Ion channels are implicated in many essential physiological events such as electrical signal propagation and cellular communication. The advent of K+ and Na+ ion channel structure determination has ...facilitated numerous investigations of molecular determinants of their behaviour. At the same time, rapid development of computer hardware and molecular simulation methodologies has made computational studies of large biological molecules in all‐atom representation tractable. The concurrent evolution of experimental structural biology with biomolecular computer modelling has yielded mechanistic details of fundamental processes unavailable through experiments alone, such as ion conduction and ion channel gating. This review is a short survey of the atomistic computational investigations of K+ and Na+ ion channels, focusing on KcsA and several voltage‐gated channels from the KV and NaV families, which have garnered many successes and engendered several long‐standing controversies regarding the nature of their structure–function relationship. We review the latest advancements and challenges facing the field of molecular modelling and simulation regarding the structural and energetic determinants of ion channel function and their agreement with experimental observations.
Structural illustration of the voltage‐gated potassium channel gating transitions studied by atomistic molecular dynamics simulations including voltage‐dependent activation/deactivation associated with channel pore opening and closing and voltage sensor domain (VSD) movement as well as C‐type inactivation processes associated with selectivity filter distortions. A single file of alternating K+ ions and water molecules in the selectivity filter demonstrates a starting configuration for a knock‐on conduction mechanism. Resting VSD/closed pore structure is shown using light‐blue contours, and activated VSD/open pore is shown using grey contours. α‐Helices are shown by white cylinders and loops by black/grey curves. Distorted (inactivated) selectivity filter (SF) is shown in pink. Charged residues on S4 are shown by blue/gray circles, K+ ions and water molecules in the SF are shown in purple and red, respectively. Illustrations are based on EAG (Whicher & MacKinnon, ) and hERG (Wang & MacKinnon, ) cryo‐EM structures.
We carried out a detailed strong lensing analysis of a sub-sample of eight galaxy clusters of the Cluster Lensing And Supernova survey with Hubble (CLASH) in the redshift range of zcluster = 0.23 − ...0.59 using extensive spectroscopic information, primarily from the Multi Unit Spectroscopic Explorer (MUSE) archival data and complemented with CLASH-VLT redshift measurements. The observed positions of the multiple images of strongly lensed background sources were used to constrain parametric models describing the cluster total mass distributions. Different models were tested in each cluster depending on the complexity of its mass distribution and on the number of detected multiple images. Four clusters show more than five spectroscopically confirmed multiple image families. In this sample, we did not make use of families that are only photometrically identified in order to reduce model degeneracies between the values of the total mass of a cluster source redshifts, in addition to systematics due to the potential misidentifications of multiple images. For the remaining four clusters, we used additional families without any spectroscopic confirmation to increase the number of strong lensing constraints up to the number of free parameters in our parametric models. We present spectroscopic confirmation of 27 multiply lensed sources, with no previous spectroscopic measurements, spanning over the redshift range of zsrc = 0.7 − 6.1. Moreover, we confirm an average of 48 galaxy members in the core of each cluster thanks to the high efficiency and large field of view of MUSE. We used this information to derive precise strong lensing models, projected total mass distributions, and magnification maps. We show that, despite having different properties (i.e. number of mass components, total mass, redshift, etc.), the projected total mass and mass density profiles of all clusters have very similar shapes when rescaled by independent measurements of M200c and R200c. Specifically, we measured the mean value of the projected total mass of our cluster sample within 10 (20)% of R200c to be 0.13 (0.32) of M200c, with a remarkably small scatter of 5 (6)%. Furthermore, the large number of high-z sources and the precise magnification maps derived in this work for four clusters add up to the sample of high-quality gravitational telescopes to be used to study the faint and distant Universe.
Using a sample of four galaxy clusters at 1.35 < z < 1.65 and 10 galaxy clusters at 0.85 < z < 1.35, we measure the environmental quenching timescale, tQ, corresponding to the time required after a ...galaxy is accreted by a cluster for it to fully cease star formation. Cluster members are selected by a photometric-redshift criterion, and categorized as star-forming, quiescent, or intermediate according to their dust-corrected rest-frame colors and magnitudes. We employ a "delayed-then-rapid" quenching model that relates a simulated cluster mass accretion rate to the observed numbers of each type of galaxy in the cluster to constrain tQ. For galaxies of mass M* 1010.5 M , we find a quenching timescale of tQ = Gyr in the z ∼ 1.5 cluster sample, and Gyr at z ∼ 1. Using values drawn from the literature, we compare the redshift evolution of tQ to timescales predicted for different physical quenching mechanisms. We find tQ to depend on host halo mass such that quenching occurs over faster timescales in clusters relative to groups, suggesting that properties of the host halo are responsible for quenching high-mass galaxies. Between z = 0 and z = 1.5, we find that tQ evolves faster than the molecular gas depletion timescale and slower than an estimated star formation rate-outflow timescale, but is consistent with the evolution of the dynamical time. This suggests that environmental quenching in these galaxies is driven by the motion of satellites relative to the cluster environment, although due to uncertainties in the atomic gas budget at high redshift, we cannot rule out quenching due to simple gas depletion.
We present ALMA CO (2-1) detections in 11 gas-rich cluster galaxies at z ∼ 1.6, constituting the largest sample of molecular gas measurements in z > 1.5 clusters to date. The observations span three ...galaxy clusters, derived from the Spitzer Adaptation of the Red-sequence Cluster Survey. We augment the >5 detections of the CO (2-1) fluxes with multi-band photometry, yielding stellar masses and infrared-derived star formation rates, to place some of the first constraints on molecular gas properties in z ∼ 1.6 cluster environments. We measure sizable gas reservoirs of 0.5-2 × 1011 M☉ in these objects, with high gas fractions (fgas) and long depletion timescales (τ), averaging 62% and 1.4 Gyr, respectively. We compare our cluster galaxies to the scaling relations of the coeval field, in the context of how gas fractions and depletion timescales vary with respect to the star-forming main sequence. We find that our cluster galaxies lie systematically off the field scaling relations at z = 1.6 toward enhanced gas fractions, at a level of ∼4 , but have consistent depletion timescales. Exploiting CO detections in lower-redshift clusters from the literature, we investigate the evolution of the gas fraction in cluster galaxies, finding it to mimic the strong rise with redshift in the field. We emphasize the utility of detecting abundant gas-rich galaxies in high-redshift clusters, deeming them as crucial laboratories for future statistical studies.
ABSTRACT
We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) hydrodynamical simulation to trace the quenching history of galaxies in its 10 most massive clusters. We use two ...criteria to identify moments when galaxies suffer significant changes in their star formation activity: (i) the instantaneous star formation rate (SFR) strongest drop, $\Gamma _{\rm SFR}^{\rm SD}$, and (ii) a ‘quenching’ criterion based on a minimum threshold for the specific SFR of ≲10$^{-11}\,\rm yr^{-1}$. We find that a large fraction of galaxies (${\gtrsim} 60\,{\rm per\,cent}$) suffer their $\Gamma _{\rm SFR}^{\rm SD}$ outside the cluster’s R200. This ‘pre-processed’ population is dominated by galaxies that are either low mass and centrals or inhabit low-mass hosts (1010.5 ≲ Mhost ≲ 1011.0 M⊙). The host mass distribution is bimodal, and galaxies that suffered their $\Gamma _{\rm SFR}^{\rm SD}$ in massive hosts ($10^{13.5} \lesssim M_{\rm host} \lesssim 10^{14.0}\, \mathrm{M}_{\odot }$) are mainly processed within the clusters. Pre-processing mainly limits the total stellar mass with which galaxies arrive in the clusters. Regarding quenching, galaxies preferentially reach this state in high-mass haloes ($10^{13.5} \lesssim M_{\rm host} \lesssim 10^{14.5}\, \mathrm{M}_{\odot }$). The small fraction of galaxies that reach the cluster already quenched have also been pre-processed, linking both criteria as different stages in the quenching process of those galaxies. For the z = 0 satellite populations, we find a sharp rise in the fraction of quenched satellites at the time of first infall, highlighting the role played by the dense cluster environment. Interestingly, the fraction of pre-quenched galaxies rise with final cluster mass. This is a direct consequence of the hierarchical cosmological model used in these simulations.
ABSTRACT
Using new and published data, we construct a sample of 160 brightest cluster galaxies (BCGs) spanning the redshift interval 0.03 < z < 1.63. We use this sample, which covers 70 per cent of ...the history of the universe, to measure the growth in the stellar mass of BCGs after correcting for the correlation between the stellar mass of the BCG and the mass of the cluster in which it lives. We find that the stellar mass of BCGs increases by a factor of 1.8 ± 0.3 between z = 0.9 and z = 0.2. Compared to earlier works, our result is closer to the predictions of semi‐analytic models. However, BCGs at z = 0.9, relative to BCGs at z = 0.2, are still a factor of 1.5 more massive than the predictions of these models. Star formation rates in BCGs at z ∼ 1 are generally too low to result in significant amounts of mass. Instead, it is likely that most of the mass build up occurs through mainly dry mergers in which perhaps half of the mass is lost to the intra‐cluster medium of the cluster.
Thanks to its outstanding angular resolution, the Atacama Large Millimeter/submillimeter Array (ALMA) has recently unambiguously identified a population of optically dark galaxies with redshifts ...greater than
z
= 3, which play an important role in the cosmic star formation in massive galaxies. In this paper we study the properties of the six optically dark galaxies detected in the 69 arcmin
2
GOODS-ALMA 1.1 mm continuum survey. While none of them are listed in the deepest
H
-band based CANDELS catalog in the GOODS-South field down to
H
= 28.16 AB, we were able to de-blend two of them from their bright neighbor and measure an
H
-band flux for them. We present the spectroscopic scan follow-up of five of the six sources with ALMA band 4. All are detected in the 2 mm continuum with signal-to-noise ratios higher than eight. One emission line is detected in AGS4 (
ν
obs
= 151.44 GHz with an
S
/
N
= 8.58) and AGS17 (
ν
obs
= 154.78 GHz with an
S
/
N
= 10.23), which we interpret in both cases as being due to the CO(6–5) line at
z
spec
AGS4
= 3.556 and
z
spec
AGS17
= 3.467, respectively. These redshifts match both the probability distribution of the photometric redshifts derived from the UV to near-infrared spectral energy distributions (SEDs) and the far-infrared SEDs for typical dust temperatures of galaxies at these redshifts. We present evidence that nearly 70% (4/6 of galaxies) of the optically dark galaxies belong to the same overdensity of galaxies at
z
∼ 3.5. overdensity The most massive one, AGS24 (
M
⋆
= 10
11.32
−0.19
+0.02
M
⊙
), is the most massive galaxy without an active galactic nucleus at
z
> 3 in the GOODS-ALMA field. It falls in the very center of the peak of the galaxy surface density, which suggests that the surrounding overdensity is a proto-cluster in the process of virialization and that AGS24 is the candidate progenitor of the future brightest cluster galaxy.
Abstract
Using VIsible MultiObject Spectrograph (VIMOS)-integral field unit (IFU) observations, we study the interstellar medium (ISM) of two star-forming dwarf galaxies, UM 461 and Mrk 600. Our aim ...was to search for the existence of metallicity inhomogeneities that might arise from infall of nearly pristine gas feeding ongoing localized star formation. The IFU data allowed us to study the impact of external gas accretion on the chemical evolution as well as the ionized gas kinematics and morphologies of these galaxies. Both systems show signs of morphological distortions, including cometary-like morphologies. We analysed the spatial variation of 12 + log(O/H) abundances within both galaxies using the direct method (Te), the widely applied HII–CHI–mistry code, as well as by employing different standard calibrations. For UM 461, our results show that the ISM is fairly well mixed, at large scales;
however, we find an off-centre and low-metallicity region with 12 + log(O/H) < 7.6 in the SW part of the brightest H ii region, using the direct method. This result is consistent with the recent infall of a metal-poor H i cloud into the region now exhibiting the lowest metallicity, which also displays localized perturbed neutral and ionized gas kinematics. Mrk 600 in contrast, appears to be chemically homogeneous on both large and small scales. The intrinsic differences in the spatially resolved properties of the ISM in our analysed galaxies are consistent with these systems being at different evolutionary stages.
Submillimeter/millimeter observations of dusty star-forming galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA) have shown that dust continuum emission generally occurs in compact ...regions smaller than the stellar distribution. However, it remains to be understood how systematic these findings are. Studies often lack homogeneity in the sample selection, target discontinuous areas with inhomogeneous sensitivities, and suffer from modest
u
v
coverage coming from single array configurations. GOODS-ALMA is a 1.1 mm galaxy survey over a continuous area of 72.42 arcmin
2
at a homogeneous sensitivity. In this version 2.0, we present a new low resolution dataset and its combination with the previous high resolution dataset from the survey, improving the
u
v
coverage and sensitivity reaching an average of
σ
= 68.4 μJy beam
−1
. A total of 88 galaxies are detected in a blind search (compared to 35 in the high resolution dataset alone), 50% at
S
/
N
peak
≥ 5 and 50% at 3.5 ≤
S
/
N
peak
≤ 5 aided by priors. Among them, 13 out of the 88 are optically dark or faint sources (
H
- or
K
-band dropouts). The sample dust continuum sizes at 1.1 mm are generally compact, with a median effective radius of
R
e
= 0
.
″
10 ± 0
.
″
05 (a physical size of
R
e
= 0.73 ± 0.29 kpc at the redshift of each source). Dust continuum sizes evolve with redshift and stellar mass resembling the trends of the stellar sizes measured at optical wavelengths, albeit a lower normalization compared to those of late-type galaxies. We conclude that for sources with flux densities
S
1.1 mm
> 1 mJy, compact dust continuum emission at 1.1 mm prevails, and sizes as extended as typical star-forming stellar disks are rare. The
S
1.1 mm
< 1 mJy sources appear slightly more extended at 1.1 mm, although they are still generally compact below the sizes of typical star-forming stellar disks.
We analyse the evolution of the red sequence in a sample of galaxy clusters at redshifts 0.8 < z < 1.5 taken from the HAWK-I Cluster Survey (HCS). The comparison with the low-redshift (0.04 < z < ...0.08) sample of the WIde-field Nearby Galaxy-cluster Survey (WINGS) and other literature results shows that the slope and intrinsic scatter of the cluster red sequence have undergone little evolution since z = 1.5. We find that the luminous-to-faint ratio and the slope of the faint end of the luminosity distribution of the HCS red sequence are consistent with those measured in WINGS, implying that there is no deficit of red galaxies at magnitudes fainter than
$M_V^{\ast }$
at high redshifts. We find that the most massive HCS clusters host a population of bright red sequence galaxies at M
V
< −22.0 mag, which are not observed in low-mass clusters. Interestingly, we also note the presence of a population of very bright (M
V
< −23.0 mag) and massive (log (M
*/M⊙) > 11.5) red sequence galaxies in the WINGS clusters, which do not include only the brightest cluster galaxies and which are not present in the HCS clusters, suggesting that they formed at epochs later than z = 0.8. The comparison with the luminosity distribution of a sample of passive red sequence galaxies drawn from the COSMOS/UltraVISTA field in the photometric redshift range 0.8 < z
phot < 1.5 shows that the red sequence in clusters is more developed at the faint end, suggesting that halo mass plays an important role in setting the time-scales for the build-up of the red sequence.
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