307 research outputs found
The influence of fiscal regulations on investment in marine fisheries: A French case study
Analysing investment drivers in fisheries is essential in understanding the long-term development of fishing capacity. This paper addresses the drivers of investment in the French commercial fishing fleets operating along the Atlantic coast, and the role of public policies have had on investment. First, we examine the changes in the capital value of the fleet, which was strongly impacted by decommissioning schemes during the nineties. We then examine drivers of investment using an unbalanced panel data set describing the investment decisions of a sample of firms over the period 1994â2004. In addition to economic variables, the estimated models account for other factors that may have an impact on investment behaviour, including the different career phases of the skipper-owners. The study concludes with a discussion of the results, and in particular of the role of fiscal policy on observed investment strategies
A method for quantifying the gamma-ray burst bias. Application in the redshift range of 0â1.1
International audienceContext. Long gamma-ray bursts (LGRBs) are related to the final stages of evolution of very massive stars. As such, they should follow the star formation rate (SFR) of galaxies. We can use them to probe for star-forming galaxies in the distant universe following this assumption. The relation between the rate of LGRBs in a given galaxy and its SFR (which we call the LGRB bias) may however be complex, as we have good indications that the LGRB hosts are not perfect analogues to the general population of star-forming galaxies. Aims. In this work, we try to quantify how the LGRB bias depends on physical parameters of their host galaxy, such as SFR or stellar mass. These trends may reveal more fundamental properties such as the role of the metallicity of LGRBs and of their progenitors .Methods. We propose an empirical method based on the comparison of stellar mass functions (and SFR distributions) of LGRB hosts and of star-forming galaxies to find how the bias depends on the stellar mass or the SFR.Results. By applying this method to a sample of LGRB hosts at redshifts lower than 1.1, where the properties of star-forming galaxies are fairly well established and where the properties of LGRB host galaxies can be deduced from observations (limiting ourselves to stellar masses higher than 109.25Mâ and SFR higher than ~1.8 Mââyr-1), we find that the LGRB bias depends on both the stellar mass and SFR. We find that the bias decreases with the SFR; that is, we see no preference for highly star-forming galaxies, once we account for the higher number of massive stars in galaxies with larger SFR. We do not find any trend with the specific star formation rate (SSFR), but the dynamical range in SSFR in our study is narrow. Through an indirect method, we relate these trends to a possible decrease in the LGRBs rate / SFR ratio with the metallicity.Conclusions. The method we propose suggests trends that may be useful to constrain models of LGRB progenitors, showing a clear decrease in the LGRB bias with the metallicity. This is promising for the future as the number of LGRB hosts studied will increase
Direct Measurement of the Photon Statistics of a Triggered Single Photon Source
We studied intensity fluctuations of a single photon source relying on the
pulsed excitation of the fluorescence of a single molecule at room temperature.
We directly measured the Mandel parameter Q(T) over 4 orders of magnitude of
observation timescale T, by recording every photocount. On timescale of a few
excitation periods, subpoissonian statistics is clearly observed and the
probablility of two-photons events is 10 times smaller than Poissonian pulses.
On longer times, blinking in the fluorescence, due to the molecular triplet
state, produces an excess of noise.Comment: 4 pages, 3 figures, 1 table submitted to Physical Review Letter
Probing the cosmic star formation using long Gamma-Ray Bursts: New constraints from the Spitzer Space Telescope
We report on IRAC-4.5mic, IRAC-8.0mic and MIPS-24mic deep observations of 16
Gamma-Ray Burst (GRBs) host galaxies performed with the Spitzer Space
Telescope, and we investigate in the thermal infrared the presence of evolved
stellar populations and dust-enshrouded star-forming activity associated with
these objects. Our sample is derived from GRBs that were identified with
sub-arcsec localization between 1997 and 2001, and only a very small fraction
(~20%) of the targeted sources is detected down to f_4.5mic ~3.5microJy and
f_24mic ~85microJy (3sigma). This likely argues against a population dominated
by massive and strongly-starbursting (i.e., SFR > ~100 Msol/yr) galaxies as it
has been recently suggested from submillimeter/radio and optical studies of
similarly-selected GRB hosts. Furthermore we find evidence that some GRBs do
not occur in the most infrared-luminous regions -- hence the most actively
star-forming environments -- of their host galaxies. Should the GRB hosts be
representative of all star-forming galaxies at high redshift, models of
infrared galaxy evolution indicate that > ~50% of GRB hosts should have f_24mic
> ~100microJy. Unless the identification of GRBs prior to 2001 was prone to
strong selection effects biasing our sample against dusty galaxies, we infer in
this context that the GRBs identified with the current techniques can not be
directly used as unbiased probes of the global and integrated star formation
history of the Universe.Comment: ApJ in press, 23 pages, 8 figures (scheduled for the ApJ 10 May 2006,
v642 2 issue). Full resolution available at
http://perceval.as.arizona.edu/~elefloch/Publis/ms_grb_spitzer.pd
Dust Properties and Star-Formation Rates in Star-Forming Dwarf Galaxies
We have used the Spitzer Space Telescope to study the dust properties of a
sample of star-forming dwarf galaxies. The differences in the mid-infrared
spectral energy distributions for these galaxies which, in general, are low
metallicity systems, indicate differences in the physical properties, heating,
and/or distribution of the dust. Specifically, these galaxies have more hot
dust and/or very small grains and less PAH emission than either spiral or
higher luminosity starburst galaxies. As has been shown in previous studies,
there is a gradual decrease in PAH emission as a function of metallicity.
Because much of the energy from star formation in galaxies is re-radiated in
the mid-infrared, star-formation rate indicators based on both line and
continuum measurements in this wavelength range are coming into more common
usage. We show that the variations in the interstellar medium properties of
galaxies in our sample, as measured in the mid-infrared, result in over an
order of magnitude spread in the computed star-formation rates.Comment: 25 pages, 11 figures, 4 tables, ApJ accepte
Planck \u27s Dusty GEMS: VIII. Dense-gas reservoirs in the most active dusty starbursts at z âŒ3
We present ALMA, NOEMA, and IRAM-30 m/EMIR observations of the high-density tracer molecules HCN, HCO+, and HNC in three of the brightest lensed dusty star-forming galaxies at zâČ 3-3.5, part of the Planck\u27s Dusty Gravitationally Enhanced subMillimetre Sources (GEMS), with the aim of probing the gas reservoirs closely associated with their exceptional levels of star formation. We obtained robust detections of ten emission lines between Jup = 4 and 6, as well as several additional upper flux limits. In PLCK_G244.8+54.9, the brightest source at z = 3.0, the HNC(5-4) line emission at 0.1âł resolution, together with other spatially-integrated line profiles, suggests comparable distributions of dense and more diffuse gas reservoirs, at least over the most strongly magnified regions. This rules out any major effect from differential lensing. This line is blended with CN(4-3) and in this source, we measure a HNC(5-4)/CN(4-3) flux ratio of 1.76 \ub10. 86. Dense-gas line profiles generally match those of mid-J CO lines, except in PLCK_G145.2+50.8, which also has dense-gas line fluxes that are relatively lower, perhaps due to fewer dense cores and more segregated dense and diffuse gas phases in this source. The HCO+/HCN 1 and HNC/HCN ⌠1 line ratios in our sample are similar to those of nearby ultraluminous infrared galaxies (ULIRGs) and consistent with photon-dominated regions without any indication of important mechanical heating or active galactic nuclei feedback. We characterize the dense-gas excitation in PLCK_G244.8+54.9 using radiative transfer models assuming pure collisional excitation and find that mid-J HCN, HCO+, and HNC lines arise from a high-density phase with an H2 density of n ⌠105-106 cm-3, although important degeneracies hinder a determination of the exact conditions. The three GEMS are consistent with extrapolations of dense-gas star-formation laws derived in the nearby Universe, adding further evidence that the extreme star-formation rates observed in the most active galaxies at z ⌠3 are a consequence of their important dense-gas contents. The dense-gas-mass fractions traced by HCN/[CI] and HCO+/[CI] line ratios are elevated, but not exceptional as compared to other lensed dusty star-forming galaxies at z > 2, and they fall near the upper envelope of local ULIRGs. Despite the higher overall gas fractions and local gas-mass surface densities observed at high redshift, the dense-gas budget of rapidly star-forming galaxies seems to have evolved little between z ⌠3 and z ⌠0. Our results favor constant dense-gas depletion times in these populations, which is in agreement with theoretical models of star formation
Planck's dusty GEMS. V. Molecular wind and clump stability in a strongly lensed star-forming galaxy at z=2.2
We report the discovery of a molecular wind signature from a massive
intensely star-forming clump of a few Msun, in the strongly
gravitationally lensed submillimeter galaxy "the Emerald" (PLCK_G165.7+49.0) at
z=2.236. The Emerald is amongst the brightest high-redshift galaxies on the
submillimeter sky, and was initially discovered with the Planck satellite. The
system contains two magnificient structures with projected lengths of 28.5" and
21" formed by multiple, near-infrared arcs, falling behind a massive galaxy
cluster at z=0.35, as well as an adjacent filament that has so far escaped
discovery in other wavebands. We used HST/WFC3 and CFHT optical and
near-infrared imaging together with IRAM and SMA interferometry of the CO(4-3)
line and 850 m dust emission to characterize the foreground lensing mass
distribution, construct a lens model with Lenstool, and calculate gravitational
magnification factors between 20 and 50 in most of the source. The majority of
the star formation takes place within two massive star-forming clumps which are
marginally gravitationally bound and embedded in a Msun,
fragmented disk with 20% gas fraction. One of the clumps shows a pronounced
blue wing in the CO(4-3) line profile, which we interpret as a wind signature.
The mass outflow rates are high enough for us to suspect that the clump might
become unbound within a few tens of Myr, unless the outflowing gas can be
replenished by gas accretion from the surrounding disk. The velocity offset of
-200 km s is above the escape velocity of the clump, but not that of the
galaxy overall, suggesting that much of this material might ultimately rain
back onto the galaxy and contribute to fueling subsequent star formation.Comment: 24 pages, 13 Figures, accepted for publication in A&
A Significant Population of Very Luminous Dust-Obscured Galaxies at Redshift z ~ 2
Observations with Spitzer Space Telescope have recently revealed a
significant population of high-redshift z~2 dust-obscured galaxies (DOGs) with
large mid-IR to UV luminosity ratios. These galaxies have been missed in
traditional optical studies of the distant universe. We present a simple method
for selecting this high-z population based solely on the ratio of the observed
mid-IR 24um to optical R-band flux density. In the 8.6 sq.deg Bootes NDWFS
Field, we uncover ~2,600 DOG candidates (= 0.089/sq.arcmin) with 24um flux
densities F24>0.3mJy and (R-[24])>14 (i.e., F[24]/F[R] > 1000). These galaxies
have no counterparts in the local universe, and become a larger fraction of the
population at fainter F24, representing 13% of the sources at 0.3~mJy. DOGs
exhibit evidence of both star-formation and AGN activity, with the brighter
24um sources being more AGN- dominated. We have measured spectroscopic
redshifts for 86 DOGs, and find a broad z distribution centered at ~2.0.
Their space density is 2.82E-5 per cubic Mpc, similar to that of bright
sub-mm-selected galaxies at z~2. These redshifts imply very large luminosities
LIR>~1E12-14 Lsun. DOGs contribute ~45-100% of the IR luminosity density
contributed by all z~2 ULIRGs, suggesting that our simple selection criterion
identifies the bulk of z~2 ULIRGs. DOGs may be the progenitors of ~4L*
present-day galaxies seen undergoing a luminous,short- lived phase of bulge and
black hole growth. They may represent a brief evolution phase between SMGs and
less obscured quasars or galaxies. [Abridged]Comment: Accepted for publication in the Astrophysical Journa
Cosmological model dependence of the galaxy luminosity function: far-infrared results in the LemaĂźtre-Tolman-Bondi model
Aims. This is the first paper of a series aiming at investigating galaxy formation and evolution in the giant-void class of the LemaĂźtre-Tolman-Bondi (LTB) models that best fits current cosmological observations. Here we investigate the luminosity function (LF) methodology, and how its estimates would be affected by a change on the cosmological model assumed in its computation. Are the current observational constraints on the allowed cosmology enough to yield robust LF results
The AGN Contribution to the Mid-IR Emission of Luminous Infrared Galaxies
We determine the contribution of AGN to the mid-IR emission of luminous
infrared galaxies (LIRGs) at z>0.6 by measuring the mid-IR dust continuum slope
of 20,039 mid-IR sources. The 24 micron sources are selected from a
Spitzer/MIPS survey of the NOAO Deep Wide-Field Survey Bo\"otes field and have
corresponding 8 micron data from the IRAC Shallow Survey. There is a clear
bimodal distribution in the 24 micron to 8 micron flux ratio. The X-ray
detected sources fall within the peak corresponding to a flat spectrum in
nufnu, implying that it is populated by AGN-dominated LIRGs, whereas the peak
corresponding to a higher 24 micron to 8 micron flux ratio is likely due to
LIRGs whose infrared emission is powered by starbursts. The 24 micron emission
is increasingly dominated by AGN at higher 24 micron flux densities (f_24): the
AGN fraction of the z>0.6 sources increases from ~9% at f_24 ~ 0.35 mJy to
74+/-20% at f_24 ~ 3 mJy in good agreement with model predictions. Deep 24
micron, small area surveys, like GOODS, will be strongly dominated by starburst
galaxies. AGN are responsible for ~ 3-7% of the total 24 micron background.Comment: 6 pages, accepted for publication in Ap
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