Search

The vast majority of star-forming galaxies are surrounded by large reservoirs of gas ejected from the interstellar medium. Ultraviolet absorption and emission lines represent powerful diagnostics to constrain the cool phase of these outflows, through resonant transitions of hydrogen and metal ions. The interpretation of these observations is often remarkably difficult as it requires detailed modelling of the propagation of the continuum and emission lines in the gas. To this aim, we present a large public grid of ≈20 000 simulated spectra that includes H I Lyα and five metal transitions associated with Mg II, C II, Si II, and Fe II which is accessible online. The spectra have been computed with the RASCAS Monte Carlo radiative transfer code for 5760 idealised spherically symmetric configurations surrounding a central point source emission, and characterised by their column density, Doppler parameter, dust opacity, wind velocity, as well as various density and velocity gradients. Designed to predict and interpret Lyα and metal line profiles, our grid exhibits a wide diversity of resonant absorption and emission features, as well as fluorescent lines. We illustrate how it can help better constrain the wind properties by performing a joint modelling of observed Lyα, C II, and Si II spectra. Using CLOUDY simulations and virial scaling relations, we also show that Lyα is expected to be a faithful tracer of the gas at T ≈ 104 − 105 K, even if the medium is highly ionised. While C II is found to probe the same range of temperatures as Lyα, other metal lines merely trace cooler phases (T ≈ 104 K). As their gas opacity strongly depends on gas temperature, incident radiation field, metallicity and dust depletion, we caution that optically thin metal lines do not necessarily originate from low H I column densities and may not accurately probe Lyman continuum leakage. [ABSTRACT FROM AUTHOR]

Context. Resonant lines are powerful probes of the interstellar and circumgalactic medium of galaxies. Their transfer in gas being a complex process, the interpretation of their observational signatures, either in absorption or in emission, is often not straightforward. Numerical radiative transfer simulations are needed to accurately describe the travel of resonant line photons in real and in frequency space, and to produce realistic mock observations. Aims. This paper introduces RASCAS, a new public 3D radiative transfer code developed to perform the propagation of any resonant line in numerical simulations of astrophysical objects. RASCAS was designed to be easily customisable and to process simulations of arbitrarily large sizes on large supercomputers. Methods. RASCAS performs radiative transfer on an adaptive mesh with an octree structure using the Monte Carlo technique. RASCAS features full MPI parallelisation, domain decomposition, adaptive load-balancing, and a standard peeling algorithm to construct mock observations. The radiative transport of resonant line photons through different mixes of species (e.g. Hi, Si ii, Mgii, Fe ii), including their interaction with dust, is implemented in a modular fashion to allow new transitions to be easily added to the code. Results. RASCAS is very accurate and efficient. It shows perfect scaling up to a minimum of a thousand cores. It has been fully tested against radiative transfer problems with analytic solutions and against various test cases proposed in the literature. Although it was designed to describe accurately the many scatterings of line photons, RASCAS may also be used to propagate photons at any wavelength (e.g. stellar continuum or fluorescent lines), or to cast millions of rays to integrate the optical depths of ionising photons, making it highly versatile. [ABSTRACT FROM AUTHOR]

Multi-Unit Spectroscopic Explorer (MUSE) observations of the cluster of galaxies CGr32 (M200 ≃ 2 × 1014 M⊙) at z = 0.73 reveal the presence of two massive star-forming galaxies with extended tails of diffuse gas detected in the [O II]λλ3727–3729 Å emission-line doublet. The tails, which have a cometary shape with a typical surface brightness of a few 10−18 erg s−1 cm−2 arcsec−2, extend up to ≃100 kpc (projected distance) from the galaxy discs, and are not associated with any stellar component. All this observational evidence suggests that the gas was removed during a ram-pressure stripping event. This observation is thus the first evidence that dynamical interactions with the intracluster medium were active when the Universe was only half its present age. The density of the gas derived using the observed [O II]λ3729/[O II]λ3726 line ratio implies a very short recombination time, suggesting that a source of ionisation is necessary to keep the gas ionised within the tail. [ABSTRACT FROM AUTHOR]

We report the discovery of a 104 kpc2 gaseous structure detected in [O ii]λλ3727, 3729 in an over-dense region of the COSMOS-Gr30 galaxy group at z ~ 0.725 with deep MUSE Guaranteed Time Observations. We estimate the total amount of diffuse ionised gas to be of the order of (~5 ± 3) × 1010 M⊙ and explore its physical properties to understand its origin and the source(s) of the ionisation. The MUSE data allow the identification of a dozen group members that are embedded in this structure through emission and absorption lines. We extracted spectra from small apertures defined for both the diffuse ionised gas and the galaxies. We investigated the kinematics and ionisation properties of the various galaxies and extended gas regions through line diagnostics (R23, O32, and [O iii]/Hβ) that are available within the MUSE wavelength range. We compared these diagnostics to photo-ionisation models and shock models. The structure is divided into two kinematically distinct sub-structures. The most extended sub-structure of ionised gas is likely rotating around a massive galaxy and displays filamentary patterns that link some galaxies. The second sub-structure links another massive galaxy that hosts an active galactic nucleus (AGN) to a low-mass galaxy, but it also extends orthogonally to the AGN host disc over ~ 35 kpc. This extent is likely ionised by the AGN itself. The location of small diffuse regions in the R23 vs. O32 diagram is compatible with photo-ionisation. However, the location of three of these regions in this diagram (low O32, high R23) can also be explained by shocks, which is supported by their high velocity dispersions. One edge-on galaxy shares the same properties and may be a source of shocks. Regardless of the hypothesis, the extended gas seems to be non-primordial. We favour a scenario where the gas has been extracted from galaxies by tidal forces and AGN triggered by interactions between at least the two sub-structures. [ABSTRACT FROM AUTHOR]

We provide, for the first time, robust observational constraints on the galaxy major merger fraction up to z ≈ 6 using spectroscopic close pair counts. Deep Multi Unit Spectroscopic Explorer (MUSE) observations in the Hubble Ultra Deep Field (HUDF) and Hubble Deep Field South (HDF-S) are used to identify 113 secure close pairs of galaxies among a parent sample of 1801 galaxies spread over a large redshift range (0.2 < z < 6) and stellar masses (107−1011 M⊙), thus probing about 12 Gyr of galaxy evolution. Stellar masses are estimated from spectral energy distribution (SED) fitting over the extensive UV-to-NIR HST photometry available in these deep Hubble fields, adding Spitzer IRAC bands to better constrain masses for high-redshift (z ⩾ 3) galaxies. These stellar masses are used to isolate a sample of 54 major close pairs with a galaxy mass ratio limit of 1:6. Among this sample, 23 pairs are identified at high redshift (z ⩾ 3) through their Lyα emission. The sample of major close pairs is divided into five redshift intervals in order to probe the evolution of the merger fraction with cosmic time. Our estimates are in very good agreement with previous close pair counts with a constant increase of the merger fraction up to z ≈ 3 where it reaches a maximum of 20%. At higher redshift, we show that the fraction slowly decreases down to about 10% at z ≈ 6. The sample is further divided into two ranges of stellar masses using either a constant separation limit of 109.5 M⊙ or the median value of stellar mass computed in each redshift bin. Overall, the major close pair fraction for low-mass and massive galaxies follows the same trend. These new, homogeneous, and robust estimates of the major merger fraction since z ≈ 6 are in good agreement with recent predictions of cosmological numerical simulations. [ABSTRACT FROM AUTHOR]

We have conducted a two-layered spectroscopic survey (10 × 1 0 ultra deep and 30 × 3 0 deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for Hubble Space Telescope (HST) continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z > 3 and to HST/F775W magnitudes as faint as ≈30 mag (AB, 1σ). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field. We assessed redshifts mainly with the spectral features [O ii] at z < 1.5 (473 objects) and Lyα at 2.9 < z < 6.7 (692 objects). With respect to F775W magnitude, a 50% completeness is reached at 26.5 mag for ultra deep and 25.5 mag for deep fields, and the completeness remains &20% up to 28–29 mag and ≈27 mag, respectively. We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures ≈80% of the targeted z ∼ 2.7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to ≈20–40%. We empirically redefine the selection boundaries to make an attempt to improve them to ≈60%. The revised boundaries allow bluer colors that capture Lyα emitters with high Lyα equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog. [ABSTRACT FROM AUTHOR]

Aims. Whereas the evolution of gas kinematics of massive galaxies is now relatively well established up to redshift z ~ 3, little is known about the kinematics of lower mass (M⋆≤ 1010M⊙) galaxies. We use MUSE, a powerful wide-field, optical integral-field spectrograph (IFS) recently mounted on the VLT, to characterize this galaxy population at intermediate redshift. Methods. We made use of the deepest MUSE observations performed so far on the Hubble Deep Field South (HDFS). This data cube, resulting from 27 h of integration time, covers a one arcmin2 field of view at an unprecedented depth (with a 1σ emission-line surface brightness limit of 1 × 10-19 erg s-1 cm-2 arcsec-2) and a final spatial resolution of ≈0.7′′. We identified a sample of 28 resolved emission-line galaxies, extending over an area that is at least twice the seeing disk, spread over a redshift interval of 0.2 to lower masses/velocities but with a higher dispersion. We find that 90% of the MUSE-HDFS galaxies with stellar masses below 109.5M⊙ have settled gas disks. The MUSE-HDFS galaxies follow the scaling relations defined in the local Universe between the specific angular momentum and stellar mass. However, we find that intermediate-redshift, star-forming galaxies fill a continuum transition from the spiral to elliptical local scaling relations, according to the dynamical state (i.e., rotation- or dispersion-dominated) of the gas. This indicates that some galaxies may lose their angular momentum and become dispersion-dominated prior to becoming passive. [ABSTRACT FROM AUTHOR]

The relation between the stellar mass (M*) and the star formation rate (SFR) characterizes how the instantaneous star formation is determined by the galaxy past star formation history and by the growth of the dark matter structures. We deconstruct the M*-SFR plane by measuring the specific SFR functions in several stellar mass bins from z = 0.2 out to z = 1.4 (specific SFR = SFR/M*, noted sSFR). Our analysis is primary based on a 24 μm selected catalogue combining the COSMOS and GOODS surveys. We estimate the SFR by combining mid- and far-infrared data for 20500 galaxies. The sSFR functions are derived in four stellar mass bins within the range 9.5 < log(M*/M☉) < 11.5. First, we demonstrate the importance of taking into account selection effects when studying the M*-SFR relation. Secondly, we find a mass-dependent evolution of the median sSFR with redshift varying as sSFR ∞ (1 + z)b, with b increasing from b = 2.88±0.12 to b = 3.78±0.60 between M* = 109.75 M☉ and M* = 1011.1 M☉, respectively. At low masses, this evolution is consistent with the cosmological accretion rate and predictions from semi-analytical models (SAM). This agreement breaks down for more massive galaxies showing the need for a more comprehensive description of the star formation history in massive galaxies. Third, we obtain that the shape of the sSFR function is invariant with time at z < 1.4 but depends on the mass. We observe a broadening of the sSFR function ranging from 0.28 dex at M* = 109.75 M☉ to 0.46 dex at M* = 1011.1 M☉. Such increase in the intrinsic scatter of the M*-SFR relation suggests an increasing diversity of star formation histories (SFHs) as the stellar mass increases. Finally, we find a gradual decline of the sSFR with stellar mass as log10(sSFR) ∞ -0.17M*.We discuss the numerous physical processes, as gas exhaustion in hot gas halos or secular evolution, which can gradually reduce the sSFR and increase the SFH diversity. [ABSTRACT FROM AUTHOR]

We explore the properties of high-redshift Lyman alpha emitters (LAEs), and their link with the Lyman-break galaxy (LBG) population, using a semi-analytic model of galaxy formation g that takes into account resonant scattering of Lyα photons in gas outflows. We can reasonably 2L reproduce the abundances of LAEs and LBGs from z ≈ 3 to 7, as well as most UV luminosity functions (LFs) of LAEs. The stronger dust attenuation for (resonant) Lyα photons compared t to UV continuum photons in bright LBGs provides a natural interpretation to the increase of 11 the LAE fraction in LBG samples, XLAE, towards fainter magnitudes. The redshift evolution of XLAE seems however very sensitive to UV magnitudes limits and equivalent width (EW) cuts. In spite of the apparent good match between the statistical properties predicted by the model and the observations, we find that the tail of the Lyα EW distribution (EW ≳ 100 Å) U cannot be explained by our model, and we need to invoke additional mechanisms. We find that 3 LAEs and LBGs span a very similar dynamical range, but bright LAEs are times rarer than LBGs in massive haloes. Moreover, massive haloes mainly contain weak LAEs in our model, a which might introduce a bias towards low-mass haloes in surveys which select sources with high-EW cuts. Overall, our results are consistent with the idea that LAEs and LBGs make a very similar galaxy population. Their apparent differences seem mainly due to EW selections, UV detection limits, and a decreasing Lyα to UV escape fraction ratio in high star formation rate galaxies. [ABSTRACT FROM AUTHOR]

We trace the formation and advection of several elements within a cosmological adaptive mesh refinement simulation of an L⋆ galaxy. We use nine realizations of the same initial conditions with different stellar initial mass functions (IMFs), mass limits for Type II and Type Ia supernovae (SNII, SNIa) and stellar lifetimes to constrain these subgrid phenomena. Our code includes self-gravity, hydrodynamics, star formation, radiative cooling and feedback from multiple sources within a cosmological framework. Under our assumptions of nucleosynthesis we find that SNII with progenitor masses of up to 100 M⊙ are required to match low-metallicity gas oxygen abundances. Tardy SNIa are necessary to reproduce the classical chemical evolution ‘knee’ in [O/Fe]–[Fe/H]: more prompt SNIa delayed time distributions do not reproduce this feature. Within our framework of hydrodynamical mixing of metals and galaxy mergers we find that chemical evolution is sensitive to the shape of the IMF and that there exists a degeneracy with the mass range of SNII. We look at the abundance plane and present the properties of different regions of the plot, noting the distinct chemical properties of satellites and a series of nested discs that have greater velocity dispersions are more α-rich and metal poor with age. [ABSTRACT FROM AUTHOR]

ABSTRACT By means of high-resolution cosmological hydrodynamical simulations of Milky Way (MW) like disc galaxies, we conduct an analysis of the associated stellar metallicity distribution functions (MDFs). After undertaking a kinematic decomposition of each simulation into spheroid and disc subcomponents, we compare the predicted MDFs to those observed in the solar neighbourhood and the Galactic bulge. The effects of the star formation density threshold are visible in the star formation histories, which show a modulation in their behaviour driven by the threshold. The derived MDFs show median metallicities lower by 0.2-0.3 dex than the MDF observed locally in the disc and in the Galactic bulge. Possible reasons for this apparent discrepancy include the use of low stellar yields and/or centrally concentrated star formation. The dispersions are larger than the one of the observed MDF; this could be due to simulated discs being kinematically hotter relative to the MW. The fraction of low-metallicity stars is largely overestimated, visible from the more negatively skewed MDF with respect to the observational sample. For our fiducial MW analogue, we study the metallicity distribution of the stars born in situ relative to those formed via accretion (from disrupted satellites), and demonstrate that this low-metallicity tail to the MDF is populated primarily by accreted stars. Enhanced supernova and stellar radiation energy feedback to the surrounding interstellar media of these pre-disrupted satellites is suggested as an important regulator of the MDF skewness. [ABSTRACT FROM AUTHOR]

Aims. We test the validity of comparing simulated field disk galaxies with the empirical properties of systems situated within environments more comparable to loose groups, including the Milky Way’s Local Group. Methods. Cosmological simulations of Milky Way-mass galaxies have been realised in two different environment samples: in the field and in loose groups environments with similar properties to the Local Group. Apart from the differing environments of the galaxies, the samples are kept as homogeneous as possible with equivalent ranges in last major merger time, halo mass and halo spin. Comparison of these two samples allow for systematic differences in the simulations to be identified. A kinematic decomposition is employed to objectively quantify the spheroid-to-disk ratio and to isolate the disk-star population. Metallicity gradients, disk scale lengths, colours, magnitudes and age-velocity dispersion relations are studied for each galaxy in the suite and the strength of the link between these and environment of the galaxies is studied. Results. Metallicity gradients are consistent with observations of HII regions in spiral galaxies and, in agreement with observations, correlate with total galaxy mass. The bulge-to-disk ratio of the galaxies show that these galaxies are less spheroid dominated than many other simulated galaxies in literature with the majority of both samples being disk dominated. We find that secular evolution and mergers dominate the spread of morphologies and metallicity gradients with no visible differences between the two environment samples. In contrast with this consistency in the two samples there is tentative evidence for a systematic difference in the velocity dispersion-age relations of galaxies in the different environments. Loose group galaxies appear to have more discrete steps in their velocity dispersion-age relations, if this is true it suggests that impulsive heating is more efficient in the stars of galaxies in denser environment than in the field. We conclude that at the current resolution of cosmological galaxy simulations field environment galaxies are sufficiently similar to those in loose groups to be acceptable proxies for comparison with the Milky Way provided that a similar assembly history is considered. [ABSTRACT FROM AUTHOR]

ABSTRACT We examine the chemical properties of five cosmological hydrodynamical simulations of an M33-like disc galaxy which have been shown previously to be consistent with the morphological characteristics and bulk scaling relations expected of late-type spirals. These simulations are part of the Making Galaxies in a Cosmological Context Project, in which stellar feedback is tuned to match the stellar mass-halo mass relationship. Each realization employed identical initial conditions and assembly histories, but differed from one another in their underlying baryonic physics prescriptions, including (a) the efficiency with which each supernova energy couples to the surrounding interstellar medium, (b) the impact of feedback associated with massive star radiation pressure, (c) the role of the minimum shut-off time for radiative cooling of Type II supernovae remnants, (d) the treatment of metal diffusion and (e) varying the initial mass function. Our analysis focusses on the resulting stellar metallicity distribution functions (MDFs) in each simulated (analogous) 'solar neighbourhood' (2-3 disc scalelengths from the galactic centre) and central 'bulge' region. We compare and contrast the simulated MDFs' skewness, kurtosis and dispersion (inter-quartile, inter-decile, inter-centile and inter-tenth-percentile regions) with that of the empirical solar neighbourhood MDF and Local Group dwarf galxies. We find that the MDFs of the simulated discs are more negatively skewed, with higher kurtosis, than those observed locally in the Milky Way and Local Group dwarfs. We can trace this difference to the simulations' very tight and correlated age-metallicity relations (compared with that of the Milky Way's solar neighbourhood), suggesting that these relations within 'dwarf' discs might be steeper than in L★ discs (consistent with the simulations' star formation histories and extant empirical data), and/or the degree of stellar orbital redistribution and migration inferred locally has not been captured in their entirety, at the resolution of our simulations. The important role of metal diffusion in ameliorating the overproduction of extremely metal-poor stars is highlighted. [ABSTRACT FROM AUTHOR]

We report about the fact that the stellar population that is born in the gas inflowing towards the central regions can be vertically unstable leading to a B/PS feature remarkably bluer that the surrounding bulge. Using new chemodynamical simulations we show that this young population does not remain as flat as the gaseous nuclear disc and buckles out of the plane to form a new boxy bulge. We show that such a young B/PS bulge can be detected in colour maps. [ABSTRACT FROM PUBLISHER]