Herschel ATLAS: The cosmic star formation history of quasar host galaxies

We present a derivation of the star formation rate per comoving volume of quasar host galaxies, derived from stacking analyses of far-infrared to mm-wave photometry of quasars with redshifts 0 I_(AB) > -32 We use the science demonstration observations of the first ~16 deg^2 from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) in which there are 240 quasars from the Sloan Digital Sky Survey (SDSS) and a further 171 from the 2dF-SDSS LRG and QSO (2SLAQ) survey. We supplement this data with a compilation of data from IRAS, ISO, Spitzer, SCUBA and MAMBO. H-ATLAS alone statistically detects the quasars in its survey area at >5σ at 250,350 and 500 μm. From the compilation as a whole we find striking evidence of downsizing in quasar host galaxy formation: low-luminosity quasars with absolute magnitudes in the range -22 > I_(AB) > -24 have a comoving star formation rate (derived from 100 μm rest-frame luminosities) peaking between redshifts of 1 and 2, while high-luminosity quasars with I_(AB) I_(AB) > -24 quasars evolves as (1 + z)^(2.3±0.7) at z I_(AB) > -28. We tentatively interpret this as a combination of a declining major merger rate with time and gas consumption reducing fuel for both black hole accretion and star formation

Far-infrared constraints on the contamination by dust-obscured galaxies of high-z dropout searches

The spectral energy distributions (SED) of dusty galaxies at intermediate redshift may look similar to very high-redshift galaxies in the optical/near infrared (NIR) domain. This can lead to the contamination of high-redshift galaxy searches based on broad-band optical/NIR photometry by lower redshift dusty galaxies because both kind of galaxies cannot be distinguished. The contamination rate could be as high as 50%. This work shows how the far-infrared (FIR) domain can help to recognize likely low-z interlopers in an optical/NIR search for high-z galaxies. We analyze the FIR SEDs of two galaxies that are proposed to be very high-redshift (z > 7) dropout candidates based on deep Hawk-I/VLT observations. The FIR SEDs are sampled with PACS/Herschel at 100 and 160 μm, with SPIRE/Herschel at 250, 350 and 500 μm and with LABOCA/APEX at 870 μm. We find that redshifts > 7 would imply extreme FIR SEDs (with dust temperatures >100 K and FIR luminosities >10^(13) L_⊙). At z ~ 2, instead, the SEDs of both sources would be compatible with those of typical ultra luminous infrared galaxies or submillimeter galaxies. Considering all available data for these sources from visible to FIR we re-estimate the redshifts and find z ~ 1.6–2.5. Owing to the strong spectral breaks observed in these galaxies, standard templates from the literature fail to reproduce the visible-to-near-IR part of the SEDs even when additional extinction is included. These sources strongly resemble dust-obscured galaxies selected in Spitzer observations with extreme visible-to-FIR colors, and the galaxy GN10 at z = 4. Galaxies with similar SEDs could contaminate other high-redshift surveys

Detecting gravitational lensing cosmic shear from samples of several galaxies using two-dimensional spectral imaging

Studies of weak gravitational lensing by large-scale structures require the measurement of the distortions introduced to the shapes of distant galaxies at the few percent level by anisotropic light deflection along the line of sight. To detect this signal on 1-10 arcmin scales in a particular field, accurate measurements of the correlations between the shapes of order 1000-10000 galaxies are required. This large-scale averaging is required to accommodate the unknown intrinsic shapes of the background galaxies, even with careful removal of systematic effects. Here an alternative is discussed. If it is possible to measure accurately the detailed dynamical structure of the background galaxies, in particular rotating disks, then it should be possible to measure directly the cosmic shear distortion, as it generally leads to a non-self-consistent rotation curve. Narrow spectral lines and excellent two-dimensional spatial resolution are required. The ideal lines and telescope are CO rotational transitions and the Atacama Large Millimeter Array (ALMA) respectively.Comment: 12 pages, 4 figures, Expected to appear in ApJ Letters Vol. 570, 10 May 2002. Replaced with final proof version correcting minor typo

Translations of culture and identity : a study of Internet use in the Haitian community

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2005.Includes bibliographical references (p. 83-95).Despite the reality of the digital divide, over the years many bridges have been built over this chasm; diverse people of diverse backgrounds, cultures and countries utilize computers and their inherent technologies. One of the communities that use the Internet is the Haitian community. A detailed study on what the Haitian community - citizens and those of the Diaspora - finds in the Internet, what they make of this tool and how they relate its possibilities to themselves will reveal a profusion of information about both the Haitian culture and about the Internet. This ethnographic research will shed light on how useful the Internet is to this particular community. These findings may be used to engineer design that is more specific to the needs of this community. This 'culturized' study is presented through the lens of theoretical frameworks that view the user as playing a dominant role in defining the nature, scope and functions of the technology. This research hopes to focus on users and the way in which they shape the Internet media to have meaning in their everyday life and culture. The research examines the way in which the role of the technology is shaped within the domestic environment - how it is manipulated to compliment existing patterns of behavior and routine. The purpose of this research is to ask what domestic Internet users do with their media and how they construct it as meaningful in the existing network of everyday life. A qualitative approach has been adopted, which prioritizes the role of the user.by Johanne A. Blain.S.M