Interstellar Silicate Dust in the z=0.89 Absorber Towards PKS 1830-211: Crystalline Silicates at High Redshift?

Abstract

We present evidence of a >10-sigma detection of the 10 micron silicate dust absorption feature in the spectrum of the gravitationally lensed quasar PKS 1830-211, produced by a foreground absorption system at redshift 0.886. We have examined more than 100 optical depth templates, derived from both observations of Galactic and extragalactic sources and laboratory measurements, in order to constrain the chemical structure of the silicate dust. We find that the best fit to the observed absorption profile is produced by laboratory crystalline olivine, with a corresponding peak optical depth of tau_10=0.27+/-0.05. The fit is slightly improved upon by including small contributions from additional materials such as silica, enstatite, or serpentine, which suggests that the dust composition may consist of a blend of crystalline silicates. Combining templates for amorphous and crystalline silicates, we find that the fraction of crystalline silicates needs to be at least 95%. Given the rarity of extragalactic sources with such a high degree of silicate crystallinity, we also explore the possibility that the observed spectral features are produced by amorphous silicates in combination with other molecular or atomic transitions, or by foreground source contamination. While we cannot rule out these latter possibilities, they lead to much poorer profile fits than for the crystalline olivine templates. If the presence of crystalline interstellar silicates in this distant galaxy is real, it would be highly unusual, given that the Milky Way interstellar matter contains essentially only amorphous silicates. It is possible that the z=0.886 absorber towards PKS 1830-211, well known for its high molecular content, has a unique star-forming environment that enables crystalline silicates to form and prevail.

67 pages, 21 figures, accepted for publication in the Astrophysical Journal

References in corpus (13)

• The distribution of silicate strength in Spitzer spectra of AGNs and ULIRGs
• A Spitzer mid-infrared spectral survey of mass-losing carbon stars in the Large Magellanic Cloud
• The Ucsd/Keck Damped Lya Abundance Database: A Decade of High Resolution Spectroscopy
• Spitzer Infrared Spectrograph Observations of Magellanic Cloud Planetary Nebulae: the nature of dust in low metallicity circumstellar ejecta
• A Spitzer Infrared Spectrograph Survey of Warm Molecular Hydrogen in Ultra-luminous Infrared Galaxies
• The Role of Sub-damped Lyman-alpha Absorbers in the Cosmic Evolution of Metals
• Probing isotopic ratios at z = 0.89: molecular line absorption in front of the quasar PKS 1830-211
• Detection of the 2175Å~ extinction feature and 21-cm absorption in two MgII systems at z~1.3
• Discovery of Extreme Carbon Stars in the Large Magellanic Cloud
• On the Crystallinity of Silicate Dust in the Interstellar Medium
• Drastic changes in the molecular absorption at redshift z=0.89 toward the quasar PKS 1830-211
• Submillimeter water and ammonia absorption by the peculiar z~0.89 interstellar medium in the gravitational lens of the PKS 1830-211 system
• 9.7 micrometer Silicate Absorption in a Damped Lyman-alpha Absorber at z=0.52

Cited by in corpus (14)

• Gamma-ray flaring activity from the gravitationally lensed blazar PKS 1830-211 observed by Fermi LAT
• Blind HI and OH absorption line search: first results with MALS and uGMRT processed using ARTIP
• The dust content of damped Lyman-alpha systems in the Sloan Digital Sky Survey
• PKS1830-211: OH and HI at z=0.89 and the first MeerKAT UHF spectrum
• Crystalline Silicates in Evolved Stars. I. Spitzer/IRS Spectroscopy of IRAS16456-3542, 18354-0638, and 23239+5754
• Search for Polycyclic Aromatic Hydrocarbons in the Outflows from Dust-Producing Wolf-Rayet Stars
• The inhomogeneous ISM toward PKS1830-211 SW - A detailed view on molecular gas at a look-back time of 7.5 Gyr
• A Tale of Three Galaxies: Anomalous Dust Properties in IRASF10398+1455, IRASF21013-0739 and SDSSJ0808+3948
• Interstellar Silicate Dust in the z=0.685 Absorber Toward TXS 0218+357
• Galaxies with Background QSOs: II. An Automated Search for Multiple Galaxy Emission Lines
• A systematic search for the spectra with features of crystalline silicates in the Spitzer IRS Enhanced Products
• A non cool-core 4.6-keV cluster around the bright nearby radio galaxy PKS B1416-493
• Carbonates and ices in the $z=0.89$ galaxy-absorber towards PKS 1830-211 and within star-forming regions of the Milky Way
• Probing the Interstellar Dust in Galaxies over > 10 Gyr of Cosmic History