A survey of weak Mg II absorbers at 0.4 < z < 2.4

Anand Narayanan, Toru Misawa, Jane C. Charlton, Tae Sun Kim

Research output: Contribution to journalReview article

32 Citations (Scopus)

Abstract

We present results from a survey of weak Mg II absorbers in the VLT/UVES spectra of 81 QSOs obtained from the ESO archive. In this survey, we identified 112 weak Mg II systems within the redshift interval 0.4 < z < 2.4 with 86% completeness down to a rest-frame equivalent width of Wr(2796) = 0.02 Å, covering a cumulative redshift path length of ΔZ ∼ 77.3. From this sample, we estimate that the number of weak absorbers per unit redshift (dN/dz) increases from 1.06 ± 0.04 at 〈z〉 = 1.9 to 1.76 ± 0.08 at 〈z〉 = 1.2 and thereafter decreases to 1.51 ± 0.09 at 〈z〉 = 0.9 and 1.06 ± 0.10 at 〈z〉 = 0.6. Thus, we find evidence for an evolution in the population of weak Mg II absorbers, with their number density peaking at z = 1.2. We also determine the equivalent width distribution of weak systems at 〈z〉 = 0.9 and 〈z〉 = 1.9. At 0.4 < z < 1.4, there is evidence for a turnover from a power law of the form n(Wr) ∝ Wr -1.04 at Wr(2796) < 0.1 Å. This turnover is more extreme at 1.4 < z < 2.4, where the equivalent width distribution is close to an extrapolation of the exponential distribution function found for strong Mg II absorbers. Based on these results, we discuss the possibility that some fraction of weak Mg II absorbers, particularly single cloud systems, are related to satellite clouds surrounding strong Mg II systems. These structures could also be analogs to Milky Way high-velocity clouds. In this context, the paucity of high-redshift weak Mg II absorbers is caused by a lack of isolated clouds accreting onto galaxies during that epoch.

Original languageEnglish (US)
Pages (from-to)1093-1105
Number of pages13
JournalAstrophysical Journal
Volume660
Issue number2 I
DOIs
StatePublished - May 10 2007

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absorbers
turnover
power law
exponential functions
completeness
European Southern Observatory
quasars
extrapolation
coverings
distribution functions
time measurement
analogs
galaxies
intervals
distribution
estimates

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Narayanan, Anand ; Misawa, Toru ; Charlton, Jane C. ; Kim, Tae Sun. / A survey of weak Mg II absorbers at 0.4 < z < 2.4. In: Astrophysical Journal. 2007 ; Vol. 660, No. 2 I. pp. 1093-1105.
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title = "A survey of weak Mg II absorbers at 0.4 < z < 2.4",
abstract = "We present results from a survey of weak Mg II absorbers in the VLT/UVES spectra of 81 QSOs obtained from the ESO archive. In this survey, we identified 112 weak Mg II systems within the redshift interval 0.4 < z < 2.4 with 86{\%} completeness down to a rest-frame equivalent width of Wr(2796) = 0.02 {\AA}, covering a cumulative redshift path length of ΔZ ∼ 77.3. From this sample, we estimate that the number of weak absorbers per unit redshift (dN/dz) increases from 1.06 ± 0.04 at 〈z〉 = 1.9 to 1.76 ± 0.08 at 〈z〉 = 1.2 and thereafter decreases to 1.51 ± 0.09 at 〈z〉 = 0.9 and 1.06 ± 0.10 at 〈z〉 = 0.6. Thus, we find evidence for an evolution in the population of weak Mg II absorbers, with their number density peaking at z = 1.2. We also determine the equivalent width distribution of weak systems at 〈z〉 = 0.9 and 〈z〉 = 1.9. At 0.4 < z < 1.4, there is evidence for a turnover from a power law of the form n(Wr) ∝ Wr -1.04 at Wr(2796) < 0.1 {\AA}. This turnover is more extreme at 1.4 < z < 2.4, where the equivalent width distribution is close to an extrapolation of the exponential distribution function found for strong Mg II absorbers. Based on these results, we discuss the possibility that some fraction of weak Mg II absorbers, particularly single cloud systems, are related to satellite clouds surrounding strong Mg II systems. These structures could also be analogs to Milky Way high-velocity clouds. In this context, the paucity of high-redshift weak Mg II absorbers is caused by a lack of isolated clouds accreting onto galaxies during that epoch.",
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Narayanan, A, Misawa, T, Charlton, JC & Kim, TS 2007, 'A survey of weak Mg II absorbers at 0.4 < z < 2.4', Astrophysical Journal, vol. 660, no. 2 I, pp. 1093-1105. https://doi.org/10.1086/512852

A survey of weak Mg II absorbers at 0.4 < z < 2.4. / Narayanan, Anand; Misawa, Toru; Charlton, Jane C.; Kim, Tae Sun.

In: Astrophysical Journal, Vol. 660, No. 2 I, 10.05.2007, p. 1093-1105.

Research output: Contribution to journalReview article

TY - JOUR

T1 - A survey of weak Mg II absorbers at 0.4 < z < 2.4

AU - Narayanan, Anand

AU - Misawa, Toru

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AU - Kim, Tae Sun

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N2 - We present results from a survey of weak Mg II absorbers in the VLT/UVES spectra of 81 QSOs obtained from the ESO archive. In this survey, we identified 112 weak Mg II systems within the redshift interval 0.4 < z < 2.4 with 86% completeness down to a rest-frame equivalent width of Wr(2796) = 0.02 Å, covering a cumulative redshift path length of ΔZ ∼ 77.3. From this sample, we estimate that the number of weak absorbers per unit redshift (dN/dz) increases from 1.06 ± 0.04 at 〈z〉 = 1.9 to 1.76 ± 0.08 at 〈z〉 = 1.2 and thereafter decreases to 1.51 ± 0.09 at 〈z〉 = 0.9 and 1.06 ± 0.10 at 〈z〉 = 0.6. Thus, we find evidence for an evolution in the population of weak Mg II absorbers, with their number density peaking at z = 1.2. We also determine the equivalent width distribution of weak systems at 〈z〉 = 0.9 and 〈z〉 = 1.9. At 0.4 < z < 1.4, there is evidence for a turnover from a power law of the form n(Wr) ∝ Wr -1.04 at Wr(2796) < 0.1 Å. This turnover is more extreme at 1.4 < z < 2.4, where the equivalent width distribution is close to an extrapolation of the exponential distribution function found for strong Mg II absorbers. Based on these results, we discuss the possibility that some fraction of weak Mg II absorbers, particularly single cloud systems, are related to satellite clouds surrounding strong Mg II systems. These structures could also be analogs to Milky Way high-velocity clouds. In this context, the paucity of high-redshift weak Mg II absorbers is caused by a lack of isolated clouds accreting onto galaxies during that epoch.

AB - We present results from a survey of weak Mg II absorbers in the VLT/UVES spectra of 81 QSOs obtained from the ESO archive. In this survey, we identified 112 weak Mg II systems within the redshift interval 0.4 < z < 2.4 with 86% completeness down to a rest-frame equivalent width of Wr(2796) = 0.02 Å, covering a cumulative redshift path length of ΔZ ∼ 77.3. From this sample, we estimate that the number of weak absorbers per unit redshift (dN/dz) increases from 1.06 ± 0.04 at 〈z〉 = 1.9 to 1.76 ± 0.08 at 〈z〉 = 1.2 and thereafter decreases to 1.51 ± 0.09 at 〈z〉 = 0.9 and 1.06 ± 0.10 at 〈z〉 = 0.6. Thus, we find evidence for an evolution in the population of weak Mg II absorbers, with their number density peaking at z = 1.2. We also determine the equivalent width distribution of weak systems at 〈z〉 = 0.9 and 〈z〉 = 1.9. At 0.4 < z < 1.4, there is evidence for a turnover from a power law of the form n(Wr) ∝ Wr -1.04 at Wr(2796) < 0.1 Å. This turnover is more extreme at 1.4 < z < 2.4, where the equivalent width distribution is close to an extrapolation of the exponential distribution function found for strong Mg II absorbers. Based on these results, we discuss the possibility that some fraction of weak Mg II absorbers, particularly single cloud systems, are related to satellite clouds surrounding strong Mg II systems. These structures could also be analogs to Milky Way high-velocity clouds. In this context, the paucity of high-redshift weak Mg II absorbers is caused by a lack of isolated clouds accreting onto galaxies during that epoch.

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