762 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&
The overmassive black hole in NGC 1277: new constraints from molecular gas kinematics
We report the detection of CO(1-0) emission from NGC 1277, a lenticular
galaxy in the Perseus Cluster. NGC 1277 has previously been proposed to host an
overmassive black hole (BH) compared to the galaxy bulge luminosity (mass),
based on stellar-kinematic measurements. The CO(1-0) emission, observed with
the IRAM Plateau de Bure Interferometer (PdBI) using both, a more compact
(2.9-arcsec resolution) and a more extended (1-arcsec resolution)
configuration, is likely to originate from the dust lane encompassing the
galaxy nucleus at a distance of 0.9 arcsec (~320 pc). The double-horned CO(1-0)
profile found at 2.9-arcsec resolution traces of
molecular gas, likely orbiting in the dust lane at $\sim 550\ \mathrm{km\
s^{-1}}\sim 2\times 10^{10}\
M_\odot\sim
1.7\times 10^{10}\ M_\odotM/L_V=6.3\sim 5\times 10^{9}\ M_\odotM/L_V=10$. While the molecular gas reservoir
may be associated with a low level of star formation activity, the extended
2.6-mm continuum emission is likely to originate from a weak AGN, possibly
characterized by an inverted radio-to-millimetre spectral energy distribution.
Literature radio and X-ray data indicate that the BH in NGC 1277 is also
overmassive with respect to the Fundamental Plane of BH activity.Comment: 15 pages, 13 figures; accepted for publication in MNRAS on 20 January
2016; updated version including minor changes and note added in proo
Self-consistent spectra from radiative GRMHD simulations of accretion onto Sgr A*
We present the first spectral energy distributions produced self-consistently
by 2.5D general relativistic magneto-hydrodynamical (GRMHD) numerical
simulations, where radiative cooling is included in the dynamical calculation.
As a case study, we focus on the accretion flow around the supermassive black
hole in the Galactic Centre, Sagittarius A* (Sgr A*), which has the best
constrained physical parameters. We compare the simulated spectra to the
observational data of Sgr A* and explore the parameter space of our model to
determine the effect of changing the initial magnetic field configuration, ion
to electron temperature ratio T_i/T_e and the target accretion rate. We find
the best description of the data for a mass accretion rate of ~ 1e-9 Msun/yr,
and rapid spin (0.7 < a_* < 0.9). The submillimeter peak flux seems largely
independent of initial conditions, while the higher energies can be very
sensitive to the initial magnetic field configuration. Finally, we also discuss
flaring features observed in some simulations, that may be due to artifacts of
the 2D configuration.Comment: Submitted to MNRAS. 13 pages, 15 figure
Cold gas in group-dominant elliptical galaxies
We present IRAM 30m telescope observations of the CO(1-0) and (2-1) lines in
a sample of 11 group-dominant elliptical galaxies selected from the CLoGS
nearby groups sample. Our observations confirm the presence of molecular gas in
4 of the 11 galaxies at >4 sigma significance, and combining these with data
from the literature we find a detection rate of 43+-14%, comparable to the
detection rate for nearby radio galaxies, suggesting that group-dominant
ellipticals may be more likely to contain molecular gas than their non-central
counterparts. Those group-dominant galaxies which are detected typically
contain ~2x10^8 Msol of molecular gas, and although most have low star
formation rates (<1 Msol/yr) they have short depletion times, indicating that
the gas must be replenished on timescales ~100 Myr. Almost all of the galaxies
contain active nuclei, and we note while the data suggest that CO may be more
common in the most radio-loud galaxies, the mass of molecular gas required to
power the active nuclei through accretion is small compared to the masses
observed. We consider possible origin mechanisms for the gas, through cooling
of stellar ejecta within the galaxies, group-scale cooling flows, and gas-rich
mergers, and find probable examples of each type within our sample, confirming
that a variety of processes act to drive the build up of molecular gas in
group-dominant ellipticals.Comment: 9 pages, 5 postscript figures, 4 tables, accepted by A&A. Revised
throughout in response to referee's comments, including updates to Table 1
and Figure 4, and addition of Figure
Resolving the molecular gas around the lensed quasar RXJ0911.4+0551
We report on high angular resolution observations of the CO(7-6) line and
millimeter continuum in the host galaxy of the gravitationally lensed (z~2.8)
quasar RXJ0911.4+0551 using the Plateau de Bure Interferometer. Our CO
observations resolve the molecular disk of the source. Using a lens model based
on HST observations we fit source models to the observed visibilities. We
estimate a molecular disk radius of 10.2 kpc and an inclination of
696\deg, the continuum is more compact and is only marginally resolved by
our observations. The relatively low molecular gas mass, Msolar, and far infrared luminosity, Lsolar, of this quasar could be explained by its relatively low
dynamical mass, Msolar. It would be a
scaled-down version the QSOs usually found at high-z. The FIR and CO
luminosities lie on the correlation found for QSOs from low to high redshifts
and the gas-to-dust ratio () is similar to the one measured in the
z=6.4 QSO, SDSS J1148+5251. Differential magnification affects the
continuum-to-line luminosity ratio, the line profile and possibly the spectral
energy distribution.Comment: Accepted for publication in A&A, revised after language editin
Energetics of the molecular gas in the H_2 luminous radio galaxy 3C 326: Evidence for negative AGN feedback
We present a detailed analysis of the gas conditions in the H_2 luminous radio galaxy 3C 326 N at z ~ 0.1, which has a low star-formation
rate (SFR ~ 0.07 M_⊙ yr^(−1)) in spite of a gas surface density similar to those in starburst galaxies. Its star-formation efficiency
is likely a factor ~ 10−50 lower than those of ordinary star-forming galaxies. Combining new IRAM CO emission-line interferometry
with existing Spitzer mid-infrared spectroscopy, we find that the luminosity ratio of CO and pure rotational H_2 line emission is factors
10−100 lower than what is usually found. This suggests that most of the molecular gas is warm. The Na D absorption-line profile of
3C 326 N in the optical suggests an outflow with a terminal velocity of ~−1800 km s^(−1) and a mass outflow rate of 30−40 M_⊙ yr^(−1),
which cannot be explained by star formation. The mechanical power implied by the wind, of order 10^(43) erg s^(−1), is comparable to the
bolometric luminosity of the emission lines of ionized and molecular gas. To explain these observations, we propose a scenario where
a small fraction of the mechanical energy of the radio jet is deposited in the interstellar medium of 3C 326 N, which powers the outflow,
and the line emission through a mass, momentum and energy exchange between the different gas phases of the ISM. Dissipation times
are of order 10^(7−8) yrs, similar or greater than the typical jet lifetime. Small ratios of CO and PAH surface brightnesses in another 7 H_2
luminous radio galaxies suggest that a similar form of AGN feedback could be lowering star-formation efficiencies in these galaxies
in a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of
≥ 10^(11) M_⊙ could generally be regulated through a fundamentally similar form of “maintenance-phase” AGN feedback
Sequence features of HLA-DRB1 locus define putative basis for gene conversion and point mutations
<p>Abstract</p> <p>Background</p> <p>HLA/MHC class II molecules show high degree of polymorphism in the human population. The individual polymorphic motifs have been suggested to be propagated and mixed by transfer of genetic material (recombination, gene conversion) between alleles, but no clear molecular basis for this has been identified as yet. A large number of MHC class II allele sequences is publicly available and could be used to analyze the sequence features behind the recombination, revealing possible basis for such recombination processes both in HLA class II genes and other genes, which recombination acts upon.</p> <p>Results</p> <p>In this study we analyzed the vast dataset of human allelic variants (49 full coding sequences, 374 full exon 2 sequences) of the most polymorphic MHC class II locus, <it>HLA-DRB1</it>, and identified many previously unknown sequence features possibly contributing to the recombination. The CpG-dinucleotide content of exon 2 (containing the antigen-binding sites and subsequently a high degree of polymorphism) was much elevated as compared to the other exons despite similar overall G+C content. Furthermore, the CpG pattern was highly conserved. We also identified more complex, highly conserved sequence motifs in exon 2. Some of these can be identified as putative recombination motifs previously found in other genes, but most are previously unidentified.</p> <p>Conclusion</p> <p>The identified sequence features could putatively act in recombination allowing either less (CpG dinucleotides) or more specific DNA cleavage (complex sequences) or homologous recombination (complex sequences).</p
Mapping the cold molecular gas in a cooling flow cluster: Abell 1795
Cold molecular gas is found in several clusters of galaxies (Edge, 2001,
Salome' & Combes, 2003): single dish telescope observations in CO(1-0) and
CO(2-1) emission lines have revealed the existence of large amounts of cold gas
(up to ~10^11 Msol) in the central region of cooling flow clusters. We present
here interferometric observations performed with the IRAM Plateau de Bure
interferometer in Abell 1795. Comparison with IRAM 30m data shows the cold gas
detected is extended suggesting a cooling flow origin. The CO features
identified are very similar to the structures observed in Halpha and with the
star forming regions observed through UV continuum excess. A large fraction of
the cold gas is not centered on the central cD, but located near brightest
X-ray emitting regions along the North-West orientated radio lobe. The cold gas
kinematics is consistent with the optical nebulosity behaviour in the very
central region. It is not in rotation around the central cD : a velocity
gradient shows the cold gas might be cooled gas from the intra-cluster medium
being accreted by the central galaxy. The optical filaments, aligned with the
cD orbit, are intimately related to the radio jets and lobes. The material
fueling the star formation certainly comes from the deposited gas, cooling more
efficiently along the edge of the radio lobes. Even if some heating mechanisms
are present, these millimetric observations show that an effective cooling to
very low temperatures indeed occurs and is probably accelerated by the presence
of the radio source.Comment: 4 pages, 4 figures, accepted for publication in A&A (Letter
Precursors’ order effect on the properties of sulfurized Cu2ZnSnS4 thin films
A dc magnetron sputtering-based method to grow high-quality Cu2ZnSnS4 (CZTS) thin films,
to be used as an absorber layer in solar cells, is being developed. This method combines dc
sputtering of metallic precursors with sulfurization in S vapour and with post-growth KCN
treatment for removal of possible undesired Cu2−xS phases. In this work, we report the results
of a study of the effects of changing the precursors’ deposition order on the final CZTS films’
morphological and structural properties. The effect of KCN treatment on the optical properties
was also analysed through diffuse reflectance measurements. Morphological, compositional
and structural analyses of the various stages of the growth have been performed using stylus
profilometry, SEM/EDS analysis, XRD and Raman Spectroscopy. Diffuse reflectance studies
have been done in order to estimate the band gap energy of the CZTS films. We tested two
different deposition orders for the copper precursor, namely Mo/Zn/Cu/Sn and
Mo/Zn/Sn/Cu. The stylus profilometry analysis shows high average surface roughness in the
ranges 300–550 nm and 230–250 nm before and after KCN treatment, respectively. All XRD
spectra show preferential growth orientation along (1 1 2) at 28.45◦. Raman spectroscopy
shows main peaks at 338 cm−1 and 287 cm−1 which are attributed to Cu2ZnSnS4. These
measurements also confirm the effectiveness of KCN treatment in removing Cu2−xS phases.
From the analysis of the diffuse reflectance measurements the band gap energy for both
precursors’ sequences is estimated to be close to 1.43 eV. The KCN-treated films show a better
defined absorption edge; however, the band gap values are not significantly affected. Hot point
probe measurements confirmed that CZTS had p-type semiconductor behaviour and C–V
analysis was used to estimate the majority carrier density giving a value of 3.3 × 1018 cm−3
Growth and Raman scattering characterization of Cu2ZnSnS4 thin films
In the present work we report the results of the growth, morphological and structural characterization of
Cu2ZnSnS4 (CZTS) thin films prepared by sulfurization of DC magnetron sputtered Cu/Zn/Sn precursor
layers. The adjustment of the thicknesses and the properties of the precursors were used to control the final
composition of the films. Its properties were studied by SEM/EDS, XRD and Raman scattering. The influence
of the sulfurization temperature on the morphology, composition and structure of the films has been
studied. With the presented method we have been able to prepare CZTS thin films with the kesterite
structure
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