28 research outputs found
Recovery and analysis of rest-frame UV emission lines in 2052 galaxies observed with MUSE at 1.5 < z < 6.4
Rest-frame ultraviolet (UV) emission lines probe electron densities, gas-phase abundances, metallicities, and ionization parameters of the emitting star-forming galaxies and their environments. The strongest main UV emission line, Lyα, has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Lyα emission becomes increasingly challenging at zââłâ6 when the neutral hydrogen fraction of the circumgalactic and intergalactic media increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large sample of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxiesâ physical properties and their Lyα emission. The sample of 2052 emission line sources with 1.5â<âzâ<â6.4 was collected from integral field data from the MUSE-Wide and MUSE-Deep surveys taken as part of Guaranteed Time Observations. The objects were selected through untargeted source detection (i.e., no preselection of sources as in dedicated spectroscopic campaigns) in the three-dimensional MUSE data cubes. We searched optimally extracted one-dimensional spectra of the full sample for UV emission features via emission line template matching, resulting in a sample of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Lyα) UV emission lines increases with survey depth, and that the emission line strength of HeâŻIIλ1640 Ă
, [OâŻIII] λ1661 + OâŻIII] λ1666, and [SiâŻIII] λ1883 + SiâŻIII] λ1892 correlate with the strength of [CâŻIII] λ1907 + CâŻIII] λ1909. The rest-frame equivalent width (EW0) of [CâŻIII] λ1907 + CâŻIII] λ1909 is found to be roughly 0.22 ± 0.18 of EW0(Lyα). We measured the velocity offsets of resonant emission lines with respect to systemic tracers. For CâŻIVλ1548 + CâŻIVλ1551 we find that ÎvCâŻIV âČ 250 km sâ1, whereas ÎvLyα falls in the range of 250â500 km sâ1 which is in agreement with previous results from the literature. The electron density ne measured from [SiâŻIII] λ1883 + SiâŻIII] λ1892 and [CâŻIII] λ1907 + CâŻIII] λ1909 line flux ratios is generally < 105 cmâ3 and the gas-phase abundance is below solar at 12â
+â
log10(O/H)â8. Lastly, we used âPhotoIonization Model Probability Density Functionsâ to infer physical parameters of the full sample and individual systems based on photoionization model parameter grids and observational constraints from our UV emission line searches. This reveals that the UV line emitters generally have ionization parameter log10(U)ââââ2.5 and metal mass fractions that scatter around Zâââ10â2, that is Zâââ0.66âZâ. Value-added catalogs of the full sample of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper
High biomass, low export regimes in the Southern Ocean
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 54 (2007): 601-638, doi:10.1016/j.dsr2.2007.01.013.This paper investigates ballasting and remineralization controls of carbon sedimentation
in the twilight zone (100-1000 m) of the Southern Ocean. Size-fractionated (<1 ÎŒm, 1-51 ÎŒm,
>51 ÎŒm) suspended particulate matter was collected by large volume in-situ filtration from the
upper 1000 m in the Subantarctic (55°S, 172°W) and Antarctic (66°S, 172°W) zones of the
Southern Ocean during the Southern Ocean Iron Experiment (SOFeX) in January-February 2002.
Particles were analyzed for major chemical constituents (POC, P, biogenic Si, CaCO3), and
digital and SEM image analyses of particles were used to aid in the interpretation of the chemical
profiles.
Twilight zone waters at 66°S in the Antarctic had a steeper decrease in POC with depth
than at 55°S in the Subantarctic, with lower POC concentrations in all size fractions at 66°S than
at 55°S, despite up to an order of magnitude higher POC in surface waters at 66°S. The decay
length scale of >51 Όm POC was significantly shorter in the upper twilight zone at 66°S (Ύe=26
m) compared to 55°S (Ύe=81 m).
Particles in the carbonate-producing 55°S did not have higher excess densities than
particles from the diatom-dominated 66°S, indicating that there was no direct ballast effect that
accounted for deeper POC penetration at 55°S. An indirect ballast effect due to differences in
particle packaging and porosities cannot be ruled out, however, as aggregate porosities were high
(~97%) and variable.
Image analyses point to the importance of particle loss rates from zooplankton grazing
and remineralization as determining factors for the difference in twilight zone POC concentrations at 55°S and 66°S, with stronger and more focused shallow remineralization at
66°S. At 66°S, an abundance of large (several mm long) fecal pellets from the surface to 150 m,
and almost total removal of large aggregates by 200 m, reflected the actions of a single or few
zooplankton species capable of grazing diatoms in the euphotic zone, coupled with a more
diverse particle feeding zooplankton community immediately below.
Surface waters with high biomass levels and high proportion of biomass in the large size
fraction were associated with low particle loading at depth, with all indications implying
conditions of low export. The 66°S region exhibits this âHigh Biomass, Low Exportâ (HBLE)
condition, with very high >51 ÎŒm POC concentrations at the surface (~2.1 ÎŒM POC), but low
concentrations below 200 m (<0.07 ΌM POC). The 66°S region remained HBLE after iron
fertilization. Iron addition at 55°S caused a ten fold increase in >51 Όm biomass concentrations
in the euphotic zone, bringing surface POC concentrations to levels found at 66°S (~3.8 ΌM),
and a concurrent decrease in POC concentrations below 200 m. The 55°S region, which began
with moderate levels of biomass and stronger particle export, transitioned to being HBLE after
iron fertilization. We propose that iron addition to already HBLE waters will not cause mass
sedimentation events. The stability of an iron-induced HBLE condition is unknown. Better
understanding of biological pump processes in non-HBLE Subantarctic waters is needed.This
work was supported by the DOE Office of Science, Biological and Environmental Research
Program. Shiptime for SOFeX was funded by NSF
The mean H alpha EW and Lyman- continuum photon production efficiency for faint z approximate to 4-5 galaxies
We present the first measurements of the Lyman-continuum photon production efficiency xi(ion.0) at z similar to 4-5 for galaxies fainter than 0.2 L* (-19 mag). xi(ion.0) quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero. Extending previous measurements of xi(ion.0) to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity. We probe xi(ion.0) to such faint magnitudes by taking advantage of 200-h depth Spitzer/IRAC observations from the GREATS program and approximate to 300 3 < z < 6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs. Stacked IRAC [3.6] [4.5] colors are derived and used to infer the H alpha rest-frame equivalent widths, which range from 403 angstrom to 2818 angstrom. The derived xi(ion.0) is log(10)(xi(ion.0)/Hz erg(-1)) = 25.36 0.08 over-20.5 < Muv <-17.5, similar to those derived for brighter galaxy samples at the same redshift and therefore suggesting that 6011 shows no strong dependence on M-UV. The xi(ion.0) values found in our sample imply that the Lyman-continuum escape fraction for M-UV approximate to-19 star-forming galaxies cannot exceed approximate to 8-20% in the reionization era
The mean H alpha EW and Lyman- continuum photon production efficiency for faint z approximate to 4-5 galaxies
We present the first measurements of the Lyman-continuum photon production efficiency xi(ion.0) at z similar to 4-5 for galaxies fainter than 0.2 L* (-19 mag). xi(ion.0) quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero. Extending previous measurements of xi(ion.0) to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity. We probe xi(ion.0) to such faint magnitudes by taking advantage of 200-h depth Spitzer/IRAC observations from the GREATS program and approximate to 300 3 < z < 6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs. Stacked IRAC [3.6] [4.5] colors are derived and used to infer the H alpha rest-frame equivalent widths, which range from 403 angstrom to 2818 angstrom. The derived xi(ion.0) is log(10)(xi(ion.0)/Hz erg(-1)) = 25.36 0.08 over-20.5 < Muv <-17.5, similar to those derived for brighter galaxy samples at the same redshift and therefore suggesting that 6011 shows no strong dependence on M-UV. The xi(ion.0) values found in our sample imply that the Lyman-continuum escape fraction for M-UV approximate to-19 star-forming galaxies cannot exceed approximate to 8-20% in the reionization era
Editorial: addiction studies at Trinity College Dublin
Plans for a special issue of Drugs: Education, Prevention and Policy based on the addiction studies component of what is now the School of Social Work and Social Policy at Trinity College Dublin were initially discussed and agreed during 2009, the 25th anniversary of the first cohort of students through Trinityâs Diploma in Addiction Studies. We had initially thought of holding a one-day conference to which we would invite Irish and international speakers but â with the support and encouragement of Professor Betsy Thom (Editor-in-Chief) â decided it might be more useful and less ephemeral to mark the anniversary by the production of a special issue of this journal.
Therefore, the articles in this issue were commissioned from staff and former students with a view, first of all, to allowing us to reflect on the overall experience of teaching addiction studies here at Trinity and, second, to explore a number of themes which, between them, might add to our understanding of addiction policy and practice in contemporary Ireland. The themes covered here are not, of course, unique to Ireland and we trust that the articles will be of interest and relevance to readers in other countries
Shaping of terminal megakaryocyte differentiation and proplatelet development by sphingosine-1-phosphate receptor S1P4.
Megakaryocytes, which mature from hematopoietic progenitors in the bone marrow, further differentiate by reorganizing their cytoplasm into long proplatelet extensions that release platelets into the circulation. The molecular mechanisms underlying this highly dynamic cytoplasmic and cytoskeletal remodeling process are only poorly understood. Here we report that sphingosine 1-phosphate receptor 4 (S1P(4)) is specifically up-regulated during the development of human megakaryocytes from progenitor cells and is expressed in mature murine megakaryocytes. Megakaryocytes generated from S1P(4)-deficient murine bone marrow showed atypical and reduced formation of proplatelets in vitro. The recovery of platelet numbers after experimental thrombocytopenia was significantly delayed in S1p4(-/-) mice. Remarkably, overexpression and stimulation of S1P(4) in human erythroleukemia HEL cells promoted endomitosis, formation of cytoplasmic extensions, and subsequent release of platelet-like particles. These observations indicate that S1P(4) is involved in shaping the terminal differentiation of megakaryocytes.-Golfier, S., Kondo, S., Schulze, T., Takeuchi, T., Vassileva, G., Achtman, A. H., Gräler, M. H., Abbondanzo, S. J., Wiekowski, M., Kremmer, E., Endo, Y., Lira, S. A., Bacon, K. B., Lipp, M. Shaping of terminal megakaryocyte differentiation and proplatelet development by sphingosine-1-phosphate receptor S1P(4)