ABSTRACT
A recent observational result finds that the quenching of satellites in groups at z = 0.08 has an angular dependence relative to the semimajor axis of the central galaxy. This observation is ...described as ‘anisotropic quenching’ or ‘angular conformity’. In this paper, I study the variation in the colour of a mass-limited sample of satellite galaxies relative to their angle from the major axis of the brightest cluster galaxy in the CLASH clusters up to z ∼ 0.5, 4 Gyr further in lookback time. The same result is found: galaxies close to the major axis are more quenched than those along the minor axis. I also find that the star-forming galaxies tend to avoid a region ±45○ from the major axis. This quenching signal is thought to be driven by AGN outflows along the minor axis, reducing the density of the intergalactic medium and thus the strength of ram pressure. Here, I will discuss potential alternative mechanisms. Finally, I note that the advent of the Legacy Survey of Space and Time (LSST) and Euclid surveys will allow for a more detailed study of this phenomenon and its evolution.
ABSTRACT
We estimate the intracluster light (ICL) component within a sample of 18 clusters detected in the XMM Cluster Survey (XCS) data using the deep (∼26.8 mag) Hyper Suprime-Cam Subaru Strategic ...Programme data release 1 i-band data. We apply a rest-frame μB = 25 mag arcsec−2 isophotal threshold to our clusters, below which we define light as the ICL within an aperture of RX,500 (X-ray estimate of R500) centred on the brightest cluster galaxy (BCG). After applying careful masking and corrections for flux losses from background subtraction, we recover ∼20 per cent of the ICL flux, approximately four times our estimate of the typical background at the same isophotal level (${\sim}5{{\ \rm per\ cent}}$). We find that the ICL makes up about ${\sim}24{{\ \rm per\ cent}}$ of the total cluster stellar mass on average (∼41 per cent including the flux contained in the BCG within 50 kpc); this value is well matched with other observational studies and semi-analytic/numerical simulations, but is significantly smaller than results from recent hydrodynamical simulations (even when measured in an observationally consistent way). We find no evidence for any links between the amount of ICL flux with cluster mass, but find a growth rate of 2–4 for the ICL between 0.1 < z < 0.5. We conclude that the ICL is the dominant evolutionary component of stellar mass in clusters from z ∼ 1. Our work highlights the need for a consistent approach when measuring ICL alongside the need for deeper imaging, in order to unambiguously measure the ICL across as broad a redshift range as possible (e.g. 10-yr stacked imaging from the Vera C. Rubin Observatory).
This paper presents new deep and wide narrow-band surveys undertaken with United Kingdom Infrared Telescope (UKIRT), Subaru and the Very Large Telescope (VLT), a unique combined effort to select ...large, robust samples of Hα star-forming galaxies at z = 0.40, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyr) in a uniform manner over ∼2 deg2 in the Cosmological Evolution Survey and Ultra Deep Survey fields. The deep multi-epoch Hα surveys reach a matched 3σ flux limit of 3 M yr−1 out to z = 2.2 for the first time, while the wide area and the coverage over two independent fields allow us to greatly overcome cosmic variance and assemble by far the largest samples of Hα emitters. Catalogues are presented for a total of 1742, 637, 515 and 807 Hα emitters, robustly selected at z = 0.40, 0.84, 1.47 and 2.23, respectively, and used to determine the Hα luminosity function and its evolution. The faint-end slope of the Hα luminosity function is found to be α = −1.60 ± 0.08 over z = 0-2.23, showing no significant evolution. The characteristic luminosity of star-forming galaxies, L*Hα, evolves significantly as log L*Hα(z) = 0.45z + log L*
z = 0. This is the first time Hα has been used to trace star formation activity with a single homogeneous survey at z = 0.4-2.23. Overall, the evolution seen with Hα is in good agreement with the evolution seen using inhomogeneous compilations of other tracers of star formation, such as far-infrared and ultraviolet, jointly pointing towards the bulk of the evolution in the last 11 Gyr being driven by a statistically similar star-forming population across cosmic time, but with a strong luminosity increase from z ∼ 0 to ∼2.2. Our uniform analysis allows us to derive the Hα star formation history (SFRH) of the Universe, showing a clear rise up to z ∼ 2.2, for which the simple parametrization log10ρSFR = −2.1(1 + z)−1 is valid over 80 per cent of the age of the Universe. The results reveal that both the shape and normalization of the Hα SFRH are consistent with the measurements of the stellar mass density growth, confirming that our Hα SFRH is tracing the bulk of the formation of stars in the Universe for z < 2.23. The star formation activity over the last ∼11 Gyr is responsible for producing ∼95 per cent of the total stellar mass density observed locally, with half of that being assembled in 2 Gyr between z = 1.2 and 2.2, and the other half in 8 Gyr (since z < 1.2). If the star formation rate density continues to decline with time in the same way as seen in the past ∼11 Gyr, then the stellar mass density of the Universe will reach a maximum which is only 5 per cent higher than the present-day value.
We have observed a sample of typical z ∼ 1 star-forming galaxies, selected from the HiZELS survey, with the new K-band Multi-Object Spectrograph (KMOS) near-infrared, multi-integral field unit ...instrument on the Very Large Telescope (VLT), in order to obtain their dynamics and metallicity gradients. The majority of our galaxies have a metallicity gradient consistent with being flat or negative (i.e. higher metallicity cores than outskirts). Intriguingly, we find a trend between metallicity gradient and specific star formation rate (sSFR), such that galaxies with a high sSFR tend to have relatively metal poor centres, a result which is strengthened when combined with data sets from the literature. This result appears to explain the discrepancies reported between different high-redshift studies and varying claims for evolution. From a galaxy evolution perspective, the trend we see would mean that a galaxy's sSFR is governed by the amount of metal-poor gas that can be funnelled into its core, triggered either by merging or through efficient accretion. In fact, merging may play a significant role as it is the starburst galaxies at all epochs, which have the more positive metallicity gradients. Our results may help to explain the origin of the fundamental metallicity relation, in which galaxies at a fixed mass are observed to have lower metallicities at higher star formation rates, especially if the metallicity is measured in an aperture encompassing only the central regions of the galaxy. Finally, we note that this study demonstrates the power of KMOS as an efficient instrument for large-scale resolved galaxy surveys.
The KMOS Redshift One Spectroscopic Survey (KROSS) is an ESO-guaranteed time survey of 795 typical star-forming galaxies in the redshift range z = 0.8-1.0 with the KMOS instrument on the Very Large ...Telescope. In this paper, we present resolved kinematics and star formation rates for 584 z ~ 1 galaxies. This constitutes the largest near-infrared Integral Field Unit survey of galaxies at z ~ 1 to date. We demonstrate the success of our selection criteria with 90 per cent of our targets found to be H alpha emitters, of which 81 per cent are spatially resolved. The fraction of the resolved KROSS sample with dynamics dominated by ordered rotation is found to be 83 plus or minus 5 per cent. However, when compared with local samples these are turbulent discs with high gas to baryonic mass fractions, ~35 per cent, and the majority are consistent with being marginally unstable (Toomre Q ~ 1). There is no strong correlation between galaxy averaged velocity dispersion and the total star formation rate, suggesting that feedback from star formation is not the origin of the elevated turbulence. We postulate that it is the ubiquity of high (likely molecular) gas fractions and the associated gravitational instabilities that drive the elevated star formation rates in these typical z ~ 1 galaxies, leading to the 10-fold enhanced star formation rate density. Finally, by comparing the gas masses obtained from inverting the star formation law with the dynamical and stellar masses, we infer an average dark matter to total mass fraction within 2.2r sub( e) (9.5 kpc) of 65 plus or minus 12 per cent, in agreement with the results from hydrodynamic simulations of galaxy formation.
ABSTRACT
We introduce Deep-CEE (Deep Learning for Galaxy Cluster Extraction and Evaluation), a proof of concept for a novel deep learning technique, applied directly to wide-field colour imaging to ...search for galaxy clusters, without the need for photometric catalogues. This technique is complementary to traditional methods and could also be used in combination with them to confirm existing galaxy cluster candidates. We use a state-of-the-art probabilistic algorithm, adapted to localize and classify galaxy clusters from other astronomical objects in Sloan Digital Sky Survey imaging. As there is an abundance of labelled data for galaxy clusters from previous classifications in publicly available catalogues, we do not need to rely on simulated data. This means we keep our training data as realistic as possible, which is advantageous when training a deep learning algorithm. Ultimately, we will apply our model to surveys such as Large Synoptic Survey Telescope and Euclid to probe wider and deeper into unexplored regions of the Universe. This will produce large samples of both high-redshift and low-mass clusters, which can be utilized to constrain both environment-driven galaxy evolution and cosmology.
ABSTRACT
We introduce AutoEnRichness, a hybrid approach that combines empirical and analytical strategies to determine the richness of galaxy clusters (in the redshift range of 0.1 ≤ z ≤ 0.35) using ...photometry data from the Sloan Digital Sky Survey Data Release 16, where cluster richness can be used as a proxy for cluster mass. In order to reliably estimate cluster richness, it is vital that the background subtraction is as accurate as possible when distinguishing cluster and field galaxies to mitigate severe contamination. AutoEnRichness is comprised of a multistage machine learning algorithm that performs background subtraction of interloping field galaxies along the cluster line of sight and a conventional luminosity distribution fitting approach that estimates cluster richness based only on the number of galaxies within a magnitude range and search area. In this proof-of-concept study, we obtain a balanced accuracy of 83.20 per cent when distinguishing between cluster and field galaxies as well as a median absolute percentage error of 33.50 per cent between our estimated cluster richnesses and known cluster richnesses within r200. In the future, we aim for AutoEnRichness to be applied on upcoming large-scale optical surveys, such as the Legacy Survey of Space and Time and Euclid, to estimate the richness of a large sample of galaxy groups and clusters from across the halo mass function. This would advance our overall understanding of galaxy evolution within overdense environments as well as enable cosmological parameters to be further constrained.
Atrial fibrillation (AF) is a highly prevalent disorder leading to heart failure, stroke, and death. Enhanced understanding of modifiable risk factors may yield opportunities for prevention. The risk ...of AF is increased in subclinical hyperthyroidism, but it is uncertain whether variations in thyroid function within the normal range or subclinical hypothyroidism are also associated with AF.
We conducted a systematic review and obtained individual participant data from prospective cohort studies that measured thyroid function at baseline and assessed incident AF. Studies were identified from MEDLINE and EMBASE databases from inception to July 27, 2016. The euthyroid state was defined as thyroid-stimulating hormone (TSH) 0.45 to 4.49 mIU/L, and subclinical hypothyroidism as TSH 4.5 to 19.9 mIU/L with free thyroxine (fT4) levels within reference range. The association of TSH levels in the euthyroid and subclinical hypothyroid range with incident AF was examined by using Cox proportional hazards models. In euthyroid participants, we additionally examined the association between fT4 levels and incident AF.
Of 30 085 participants from 11 cohorts (278 955 person-years of follow-up), 1958 (6.5%) had subclinical hypothyroidism and 2574 individuals (8.6%) developed AF during follow-up. TSH at baseline was not significantly associated with incident AF in euthyroid participants or those with subclinical hypothyroidism. Higher fT4 levels at baseline in euthyroid individuals were associated with increased AF risk in age- and sex-adjusted analyses (hazard ratio, 1.45; 95% confidence interval, 1.26-1.66, for the highest quartile versus the lowest quartile of fT4;
for trend ≤0.001 across quartiles). Estimates did not substantially differ after further adjustment for preexisting cardiovascular disease.
In euthyroid individuals, higher circulating fT4 levels, but not TSH levels, are associated with increased risk of incident AF.
ABSTRACT
We introduce Z-Sequence, a novel empirical model that utilizes photometric measurements of observed galaxies within a specified search radius to estimate the photometric redshift of galaxy ...clusters. Z-Sequence itself is composed of a machine learning ensemble based on the k-nearest neighbours algorithm. We implement an automated feature selection strategy that iteratively determines appropriate combinations of filters and colours to minimize photometric redshift prediction error. We intend for Z-Sequence to be a standalone technique but it can be combined with cluster finders that do not intrinsically predict redshift, such as our own DEEP-CEE. In this proof-of-concept study, we train, fine-tune, and test Z-Sequence on publicly available cluster catalogues derived from the Sloan Digital Sky Survey. We determine the photometric redshift prediction error of Z-Sequence via the median value of |Δ$z$|/(1 + $z$) (across a photometric redshift range of 0.05 ≤ $z$ ≤ 0.6) to be ∼0.01 when applying a small search radius. The photometric redshift prediction error for test samples increases by 30–50 per cent when the search radius is enlarged, likely due to line-of-sight interloping galaxies. Eventually, we aim to apply Z-Sequence to upcoming imaging surveys such as the Legacy Survey of Space and Time to provide photometric redshift estimates for large samples of as yet undiscovered and distant clusters.
The use of levothyroxine to treat subclinical hypothyroidism is controversial. We aimed to determine whether levothyroxine provided clinical benefits in older persons with this condition.
We ...conducted a double-blind, randomized, placebo-controlled, parallel-group trial involving 737 adults who were at least 65 years of age and who had persisting subclinical hypothyroidism (thyrotropin level, 4.60 to 19.99 mIU per liter; free thyroxine level within the reference range). A total of 368 patients were assigned to receive levothyroxine (at a starting dose of 50 μg daily, or 25 μg if the body weight was <50 kg or the patient had coronary heart disease), with dose adjustment according to the thyrotropin level; 369 patients were assigned to receive placebo with mock dose adjustment. The two primary outcomes were the change in the Hypothyroid Symptoms score and Tiredness score on a thyroid-related quality-of-life questionnaire at 1 year (range of each scale is 0 to 100, with higher scores indicating more symptoms or tiredness, respectively; minimum clinically important difference, 9 points).
The mean age of the patients was 74.4 years, and 396 patients (53.7%) were women. The mean (±SD) thyrotropin level was 6.40±2.01 mIU per liter at baseline; at 1 year, this level had decreased to 5.48 mIU per liter in the placebo group, as compared with 3.63 mIU per liter in the levothyroxine group (P<0.001), at a median dose of 50 μg. We found no differences in the mean change at 1 year in the Hypothyroid Symptoms score (0.2±15.3 in the placebo group and 0.2±14.4 in the levothyroxine group; between-group difference, 0.0; 95% confidence interval CI, -2.0 to 2.1) or the Tiredness score (3.2±17.7 and 3.8±18.4, respectively; between-group difference, 0.4; 95% CI, -2.1 to 2.9). No beneficial effects of levothyroxine were seen on secondary-outcome measures. There was no significant excess of serious adverse events prespecified as being of special interest.
Levothyroxine provided no apparent benefits in older persons with subclinical hypothyroidism. (Funded by European Union FP7 and others; TRUST ClinicalTrials.gov number, NCT01660126 .).
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