We study the evolution of galaxies and the circumgalactic medium (CGM) through cosmic time by correlating ∼50,000 Mg ii absorbers, tracers of cool gas (∼104 K), detected in the Sloan Digital Sky ...Survey quasar spectra with galaxies detected in the DESI Legacy Imaging Surveys. By doing so, we extract the properties of galaxies associated with absorbers from redshift 0.4 to 1.3 with effectively ∼15,000 pairs and explore the covering fraction of Mg ii absorbers as a function of galaxy type, stellar mass, impact parameter, and redshift. We find that the gas covering fraction increases with stellar mass of galaxies by . However, after we normalize the impact parameter by the virial radius of dark matter halos, the gas profiles around galaxies with masses ranging from 109 to become weakly dependent on stellar mass. In addition, the gas distribution depends on galaxy type: the covering fraction within around star-forming galaxies is 2-4 times higher than that around passive galaxies at all redshifts. We find that the covering fraction of strong absorbers ( ) around both types of galaxies evolves significantly with redshift, similarly to the evolution of star formation rate (SFR) of galaxies, while such an evolution is not detected for weak absorbers ( ). We quantify the H i mass traced by strong absorbers and find that the gas mass around galaxies evolves consistently with the SFR of galaxies. This result suggests that the properties of galaxies and their CGM coevolve through cosmic time. Finally, we discuss the origins of strong absorbers around passive galaxies and argue that its redshift evolution may trace the star formation activity of satellite galaxies.
We study the distribution and kinematics of the cool circumgalactic medium (CGM) of emission line galaxies (ELGs) traced by metal absorption lines. Using about 200,000 ELGs from SDSS-IV eBOSS and ...half a million background quasars from SDSS, we measure the median absorption strength of Mg ii and Fe ii lines in quasar spectra for impact parameters ranging from 10 kpc to 1 Mpc. For comparison, we measure the same quantity around luminous red galaxies (LRGs). On scales greater than 100 kpc both ELGs and LRGs exhibit similar absorption profiles. However, metal absorption is 5-10 times stronger around ELGs on smaller scales. The metal absorption strength is anisotropic, with an excess along the minor axis of the galaxies, indicating an outflow origin of the absorbing gas. The ratio between the velocity dispersion of the cool CGM and that of its host dark matter halo is about one for ELGs but about half for LRGs. These results show that the dichotomy of galaxy types is reflected in both the density distribution and kinematics of the CGM traced by metal absorption lines. Our results provide strong evidence that the CGM of ELGs is enriched by gas outflows generated by star formation.
Metal abundance and its evolution are studied for Mg ii quasar absorption line systems from their weak, unsaturated spectral lines using stacked spectra from the archived data of the Sloan Digital ...Sky Survey. They show an abundance pattern that resembles that of the Galactic halo or Small Magellanic Cloud, with metallicity Z/H showing an evolution from redshift z = 2 to 0.5: metallicity becomes approximately solar or even larger at . We show that the evolution of the metal abundance traces the cumulative amount of the hydrogen fuel consumed in star formation in galaxies. With the aid of a spectroscopic simulation code, we infer the median gas density of the cloud to be roughly 0.3 , with which the elemental abundance in various ionization stages, in particular C i, is consistently explained. This gas density implies that the size of the Mg ii clouds is of the order of 0.03 kpc, which suggests that individual Mg ii clouds around a galaxy are of a baryonic mass typically . This means that Mg ii clouds are numerous and "foamy," rather than a large entity that covers a sizable fraction of galaxies with a single cloud.
On the environments of giant radio galaxies Lan 藍鼎文, Ting-Wen; Xavier Prochaska, J
Monthly notices of the Royal Astronomical Society,
04/2021, Volume:
502, Issue:
4
Journal Article
Peer reviewed
Open access
ABSTRACT
We test the hypothesis that environments play a key role in enabling the growth of enormous radio structures spanning more than 700 kpc, an extreme population of radio galaxies called giant ...radio galaxies (GRGs). To achieve this, we explore (1) the relationships between the occurrence of GRGs and the surface number density of surrounding galaxies, including satellite galaxies and galaxies from neighbouring haloes, and (2) the GRG locations towards large-scale structures. The analysis is done by making use of a homogeneous sample of 110 GRGs detected from the LOFAR Two-metre Sky Survey in combination with photometric galaxies from the DESI Legacy Imaging Surveys and a large-scale filament catalogue from the Sloan Digital Sky Survey. Our results show that the properties of galaxies around GRGs are similar with that around the two control samples, consisting of galaxies with optical colours and luminosity matched to the properties of the GRG host galaxies. Additionally, the properties of surrounding galaxies depend on neither their relative positions to the radio jet/lobe structures nor the sizes of GRGs. We also find that the locations of GRGs and the control samples with respect to the nearby large-scale structures are consistent with each other. These results demonstrate that there is no correlation between the GRG properties and their environments traced by stars, indicating that external galaxy environments are not the primary cause of the large sizes of the radio structures. Finally, regarding radio feedback, we show that the fraction of blue satellites does not correlate with the GRG properties, suggesting that the current epoch of radio jets has minimal influence on the nature of their surrounding galaxies.
We characterize the luminosity functions of galaxies residing in z ∼ 0 groups and clusters over the broadest ranges of luminosity and mass reachable by the Sloan Digital Sky Survey. Our measurements ...cover four orders of magnitude in luminosity, down to about M
r = −12 mag or L = 107 L⊙, and three orders of magnitude in halo mass, from 1012 to 1015 M⊙. We find a characteristic scale, M
r ∼ −18 mag or L ∼ 109 L⊙, below which the slope of the luminosity function becomes systematically steeper. This trend is present for all halo masses and originates mostly from red satellites. This ubiquitous faint-end upturn suggests that it is formation, rather than halo-specific environmental effect, that plays a major role in regulating the stellar masses of faint satellites. We show that the satellite luminosity functions can be described in a simple manner by a double Schechter function with amplitudes scaling with halo mass over the entire range of observables. Combining these conditional luminosity functions with the dark matter halo mass function, we accurately recover the entire field luminosity function over 10 visual magnitudes and reveal that satellite galaxies dominate the field luminosity function at magnitudes fainter than −17. We find that the luminosity functions of blue and red satellite galaxies show distinct shapes and we present estimates of the stellar mass fraction as a function of halo mass and galaxy type. Finally, using a simple model, we demonstrate that the abundances and the faint-end slopes of blue and red satellite galaxies can be interpreted in terms of their formation history, with two distinct modes separated by some characteristic time.
ABSTRACT
We study the properties of magnetic fields in the circumgalactic medium (CGM) of z < 1 galaxies by correlating Faraday rotation measures (RMs) of ∼1000 high-redshift radio sources with the ...foreground galaxy number density estimated from the DESI Legacy Imaging Surveys. This method enables us to extract signals of RMs contributed by intervening gas around multiple galaxies. Our results show that there is no detectable correlation between the distribution of RMs and the number of foreground galaxies, contrary to several previous results. Utilizing the non-detection signals, we estimate 3σ upper limits to the RMs from the CGM of $\sim \!20 \rm \ rad\, m^{-2}$ within 50 kpc and $\sim \!10 \rm \ rad \, m^{-2}$ at separations of 100 kpc. By adopting a column density distribution of ionized gas obtained from absorption-line measurements, we further estimate the strengths of coherent magnetic fields parallel to the line of sight of $\lt \rm 2 \ \mu G$ in the CGM. We show that the estimated upper limits of RMs and magnetic field strengths are sufficient to constrain outputs of recent galaxy magnetohydrodynamic simulations. Finally, we discuss possible causes for the inconsistency between our results and previous works.
Abstract
We develop a semi-analytic model to explore the physical properties of cool pressure-confined circumgalactic clouds with mass ranging from 10 to $10^{8} \, \rm M_{\odot }$ in a hot diffuse ...halo. We consider physical effects that control the motion and mass-loss of the clouds, and estimate the lifetime and the observed properties of individual cool gas clouds inferred from the cloudy simulation. Our results show that the cool pressure-confined gas clouds have physical properties consistent with absorption line systems with neutral hydrogen column densities $N_{\rm H\,{\small I}}\ge 10^{18.5} \rm cm^{-2}$ such as strong metal absorbers, sub-damped Lyman alpha systems, and damped Lyman alpha systems. The cool circumgalactic clouds are transient due to evaporation and recycling and therefore a constant replenishment is needed to maintain the cool cirumgalactic medium (CGM). We further model the ensemble properties of the cool CGM with clouds originated from outflows, inflows, or/and in situ formation with a range of initial cloud mass function and velocity distribution. We find that only with a certain combination of parameters, an outflow model can broadly reproduce three cool gas properties around star-forming galaxies simultaneously: the spatial distribution, down-the-barrel outflow absorption, and gas velocity dispersion. Both a constant in situ model and gas inflow model can reproduce the observed covering fractions of high $\rm \mathit{ N}_{H\,{\small I}}$ gas around passive galaxies but they fail to reproduce sufficient number of low $\rm \mathit{ N}_{H\,{\small I}}$ systems. The limitations and the failures of the current models are discussed. Our results illustrate that semi-analytic modelling is a promising tool to understand the physics of the cool CGM which is usually unresolved by state-of-the-art cosmological hydrodynamic simulations.
Abstract
With the growth of the global population and the increasing frequency of natural disasters, crop yields must be steadily increased to enhance human adaptability to risks. Pre-harvest ...sprouting (PHS), a term mainly used to describe the phenomenon in which grains germinate on the mother plant directly before harvest, is a serious global problem for agricultural production. After domestication, the dormancy level of cultivated crops was generally lower than that of their wild ancestors. Although the shortened dormancy period likely improved the industrial performance of cereals such as wheat, barley, rice, and maize, the excessive germination rate has caused frequent PHS in areas with higher rainfall, resulting in great economic losses. Here, we systematically review the causes of PHS and its consequences, the major indicators and methods for PHS assessment, and emphasize the biological significance of PHS in crop production. Wheat quantitative trait loci functioning in the control of PHS are also comprehensively summarized in a meta-analysis. Finally, we use Arabidopsis as a model plant to develop more complete PHS regulatory networks for wheat. The integration of this information is conducive to the development of custom-made cultivated lines suitable for different demands and regions, and is of great significance for improving crop yields and economic benefits.
Pre-harvest sprouting has a negative effect on cereal yield and quality, and understanding the genetic and regulatory mechanisms underlying it is of great agricultural and economic significance.
ABSTRACT
Observed reddening in the circum-galactic medium (CGM) indicates a significant abundance of small grains, of which the origin is still to be clarified. We examine a possible path of ...small-grain production through shattering of pre-existing large grains in the CGM. Possible sites where shattering occurs on a reasonable time-scale are cool clumps with hydrogen number density nH ∼ 0.1 cm−3 and gas temperature Tgas ∼ 104 K, which are shown to exist through observations of Mg ii absorbers. We calculate the evolution of grain size distribution in physical conditions appropriate for cool clumps in the CGM, starting from a large-grain-dominated distribution suggested from theoretical studies. With an appropriate gas turbulence model expected from the physical condition of cold clumps (maximum eddy size and velocity of ∼100 pc and 10 km s−1, respectively), together with the above gas density and temperature and the dust-to-gas mass ratio inferred from observations (0.006), we find that small-grain production occurs on a time-scale (a few × 108 yr) comparable to the lifetime of cool clumps derived in the literature. Thus, the physical conditions of the cool clouds are favourable for small-grain production. We also confirm that the reddening becomes significant on the above time-scale. Therefore, we conclude that small-grain production by shattering is a probable cause for the observed reddening in the CGM. We also mention the effect of grain materials (or their mixtures) on the reddening at different redshifts (1 and 2).
We use star, galaxy and quasar spectra taken by the Sloan Digital Sky Survey to map out the distribution of diffuse interstellar bands (DIBs) induced by the Milky Way. After carefully removing the ...intrinsic spectral energy distribution of each source, we show that by stacking thousands of spectra, it is possible to measure statistical flux fluctuations at the 10−3 level, detect more than 20 DIBs and measure their strength as a function of position on the sky. We create a map of DIB absorption covering about 5000 deg2 and measure correlations with various tracers of the interstellar medium: atomic and molecular hydrogen, dust and polycyclic aromatic hydrocarbons (PAHs). After recovering known correlations, we show that each DIB has a different dependence on atomic and molecular hydrogen: while they are all positively correlated with
$N_{\rm {H\scriptscriptstyle I}}$
, they exhibit a range of behaviours with
$N_{\rm {H_2}}$
showing positive, negative or no correlation. We show that a simple parametrization involving only
$N_{\rm {H\scriptscriptstyle I}}$
and
$N_{\rm {H_2}}$
applied to all the DIBs is sufficient to reproduce a large collection of observational results reported in the literature: it allows us to naturally describe the relations between DIB strength and dust reddening (including the so-called skin effect), the related scatter, DIB pair-wise correlations and families, the affinity for σ/ζ-type environments and other correlations related to molecules. Our approach allows us to characterize DIB dependencies in a simple manner and provides us with a metric to characterize the similarity between different DIBs.
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