Spitzer IRAC infrared colours of submillimetre-bright galaxies     

Min S. Yun  Itziar Aretxaga  Matthew L. N. Ashby  Jason Austermann  Giovanni G. Fazio  Mauro Giavalisco  Jia–Sheng Huang  David H. Hughes  Sungeun Kim  James D. Lowenthal  Thushara Perera  Kim Scott  Grant Wilson  Joshua D. Younger 《Monthly notices of the Royal Astronomical Society》2008,389(1):333-340

High-redshift submillimetre-bright galaxies identified by blank field surveys at millimetre and submillimetre wavelengths appear in the region of the Infra Red Array Camera (IRAC) colour–colour diagrams previously identified as the domain of luminous active galactic nuclei (AGNs). Our analysis using a set of empirical and theoretical dusty starburst spectral energy distribution (SED) models shows that power-law continuum sources associated with hot dust heated by young (≲100 Myr old), extreme starbursts at z > 2 also occupy the same general area as AGNs in the IRAC colour–colour plots. A detailed comparison of the IRAC colours and SEDs demonstrates that the two populations are distinct from each other, with submillimetre-bright galaxies having a systematically flatter IRAC spectrum (≳1 mag bluer in the observed [4.5]–[8.0] colour). Only about 20 per cent of the objects overlap in the colour–colour plots, and this low fraction suggests that submillimetre galaxies powered by a dust-obscured AGN are not common. The red infrared colours of the submillimetre galaxies are distinct from those of the ubiquitous foreground IRAC sources, and we propose a set of infrared colour selection criteria for identifying SMG counterparts that can be used even in the absence of radio or Multiband Imaging Photometer for Spitzer (MIPS) 24 μm data.  相似文献   

An AzTEC 1.1 mm survey of the GOODS-N field – II. Multiwavelength identifications and redshift distribution     

Edward L. Chapin  Alexandra Pope †  Douglas Scott  Itziar Aretxaga  Jason E. Austermann  Ranga-Ram Chary  Kristen Coppin  Mark Halpern  David H. Hughes  James D. Lowenthal  Glenn E. Morrison  Thushara A. Perera  Kimberly S. Scott  Grant W. Wilson  Min S. Yun 《Monthly notices of the Royal Astronomical Society》2009,398(4):1793-1808

We present results from a multiwavelength study of 29 sources (false detection probabilities <5 per cent) from a survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field at 1.1 mm using the Astronomical Thermal Emission Camera (AzTEC). Comparing with existing 850 μm Submillimetre Common-User Bolometer Array (SCUBA) studies in the field, we examine differences in the source populations selected at the two wavelengths. The AzTEC observations uniformly cover the entire survey field to a 1σ depth of ∼1 mJy. Searching deep 1.4 GHz Very Large Array (VLA) and Spitzer 3–24 μm catalogues, we identify robust counterparts for 21 1.1 mm sources, and tentative associations for the remaining objects. The redshift distribution of AzTEC sources is inferred from available spectroscopic and photometric redshifts. We find a median redshift of   z = 2.7  , somewhat higher than   z = 2.0  for  850 μm  selected sources in the same field, and our lowest redshift identification lies at a spectroscopic redshift   z = 1.1460  . We measure the 850 μm to 1.1 mm colour of our sources and do not find evidence for '850 μm dropouts', which can be explained by the low signal-to-noise ratio of the observations. We also combine these observed colours with spectroscopic redshifts to derive the range of dust temperatures T , and dust emissivity indices β for the sample, concluding that existing estimates   T ∼ 30 K  and  β∼ 1.75  are consistent with these new data.  相似文献   

Predicting plausible impacts of sets of climate and land use change scenarios on water resources   总被引：3，自引：0，他引：3  

Susanna T.Y. Tong  Yu SunThushara Ranatunga  Jie HeY. Jeffrey Yang 《Applied geography (Sevenoaks, England)》2012,32(2):477-489

Our world is changing at an unprecedented rate in terms of climate and land use, but these changes can affect our water resources. Hence, we need a methodology that can predict both their individual and agglomerative ramifications. Using the Little Miami River (LMR) watershed as a case study, this paper describes a spatial analytical approach integrating mathematical modeling and geographical information sciences to quantitatively examine the relative importance of the separate and combined hydrologic and water quality impacts of climate and land use changes.The Hydrologic Simulation Program - Fortran (HSPF) model was chosen in this study to simulate stream flow and nutrient transport process. Five hypothetical climate change scenarios were used to cover the possible ranges of variability in the year 2050. An enhanced population-coupled Markov-Cellular Automata (CA-Markov) land use model was developed to predict the 2050 land use pattern. When these scenarios were incorporated into the HSPF model, the future conditions in the LMR basin were postulated. The findings demonstrated that: 1) the LMR watershed would experience an increase in flow and nutrients under the 2050 land use projection, 2) stream flow and water quality impacts would be amplified when both climate and land use changes were simultaneously considered, 3) land use change (and in the case of the LMR watershed, urbanization) could help to alleviate water shortage during the dry years, 4) total phosphorus and nitrogen would increase under all future climate and land use scenarios; the highest increase was found under the combined wettest and future land use scenarios, and 5) the described approach is effective in simulating the hydrologic and water quality effects of climate and land use changes in a basin scale. These results are relevant to planners; they can be useful in formulating realistic watershed management policies and mitigation measures.  相似文献   

An approach to measure parameter sensitivity in watershed hydrological modelling     

Thushara Ranatunga  Y. Jeffrey Yang 《水文科学杂志》2017,62(1):76-92

Hydrological responses vary spatially and temporally according to watershed characteristics. In this study, the hydrological models that we developed earlier for the Little Miami River (LMR) and Las Vegas Wash (LVW) watersheds in the USA were used for detailed sensitivity analyses. To compare the relative sensitivities of the hydrological parameters of these two models, we used normalized root mean square error (NRMSE). By combining the NRMSE index with the flow duration curve analysis, we derived an approach to measure parameter sensitivities under different flow regimes. Results show that the parameters related to groundwater are highly sensitive in the LMR watershed, whereas the LVW watershed is primarily sensitive to near-surface and impervious parameters. The high and medium flows are more impacted by most of the parameters. The low flow regime was highly sensitive to groundwater-related parameters. Moreover, our approach is found to be useful in facilitating model development and calibration.