We extend the halo occupation distribution (HOD) framework to generate mock galaxy catalogues exhibiting varying levels of ‘galactic conformity’, which has emerged as a potentially powerful probe of ...environmental effects in galaxy evolution. Our model correlates galaxy colours in a group with the concentration of the common parent dark halo through a ‘group quenching efficiency’ ρ which makes older, more concentrated haloes at fixed mass preferentially host redder galaxies. We find that, for a specific value of ρ, this 1-halo conformity matches corresponding measurements in a group catalogue based on the Sloan Digital Sky Survey. Our mocks also display conformity at large separations from isolated objects, potentially an imprint of halo assembly bias. A detailed study – using mocks with assembly bias erased while keeping 1-halo conformity intact – reveals a rather nuanced situation, however. At separations ≲4 Mpc, conformity is mainly a 1-halo effect dominated by the largest haloes and is not a robust indicator of assembly bias. Only at very large separations (≳8 Mpc) does genuine 2-halo conformity, driven by the assembly bias of small haloes, manifest distinctly. We explain all these trends in standard halo model terms. Our model opens the door to parametrized HOD analyses that self-consistently account for galactic conformity at all scales.
ABSTRACT
In this work, we investigate the systematic uncertainties that arise from the calculation of the peculiar velocity when estimating the Hubble constant (H0) from gravitational wave standard ...sirens. We study the GW170817 event and the estimation of the peculiar velocity of its host galaxy, NGC 4993, when using Gaussian smoothing over nearby galaxies. NGC 4993 being a relatively nearby galaxy, at ∼40 Mpc away, is subject to a significant effect of peculiar velocities. We demonstrate a direct dependence of the estimated peculiar velocity value on the choice of smoothing scale. We show that when not accounting for this systematic, a bias of ${\sim }200~{\rm km\, s^{-1}}$ in the peculiar velocity incurs a bias of ${\sim }4~{\rm km\, s^{-1}\, Mpc^{-1}}$ on the Hubble constant. We formulate a Bayesian model that accounts for the dependence of the peculiar velocity on the smoothing scale and by marginalizing over this parameter we remove the need for a choice of smoothing scale. The proposed model yields $H_0 = 68.6 ^{+14.0} _{-8.5}~{\rm km\, s^{-1}\, Mpc^{-1}}$. We demonstrate that under this model a more robust unbiased estimate of the Hubble constant from nearby GW sources is obtained.
Abstract
We investigate the relationship between the quenching of star formation and the structural transformation of massive galaxies, using a large sample of photometrically selected post-starburst ...galaxies in the UKIDSS Ultra-Deep Survey field. We find that post-starburst galaxies at high redshift (z > 1) show high Sérsic indices, significantly higher than those of active star-forming galaxies, but with a distribution that is indistinguishable from the old quiescent population. We conclude that the morphological transformation occurs before (or during) the quenching of star formation. Recently quenched galaxies are also the most compact; we find evidence that massive post-starburst galaxies (M* > 1010.5 M⊙) at high redshift (z > 1) are on average smaller than comparable quiescent galaxies at the same epoch. Our findings are consistent with a scenario in which massive passive galaxies are formed from three distinct phases: (1) gas-rich dissipative collapse to very high densities, forming the proto-spheroid, (2) rapid quenching of star formation to create the ‘red nugget’ with post-starburst features and (3) a gradual growth in size as the population ages, perhaps as a result of minor mergers.
ABSTRACT
We present the first study of the large-scale clustering of post-starburst (PSB) galaxies in the high-redshift Universe (0.5 < z < 3.0). We select ∼4000 PSB galaxies photometrically, the ...largest high-redshift sample of this kind, from two deep large-scale near-infrared surveys: the UKIDSS Ultra Deep Survey Data Release 11 and the Cosmic Evolution Survey. Using angular cross-correlation techniques, we estimate the halo masses for this large sample of PSB galaxies and compare them with quiescent and star-forming galaxies selected in the same fields. We find that low-mass, low-redshift (0.5 < z < 1.0) PSB galaxies preferentially reside in very high mass dark matter haloes (Mhalo > 1014 M⊙), suggesting that they are likely to be infalling satellite galaxies in cluster-like environments. High-mass PSB galaxies are more weakly clustered at low redshifts, but they reside in higher mass haloes with increasing look-back time, suggesting strong redshift-dependent halo downsizing. These key results are consistent with previous results, suggesting that two main channels are responsible for the rapid quenching of galaxies. While high-redshift (z > 1) galaxies appear to be quenched by secular feedback mechanisms, processes associated with dense environments are likely to be the key driver of rapid quenching in the low-redshift Universe (z < 1). Finally, we show that the clustering of photometrically selected PSBs is consistent with them being direct descendants of highly dust-enshrouded submillimetre galaxies, providing tantalizing evidence for the oft-speculated evolutionary pathway from starburst to quiescence.
ABSTRACT
We conduct the first study of how the relative quenching probability of galaxies depends on environment over the redshift range 0.5 < z < 3, using data from the UKIDSS Ultra Deep Survey. By ...constructing the stellar mass functions for quiescent and post-starburst (PSB) galaxies in high-, medium-, and low-density environments to z = 3, we find an excess of quenched galaxies in dense environments out to at least z ∼ 2. Using the growth rate in the number of quenched galaxies, combined with the star-forming galaxy mass function, we calculate the probability that a given star-forming galaxy is quenched per unit time. We find a significantly higher quenching rate in dense environments (at a given stellar mass) at all redshifts. Massive galaxies (M* > 1010.7 M⊙) are on average 1.7 ± 0.2 times more likely to quench per Gyr in the densest third of environments compared to the sparsest third. Finally, we compare the quiescent galaxy growth rate to the rate at which galaxies pass through a PSB phase. Assuming a visibility time-scale of 500 Myr, we find that the PSB route can explain ∼50 per cent of the growth in the quiescent population at high stellar mass (M* > 1010.7 M⊙) in the redshift range 0.5 < z < 3, and potentially all of the growth at lower stellar masses.
Submillimetre galaxies (SMGs) are among the most luminous dusty galaxies in the Universe, but their true nature remains unclear; are SMGs the progenitors of the massive elliptical galaxies we see in ...the local Universe, or are they just a short-lived phase among more typical star-forming galaxies? To explore this problem further, we investigate the clustering of SMGs identified in the SCUBA-2 Cosmology Legacy Survey. We use a catalogue of submillimetre (850 mu m) source identifications derived using a combination of radio counterparts and colour/infrared selection to analyse a sample of 610 SMG counterparts in the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Survey (UKIDSS) Ultra Deep Survey (UDS), making this the largest high-redshift sample of these galaxies to date. Using angular cross-correlation techniques, we estimate the halo masses for this large sample of SMGs and compare them with passive and star-forming galaxies selected in the same field. We find that SMGs, on average, occupy high-mass dark matter haloes ... at redshifts z > 2.5, consistent with being the progenitors of massive quiescent galaxies in present-day galaxy clusters. We also find evidence of downsizing, in which SMG activity shifts to lower mass haloes at lower redshifts. In terms of their clustering and halo masses, SMGs appear to be consistent with other star-forming galaxies at a given redshift. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
We investigate the relationship between environment and galaxy evolution in the redshift range 0.5 < z < 1.0. Galaxy overdensities are selected using a friends-of-friends algorithm, applied ...to deep photometric data in the Ultra-Deep Survey field. A study of the resulting stellar mass functions reveals clear differences between cluster and field environments, with a strong excess of low-mass rapidly quenched galaxies in cluster environments compared to the field. Cluster environments also show a corresponding deficit of young, low-mass star-forming galaxies, which show a sharp radial decline towards cluster centres. By comparing mass functions and radial distributions, we conclude that young star-forming galaxies are rapidly quenched as they enter overdense environments, becoming post-starburst galaxies before joining the red sequence. Our results also point to the existence of two environmental quenching pathways operating in galaxy clusters, operating on different time-scales. Fast quenching acts on galaxies with high specific star formation rates, operating on time-scales shorter than the cluster dynamical time (<1 Gyr). In contrast, slow quenching affects galaxies with moderate specific star formation rates, regardless of their stellar mass, and acts on longer time-scales (≳ 1 Gyr). Of the cluster galaxies in the stellar mass range 9.0 < log (M/M⊙) < 10.5 quenched during this epoch, we find that 73 per cent were transformed through fast quenching, while the remaining 27 per cent followed the slow quenching route.
Bauxite residue is a highly alkaline material generated from the production of alumina in which bauxite is dissolved in caustic soda. Approximately 4.4 billion tons of bauxite residues are either ...stockpiled or landfilled, creating environmental risks either from the generation of dust or migration of filtrates. High alkalinity is the critical factor restricting complete utilization of bauxite residues, whilst the application of alkaline regulation agents is costly and difficult to apply widely. For now, current industrial wastes, such as waste acid, ammonia nitrogen wastewater, waste gypsum and biomass, have become major problems restricting the development of the social economy. Regulation of bauxite residues alkalinity by industrial waste was proposed to achieve ‘waste control by waste’ with good economic and ecological benefits. This review will focus on the origin and transformation of alkalinity in bauxite residues using typical industrial waste. It will propose key research directions with an emphasis on alkaline regulation by industrial waste, whilst also providing a scientific reference point for their potential use as amendments to enhance soil formation and establish vegetation on bauxite residue disposal areas (BRDAs) following large-scale disposal.
ABSTRACT
Photometric redshifts are commonly used to measure the distribution of galaxies in large surveys. However, the demands of ongoing and future large-scale cosmology surveys place very ...stringent limits on the redshift performance that are difficult to meet. A new approach to meet this precision need is forward modelling, which is underpinned by realistic simulations. In the work presented here, we use simulations to study the sensitivity of redshift distributions to the underlying galaxy population demographics. We do this by varying the redshift evolving parameters of the Schechter function for two galaxy populations: star-forming and quenched galaxies. Each population is characterized by eight parameters. We find that the redshift distribution of shallow surveys, such as the Sloan Digital Sky Survey (SDSS), is mainly sensitive to the parameters for quenched galaxies. However, for deeper surveys such as the Dark Energy Survey (DES) and the Hyper Suprime-Cam (HSC), the star-forming parameters have a stronger impact on the redshift distribution. Specifically, the slope of the characteristic magnitude, aM, for star-forming galaxies has overall the strongest impact on the redshift distribution. Decreasing aM by 148 per cent (its given uncertainty) shifts the mean redshift by ∼45 per cent. We explore which combination of colour and magnitude measurements is most sensitive to aM and we find that each colour–magnitude pair studied is similarly affected by a modification of aM.
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