A fundamental quest of modern astronomy is to locate the earliest galaxies and study how they influenced the intergalactic medium a few hundred million years after the Big Bang
. The abundance of ...star-forming galaxies is known to decline
from redshifts of about 6 to 10, but a key question is the extent of star formation at even earlier times, corresponding to the period when the first galaxies might have emerged. Here we report spectroscopic observations of MACS1149-JD1
, a gravitationally lensed galaxy observed when the Universe was less than four per cent of its present age. We detect an emission line of doubly ionized oxygen at a redshift of 9.1096 ± 0.0006, with an uncertainty of one standard deviation. This precisely determined redshift indicates that the red rest-frame optical colour arises from a dominant stellar component that formed about 250 million years after the Big Bang, corresponding to a redshift of about 15. Our results indicate that it may be possible to detect such early episodes of star formation in similar galaxies with future telescopes.
Abstract
We present a strong lensing analysis on the massive cluster Abell 370 (A370; z = 0.375), using a combination of deep multiband Hubble Space Telescope (HST) imaging and Multi-Unit ...Spectroscopic Explorer (MUSE) spectroscopy. From only 2 h of the MUSE data, we are able to measure 120 redshifts in the southern BCG area, including several multiply imaged lens systems. In total, we increase the number of multiply imaged systems with a secure redshift from 4 to 15, nine of which are newly discovered. Of these, eight are located at z > 3, greatly extending the redshift range of spectroscopically confirmed systems over previous work. Using these systems as constraints, we update a parametric lens model of A370, probing the mass distribution from cluster to galaxy scales. Overall, we find that a model with only two cluster-scale dark matter haloes (one for each BCG) does a poor job of fitting these new image constraints. Instead, two additional mass clumps – a central ‘bar’ of mass located between the BCGs, and another clump located within a ‘crown’ of galaxies in the northern part of the cluster field – provide significant improvements to the fit. Additional physical evidence suggests these clumps are indeed real features of the system, but with relatively few image constraints in the crown region, this claim is difficult to evaluate from a modelling perspective. Additional MUSE observations of A370 covering the entire strong-lensing region will greatly help these efforts, further improving our understanding of this intriguing cluster.
Abstract
We present an ALMA 1.3 mm (Band 6) continuum survey of lensed submillimeter galaxies (SMGs) at
z
= 1.0 to ∼3.2 with an angular resolution of ∼0.″2. These galaxies were uncovered by the ...Herschel Lensing Survey and feature exceptionally bright far-infrared continuum emission (
S
peak
≳ 90 mJy) owing to their lensing magnification. We detect 29 sources in 20 fields of massive galaxy clusters with ALMA. Using both the Spitzer/IRAC (3.6/4.5
μ
m) and ALMA data, we have successfully modeled the surface brightness profiles of 26 sources in the rest-frame near- and far-infrared. Similar to previous studies, we find the median dust-to-stellar continuum size ratio to be small (
R
e,dust
/
R
e,star
= 0.38 ± 0.14) for the observed SMGs, indicating that star formation is centrally concentrated. This is, however, not the case for two spatially extended main-sequence SMGs with a low surface brightness at 1.3 mm (≲0.1 mJy arcsec
−2
), in which the star formation is distributed over the entire galaxy (
R
e,dust
/
R
e,star
> 1). As a whole, our SMG sample shows a tight anticorrelation between (
R
e,dust
/
R
e,star
) and far-infrared surface brightness (Σ
IR
) over a factor of ≃1000 in Σ
IR
. This indicates that SMGs with less vigorous star formation (i.e., lower Σ
IR
) lack central starburst and are likely to retain a broader spatial distribution of star formation over the whole galaxies (i.e., larger
R
e,dust
/
R
e,star
). The same trend can be reproduced with cosmological simulations as a result of central starburst and potentially subsequent “inside-out” quenching, which likely accounts for the emergence of compact quiescent galaxies at
z
∼ 2.
Abstract
We present direct spectroscopic measurements of the broad 2175 Å absorption feature in 505 star-forming main-sequence galaxies at 1.3 ≤
z
≤ 1.8 using individual and stacked spectra from the ...zCOSMOS-deep survey. Significant 2175 Å excess absorption features of moderate strength are measured, especially in the composite spectra. The excess absorption is well described by a Drude profile. The bump amplitude expressed in units of
k
(
λ
) =
A
(
λ
)/
E
(
B
−
V
), relative to the featureless Calzetti et al. law, has a range
B
k
≈ 0.2–0.8. The bump amplitude decreases with the specific star formation rate (sSFR), while it increases moderately with the stellar mass. However, a comparison with local “starburst” galaxies shows that the high-redshift main-sequence galaxies have stronger bump features, despite having a higher sSFR than the local sample. Plotting the bump strength against the
Δ
logsSFR
≡
log
SFR
/
SFR
MS
relative to the main sequence, however, brings the two samples into much better concordance. This may indicate that it is the recent star formation history of the galaxies that determines the bump strength through the destruction of small carbonaceous grains by supernovae and intense radiation fields coupled with the time delay of ∼1 Gyr in the appearance of carbon-rich asymptotic giant branch stars.
The MUSE Hubble Ultra Deep Field Survey Kusakabe, Haruka; Blaizot, Jérémy; Garel, Thibault ...
Astronomy and astrophysics (Berlin),
06/2020, Letnik:
638
Journal Article
Recenzirano
Odprti dostop
Context. The Ly α emitter (LAE) fraction, X LAE , is a potentially powerful probe of the evolution of the intergalactic neutral hydrogen gas fraction. However, uncertainties in the measurement of X ...LAE are still under debate. Aims. Thanks to deep data obtained with the integral field spectrograph Multi Unit Spectroscopic Explorer (MUSE), we can measure the evolution of the LAE fraction homogeneously over a wide redshift range of z ≈ 3–6 for UV-faint galaxies (down to UV magnitudes of M 1500 ≈ −17.75). This is a significantly fainter range than in former studies ( M 1500 ≤ −18.75) and it allows us to probe the bulk of the population of high-redshift star-forming galaxies. Methods. We constructed a UV-complete photometric-redshift sample following UV luminosity functions and measured the Ly α emission with MUSE using the latest (second) data release from the MUSE Hubble Ultra Deep Field Survey. Results. We derived the redshift evolution of X LAE for M 1500 ∈ − 21.75; −17.75 for the first time with a equivalent width range EW (Ly α ) ≥ 65 Å and found low values of X LAE ≲ 30% at z ≲ 6. The best-fit linear relation is X LAE = 0.07 +0.06 −0.03 z − 0.22 +0.12 −0.24 . For M 1500 ∈ − 20.25; −18.75 and EW (Ly α ) ≥ 25 Å, our X LAE values are consistent with those in the literature within 1 σ at z ≲ 5, but our median values are systematically lower than reported values over the whole redshift range. In addition, we do not find a significant dependence of X LAE on M 1500 for EW (Ly α ) ≥ 50 Å at z ≈ 3–4, in contrast with previous work. The differences in X LAE mainly arise from selection biases for Lyman Break Galaxies (LBGs) in the literature: UV-faint LBGs are more easily selected if they have strong Ly α emission, hence X LAE is biased towards higher values when those samples are used. Conclusions. Our results suggest either a lower increase of X LAE towards z ≈ 6 than previously suggested, or even a turnover of X LAE at z ≈ 5.5, which may be the signature of a late or patchy reionization process. We compared our results with predictions from a cosmological galaxy evolution model. We find that a model with a bursty star formation (SF) can reproduce our observed LAE fractions much better than models where SF is a smooth function of time.
Abstract
We present an ALMA-Herschel joint analysis of sources detected by the ALMA Lensing Cluster Survey (ALCS) at 1.15 mm. Herschel/PACS and SPIRE data at 100–500
μ
m are deblended for 180 ALMA ...sources in 33 lensing cluster fields that are detected either securely (141 sources; in our main sample) or tentatively at S/N ≥ 4 with cross-matched HST/Spitzer counterparts, down to a delensed 1.15 mm flux density of ∼0.02 mJy. We performed far-infrared spectral energy distribution modeling and derived the physical properties of dusty star formation for 125 sources (109 independently) that are detected at >2
σ
in at least one Herschel band. A total of 27 secure ALCS sources are not detected in any Herschel bands, including 17 optical/near-IR-dark sources that likely reside at
z
= 4.2 ± 1.2. The 16th, 50th, and 84th percentiles of the redshift distribution are 1.15, 2.08, and 3.59, respectively, for ALCS sources in the main sample, suggesting an increasing fraction of
z
≃ 1 − 2 galaxies among fainter millimeter sources (
f
1150
∼ 0.1 mJy). With a median lensing magnification factor of
μ
=
2.6
−
0.8
+
2.6
, ALCS sources in the main sample exhibit a median intrinsic star formation rate of
94
−
54
+
84
M
⊙
yr
−1
, lower than that of conventional submillimeter galaxies at similar redshifts by a factor of ∼3. Our study suggests weak or no redshift evolution of dust temperature with
L
IR
< 10
12
L
⊙
galaxies within our sample at
z
≃ 0 − 2. At
L
IR
> 10
12
L
⊙
, the dust temperatures show no evolution across
z
≃ 1–4 while being lower than those in the local universe. For the highest-redshift source in our sample (
z
= 6.07), we can rule out an extreme dust temperature (>80 K) that was reported for MACS0416 Y1 at
z
= 8.31.
Hydrogen Ly
α
haloes (LAHs) are commonly used as a tracer of the circumgalactic medium (CGM) at high redshifts. In this work, we aim to explore the existence of Ly
α
haloes around individual ...UV-selected galaxies, rather than around Ly
α
emitters (LAEs), at high redshifts. Our sample was continuum-selected with
F
775
W
≤ 27.5, and spectroscopic redshifts were assigned or constrained for all the sources thanks to the deepest (100- to 140-h) existing Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) data with adaptive optics. The final sample includes 21 galaxies that are purely
F
775
W
-magnitude selected within the redshift range
z
≈ 2.9 − 4.4 and within a UV magnitude range −20 ≤
M
1500
≤ −18, thus avoiding any bias toward LAEs. We tested whether galaxy’s Ly
α
emission is significantly more extended than the MUSE PSF-convolved continuum component. We find 17 LAHs and four non-LAHs. We report the first individual detections of extended Ly
α
emission around non-LAEs. The Ly
α
halo fraction is thus as high as 81.0
−11.2
+10.3
%, which is close to that for LAEs at
z
= 3 − 6 in the literature. This implies that UV-selected galaxies generally have a large amount of hydrogen in their CGM. We derived the mean surface brightness (SB) profile for our LAHs with cosmic dimming corrections and find that Ly
α
emission extends to 5.4 arcsec (≃40 physical kpc at the midpoint redshift
z
= 3.6) above the typical 1
σ
SB limit. The incidence rate of surrounding gas detected in Ly
α
per one-dimensional line of sight per unit redshift, d
n
/d
z
, is estimated to be 0.76
−0.09
+0.09
for galaxies with
M
1500
≤ −18 mag at
z
≃ 3.7. Assuming that Ly
α
emission and absorption arise in the same gas, this suggests, based on abundance matching, that LAHs trace the same gas as damped Ly
α
systems (DLAs) and sub-DLAs.
Abstract
We present the first estimate of the Ly α luminosity function using blind spectroscopy from the Multi Unit Spectroscopic Explorer, MUSE, in the Hubble Deep Field-South. Using automatic ...source-detection software, we assemble a homogeneously detected sample of 59 Ly α emitters covering a flux range of −18.0 < log10 (F) < −16.3 (erg s−1 cm−2), corresponding to luminosities of 41.4 < log10 (L) < 42.8 (erg s−1). As recent studies have shown, Ly α fluxes can be underestimated by a factor of 2 or more via traditional methods, and so we undertake a careful assessment of each object's Ly α flux using a curve-of-growth analysis to account for extended emission. We describe our self-consistent method for determining the completeness of the sample, and present an estimate of the global Ly α luminosity function between redshifts 2.91 < z < 6.64 using the 1/V
max estimator. We find that the luminosity function is higher than many number densities reported in the literature by a factor of 2–3, although our result is consistent at the 1σ level with most of these studies. Our observed luminosity function is also in good agreement with predictions from semi-analytic models, and shows no evidence for strong evolution between the high- and low-redshift halves of the data. We demonstrate that one's approach to Ly α flux estimation does alter the observed luminosity function, and caution that accurate flux assessments will be crucial in measurements of the faint-end slope. This is a pilot study for the Ly α luminosity function in the MUSE deep-fields, to be built on with data from the Hubble Ultra Deep Field that will increase the size of our sample by almost a factor of 10.
We investigate how the O ii properties and the morphologies of galaxies in clusters and groups at image depend on projected local galaxy density, and compare with the field at similar redshifts and ...clusters at low z. In both nearby and distant clusters, higher density regions contain proportionally fewer star-forming galaxies, and the average O ii equivalent width of star-forming galaxies is independent of local density. However, in distant clusters the average current star formation rate (SFR) in star- forming galaxies seems to peak at densities similar to 15-40 galaxies Mpc super(-2). At odds with low-z results, at high z the relation between star-forming fraction and local density varies from high- to low-mass clusters. Overall, our results suggest that at high z the current star formation (SF) activity in star-forming galaxies does not depend strongly on global or local environment, though the possible SFR peak seems at odds with this conclusion. We find that the cluster SFR normalized by cluster mass anticorrelates with mass and correlates with the star-forming fraction. These trends can be understood given (1) that the average star-forming galaxy forms about 1 M sub(image) yr super(-1) (uncorrected for dust) in all clusters; (2) that the total number of galaxies scales with cluster mass; and (3) the dependence of star-forming fraction on cluster mass. We present the morphology-density (MD) relation for our image clusters, and uncover that the decline of the spiral fraction with density is entirely driven by galaxies of type Sc or later. For galaxies of a given Hubble type, we see no evidence that SF properties depend on local environment. In contrast with recent findings at low z, in our distant clusters the SF-density relation and the MD relation are equivalent, suggesting that neither of the two is more fundamental than the other.
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