While most of the intergalactic medium (IGM) today is permeated by ionized hydrogen, it was largely filled with neutral hydrogen for the first 700 million years after the big bang. The process that ...ionized the IGM (cosmic reionization) is expected to be spatially inhomogeneous, with fainter galaxies likely playing a significant role. However, we still have only a few direct constraints on the reionization process. Here we report spectroscopic confirmation of two galaxies and very likely a third galaxy in a group (hereafter EGS77) at redshift z = 7.7, merely 680 Myr after the big bang. The physical separation among the three members is <0.7 Mpc. We estimate the radius of ionized bubble of the brightest galaxy to be about 1.02 Mpc, and show that the individual ionized bubbles formed by all three galaxies likely overlap significantly, forming a large yet localized ionized region, indicative of inhomogeneity in the reionization process. It is striking that two of three galaxies in EGS77 are quite faint in the continuum, thanks to our selection using their Ly line emission in the narrowband filter. Indeed, one is the faintest spectroscopically confirmed galaxy yet discovered at such high redshifts. Our observations provide direct constraints on the process of cosmic reionization, and allow us to investigate the properties of sources responsible for reionizing the universe.
In this paper we describe the first data release of the UltraVISTA near-infrared imaging survey of the COSMOS field. We summarise the key goals and design of the survey and provide a detailed ...description of our data reduction techniques. We provide stacked, sky-subtracted images in YJHKs and narrow-band filters constructed from data collected during the first year of UltraVISTA observations. Our stacked images reach 5σAB depths in an aperture of 2″ diameter of ~25 in Y and ~24 in JHKs bands and all have sub-arcsecond seeing. To this 5σ limit, our Ks catalogue contains 216 268 sources. We carry out a series of quality assessment tests on our images and catalogues, comparing our stacks with existing catalogues. The 1σ astrometric rms in both directions for stars selected with 17.0 < Ks(AB) < 19.5 is ~0.08″ in comparison to the publicly-available COSMOS ACS catalogues. Our images are resampled to the same pixel scale and tangent point as the publicly available COSMOS data and so may be easily used to generate multi-colour catalogues using this data. All images and catalogues presented in this paper are publicly available through ESO’s “phase 3” archiving and distribution system and from the UltraVISTA web site.
Abstract The Lyman alpha (Ly α) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km s−1 compared to the systemic redshift. This ...large offset hampers follow-up surveys, galaxy pair statistics, and correlations with quasar absorption lines when only Ly α is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the Ly α line profile. We use spectroscopic observations of Ly α emitters for which a precise measurement of the systemic redshift is available. Our sample contains 13 sources detected between z ≈ 3 and z ≈ 6 as part of various multi-unit spectroscopic explorer guaranteed time observations. We also include a compilation of spectroscopic Ly α data from the literature spanning a wide redshift range (z ≈ 0–8). First, restricting our analysis to double-peaked Ly α spectra, we find a tight correlation between the velocity offset of the red peak with respect to the systemic redshift, $V_{\rm peak}^{\rm red}$, and the separation of the peaks. Secondly, we find a correlation between $V_{\rm peak}^{\rm red}$ and the full width at half-maximum of the Ly α line. Fitting formulas to estimate systemic redshifts of galaxies with an accuracy of ≤100 km s−1, when only the Ly α emission line is available, are given for the two methods.
We report the discovery of diffuse extended Ly
α
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 Ly
α
...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 Ly
α
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 Ly
α
luminosity from these filaments comes from beyond the circumgalactic medium of any identified Ly
α
emitter. Fluorescent Ly
α
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 Ly
α
emission of a large population of ultra low-luminosity Ly
α
emitters (< 10
40
erg s
−1
), provided that the faint end of the Ly
α
luminosity function is steep (
α
⪅ −1.8), it extends down to luminosities lower than 10
38
− 10
37
erg s
−1
, and the clustering of these Ly
α
emitters is significant (filling factor < 1/6). If these Ly
α
emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates < 10
−4
M
⊙
yr
−1
. These observations provide the first detection of the cosmic web in Ly
α
emission in typical filamentary environments and the first observational clue indicating the existence of a large population of ultra low-luminosity Ly
α
emitters at high redshift.
We report the discovery of eMACSJ1341-QG-1, a quiescent galaxy at z = 1.594 located behind the massive galaxy cluster eMACSJ1341.9-2442 (z = 0.835). The system was identified as a gravitationally ...lensed triple image in Hubble Space Telescope images obtained as part of a snapshot survey of the most X-ray luminous galaxy clusters at z > 0.5 and spectroscopically confirmed in ground-based follow-up observations with the ESO/X-Shooter spectrograph. From the constraints provided by the triple image, we derive a first, crude model of the mass distribution of the cluster lens, which predicts a gravitational amplification of a factor of ∼30 for the primary image and a factor of ∼6 for the remaining two images of the source, making eMACSJ1341-QG-1 by far the most strongly amplified quiescent galaxy discovered to date. Our discovery underlines the power of SNAPshot observations of massive, X-ray selected galaxy clusters for lensing-assisted studies of faint background populations.
Contact. This paper presents the results obtained with the Multi-Unit Spectroscopic Explorer (MUSE) at the ESO Very Large Telescope on the faint end of the Lyman-alpha luminosity function (LF) based ...on deep observations of four lensing clusters. The goal of our project is to set strong constraints on the relative contribution of the Lyman-alpha emitter (LAE) population to cosmic reionization. Aims. The precise aim of the present study is to further constrain the abundance of LAEs by taking advantage of the magnification provided by lensing clusters to build a blindly selected sample of galaxies which is less biased than current blank field samples in redshift and luminosity. By construction, this sample of LAEs is complementary to those built from deep blank fields, whether observed by MUSE or by other facilities, and makes it possible to determine the shape of the LF at fainter levels, as well as its evolution with redshift. Methods. We selected a sample of 156 LAEs with redshifts between 2.9 ≤ z ≤ 6.7 and magnification-corrected luminosities in the range 39 ≲ log LLyα erg s−1 ≲43. To properly take into account the individual differences in detection conditions between the LAEs when computing the LF, including lensing configurations, and spatial and spectral morphologies, the non-parametric 1/Vmax method was adopted. The price to pay to benefit from magnification is a reduction of the effective volume of the survey, together with a more complex analysis procedure to properly determine the effective volume Vmax for each galaxy. In this paper we present a complete procedure for the determination of the LF based on IFU detections in lensing clusters. This procedure, including some new methods for masking, effective volume integration and (individual) completeness determinations, has been fully automated when possible, and it can be easily generalized to the analysis of IFU observations in blank fields. Results. As a result of this analysis, the Lyman-alpha LF has been obtained in four different redshift bins: 2.9 < z < 6, 7, 2.9 < z < 4.0, 4.0 < z < 5.0, and 5.0 < z < 6.7 with constraints down to log LLyα = 40.5. From our data only, no significant evolution of LF mean slope can be found. When performing a Schechter analysis also including data from the literature to complete the present sample towards the brightest luminosities, a steep faint end slope was measured varying from α = −1.69−0.08+0.08 α = − 1 . 69 − 0.08 + 0.08 $ \alpha = -1.69^{+0.08}_{-0.08} $ to α = −1.87−0.12+0.12 α = − 1 . 87 − 0.12 + 0.12 $ \alpha = -1.87^{+0.12}_{-0.12} $ between the lowest and the highest redshift bins. Conclusions. The contribution of the LAE population to the star formation rate density at z ∼ 6 is ≲50% depending on the luminosity limit considered, which is of the same order as the Lyman-break galaxy (LBG) contribution. The evolution of the LAE contribution with redshift depends on the assumed escape fraction of Lyman-alpha photons, and appears to slightly increase with increasing redshift when this fraction is conservatively set to one. Depending on the intersection between the LAE/LBG populations, the contribution of the observed galaxies to the ionizing flux may suffice to keep the universe ionized at z ∼ 6.
We present deep 10 h VLT/XSHOOTER spectroscopy for an extraordinarily luminous and extended Ly α emitter at z = 6.595 referred to as Himiko and first discussed by Ouchi et al., with the purpose of ...constraining the mechanisms powering its strong emission. Complementary to the spectrum, we discuss near-infrared imaging data from the CANDELS survey. We find neither for He II nor any metal line a significant excess, with 3σ upper limits of 6.8, 3.1, and 5.8 × 10−18 erg s−1 cm−2 for C IV λ1549, He II λ1640, C III λ1909, respectively, assuming apertures with 200 km s−1 widths and offset by −250 km s−1 w.r.t. to the peak Ly α redshift. These limits provide strong evidence that an AGN is not a major contribution to Himiko's Ly α flux. Strong conclusions about the presence of Pop III star formation or gravitational cooling radiation are not possible based on the obtained He II upper limit. Our Ly α spectrum confirms both spatial extent and flux (8.8 ± 0.5 × 10−17 erg s−1 cm−2) of previous measurements. In addition, we can unambiguously exclude any remaining chance of it being a lower redshift interloper by significantly detecting a continuum redwards of Ly α, while being undetected bluewards.
We serendipitously discovered in the
Herschel
Reference Survey an extremely bright infrared source with
S
500
∼ 120 mJy in the line of sight of the Virgo cluster which we name Red Virgo 4 (RV4). ...Based on IRAM/EMIR and IRAM/NOEMA detections of the CO(5−4), CO(4−3), and CI lines, RV4 is located at a redshift of 4.724, yielding a total observed infrared luminosity of 1.1 ± 0.6 × 10
14
L
⊙
. At the position of the
Herschel
emission, three blobs are detected with the VLA at 10 cm. The CO(5−4) line detection of each blob confirms that they are at the same redshift with the same line width, indicating that they are multiple images of the same source. In
Spitzer
and deep optical observations, two sources, High-
z
Lens 1 (HL1) West and HL1 East, are detected at the center of the three VLA/NOEMA blobs. These two sources are placed at
z
= 1.48 with X-shooter spectra, suggesting that they could be merging and gravitationally lensing the emission of RV4. HL1 is the second most distant lens known to date in strong lensing systems. Constrained by the position of the three VLA/NOEMA blobs, the Einstein radius of the lensing system is 2.2″ ± 0.2 (20 kpc). The high redshift of HL1 and the large Einstein radius are highly unusual for a strong lensing system. In this paper, we present the insterstellar medium properties of the background source RV4. Different estimates of the gas depletion time yield low values suggesting that RV4 is a starburst galaxy. Among all high-
z
submillimeter galaxies, this source exhibits one of the lowest
L
CI
to
L
IR
ratios, 3.2 ± 0.9 × 10
−6
, suggesting an extremely short gas depletion time of only 14 ± 5 Myr. It also shows a relatively high
L
CI
to
L
CO(4−3)
ratio (0.7 ± 0.2) and low
L
CO(5−4)
to
L
IR
ratio (only ∼50% of the value expected for normal galaxies) hinting at low density of gas. Finally, we discuss the short depletion time of RV4. It can be explained by either a very high star formation efficiency, which is difficult to reconcile with major mergers simulations of high-
z
galaxies, or a rapid decrease of star formation, which would bias the estimate of the depletion time toward an artificially low value.
The sub-population of quasars reddened by intrinsic or intervening clouds of dust are known to be underrepresented in optical quasar surveys. By defining a complete parent sample of the brightest and ...spatially unresolved quasars in the COSMOS field, we quantify to which extent this sub-population is fundamental to our understanding of the true population of quasars. By using the available multiwavelength data of various surveys in the COSMOS field, we built a parent sample of 33 quasars brighter than J = 20 mag, identified by reliable X-ray to radio wavelength selection techniques. Spectroscopic follow-up with the NOT/ALFOSC was carried out for four candidate quasars that had not been targeted previously to obtain a 100% redshift completeness of the sample. The population of high AV quasars (HAQs), a specific sub-population of quasars selected from optical/near-infrared photometry, some of which were shown to be missed in large optical surveys such as SDSS, is found to contribute 21%+9-5 of the parent sample. The full population of bright spatially unresolved quasars represented by our parent sample consists of 39%+9-8 reddened quasars defined by having AV > 0.1, and 21%+9-5 of the sample having E(B−V) > 0.1 assuming the extinction curve of the Small Magellanic Cloud. We show that the HAQ selection works well for selecting reddened quasars, but some are missed because their optical spectra are too blue to pass the g−r color cut in the HAQ selection. This is either due to a low degree of dust reddening or anomalous spectra. We find that the fraction of quasars with contributing light from the host galaxy, causing observed extended spatial morphology, is most dominant at z ≲ 1. At higher redshifts the population of spatially unresolved quasars selected by our parent sample is found to be representative of the full population of bright active galactic nuclei at J< 20 mag. This work quantifies the bias against reddened quasars in studies that are based solely on optical surveys.
Context. High redshift star-forming galaxies are discovered routinely because of a flux excess in narrowband filters caused by an emission line. In most cases, the width of such filters is broader ...than typical line widths, and the throughput of the filters varies substantially within the bandpass. This leads to substantial uncertainties in redshifts and fluxes that are derived from the observations with one specific narrowband filter. Aims. The uncertainty in measured line parameters can be sharply reduced by using repeated observations of the same target field with filters that have overlapping passbands but differ slightly in central wavelength or wavelength dependence of the effective filter curve. Such data are routinely collected with some large field imaging cameras that use multiple detectors and a separate filter for each of the detectors. An example is the European Southern Observatory’s VISTA InfraRed CAMera (VIRCAM). Methods. We developed a method of determining more accurate redshift and line flux estimates from the ratio of apparent fluxes measured from observations in different narrowband filters and several matching broadband filters. A parameterized model of the line and continuum flux is used to predict the flux ratios as a function of redshift based on the known filter curves. These model predictions are then used to determine the most likely redshift and line flux. Results. We tested the obtainable quality of parameter estimation for the example of Hα in the VIRCAM NB118 filters both on simulated and actual observations where the latter were based on the UltraVISTA DR2 data set. We combined the narrowband data with deep broadband data in Y, J, and H. We find that with this method, the errors in the measured lines fluxes can be reduced up to almost an order of magnitude. Conclusions. We conclude that existing narrowband data can be used to derive accurate line fluxes if the observations include images taken with sufficiently different filter curves. For the UltraVISTA survey, the best-suited narrowband filter combinations allow an accuracy in wavelength of better than 1 nm and in flux of better than 15% at any redshift within the bandpass of the filters. In contrast, analyzing the data without exploiting the difference in filter curves leads to an uncertainty in wavelength of 10 nm and up to an order of magnitude errors in line flux estimates.
PDF
