A deep search for 21-cm absorption in high redshift damped Lyman-<i>α</i>systems

Kanekar, Nissim; Chengalur, Jayaram N.

doi:10.1051/0004-6361:20021922

Cited by 122 publications

(249 citation statements)

References 73 publications

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“…It can be seen that depletion is larger, [Fe/Zn] ∼ −0.65, in the strongest absorption component. It should be noticed that 21 cm absorption has been reported by Kanekar & Chengalur (2003) at this velocity (∼−28 km s −1 ), revealing dense gas. The difference in depletion between the strongest subcomponent (at −28 km s −1 ) and the gas at v ∼ −40 km s −1 is significant (about a factor of two larger than 3σ).…”

Section: Q 1157+014mentioning

confidence: 64%

Relative abundance pattern along the profile of high redshift Damped Lyman-$\vec \alpha$ systems

Rodriguez¹,

Petitjean

Aracil³

et al. 2006

A&A

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We investigated abundance ratios along the profiles of six high-redshift Damped Lyman-α systems, three of them associated with H 2 absorption, and derived optical depths in each velocity pixel. The variations of the pixel abundance ratios were found to be remarkably small and usually smaller than a factor of two within a profile. This result holds even when considering independent sub-clumps in the same system. The depletion factor is significantly enhanced only in those components where H 2 is detected. There is a strong correlation between [Fe/S] and [Si/S] abundances ratios, showing that the abundance ratio patterns are definitely related to the presence of dust. The depletion pattern is usually close to the one seen in the warm halo gas of our Galaxy.

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Section: Q 1157+014mentioning

confidence: 64%

Relative abundance pattern along the profile of high redshift Damped Lyman-$\vec \alpha$ systems

Rodriguez¹,

Petitjean

Aracil³

et al. 2006

A&A

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“…Perhaps we are penalized by the small number statistics or, more important, there may be fundamental differences between high and low redshift DLAs. The results by Kanekar & Chengalur (2003) may be relevant here. Indeed, they derived estimates of the spin temperature, T s , in 24 DLAs and found that all DLAs with high spin temperatures, T s > 1000 K, are identified with dwarf or low surface brightness galaxies, while DLAs with low T s are associated with large, luminous galaxies.…”

Section: Summary and Concluding Remarksmentioning

confidence: 86%

A new comprehensive set of elemental abundances in DLAs

Dessauges‐Zavadsky¹,

Prochaska

D’Odorico

et al. 2005

A&A

101

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We present new, comprehensive sets of elemental abundances for seven damped Lyα systems (DLAs) in the redshift range z abs = 1.8−2.5. These were derived from UVES/VLT spectra combined with existing HIRES/Keck spectra. We detected 54 metal-line transitions, and obtained the column density measurements of 30 ions from 22 elements, − B, C, N, O, Mg, Al, Si, P, S, Cl, Ar, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, As, Kr. Together with the four DLAs analyzed in Dessauges-Zavadsky et al. (2004, A&A, 416, 79), we have a sample of eleven DLA galaxies with uniquely comprehensive and homogeneous abundance measurements. These observations allow one to study in detail the abundance patterns of a wide range of elements and the chemical variations in the interstellar medium of galaxies outside the Local Group. Comparing the gas-phase abundance ratios of these high redshift galaxies, we found that they show low rms dispersions, reaching only up 2-3 times the statistical errors for the majority of elements. This uniformity is remarkable given that the quasar sightlines cross gaseous regions with H i column densities spanning over one order of magnitude and metallicities ranging from 1/55 to 1/5 solar. The uniformity is also remarkable since DLAs are expected (and observed at low redshift) to be associated with a wide range of galaxy types. This implies the respective star formation histories seem to have conspired to yield one set of relative abundances. We examined the gas-phase abundance patterns of interstellar medium "clouds" within the DLA galaxies detected along the velocity profiles. By considering all the clouds of all the DLAs studied together, we observe a high dispersion in several abundance ratios, indicating that chemical variations seem to be more confined to individual clouds within the DLA galaxies than to integrated profiles. We found unambiguous correlations between [Si/Fe] The sources of these variations are both the differential dust depletion and/or ionization effects; however, no evidence for variations due to different star formation histories could be highlighted. These observations place large constraints on the mixing timescales of protogalaxies and on scenarios of galaxy formation within the CDM hierarchical theory. Finally, we provide an astrophysical determination of the oscillator strength of the Ni ii λ 1317 transition.

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“…More recently, Kanekar & Chengalur (2003) deduced a 95% confidence lower limit of T s > 1:4 Â 10 4 K for the z ¼ 3:062 DLA toward Q0336À01. By contrast, we infer an equilibrium temperature of %100 K from the presence of C ii* absorption in this DLA (see Table 1 in Paper I).…”

Section: No 1 2003mentioning

confidence: 99%

“…Whereas spin temperatures in nearby spirals are less than 300 K (Dickey & Lockman 1990), the spin temperatures in most DLAs exceed 500 K (Chengalur & Kanekar 2000). The discrepancy is greatest at z > 3, where several DLAs exhibit T s > 2000 K. Because the kinetic temperature, T, equals the spin temperature in most scenarios, the high values of T s have been interpreted as indicators of gas in the WNM rather than CNM phase (Carilli et al 1996;Kanekar & Chengalur 2001;Chengalur & Kanekar 2000). This poses an interesting dilemma, as C ii* absorption, which must arise in the CNM in most DLAs, is detected in two DLAs with high inferred spin temperatures.…”

Section: High Spin Temperatures At Large Redshiftsmentioning

confidence: 99%

Cii* Absorption in Damped Lyα Systems. II. A New Window on the Star Formation History of the Universe

Wolfe

Gawiser

Prochaska

2003

ApJ

115

146

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Starting from the star formation rate (SFR) per unit area, _ Ã Ã , determined for damped Ly systems (DLAs) using the C ii* method, we obtain the SFR per unit comoving volume, _ Ã Ã ðzÞ, at z % 3. Pure warm neutral medium (WNM) solutions are ruled out since they generate more bolometric background radiation than observed, but the two-phase solutions dominated by the cold neutral medium (CNM) are consistent with the backgrounds. We find that _ Ã Ã ðzÞ for DLAs agrees with the _ Ã Ã ðzÞ for the Lyman break galaxies (LBGs). Although the mass of produced stars indicated by the SFRs is consistent with the current densities of known stellar populations, the mass of metals produced by z ¼ 2:5 is 30 times larger than detected in absorption in DLAs. Of the three possible solutions to this '' missing metals '' problem, the most likely appears to be that star formation occurs in compact bulge regions. We search for evidence of feedback and find no correlations between _ Ã Ã and N(H i), but possible correlations between _ Ã Ã and low-ion velocity width and _ Ã Ã and metal abundance. We show that (1) the correlation between cooling rate and dust-to-gas ratio is positive evidence for grain photoelectric heating, (2) the cosmic microwave background (CMB) does not significantly populate the C ii excited fine-structure states, and (3) the ratio of C ii* to resonance-line optical depths is a sensitive probe of the multiphase structure of the DLA gas. We address recent arguments that DLAs are comprised only of WNM gas and show them to be inconclusive. Despite the rough agreement between _ Ã Ã ðzÞ for DLAs and LBGs, current evidence indicates that these are distinct populations.

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A deep search for 21-cm absorption in high redshift damped Lyman-αsystems

Cited by 122 publications

References 73 publications

Relative abundance pattern along the profile of high redshift Damped Lyman-$\vec \alpha$ systems

Relative abundance pattern along the profile of high redshift Damped Lyman-$\vec \alpha$ systems

A new comprehensive set of elemental abundances in DLAs

Cii* Absorption in Damped Lyα Systems. II. A New Window on the Star Formation History of the Universe

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