1,138 research outputs found
ALMA imaging of SDP.81 - I. A pixelated reconstruction of the far-infrared continuum emission
We present a sub-50 pc-scale analysis of the gravitational lens system SDP.81
at redshift 3.042 using Atacama Large Millimetre/submillimetre Array (ALMA)
science verification data. We model both the mass distribution of the
gravitational lensing galaxy and the pixelated surface brightness distribution
of the background source using a novel Bayesian technique that fits the data
directly in visibility space. We find the 1 and 1.3 mm dust emission to be
magnified by a factor of u_tot = 17.6+/-0.4, giving an intrinsic total
star-formation rate of 315+/-60 M_sol/yr and a dust mass of 6.4+/-1.5*10^8
M_sol. The reconstructed dust emission is found to be non-uniform, but composed
of multiple regions that are heated by both diffuse and strongly clumped
star-formation. The highest surface brightness region is a ~1.9*0.7 kpc
disk-like structure, whose small extent is consistent with a potential
size-bias in gravitationally lensed starbursts. Although surrounded by extended
star formation, with a density of 20-30+/-10 M_sol/yr/kpc^2, the disk contains
three compact regions with densities that peak between 120-190+/-20
M_sol/yr/kpc^2. Such star-formation rate densities are below what is expected
for Eddington-limited star-formation by a radiation pressure supported
starburst. There is also a tentative variation in the spectral slope of the
different star-forming regions, which is likely due to a change in the dust
temperature and/or opacity across the source.Comment: MNRAS accepted 2015 April 1
ALMA imaging of SDP.81 - II. A pixelated reconstruction of the CO emission lines
We present a sub-100 pc-scale analysis of the CO molecular gas emission and
kinematics of the gravitational lens system SDP.81 at redshift 3.042 using
Atacama Large Millimetre/submillimetre Array (ALMA) science verification data
and a visibility-plane lens reconstruction technique. We find clear evidence
for an excitation dependent structure in the unlensed molecular gas
distribution, with emission in CO (5-4) being significantly more diffuse and
structured than in CO (8-7). The intrinsic line luminosity ratio is r_8-7/5-4 =
0.30 +/- 0.04, which is consistent with other low-excitation starbursts at z ~
3. An analysis of the velocity fields shows evidence for a star-forming disk
with multiple velocity components that is consistent with a
merger/post-coalescence merger scenario, and a dynamical mass of M(< 1.56 kpc)
= 1.6 +/- 0.6 x 10^10 M_sol . Source reconstructions from ALMA and the Hubble
Space Telescope show that the stellar component is offset from the molecular
gas and dust components. Together with Karl G. Jansky Very Large Array CO (1-0)
data, they provide corroborative evidence for a complex ~2 kpc-scale starburst
that is embedded within a larger ~15 kpc structure.Comment: MNRAS accepted, 6th July 201
Probing Cool and Warm Infrared Galaxies using Photometric and Structural Measures
We have analyzed a sample of nearby cool and warm infrared (IR) galaxies
using photometric and structural parameters. The set of measures include
far-infrared color (), total IR
luminosity (), radio surface brightness as well as radio,
near-infrared, and optical sizes. In a given luminosity range cool and warm
galaxies are considered as those sources that are found approximately below and above the mean color in the far-infrared
diagram. We find that galaxy radio surface brightness is well correlated with
color whereas size is less well correlated with color. Our analysis indicates
that IR galaxies that are dominated by cool dust are large, massive spirals
that are not strongly interacting or merging and presumably the ones with the
least active star formation. Dust in these cool objects is less centrally
concentrated than in the more typical luminous and ultra-luminous IR galaxies
that are dominated by warm dust. Our study also shows that low luminosity early
type unbarred and transitional spirals are responsible for the large scatter in
the diagram. Among highly luminous galaxies, late type unbarred
spirals are predominately warm, and early type unbarred and barred are
systematically cooler. We highlight the significance of diagram
in terms of local and high redshifts sub-millimeter galaxies.Comment: Accepted for publication in ApJ, 2006, 23 pages, 3 postscript
figures, 1 table. The table can be obtained on request from the author
CO excitation in the Seyfert galaxy NGC7130
We present a coherent multi-band modelling of the CO Spectral Energy
Distribution of the local Seyfert Galaxy NGC7130 to assess the impact of the
AGN activity on the molecular gas. We take advantage of all the available data
from X-ray to the sub-mm, including ALMA data. The high-resolution (~0.2") ALMA
CO(6-5) data constrain the spatial extension of the CO emission down to ~70 pc
scale. From the analysis of the archival CHANDRA and NuSTAR data, we infer the
presence of a buried, Compton-thick AGN of moderate luminosity, L_2-10keV ~
1.6x10^{43} ergs-1. We explore photodissociation and X-ray-dominated regions
(PDRs and XDRs) models to reproduce the CO emission. We find that PDRs can
reproduce the CO lines up to J~6, however, the higher rotational ladder
requires the presence of a separate source of excitation. We consider X-ray
heating by the AGN as a source of excitation, and find that it can reproduce
the observed CO Spectral Energy Distribution. By adopting a composite PDR+XDR
model, we derive molecular cloud properties. Our study clearly indicates the
capabilities offered by current-generation of instruments to shed light on the
properties of nearby galaxies adopting state-of-the art physical modelling.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Far-infrared line spectra of active galaxies from the Herschel/PACS Spectrometer: the complete database
We present a coherent database of spectroscopic observations of far-IR
fine-structure lines from the Herschel/PACS archive for a sample of 170 local
AGN, plus a comparison sample of 20 starburst galaxies and 43 dwarf galaxies.
Published Spitzer/IRS and Herschel/SPIRE line fluxes are included to extend our
database to the full 10-600 spectral range. The observations are
compared to a set of CLOUDY photoionisation models to estimate the above
physical quantities through different diagnostic diagrams. We confirm the
presence of a stratification of gas density in the emission regions of the
galaxies, which increases with the ionisation potential of the emission lines.
The new [OIV]25.9/[OIII]88 vs [NeIII]15.6/[NeII]12.8 diagram is proposed as the best diagnostic to separate: AGN activity
from any kind of star formation; and low-metallicity dwarf galaxies from
starburst galaxies. Current stellar atmosphere models fail to reproduce the
observed [OIV]25.9/[OIII]88 ratios, which are much higher when
compared to the predicted values. Finally, the ([NeIII]15.6 +
[NeII]12.8)/([SIV]10.5 + [SIII]18.7) ratio is proposed as
a promising metallicity tracer to be used in obscured objects, where optical
lines fail to accurately measure the metallicity. The diagnostic power of mid-
to far-infrared spectroscopy shown here for local galaxies will be of crucial
importance to study galaxy evolution during the dust-obscured phase at the peak
of the star formation and black-hole accretion activity (). This
study will be addressed by future deep spectroscopic surveys with present and
forthcoming facilities such as JWST, ALMA, and SPICA.Comment: Accepted for publication in the ApJ
Self-tuned quantum dot gain in photonic crystal lasers
We demonstrate that very few (1 to 3) quantum dots as a gain medium are
sufficient to realize a photonic crystal laser based on a high-quality
nanocavity. Photon correlation measurements show a transition from a thermal to
a coherent light state proving that lasing action occurs at ultra-low
thresholds. Observation of lasing is unexpected since the cavity mode is in
general not resonant with the discrete quantum dot states and emission at those
frequencies is suppressed. In this situation, the quasi-continuous quantum dot
states become crucial since they provide an energy-transfer channel into the
lasing mode, effectively leading to a self-tuned resonance for the gain medium.Comment: 4 pages, 4 figures, submitted to Phys. Re
Star formation properties of sub-mJy radio sources
We investigate the star formation properties of ~800 sources detected in one
of the deepest radio surveys at 1.4 GHz. Our sample spans a wide redshift range
(~0.1 - 4) and about four orders of magnitude in star formation rate (SFR). It
includes both star forming galaxies (SFGs) and active galactic nuclei (AGNs),
further divided into radio-quiet and radio-loud objects. We compare the SFR
derived from the far infrared luminosity, as traced by Herschel, with the SFR
computed from their radio emission. We find that the radio power is a good SFR
tracer not only for pure SFGs but also in the host galaxies of RQ AGNs, with no
significant deviation with redshift or specific SFR. Moreover, we quantify the
contribution of the starburst activity in the SFGs population and the
occurrence of AGNs in sources with different level of star formation. Finally
we discuss the possibility of using deep radio survey as a tool to study the
cosmic star formation history.Comment: 18 pages, 14 figures, 1 table (available in its entirety as ancillary
data
Controlling the dynamics of a coupled atom-cavity system by pure dephasing : basics and potential applications in nanophotonics
The influence of pure dephasing on the dynamics of the coupling between a
two-level atom and a cavity mode is systematically addressed. We have derived
an effective atom-cavity coupling rate that is shown to be a key parameter in
the physics of the problem, allowing to generalize the known expression for the
Purcell factor to the case of broad emitters, and to define strategies to
optimize the performances of broad emitters-based single photon sources.
Moreover, pure dephasing is shown to be able to restore lasing in presence of
detuning, a further demonstration that decoherence can be seen as a fundamental
resource in solid-state cavity quantum electrodynamics, offering appealing
perspectives in the context of advanced nano-photonic devices.Comment: 10 pages, 7 figure
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