Abstract
Cosmological simulations suggest that most of the matter in the Universe is distributed along filaments connecting galaxies. Illuminated by the cosmic UV background (UVB), these structures ...are expected to glow in fluorescent Ly α emission with a surface brightness (SB) that is well below current limits for individual detections. Here, we perform a stacking analysis of the deepest MUSE/VLT data using three-dimensional regions (subcubes) with orientations determined by the position of neighbouring Ly α galaxies at 3 < z < 4. Our method increase the probability of detecting filamentary Ly α emission, provided that these structures are Lyman-limit systems (LLSs). By stacking 390 oriented subcubes we reach a 2σ sensitivity level of SB ≈ 0.44 × 10−20 erg s−1 cm−2 arcsec−2 in an aperture of 1 arcsec2 × 6.25 Å, three times below the expected fluorescent Ly α signal from the Haardt & Madau UVB at z ∼ 3.5. No detectable emission is found on intergalactic scales, implying that at least two thirds of our subcubes do not contain oriented LLSs. On the other hand, significant emission is detected in the circumgalactic medium (CGM) in the direction of the neighbours. The signal is stronger for galaxies with a larger number of neighbours and appears to be independent of any other galaxy properties. We estimate that preferentially oriented satellite galaxies cannot contribute significantly to this signal, suggesting instead that gas densities in the CGM are typically larger in the direction of neighbouring galaxies on cosmological scales.
The MUSE Hubble Ultra Deep Field Survey Bacon, Roland; Conseil, Simon; Mary, David ...
Astronomy and astrophysics (Berlin),
12/2017, Volume:
608
Journal Article
Peer reviewed
Open access
We present the MUSE
Hubble
Ultra Deep Survey, a mosaic of nine MUSE fields covering 90% of the entire HUDF region with a 10-h deep exposure time, plus a deeper 31-h exposure in a single 1.15 arcmin
2
...field. The improved observing strategy and advanced data reduction results in datacubes with sub-arcsecond spatial resolution (0.̋65 at 7000 Å) and accurate astrometry (0.̋07 rms). We compare the broadband photometric properties of the datacubes to HST photometry, finding a good agreement in zeropoint up to
m
AB
= 28 but with an increasing scatter for faint objects. We have investigated the noise properties and developed an empirical way to account for the impact of the correlation introduced by the 3D drizzle interpolation. The achieved 3
σ
emission line detection limit for a point source is 1.5 and 3.1 × 10
-19
erg s
-1
cm
-2
for the single ultra-deep datacube and the mosaic, respectively. We extracted 6288 sources using an optimal extraction scheme that takes the published HST source locations as prior. In parallel, we performed a blind search of emission line galaxies using an original method based on advanced test statistics and filter matching. The blind search results in 1251 emission line galaxy candidates in the mosaic and 306 in the ultradeep datacube, including 72 sources without HST counterparts (
m
AB
> 31). In addition 88 sources missed in the HST catalog but with clear HST counterparts were identified. This data set is the deepest spectroscopic survey ever performed. In just over 100 h of integration time, it provides nearly an order of magnitude more spectroscopic redshifts compared to the data that has been accumulated on the UDF over the past decade. The depth and high quality of these datacubes enables new and detailed studies of the physical properties of the galaxy population and their environments over a large redshift range.
The MUSE Hubble Ultra Deep Field Survey Feltre, Anna; Bacon, Roland; Tresse, Laurence ...
Astronomy and astrophysics (Berlin),
09/2018, Volume:
617
Journal Article
Peer reviewed
Open access
The physical origin of the near-ultraviolet Mg
II
emission remains an underexplored domain, unlike more typical emission lines that are detected in the spectra of star-forming galaxies. We explore ...the nebular and physical properties of a sample of 381 galaxies between 0.70 <
z
< 2.34 drawn from the MUSE
Hubble
Ultra Deep Survey. The spectra of these galaxies show a wide variety of profiles of the Mg
II
λλ
2796, 2803 resonant doublet, from absorption to emission. We present a study on the main drivers for the detection of Mg
II
emission in galaxy spectra. By exploiting photoionization models, we verified that the emission-line ratios observed in galaxies with Mg
II
in emission are consistent with nebular emission from H
II
regions. From a simultaneous analysis of MUSE spectra and ancillary
Hubble
Space Telescope information through spectral energy distribution fitting, we find that galaxies with Mg
II
in emission have lower stellar masses, smaller sizes, bluer spectral slopes, and lower optical depth than those with absorption. This leads us to suggest that Mg
II
emission is a potential tracer of physical conditions that are not merely related to those of the ionized gas. We show that these differences in Mg
II
emission and absorption can be explained in terms of a higher dust and neutral gas content in the interstellar medium (ISM) of galaxies showing Mg
II
in absorption, which confirms the extreme sensitivity of Mg
II
to the presence of the neutral ISM. We conclude with an analogy between the Mg
II
doublet and the Ly
α
line that lies in their resonant nature. Further investigations with current and future facilities, including the
James Webb
Space Telescope, are promising because the detection of Mg
II
emission and its potential connection with Ly
α
could provide new insights into the ISM content in the early Universe.
The Arabidopsis ARGONAUTE1 (AGO1) and ZWILLE/PINHEAD/AGO10 (ZLL) proteins act in the miRNA and siRNA pathways and are essential for multiple processes in development. Here, we analyze what determines ...common and specific function of both proteins. Analysis of ago1 mutants with partially compromised AGO1 activity revealed that loss of ZLL function re-establishes both siRNA and miRNA pathways for a subset of AGO1 target genes. Loss of ZLL function in ago1 mutants led to increased AGO1 protein levels, whereas AGO1 mRNA levels were unchanged, implicating ZLL as a negative regulator of AGO1 at the protein level. Since ZLL, unlike AGO1, is not subjected to small RNA-mediated repression itself, this cross regulation has the potential to adjust RNA silencing activity independent of feedback dynamics. Although AGO1 is expressed in a broader pattern than ZLL, expression of AGO1 from the ZLL promoter restored transgene PTGS and most developmental defects of ago1, whereas ZLL rescued only a few AGO1 functions when expressed from the AGO1 promoter, suggesting that the specific functions of AGO1 and ZLL are mainly determined by their protein sequence. Protein domain swapping experiments revealed that the PAZ domain, which in AGO1 is involved in binding small RNAs, is interchangeable between both proteins, suggesting that this common small RNA-binding domain contributes to redundant functions. By contrast, the conserved MID and PIWI domains, which are involved in 5'-end small RNA selectivity and mRNA cleavage, and the non-conserved N-terminal domain, to which no function has been assigned, provide specificity to AGO1 and ZLL protein function.
Abstract
Using an ultra-deep blind survey with the MUSE integral field spectrograph on the European Southern Observatory Very Large Telescope, we obtain spectroscopic redshifts to a depth never ...before explored: galaxies with observed magnitudes
m
AB
≳ 30–32. Specifically, we detect objects via Ly
α
emission at 2.9 <
z
< 6.7 without individual continuum counterparts in areas covered by the deepest optical/near-infrared imaging taken by the
Hubble Space Telescope
, the Hubble Ultra Deep Field. In total, we find 102 such objects in 9 square arcminutes at these redshifts. Detailed stacking analyses confirm the Ly
α
emission as well as the 1216 Å breaks and faint ultraviolet continua (
M
UV
∼ −15). This makes them the faintest spectroscopically confirmed objects at these redshifts, similar to the sources believed to reionize the universe. A simple model for the expected fraction of detected/undetected Ly
α
emitters as a function of luminosity is consistent with these objects being the high-equivalent width tail of the normal Ly
α
-emitter population at these redshifts.
Using SINFONI Halpha, NII, and SII AO data of 27 z ~ 2 star-forming galaxies (SFGs) from the SINS and zC-SINF surveys, we explore the dependence of outflow strength (via the broad flux fraction) on ...various galaxy parameters. For galaxies that have evidence for strong outflows, we find that the broad emission is spatially extended to at least the half-light radius (~a few kpc). Decomposition of the SII doublet into broad and narrow components suggests that this outflowing gas probably has a density of ~10-100 cm super(-3), less than that of the star-forming gas (600 cm super(-3)). There is a strong correlation of the Halpha broad flux fraction with the star formation surface density of the galaxy, with an apparent threshold for strong outflows occurring at 1 M sub(middot in circle) yr super(-1) kpc super(-2). Above this threshold, we find that SFGs with log m sub(*) > 10 have similar or perhaps greater wind mass-loading factors (eta = M sub(out)/SFR) and faster outflow velocities than lower mass SFGs, suggesting that the majority of outflowing gas at z ~ 2 may derive from high-mass SFGs. The mass-loading factor is also correlated with the star formation rate (SFR), galaxy size, and inclination, such that smaller, more star-forming, and face-on galaxies launch more powerful outflows. We propose that the observed threshold for strong outflows and the observed mass loading of these winds can be explained by a simple model wherein break-out of winds is governed by pressure balance in the disk.
Meiotic crossovers (COs) are important for reshuffling genetic information between homologous chromosomes and they are essential for their correct segregation. COs are unevenly distributed along ...chromosomes and the underlying mechanisms controlling CO localization are not well understood. We previously showed that meiotic COs are mis-localized in the absence of AXR1, an enzyme involved in the neddylation/rubylation protein modification pathway in Arabidopsis thaliana. Here, we report that in axr1-/-, male meiocytes show a strong defect in chromosome pairing whereas the formation of the telomere bouquet is not affected. COs are also redistributed towards subtelomeric chromosomal ends where they frequently form clusters, in contrast to large central regions depleted in recombination. The CO suppressed regions correlate with DNA hypermethylation of transposable elements (TEs) in the CHH context in axr1-/- meiocytes. Through examining somatic methylomes, we found axr1-/- affects DNA methylation in a plant, causing hypermethylation in all sequence contexts (CG, CHG and CHH) in TEs. Impairment of the main pathways involved in DNA methylation is epistatic over axr1-/- for DNA methylation in somatic cells but does not restore regular chromosome segregation during meiosis. Collectively, our findings reveal that the neddylation pathway not only regulates hormonal perception and CO distribution but is also, directly or indirectly, a major limiting pathway of TE DNA methylation in somatic cells.
The extent of epigenetic variation is currently well documented, but the number of natural epialleles described so far remains very limited. Determining the relevance of epigenetic changes for ...natural variation is an important question of research that we investigate by isolating natural epialleles segregating in Arabidopsis recombinant populations. We previously described a genetic incompatibility among Arabidopsis strains based on the silencing of a gene involved in fitness. Here, we isolated a new epiallele resulting from the silencing of a transfer-RNA editing gene in an Arabidopsis accession from the Netherlands (Nok-1). Crosses with the reference accession Col-0 show a complete incompatibility between this epiallele and another locus localized on a different chromosome. We demonstrate that conversion of an unmethylated version of this allele occurs in hybrids, associated with modifications of small RNA populations. These epialleles can also spontaneously revert within the population. Furthermore, we bring evidence that neither METHYLTRANSFERASE 1, maintaining methylation at CGs, nor components of RNA-directed DNA methylation, are key factors for the transmission of the epiallele over generations. This depends only on the self-reinforcing loop between CHROMOMETHYLASE 3 and KRYPTONITE, involving DNA methylated in the CHG context and histone H3 lysine 9 methylation. Our findings reveal a predominant role of this loop in maintaining a natural epiallele.
ABSTRACT
We investigate whether the dust content of the circum-galactic medium (CGM) depends on the location of the quasar sightline with respect to the galaxy major-axis using 13 galaxy-Mg ii ...absorber pairs (9–81 kpc distance) from the MusE GAs FLOw and Wind (MEGAFLOW) survey at 0.4 < z < 1.4. The dust content of the CGM is obtained from Zn/Fe using ultraviolet and visual echelle spectrograph data. When a direct measurement of Zn/Fe is unavailable, we estimate the dust depletion from a method that consists in solving for the depletion from multiple singly ionized ions (e.g. Mn ii, Cr ii, and Zn ii) since each ion depletes on dust grains at different rates. We find a positive correlation between the azimuthal angle and Zn/Fe with a Pearson’s r = 0.70 ± 0.14. The sightlines along the major axis show Zn/Fe < 0.5, whereas the Zn/Fe is > 0.8 along the minor axis. These results suggest that the CGM along the minor axis is on average more metal enriched (by ≈ 1 dex) than the gas located along the major axis of galaxies provided that dust depletion is a proxy for metallicity. This anisotropic distribution is consistent with recent results on outflow and accretion in hydro-dynamical simulations.
We analyze the spectra, spatial distributions, and kinematics of H alpha , NII, and SII emission in a sample of 38, z ~ 2.2 UV/optically selected star-forming galaxies (SFGs) from the SINS and ...zC-SINF surveys, 34 of which were observed in the adaptive optics mode of SINFONI and 30 of those contain data presented for the first time here. This is supplemented by kinematic data from 43 z ~ 1-2.5 galaxies from the literature. None of these 81 galaxies is an obvious major merger. We find that the kinematic classification of high-z SFGs as "dispersion dominated" or "rotation dominated" correlates most strongly with their intrinsic sizes. Smaller galaxies are more likely "dispersion-dominated" for two main reasons: (1) the rotation velocity scales linearly with galaxy size but intrinsic velocity dispersion does not depend on size or may even increase in smaller galaxies, and as such, their ratio is systematically lower for smaller galaxies, and (2) beam smearing strongly decreases large-scale velocity gradients and increases observed dispersion much more for galaxies with sizes at or below the resolution. Dispersion-dominated SFGs may thus have intrinsic properties similar to "rotation-dominated" SFGs, but are primarily more compact, lower mass, less metal enriched, and may have higher gas fractions, plausibly because they represent an earlier evolutionary state.
PDF
