Exploring HeIIλ{\lambda}1640 emission line properties at z∼2−4{z\sim2-4}

Deep optical spectroscopic surveys of galaxies provide us a unique opportunity to investigate rest-frame ultra-violet (UV) emission line properties of galaxies at ${z \sim 2-4.5}$. Here we combine VLT/MUSE Guaranteed Time Observations of the Hubble Deep Field South, Ultra Deep Field, COSMOS, and several quasar fields with other publicly available data from VLT/VIMOS and VLT/FORS2 to construct a catalogue of HeII${\lambda}$1640 emitters at ${z\sim2}$. The deepest areas of our MUSE pointings reach a ${3\sigma}$ line flux limit of 3.1${\times}$10-19 erg/ s/ cm$^2$. After discarding broad line active galactic nuclei we find 13 HeII${\lambda}$1640 detections from MUSE with a median MUV = $-20.1$ and 21 tentative HeII${\lambda}$1640 detections from other public surveys. Excluding Ly${\alpha}$, all except two galaxies in our sample show at least one other rest-UV emission line, with CIII]${\lambda}$1907,${\lambda}$1909 being the most prominent. We use multi-wavelength data available in the Hubble legacy fields to derive basic galaxy properties of our sample via spectral energy distribution fitting techniques. Taking advantage of the high quality spectra obtained by MUSE (${\sim10 - 30}$h of exposure time per pointing), we use photo-ionisation models to study the rest-UV emission line diagnostics of the HeII${\lambda}$1640 emitters. Line ratios of our sample can be reproduced by moderately sub-solar photo-ionisation models, however, we find that including effects of binary stars lead to degeneracies in most free parameters. Even after considering extra ionising photons produced by extreme sub-solar metallicity binary stellar models, photo-ionisation models are unable to reproduce rest-frame HeII${\lambda}$1640 equivalent widths (${\sim}$ 0.2 - 10 A), thus additional mechanisms are necessary in models to match the observed HeII${\lambda}$1640 properties.Comment: Accepted to A&A, 31 pages, 17 figure

Spatially resolved signature of quenching in star-forming galaxies

Understanding when, how, and where star formation ceased (quenching) within galaxies is still a critical subject in galaxy evolution studies. Taking advantage of the new methodology developed by Quai et al, to select recently quenched galaxies, we explored the spatial information provided by the WU data to get critical insights on this process. In particular, we analyse 10 SDSS-IV MaNGA galaxies that show regions with low [OIII]/II alpha, compatible with a recent quenching of the star formation. We compare the properties of these 10 galaxies with those of a control sample of 8 MaNGA galaxies with ongoing star formation in the same stellar mass, redshift, and gas-phase metallicity range. The quenching regions found are located between 0.5 and 1.1 effective radii from the centre. This result is supported by the analysis of the average radial profile of the ionization parameter, which reaches a minimum at the same radii, while the one of the star-forming sample shows an almost flat trend. These quenching regions occupy a total area between similar to 15 and 45 per cent of our galaxies, Moreover, the average radial profile of the star formation rate surface density of our sample is lower and Clatter than that of the control sample, at any radii, suggesting a systematic suppression of the star formation in the inner part of our galaxies, Finally, the radial profiles of gas-phase metallicity of the two samples have a similar slope and normalization, Our results cannot be ascribed to a difference in the intrinsic properties of the analysed galaxies, suggesting a quenching scenario more complicated than a simple inside-out quenching

LAstroSat detection of Lyman continuum emission from a z = 1.42 galaxy

One of the outstanding problems of current observational cosmology is to understand the nature of sources that produced the bulk of the ionizing radiation after the Cosmic Dark Age. Direct detection of these reionization sources1 is practically infeasible at high redshift (z) due to the steep decline of intergalactic medium transmission2. However, a number of low-z analogues emitting Lyman continuum at 900 Å restframe are now detected at z \u3c 0.4 (refs. 4) and there are also detections in the range 2.5 \u3c z \u3c 3.5 (refs. 9). Here we report the detection of Lyman continuum emission with a high escape fraction (\u3e20%) from a low-mass clumpy galaxy at z = 1.42, in the middle of the redshift range where no detection has been made before and near the peak of the cosmic star-formation history15. The observation was made in the Hubble Extreme Deep Field16 by the wide-field Ultraviolet Imaging Telescope17 onboard AstroSat18. This detection of extreme ultraviolet radiation from a distant galaxy at a restframe wavelength of 600 Å opens up a new window to constrain the shape of the ionization spectrum. Further observations with AstroSat should substantially increase the sample of Lyman-continuum-leaking galaxies at cosmic noon

Properties and redshift evolution of star-forming galaxies with high [0 III]/[O II] ratios with MUSE at 0.28 < z < 0.85

ISSN:0004-6361ISSN:1432-074

The MUSE Hubble Ultra Deep Field Survey: VII. Fe II emission in star-forming galaxies

International audienceNon-resonant Fe ii* (λ2365, λ2396, λ2612, λ2626) emission can potentially trace galactic winds in emission and provide useful constraints to wind models. From the 3.15′ × 3.15′ mosaic of the Hubble Ultra Deep Field (UDF) obtained with the VLT/MUSE integral field spectrograph, we identify a statistical sample of 40 Fe ii* emitters and 50 Mg ii (λλ2796,2803) emitters from a sample of 271 [O ii]λλ3726,3729 emitters with reliable redshifts from z = 0.85−1.50 down to 2 × 10-18 (3σ) ergs s-1 cm-2 (for [O ii]), covering the M⋆ range from 108−1011 M⊙. The Fe ii* and Mg ii emitters follow the galaxy main sequence, but with a clear dichotomy. Galaxies with masses below 109 M⊙ and star formation rates (SFRs) of ≲ 1 M⊙ yr-1 have Mg ii emission without accompanying Fe ii* emission, whereas galaxies with masses above 1010 M⊙ and SFRs ≳ 10 M⊙ yr-1 have Fe ii* emission without accompanying Mg ii emission. Between these two regimes, galaxies have both Mg ii and Fe ii* emission, typically with Mg ii P Cygni profiles. Indeed, the Mg ii profile shows a progression along the main sequence from pure emission to P Cygni profiles to strong absorption, due to resonant trapping. Combining the deep MUSE data with HST ancillary information, we find that galaxies with pure Mg ii emission profiles have lower SFR surface densities than those with either Mg ii P Cygni profiles or Fe ii* emission. These spectral signatures produced through continuum scattering and fluorescence, Mg ii P Cygni profiles and Fe ii* emission, are better candidates for tracing galactic outflows than pure Mg ii emission, which may originate from H ii regions. We compare the absorption and emission rest-frame equivalent widths for pairs of Fe ii transitions to predictions from outflow models and find that the observations consistently have less total re-emission than absorption, suggesting either dust extinction or non-isotropic outflow geometries