38 research outputs found
The MUSE Hubble Ultra Deep Field Survey X. Ly Equivalent Widths at
We present rest-frame Ly equivalent widths (EW) of 417 Ly
emitters (LAEs) detected with Multi Unit Spectroscopic Explorer (MUSE) on the
Very Large Telescope (VLT) at in the Hubble Ultra Deep Field.
Based on the deep MUSE spectroscopy and ancillary Hubble Space Telescope (HST)
photometry data, we carefully measured EW values taking into account extended
Ly emission and UV continuum slopes (). Our LAEs reach
unprecedented depths, both in Ly luminosities and UV absolute
magnitudes, from log(/erg s) 41.0 to 43.0 and
from Muv -16 to -21 (0.01-1.0 ). The EW values span the
range of 5 to 240 \AA\ or larger, and their distribution can be well
fitted by an exponential law exp(EW/). Owing to
the high dynamic range in Muv, we find that the scale factor, ,
depends on Muv in the sense that including fainter Muv objects increases
, i.e., the Ando effect. The results indicate that selection
functions affect the EW scale factor. Taking these effects into account, we
find that our values are consistent with those in the literature
within uncertainties at at a given threshold of Muv
and . Interestingly, we find 12 objects with EW \AA\
above uncertainties. Two of these 12 LAEs show signatures of merger
or AGN activity: the weak CIV emission line. For the remaining
10 very large EW LAEs, we find that the EW values can be reproduced by young
stellar ages ( Myr) and low metallicities ( ). Otherwise, at least part of the Ly emission in these LAEs
needs to arise from anisotropic radiative transfer effects, fluorescence by
hidden AGN or quasi-stellar object activity, or gravitational cooling.Comment: 22 pages, 12 figures, 9 tables, accepted for publication in A&A (MUSE
UDF Series Paper X
Median Surface Brightness Profiles of Lyman- Haloes in the MUSE Extremely Deep Field
We present the median surface brightness profiles of diffuse Ly
haloes (LAHs) around star-forming galaxies by stacking 155 spectroscopically
confirmed Ly emitters (LAEs) at 3<z<4 in the MUSE Extremely Deep Field
(MXDF), with median Ly luminosity . After correcting for a systematic surface brightness
offset we identified in the datacube, we detect extended Ly emission
out to a distance of 270 kpc. The median Ly surface brightness profile
shows a power-law decrease in the inner 20 kpc, and a possible flattening trend
at larger distance. This shape is similar for LAEs with different Ly
luminosities, but the normalisation of the surface brightness profile increases
with luminosity. At distances larger than 50 kpc, we observe strong overlap of
adjacent LAHs, and the Ly surface brightness is dominated by the LAHs
of nearby LAEs. We find no clear evidence of redshift evolution of the observed
Ly profiles when comparing with samples at 4<z<5 and 5<z<6. Our results
are consistent with a scenario in which the inner 20 kpc of the LAH is powered
by star formation in the central galaxy, while the LAH beyond a radius of 50
kpc is dominated by photons from surrounding galaxies.Comment: Submitted to A&
A First Look at the Abundance Pattern -- O/H, C/O, Ne/O, and Fe/O -- in Galaxies with JWST/NIRSpec
We analyze the rest-frame near-UV and optical nebular spectra of three z > 7
galaxies from the Early Release Observations taken with the Near-Infrared
Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST). These three
high-z galaxies show the detection of several strong-emission nebular lines,
including the temperature-sensitive [O III] 4363 line, allowing us to
directly determine the nebular conditions and gas-phase abundances for O/H,
C/O, Ne/O, and Fe/O. We derive O/H abundances and ionization parameters that
are generally consistent with other recent analyses. The lowest-mass galaxy has
a large O/H uncertainty, which as a significant effect on anchoring the
mass-metallicity relationship (i.e., slope) and tests of its redshift
evolution. We also detect the C III] 1907,1909 emission in a
z > 8 galaxy from which we determine the most distant C/O abundance to date.
This valuable detection provides the first test of C/O redshift evolution out
to high-redshift. For neon, we use the high-ionization [Ne III] 3869
line to measure the first Ne/O abundances at z>7, finding no evolution in this
-element ratio. To investigate the Fe abundance, we explore the
tentative detection of weak [Fe II] and [Fe III] lines in a z>8 galaxy, which
would indicate a rapid build up of metals. Importantly, we demonstrate that
properly flux-calibrated and higher S/N spectra are crucial to robustly
determine the abundance pattern in z>7 galaxies with NIRSpec/JWST.Comment: Submitted to The Astrophysical Journal Letters. Comments welcom
Reionization with star-forming galaxies: insights from the Low-z Lyman Continuum Survey
The fraction of ionizing photons escaping from galaxies, , is at the
same time a crucial parameter in modelling reionization and a very poorly known
quantity, especially at high redshift. Recent observations are starting to
constrain the values of in low-z star-forming galaxies, but the
validity of this comparison remains to be verified. Applying at high-z the
empirical relation between and the UV slope trends derived from the
Low-z Lyman Continuum Survey, we use the DELPHI semi-analytical galaxy
formation model to estimate the global ionizing emissivity of high-z galaxies,
which we use to compute the resulting reionization history. We find that both
the global ionizing emissivity and reionization history match the observational
constraints. Assuming that the low-z correlations hold during the epoch of
reionization, we find that galaxies with
are the main drivers of reionization. We derive a population-averaged at z=4.5, 6, 8.Comment: 5+1 page, 3 figures, submitted to A&
On the evolution of the size of Lyman alpha halos across cosmic time: no change in the circumgalactic gas distribution when probed by line emission
Lyman (Ly) is now routinely used as a tool for studying
high-redshift galaxies and its resonant nature means it can trace neutral
hydrogen around star-forming galaxies. Integral field spectrograph measurements
of high-redshift Ly emitters indicate that significant extended
Ly halo emission is ubiquitous around such objects. We present a sample
of redshift 0.23 to 0.31 galaxies observed with the Hubble Space Telescope
selected to match the star formation properties of high- samples while
optimizing the observations for detection of low surface brightness Ly
emission. The Ly escape fractions range between 0.7\% and 37\%, and we
detect extended Ly emission around six out of seven targets. We find
Ly halo to UV scale length ratios around 6:1 which is marginally lower
than high-redshift observations, and halo flux fractions between 60\% and 85\%
-- consistent with high-redshift observations -- when using comparable methods.
However, our targets show additional extended stellar UV emission: we
parametrize this with a new double exponential model. We find that this
parametrization does not strongly affect the observed Ly halo
fractions. We find that deeper H data would be required to firmly
determine the origin of Ly halo emission, however, there are
indications that H is more extended than the central FUV profile,
potentially indicating conditions favorable for the escape of ionizing
radiation. We discuss our results in the context of high-redshift galaxies,
cosmological simulations, evolutionary studies of the circumgalactic medium in
emission, and the emission of ionizing radiation.Comment: 20 page, 14 figures, 6 tables. Accepted for publication in MNRA
JWST/NIRSpec Measurements of Extremely Low Metallicities in High Equivalent Width Lyman- Emitters
Deep VLT/MUSE optical integral field spectroscopy has recently revealed an
abundant population of ultra-faint galaxies (15; 0.01 )
at 2.96.7 due to their strong Lyman- emission. The implied
Lyman- equivalent widths are in excess of 100-200 Angstrom, challenging
existing models of normal star formation and implying extremely young ages,
small stellar masses, and a very low amount of metal enrichment. We use
JWST/NIRSpec's microshutter array to follow-up 45 of these galaxies (11h in
G235M/F170LP and 7h in G395M/F290LP), as well as 45 lower-equivalent width
Lyman- emitters. Our spectroscopy covers the range 1.75.1 micron in
order to target strong optical emission lines: H, [OIII], H, and
[NII]. Individual measurements as well as stacks reveal line ratios consistent
with a metal poor nature (230% ) and intense ionizing radiation
fields. The galaxies with the highest equivalent widths of Lyman-, in
excess of 120 Angstrom, have lower gas-phase metallicities than those with
lower equivalent widths. This implies a selection based on Lyman-
equivalent width is an efficient technique for identifying younger, less
chemically enriched systems.Comment: 13 pages, 4 appendices; submitted to AAS Journal
The nature of CR7 revealed with MUSE:A young starburst powering extended Lyman-α emission at z=6.6
CR7 is among the most luminous Lyman-α emitters (LAEs) known at z = 6.6 and consists of at least three UV components that are surrounded by Lyman-α (Lyα) emission. Previous studies have suggested that it may host an extreme ionising source. Here, we present deep integral field spectroscopy of CR7 with VLT/MUSE. We measure extended emission with a similar halo scale length as typical LAEs at z ≈ 5. CR7’s Lyα halo is clearly elongated along the direction connecting the multiple components, likely tracing the underlying gas distribution. The Lyα emission originates almost exclusively from the brightest UV component, but we also identify a faint kinematically distinct Lyα emitting region nearby a fainter component. Combined with new near-infrared data, the MUSE data show that the rest-frame Lyα equivalent width (EW) is ≈100 Å. This is a factor four higher than the EW measured in low-redshift analogues with carefully matched Lyα profiles (and thus arguably HI column density), but this EW can plausibly be explained by star formation. Alternative scenarios requiring AGN powering are also disfavoured by the narrower and steeper Lyα spectrum and much smaller IR to UV ratio compared to obscured AGN in other Lyα blobs. CR7’s Lyα emission, while extremely luminous, resembles the emission in more common LAEs at lower redshifts very well and is likely powered by a young metal poor starburst
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The MUSE Extremely Deep Field: The cosmic web in emission at high redshift
We report the discovery of diffuse extended Lyα emission from redshift 3.1 to 4.5, tracing cosmic web filaments on scales of 2.5-4 cMpc. These structures have been observed in overdensities of Lyα emitters in the MUSE Extremely Deep Field, a 140 h deep MUSE observation located in the Hubble Ultra-Deep Field. Among the 22 overdense regions identified, five are likely to harbor very extended Lyα emission at high significance with an average surface brightness of 5 × 10-20 erg s-1 cm-2 arcsec-2. Remarkably, 70% of the total Lyα luminosity from these filaments comes from beyond the circumgalactic medium of any identified Lyα emitter. Fluorescent Lyα emission powered by the cosmic UV background can only account for less than 34% of this emission at z ≈ 3 and for not more than 10% at higher redshift. We find that the bulk of this diffuse emission can be reproduced by the unresolved Lyα emission of a large population of ultra low-luminosity Lyα emitters (< 1040 erg s-1), provided that the faint end of the Lyα luminosity function is steep (α ⪅ -1.8), it extends down to luminosities lower than 1038 - 1037 erg s-1, and the clustering of these Lyα emitters is significant (filling factor < 1/6). If these Lyα emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates < 10-4M yr-1. These observations provide the first detection of the cosmic web in Lyα emission in typical filamentary environments and the first observational clue indicating the existence of a large population of ultra low-luminosity Lyα emitters at high redshift. © R. Bacon et al. 2021
Dark galaxy candidates at redshift∼ 3.5 detected with MUSE
Recent theoretical models suggest that the early phase of galaxy formation could involve an epoch when galaxies
are gas rich but inefficient at forming stars: a “dark galaxy” phase. Here, we report the results of our Multi-Unit
Spectroscopic Explorer (MUSE) survey for dark galaxies fluorescently illuminated by quasars at z > 3. Compared
to previous studies which are based on deep narrowband (NB) imaging, our integral field survey provides a nearly
uniform sensitivity coverage over a large volume in redshift space around the quasars as well as full spectral
information at each location. Thanks to these unique features, we are able to build control samples at large redshift
distances from the quasars using the same data taken under the same conditions. By comparing the rest-frame
equivalent width (EW0) distributions of the Lyα sources detected in proximity to the quasars and in control
samples, we detect a clear correlation between the locations of high-EW0 objects and the quasars. This correlation
is not seen in other properties, such as Lyα luminosities or volume overdensities, suggesting the possible
fluorescent nature of at least some of these objects. Among these, we find six sources without continuum
counterparts and EW0 limits larger than 240 Å that are the best candidates for dark galaxies in our survey at
z > 3.5. The volume densities and properties, including inferred gas masses and star formation efficiencies, of
these dark galaxy candidates are similar to those of previously detected candidates at z ≈ 2.4 in NB surveys.
Moreover, if the most distant of these are fluorescently illuminated by the quasar, our results also provide a lower
limit of t = 60 Myr on the quasar lifetime.peer-reviewe