5 research outputs found
A comprehensive study on the relation between the metal enrichment of ionised and atomic gas in star-forming galaxies
We study the relation between the metallicities of ionised and neutral gas in
star-forming galaxies at z=0-3 using the EAGLE cosmological, hydrodynamical
simulations. This is done by constructing a dense grid of sightlines through
the simulated galaxies and obtaining the star formation rate- and HI column
density-weighted metallicities, Z_{SFR} and Z_{HI}, for each sightline as
proxies for the metallicities of ionised and neutral gas, respectively. We find
Z_{SFR} > Z_{HI} for almost all sightlines, with their difference generally
increasing with decreasing metallicity. The stellar masses of galaxies do not
have a significant effect on this trend, but the positions of the sightlines
with respect to the galaxy centres play an important role: the difference
between the two metallicities decreases when moving towards the galaxy centres,
and saturates to a minimum value in the central regions of galaxies,
irrespective of redshift and stellar mass. This implies that the mixing of the
two gas phases is most efficient in the central regions of galaxies where
sightlines generally have high column densities of HI. However, a high HI
column density alone does not guarantee a small difference between the two
metallicities. In galaxy outskirts, the inefficiency of the mixing of
star-forming gas with HI seems to dominate over the dilution of heavy elements
in HI through mixing with the pristine gas. We find good agreement between the
available observational data and the ZSFR-ZHI relation predicted by the EAGLE
simulations. Though, observed regions with a nuclear starburst mode of star
formation appear not to follow the same relation.Comment: Under review with Ap
The distribution and properties of DLAs at z ≤ 2 in the EAGLE simulations
Determining the spatial distribution and intrinsic physical properties of neutral hydrogen on cosmological scales is one of the key goals of next-generation radio surveys. We use the EAGLE galaxy formation simulations to assess the properties of damped Lyman α absorbers (DLAs) that are associated with galaxies and their underlying dark matter haloes between 0 ≤ z ≤ 2. We find that the covering fraction of DLAs increases at higher redshift; a significant fraction of neutral atomic hydrogen (H I) resides in the outskirts of galaxies with stellar mass ≥1010 M⊙; and the covering fraction of DLAs in the circumgalactic medium (CGM) is enhanced relative to that of the interstellar medium (ISM) with increasing halo mass. Moreover, we find that the mean density of the H I in galaxies increases with increasing stellar mass, while the DLAs in high- and low-halo mass systems have higher column densities than those in galaxies with intermediate halo masses (∼1012 M⊙ at z = 0). These high-impact CGM DLAs in high-stellar mass systems tend to be metal poor, likely tracing smooth accretion. Overall, our results point to the CGM playing an important role in DLA studies at high redshift (z ≥ 1). However, their properties are impacted both by numerical resolution and the detailed feedback prescriptions employed in cosmological simulations, particularly that of active galactic nuclei
The First Large Absorption Survey in H i (FLASH): I. Science goals and survey design
We describe the scientific goals and survey design of the First Large
Absorption Survey in HI (FLASH), a wide field survey for 21-cm line absorption
in neutral atomic hydrogen (HI) at intermediate cosmological redshifts. FLASH
will be carried out with the Australian Square Kilometre Array Pathfinder
(ASKAP) radio telescope and is planned to cover the sky south of deg at frequencies between 711.5 and 999.5MHz. At redshifts between
and (look back times of 4 - 8Gyr), the HI content of the
Universe has been poorly explored due to the difficulty of carrying out radio
surveys for faint 21-cm line emission and, at ultra-violet wavelengths,
space-borne searches for Damped Lyman- absorption in quasar spectra.
The ASKAP wide field of view and large spectral bandwidth, in combination with
a radio-quiet site, will enable a search for absorption lines in the radio
spectra of bright continuum sources over 80% of the sky. This survey is
expected to detect at least several hundred intervening 21-cm absorbers, and
will produce an HI-absorption-selected catalogue of galaxies rich in cool,
star-forming gas, some of which may be concealed from optical surveys.
Likewise, at least several hundred associated 21-cm absorbers are expected to
be detected within the host galaxies of radio sources at ,
providing valuable kinematical information for models of gas accretion and
jet-driven feedback in radio-loud active galactic nuclei. FLASH will also
detect OH 18-cm absorbers in diffuse molecular gas, megamaser OH emission,
radio recombination lines, and stacked HI emission.Comment: 31 pages, 10 figures, 6 tables, accepted for publication in PAS
The First Large Absorption Survey in H I (FLASH): I. science goals and survey design
We describe the scientific goals and survey design of the First Large Absorption Survey in HI (FLASH), a wide field survey for 21-cm line absorption in neutral atomic hydrogen (H I) at intermediate cosmological redshifts. FLASH will be carried out with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope and is planned to cover the sky south of δ≈+40 deg at frequencies between 711.5 and 999.5MHz. At redshifts between z = 0.4 and 1.0 (look-back times of 4 – 8Gyr), the H I content of the Universe has been poorly explored due
to the difficulty of carrying out radio surveys for faint 21-cm line emission and, at ultra-violet wavelengths, space-borne searches for Damped Lyman-α absorption in quasar spectra. The ASKAP wide field of view and large spectral bandwidth, in combination with a radio-quiet site, will enable a search for absorption lines in the radio spectra of bright continuum sources over 80% of the sky. This survey is expected to detect at least several hundred intervening 21-cm absorbers and will produce an H I-absorption-selected catalogue of galaxies rich in cool, star-forming gas, some of which may be concealed from optical surveys. Likewise, at least several hundred associated 21-cm absorbers are expected to be detected within the host galaxies of radio sources at 0.4 <z <1.0, providing valuable kinematical information for models of gas accretion and jet-driven feedback in radio-loud active galactic nuclei. FLASH will also detect OH 18-cm absorbers in diffuse molecular gas, megamaser OH emission, radio recombination lines, and stacked H I emission