4,769 research outputs found
Early star formation traced by the highest redshift quasars
The iron abundance relative to alpha-elements in the circumnuclear region of
quasars is regarded as a clock of the star formation history and, more
specifically, of the enrichment by SNIa. We investigate the iron abundance in a
sample of 22 quasars in the redshift range 3.0<z<6.4 by measuring their rest
frame UV FeII bump, which is shifted into the near-IR, and by comparing it with
the MgII 2798 flux. The observations were performed with a device that can
obtain near-IR spectra in the range 0.8-2.4 um in one shot, thereby enabling an
optimal removal of the continuum underlying the FeII bump. We detect iron in
all quasars including the highest redshift (z=6.4) quasar currently known. The
uniform observational technique and the wide redshift range allows a reliable
study of the trend of the FeII/MgII ratio with redshift. We find the FeII/MgII
ratio is nearly constant at all redshifts, although there is marginal evidence
for a higher FeII/MgII ratio in the quasars at z~6. If the FeII/MgII ratio
reflects the Fe/alpha abundance, this result suggests that the z~6 quasars have
already undergone a major episode of iron enrichment. We discuss the possible
implications of this finding for the star formation history at z>6. We also
detect a population of weak iron emitters at z~4.5, which are possibly hosted
in systems that evolved more slowly. Alternatively, the trend of the FeII/MgII
ratio at high redshift may reflect significantly different physical conditions
of the circumnuclear gas in such high redshift quasars.Comment: Replaced to match the accepted version (ApJL in press), 5 page
Near-infrared K-band Spectroscopic Investigation of Seyfert 2 Nuclei in the CfA and 12 Micron Samples
We present near-infrared K-band slit spectra of the nuclei of 25 Seyfert 2
galaxies in the CfA and 12 micron samples. The strength of the CO absorption
features at 2.3-2.4 micron produced by stars is measured in terms of a
spectroscopic CO index. A clear anti-correlation between the observed CO index
and the nuclear K-L color is present, suggesting that a featureless hot dust
continuum heated by an AGN contributes significantly to the observed K-band
fluxes in the nuclei of Seyfert 2 galaxies. After correction for this AGN
contribution, we estimate nuclear stellar K-band luminosities for all sources,
and CO indices for sources with modestly large observed CO indices. The
corrected CO indices for 10 (=40%) Seyfert 2 nuclei are found to be as high as
those observed in star-forming or elliptical (=spheroidal) galaxies. We combine
the K-band data with measurements of the L-band 3.3 micron polycyclic aromatic
hydrocarbon (PAH) emission feature, another powerful indicator for
star-formation, and find that the 3.3 micron PAH to K-band stellar luminosity
ratios are substantially smaller than those of starburst galaxies. Our results
suggest that the 3.3 micron PAH emission originates in the putative nuclear
starbursts in the dusty tori surrounding the AGNs, because of its high surface
brightness, whereas the K-band CO absorption features detected at the nuclei
are dominated by old bulge (=spheroid) stars, and thus may not be a powerful
indicator for the nuclear starbursts. We see no clear difference in the
strength of the CO absorption and PAH emission features between the CfA and 12
micron Seyfert 2s.Comment: 28 pages, 6 figures, accepted for publication in ApJ (10 October
2004, v614 issue
The TNG Near Infrared Camera Spectrometer
NICS (acronym for Near Infrared Camera Spectrometer) is the near-infrared
cooled camera-spectrometer that has been developed by the Arcetri Infrared
Group at the Arcetri Astrophysical Observatory, in collaboration with the
CAISMI-CNR for the TNG (the Italian National Telescope Galileo at La Palma,
Canary Islands, Spain).
As NICS is in its scientific commissioning phase, we report its observing
capabilities in the near-infrared bands at the TNG, along with the measured
performance and the limiting magnitudes. We also describe some technical
details of the project, such as cryogenics, mechanics, and the system which
executes data acquisition and control, along with the related software.Comment: 7 pages, 5 figures, compiled with A&A macros. A&A in pres
The connection between the peaks in velocity dispersion and star-forming clumps of turbulent galaxies
We present Keck/OSIRIS adaptive optics observations with 150-400 pc spatial
sampling of 7 turbulent, clumpy disc galaxies from the DYNAMO sample
(). DYNAMO galaxies have previously been shown to be well matched
in properties to main sequence galaxies at . Integral field
spectroscopy observations using adaptive optics are subject to a number of
systematics including a variable PSF and spatial sampling, which we account for
in our analysis. We present gas velocity dispersion maps corrected for these
effects, and confirm that DYNAMO galaxies do have high gas velocity dispersion
(\kms), even at high spatial sampling. We find statistically
significant structure in 6 out of 7 galaxies. The most common distance between
the peaks in velocity dispersion and emission line peaks is ~kpc, we
note this is very similar to the average size of a clump measured with HST
H maps. This could suggest that the peaks in velocity dispersion in
clumpy galaxies likely arise due to some interaction between the clump and the
surrounding ISM of the galaxy, though our observations cannot distinguish
between outflows, inflows or velocity shear. Observations covering a wider area
of the galaxies will be needed to confirm this result.Comment: Accepted for publication in MNRA
Experience with statically-generated proxies for facilitating Java runtime specialisation
Issues pertaining to mechanisms which can be used to change the behaviour of Java classes at runtime are discussed. The proxy mechanism is compared to, and contrasted with other standard approaches to this problem. Some of the problems the proxy mechanism is subject to are expanded upon. The question of whether statically-developed proxies are a viable alternative to bytecode rewriting was investigated by means of the JavaCloak system, which uses statically-generated proxies to alter the runtime behaviour of externally-developed code. The issues addressed include ensuring the type safety, dealing with the self problem, object encapsulation, and issues of object identity and equality. Some performance figures are provided which demonstrate the load the JavaCloak proxy mechanism places on the system
Multicolour Optical Imaging of IR-Warm Seyfert Galaxies. V. Morphologies and Interactions. Challenging the Orientation Model
This paper is the last in a series, investigating the optical properties of a
sample of mid-IR Warm Seyfert galaxies and of a control sample of mid-IR cold
galaxies. In the present paper we parametrize the morphologies and interaction
properties of the host galaxies and combine these with the major conclusions in
our previous papers. Our results confirm that nuclear activity is linked to
galactic interactions. We suggest an alternative view for the simple
orientation-obscuration model postulated for Seyfert types 1 and 2, that takes
into account the time evolution of their environmental and morphological
properties. Within this view, an evolutionary link between starburst-dominated
and AGN-dominated IR emission is also suggested, to account for the
observational discriminator (mid-IR excess) between our Warm and Cold samples.Comment: 24 pages, including 6 figures and 3 tables (figure 5 included as
independent file), Submitted to Ap
Limits to Sympathetic Evaporative Cooling of a Two-Component Fermi Gas
We find a limit cycle in a quasi-equilibrium model of evaporative cooling of
a two-component fermion gas. The existence of such a limit cycle represents an
obstruction to reaching the quantum ground state evaporatively. We show that
evaporatively the \beta\mu ~ 1. We speculate that one may be able to cool an
atomic fermi gas further by photoassociating dimers near the bottom of the
fermi sea.Comment: Submitted to Phys. Rev
Wigner's representation of quantum mechanics in integral form and its applications
This document is the Accepted Manuscript version of the following article: Dimitris Kakofengitis, Maxime Oliva, and Ole Steuernagel, âWigner's representation of quantum mechanics in integral form and its applicationsâ, Physical Review A, Vol. 95, 022127, published 27 February 2017. DOI: https://doi.org/10.1103/PhysRevA.95.022127 ©2017 American Physical Society.We consider quantum phase space dynamics using the Wigner representation of quantum mechanics. We stress the usefulness of the integral form for the description of Wigner's phase space current~ as an alternative to the popular Moyal bracket. The integral form brings out the symmetries between momentum and position representations of quantum mechanics, is numerically stable, and allows us to perform some calculations using elementary integrals instead of Groenewold star-products. Our central result is an explicit, elementary proof which shows that only systems up to quadratic in their potential fulfil Liouville's theorem of volume preservation in quantum mechanics. Contrary to a recent suggestion, our proof shows that the non-Liouvillian character of quantum phase space dynamics cannot be transformed away.Peer reviewedFinal Accepted Versio
The Nuclear Stellar Cluster in the Seyfert~1 Galaxy NGC 3227: High Angular Resolution NIR Imaging and Spectroscopy
NIR high angular resolution speckle imaging and imaging spectroscopy of the
nuclear region (10'' ~ 840pc) of the Seyfert1 galaxy NGC3227 are presented. A
nuclear stellar cluster is slightly resolved in the J and H band with
increasing contribution to the NIR continuum from the K to the J band. The
stellar absorption lines are extended compared to the neighboring continuum
suggesting a cluster size of ~ 70pc FWHM. Analysis of those lines suggests that
the stars are contributing about 65% (40%) of the total continuum emission in
the H (K) band in a 3.6'' aperture. Population synthesis in conjunction with
NIR spectral synthesis indicates an age of 25 to 50 Myr when red supergiants
contribute most to the NIR light. This is supported by published optical data
on the MgIb line and the CaII triplet. Although a higher age of ~ 0.5 Gyr where
AGB stars dominate the NIR light can not be excluded, the observed parameters
are at the limit of those expected for a cluster dominated by AGB stars.
However, in either case the resolved stellar cluster contributes only about ~
15 % of the total dynamical mass in the inner 300pc implying another much older
stellar population. Pure constant star formation over the last 10 Gyr can be
excluded. Therefore, at least two star formation/starburst events took place in
the nucleus of NGC3227. Since such sequences in the nuclear star formation
history are also observed in the nuclei of other galaxies a link between the
activity of the star formation and the AGN itself seems likely.Comment: accepted for publication in the Astrophysical Journal, 46 pages, 15
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