366 research outputs found
Clumpy Galaxies in CANDELS. I. The Definition of UV Clumps and the Fraction of Clumpy Galaxies at 0.5<z<3
Although giant clumps of stars are crucial to galaxy formation and evolution,
the most basic demographics of clumps are still uncertain, mainly because the
definition of clumps has not been thoroughly discussed. In this paper, we study
the basic demographics of clumps in star-forming galaxies (SFGs) at 0.5<z<3,
using our proposed physical definition that UV-bright clumps are discrete
star-forming regions that individually contribute more than 8% of the
rest-frame UV light of their galaxies. Clumps defined this way are
significantly brighter than the HII regions of nearby large spiral galaxies,
either individually or blended, when physical spatial resolution and
cosmological dimming are considered. Under this definition, we measure the
fraction of SFGs that contain at least one off-center clump (Fclumpy) and the
contributions of clumps to the rest-frame UV light and star formation rate of
SFGs in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample
consists of 3239 galaxies with axial ratio q>0.5. The redshift evolution of
Fclumpy changes with the stellar mass (M*) of the galaxies. Low-mass
(log(M*/Msun)<9.8) galaxies keep an almost constant Fclumpy of about 60% from
z~3.0 to z~0.5. Intermediate-mass and massive galaxies drop their Fclumpy from
55% at z~3.0 to 40% and 15%, respectively, at z~0.5. We find that (1) the trend
of disk stabilization predicted by violent disk instability matches the Fclumpy
trend of massive galaxies; (2) minor mergers are a viable explanation of the
Fclumpy trend of intermediate-mass galaxies at z<1.5, given a realistic
observability timescale; and (3) major mergers are unlikely responsible for the
Fclumpy trend in all masses at z<1.5. The clump contribution to the rest-frame
UV light of SFGs shows a broad peak around galaxies with log(M*/Msun)~10.5 at
all redshifts, possibly linked to the molecular gas fraction of the galaxies.
(Abridged)Comment: 22 pages, 15 figures. Appeared in ApJ (2015, 800, 39). A few typos
correcte
Compaction and Quenching of High-z Galaxies in Cosmological Simulations: Blue and Red Nuggets
We use cosmological simulations to study a characteristic evolution pattern
of high redshift galaxies. Early, stream-fed, highly perturbed, gas-rich discs
undergo phases of dissipative contraction into compact, star-forming systems
(blue nuggets) at z~4-2. The peak of gas compaction marks the onset of central
gas depletion and inside-out quenching into compact ellipticals (red nuggets)
by z~2. These are sometimes surrounded by gas rings or grow extended dry
stellar envelopes. The compaction occurs at a roughly constant specific
star-formation rate (SFR), and the quenching occurs at a constant stellar
surface density within the inner kpc (). Massive galaxies quench
earlier, faster, and at a higher than lower-mass galaxies, which
compactify and attempt to quench more than once. This evolution pattern is
consistent with the way galaxies populate the SFR-radius-mass space, and with
gradients and scatter across the main sequence. The compaction is triggered by
an intense inflow episode, involving (mostly minor) mergers, counter-rotating
streams or recycled gas, and is commonly associated with violent disc
instability. The contraction is dissipative, with the inflow rate >SFR, and the
maximum anti-correlated with the initial spin parameter, as
predicted by Dekel & Burkert (2014). The central quenching is triggered by the
high SFR and stellar/supernova feedback (possibly also AGN feedback) due to the
high central gas density, while the central inflow weakens as the disc
vanishes. Suppression of fresh gas supply by a hot halo allows the long-term
maintenance of quenching once above a threshold halo mass, inducing the
quenching downsizing.Comment: Resubmitted to MNRAS after responding to referee's comments; Updated
and added two figure
Filaments of The Slime Mold Cosmic Web And How They Affect Galaxy Evolution
We present a novel method for identifying cosmic web filaments using the
IllustrisTNG (TNG100) cosmological simulations and investigate the impact of
filaments on galaxies. We compare the use of cosmic density field estimates
from the Delaunay Tessellation Field Estimator (DTFE) and the Monte Carlo
Physarum Machine (MCPM), which is inspired by the slime mold organism, in the
DisPerSE structure identification framework. The MCPM-based reconstruction
identifies filaments with higher fidelity, finding more low-prominence/diffuse
filaments and better tracing the true underlying matter distribution than the
DTFE-based reconstruction. Using our new filament catalogs, we find that most
galaxies are located within 1.5-2.5 Mpc of a filamentary spine, with little
change in the median specific star formation rate and the median galactic gas
fraction with distance to the nearest filament. Instead, we introduce the
filament line density, {\Sigma}fil(MCPM), as the total MCPM overdensity per
unit length of a local filament segment, and find that this parameter is a
superior predictor of galactic gas supply and quenching. Our results indicate
that most galaxies are quenched and gas-poor near high-line density filaments
at z10.5 galaxies is mainly driven by
mass, while lower-mass galaxies are significantly affected by the filament line
density. In high-line density filaments, satellites are strongly quenched,
whereas centrals have reduced star formation, but not gas fraction, at z<=0.5.
We discuss the prospect of applying our new filament identification method to
galaxy surveys with SDSS, DESI, Subaru PFS, etc. to elucidate the effect of
large-scale structure on galaxy formation.Comment: Submitted to ApJ, comments welcome. Data available at
https://github.com/farhantasy/CosmicWeb-Galaxies
Mitigation and screening for environmental assessment
This article considers how, as a matter of law and policy, mitigation measures should be taken into account in determining whether a project will have significant environmental effects and therefore be subject to assessment under the EU Environmental Impact Assessment (EIA) Directive. This is not straightforward: it is problematic to distinguish clearly between an activity and the measures proposed to minimise or mitigate for the adverse consequences of the activity. The issue is a salient one in impact assessment law, but under-explored in the literature and handled with some difficulty by the courts. I argue that there is an unnecessarily and undesirably narrow approach currently taken under the EIA Directive, which could be improved upon by taking a more adaptive approach; alternatively a heightened standard of review of ‘significance’, and within this of the scope for mitigation measures to bring projects beneath the significance threshold, may also be desirable
Bulge growth through disk instabilities in high-redshift galaxies
The role of disk instabilities, such as bars and spiral arms, and the
associated resonances, in growing bulges in the inner regions of disk galaxies
have long been studied in the low-redshift nearby Universe. There it has long
been probed observationally, in particular through peanut-shaped bulges. This
secular growth of bulges in modern disk galaxies is driven by weak,
non-axisymmetric instabilities: it mostly produces pseudo-bulges at slow rates
and with long star-formation timescales. Disk instabilities at high redshift
(z>1) in moderate-mass to massive galaxies (10^10 to a few 10^11 Msun of stars)
are very different from those found in modern spiral galaxies. High-redshift
disks are globally unstable and fragment into giant clumps containing 10^8-10^9
Msun of gas and stars each, which results in highly irregular galaxy
morphologies. The clumps and other features associated to the violent
instability drive disk evolution and bulge growth through various mechanisms,
on short timescales. The giant clumps can migrate inward and coalesce into the
bulge in a few 10^8 yr. The instability in the very turbulent media drives
intense gas inflows toward the bulge and nuclear region. Thick disks and
supermassive black holes can grow concurrently as a result of the violent
instability. This chapter reviews the properties of high-redshift disk
instabilities, the evolution of giant clumps and other features associated to
the instability, and the resulting growth of bulges and associated sub-galactic
components.Comment: 37 pages, 9 figures. Invited refereed review to appear in "Galactic
Bulges", E. Laurikainen, D. Gadotti, R. Peletier (eds.), Springe
Observational Diagnostics of Gas Flows: Insights from Cosmological Simulations
Galactic accretion interacts in complex ways with gaseous halos, including
galactic winds. As a result, observational diagnostics typically probe a range
of intertwined physical phenomena. Because of this complexity, cosmological
hydrodynamic simulations have played a key role in developing observational
diagnostics of galactic accretion. In this chapter, we review the status of
different observational diagnostics of circumgalactic gas flows, in both
absorption (galaxy pair and down-the-barrel observations in neutral hydrogen
and metals; kinematic and azimuthal angle diagnostics; the cosmological column
density distribution; and metallicity) and emission (Lya; UV metal lines; and
diffuse X-rays). We conclude that there is no simple and robust way to identify
galactic accretion in individual measurements. Rather, progress in testing
galactic accretion models is likely to come from systematic, statistical
comparisons of simulation predictions with observations. We discuss specific
areas where progress is likely to be particularly fruitful over the next few
years.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dave, to be published by
Springer. Typos correcte
Germline-Focused Analysis of Tumour-Only Sequencing: Recommendations from the ESMO Precision Medicine Working Group.
It is increasingly common in oncology practice to perform tumour sequencing using large cancer panels. For pathogenic sequence variants in cancer susceptibility genes identified on tumour-only sequencing, it is often unclear whether they are of somatic or constitutional (germline) origin. There is wide-spread disparity regarding both the extent to which systematic 'germline-focused analysis' is performed upon tumour sequencing data and for which variants follow-up analysis of a germline sample is performed. Here we present analyses of paired sequencing data from 17,152 cancer samples, in which 1494 pathogenic sequence variants were identified across 65 cancer susceptibility genes. From these analyses, the European Society of Medical Oncology Precision Medicine Working Group Germline Subgroup have generated (i) recommendations regarding germline-focused analyses of tumour-only sequencing data, (ii) indications for germline follow-up testing and (iii) guidance on patient information-giving and consent
Gas Accretion and Star Formation Rates
Cosmological numerical simulations of galaxy evolution show that accretion of
metal-poor gas from the cosmic web drives the star formation in galaxy disks.
Unfortunately, the observational support for this theoretical prediction is
still indirect, and modeling and analysis are required to identify hints as
actual signs of star-formation feeding from metal-poor gas accretion. Thus, a
meticulous interpretation of the observations is crucial, and this
observational review begins with a simple theoretical description of the
physical process and the key ingredients it involves, including the properties
of the accreted gas and of the star-formation that it induces. A number of
observations pointing out the connection between metal-poor gas accretion and
star-formation are analyzed, specifically, the short gas consumption time-scale
compared to the age of the stellar populations, the fundamental metallicity
relationship, the relationship between disk morphology and gas metallicity, the
existence of metallicity drops in starbursts of star-forming galaxies, the
so-called G dwarf problem, the existence of a minimum metallicity for the
star-forming gas in the local universe, the origin of the alpha-enhanced gas
forming stars in the local universe, the metallicity of the quiescent BCDs, and
the direct measurements of gas accretion onto galaxies. A final section
discusses intrinsic difficulties to obtain direct observational evidence, and
points out alternative observational pathways to further consolidate the
current ideas.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springe
Hereditary palmoplantar keratoderma - phenotypes and mutations in 64 patients
Background Hereditary palmoplantar keratodermas (PPK) represent a heterogeneous group of rare skin disorders with epidermal hyperkeratosis of the palms and soles, with occasional additional manifestations in other tissues. Mutations in at least 69 genes have been implicated in PPK, but further novel candidate genes and mutations are still to be found. Objectives To identify mutations underlying PPK in a cohort of 64 patients. Methods DNA of 48 patients was analysed on a custom-designed in-house panel for 35 PPK genes, and 16 patients were investigated by a diagnostic genetic laboratory either by whole-exome sequencing, gene panels or targeted single-gene sequencing. Results Of the 64 PPK patients, 32 had diffuse (50%), 19 focal (30%) and 13 punctate (20%) PPK. None had striate PPK. Pathogenic mutations in altogether five genes were identified in 31 of 64 (48%) patients, the majority (22/31) with diffuse PPK. Of them, 11 had a mutation in AQP5, five in SERPINB7, four in KRT9 and two in SLURP1. AAGAB mutations were found in nine punctate PPK patients. New mutations were identified in KRT9 and AAGAB. No pathogenic mutations were detected in focal PPK. Variants of uncertain significance (VUS) in PPK-associated and other genes were observed in 21 patients that might explain their PPK. No suggestive pathogenic variants were found for 12 patients. Conclusions Diffuse PPK was the most common (50%) and striate PPK was not observed. We identified pathogenic mutations in 48% of our PPK patients, mainly in five genes: AQP5, AAGAB, KRT9, SERPINB7 and SLURP1.Peer reviewe
The Extended [C ii] under Construction? Observation of the Brightest High-z Lensed Star-forming Galaxy at z = 6.2
We present results of [C ii] 158 μm emission line observations, and report the spectroscopic redshift confirmation of a strongly lensed (μ ∼ 20) star-forming galaxy, MACS0308-zD1 at z = 6.2078 ± 0.0002. The [C ii] emission line is detected with a signal-to-noise ratio >6 within the rest-frame UV-bright clump of the lensed galaxy (zD1.1) and exhibits multiple velocity components; the narrow [C ii] has a velocity full width half maximum (FWHM) of 110 ± 20 km s−1, while broader [C ii] is seen with an FWHM of 230 ± 50 km s−1. The broader [C ii] component is blueshifted (−80 ± 20 km s−1) with respect to the narrow [C ii] component, and has a morphology that extends beyond the UV-bright clump. We find that, while the narrow [C ii] emission is most likely associated with zD1.1, the broader component is possibly associated with a physically distinct gas component from zD1.1 (e.g., outflowing or inflowing gas). Based on the nondetection of λ158μm dust continuum, we find that MACS0308-zD1's star formation activity occurs in a dust-free environment indicated by a strong upper limit of infrared luminosity ≲9 × 108L⊙. Targeting this strongly lensed faint galaxy for follow-up Atacama Large Millimeter/submillimeter Array and JWST observations will be crucial to characterize the details of typical galaxy growth in the early Universe
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