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High-redshift Galaxies (high-redshift + galaxy)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

A homogeneous sample of sub-damped Lyman systems , IV.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007
Global metallicity evolution
ABSTRACT An accurate method to measure the abundance of high-redshift galaxies involves the observation of absorbers along the line of sight towards a background quasar. Here, we present abundance measurements of 13 z, 3 sub-damped Lyman , (sub-DLA) systems (quasar absorbers with H i column density in the range 19 < log N(H i) < 20.3 cm,2) based on high-resolution observations with the VLT UVES spectrograph. These observations more than double the amount of metallicity information for sub-DLAs available at z > 3. These new data, combined with other sub-DLA measurements from the literature, confirm the stronger evolution of metallicity with redshift for sub-DLAs than for the classical damped Lyman , absorbers. In addition, these observations are used to compute for the first time, using photoionization modelling in a sample of sub-DLAs, the fraction of gas that is ionized. Based on these results, we calculate that sub-DLAs contribute no more than 6 per cent of the expected amount of metals at z, 2.5. We therefore conclude that, even if sub-DLAs are found to be more metal-rich than classical DLAs, their contribution is insufficient to solve the so-called ,missing-metals' problem. [source]

The kinematical structure of gravitationally lensed arcs

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
Ole Möller
ABSTRACT In this paper, the expected properties of the velocity fields of strongly lensed arcs behind galaxy clusters are investigated. The velocity profile along typical lensed arcs is determined by ray-tracing light rays from a model source galaxy through parametric cluster toy models consisting of individual galaxies embedded in a dark cluster halo. We find that strongly lensed arcs of high-redshift galaxies show complex velocity structures that are sensitive to the details of the mass distribution within the cluster, in particular at small scales. From fits to the simulated imaging and kinematic data, we demonstrate that reconstruction of the source velocity field is in principle feasible. Two-dimensional kinematic information obtained with integral field units on large ground-based telescopes in combination with adaptive optics will allow the reconstruction of rotation curves of lensed high redshift galaxies. This makes it possible to determine the mass-to-light ratios of galaxies at redshifts z > 1 out to about 2,3 scalelengths with better than ,20 per cent accuracy. We also discuss the possibilities of using two-dimensional kinematic information along the arcs to give additional constraints on the cluster lens mass models. [source]

Mission: impossible (escape from the Lyman limit)

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2003
A. Fernández-Soto
ABSTRACT We investigate the intrinsic opacity of high-redshift galaxies to outgoing ionizing photons using high-quality photometry of a sample of 27 spectroscopically identified galaxies of redshift 1.9 < z < 3.5 in the Hubble Deep Field. Our measurement is based on maximum-likelihood fitting of model galaxy spectral energy distributions , including the effects of intrinsic Lyman-limit absorption and random realizations of intervening Lyman-series and Lyman-limit absorption , to photometry of galaxies from space- and ground-based broad-band images. Our method provides several important advantages over the methods used by previous groups, including most importantly that two-dimensional sky subtraction of faint-galaxy images is more robust than one-dimensional sky subtraction of faint-galaxy spectra. We find at the 3,statistical confidence level that on average no more than 4 per cent of the ionizing photons escape galaxies of redshift 1.9 < z < 3.5. This result is consistent with observations of low- and moderate-redshift galaxies but is in direct contradiction to a recent result based on medium-resolution spectroscopy of high-redshift (z, 3) galaxies. Dividing our sample into subsamples according to luminosity, intrinsic ultraviolet colour and redshift, we find no evidence for selection effects that could explain such a discrepancy. Even when all systematic effects are included, the data could not realistically accommodate any escape fraction value larger than ,15 per cent. [source]

The nature of high-redshift galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001
Rachel S. Somerville
Using semi-analytic models of galaxy formation set within the cold dark matter (CDM) merging hierarchy, we investigate several scenarios for the nature of the high-redshift ) Lyman-break galaxies (LBGs). We consider a ,collisional starburst' model in which bursts of star formation are triggered by galaxy,galaxy mergers, and find that a significant fraction of LBGs are predicted to be starbursts. This model reproduces the observed comoving number density of bright LBGs as a function of redshift and the observed luminosity function at and with a reasonable amount of dust extinction. Model galaxies at have star formation rates, half-light radii, colours and internal velocity dispersions that are in good agreement with the data. Global quantities such as the star formation rate density and cold gas and metal content of the Universe as a function of redshift also agree well. Two ,quiescent' models without starbursts are also investigated. In one, the star formation efficiency in galaxies remains constant with redshift, while in the other, it scales inversely with disc dynamical time, and thus increases rapidly with redshift. The first quiescent model is strongly ruled out, as it does not produce enough high-redshift galaxies once realistic dust extinction is accounted for. The second quiescent model fits marginally, but underproduces cold gas and very bright galaxies at high redshift. A general conclusion is that star formation at high redshift must be more efficient than locally. The collisional starburst model appears to accomplish this naturally without violating other observational constraints. [source]

Disc formation and the origin of clumpy galaxies at high redshift

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2009
Oscar Agertz
ABSTRACT Observations of high-redshift galaxies have revealed a multitude of large clumpy rapidly star-forming galaxies. Their formation scenario and their link to present-day spirals are still unknown. In this Letter, we perform adaptive mesh refinement simulations of disc formation in a cosmological context that are unrivalled in terms of mass and spatial resolution. We find that the so-called ,chain-galaxies' and ,clump-clusters' are a natural outcome of early epochs of enhanced gas accretion from cold dense streams as well as tidally and ram-pressured stripped material from minor mergers and satellites. Through interaction with the hot halo gas, this freshly accreted cold gas settles into a large disc-like system, not necessarily aligned to an older stellar component, that undergoes fragmentation and subsequent star formation, forming large clumps in the mass range 107,109 M,. Galaxy formation is a complex process at this important epoch when most of the central baryons are being acquired through a range of different mechanisms , we highlight that a rapid mass loading epoch is required to fuel the fragmentation taking place in the massive arms in the outskirts of extended discs, an accretion mode that occurs naturally in the hierarchical assembly process at early epochs. [source]