Extremely Large Telescope

Abstract:

Aims. We aim to demonstrate that the Herschel-ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods. We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results. We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme. © 2010 ESO.

Abstract:

We present observations of a very massive galaxy at z = 1.82 that show that its morphology, size, velocity dispersion, and stellar population properties are fully consistent with those expected for passively evolving progenitors of today's giant ellipticals. These findings are based on a deep optical rest-frame spectrum obtained with the Multi-Object InfraRed Camera and Spectrograph on the Subaru Telescope of a high-z passive galaxy candidate (pBzK) from the COSMOS field, for which we accurately measure its redshift of z = 1.8230 and obtain an upper limit on its velocity dispersion σ* < 326 km s-1. By detailed stellar population modeling of both the galaxy broadband spectral energy distribution and the rest-frame optical spectrum, we derive a star formation-weighted age and formation redshift of tsf ≃ 1-2 Gyr and zform ≃ 2.5-4, and a stellar mass of M * ≃ (3-4) × 1011 M⊙. This is in agreement with a virial mass limit of Mvir < 7 × 1011 M⊙, derived from the measured σ* value and stellar half-light radius, as well as with the dynamical mass limit based on the Jeans equations. In contrast to previously reported super-dense passive galaxies at z ∼ 2, the present galaxy at z = 1.82 appears to have both size and velocity dispersion similar to early-type galaxies in the local universe with similar stellar mass. This suggests that z 2 massive and passive galaxies may exhibit a wide range of properties, then possibly following quite different evolutionary histories from z ∼ 2 to z = 0. © 2010 The American Astronomical Society. All rights reserved.