1,050 research outputs found
A Kiloparsec-Scale Hyper-Starburst in a Quasar Host Less than 1 Gigayear after the Big Bang
The host galaxy of the quasar SDSS J114816.64+525150.3 (at redshift z=6.42,
when the Universe was <1 billion years old) has an infrared luminosity of
2.2x10^13 L_sun, presumably significantly powered by a massive burst of star
formation. In local examples of extremely luminous galaxies such as Arp220, the
burst of star formation is concentrated in the relatively small central region
of <100pc radius. It is unknown on which scales stars are forming in active
galaxies in the early Universe, which are likely undergoing their initial burst
of star formation. We do know that at some early point structures comparable to
the spheroidal bulge of the Milky Way must have formed. Here we report a
spatially resolved image of [CII] emission of the host galaxy of
J114816.64+525150.3 that demonstrates that its star forming gas is distributed
over a radius of ~750pc around the centre. The surface density of the star
formation rate averaged over this region is ~1000 M_sun/yr/kpc^2. This surface
density is comparable to the peak in Arp220, though ~2 orders of magnitudes
larger in area. This vigorous star forming event will likely give rise to a
massive spheroidal component in this system.Comment: Nature, in press, Feb 5 issue, p. 699-70
Ionized Nitrogen at High Redshift
We present secure [N II]_(205 μm) detections in two millimeter-bright, strongly lensed objects at high redshift, APM 08279+5255 (z = 3.911) and MM 18423+5938 (z = 3.930), using the IRAM Plateau de Bure Interferometer. Due to its ionization energy [N II]_(205 μm) is a good tracer of the ionized gas phase in the interstellar medium. The measured fluxes are S([N II]_(205 μm)) = (4.8 ± 0.8) Jy km s^(–1) and (7.4 ± 0.5) Jy km s^(–1), respectively, yielding line luminosities of L([N II]_(205 μm)) = (1.8 ± 0.3) × 10^9 μ^(–1) L_⊙ for APM 08279+5255 and L([N II]_(205 μm)) = (2.8 ± 0.2) × 10(^9) μ^(–1) L_⊙ for MM 18423+5938. Our high-resolution map of the [N II]_(205 μm) and 1 mm continuum emission in MM 18423+5938 clearly resolves an Einstein ring in this source and reveals a velocity gradient in the dynamics of the ionized gas. A comparison of these maps with high-resolution EVLA CO observations enables us to perform the first spatially resolved study of the dust continuum-to-molecular gas surface brightness (Σ_(FIR)α Σ^N_CO, which can be interpreted as the star formation law) in a high-redshift object. We find a steep relation (N = 1.4 ± 0.2), consistent with a starbursting environment. We measure a [N II]_(205 μm)/FIR luminosity ratio in APM 08279+5255 and MM 18423+5938 of 9.0 × 10^(–6) and 5.8 × 10^(–6), respectively. This is in agreement with the decrease of the [N II]_(205 μm)/FIR ratio at high FIR luminosities observed in local galaxies
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
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
ALMA Multi-line Imaging of the Nearby Starburst Galaxy NGC 253
We present spatially resolved (50 pc) imaging of molecular gas species
in the central kiloparsec of the nearby starburst galaxy NGC 253, based on
observations taken with the Atacama Large Millimeter/submillimeter Array
(ALMA). A total of 50 molecular lines are detected over a 13 GHz bandwidth
imaged in the 3 mm band. Unambiguous identifications are assigned for 27 lines.
Based on the measured high CO/CO isotopic line ratio (350), we
show that CO(1-0) has moderate optical depths. A comparison of the HCN
and HCO with their C-substituted isotopologues shows that the
HCN(1-0) and HCO(1-0) lines have optical depths at least comparable to
CO(1-0). HCN/HCO (and HCN/HNC) line ratios
provide tighter constraints on dense gas properties in this starburst. SiO has
elevated abundances across the nucleus. HNCO has the most distinctive
morphology of all the bright lines, with its global luminosity dominated by the
outer parts of the central region. The dramatic variation seen in the HNCO/SiO
line ratio suggests that some of the chemical signatures of shocked gas are
being erased in the presence of dominating central radiation fields (traced by
CH and CN). High density molecular gas tracers (including HCN, HCO,
and CN) are detected at the base of the molecular outflow. We also detect
hydrogen recombination lines that, like their counterparts,
show compact, centrally peaked morphologies, distinct from the molecular gas
tracers. A number of sulfur based species are mapped (CS, SO, NS, CS,
HCS and CHSH) and have morphologies similar to SiO.Comment: 20 pages, 10 figures, accepted to the Astrophysical Journa
Detection of Emission from the CN Radical in the Cloverleaf Quasar at z=2.56
We report the detection of CN(N=3-2) emission towards the Cloverleaf quasar
(z=2.56) based on observations with the IRAM Plateau de Bure Interferometer.
This is the first clear detection of emission from this radical at high
redshift. CN emission is a tracer of dense molecular hydrogen gas (n(H2) > 10^4
cm^{-3}) within star-forming molecular clouds, in particular in regions where
the clouds are affected by UV radiation. The HCN/CN intensity ratio can be used
as a diagnostic for the relative importance of photodissociation regions (PDRs)
in a source, and as a sensitive probe of optical depth, the radiation field,
and photochemical processes. We derive a lensing-corrected CN(N=3-2) line
luminosity of L'(CN(3-2) = (4.5 +/- 0.5) x 10^9 K km/s pc^2. The ratio between
CN luminosity and far-infrared luminosity falls within the scatter of the same
relationship found for low-z (ultra-) luminous infrared galaxies. Combining our
new results with CO(J=3-2) and HCN(J=1-0) measurements from the literature and
assuming thermal excitation for all transitions, we find a CO/CN luminosity
ratio of 9.3 +/- 1.9 and a HCN/CN luminosity ratio of 0.95 +/- 0.15. However,
we find that the CN(N=3-2) line is likely only subthermally excited, implying
that those ratios may only provide upper limits for the intrinsic 1-0 line
luminosity ratios. We conclude that, in combination with other molecular gas
tracers like CO, HCN, and HCO+, CN is an important probe of the physical
conditions and chemical composition of dense molecular environments at high
redshift.Comment: 6 pages, 5 figures, 1 table, to appear in ApJ (accepted May 23, 2007
Molecular Gas in M82: Resolving the Outflow and Streamers
We present a high-resolution (3.6'', 70pc) CO(1-0) mosaic of the molecular
gas in M 82 covering an area of 2.5' x 3.5' (2.8kpc x 3.9kpc) obtained with the
OVRO millimeter interferometer. The observations reveal the presence of huge
amounts of molecular gas (> 70% of the total molecular mass, M_tot=1.3 x 10^9
M_sun) outside the central 1 kpc disk. Molecular streamers are detected in and
below M82's disk out to distances from the center of 1.7 kpc. Some of these
streamers are well correlated with optical absorption features; they form the
basis of some of the prominent tidal HI features around M 82. This provides
evidence that the molecular gas within M 82's optical disk is disrupted by the
interaction with M 81. Molecular gas is found in M 82's outflow/halo, reaching
distances up to 1.2 kpc below the plane; CO line-splitting has been detected
for the first time in the outflow. The maximum outflow velocity is 230 km/s; we
derive an opening angle of 55 deg for the molecular outflow cone. The total
amount of gas in the outflow is >3 x 10^8 M_sun and its kinetic energy is of
order 10^55 erg, about one percent of the estimated total mechanical energy
input of M 82's starburst. Our study implies that extreme starburst
environments can move significant amounts of molecular gas in to a galaxy's
halo (and even to the intergalactic medium).Comment: accepted for publication in the ApJ Letters full PS file @
http://www.aoc.nrao.edu/~fwalter/walter_m82.p
BR1202-0725: An Extreme Multiple Merger at z = 4.7
The radio-quiet quasar BR1202-0725 (z=4.695) is a remarkable source with a
bright Northwest (NW) companion detected at submm and radio wavelengths but
invisible in the optical. In the absence of amplification by gravitational
lensing, BR1202-0725 would be the most luminous binary CO and FIR source in the
Universe. In this paper, we report observations with the IRAM Plateau de Bure
interferometer of BR1202-0725 in the redshifted emission of the CO(5-4) and
(7-6) lines, the [C I](3P2-3P1) line, a high angular resolution (0.3 x 0.8
arcsec) 1.3 mm map of the rest-frame, far-IR dust continuum, and a search for
the CO(11-10) line. We compare these results with recent ALMA data in the [C
II] line. Both the quasar host galaxy and its NW companion are spatially
resolved in the molecular line emission and the dust continuum. The CO profile
of the NW companion is very broad with a full width at half maximum of 1000 +/-
130 km/s, compared to 360 +/- 40 km/s for the quasar host galaxy to the
Southeast (SE). The difference in linewidths and center velocities, and the
absence of any lens candidate or arc-like structure in the field, at any
wavelength, show that the obscured NW galaxy and the SE quasar host galaxy
cannot be lensed images of the same object. Instead, we find morphological and
kinematic evidence for sub-structures in both the NW and SE sources. We
interpret these results as strong indications that the BR1202-0725 complex is a
group of young, interacting, and highly active starburst galaxies.Comment: Minor changes to agree with published versio
A sensitive search for CO J=1-0 emission in 4C 41.17: high-excitation molecular gas at z=3.8
We report sensitive imaging observations of the CO J=1-0 line emission in the
powerful high-redshift radio galaxy 4C 41.17 (z=3.8) with the NRAO Very Large
Array (VLA), conducted in order to detect the large concomitant H_2 gas
reservoir recently unveiled in this system by De Breuck et al (2005) via the
emission of the high excitation J=4-3 line. Our observations fail to detect the
J=1-0 line but yield sensitive lower limits on the R_43=(4-3)/(1-0) brightness
temperature ratio of R_43 ~ 0.55 - >1.0 for the bulk of the H_2 gas mass. Such
high ratios are typical of the high-excitation molecular gas phase ``fueling''
the star formation in local starbursts, but quite unlike these objects, much of
the molecular gas in 4C 41.17 seems to be in such a state, and thus
participating in the observed starburst episode. The widely observed and unique
association of highly excited molecular gas with star forming sites allows CO
line emission with large (high-J)/(low-J) intensity ratios to serve as an
excellent ``marker'' of the spatial distribution of star formation in distant
dust-obscured starbursts, unaffected by extinction.Comment: 7 Pages including 8 PostScript figures. Accepted for publication in
Astronomy & Astrophysic
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