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THE LUMINOSITY-LINEWIDTH RELATION AS A PROBE OF THE EVOLUTION OF FIELD GALAXIES
GUHATHAKURTA PURAGRA,ING KRISTINE,RIX HANS-WALTER,COLLESS MATTHEW,WILLIAMS TED The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1
The nature of distant faint blue field galaxies remains a mystery, despite the fact that much attention has been devoted to this subject in the last decade. Galaxy counts, particularly those in the optical and near ultraviolet bandpasses, have been demonstrated to be well in excess of those expected in the 'no-evolution' scenario. This has usually been taken to imply that galaxies were brighter in the past, presumably due to a higher rate of star formation. More recently, redshift surveys of galaxies as faint as B$\~$24 have shown that the mean redshift of faint blue galaxies is lower than that predicted by standard evolutionary models (de-signed to fit the galaxy counts). The galaxy number count data and redshift data suggest that evolutionary effects are most prominent at the faint end of the galaxy luminosity function. While these data constrain the form of evolution of the overall luminosity function, they do not constrain evolution in individual galaxies. We are carrying out a series of observations as part of a long-term program aimed at a better understanding of the nature and amount of luminosity evolution in individual galaxies. Our study uses the luminosity-linewidth relation (Tully-Fisher relation) for disk galaxies as a tool to study luminosity evolution. Several studies of a related nature are being carried out by other groups. A specific experiment to test a 'no-evolution' hypothesis is presented here. We have used the AUTOFIB multifibre spectro-graph on the 4-metre Anglo-Australian Telescope (AAT) and the Rutgers Fabry-Perot imager on the Cerro Tolalo lnteramerican Observatory (CTIO) 4-metre tele-scope to measure the internal kinematics of a representative sample of faint blue field galaxies in the red-shift range z = 0.15-0.4. The emission line profiles of [OII] and [OIII] in a typical sample galaxy are significantly broader than the instrumental resolution (100-120 km $s^{-l}$), and it is possible to make a reliable de-termination of the linewidth. Detailed and realistic simulations based on the properties of nearby, low-luminosity spirals are used to convert the measured linewidth into an estimate of the characteristic rotation speed, making statistical corrections for the effects of inclination, non-uniform distribution of ionized gas, rotation curve shape, finite fibre aperture, etc.. The (corrected) mean characteristic rotation speed for our distant galaxy sample is compared to the mean rotation speed of local galaxies of comparable blue luminosity and colour. The typical galaxy in our distant sample has a B-band luminosity of about 0.25 L$\ast$ and a colour that corresponds to the Sb-Sd/Im range of Hub-ble types. Details of the AUTOFIB fibre spectroscopic study are described by Rix et al. (1996). Follow-up deep near infrared imaging with the 10-metre Keck tele-scope+ NIRC combination and high angular resolution imaging with the Hubble Space Telescope's WFPC2 are being used to determine the structural and orientation parameters of galaxies on an individual basis. This information is being combined with the spatially resolved CTIO Fabry-Perot data to study the internal kinematics of distant galaxies (Ing et al. 1996). The two main questions addressed by these (preliminary studies) are: 1. Do galaxies of a given luminosity and colour have the same characteristic rotation speed in the distant and local Universe? The distant galaxies in our AUTOFIB sample have a mean characteristic rotation speed of $\~$70 km $s^{-l}$ after correction for measurement bias (Fig. 1); this is inconsistent with the characteristic rotation speed of local galaxies of comparable photometric proper-ties (105 km $s^{-l}$) at the > $99\%$ significance level (Fig. 2). A straightforward explanation for this discrepancy is that faint blue galaxies were about 1-1.5 mag brighter (in the B band) at z $\~$ 0.25 than their present-day counterparts. 2. What i
THE SEGUE K GIANT SURVEY. III. QUANTIFYING GALACTIC HALO SUBSTRUCTURE
Janesh, William,Morrison, Heather L.,Ma, Zhibo,Rockosi, Constance,Starkenburg, Else,Xue, Xiang Xiang,Rix, Hans-Walter,Harding, Paul,Beers, Timothy C.,Johnson, Jennifer,Lee, Young Sun,Schneider, Donald American Astronomical Society 2016 The Astrophysical journal Vol.816 No.2
<P>We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5-125 kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey's Sloan Extension for Galactic Understanding and Exploration project. Using a position-velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earlier work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (similar to 33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity.</P>
An ALMA [C ii] Survey of 27 Quasars at<i>z</i>> 5.94
Decarli, Roberto,Walter, Fabian,Venemans, Bram P.,Bañ,ados, Eduardo,Bertoldi, Frank,Carilli, Chris,Fan, Xiaohui,Farina, Emanuele Paolo,Mazzucchelli, Chiara,Riechers, Dominik,Rix, Hans-Walter,Str American Astronomical Society 2018 The Astrophysical journal Vol.854 No.2
Dust Emission in an Accretion-rate-limited Sample of <i>z</i> ≳ 6 Quasars
Venemans, Bram P.,Decarli, Roberto,Walter, Fabian,Bañ,ados, Eduardo,Bertoldi, Frank,Fan, Xiaohui,Farina, Emanuele Paolo,Mazzucchelli, Chiara,Riechers, Dominik,Rix, Hans-Walter,Wang, Ran,Yang, Yu American Astronomical Society 2018 The Astrophysical journal Vol.866 No.2
Sustainable Development and Energy Geotechnology− Potential Roles for Geotechnical Engineering
R. J. Fragaszy,산타마리나,A. Amekudzi,D. Assimaki,R. Bachus,S. E. Burns,M. Cha,조계춘,D. D. Cortes,S. Dai,D. N. Espinoza,L. Garrow,H. Huang,J. Jang,J. W. Jung,S. Kim,K. Kurtis,이창호,C. Pasten,H. Phadnis,G. Rix 대한토목학회 2011 KSCE Journal of Civil Engineering Vol.15 No.4
The world is facing unprecedented challenges related to energy resources, global climate change, material use, and waste generation. Failure to address these challenges will inhibit the growth of the developing world and will negatively impact the standard of living and security of future generations in all nations. The solutions to these challenges will require multidisciplinary research across the social and physical sciences and engineering. Although perhaps not always recognized, geotechnical engineering expertise is critical to the solution of many energy and sustainability-related problems. Hence, geotechnical engineers and academicians have opportunity and responsibility to contribute to the solution of these worldwide problems. Research will need to be extended to non-standard issues such as thermal properties of soils; sediment and rock response to extreme conditions and at very long time scales; coupled hydro-chemo-thermo-bio-mechanical processes; positive feedback systems; the development of discontinuities; biological modification of soil properties; spatial variability; and emergent phenomena. Clearly, the challenges facing geotechnical engineering in the future will require a much broader knowledge base than our traditional educational programs provide. The geotechnical engineering curricula, from undergraduate education through continuing professional education, must address the changing needs of a profession that will increasingly be engaged in alternative/renewable energy production; energy efficiency; sustainable design, enhanced and more efficient use of natural resources, waste management, and underground utilization.