1996/09/11 by Michael Rauch, Martin G. Haehnelt, Matthias Steinmetz · 9 citations
Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Galaxy #Lyman limit #Metallicity #Optics #Physics #Redshift #Spectral line #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/304085
published as Astrophys.J.481:601-624,1997 · 41 pages, LaTeX , 19 postscript figures included; submitted to ApJ. The paper can also be retrieved at http://www.caltech.edu/~mr/preprints/clumps.ps.gz and at ftp://phobos.caltech.edu/users/mr/preprints/clumps.ps.gz
arxiv created 1996/09/11 · openalex publication_date 1997/06/01 · arxiv updated 2016/08/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
In a hierarchical cosmogony, galaxies build up by continuous merging of smaller structures. At z = 3, the matter content of a typical present-day galaxy is dispersed over several individual clumps embedded in sheetlike structures, often aligned along filaments. We have used hydrodynamical simulations to investigate the spatial distribution and absorption properties of metal-enriched gas in such regions of ongoing galaxy formation. The metal and hydrogen absorption features produced by the collapsing structures closely resemble observed QSO absorption systems over a wide range in H I column density. Strong C II and Si IV absorption occurs for lines of sight passing the densest regions close to the center of the protogalactic clumps, while C IV is a good tracer of the prominent filamentary structures and O VI becomes the strongest absorption feature for lines of sight passing through low-density regions far away from fully collapsed objects. The observed column density ratios of the different ionic species at z = 3 can be well reproduced if a mean metallicity [Z/H] = -2.5, relative abundances as found in metal-poor stars, a UV background with intensity J -22 = 3 at the Lyman limit, and either a power-law spectrum ( J ∝ ν -1.5 ) or the spectral shape proposed by Haardt & Madau are assumed. The observed scatter in [C/H] is about a magnitude larger than that in the simulations, which suggests an inhomogeneous metal distribution. Observed and simulated Doppler parameter distributions of H I and C IV absorption lines are in good agreement, which indicates that shock heating due to gravitational collapse is a second important heating agent in addition to photoionization heating. The large velocity spreads seen in some C IV systems may be due to the occasional alignments of the observer's line of sight with expanding large-scale filaments. Both high-ionization multicomponent heavy-element absorbers and damped Lyα systems can arise from groups of moderately sized protogalactic clumps ( M baryon ~ 10 9 M ☉ ). Recent detections of star-forming galaxies at similar redshifts are consistent with this picture.