Cospatial 21 cm and metal-line absorbers in the epoch of reionization -- I : Incidence and observability

Abstract

Overdense, metal-rich regions, shielded from stellar radiation might remain neutral throughout reionization and produce metal as well as 21 cm absorption lines. Simultaneous absorption from metals and 21 cm can complement each other as probes of underlying gas properties. We use Aurora, a suite of high resolution radiation-hydrodynamical simulations of galaxy formation, to investigate the occurrence of such "aligned" absorbers. We calculate absorption spectra for 21 cm, OI, CII, SiII and FeII. We find velocity windows with absorption from at least one metal and 21 cm, and classify the aligned absorbers into two categories: 'aligned and cospatial absorbers' and 'aligned but not cospatial absorbers'. While 'aligned and cospatial absorbers' originate from overdense structures and can be used to trace gas properties, 'aligned but not cospatial absorbers' are due to peculiar velocity effects. The incidence of absorbers is redshift dependent, as it is dictated by the interplay between reionization and metal enrichment, and shows a peak at $z\approx 8$ for the aligned and cospatial absorbers. While aligned but not cospatial absorbers disappear towards the end of reionization because of the lack of an ambient 21 cm forest, aligned and cospatial absorbers are associated with overdense pockets of neutral gas which can be found at lower redshift. We produce mock observations for a set of sightlines for the next generation of telescopes like the ELT and SKA1-LOW, finding that given a sufficiently bright background quasar, these telescopes will be able to detect both types of absorbers throughout reionization.

Accepted in MNRAS. Comments welcome

References in corpus (24)

• The NumPy array: a structure for efficient numerical computation
• A luminous quasar at a redshift of z = 7.085
• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• Chemical enrichment in cosmological, smoothed particle hydrodynamics simulations
• Model-independent evidence in favor of an end to reionization by z~6
• A Luminous Quasar at Redshift 7.642
• The Global 21 Centimeter Background from High Redshifts
• Evolution of the 21 cm signal throughout cosmic history
• A downturn in intergalactic CIV as redshift 6 is approached
• TRAPHIC - Radiative Transfer for Smoothed Particle Hydrodynamics Simulations
• Intergalactic CIV absorption at redshifts 5.4 to 6
• The discovery of a highly accreting, radio-loud quasar at z=6.82
• New Constraints on Quasar Evolution: Broad Line Velocity Shifts over $1.5\lesssim z\lesssim 7.5$
• High Redshift Intergalactic C IV Abundance Measurements from the Near-Infrared Spectra of Two z~6 QSOs
• Multi-frequency, thermally coupled radiative transfer with TRAPHIC: Method and tests
• Constraining the quasar radio-loud fraction at $z\sim 6$ with deep radio observations
• The ionizing background at the end of overlap
• A deep search for metals near redshift 7: the line-of-sight towards ULAS J1120+0641
• The evolution of the Si IV content in the Universe from the epoch of reionization to cosmic noon
• The earliest galaxies seen in 21 cm line absorption
• Aligned metal absorbers and the ultraviolet background at the end of reionization
• Simulated metal and HI absorption lines at the conclusion of Reionization
• SCUBA2 High Redshift Bright Quasar Survey: Far-infrared Properties and Weak-line Features
• A [C II] 158$\mu$m Emitter Associated with an OI Absorber at the End of the Reionization Epoch