Galaxy formation and evolution

Abstract:

PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed 2.5-m optical/ infrared telescope to be located at Dome C on the Antarctic plateau. The atmospheric conditions at Dome C deliver a high sensitivity, high photometric precision, wide-field, high spatial resolution, and high-cadence imaging capability to the PILOT telescope. These capabilities enable a unique scientific potential for PILOT, which is addressed in this series of papers. The current paper presents a series of projects dealing with the distant (redshift >1) Universe, that have been identified as key science drivers for the PILOT facility. The potential for PILOT to detect the first populations of stars to form in the early Universe, via infrared projects searching for pair-instability supernovae and gamma-ray burst afterglows, is investigated. Two projects are proposed to examine the assembly and evolution of structure in the Universe: an infrared survey searching for the first evolved galaxies at high redshift, and an optical survey aimed at characterising moderate-redshift galaxy clusters. Finally, a large-area weak-lensing survey and a program to obtain supernova infrared light-curves are proposed to examine the nature and evolution of dark energy and dark matter. © Astronomical Society of Australia 2009.

Abstract:

We present the Spectroscopic Imaging survey in the near-infrared (near-IR) with SINFONI (SINS) of high-redshift galaxies. With 80 objects observed and 63 detected in at least one rest-frame optical nebular emission line, mainly Hα, SINS represents the largest survey of spatially resolved gas kinematics, morphologies, and physical properties of star-forming galaxies at z 1-3. We describe the selection of the targets, the observations, and the data reduction. We then focus on the "SINS Hα sample," consisting of 62 rest-UV/optically selected sources at 1.3 < z < 2.6 for which we targeted primarily the Hα and [N II] emission lines. Only ≈ 30% of this sample had previous near-IR spectroscopic observations. The galaxies were drawn from various imaging surveys with different photometric criteria; as a whole, the SINS Hα sample covers a reasonable representation of massive M* ≳ 1010 M ·star-forming galaxies at z 1.5-2.5, with some bias toward bluer systems compared to pure K-selected samples due to the requirement of secure optical redshift. The sample spans 2 orders of magnitude in stellar mass and in absolute and specific star formation rates, with median values ≈ 3 × 1010 M ·, ≈ 70 M· yr-1, and 3 Gyr-1. The ionized gas distribution and kinematics are spatially resolved on scales ranging from 1.5 kpc for adaptive optics assisted observations to typically 4-5 kpc for seeing-limited data. The Hα morphologies tend to be irregular and/or clumpy. About one-third of the SINS Hα sample galaxies are rotation-dominated yet turbulent disks, another one-third comprises compact and velocity dispersion-dominated objects, and the remaining galaxies are clear interacting/merging systems; the fraction of rotation-dominated systems increases among the more massive part of the sample. The Hα luminosities and equivalent widths suggest on average roughly twice higher dust attenuation toward the H II regions relative to the bulk of the stars, and comparable current and past-averaged star formation rates. © 2009. The American Astronomical Society.

Abstract:

We report on two quantitative, morphological estimators of the filamentary structure of the Cosmic Web, the so-called global and local skeletons. The first, based on a global study of the matter density gradient flow, allows us to study the connectivity between a density peak and its surroundings, with direct relevance to the anisotropic accretion via cold flows on galactic halos. From the second, based on a local constraint equation involving the derivatives of the field, we can derive predictions for powerful statistics, such as the differential length and the relative saddle to extrema counts of the Cosmic web as a function of density threshold (with application to percolation of structures and connectivity), as well as a theoretical framework to study their cosmic evolution through the onset of gravity-induced non-linearities.

Abstract:

Context. In the past decade or so, using numerical N-body simulations to describe the gravitational clustering of dark matter (DM) in an expanding universe has become the tool of choice for tackling the issue of hierarchical galaxy formation. As mass resolution increases with the power of supercomputers, one is able to grasp finer and finer details of this process, resolving more and more of the inner structure of collapsed objects. This begs one to revisit time and again the post-processing tools with which one transforms particles into "invisible" dark matter haloes and from thereon into luminous galaxies.Aims. Although a fair amount of work has been devoted to growing Monte-Carlo merger trees that resemble those built from an N-body simulation, comparatively little effort has been invested in quantifying the caveats one necessarily encounters when one extracts trees directly from such a simulation. To somewhat revert the tide, this paper seeks to provide its reader with a comprehensive study of the problems one faces when following this route.Methods. The first step in building merger histories of dark matter haloes and their subhaloes is to identify these structures in each of the time outputs (snapshots) produced by the simulation. Even though we discuss a particular implementation of such an algorithm (called AdaptaHOP) in this paper, we believe that our results do not depend on the exact details of the implementation but instead extend to most if not all (sub)structure finders. To illustrate this point in the appendix we compare AdaptaHOP's results to the standard friend-of-friend (FOF) algorithm, widely utilised in the astrophysical community. We then highlight different ways of building merger histories from AdaptaHOP haloes and subhaloes, contrasting their various advantages and drawbacks.Results. We find that the best approach to (sub)halo merging histories is through an analysis that goes back and forth between identification and tree building rather than one that conducts a straightforward sequential treatment of these two steps. This is rooted in the complexity of the merging trees that have to depict an inherently dynamical process from the partial temporal information contained in the collection of instantaneous snapshots available from the N-body simulation. However, we also propose a simpler sequential "Most massive Substructure Method" (MSM) whose trees approximate those obtained via the more complicated non sequential method. © 2009 ESO.