566 research outputs found
Inhomogeneous metal enrichment at z \sim 1.9: the Lyman limit systems in the spectrum of the HDF-S quasar
We present a detailed analysis of three metal absorption systems observed in
the spectrum of the HDF-South quasar J2233-606 (z_em = 2.238), taking advantage
of new VLT-UVES high resolution data (R=45000, S/N = 40-60, \lambda\lambda
3050-10000 \AA). Three main components, spanning about 300 km/s, can be
individuated in the Lyman limit system at z~1.92. They show a surprisingly
large variation in metallicities, respectively ~1/500, 1/8 and 1/100 solar. The
large value found for the second component at z=1.9259, suggests that the line
of sight crosses a star-forming region. In addition, there is a definite
correlation between velocity position and ionisation state in this component,
which we interpret as a possible signature of an expanding H II region. The
systems at z~1.94 and z~1.87 have also high metallicity, ~1/4 and 1/3 solar. We
find that photoionisation and collisional ionisation are equal alternatives to
explain the high excitation phase revealed by O VI absorption, seen in these
two systems. From the width of the Si IV, C IV, Si III and C III lines in the
system at z~1.87, we can estimate the temperature of the gas to be log T ~ 4.7,
excluding collisional ionisation. Finally, we compute the Si IV/C IV ratio for
all Voigt profile components in a sample of log N(C IV) > 14 systems at z < 2.
The values show a dispersion of more than an order of magnitude and most of
them are much larger than what is observed for weaker systems. This is probably
an indication that high column density systems preferably originate in galactic
halos and are mostly influenced by local ionising sources.Comment: 11 pages, 11 figures, accepted by A&A main journa
Multiwavelength investigation of a near-solar metallicity sub-DLA at z =1.3647 towards PKS 0237-233
We searched for 21-cm absorption associated with the z_abs = 1.3647
absorption system toward PKS 0237-233 using the GMRT. A high quality UVES
spectrum shows that C I and C I* are detected at this redshift together with C
II*, Mg I, Mg II, Si II, Al II, Fe II and Mn II. The complex profiles, spread
over ~300 km/s, are fitted with 21 Voigt profile components. None of these
components are detected in 21-cm absorption down to a detection limit of
\tau(3\sigma)\le 3x10^{-3} (or N(HI)/T_S <10^{17} cm ^-2 K^-1). We derive log
N(HI)<19.300.30 using the Lyman alpha absorption line detected in the IUE
spectrum of the quasar. Mg II, Si II and Al II column densities are consistent
with near solar metallicity and we measure [O/H]>-0.33. Using photoionization
models constrained by the fine-structure excitations of C I and C II, and the
21-cm optical depth, we show that the C I absorption arises predominantly
either in WIM or WNM in ionization and thermal equilibrium with the
meta-galactic UV background dominated by QSOs and star forming galaxies. The
estimated thermal pressure of the gas is of the same order of magnitude over
different velocity ranges through the absorption profile (2.6\le log [P/k
cm^{-3} K]\le 4.0). The gas-phase metallicity corrected for ionization is Z>0.5
Z_\odot with a signature of Fe co-production elements being under abundant
compared to \alpha-process elements by ~0.5 dex. At z>1.9, C I absorption is
usually associated with H_2 absorption arising from cold gas in DLAs. This
system and the z=2.139 toward Tol 1037-270 are the only two systems known which
show that C I absorption can also be detected in warm gas provided the
metallicity is high enough. Interestingly, both the systems are part of unusual
concentrations of absorption lines.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Science and the “Civilizing Mission”: <br />France and the Colonial Enterprise
Which part was played by science in the French “civilizing mission” ? From the 1880s, the interests of science were combined with those of national prestige. Colonization was undertaken in the name of science. To civilize, in official French colonial ideology, was to bring the benefits of science, just as for other countries, it was to bring the benefits of religion or free trade. The “civilizing mission” thus managed to combine elements of Eurocentrism and scientism. It represented a cultural consensus from the 1880s until the 1930s, and conditioned many generations of French scientists in their training, in their scientific practices, and in their mentalities. Many societies and institutions were established to organize colonial scientific activities : learned societies (Geographical Society, Anthropological Society, and so on), the Association Science and Colonies, the Colonial Academy of Science, the Colonila Scientific Congresses,...The aim of this essay is to analyse this colonial function of science, far to be only a technical tool. It is to describe how it occupied such a central part in colonial ideology and policy from the 1880s, with the name of "civilizing mission"
Quand la politique interpelle les historiens des sciences. L'Académie Internationale d'Histoire des Sciences dans les années 1930 et 1940
Communication présentée à l'Université de Lille en mai 2007 lors du symposium organisé par la Société Française d'Histoire des Sciences et des techniques "Quelle histoire font les historiens des sciences ? État des lieux des méthodes en histoire des sciences et des techniques ". En cours de publication dans les Actes.Les congrès internationaux d'histoire des sciences ont rarement été à l'abri des controverses politiques ou sociales, notamment dans les années 1930 et 1940. L'Académie internationale d'histoire des sciences, organisatrice des premiers congrès, n'a pu échapper aux débats publics sur le fascisme ou sur la fonction sociale de la science et de l'histoire des sciences. Le cas du 2e congrès (Londres, 1931) a été très étudié, avec la présence d'une délégation soviétique dirigée par Boukharine. Le 3e congrès, programmé à Berlin pour 1934, a été déplacé au Portugal après d'âpres débats. Le 4e a eu lieu en 1937 à Prague. Après une interruption pendant la guerre, le 5e congrès (Lausanne 1947) a vu la création de l'Union internationale d'histoire des sciences, avec une commission "histoire des relations sociales de la science" (Léon Rosenfeld, Samuel Lilley) sous la pression politique de l'Unesco, et plus particulièrement de Joseph Needham et de ses amis progressistes
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