15 research outputs found
NMA Survey of CO and HCN Emission from Nearby Active Galaxies
High resolution (a few arcseconds) observations of CO(1-0) and HCN(1-0)
emission from nearby Seyfert galaxies have been conducted with the Nobeyama
Millimeter Array. Based on the observed CO distributions and kinematics,we
suggest that a small scale (a few 100 pc - a few kpc) distortion of the
underlying potential seems to be necessary for Seyfert activity, although it is
not a sufficient condition. We also find that the Toomre's Q values in the
centers of Seyfert galaxies tend to be larger than unity, indicating the
circumnuclear molecular gas disks around Seyfert nuclei would be
gravitationally stable. The HCN/CO integrated intensity ratios (R_HCN/CO) range
over an order of magnitude, from 0.086 to 0.6. The Seyfert galaxies with high
R_HCN/CO may have an extended (r ~ 100 pc scale) envelope of obscuring
material. The presence of kpc scale jet/ outflow might be also related to the
extremely high R_HCN/CO.Comment: To appear in the Proceedings of the 3rd Cologne-Zermatt Symposium,
``The Physics and Chemistry of the Interstellar Medium'
Formation of a Massive Black Hole at the Center of the Superbubble in M82
We performed 12CO(1-0), 13CO(1-0), and HCN(1-0) interferometric observations
of the central region (about 450 pc in radius) of M82 with the Nobeyama
Millimeter Array, and have successfully imaged a molecular superbubble and
spurs. The center of the superbubble is clearly shifted from the nucleus by 140
pc. This position is close to that of the massive black hole (BH) of >460 Mo
and the 2.2 micron secondary peak (a luminous supergiant dominated cluster),
which strongly suggests that these objects may be related to the formation of
the superbubble. Consideration of star formation in the cluster based on the
infrared data indicates that (1) energy release from supernovae can account for
the kinetic energy of the superbubble, (2) the total mass of stellar-mass BHs
available for building-up the massive BH may be much higher than 460 Mo, and
(3) it is possible to form the middle-mass BH of 100-1000 Mo within the
timescale of the superbubble. We suggest that the massive BH was produced and
is growing in the intense starburst region.Comment: 9 pages, 3 figures, to appear in ApJ Lette
Mid-infrared spectroscopy of infrared-luminous galaxies at z~0.5-3
We present results on low-resolution mid-infrared (MIR) spectra of 70
infrared-luminous galaxies obtained with the Infrared Spectrograph (IRS)
onboard Spitzer. We selected sources from the European Large Area Infrared
Survey (ELAIS) with S15 > 0.8 mJy and photometric or spectroscopic z > 1. About
half of the sample are QSOs in the optical, while the remaining sources are
galaxies, comprising both obscured AGN and starbursts. We classify the spectra
using well-known infrared diagnostics, as well as a new one that we propose,
into three types of source: those dominated by an unobscured AGN (QSOs),
obscured AGN, and starburst-dominated sources. Starbursts concentrate at z ~
0.6-1.0 favored by the shift of the 7.7-micron PAH band into the selection 15
micron band, while AGN spread over the 0.5 < z < 3.1 range. Star formation
rates (SFR) are estimated for individual sources from the luminosity of the PAH
features. An estimate of the average PAH luminosity in QSOs and obscured AGN is
obtained from the composite spectrum of all sources with reliable redshifts.
The estimated mean SFR in the QSOs is 50-100 Mo yr^-1, but the implied FIR
luminosity is 3-10 times lower than that obtained from stacking analysis of the
FIR photometry, suggesting destruction of the PAH carriers by energetic photons
from the AGN. The SFR estimated in obscured AGN is 2-3 times higher than in
QSOs of similar MIR luminosity. This discrepancy might not be due to luminosity
effects or selection bias alone, but could instead indicate a connection
between obscuration and star formation. However, the observed correlation
between silicate absorption and the slope of the near- to mid-infrared spectrum
is compatible with the obscuration of the AGN emission in these sources being
produced in a dust torus.Comment: 32 pages, 24 figures, 15 tables, accepted for publication in MNRA
Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71. I. Simultaneous broadband observations during November 2003
Some intra-day variable, compact extra-galactic radio sources show brightness
temperatures severely exceeding 10^{12} K, the limit set by catastrophic
inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation.
The violation of the IC limit, possible under non-stationary conditions, would
lead to IC avalanches in the soft-gamma-ray energy band during transient
periods. For the first time, broadband signatures of possible IC catastrophes
were searched for in S5 0716+71. A multifrequency observing campaign targetting
S5 0716+71 was carried out in November 2003 under the framework of the European
Network for the Investigation of Galactic nuclei through Multifrequency
Analysis (ENIGMA) together with a campaign by the Whole Earth Blazar Telescope
(WEBT), involving a pointing by the soft-gamma-ray satellite INTEGRAL, optical,
near-infrared, sub-millimeter, millimeter, radio, and Very Long Baseline Array
(VLBA) monitoring. S5 0716+71 was very bright at radio frequencies and in a
rather faint optical state during the INTEGRAL pointing; significant inter-day
and low intra-day variability was recorded in the radio regime, while typical
fast variability features were observed in the optical band. No correlation was
found between the radio and optical emission. The source was not detected by
INTEGRAL, neither by the X-ray monitor JEM-X nor by the gamma-ray imager ISGRI,
but upper limits to the source emission in the 3-200 keV energy band were
estimated. A brightness temperature Tb>2.1x10^{14} K was inferred from the
radio variability, but no corresponding signatures of IC avalanches were
recorded at higher energies. The absence of IC-catastrophe signatures provides
either a lower limit delta>8 to the Doppler factor affecting the radio emission
or strong constraints for modelling of the Compton catastrophes in S5 0716+71.Comment: 15 pages, 3 EPS figures, 3 tables, to appear in A&
Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71
Aims. The BL Lac object S5 0716+71 was observed in a global multi-frequency campaign
to search for rapid and correlated flux density variability and signatures of an
inverse-Compton (IC) catastrophe during the states of extreme apparent brightness
temperatures.
Methods. The observing campaign involved simultaneous ground-based monitoring at radio to
IR/optical wavelengths and was centered around a 500-ks pointing with the INTEGRAL
satellite (November 10-17, 2003). Here, we present the combined analysis and results
of the radio observations, covering the cm- to sub-mm bands. This facilitates a detailed
study of the variability characteristics of an inter- to intra-day variable IDV source
from cm- to the short mm-bands. We further aim to constrain the variability brightness
temperatures (TB) and Doppler factors (δ) comparing the radio-bands with the hard
X-ray emission, as seen by INTEGRAL at 3-200 keV.
Results. 0716+714 was in an exceptionally high state and different (slower) phase of short-term variability, when compared to the past, most likely due to a pronounced outburst shortly before the campaign.
The flux density variability in the cm- to mm-bands is dominated by a ~4 day time
scale amplitude increase of up to ~35%, systematically more pronounced towards
shorter wavelengths. The cross-correlation analysis reveals systematic time-lags with the
higher frequencies varying earlier, similar to canonical variability on longer time-scales.
The increase of the variability amplitudes with frequency contradicts expectations from
standard interstellar scintillation (ISS) and suggests a source-intrinsic origin for the
observed inter-day variability. We find an inverted synchrotron spectrum peaking near 90 GHz,
with the peak flux increasing during the first 4 days. The lower limits to TB derived
from the inter-day variations exceed the 1012 K IC-limit by up to 3-4 orders of magnitude.
Assuming relativistic boosting, our different estimates of δ yield robust and self-consistent lower limits of – in good agreement with obtained from VLBI studies and the IC-Doppler factors > 14-16 obtained from the INTEGRAL data.
Conclusions. The non-detection of S5 0716+714 with INTEGRAL in this campaign excludes an excessively high
X-ray flux associated with a simultaneous IC catastrophe. Since a strong contribution from
ISS can be excluded, we conclude that relativistic Doppler boosting naturally explains the
apparent violation of the theoretical limits. All derived Doppler factors are internally
consistent, agree with the results from different observations and can be explained within
the framework of standard synchrotron-self-Compton (SSC) jet models of AGN
Spectroscopic properties of new IR galaxies detected in the European Large Area ISO Survey.
We present preliminary results of multi-object spectroscopy of new mid-, and far-infrared selected galaxies detected in the European Large Area ISO Survey (ELAIS). The data have been obtained with the fibre spectrographs WYFFOS at the William Herschel Telescope (Observatorio del Roque de los Muchachos, ORM, Canary Islands) and Hydra at the WIYN Telescope (Kitt Peak Observatory, Arizona). The sample includes ISO sources detected at 7, 15 and 90 microns and radio sources from our deep VLA survey in the ELAIS areas
Quorum sensing network in clinical strains of A. baumannii : AidA is a new quorum quenching enzyme
Acinetobacter baumannii is an important pathogen that causes nosocomial infections generally associated with high mortality and morbidity in Intensive Care Units (ICUs). Currently, little is known about the Quorum Sensing (QS)/Quorum Quenching (QQ) systems of this pathogen. We analyzed these mechanisms in seven clinical isolates of A. baumannii. Microarray analysis of one of these clinical isolates, Ab1 (A. baumannii ST-2-clon-2010), previously cultured in the presence of 3-oxo-C12-HSL (a QS signalling molecule) revealed a putative QQ enzyme (α/β hydrolase gene, AidA). This QQ enzyme was present in all nonmotile clinical isolates (67% of which were isolated from the respiratory tract) cultured in nutrient depleted LB medium. Interestingly, this gene was not located in the genome of the only motile clinical strain growing in this medium (A. baumannii strain Ab421-GEIH-2010 [Ab7], isolated from a blood sample). The AidA protein expressed in E. coli showed QQ activity. Finally, we observed downregulation of the AidA protein (QQ system attenuation) in the presence of HO (ROS stress). In conclusion, most of the A. baumannii clinical strains were not surface motile (84%) and were of respiratory origin (67%). Only the pilT gene was involved in surface motility and related to the QS system. Finally, a new QQ enzyme (α/β hydrolase gene, AidA protein) was detected in these strains