1,169 research outputs found
A Sensitive Search for [N II]205 μm Emission in a z = 6.4 Quasar Host Galaxy
We present a sensitive search for the 3P1 → 3P0 ground-state fine structure line at 205 μm of ionized nitrogen ([N II]205μm) in one of the highest-redshift quasars (J1148+5251 at z = 6.42) using the IRAM 30 m telescope. The line is not detected at a (3σ) depth of 0.47 Jy km s^−1, corresponding to a [N II]205μm luminosity limit of L[N II] 7) using the Atacama Large Millimeter/submillimeter Array, for which the highly excited rotational transitions of CO will be shifted outside the accessible (sub-)millimeter bands
Bell-state preparation for electron spins in a semiconductor double quantum dot
A robust scheme for state preparation and state trapping for the spins of two
electrons in a semiconductor double quantum dot is presented. The system is
modeled by two spins coupled to two independent bosonic reservoirs. Decoherence
effects due to this environment are minimized by application of optimized
control fields which make the target state to the ground state of the isolated
driven spin system. We show that stable spin entanglement with respect to pure
dephasing is possible. Specifically, we demonstrate state trapping in a
maximally entangled state (Bell state) in the presence of decoherence.Comment: 9 pages, 4 figure
Detecting the Most Distant (z>7) Objects with ALMA
Detecting and studying objects at the highest redshifts, out to the end of
Cosmic Reionization at z>7, is clearly a key science goal of ALMA. ALMA will in
principle be able to detect objects in this redshift range both from high-J
(J>7) CO transitions and emission from ionized carbon, [CII], which is one of
the main cooling lines of the ISM. ALMA will even be able to resolve this
emission for individual targets, which will be one of the few ways to determine
dynamical masses for systems in the Epoch of Reionization. We discuss some of
the current problems regarding the detection and characterization of objects at
high redshifts and how ALMA will eliminate most (but not all) of them.Comment: to appear in Astrophysics and Space Science, "Science with ALMA: a
new era for Astrophysics", ed. R. Bachille
Quantum Decoherence of Two Qubits
It is commonly stated that decoherence in open quantum systems is due to
growing entanglement with an environment. In practice, however, surprisingly
often decoherence may equally well be described by random unitary dynamics
without invoking a quantum environment at all. For a single qubit, for
instance, pure decoherence (or phase damping) is always of random unitary type.
Here, we construct a simple example of true quantum decoherence of two qubits:
we present a feasible phase damping channel of which we show that it cannot be
understood in terms of random unitary dynamics. We give a very intuitive
geometrical measure for the positive distance of our channel to the convex set
of random unitary channels and find remarkable agreement with the so-called
Birkhoff defect based on the norm of complete boundedness.Comment: 5 pages, 4 figure
Imaging the molecular gas in a submm galaxy at z = 4.05: cold mode accretion or a major merger?
We present a high resolution (down to 0.18"), multi-transition imaging study
of the molecular gas in the z = 4.05 submillimeter galaxy GN20. GN20 is one of
the most luminous starburst galaxy known at z > 4, and is a member of a rich
proto-cluster of galaxies at z = 4.05 in GOODS-North. We have observed the CO
1-0 and 2-1 emission with the VLA, the CO 6-5 emission with the PdBI
Interferometer, and the 5-4 emission with CARMA. The H_2 mass derived from the
CO 1-0 emission is 1.3 \times 10^{11} (\alpha/0.8) Mo. High resolution imaging
of CO 2-1 shows emission distributed over a large area, appearing as partial
ring, or disk, of ~ 10kpc diameter. The integrated CO excitation is higher than
found in the inner disk of the Milky Way, but lower than that seen in high
redshift quasar host galaxies and low redshift starburst nuclei. The VLA CO 2-1
image at 0.2" resolution shows resolved, clumpy structure, with a few brighter
clumps with intrinsic sizes ~ 2 kpc. The velocity field determined from the CO
6-5 emission is consistent with a rotating disk with a rotation velocity of ~
570 km s^{-1} (using an inclination angle of 45^o), from which we derive a
dynamical mass of 3 \times 10^{11} \msun within about 4 kpc radius. The star
formation distribution, as derived from imaging of the radio synchrotron and
dust continuum, is on a similar scale as the molecular gas distribution. The
molecular gas and star formation are offset by ~ 1" from the HST I-band
emission, implying that the regions of most intense star formation are highly
dust-obscured on a scale of ~ 10 kpc. The large spatial extent and ordered
rotation of this object suggests that this is not a major merger, but rather a
clumpy disk accreting gas rapidly in minor mergers or smoothly from the
proto-intracluster medium. ABSTRACT TRUNCATEDComment: 33 pages, 8 figures, submitted to the ApJ, aas latex forma
Molecular gas in QSO host galaxies at z>5
We present observations with the IRAM Plateau de Bure Interferometer of three
QSOs at z>5 aimed at detecting molecular gas in their host galaxies as traced
by CO transitions. CO (5-4) is detected in SDSSJ033829.31+002156.3 at z=5.0267,
placing it amongst the most distant sources detected in CO. The CO emission is
unresolved with a beam size of ~1", implying that the molecular gas is
contained within a compact region, less than ~3kpc in radius. We infer an upper
limit on the dynamical mass of the CO emitting region of ~3x10^10
Msun/sin(i)^2. The comparison with the Black Hole mass inferred from near-IR
data suggests that the BH-to-bulge mass ratio in this galaxy is significantly
higher than in local galaxies. From the CO luminosity we infer a mass reservoir
of molecular gas as high as M(H2)=2.4x10^10 Msun, implying that the molecular
gas accounts for a significant fraction of the dynamical mass. When compared to
the star formation rate derived from the far-IR luminosity, we infer a very
short gas exhaustion timescale (~10^7 yrs), comparable to the dynamical
timescale. CO is not detected in the other two QSOs (SDSSJ083643.85+005453.3
and SDSSJ163033.90+401209.6) and upper limits are given for their molecular gas
content. When combined with CO observations of other type 1 AGNs, spanning a
wide redshift range (0<z<6.4), we find that the host galaxy CO luminosity
(hence molecular gas content) and the AGN optical luminosity (hence BH
accretion rate) are correlated, but the relation is not linear: L(CO) ~
[lambda*L_lambda(4400A)]^0.72. Moreover, at high redshifts (and especially at
z>5) the CO luminosity appears to saturate. We discuss the implications of
these findings in terms of black hole-galaxy co-evolution.Comment: Accepted for publication in A&A Letters, 6 pages, 3 figure
Hepatic progenitor cells from adult human livers for cell transplantation.
Objective: Liver regeneration is mainly based on cellular
self-renewal including progenitor cells. Efforts have been
made to harness this potential for cell transplantation, but
shortage of hepatocytes and premature differentiated
progenitor cells from extra-hepatic organs are limiting
factors. Histological studies implied that resident cells in
adult liver can proliferate, have bipotential character and
may be a suitable source for cell transplantation.
Methods: Particular cell populations were isolated after
adequate tissue dissociation. Single cell suspensions were
purified by Thy-1 positivity selection, characterised in vitro
and transplanted in immunodeficient Pfp/Rag2 mice.
Results: Thy-1+ cells that are mainly found in the portal
tract and the surrounding parenchyma, were isolated from
surgical liver tissue with high yields from specimens with
histological signs of regeneration. Thy-1+ cell populations
were positive for progenitor (CD34, c-kit, CK14, M2PK,
OV6), biliary (CK19) and hepatic (HepPar1) markers
revealing their progenitor as well as hepatic and biliary
nature. The potential of Thy-1+ cells for differentiation in
vitro was demonstrated by increased mRNA and protein
expression for hepatic (CK18, HepPar1) and biliary (CK7)
markers during culture while progenitor markers CK14,
chromogranin A and nestin were reduced. After
transplantation of Thy-1+ cells into livers of immunodeficient
mice, engraftment was predominantly seen in the
periportal portion of the liver lobule. Analysis of in situ
material revealed that transplanted cells express human
hepatic markers HepPar1 and albumin, indicating functional
engraftment.
Conclusion: Bipotential progenitor cells from human
adult livers can be isolated using Thy-1 and might be a
potential candidate for cell treatment in liver diseases
First Detection of HCO+ Emission at High Redshift
We report the detection of HCO+(1-0) emission towards the Cloverleaf quasar
(z=2.56) through observations with the Very Large Array. This is the first
detection of ionized molecular gas emission at high redshift (z>2). HCO+
emission is a star formation indicator similar to HCN, tracing dense molecular
hydrogen gas (n(H_2) ~= 10^5 cm^{-3}) within star-forming molecular clouds. We
derive a lensing-corrected HCO+ line luminosity of L'(HCO+) = 3.5 x 10^9 K km/s
pc^2. Combining our new results with CO and HCN measurements from the
literature, we find a HCO+/CO luminosity ratio of 0.08 and a HCO+/HCN
luminosity ratio of 0.8. These ratios fall within the scatter of the same
relationships found for low-z star-forming galaxies. However, a HCO+/HCN
luminosity ratio close to unity would not be expected for the Cloverleaf if the
recently suggested relation between this ratio and the far-infrared luminosity
were to hold. We conclude that a ratio between HCO+ and HCN luminosity close to
1 is likely due to the fact that the emission from both lines is optically
thick and thermalized and emerges from dense regions of similar volumes. The
CO, HCN and HCO+ luminosities suggest that the Cloverleaf is a composite
AGN--starburst system, in agreement with the previous finding that about 20% of
the total infrared luminosity in this system results from dust heated by star
formation rather than heating by the AGN. We conclude that HCO+ is potentially
a good tracer for dense molecular gas at high redshift.Comment: 5 pages, 3 figures, ApJL, in press (accepted May 17, 2006
The Low CO Content of the Extremely Metal Poor Galaxy I Zw 18
We present sensitive molecular line observations of the metal-poor blue
compact dwarf I Zw 18 obtained with the IRAM Plateau de Bure interferometer.
These data constrain the CO J=1-0 luminosity within our 300 pc (FWHM) beam to
be L_CO < 1 \times 10^5 K km s^-1 pc^2 (I_CO < 1 K km s^-1), an order of
magnitude lower than previous limits. Although I Zw 18 is starbursting, it has
a CO luminosity similar to or less than nearby low-mass irregulars (e.g. NGC
1569, the SMC, and NGC 6822). There is less CO in I Zw 18 relative to its
B-band luminosity, HI mass, or star formation rate than in spiral or dwarf
starburst galaxies (including the nearby dwarf starburst IC 10). Comparing the
star formation rate to our CO upper limit reveals that unless molecular gas
forms stars much more efficiently in I Zw 18 than in our own galaxy, it must
have a very low CO-to-H_2 ratio, \sim 10^-2 times the Galactic value. We detect
3mm continuum emission, presumably due to thermal dust and free-free emission,
towards the radio peak.Comment: 5 pages in emulateapj style, accepted by the Astrophysical Journa
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