The chemical and ionization conditions in weak mg II absorbers

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

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

We present an analysis of the chemical and ionization conditions in a sample of 100 weak Mg n absorbers identified in the VLT/UVES archive of quasar spectra. In addition to Mg II, we present equivalent width and column density measurements of other low ionization species such as Mg I, Fe II, Al II, C II, Si II, and also Al III. We find that the column densities of C II and Si II are strongly correlated with the column density of Mg II, with minimal scatter in the relationships. The column densities of Fe II exhibit an appreciable scatter when compared with the column density of Mg II, with some fraction of clouds having N(Fe II) ̃ N(Mg II), in which case the density is constrained to nH > 0.05 cm-3. Other clouds in which N(Fe II) » N(Mg II) have much lower densities. From ionization models, we infer that the metallicity in a significant fraction of weak Mg II clouds is constrained to values of solar or higher, if they are sub-Lyman-limit systems. Based on the observed constraints, we hypothesize that weak Mg n absorbers are predominantly tracing two different astrophysical processes/structures. A significant population of weak Mg II clouds, those in which N(Fe II) » N(Mg II), identified at both low (z ̃ 1) and high (z ̃ 2) redshift, are likely to be tracing gas in the extended halos of galaxies, analogous to the Galactic high-velocity clouds. These absorbers might correspond to a-enhanced interstellar gas expelled from star-forming galaxies, in correlated supernova events. The N(Mg II) and N(Fe II)/N(Mg II) in such clouds are also closely comparable to those measured for the high-velocity components in strong Mg n systems. An evolution is found in N(Fe II)/N(Mg II) fromz = 2.4 to z = 0.4, with an absence of weak Mg II clouds with N(Fe II)̃N(Mg II) at high-z. The N(Fe II) ̃N(Mg II) clouds, which are prevalent at lower redshifts (z < 1.5), must be tracing Type la enriched gas in small, high-metallicity pockets in dwarf galaxies, tidal debris, or other intergalactic structures.

Original languageEnglish (US)
Pages (from-to)782-815
Number of pages34
JournalAstrophysical Journal
Volume689
Issue number2
DOIs
StatePublished - Dec 20 2008

Fingerprint

absorbers
ionization
tracing
metallicity
gas
galaxies
interstellar gas
chemical
dwarf galaxies
gases
debris
quasars
supernovae
halos
astrophysics
stars

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Narayanan, Anand ; Charlton, Jane C. ; Misawa, Toru ; Green, Rebecca E. ; Kim, Tae Sun. / The chemical and ionization conditions in weak mg II absorbers. In: Astrophysical Journal. 2008 ; Vol. 689, No. 2. pp. 782-815.
@article{1639e35e065d4f66b550d398f5126371,
title = "The chemical and ionization conditions in weak mg II absorbers",
abstract = "We present an analysis of the chemical and ionization conditions in a sample of 100 weak Mg n absorbers identified in the VLT/UVES archive of quasar spectra. In addition to Mg II, we present equivalent width and column density measurements of other low ionization species such as Mg I, Fe II, Al II, C II, Si II, and also Al III. We find that the column densities of C II and Si II are strongly correlated with the column density of Mg II, with minimal scatter in the relationships. The column densities of Fe II exhibit an appreciable scatter when compared with the column density of Mg II, with some fraction of clouds having N(Fe II) ̃ N(Mg II), in which case the density is constrained to nH > 0.05 cm-3. Other clouds in which N(Fe II) » N(Mg II) have much lower densities. From ionization models, we infer that the metallicity in a significant fraction of weak Mg II clouds is constrained to values of solar or higher, if they are sub-Lyman-limit systems. Based on the observed constraints, we hypothesize that weak Mg n absorbers are predominantly tracing two different astrophysical processes/structures. A significant population of weak Mg II clouds, those in which N(Fe II) » N(Mg II), identified at both low (z ̃ 1) and high (z ̃ 2) redshift, are likely to be tracing gas in the extended halos of galaxies, analogous to the Galactic high-velocity clouds. These absorbers might correspond to a-enhanced interstellar gas expelled from star-forming galaxies, in correlated supernova events. The N(Mg II) and N(Fe II)/N(Mg II) in such clouds are also closely comparable to those measured for the high-velocity components in strong Mg n systems. An evolution is found in N(Fe II)/N(Mg II) fromz = 2.4 to z = 0.4, with an absence of weak Mg II clouds with N(Fe II)̃N(Mg II) at high-z. The N(Fe II) ̃N(Mg II) clouds, which are prevalent at lower redshifts (z < 1.5), must be tracing Type la enriched gas in small, high-metallicity pockets in dwarf galaxies, tidal debris, or other intergalactic structures.",
author = "Anand Narayanan and Charlton, {Jane C.} and Toru Misawa and Green, {Rebecca E.} and Kim, {Tae Sun}",
year = "2008",
month = "12",
day = "20",
doi = "10.1086/592763",
language = "English (US)",
volume = "689",
pages = "782--815",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2",

}

Narayanan, A, Charlton, JC, Misawa, T, Green, RE & Kim, TS 2008, 'The chemical and ionization conditions in weak mg II absorbers', Astrophysical Journal, vol. 689, no. 2, pp. 782-815. https://doi.org/10.1086/592763

The chemical and ionization conditions in weak mg II absorbers. / Narayanan, Anand; Charlton, Jane C.; Misawa, Toru; Green, Rebecca E.; Kim, Tae Sun.

In: Astrophysical Journal, Vol. 689, No. 2, 20.12.2008, p. 782-815.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The chemical and ionization conditions in weak mg II absorbers

AU - Narayanan, Anand

AU - Charlton, Jane C.

AU - Misawa, Toru

AU - Green, Rebecca E.

AU - Kim, Tae Sun

PY - 2008/12/20

Y1 - 2008/12/20

N2 - We present an analysis of the chemical and ionization conditions in a sample of 100 weak Mg n absorbers identified in the VLT/UVES archive of quasar spectra. In addition to Mg II, we present equivalent width and column density measurements of other low ionization species such as Mg I, Fe II, Al II, C II, Si II, and also Al III. We find that the column densities of C II and Si II are strongly correlated with the column density of Mg II, with minimal scatter in the relationships. The column densities of Fe II exhibit an appreciable scatter when compared with the column density of Mg II, with some fraction of clouds having N(Fe II) ̃ N(Mg II), in which case the density is constrained to nH > 0.05 cm-3. Other clouds in which N(Fe II) » N(Mg II) have much lower densities. From ionization models, we infer that the metallicity in a significant fraction of weak Mg II clouds is constrained to values of solar or higher, if they are sub-Lyman-limit systems. Based on the observed constraints, we hypothesize that weak Mg n absorbers are predominantly tracing two different astrophysical processes/structures. A significant population of weak Mg II clouds, those in which N(Fe II) » N(Mg II), identified at both low (z ̃ 1) and high (z ̃ 2) redshift, are likely to be tracing gas in the extended halos of galaxies, analogous to the Galactic high-velocity clouds. These absorbers might correspond to a-enhanced interstellar gas expelled from star-forming galaxies, in correlated supernova events. The N(Mg II) and N(Fe II)/N(Mg II) in such clouds are also closely comparable to those measured for the high-velocity components in strong Mg n systems. An evolution is found in N(Fe II)/N(Mg II) fromz = 2.4 to z = 0.4, with an absence of weak Mg II clouds with N(Fe II)̃N(Mg II) at high-z. The N(Fe II) ̃N(Mg II) clouds, which are prevalent at lower redshifts (z < 1.5), must be tracing Type la enriched gas in small, high-metallicity pockets in dwarf galaxies, tidal debris, or other intergalactic structures.

AB - We present an analysis of the chemical and ionization conditions in a sample of 100 weak Mg n absorbers identified in the VLT/UVES archive of quasar spectra. In addition to Mg II, we present equivalent width and column density measurements of other low ionization species such as Mg I, Fe II, Al II, C II, Si II, and also Al III. We find that the column densities of C II and Si II are strongly correlated with the column density of Mg II, with minimal scatter in the relationships. The column densities of Fe II exhibit an appreciable scatter when compared with the column density of Mg II, with some fraction of clouds having N(Fe II) ̃ N(Mg II), in which case the density is constrained to nH > 0.05 cm-3. Other clouds in which N(Fe II) » N(Mg II) have much lower densities. From ionization models, we infer that the metallicity in a significant fraction of weak Mg II clouds is constrained to values of solar or higher, if they are sub-Lyman-limit systems. Based on the observed constraints, we hypothesize that weak Mg n absorbers are predominantly tracing two different astrophysical processes/structures. A significant population of weak Mg II clouds, those in which N(Fe II) » N(Mg II), identified at both low (z ̃ 1) and high (z ̃ 2) redshift, are likely to be tracing gas in the extended halos of galaxies, analogous to the Galactic high-velocity clouds. These absorbers might correspond to a-enhanced interstellar gas expelled from star-forming galaxies, in correlated supernova events. The N(Mg II) and N(Fe II)/N(Mg II) in such clouds are also closely comparable to those measured for the high-velocity components in strong Mg n systems. An evolution is found in N(Fe II)/N(Mg II) fromz = 2.4 to z = 0.4, with an absence of weak Mg II clouds with N(Fe II)̃N(Mg II) at high-z. The N(Fe II) ̃N(Mg II) clouds, which are prevalent at lower redshifts (z < 1.5), must be tracing Type la enriched gas in small, high-metallicity pockets in dwarf galaxies, tidal debris, or other intergalactic structures.

UR - http://www.scopus.com/inward/record.url?scp=58149123036&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=58149123036&partnerID=8YFLogxK

U2 - 10.1086/592763

DO - 10.1086/592763

M3 - Article

AN - SCOPUS:58149123036

VL - 689

SP - 782

EP - 815

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

ER -