The first year of JWST has revealed a surprisingly large number of luminous galaxy candidates beyond z>10. While some galaxies are already spectroscopically confirmed, there is mounting evidence that a subsample of the candidates with particularly red inferred UV colors are in fact lower redshift contaminants.These interlopers are often found to be HST-dark or optically-fain galaxies at z~2-6, a population key to understanding dust-obscured star formation throughout cosmic time. This paper demonstrates the complementarity of ground-based mm-interferometry and JWST infrared imaging to unveil the true nature of red 1.5-2.0 um dropouts that have been selected as ultra-high-redshift galaxy candidates. We present NOEMA Polyfix follow-up observations of four JWST red 1.5-2.0 um dropouts selected by Yan et al. 2023 as ultra-high-redshift candidates in the PEARLS field. The new NOEMA observations constrain the rest-frame far-infrared continuum emission and efficiently discriminate between intermediate- and high-redshift solutions. We report >10sigma NOEMA continuum detections of all our target galaxies at observed frequencies of 236 and 252 GHz, with FIR slopes indicating a redshift z<5. We model their optical-to-FIR spectral energy distribution (SED) with multiple SED codes, and find that they are not z>10 galaxies but instead dust-obscured, massive star-forming galaxies at z~2-4. The contribution to the cosmic star-formation rate density of such sources is not negligible at z~3.5 (phi > 1.9-4.4 x10^-3 cMpc^-3), in line with previous studies of optically-faint/sub-millimeter galaxies. This work showcases a new way to select intermediate- to high-redshift dust-obscured galaxies in JWST fields with minimal wavelength coverage to open a new window on obscured star-formation at intermediate redshifts
We present Atacama Large Millimeter/submillimeter Array (ALMA) [C II] 158 μm and dust continuum observations of the z = 6.79 quasar J0109-3047 at a resolution of 0.045 arcsec (~300 pc). The dust and [C II] emission are enclosed within a ~500 pc radius, with the central beam (r < 144 pc) accounting for ~25% (8%) of the total continuum ([C II]) emission. The far-infrared (FIR) luminosity density increases radially from ~5 × 10^11 Lsun kpc^-2 to a central value of ~70 × 10^11 Lsun kpc^-2 (SFRD ~50-700 Msun/yr kpc^-2). The [C II] kinematics are dispersion dominated with a constant velocity dispersion of 137+-6 km s^1. The constant dispersion implies that the underlying mass distribution is not centrally peaked, consistent with the expectations of a flat gas mass profile. The lack of an upturn in velocity dispersion within the central beam is inconsistent with a black hole mass greater than M BH < 6.5 × 10^8 Msun (2sigma level), unless highly fine-tuned changes in the interstellar medium properties conspire to produce a decrease of the gas mass in the central beam comparable to the black hole mass. Our observations therefore imply either that (a) the black hole is less massive than previously measured, or (b) the central peak of the FIR and [C II] emission are not tracing the location of the black hole, as suggested by the tentative offset between the near-infrared position of the quasar and the ALMA continuum emission.
We report new Northern Extended Millimeter Array (NOEMA) observations of the CII, NII and OI atomic fine structure lines and dust continuum emission of J1148+5251, a z=6.42 quasar, that probe the physical properties of its interstellar medium (ISM). The radially-averaged CII and dust continuum emission have similar extensions (up to θ=2.51+0.46−0.25 arcsec, corresponding to r=9.8+3.3−2.1 kpc accounting for beam-convolution), confirming that J1148+5251 is the quasar with the largest CII-emitting has reservoir known at these epochs.Moreover, if the CII emission is examined only along its NE-SW axis, a significant excess (>5.8σ) of CII emission (with respect to the dust) is detected. The new wide–bandwidth observations enable us to accurately constrain the continuum emission, and do not statistically require the presence of broad CII line wings that were reported in previous studies. We also report the first detection of the OI and (tentatively) NII emission lines in J1148+5251. Using Fine Structure Lines (FSL) ratios of the [CII], NII, OI and previously measured CI emission lines, we show that J1148+5251 has similar ISM conditions compared to lower–redshift (ultra)-luminous infrared galaxies. CLOUDY modelling of the FSL ratios exclude X–ray dominated regions (XDR) and favours photodissociation regions (PDR) as the origin of the FSL emission. We find that a high radiation field (103.5−4.5G0), high gas density (n≃103.5−4.5cm−3) and HI column density of 1023cm−2 reproduce the observed FSL ratios well.
We quantify galaxy overdensities around three high-redshift quasars with known [CII] 158 μm companions: PJ231-20 (z = 6.59), PJ308-21 (z = 6.24), and J0305-3150 (z = 6.61). Recent SCUBA2 imaging revealed the presence of 17 submillimeter galaxies (SMGs) with sky separations 0.‘7 < θ < 2.‘4 from these three quasars. We present ALMA Band 6 follow-up observations of these SCUBA2-selected SMGs to confirm their nature and redshift. We also search for continuum-undetected [C II]158 μm emitters in the ALMA pointings and make use of archival MUSE observations to search for Lyα emitters (LAEs) associated with the quasars. While most of the SCUBA2-selected sources are detected with ALMA in the continuum, no [C II]158 μm line emission could be detected, indicating that they are not at the quasar redshifts. Based on the serendipitous detection of CO 7-6 and [C I]809 μm emission lines, we find that four SMGs in the field of PJ231-20 are at z ~ 2.4, which is coincident with the redshift of an Mg II absorber in the quasar rest-frame UV spectrum. We report the discovery of two LAEs within <0.6 cMpc of PJ231-20 at the same redshift, indicating an LAE overdensity around this quasar. Taken together, these observations provide new constraints on the large-scale excess of Lyα- and [C II]158 μm-emitting galaxies around z > 6 quasars and suggest that only wide-field observations, such as MUSE, ALMA, or JWST mosaics, can reveal a comprehensive picture of large-scale structure around quasars in the first billion years of the universe.
We report the discovery of a double-peaked Lyman-alpha profile in a galaxy at $z=6.803$, A370p z1, in the parallel Frontier Field of Abell 370. The velocity separation between the blue and red peaks of the Lyman-alpha profile ($\Delta v=101_{-19}^{+38} (\pm 48), \rm{km s}^{-1}$) suggests an extremely high escape fraction of ionising photons $> 59(51)% (2\sigma)$. The spectral energy distribution indicates a young ($50$ Myr), star-forming ($12\pm 6 , \rm{M} \odot \rm{yr}^{-1}$) galaxy with an IRAC excess implying strong [OIII]+H$\beta$ emission. On the basis of the high escape fraction measured, we demonstrate that A370p z1 was solely capable of creating an ionised bubble sufficiently large to account for the blue component of its Lyman-alpha profile. We discuss whether A370p z1 may be representative of a larger population of luminous $z\simeq7 $ double-peaked Lyman-alpha emitting sources with high escape fractions that self-ionised their surroundings without contributions from associated UV-fainter sources.
We present improved results of the measurement of the correlation between galaxies and the intergalactic medium (IGM) transmission at the end of reionisation. We have gathered a sample of $13$ spectroscopically confirmed Lyman-break galaxies (LBGs) and $21$ Lyman-$\alpha$ emitters (LAEs) at angular separations $20’’ \lesssim \theta \lesssim 10’$ ($\sim 0.1-4$ pMpc at $z\sim 6$) from the sightlines to $8$ background $z\gtrsim 6$ quasars. We report for the first time the detection of an excess of Lyman-$\alpha$ transmission spikes at $\sim 10-60$ cMpc from LAEs ($3.2\sigma$) and LBGs ($1.9\sigma$). We interpret the data with an improved model of the galaxy-Lyman-$\alpha$ transmission and two-point cross-correlations which includes the enhanced photoionisation due to clustered faint sources, enhanced gas densities around the central bright objects and spatial variations of the mean free path. The observed LAE(LBG)-Lyman-$\alpha$ transmission spike two-point cross-correlation function (2PCCF) constrains the luminosity-averaged escape fraction of all galaxies contributing to reionisation to $\langle f_{\rm esc} \rangle_{M_{\rm UV}<-12} = 0.14_{-0.05}^{+0.28},(0.23_{-0.12}^{+0.46})$. We investigate if the 2PCCF measurement can determine whether bright or faint galaxies are the dominant contributors to reionisation. Our results show that a contribution from faint galaxies ($M_{\rm UV} > -20 (2\sigma)$) is necessary to reproduce the observed 2PCCF and that reionisation might be driven by different sub-populations around LBGs and LAEs at $z\sim 6$.
We present the results of a model-independent investigation of the rest-frame UV spectra from a comprehensive sample of $394$ quasars in the redshift range $1.5\leq z \leq 7.5$. We fit the main Broad Emission Lines (BELs) in the rest-frame range $1280 \text{ \AA} \leq \lambda \leq 3000 \text{ \AA}$ (OI,CII,SiIV, CIII], CIV and MgII) with a lightly-supervised spline fitting technique. Redshifts are derived from the peaks of each fitted BEL and used to compute relative velocity shifts. We show that our method gives unbiased velocity shifts and is insensitive to spectral resolution and instrumental parameters. It is found that the average blueshift of the CIV line with respect to several low-ionisation lines in luminosity-matched samples does not significantly evolve over $1.5\gtrsim z\gtrsim6$. However, the average blueshift increases significantly by a factor $\sim 2.5$ at $z\gtrsim 6$. We propose that this redshift evolution can be explained by CIV winds launched perpendicularly to an accretion disk with increased torus opacity at high-redshift, coupled with a potential orientation-driven selection bias. Our results open new exciting avenues of investigation into young quasars in the reionisation epoch.
We present a sample of 12 quasi-stellar objects (QSOs) that potentially act as strong gravitational lenses on background emission line galaxies (ELG) or Lyman-α emitters (LAEs) selected through a systematic search of the 297 301 QSOs in the Sloan Digital Sky Survey (SDSS)-III Data Release 12. Candidates were identified by looking for compound spectra, where emission lines at a redshift larger than that of the quasar can be identified in the residuals after a QSO spectral template is subtracted from the observed spectra. The narrow diameter of BOSS fibers (2″) then ensures that the object responsible for the additional emission lines must lie close to the line of sight of the QSO and hence provides a high probability of lensing. Among the 12 candidates identified, nine have definite evidence for the presence of a background ELG identified by at least four higher-redshift nebular emission lines. The remaining three probable candidates present a strong asymmetrical emission line attributed to a background Lyman-α emitter (LAE). The QSO-ELG (QSO-LAE) lens candidates have QSO lens redshifts in the range 0.24 ≲ zQSO ≲ 0.66 (0.75 ≲ zQSO ≲ 1.23 ) and background galaxy redshifts in the range 0.48 ≲ zS, ELG ≲ 0.94 (2.17 ≲ zS, LAE ≲ 4.48). We show that the algorithmic search is complete at > 90% for QSO-ELG systems, whereas it falls at 40-60% for QSO-LAE, depending on the redshift of the source. Upon confirmation of the lensing nature of the systems, this sample may quadruple the number of known QSOs acting as strong lenses. We have determined the completeness of our search, which allows future studies to compute lensing probabilities of galaxies by QSOs and differentiate between different QSO models. Future imaging of the full sample and lens modelling offers a unique approach to study and constrain key properties of QSOs.
We present a new method to study the contribution of faint sources to the UV background using the 1D correlation of metal absorbers with the intergalactic medium (IGM) transmission in a Quasi Stellar Object (QSO) sightline. We take advantage of a sample of $25$ high signal-to-noise ratio QSO spectra to retrieve $150$ triply-ionised carbon (CIV) absorbers at $4.5\lesssim z\lesssim 6.2$, of which $37$ systems whose expected H{~\small I} absorption lie in the Lyman-$\alpha$ forest. We derive improved constraints on the cosmic density of at $4.3< z < 6.2$ and infer from abundance-matching that CIV absorbers trace $M_{\text{UV}}\lesssim -16$ galaxies. Correlation with the Lyman-$\alpha$ forest of the QSOs indicates that these objects are surrounded by a highly opaque region at $r\lesssim 5 $ cMpc/h followed by an excess of transmission at $r\gtrsim 10$ cMpc/h detected at $2.7\sigma$. This is in contrast to equivalent measurements at lower redshifts where only the opaque trough is detected. We interpret this excess as a statistical enhancement of the local photoionisation rate due to clustered faint galaxies around the CIV sabsorbers. Using the analytical framework described in Paper I of this series, we derive a constraint on the average product of the escape fraction and the Lyman continuum photon production efficiency of the galaxy population clustered around the CIV absorbers, $\log \langle f_{\text{esc}}\xi_{\text{ion}}\rangle /[{\rm erg^{-1}~Hz}] = 25.01^{+0.30}_{-0.19}$. This implies that faint galaxies beyond the reach of current facilities may have harder radiation fields and/or larger escape fractions than currently detected objects at the end of the reionisation epoch.