Abstract
The time frame in which hydrogen reionization occurred is highly uncertain, but can be constrained by observations of Lyman-alpha (Ly
α
) emission from distant sources. Neutral hydrogen in ...the intergalactic medium (IGM) attenuates Ly
α
photons emitted by galaxies. As reionization progressed the IGM opacity decreased, increasing Ly
α
visibility. The galaxy Ly
α
luminosity function (LF) is thus a useful tool to constrain the timeline of reionization. In this work, we model the Ly
α
LF as a function of redshift,
z
= 5–10, and average IGM neutral hydrogen fraction,
x
¯
Hɪ
. We combine the Ly
α
luminosity probability distribution obtained from inhomogeneous reionization simulations with a model for the UV LF to model the Ly
α
LF. As the neutral fraction increases, the average number density of Ly
α
emitting galaxies decreases, and are less luminous, though for
x
¯
Hɪ
≲
0.4
there is only a small decrease in the Ly
α
LF. We use our model to infer the IGM neutral fraction at
z
= 6.6, 7.0, and 7.3 from observed Ly
α
LFs. We conclude that there is a significant increase in the neutral fraction with increasing redshift:
x
¯
Hɪ
(
z
=
6.6
)
=
0.08
−
0.05
+
0.08
,
x
¯
Hɪ
(
z
=
7.0
)
=
0.28
±
0.05
and
x
¯
Hɪ
(
z
=
7.3
)
=
0.83
−
0.07
+
0.06
. We predict trends in the Ly
α
luminosity density and Schechter parameters as a function of redshift and the neutral fraction. We find that the Ly
α
luminosity density decreases as the universe becomes more neutral. Furthermore, as the neutral fraction increases, the faint-end slope of the Ly
α
LF steepens, and the characteristic Ly
α
luminosity shifts to lower values; hence, we conclude that the evolving shape of the Ly
α
LF—not just its integral—is an important tool to study reionization.
Abstract
We develop a new method to determine the distance between a high-redshift galaxy and a foreground screen of atomic hydrogen. In a partially neutral universe, and assuming spherical symmetry, ...this equates to the radius of an ionized “bubble” (
R
B
) surrounding the galaxy. The method requires an observed Ly
α
equivalent width, its velocity offset from systemic, and an input Ly
α
profile for which we adopt scaled versions of the profiles observed in low-
z
galaxies. We demonstrate the technique in a sample of 23 galaxies at
z
> 6, including 8 at
z
= 7.2–10.6 recently observed with JWST. Our model estimates the emergent Ly
α
properties and the foreground distance to the absorbing intergalactic medium. We find that galaxies at
z
> 7.5 occupy smaller bubbles (∼0.5–1 pMpc) than those at lower
z
. With a relationship that is secure at 99% confidence, we empirically demonstrate the growth of ionized regions during the reionization epoch for the first time. We independently estimate the upper limit on the Strömgren radii (
R
S
), and derive the escape fraction of ionizing photons (
f
esc
LyC
) from the ratio of
R
B
/
R
S
, deriving a median value of 5%, which, on average, represents the lower end of the photon budget necessary for reionization.
Abstract
By clearing neutral gas away from a young starburst, superwinds may regulate the escape of Lyman continuum (LyC) photons from star-forming galaxies. However, models predict that superwinds ...may not launch in the most extreme, compact starbursts. We explore the role of outflows in generating low optical depths in the Green Peas (GPs), the only known star-forming population with several confirmed and candidate LyC-leaking galaxies. With
Hubble Space Telescope
UV spectra of 25 low-redshift GPs, including new observations of 13 of the most highly ionized GPs, we compare the kinematics of UV absorption lines with indirect H
i
optical depth diagnostics: Ly
α
escape fraction, Ly
α
peak separation, or low-ionization absorption line equivalent width. The data suggest that high-ionization kinematics tracing superwind activity may correlate with low optical depth in some objects. However, the most extreme GPs, including many of the best candidate LyC emitters with weak low-ionization absorption and strong, narrow Ly
α
profiles, show the
lowest
velocities. These results are consistent with models for suppressed superwinds, which suggests that outflows may not be the only cause of LyC escape from galaxies.
ABSTRACT
Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo have recently published the upper limit measurement of persistent directional stochastic ...gravitational-wave background (SGWB) based on data from their first and second observing runs. In this paper, we investigate whether a correlation exists between this maximal likelihood SGWB map and the electromagnetic (EM) tracers of matter structure in the Universe, such as galaxy number counts. The method we develop will improve the sensitivity of future searches for anisotropy in the SGWB and expand the use of SGWB anisotropy to probe the formation of structure in the Universe. In order to compute the cross-correlation, we used the spherical harmonic decomposition of SGWB in multiple frequency bands and converted them into pixel-based sky maps in healpix basis. For the EM part, we use the Sloan Digital Sky Survey alaxy catalogue and form healpix sky maps of galaxy number counts at the same angular resolution as the SGWB maps. We compute the pixel-based coherence between these SGWB and galaxy count maps. After evaluating our results in different SGWB frequency bands and in different galaxy redshift bins, we conclude that the coherence between the SGWB and galaxy number count maps is dominated by the null measurement noise in the SGWB maps, and therefore not statistically significant. We expect the results of this analysis to be significantly improved by using the more sensitive upcoming SGWB measurements based on the third observing run of Advanced LIGO and Advanced Virgo.
Abstract
Pox 186 is an exceptionally small dwarf starburst galaxy hosting a stellar mass of ∼10
5
M
⊙
. Undetected in H
i
(
M
< 10
6
M
⊙
) from deep 21 cm observations and with an O
iii
/O
ii
...(5007/3727) ratio of 18.3 ± 0.11, Pox 186 is a promising candidate Lyman continuum emitter. It may be a possible analog of low-mass reionization-era galaxies. We present a spatially resolved kinematic study of Pox 186 and identify two distinct ionized gas components: a broad one with
σ
> 400 km s
−1
and a narrow one with
σ
< 30 km s
−1
. We find strikingly different morphologies between the two components and direct evidence of outflows as seen in the high-velocity gas. Possible physical mechanisms driving the creation of high-velocity gas seen in O
iii
are discussed, from outflow geometry to turbulent mixing between a hot (10
6
K) star-cluster wind and cooler (10
4
K) gas clouds. We find a modest mass-outflow rate of 0.022
M
⊙
yr
−1
with a small mass-loading factor of 0.5, consistent with other low-mass galaxies. Finally, we compare the mass-loading factor of Pox 186 with extrapolations from numerical simulations and discuss possible reasons for the apparent discrepancy between them.
ABSTRACT
We present a robust measurement of the rest-frame UV luminosity function (LF) and its evolution during the peak epoch of cosmic star formation at
. We use our deep near-ultraviolet imaging ...from WFC3/UVIS on the
Hubble Space Telescope
and existing Advanced Camera for Surveys (ACS)/WFC and WFC3/IR imaging of three lensing galaxy clusters, Abell 2744 and MACS J0717 from the Hubble Frontier Field survey and Abell 1689. Combining deep UV imaging and high magnification from strong gravitational lensing, we use photometric redshifts to identify 780 ultra-faint galaxies with
AB mag at
. From these samples, we identified five new, faint, multiply imaged systems in A1689. We run a Monte Carlo simulation to estimate the completeness correction and effective volume for each cluster using the latest published lensing models. We compute the rest-frame UV LF and find the best-fit faint-end slopes of
,
, and
at
,
, and
, respectively. Our results demonstrate that the UV LF becomes steeper from
to
with no sign of a turnover down to
AB mag. We further derive the UV LFs using the Lyman break “dropout” selection and confirm the robustness of our conclusions against different selection methodologies. Because the sample sizes are so large and extend to such faint luminosities, the statistical uncertainties are quite small, and systematic uncertainties (due to the assumed size distribution, for example) likely dominate. If we restrict our analysis to galaxies and volumes above
completeness in order to minimize these systematics, we still find that the faint-end slope is steep and getting steeper with redshift, though with slightly shallower (less negative) values (
, −1.69 ± 0.07, and −1.79 ± 0.08 for
, 1.9, and 2.6, respectively). Finally, we conclude that the faint star-forming galaxies with UV magnitudes of
covered in this study produce the majority (55%–60%) of the unobscured UV luminosity density at
.
Abstract
Studying the galaxies responsible for reionization is often conducted through local reionization-era analogs; however, many of these local analogs are too massive to be representative of the ...low-mass star-forming galaxies that are thought to play a dominant role in reionization. The local, low-mass dwarf starburst galaxy Pox 186 is one such system with physical conditions representative of a reionization-era starburst galaxy. We present deep ultraviolet (UV) spectroscopy of Pox 186 to study its stellar population and ionization conditions and to compare these conditions to other local starburst galaxies. The new Cosmic Origins Spectrograph data are combined with archival observations to cover ∼1150–2000 Å and allow for an assessment of Pox 186's stellar population, the relative enrichment of C and O, and the escape of ionizing photons. We detect significant Ly
α
and low-ionization state absorption features, indicative of previously undetected neutral gas in Pox 186. The C/O relative abundance, log(C/O) = −0.62 ± 0.02, is consistent with other low-metallicity dwarf galaxies and suggests a comparable star formation history in these systems. We compare UV line ratios in Pox 186 to those of dwarf galaxies and photoionization models, and we find excellent agreement for the ratios utilizing the intense C
iii
, O
iii
, and double-peaked C
iv
lines. However, the UV and optical He
ii
emission is faint and distinguishes Pox 186 from other local starburst dwarf galaxies. We explore mechanisms that could produce faint He
ii
, which have implications for the low-mass reionization-era galaxies that may have similar ionization conditions.
A struggle to reionize the Universe? Scarlata, Claudia
Science (American Association for the Advancement of Science),
2024-May-24, 2024-05-24, 20240524, Letnik:
384, Številka:
6698
Journal Article
Recenzirano
Reservoirs of neutral hydrogen may block ionizing radiation from escaping distant galaxies.
ABSTRACT To date, no direct detection of Lyman continuum emission has been measured for intermediate-redshift ( ) star-forming galaxies. We combine Hubble Space Telescope grism spectroscopy with ...GALEX UV and ground-based optical imaging to extend the search for escaping Lyman continuum to a large (∼600) sample of low-mass ( 9.3 ), moderately star-forming ( 10 yr−1) galaxies selected initially on H emission. The characteristic escape fraction of LyC from star-forming galaxies (SFGs) that populate this parameter space remains weakly constrained by previous surveys, but these faint (sub-L ) SFGs are assumed to play a significant role in the reionization of neutral hydrogen in the intergalactic medium (IGM) at high redshift . We do not make an unambiguous detection of escaping LyC radiation from this sample, individual non-detections to constrain the absolute Lyman continuum escape fraction, (3 ). We measure an upper limit of from a sample of SFGs selected on high H equivalent width (EW ), which are thought to be close analogs of high redshift sources of reionization. For reference, we also present an emissivity-weighted escape fraction that is useful for measuring the general contribution SFGs to the ionizing UV background. In the discussion, we consider the implications of these intermediate redshift constraints for the reionization of hydrogen in the IGM at high ( ) redshift. If we assume our SFGs, for which we measure this emissivity-weighted , are analogs to the high redshift sources of reionization, we find it is difficult to reconcile reionization by faint ( ) SFGs with a low escape fraction ( ), with constraints from independent high redshift observations. If evolves with redshift, reionization by SFGs may be consistent with observations from Planck.
ABSTRACT We present photometry and derived redshifts from up to eleven bandpasses for 9927 galaxies in the Hubble Ultra Deep field (UDF), covering an observed wavelength range from the ...near-ultraviolet (NUV) to the near-infrared (NIR) with Hubble Space Telescope observations. Our Wide Field Camera 3 (WFC3)/UV F225W, F275W, and F336W image mosaics from the ultra-violet UDF (UVUDF) imaging campaign are newly calibrated to correct for charge transfer inefficiency, and use new dark calibrations to minimize background gradients and pattern noise. Our NIR WFC3/IR image mosaics combine the imaging from the UDF09 and UDF12 campaigns with CANDELS data to provide NIR coverage for the entire UDF field of view. We use aperture-matched point-spread function corrected photometry to measure photometric redshifts in the UDF, sampling both the Lyman break and Balmer break of galaxies at - , and one of the breaks over the rest of the redshift range. Our comparison of these results with a compilation of robust spectroscopic redshifts shows an improvement in the galaxy photometric redshifts by a factor of two in scatter and a factor three in outlier fraction (OLF) over previous UDF catalogs. The inclusion of the new NUV data is responsible for a factor of two decrease in the OLF compared to redshifts determined from only the optical and NIR data, and improves the scatter at and at . The panchromatic coverage of the UDF from the NUV through the NIR yields robust photometric redshifts of the UDF, with the lowest OLF available.
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