroy central
stellar cusps. The interpretation of the X-ray background yields important
constraints on the history of AGN activity and obscuration, and the census of
AGN at low and at high redshifts reveals the downsizing effect, already
observed for star formation. History appears quite different for bright QSO and
low-luminosity AGN: the first grow rapidly at high z, and their number density
decreases then sharply, while the density of low-luminosity objects peaks more
recently, and then decreases smoothly.Comment: 31 pages, 13 figures, review paper for Astrophysics Update
A constant NH(1-0)-to-HCN(1-0) ratio on kiloparsec scales
Nitrogen hydrides such as NH and NH are widely used by Galactic
observers to trace the cold dense regions of the interstellar medium. In
external galaxies, because of limited sensitivity, HCN has become the most
common tracer of dense gas over large parts of galaxies. We provide the first
systematic measurements of NH(1-0) across different environments of an
external spiral galaxy, NGC6946. We find a strong correlation ()
between the HCN(1-0) and NH(1-0) intensities across the inner
of the galaxy, at kiloparsec scales. This correlation is
equally strong between the ratios NH(1-0)/CO(1-0) and HCN(1-0)/CO(1-0),
tracers of dense gas fractions (). We measure an average
intensity ratio of NH(1-0)/HCN(1-0) over our set of five
IRAM-30m pointings. These trends are further supported by existing measurements
for Galactic and extragalactic sources. This narrow distribution in the average
ratio suggests that the observed systematic trends found in kiloparsec-scale
extragalactic studies of and the efficiency of dense gas
(SFE) would not change if we employed NH(1-0) as a
more direct tracer of dense gas. At kiloparsec scales our results indicate that
the HCN(1-0) emission can be used to predict the expected NH(1-0) over
those regions. Our results suggest that, even if HCN(1-0) and NH(1-0)
trace different density regimes within molecular clouds, subcloud differences
average out at kiloparsec scales, yielding the two tracers proportional to each
other.Comment: Accepted for publication in Astronomy & Astrophysic
Secondary crystalline phases identification in Cu2ZnSnSe4 thin films: contributions from Raman scattering and photoluminescence
In this work, we present the Raman peak
positions of the quaternary pure selenide compound
Cu2ZnSnSe4 (CZTSe) and related secondary phases that
were grown and studied under the same conditions. A vast
discussion about the position of the X-ray diffraction
(XRD) reflections of these compounds is presented. It is
known that by using XRD only, CZTSe can be identified
but nothing can be said about the presence of some secondary
phases. Thin films of CZTSe, Cu2SnSe3, ZnSe,
SnSe, SnSe2, MoSe2 and a-Se were grown, which allowed
their investigation by Raman spectroscopy (RS). Here we
present all the Raman spectra of these phases and discuss
the similarities with the spectra of CZTSe. The effective
analysis depth for the common back-scattering geometry
commonly used in RS measurements, as well as the laser penetration depth for photoluminescence (PL) were estimated
for different wavelength values. The observed
asymmetric PL band on a CZTSe film is compatible with
the presence of CZTSe single-phase and is discussed in the
scope of the fluctuating potentials’ model. The estimated
bandgap energy is close to the values obtained from
absorption measurements. In general, the phase identification
of CZTSe benefits from the contributions of RS and
PL along with the XRD discussion.info:eu-repo/semantics/publishedVersio
Decadal soil carbon accumulation across Tibetan permafrost regions
Acknowledgements We thank the members of Peking University Sampling Teams (2001–2004) and IBCAS Sampling Teams (2013–2014) for assistance in field data collection. We also thank the Forestry Bureau of Qinghai Province and the Forestry Bureau of Tibet Autonomous Region for their permission and assistance during the sampling process. This study was financially supported by the National Natural Science Foundation of China (31670482 and 31322011), National Basic Research Program of China on Global Change (2014CB954001 and 2015CB954201), Chinese Academy of Sciences-Peking University Pioneer Cooperation Team, and the Thousand Young Talents Program.Peer reviewedPostprintPostprin
SKA Science Data Challenge 2: analysis and results
The Square Kilometre Array Observatory (SKAO) will explore the radio sky to
new depths in order to conduct transformational science. SKAO data products
made available to astronomers will be correspondingly large and complex,
requiring the application of advanced analysis techniques to extract key
science findings. To this end, SKAO is conducting a series of Science Data
Challenges, each designed to familiarise the scientific community with SKAO
data and to drive the development of new analysis techniques. We present the
results from Science Data Challenge 2 (SDC2), which invited participants to
find and characterise 233245 neutral hydrogen (Hi) sources in a simulated data
product representing a 2000~h SKA MID spectral line observation from redshifts
0.25 to 0.5. Through the generous support of eight international supercomputing
facilities, participants were able to undertake the Challenge using dedicated
computational resources. Alongside the main challenge, `reproducibility awards'
were made in recognition of those pipelines which demonstrated Open Science
best practice. The Challenge saw over 100 participants develop a range of new
and existing techniques, with results that highlight the strengths of
multidisciplinary and collaborative effort. The winning strategy -- which
combined predictions from two independent machine learning techniques to yield
a 20 percent improvement in overall performance -- underscores one of the main
Challenge outcomes: that of method complementarity. It is likely that the
combination of methods in a so-called ensemble approach will be key to
exploiting very large astronomical datasets.Comment: Under review by MNRAS; 28 pages, 16 figure
Identifying water stress-response mechanisms in citrus by in silico transcriptome analysis
Adipo/cytokines in atherosclerotic secretomes: increased visfatin levels in unstable carotid plaque
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