522 research outputs found
SUBARU and e-Merlin observations of NGC3718. Diaries of an SMBH recoil?
NGC3718 is a LINER galaxy, lying at a distance of about
Mpc away from earth and its similarities with NGC5128 often award it the name
"northern Centaurus A". We use high angular resolution ( mas) e-Merlin
radio and SUBARU NIR ( mas) data, to take a detailed view of the
processes taking place in its central region. In order to preserve some
objectivity in our interpretation, we combine our results with literature
values and findings from previous studies. Our NIR maps suggest, on one hand,
that towards the stellar bulge there are no large scale absorption phenomena
caused by the apparent dust lane and, on the other, that there is a significant
(local) contribution from hot ( K) dust to the nuclear NIR emission.
The position where this takes place appears to be closer to the offset compact
radio emission from our e-Merlin cm map, lying offset by pc from
the center of the underlying stellar bulge. The shape of the radio map suggests
the presence of one (or possibly two, forming an X-shape) bipolar structure(s)
() arcsec across, which combined with the balance between the
gas and the stellar velocity dispersions and the presence of hard X-ray
emission, point towards effects expected by AGN feedback. We also argue that
NGC3718 has a "core" in its surface brightness profile, despite the fact that
it is a gas-rich galaxy and we discuss its mixed photometric and spectroscopic
characteristics. The latter combined with the observed spatial and radio
offsets, the relative redshift between the broad and the narrow
line, the limited star formation activity and AGN
feedback, strongly imply the existence of an SMBH recoil. Finally, we discuss a
possible interpretation, that could naturally incorporate all these findings
into one physically consistent picture.Comment: 18 pages, 18 figures, 3 tables, accepted for publications in A&
Line and Continuum Variability in Active Galaxies
We compared optical spectroscopic and photometric data for 18 AGN galaxies
over 2 to 3 epochs, with time intervals of typically 5 to 10 years. We used the
Multi-Object Double Spectrograph (MODS) at the Large Binocular Telescope (LBT)
and compared the spectra to data taken from the SDSS database and the
literature. We find variations in the forbidden oxygen lines as well as in the
hydrogen recombination lines of these sources. For 4 of the sources we find
that, within the calibration uncertainties, the variations in continuum and
line spectra of the sources are very small. We argue that it is mainly the
difference in black hole mass between the samples that is responsible for the
different degree of continuum variability. In addition we find that for an
otherwise constant accretion rate the total line variability (dominated by the
narrow line contributions) reverberates the continuum variability with a
dependency . Since
this dependency is prominently expressed in the narrow line emission it implies
that the luminosity dominating part of the narrow line region must be very
compact with a size of the order of at least 10 light years. A comparison to
literature data shows that these findings describe the variability
characteristics of a total of 61 broad and narrow line sources.Comment: 30 pages including the appendix, 18 figures including the appendix.
Accepted 2015 September 3. Received 2015 August 24; in original form 2015
July 3 in Monthly Notices of the Royal Astronomical Societ
Sequential star formation in IRAS 06084-0611 (GGD 12-15): From intermediate-mass to high-mass stars
Context. The formation and early evolution of high- and intermediate-mass
stars towards the main sequence involves the interplay of stars in a clustered
and highly complex environment. To obtain a full census of this interaction,
the Formation and Early evolution of Massive Stars (FEMS) collaboration studies
a well-selected sample of 10 high-mass star-forming regions. Aims. In this
study we examine the stellar content of the high-mass star-forming region
centered on IRAS 06084-0611 in the Monoceros R2 cloud. Methods. Using the
near-infrared H- and K-band spectra from the VLT/SINFONI instrument on the ESO
Very Large Telescope (VLT)and photometric near-infrared NTT/SOFI, 2MASS and
Spitzer/IRAC data, we were able to determine the spectral types for the most
luminous stars in the cluster. Results. Two very young and reddened massive
stars have been detected by SINFONI: a massive Young Stellar Object (YSO) con-
sistent with an early-B spectral type and a Herbig Be star. Furthermore, stars
of spectral type G and K are detected while still in the Pre-Main Sequence
(PMS) phase. We derive additional properties such as temperatures, extinctions,
radii and masses. We present a Hertzsprung-Russell diagram and find most
objects having intermediate masses between \sim1.5-2.5 M\odot. For these stars
we derive a median cluster age of \sim4 Myr. Conclusions. Using Spitzer/IRAC
data we confirm earlier studies that the younger class 0/I objects are
centrally located while the class II objects are spread out over a larger area,
with rough scale size radii of \sim0.5 pc and \sim1.25 pc respectively.
Moreover, the presence of a massive YSO, an ultracompact H ii region and highly
reddened objects in the center of the cluster suggest a much younger age of < 1
Myr. A possible scenario for this observation would be sequential star
formation along the line of sight; from a cluster of intermediate-mass to
high-mass stars.Comment: 14 pages, 10 figures, 2 tables. Astronomy and Astrophysic
VLA 3.5 cm continuum sources in the Serpens cloud core
We present VLA 3.5 cm continuum observations of the Serpens cloud core. 22
radio continuum sources are detected. 16 out of the 22 cm sources are suggested
to be associated with young stellar objects (Class 0, Class I, flat-spectrum,
and Class II) of the young Serpens cluster. The rest of the VLA sources
plausibly are background objects. Most of the Serpens cm sources likely
represent thermal radio jets; on the other hand, the radio continuum emission
of some sources could be due to a gyrosynchroton mechanism arising from
coronally active young stars. The Serpens VLA sources are spatially distributed
into two groups; one of them located towards the NW clump of the Serpens core,
where only Class 0 and Class I protostars are found to present cm emission, and
a second group located towards the SE clump, where radio continuum sources are
associated with objects in evolutionary classes from Class 0 to Class II. This
subgrouping is similar to that found in the near IR, mid-IR and mm wavelength
regimes.Comment: 2 figures, accepted by Astronomical journa
Probing the Early Evolution of Young High-Mass Stars
Near-infrared imaging surveys of high-mass star-forming regions reveal an
amazingly complex interplay between star formation and the environment
(Churchwell et al. 2006; Alvarez et al. 2004). By means of near-IR spectroscopy
the embedded massive young stars can be characterized and placed in the context
of their birth site. However, so far spectroscopic surveys have been hopelessly
incomplete, hampering any systematic study of these very young massive stars.
New integral field instrumentation available at ESO has opened the possibility
to take a huge step forward by obtaining a full spectral inventory of the
youngest massive stellar populations in star-forming regions currently
accessible. Simultaneously, the analysis of the extended emission allows the
characterization of the environmental conditions. The Formation and Early
Evolution of Massive Stars (FEMS) collaboration aims at setting up a large
observing campaign to obtain a full census of the stellar content, ionized
material, outflows and PDR's over a sample of regions that covers a large
parameter space. Complementary radio, mm and infrared observations will be used
for the characterization of the deeply embedded population. For the first eight
regions we have obtained 40 hours of SINFONI observations. In this
contribution, we present the first results on three regions that illustrate the
potential of this strategy.Comment: To appear in ASP Conf. Proceedings of "Massive Star Formation:
Observations confront Theory", H. Beuther et al. (eds.), held in Heidelberg,
September 200
How to Create an Innovation Accelerator
Too many policy failures are fundamentally failures of knowledge. This has
become particularly apparent during the recent financial and economic crisis,
which is questioning the validity of mainstream scholarly paradigms. We propose
to pursue a multi-disciplinary approach and to establish new institutional
settings which remove or reduce obstacles impeding efficient knowledge
creation. We provided suggestions on (i) how to modernize and improve the
academic publication system, and (ii) how to support scientific coordination,
communication, and co-creation in large-scale multi-disciplinary projects. Both
constitute important elements of what we envision to be a novel ICT
infrastructure called "Innovation Accelerator" or "Knowledge Accelerator".Comment: 32 pages, Visioneer White Paper, see http://www.visioneer.ethz.c
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