9,228 research outputs found
A star-forming galaxy at z= 5.78 in the Chandra Deep Field South
No full textWe report the discovery of a luminous z = 5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an ‘i-drop’ from the GOODS public survey imaging with the Hubble Space Telescope/Advanced Camera for Surveys (object 3 in the work of Stanway, Bunker & McMahon 2003). The large colour of (i′−z′)AB = 1.6 indicated a spectral break consistent with the Lyman α forest absorption shortward of Lyman α at z≈ 6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08 arcsec, so rhl 5. Our spectroscopic redshift for this object confirms the validity of the i′-drop technique of Stanway et al. to select star-forming galaxies atz≈ 6
The star formation rate of the Universe atz≈ 6 from the Hubble ultra-Deep Field
No full textWe determine the abundance of i′-band dropouts in the recently released HST/ACS Hubble Ultra-Deep Field (UDF). Because the majority of these sources are likely to be z≈ 6 galaxies whose flux decrement between the F775W i′-band and F850LP z′-band arises from Lyman-α absorption, the number of detected candidates provides a valuable upper limit to the unextincted star formation rate at this redshift. We demonstrate that the increased depth of UDF enables us to reach an 8 σ limiting magnitude of z′AB= 28.5 (equivalent to 1.5 h−270 M⊙ yr−1 at z= 6.1, or 0.1 L⋆UV for the z≈ 3U-drop population), permitting us to address earlier ambiguities arising from the unobserved form of the luminosity function. We identify 54 galaxies (and only one star) at z′AB 1.3 over the deepest 11-arcmin2 portion of the UDF. The characteristic luminosity (L⋆) is consistent with values observed at z≈ 3. The faint end slope (α) is less well constrained, but is consistent with only modest evolution. The main change appears to be in the number density (Φ*). Specifically, and regardless of possible contamination from cool stars and lower-redshift sources, the UDF data support our previous result that the star formation rate at z≈ 6 was approximately six times less than at z≈ 3. This declining comoving star formation rate [0.005 h70 M⊙ yr−1 Mpc−3 at z≈ 6 at LUV > 0.1 L⋆ for a Salpeter initial mass function (IMF)] poses an interesting challenge for models which suggest that LUV > 0.1 L⋆ star-forming galaxies at z≃ 6 reionized the Universe. The short-fall in ionizing photons might be alleviated by galaxies fainter than our limit, or a radically different IMF. Alternatively, the bulk of reionization might have occurred at z≫ 6
Lyman break galaxies and the star formation rate of the Universe at z ~ 6
No full textWe determine the space density of UV-luminous starburst galaxies at z≈ 6 using deep HST ACS SDSS-i′ (F775W) and SDSS-z′ (F850LP) and VLT ISAAC J and Ks band imaging of the Chandra Deep Field South. We find eight galaxies and one star with (i′−z′) > 1.5 to a depth of z′AB= 25.6 (an 8σ detection in each of the 3 available ACS epochs). This corresponds to an unobscured star formation rate of ≈15 h−270 M⊙ yr−1 at z= 5.9, equivalent to L* for the Lyman-break population at z= 3–4 (ΩΛ= 0.7, ΩM= 0.3). We are sensitive to star-forming galaxies at 5.6 ≲z≲ 7.0 with an effective comoving volume of ≈1.8 × 105h−370 Mpc3 after accounting for incompleteness at the higher redshifts due to luminosity bias. This volume should encompass the primeval subgalactic-scale fragments of the progenitors of about a thousand L* galaxies at the current epoch. We determine a volume-averaged global star formation rate of (6.7 ± 2.7) × 10−4h70 M⊙ yr−1 Mpc−3 at z∼ 6 from rest-frame UV selected starbursts at the bright end of the luminosity function: this is a lower limit because of dust obscuration and galaxies below our sensitivity limit. This measurement shows that at z∼ 6 the star formation density at the bright end is a factor of ∼6 times less than that determined by Steidel et al. for a comparable sample of UV-selected galaxies at z= 3–4, and so extends our knowledge of the star formation history of the Universe to earlier times than previous work and into the epoch where reionization may have occurred
Migrant’s Remittances: Channeling Globalization (with R. G. Anghel, M. Piracha), In L.S. Talani and S. McMahon (Eds.), Handbook of International Political Economy of Migration, Edward Elgar Publishing, 2015. ISBN: 9781782549895
No full textMigrants’ Remittances: Channeling Globalization
No full textMigration is a global phenomenon which touches every country in the world as sending, transit or receiving countries. Remittances represent one of the most consistent outcomes of migration. Through remittances, migrants transfer funds, information, ideas and practices. Remittances link societies of origin and destination by multiple processes of mobility and exchange
Effect of in-season moisture on carbon, nitrogen, and phosphorus in alkaline, semi-arid soils
No full textClaire McMahon, Roger Armstrong, Therese McBeath and Mike McLaughli
Reply [to “Comment on ‘Evaluation of automated techniques for base flow and recession analyses’ by R. J. Nathan and T. A. McMahon”]
No full textA set of nine principles for distributed-design information storing
No full textThe issues of distributed working are many, with problems relating to information access and information acquisition the most common (Crabtree et al., 1997). Keeping track of project and team information is becoming more complex as design is increasingly being carried out collaboratively by geographically dispersed design teams across different time zones. The literature notes that little prescription or guidance exists on information management for designers (Culley et al., 1999) and Hicks (2007) highlights a relative lack of overall principles for improving information management. Additionally, evidence from earlier studies by the author into ‘How information is stored in distributed design project work’ reinforces the need for guidance, particularly in a distributed context (Grierson, 2008). Distributed information collections were found to be unorganised, contained unclear information and lacked context. Storing and sharing of distributed information was often time consuming and the tools awkward to use. This can lead to poor project progress and can impact directly on the quality and success of project outcomes (Grierson et al., 2004, 2006). This paper seeks to address these issues by presenting the development, implementation and evaluation of a set of Principles and a Framework to support distributed design information storing in the context of a Global Design class. Through both quantitative and qualitative evaluation methods the Principles were found to help in a number of ways – with the easy access of information; the structuring and organising of information; the creation of an information strategy; the making of information clear and concise; the supporting of documentation during project work; and the strengthening of team work; all helping teams to work towards project outcomes
The devil in the (demographic) detail
No full textCorey J. A. Bradshaw, Clive R. McMahon and Barry W. Broo
First report of Pseudomonas syringae on olives (Olea europaea) in South Australia
No full textPseudomonas syringae was recorded on olives (Olea europaea) for the first time in South Australia in March 2001 from a property approximately 30 km south of Adelaide, South Australia. The bacterium was recovered from sunken brown stem lesions on 2-year-old olive trees cv. Barnea. In the following season from December 2001, further infections were observed on 3-year-old trees of the same cultivar in an adjacent planting on the same property, with branch death occurring on many of the affected trees.B. H. Hall, E. J. Cother, D. Noble, R. McMahon and T. J. Wick
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