2014/02/12 by Rajeshwari Dutta, R. Dutta, R. Srianand +4
Chemistry · Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atomic carbon #Chemistry #Galaxies: Formation, Evolution, Phenomena #Galaxy #Hydrogen #Ionization #Metal #Metallicity #Photoionization #Physics #Population #Quasar #Redshift #Spectral line #Star formation #Stellar, planetary, and galactic studies #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stu260
21 pages, 17 figures, 8 tables, Accepted for publication in the MNRAS
arxiv created 2014/02/12 · openalex publication_date 2014/03/10 · arxiv updated 2015/06/18 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present a detailed high spectral resolution (R ∼ 40 000) study of five high-z damped Lyman α systems (DLAs) and one sub- DLA detected along four QSO sightlines. Four of these DLAs are very metal poor with [Fe/H] ≤ −2. One of them, at zabs = 4.202 87 towards J0953−0504, is the most metal-poor DLA at z > 4 known till date. This system shows no enhancement of C over Fe and O, and standard Population II star yields can explain its relative abundance pattern. The DLA at zabs = 2.340 06 towards J0035−0918 has been claimed to be the most carbon-enhanced metal-poor DLA. However, we show that thermal broadening is dominant in this system and, when this effect is taken into account, the measured carbon enhancement ([C/Fe] = 0.45 ± 0.19) becomes ∼10 times less than what was reported previously. The gas temperature in this DLA is estimated to be in the range of 5000–8000 K, consistent with a warm neutral medium phase. From photoionization modelling of two of the DLAs showing C ii* absorption, we find that the metagalactic background radiation alone is not sufficient to explain the observed C ii* cooling rate, and local heating sources, probably produced by in situ star formation, are needed. Cosmic ray heating is found to contribute ≳60 per cent to the total heating in these systems. Using a sample of metal-poor DLAs with C ii* measurements, we conclude that the cosmic ray ionization rate is equal to or greater than that seen in the Milky Way in ∼33 per cent of the systems with C ii* detections.