292 research outputs found
The Brightest Ly Emitter: Pop III or Black Hole?
CR7 is the brightest emitter (LAE) known to date,
and spectroscopic follow-up by Sobral et al. (2015) suggests that CR7 might
host Population (Pop) III stars. We examine this interpretation using
cosmological hydrodynamical simulations. Several simulated galaxies show the
same "Pop III wave" pattern observed in CR7. However, to reproduce the extreme
CR7 /HeII1640 line luminosities () a
top-heavy IMF and a massive () PopIII burst with age
Myr are required. Assuming that the observed properties of and HeII emission are typical for Pop III, we predict that in the
COSMOS/UDS/SA22 fields, 14 out of the 30 LAEs at with should also host Pop III stars producing an
observable . As an alternate
explanation, we explore the possibility that CR7 is instead powered by
accretion onto a Direct Collapse Black Hole (DCBH). Our model predicts
, , and X-ray luminosities that are in agreement
with the observations. In any case, the observed properties of CR7 indicate
that this galaxy is most likely powered by sources formed from pristine gas. We
propose that further X-ray observations can distinguish between the two above
scenarios.Comment: 6 pages, 4 figure
Probing the AGN Unification Model at redshift z 3 with MUSE observations of giant Ly nebulae
A prediction of the classic active galactic nuclei (AGN) unification model is
the presence of ionisation cones with different orientations depending on the
AGN type. Confirmations of this model exist for present times, but it is less
clear in the early Universe. Here, we use the morphology of giant Ly
nebulae around AGNs at redshift z3 to probe AGN emission and therefore
the validity of the AGN unification model at this redshift. We compare the
spatial morphology of 19 nebulae previously found around type I AGNs with a new
sample of 4 Ly nebulae detected around type II AGNs. Using two
independent techniques, we find that nebulae around type II AGNs are more
asymmetric than around type I, at least at radial distances ~physical kpc
(pkpc) from the ionizing source. We conclude that the type I and type II AGNs
in our sample show evidence of different surrounding ionising geometries. This
suggests that the classical AGN unification model is also valid for
high-redshift sources. Finally, we discuss how the lack of asymmetry in the
inner parts (r30 pkpc) and the associated high values of the HeII to
Ly ratios in these regions could indicate additional sources of (hard)
ionizing radiation originating within or in proximity of the AGN host galaxies.
This work demonstrates that the morphologies of giant Ly nebulae can be
used to understand and study the geometry of high redshift AGNs on
circum-nuclear scales and it lays the foundation for future studies using much
larger statistical samples.Comment: 15 pages, 13 figures, accepted for publication in MNRA
Unveiling the most luminous Lyman-a emitters in the epoch of reionisation
Distant luminous Lyman-a emitters are excellent targets for detailed observations of galaxies in the epoch of reionisation. Spatially resolved observations of these galaxies allow us to simultaneously probe the emission from young stars, partially ionised gas in the interstellar medium and to constrain the properties of the surrounding hydrogen in the circumgalactic medium. We review recent results from (spectroscopic) follow-up studies of the rest-frame UV, Lyman-a and [CII] emission in luminous galaxies observed 1/4500 Myr after the Big Bang with ALMA, HST/WFC3 and VLT/X-SHOOTER. These galaxies likely reside in early ionised bubbles and are complex systems, consisting of multiple well separated and resolved components where traces of metals are already present
A 1.4 deg^2 blind survey for C II], C III] and C IV at z ~ 0.7-1.5 - II. Luminosity functions and cosmic average line ratios
Article / Letter to editorSterrewach
The Fundamental Plane of star formation in galaxies revealed by the EAGLE hydrodynamical simulations
We investigate correlations between different physical properties of star-forming galaxies in the ‘Evolution and Assembly of GaLaxies and their Environments’ (EAGLE) cosmological hydrodynamical simulation suite over the redshift range 0 ≤ z ≤ 4.5. A principal component analysis reveals that neutral gas fraction (fgas,neutral), stellar mass (Mstellar) and star formation rate (SFR) account for most of the variance seen in the population, with galaxies tracing a two-dimensional, nearly flat, surface in the three-dimensional space of fgas, neutral–Mstellar–SFR with little scatter. The location of this plane varies little with redshift, whereas galaxies themselves move along the plane as their fgas, neutral and SFR drop with redshift. The positions of galaxies along the plane are highly correlated with gas metallicity. The metallicity can therefore be robustly predicted from fgas, neutral, or from the Mstellar and SFR. We argue that the appearance of this ‘Fundamental Plane of star formation’ is a consequence of self-regulation, with the plane's curvature set by the dependence of the SFR on gas density and metallicity. We analyse a large compilation of observations spanning the redshift range 0 ≲ z ≲ 3, and find that such a plane is also present in the data. The properties of the observed Fundamental Plane of star formation are in good agreement with EAGLE's predictions
EIGER II. first spectroscopic characterisation of the young stars and ionised gas associated with strong H and [OIII] line-emission in galaxies at z=5-7 with JWST
We present emission-line measurements and physical interpretations for a
sample of 117 [OIII] emitting galaxies at , using the first deep
JWST/NIRCam wide field slitless spectroscopic observations. Our 9.7-hour
integration is centered upon the quasar J0100+2802 -- the first of six
fields targeted by the EIGER survey -- and covers microns. We
detect 133 [OIII] doublets, but merge pairs within 10 kpc and 600 km
s, motivated by their small scale clustering excess. We detect H
in 68 and H emission in two galaxies. The galaxies are characterised by
a UV luminosity M ( to ), stellar mass
~ M, H and [OIII] EWs 850
Angstrom (up to 3000 Angstrom), young ages (~100 Myr), a highly excited
interstellar medium ([OIII]/H) and low dust attenuations. These
high EWs are very rare in the local Universe, but we show they are ubiquitous
at based on the measured number densities. The stacked spectrum
reveals H and [OIII] which shows that the galaxies are
typically dust and metal poor (E(B-V)=0.1, 12+log(O/H)=7.4) with a high
electron temperature ( K) and a production efficiency of ionising
photons ( Hz erg). We further show the
existence of a strong mass-metallicity relation. The young highly ionising
stellar populations, moderately low metallicities, low dust attenuations and
high ionisation state in z~6 galaxies conspire to maximise the [OIII] output
from galaxies, yielding an [OIII] luminosity density at z~6 that is
significantly higher than at z~2, despite the order of magnitude decline in
cosmic star formation. Thus, [OIII] emission-line surveys with JWST prove a
highly efficient method to trace the galaxy density in the epoch of
reionization.Comment: Accepted for publication in ApJ. Main text 22 pages, 20 figures. Main
results in Figs 14 (Xi_ion), 15 (MEx diagram),17 (MZR), 19 ([OIII] luminosity
density
EIGER I. a large sample of [OIII]-emitting galaxies at and direct evidence for local reionization by galaxies
We present a first sample of 117 [OIII]4960,5008-selected
star-forming galaxies at detected in JWST/NIRCam 3.5m
slitless spectroscopy of a arcmin field centered on the
hyperluminous quasar SDSS J0100+2802, obtained as part of the EIGER
(Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization)
survey. Three prominent galaxy overdensities are observed, one of them at the
redshift of the quasar. Galaxies are found within 200 pkpc and 105 km s
of four known metal absorption-line systems in this redshift range. We focus on
the role of the galaxies in ionizing the surrounding intergalactic medium (IGM)
during the later stages of cosmic reionization and construct the mean
Ly and Ly transmission as a function of distance from the
galaxies. At the lowest redshifts in our study, , the IGM
transmission rises monotonically with distance from the galaxies. This is as
expected when galaxies reside at peaks in the overdensity field of an IGM that
is ionized by more or less uniform ionizing background, and has been seen at
lower redshifts. In contrast, at , the transmission of both
Ly and Ly first increases with distance, but then peaks at a
distance of 5 cMpc before declining. This peak in transmission is qualitatively
similar to that seen (albeit at smaller distances and higher redshifts) in the
THESAN simulations. Finally, in the region where the
additional ionizing radiation from the quasar dominates, the monotonic increase
in transmission with distance is re-established. This result is interpreted to
represent evidence that the transmission of the IGM at towards
J0100+2802 results from the ``local'' ionizing radiation of galaxies that
dominates over the much reduced cosmic background.Comment: 24 pages, 14 figures, submitted to ApJ, comments welcom
Compact [C II] emitters around a C IV absorption complex at redshift 5.7
The physical conditions of the circumgalactic medium are probed by
intervening absorption-line systems in the spectrum of background quasi-stellar
objects out to the epoch of cosmic reionization. A correlation between the
ionization state of the absorbing gas and the nature of the nearby galaxies has
been suggested by the sources detected either in Lyalpha or [C ii] 158 m near
to respectively highly-ionized and neutral absorbers. This is also likely
linked to the global changes in the incidence of absorption systems of
different types and the process of cosmic reionization. Here we report the
detection of two [C ii]-emitting galaxies at redshift that are
associated with a complex high-ionization C iv absorption system. These objects
are part of an overdensity of galaxies and have compact sizes (< 2.4 kpc) and
narrow line widths (FWHM 62--64 km s-1). Hydrodynamic simulations
predict that similar narrow [C ii] emission may arise from the heating of small
( 3 kpc) clumps of cold neutral medium or a compact photodissociation
region. The lack of counterparts in the rest-frame ultraviolet indicates severe
obscuration of the sources that are exciting the [C ii] emission. These results
may suggest a connection between the properties of the [C ii] emission, the
rare overdensity of galaxies and the unusual high ionization state of the gas
in this region.Comment: Published in Nature on 10 May 2023; authors' version; link to the
paper: https://www.nature.com/articles/s41586-023-05901-
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