540 research outputs found
Specializzazione produttiva e crescita: un'analisi mediante indicatori
Il paper analizza l\u2019evoluzione dei percorsi della specializzazione produttiva dell\u2019Italia e dei suoi principali partner commerciali (Francia, Germania e Stati Uniti).
Nella sezione metodologica, \ue8 discussa l\u2019efficacia dell\u2019indice di Lafay quale indicatore di specializzazione. In tale prospettiva si propongono alcune modifiche ed integrazioni rispetto alla sua espressione originale, al fine di individuare aspetti specifici riferiti alla teoria dei vantaggi comparati. Si discutono infine alcune implicazioni empiriche, che confermano la specializzazione della manifattura italiana in settori low-tech; esse mostrano come, a differenza di gran parte degli altri Paesi sviluppati, l\u2019Italia sia specializzata in settori scarsamente coinvolti nell\u2019attuale tendenza verso la globalizzazione dei sistemi economici
Cool outflows in galaxies and their implications
Neutral-atomic and molecular outflows are a common occurrence in galaxies,
near and far. They operate over the full extent of their galaxy hosts, from the
innermost regions of galactic nuclei to the outermost reaches of galaxy halos.
They carry a substantial amount of material that would otherwise have been used
to form new stars. These cool outflows may have a profound impact on the
evolution of their host galaxies and environments. This article provides an
overview of the basic physics of cool outflows, a comprehensive assessment of
the observational techniques and diagnostic tools used to characterize them, a
detailed description of the best-studied cases, and a more general discussion
of the statistical properties of these outflows in the local and distant
universe. The remaining outstanding issues that have not yet been resolved are
summarized at the end of the review to inspire new research directions.STFC and ER
Quasar Feedback in the Ultraluminous Infrared Galaxy F11119+3257: Connecting the Accretion Disk Wind with the Large-Scale Molecular Outflow
In Tombesi et al. (2015), we reported the first direct evidence for a quasar
accretion disk wind driving a massive molecular outflow. The target was
F11119+3257, an ultraluminous infrared galaxy (ULIRG) with unambiguous type-1
quasar optical broad emission lines. The energetics of the accretion disk wind
and molecular outflow were found to be consistent with the predictions of
quasar feedback models where the molecular outflow is driven by a hot
energy-conserving bubble inflated by the inner quasar accretion disk wind.
However, this conclusion was uncertain because the energetics were estimated
from the optically thick OH 119 um transition profile observed with Herschel.
Here, we independently confirm the presence of the molecular outflow in
F11119+3257, based on the detection of broad wings in the CO(1-0) profile
derived from ALMA observations. The broad CO(1-0) line emission appears to be
spatially extended on a scale of at least ~7 kpc from the center. Mass outflow
rate, momentum flux, and mechanical power of (80-200) R_7^{-1} M_sun/yr,
(1.5-3.0) R_7^{-1} L_AGN/c, and (0.15-0.40)% R_7^{-1} L_AGN are inferred from
these data, assuming a CO-to-H_2 conversion factor appropriate for a ULIRG (R_7
is the radius of the outflow normalized to 7 kpc and L_AGN is the AGN
luminosity). These rates are time-averaged over a flow time scale of 7x10^6
yrs. They are similar to the OH-based rates time-averaged over a flow time
scale of 4x10^5 yrs, but about a factor 4 smaller than the local
("instantaneous"; <10^5 yrs) OH-based estimates cited in Tombesi et al. The
implications of these new results are discussed in the context of time-variable
quasar-mode feedback and galaxy evolution. The need for an energy-conserving
bubble to explain the molecular outflow is also re-examined.Comment: 15 pages, 6 figures, 4 tables, accepted for publication in Ap
HI and OH absorption in the lensing galaxy of MG J0414+0534
We report the detection of \HI 21-cm absorption in the early-type
lensing galaxy towards MG J0414+0534 with the Green Bank Telescope. The
absorption, with total , is resolved into two strong components, probably due to the two
strongest lens components, which are separated by 0.4\arcsec. Unlike the other
three lenses which have been detected in \HI, J0414+0534 does not exhibit
strong OH absorption, giving a OH/\HI column density ratio of N_{\rm
OH}/N_{\rm HI}\lapp10^{-6} (for K, K and
). This underabundance of molecular gas may indicate
that the extreme optical--near-IR colour () along the line-of-sight
is not due to the lens. We therefore suggest that despite the strong upper
limits on molecular absorption at the quasar redshift, as traced by millimetre
lines, the extinction occurs primarily in the quasar host galaxy.Comment: Accepted by MNRAS Letters, 5 (and a bit) pages, 5 figure
Indications of a sub-linear and non-universal Kennicutt-Schmidt relationship
We estimate the parameters of the Kennicutt-Schmidt (KS) relationship,
linking the star formation rate (Sigma_SFR) to the molecular gas surface
density (Sigma_mol), in the STING sample of nearby disk galaxies using a
hierarchical Bayesian method. This method rigorously treats measurement
uncertainties, and provides accurate parameter estimates for both individual
galaxies and the entire population. Assuming standard conversion factors to
estimate Sigma_SFR and Sigma_mol from the observations, we find that the KS
parameters vary between galaxies, indicating that no universal relationship
holds for all galaxies. The KS slope of the whole population is 0.76, with the
2sigma range extending from 0.58 to 0.94. These results imply that the
molecular gas depletion time is not constant, but varies from galaxy to galaxy,
and increases with the molecular gas surface density. Therefore, other galactic
properties besides just Sigma_mol affect Sigma_SFR, such as the gas fraction or
stellar mass. The non-universality of the KS relationship indicates that a
comprehensive theory of star formation must take into account additional
physical processes that may vary from galaxy to galaxy.Comment: 7 pages, 2 figures, 1 table. Updated to match MNRAS accepted versio
The Structure of a Low-Metallicity Giant Molecular Cloud Complex
To understand the impact of low metallicities on giant molecular cloud (GMC)
structure, we compare far infrared dust emission, CO emission, and dynamics in
the star-forming complex N83 in the Wing of the Small Magellanic Cloud. Dust
emission (measured by Spitzer as part of the S3MC and SAGE-SMC surveys) probes
the total gas column independent of molecular line emission and traces
shielding from photodissociating radiation. We calibrate a method to estimate
the dust column using only the high-resolution Spitzer data and verify that
dust traces the ISM in the HI-dominated region around N83. This allows us to
resolve the relative structures of H2, dust, and CO within a giant molecular
cloud complex, one of the first times such a measurement has been made in a
low-metallicity galaxy. Our results support the hypothesis that CO is
photodissociated while H2 self-shields in the outer parts of low-metallicity
GMCs, so that dust/self shielding is the primary factor determining the
distribution of CO emission. Four pieces of evidence support this view. First,
the CO-to-H2 conversion factor averaged over the whole cloud is very high 4-11
\times 10^21 cm^-2/(K km/s), or 20-55 times the Galactic value. Second, the
CO-to-H2 conversion factor varies across the complex, with its lowest (most
nearly Galactic) values near the CO peaks. Third, bright CO emission is largely
confined to regions of relatively high line-of-sight extinction, A_V >~ 2 mag,
in agreement with PDR models and Galactic observations. Fourth, a simple model
in which CO emerges from a smaller sphere nested inside a larger cloud can
roughly relate the H2 masses measured from CO kinematics and dust.Comment: 17 pages, 10 figures (including appendix), accepted for publication
in the Astrophysical Journa
New insights on the dense molecular gas in NGC253 as traced by HCN and HCO+
We have imaged the central ~1kpc of the circumnuclear starburst disk in the
galaxy NGC253 in the HCN(1-0), HCO+(1-0), and CO(1-0) transitions at 60pc
resolution using the Owens Valley Radio Observatory Millimeter-Wavelength Array
(OVRO). We have also obtained Atacama Pathfinder Experiment (APEX) observations
of the HCN(4-3) and the HCO+(4-3) lines of the starburst disk. We find that the
emission from the HCN(1-0) and HCO+(1-0) transitions, both indicators of dense
molecular gas, trace regions which are non-distinguishable within the
uncertainties of our observations. Even though the continuum flux varies by
more than a factor 10 across the starburst disk, the HCN/HCO+ ratio is constant
throughout the disk, and we derive an average ratio of 1.1+/-0.2. From an
excitation analysis we find that all lines from both molecules are subthermally
excited and that they are optically thick. This subthermal excitation implies
that the observed HCN/HCO+ line ratio is sensitive to the underlying chemistry.
The constant line ratio thus implies that there are no strong abundance
gradients across the starburst disk of NGC253. This finding may also explain
the variations in L'(HCN)/L'(HCO+) between different star forming galaxies both
nearby and at high redshifts.Comment: 9 pages, 12 figures, ApJ in press (volume 666 September
SubmilliJansky Transients in Archival Radio Observations
[ABRIDGED] We report the results of a 944-epoch survey for transient sources
with archival data from the Very Large Array spanning 22 years with a typical
epoch separation of 7 days. Observations were obtained at 5 or 8.4 GHz for a
single field of view with a full-width at half-maximum of 8.6' and 5.1',
respectively, and achieved a typical point-source detection threshold at the
beam center of ~300 microJy per epoch. Ten transient sources were detected with
a significance threshold such that only one false positive would be expected.
Of these transients, eight were detected in only a single epoch. Two transients
were too faint to be detected in individual epochs but were detected in
two-month averages. None of the ten transients was detected in longer-term
averages or associated with persistent emission in the deep image produced from
the combination of all epochs. The cumulative rate for the short timescale
radio transients above 370 microJy at 5 and 8.4 GHz is 0.07 < R < 40 deg^-2
yr^-1, where the uncertainty is due to the unknown duration of the transients,
20 min < t_char < 7 days. A two-epoch survey for transients will detect 1.5 +/-
0.4 transient per square degrees above a flux density of 370 microJy. Two
transients are associated with galaxies at z=0.040 and z=0.249. These may be
similar to the peculiar Type Ib/c radio supernova SN 1998bw associated with GRB
980428. Six transients have no counterparts in the optical or infrared (R=27,
Ks=18). The hosts and progenitors of these transients are unknown.Comment: Accepted for ApJ; full quality figures available at
http://astro.berkeley.edu/~gbower/ps/rt.pd
High-Resolution Measurements of the Dark Matter Halo of NGC 2976: Evidence for a Shallow Density Profile
We have obtained two-dimensional velocity fields of the dwarf spiral galaxy
NGC 2976 in Halpha and CO. The high spatial (~75 pc) and spectral (13 km/s and
2 km/s, respectively) resolution of these observations, along with our
multicolor optical and near-infrared imaging, allow us to measure the shape of
the density profile of the dark matter halo with good precision. We find that
the total (baryonic plus dark matter) mass distribution of NGC 2976 follows a
rho_tot ~ r^(-0.27 +/- 0.09) power law out to a radius of 1.8 kpc, assuming
that the observed radial motions provide no support. The density profile
attributed to the dark halo is even shallower, consistent with a nearly
constant density of dark matter over the entire observed region. A maximal disk
fit yields an upper limit to the K-band stellar mass-to-light ratio (M*/L_K) of
0.09^{+0.15}_{-0.08} M_sun/L_sun,K (including systematic uncertainties), with
the caveat that for M*/L_K > 0.19 M_sun/L_sun,K the dark matter density
increases with radius, which is unphysical. Assuming 0.10 M_sun/L_sun,K <
M*/L_K < 0.19 M_sun/L_sun,K, the dark matter density profile lies between
rho_dm ~ r^-0.17 and rho_dm ~ r^-0.01. Therefore, independent of any
assumptions about the stellar disk or the functional form of the density
profile, NGC 2976 does not contain a cuspy dark matter halo. We also
investigate some of the systematic effects that can hamper rotation curve
studies, and show that 1) longslit rotation curves are far more vulnerable to
systematic errors than two-dimensional velocity fields, 2) NGC 2976 contains
large radial motions at small radii, and 3) the Halpha and CO velocity fields
of NGC 2976 agree within their uncertainties. [slightly abridged]Comment: 30 pages, 4 tables, 13 figures (7 in color; Figures 1 and 3 are
low-resolution to save space). Accepted for publication in ApJ. Version with
full-resolution figures available at
http://astro.berkeley.edu/~bolatto/ngc2976rotation.ps (46 MB
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