Rest-frame Optical Emission Lines Research Articles

Ionised gas kinematics and dynamical masses of z ≳ 6 galaxies from JADES/NIRSpec high-resolution spectroscopy

We explore the kinematic gas properties of six 5.5 < z < 7.4 galaxies in the JWST Advanced Deep Extragalactic Survey (JADES), using high-resolution JWST/NIRSpec multi-object spectroscopy of the rest-frame optical emission lines [OIII] and Hα. The objects are small and of low stellar mass (∼1 kpc; M* ∼ 107 − 9 M⊙), less massive than any galaxy studied kinematically at z > 1 thus far. The cold gas masses implied by the observed star formation rates are about ten times higher than the stellar masses. We find that their ionised gas is spatially resolved by JWST, with evidence for broadened lines and spatial velocity gradients. Using a simple thin-disc model, we fit these data with a novel forward-modelling software that accounts for the complex geometry, point spread function, and pixellation of the NIRSpec instrument. We find the sample to include both rotation- and dispersion-dominated structures, as we detect velocity gradients of v(re)∼100 − 150 km s−1, and we find velocity dispersions of σ0 ∼ 30 − 70 km s−1 that are comparable to those at cosmic noon. The dynamical masses implied by these models (Mdyn ∼ 109 − 10 M⊙) are higher than the stellar masses by up to a factor 40, and they are higher than the total baryonic mass (gas + stars) by a factor of ∼3. Qualitatively, this result is robust even if the observed velocity gradients reflect ongoing mergers rather than rotating discs. Unless the observed emission line kinematics is dominated by outflows, this implies that the centres of these galaxies are dominated by dark matter or that star formation is three times less efficient, leading to higher inferred gas masses.

GA-NIFS: Early-stage feedback in a heavily obscured active galactic nucleus at z = 4.76

Dust-obscured galaxies are thought to represent an early evolutionary phase of massive galaxies in which the active galactic nucleus (AGN) is still deeply buried in significant amounts of dusty material and its emission is strongly suppressed. The unprecedented sensitivity of the James Webb Space Telescope (JWST) enabled us for the first time to detect the rest-frame optical emission of heavily obscured AGNs and unveil the properties of the hidden accreting super-massive black holes (BHs). In this work, we present the JWST/NIRSpec integral field spectroscopy (IFS) data of ALESS073.1, a massive (log(M⋆/M⊙) = 10.98) dusty, star-forming galaxy at z = 4.755 hosting an AGN at its center. The detection of a very broad (> 9000 km s−1) Hα emission associated with the broad line region (BLR) confirms the presence of a BH (log(MBH/M⊙) > 8.7) accreting at less than 18% of its Eddington limit. The identification of the BLR classifies the target as a type 1 AGN despite the observed high column density of NH ∼ 1024 cm−2. The rest-frame optical emission lines also reveal a fast (∼1700 km s−1) ionized gas outflow marginally resolved in the galaxy center. The high sensitivity of NIRSpec allowed us to perform the kinematic analysis of the narrow Hα component, which indicates that the warm ionized gas velocity field is consistent with disk rotation. Interestingly, we find that in the innermost nuclear regions (< 1.5 kpc), the intrinsic velocity dispersion of the disk reaches ∼150 km s−1, which is ∼2 − 3 times higher than the velocity dispersion inferred from the [C II] 158 μm line tracing mostly cold gas. Since at large radii the velocity dispersion of the warm and cold gas are comparable, we conclude that the outflows are injecting turbulence in the warm ionized gas in the central region, but they are not sufficiently powerful to disrupt the dense gas and quench star formation. These findings support the scenario that dust-obscured galaxies represent the evolutionary stage preceding the unobscured quasar when all gas and dust are removed from the host.

JWST discovers an AGN ionization cone but only weak radiatively driven feedback in a powerful z ≈ 3.5 radio-loud AGN

We present the first results from a JWST program studying the role played by powerful radio jets in the evolution of the most massive galaxies at the onset of cosmic noon. Using NIRSpec integral field spectroscopy, we detected 24 rest-frame optical emission lines from the z = 3.5892 radio galaxy 4C+19.71, which contains one of the most energetic radio jets known, making it perfect for testing radio mode feedback on the interstellar medium (ISM) of a M⋆ ∼ 1011 M⊙ galaxy. The rich spectrum enables line ratio diagnostics, showing that the radiation from the active galactic nucleus (AGN) dominates the ionization of the entire ISM out to at least 25 kpc, the edge of the detection. Subkiloparsec resolution reveals filamentary structures and emission blobs in the warm ionized ISM distributed on scales of ∼5 to ∼20 kpc. A large fraction of the extended gaseous nebula is located near the systemic velocity. This nebula thus may be the patchy ISM that is illuminated by the AGN after the passage of the jet. A radiative-driven outflow was observed within ∼5 kpc from the nucleus. The inefficient coupling (≲10−4) between this outflow and the quasar and the lack of extreme gas motions on galactic scales are inconsistent with other high-z powerful quasars. Combining our data with ground-based studies, we conclude that only a minor fraction of the feedback processes is happening on < 25 kpc scales.

First Results from the JWST Early Release Science Program Q3D: Powerful Quasar-driven Galactic Scale Outflow at z = 3

Quasar-driven galactic outflows are a major driver of the evolution of massive galaxies. We report observations of a powerful galactic-scale outflow in a z = 3 extremely red and intrinsically luminous (L bol ≃ 5 × 1047erg s−1) quasar SDSSJ1652 + 1728 with the Near-infrared Spectrograph on board JWST. We analyze the kinematics of rest-frame optical emission lines and identify the quasar-driven outflow extending out to ∼10 kpc from the quasar with a velocity offset of (v r = ± 500 km s−1) and high velocity dispersion (FWHM = 700–2400 km s−1). Due to JWST’s unprecedented surface brightness sensitivity in the near-infrared, we unambiguously show that the powerful high velocity outflow in an extremely red quasar encompasses a large swath of the host galaxy’s interstellar medium. Using the kinematics and dynamics of optical emission lines, we estimate the mass outflow rate—in the warm ionized phase alone—to be at least 2300 ± 1400 M ⊙ yr−1. We measure a momentum flux ratio between the outflow and the quasar accretion disk of ∼1 on a kpc scale, indicating that the outflow was likely driven in a relatively high (>1023cm−2) column density environment through radiation pressure on dust grains. We find a coupling efficiency between the bolometric luminosity of the quasar and the outflow of 0.1%, matching the theoretical prediction of the minimum coupling efficiency necessary for negative quasar feedback. The outflow has sufficient energetics to drive the observed turbulence seen in shocked regions of the quasar host galaxy, which are likely directly responsible for prolonging the time that it takes for gas to cool efficiently.

EPOCHS IX. When cosmic dawn breaks: evidence for evolved stellar populations in 7 < z < 12 galaxies from PEARLS GTO and public NIRCam imaging

ABSTRACT The presence of evolved stars in high-redshift galaxies can place valuable indirect constraints on the onset of star formation in the Universe. Thus, we use PEARLS GTO (Prime Extragalactic Areas for Reionization and Lensing Science Guaranteed Time Observations) and public NIRCam (Near Infrared Camera) photometric data to search for Balmer-break candidate galaxies at 7 < z < 12. We find that our Balmer-break candidates at z ∼ 10.5 tend to be older (115 Myr), have lower inferred [O iii] + Hβ equivalent widths (120 Å), have lower specific star formation rates (6 Gyr−1) and redder UV slopes (β = −1.8) than our control sample of galaxies. However, these trends all become less strong at z ∼ 8, where the F444W filter now probes the strong rest-frame optical emission lines, thus providing additional constraints on the current star formation activity of these galaxies. Indeed, the bursty nature of epoch of reionization galaxies can lead to a disconnect between their current spectral energy distribution (SED) profiles and their more extended star formation histories. We discuss how strong emission lines, the cumulative effect of weak emission lines, dusty continua, and active galactic nuclei can all contribute to the photometric excess seen in the rest-frame optical, thus mimicking the signature of a Balmer break. Additional medium-band imaging will thus be essential to more robustly identify Balmer-break galaxies. However, the Balmer break alone cannot serve as a definitive proxy for the stellar age of galaxies, being complexly dependent on the star formation history. Ultimately, deep Near Infrared Spectrograph (NIRSpec) continuum spectroscopy and Mid-Infrared Instrument (MIRI) imaging will provide the strongest indirect constraints on the formation era of the first galaxies in the Universe, thereby revealing when cosmic dawn breaks.

A SPectroscopic Survey of Biased Halos in the Reionization Era (ASPIRE): JWST Discovers an Overdensity around a Metal Absorption-selected Galaxy at z ∼ 5.5

The launch of JWST opens a new window for studying the connection between metal-line absorbers and galaxies at the end of the Epoch of Reionization. Previous studies have detected absorber–galaxy pairs in limited quantities through ground-based observations. To enhance our understanding of the relationship between absorbers and their host galaxies at z > 5, we utilized the NIRCam wide-field slitless spectroscopy to search for absorber-associated galaxies by detecting their rest-frame optical emission lines (e.g., [O III] + Hβ). We report the discovery of a Mg ii-associated galaxy at z = 5.428 using data from the JWST ASPIRE program. The Mg ii absorber is detected on the spectrum of quasar J0305–3150 with a rest-frame equivalent width of 0.74 Å. The associated galaxy has an [O III] luminosity of 1042.5 erg s−1 with an impact parameter of 24.9 pkpc. The joint Hubble Space Telescope–JWST spectral energy distribution (SED) implies a stellar mass and star formation rate of M * ≈ 108.8 M ⊙, star-formation rate ≈ 10 M ⊙ yr−1. Its [O III] equivalent width and stellar mass are typical of [O III] emitters at this redshift. Furthermore, connecting the outflow starting time to the SED-derived stellar age, the outflow velocity of this galaxy is ∼300 km s−1, consistent with theoretical expectations. We identified six additional [O III] emitters with impact parameters of up to ∼300 pkpc at similar redshifts (∣dv∣ < 1000 km s−1). The observed number is consistent with that in cosmological simulations. This pilot study suggests that systematically investigating the absorber–galaxy connection within the ASPIRE program will provide insights into the metal-enrichment history in the early Universe.

GA-NIFS: Black hole and host galaxy properties of twoz≃ 6.8 quasars from the NIRSpec IFU

Aims.Integral field spectroscopy (IFS) with JWST NIRSpec will significantly improve our understanding of the first quasars, by providing spatially resolved, infrared spectroscopic capabilities that cover key rest-frame optical emission lines that have been previously unobservable.Methods.Here we present our results from the first twoz &gt; 6 quasars observed as a part of the Galaxy Assembly with NIRSpec IFS (GA-NIFS) GTO programme, with DELS J0411–0907 atz = 6.82 and VDES J0020–3653 atz = 6.86.Results.By observing the Hβ, [O III]λλ4959, 5007, and Hαemission lines in these high-zquasars for the first time, we measured accurate black hole masses,MBH = 1.85−0.8+2 × 109 M⊙and 2.9−1.3+3.5 × 109M⊙, corresponding to Eddington ratios ofλEdd = 0.8−0.4+0.7and 0.4−0.2+0.3for DELS J0411–0907 and VDES J0020–3653, respectively. These provide a key comparison for existing estimates from the more uncertain Mg IIline. We performed quasar–host decomposition using models of the quasars’ broad lines to measure the underlying host galaxies. We also discovered multiple emission line regions surrounding each of the host galaxies, which are likely companion galaxies undergoing mergers with these hosts. We measured the star formation rates, excitation mechanisms, and dynamical masses of the hosts and companions, measuring theMBH/Mdynratios at highzusing these estimators for the first time. DELS J0411–0907 and VDES J0020–3653 both lie above the local black hole–host mass relation, and are consistent with the existing observations ofz ≳ 6 quasar host galaxies with ALMA. We detected ionised outflows in [O III]λλ4959, 5007 and Hβfrom both quasars, with mass outflow rates of 58−37+44and 525−92+75 M⊙yr−1for DELS J0411–0907 and VDES J0020–3653, much larger than their host star formation rates of &lt; 33 and &lt; 54 M⊙yr−1, respectively.Conclusions.This work highlights the exceptional capabilities of the JWST NIRSpec IFU for observing quasars in the early Universe.

Gemini Near Infrared Spectrograph–Distant Quasar Survey: Augmented Spectroscopic Catalog and a Prescription for Correcting UV-based Quasar Redshifts

Quasars at z ≳ 1 most often have redshifts measured from rest-frame ultraviolet emission lines. One of the most common such lines, C iv λ1549, shows blueshifts up to ≈5000 km s−1 and in rare cases even higher. This blueshifting results in highly uncertain redshifts when compared to redshift determinations from rest-frame optical emission lines, e.g., from the narrow [O iii] λ5007 feature. We present spectroscopic measurements for 260 sources at 1.55 ≲ z ≲ 3.50 having −28.0 ≲ M i ≲ − 30.0 mag from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS) catalog, augmenting the previous iteration, which contained 226 of the 260 sources whose measurements are improved upon in this work. We obtain reliable systemic redshifts based on [O iii] λ5007 for a subset of 121 sources, which we use to calibrate prescriptions for correcting UV-based redshifts. These prescriptions are based on a regression analysis involving C iv full-width-at-half-maximum intensity and equivalent width, along with the UV continuum luminosity at a rest-frame wavelength of 1350 Å. Applying these corrections can improve the accuracy and the precision in the C iv-based redshift by up to ∼850 km s−1 and ∼150 km s−1, respectively, which correspond to ∼8.5 and ∼1.5 Mpc in comoving distance at z = 2.5. Our prescriptions also improve the accuracy of the best available multifeature redshift determination algorithm by ∼100 km s−1, indicating that the spectroscopic properties of the C iv emission line can provide robust redshift estimates for high-redshift quasars. We discuss the prospects of our prescriptions for cosmological and quasar studies utilizing upcoming large spectroscopic surveys.

JWST’s PEARLS: TN J1338–1942 – I. Extreme jet-triggered star formation in a z = 4.11 luminous radio galaxy

ABSTRACT We present the first JWST observations of the z = 4.11 luminous radio galaxy TN J1338–1942, obtained as part of the ‘Prime Extragalactic Areas for Reionization and Lensing Science’ (‘PEARLS’) project. Our NIRCam observations, designed to probe the key rest-frame optical continuum and emission line features at this redshift, enable resolved spectral energy distribution modelling that incorporates both a range of stellar population assumptions and radiative shock models. With an estimated stellar mass of log10(M/M⊙) ∼ 10.9, TN J1338–1942 is confirmed to be one of the most massive galaxies known at this epoch. Our observations also reveal extremely high equivalent-width nebular emission coincident with the luminous AGN jets that is best fit by radiative shocks surrounded by extensive recent star formation. We estimate the total star-formation rate (SFR) could be as high as $\sim 1600\, \text{M}_{\odot }\, \text{yr}^{-1}$ , with the SFR that we attribute to the jet induced burst conservatively $\gtrsim 500\, \text{M}_{\odot }\, \text{yr}^{-1}$ . The mass-weighted age of the star-formation, tmass &amp;lt; 4 Myr, is consistent with the likely age of the jets responsible for the triggered activity and significantly younger than that measured in the core of the host galaxy. The extreme scale of the potential jet-triggered star-formation activity indicates the potential importance of positive AGN feedback in the earliest stages of massive galaxy formation, with our observations also illustrating the extraordinary prospects for detailed studies of high-redshift galaxies with JWST.

Early Results from GLASS-JWST. IV. Spatially Resolved Metallicity in a Low-mass z ∼ 3 Galaxy with NIRISS* *Based on observations acquired by the JWST under the ERS program ID 1324 (PI T. Treu).

We report the first gas-phase metallicity map of a distant galaxy measured with the James Webb Space Telescope (JWST). We use the NIRISS slitless spectroscopy acquired by the GLASS Early Release Science program to spatially resolve the rest-frame optical nebular emission lines in a gravitationally lensed galaxy at z = 3.06 behind the A2744 galaxy cluster. This galaxy (dubbed GLASS-Zgrad1) has stellar mass ∼108.6 M ⊙, instantaneous star formation rate ∼8.6 M ⊙ yr−1 (both corrected for lensing magnification), and global metallicity one-fourth solar. From its emission-line maps ([O iii], Hβ, Hγ, [Ne iii], and [O ii]), we derive its spatial distribution of gas-phase metallicity using a well-established forward-modeling Bayesian inference method. The exquisite resolution and sensitivity of JWST/NIRISS, combined with lensing magnification, enable us to resolve this z ∼ 3 dwarf galaxy in ≳50 resolution elements with sufficient signal, an analysis hitherto not possible. We find that the radial metallicity gradient of GLASS-Zgrad1 is strongly inverted (i.e., positive): = 0.165 ± 0.023 dex kpc−1. This measurement is robust at confidence level against known systematics. This positive gradient may be due to tidal torques induced by a massive nearby (∼15 kpc projected) galaxy, which can cause inflows of metal-poor gas into the central regions of GLASS-Zgrad1. These first results showcase the power of JWST wide-field slitless spectroscopic modes to resolve the mass assembly and chemical enrichment of low-mass galaxies in and beyond the peak epoch of cosmic star formation (z ≳ 2). Reaching masses ≲ 109 M ⊙ at these redshifts is especially valuable to constrain the effects of galactic feedback and environment and is possible only with JWST’s new capabilities.

Signs of environmental effects on star-forming galaxies in the Spiderweb protocluster at z = 2.16

ABSTRACT We use multi-object near-infrared spectroscopy with VLT/KMOS to investigate the role of the environment in the evolution of the ionized gas properties of narrow-band-selected H α emitters (HAEs) in the Spiderweb protocluster at z = 2.16. Based on rest-frame optical emission lines, H α and [N ii]λ6584, we confirm the cluster membership of 39 of our targets (i.e. 93 per cent success rate), and measure their star formation rates (SFR), gas-phase oxygen abundances, and effective radius. We parametrize the environment where our targets reside using local and global density indicators based on previous samples of spectroscopic and narrow-band cluster members. We find that star-forming galaxies embedded in the Spiderweb protocluster display SFRs compatible with those of the main sequence and morphologies comparable to those of late-type galaxies at z = 2.2 in the field. We also report a mild gas-phase metallicity enhancement (0.06 ± 0.03 dex) at intermediate stellar masses. Furthermore, we identify two UVJ-selected quiescent galaxies with residual H α-based star formation and find signs of extreme dust obscuration in a small sample of starbursty submillimetre galaxies based on their FIR and H α emission. Interestingly, the spatial distribution of these objects differs from the rest of HAEs, avoiding the protocluster core. Finally, we explore the gas fraction–gas metallicity diagram for seven galaxies with molecular gas masses measured by ATCA using CO(1−0). In the context of the gas-regulator model, our objects are consistent with relatively low mass-loading factors, suggesting lower outflow activity than field samples at the cosmic noon and thus, hinting at the onset of environmental effects in this massive protocluster.

First insights into the ISM at z &amp;gt; 8 with JWST: possible physical implications of a high [O iii] λ4363/[O iii] λ5007

ABSTRACT We present a detailed analysis of the rest-frame optical emission line ratios for three spectroscopically confirmed galaxies at z &amp;gt; 7.5. The galaxies were identified in the James Webb Space Telescope (JWST) Early Release Observations field SMACS J0723.3 − 7327. By quantitatively comparing Balmer and oxygen line ratios of these galaxies with various low-redshift ‘analogue’ populations (e.g. Green Peas, Blueberries, etc.), we show that no single analogue population captures the diversity of line ratios of all three galaxies observed at z &amp;gt; 7.5. We find that S06355 at z = 7.67 and S10612 at z = 7.66 are similar to local Green Peas and Blueberries. In contrast, S04590 at z = 8.50 appears to be significantly different from the other two galaxies, most resembling extremely low-metallicity systems in the local Universe. Perhaps the most striking spectral feature in S04590 is the curiously high [O iii] λ4363/[O iii] λ5007 ratio (RO3) of 0.048 (or 0.055 when dust-corrected), implying either extremely high electron temperatures, &amp;gt;3 × 104 K, or gas densities &amp;gt;104 cm−3. Observed line ratios indicate that this galaxy is unlikely to host an AGN. Using photoionization modelling, we show that the inclusion of high-mass X-ray binaries or a high cosmic ray background in addition to a young, low-metallicity stellar population can provide the additional heating necessary to explain the observed high RO3 while remaining consistent with other observed line ratios. Our models represent a first step at accurately characterizing the dominant sources of photoionization and heating at very high redshifts, demonstrating that non-thermal processes may become important as we probe deeper into the Epoch of Reionization.

First look with JWST spectroscopy: Resemblance among z ∼ 8 galaxies and local analogs

Deep images and near-IR spectra of galaxies in the field of the lensing cluster SMACS J0723.3−7327 were recently taken as part of the Early Release Observations (EROs) program of the James Webb Space Telescope (JWST). Among these, two NIRSpec spectra of galaxies, at z = 7.7 and at z = 8.5, were obtained, revealing, for the first time, the rest-frame optical emission line spectra of galaxies in the epoch of reionization, including the detection of the important [O III]λ4363 auroral line (see JWST PR 2022-035). We present an analysis of the emission line properties of these galaxies, finding that these galaxies have a high excitation (as indicated by high ratios of [O III]λ5007/[O II] λ3727, [Ne III] λ3869/[O II] λ3727), strong [O III]λ4363, high equivalent widths, and other properties typical of low-metallicity star-forming galaxies. Using the direct method, we determined oxygen abundances of 12 + log(O/H)≈7.9 in two z = 7.7 galaxies and a lower metallicity of 12 + log(O/H)≈7.4 − 7.5 (∼5% solar) in the z = 8.5 galaxy using different strong line methods. More accurate metallicity determinations will require better data. With stellar masses estimated from spectral energy distribution (SED) fits, we find that the three galaxies lie close to or below the z ∼ 2 mass-metallicity relation. Overall, these first galaxy spectra at z ∼ 8 show a strong resemblance in their the emission line properties of galaxies in the epoch of reionization with those of relatively rare local analogs previously studied with the SDSS. Clearly, the first JWST observations demonstrate already the incredible power of spectroscopy to reveal the properties of galaxies in the early Universe.

First Peek with JWST/NIRCam Wide-field Slitless Spectroscopy: Serendipitous Discovery of a Strong [O iii]/Hα Emitter at z = 6.11

We report the serendipitous discovery of an [O iii] λ λ4959/5007 and Hα line emitter in the Epoch of Reionization (EoR) with the James Webb Space Telescope (JWST) commissioning data taken in the NIRCam wide-field slitless spectroscopy (WFSS) mode. Located ∼55″ away from the flux calibrator P330-E, this galaxy exhibits bright [O iii] λ λ4959/5007 and Hα lines detected at 3.7σ, 9.9σ, and 5.7σ, respectively, with a spectroscopic redshift of z = 6.112 ± 0.001. The total Hβ+[O iii] equivalent width is 664 ± 98 Å (454 ± 78 Å from the [O iii] λ5007 line). This provides direct spectroscopic evidence for the presence of strong rest-frame optical lines (Hβ+[O iii] and Hα) in EoR galaxies as inferred previously from the analyses of the Spitzer/IRAC spectral energy distributions (SEDs). Two spatial and velocity components are identified in this source, possibly indicating that this system is undergoing a major merger, which might have triggered the ongoing starburst with strong nebular emission lines over a timescale of ∼2 Myr, as our SED modeling suggests. The tentative detection of He ii λ4686 line (1.9σ), if real, may indicate the existence of very young and metal-poor star-forming regions with a hard UV radiation field. Finally, this discovery demonstrates the power and readiness of the JWST/NIRCam WFSS mode, and marks the beginning of a new era for extragalactic astronomy, in which EoR galaxies can be routinely discovered via blind slitless spectroscopy through the detection of rest-frame optical emission lines.

Modelling type 1 quasar colours in the era of Rubin and Euclid

ABSTRACT We construct a parametric SED model which is able to reproduce the average observed SDSS–UKIDSS–WISE quasar colours to within one-tenth of a magnitude across a wide range of redshift (0 &amp;lt; z &amp;lt; 5) and luminosity (−22 &amp;gt; Mi &amp;gt; −29). This model is shown to provide accurate predictions for the colours of known quasars which are less luminous than those used to calibrate the model parameters, and also those at higher redshifts z &amp;gt; 5. Using a single parameter, the model encapsulates an up-to-date understanding of the intra-population variance in the rest-frame ultraviolet and optical emission lines of luminous quasars. At fixed redshift, there are systematic changes in the average quasar colours with apparent i-band magnitude, which we find to be well explained by the contribution from the host galaxy and our parametrization of the emission-line properties. By including redshift as an additional free parameter, the model could be used to provide photometric redshifts for individual objects. For the population as a whole we find that the average emission line and host-galaxy contributions can be well described by simple functions of luminosity which account for the observed changes in the average quasar colours across 18.1 &amp;lt; iAB &amp;lt; 21.5. We use these trends to provide predictions for quasar colours at the luminosities and redshifts which will be probed by the Rubin Observatory LSST and ESA-Euclid wide survey. The model code is applicable to a wide range of upcoming photometric and spectroscopic surveys, and is made publicly available.

The MOSDEF Survey: Environmental Dependence of the Gas-phase Metallicity of Galaxies at 1.4 ≤ z ≤ 2.6*

Abstract Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field survey, we investigate the role of the local environment in the gas-phase metallicity of galaxies. The local environment measurements are derived from accurate and uniformly calculated photometric redshifts with well-calibrated probability distributions. Based on rest-frame optical emission lines, [N ii]λ6584 and Hα, we measure gas-phase oxygen abundances of 167 galaxies at 1.37 ≤ z ≤ 1.7 and 303 galaxies at 2.09 ≤ z ≤ 2.61, located in diverse environments. We find that at z ∼ 1.5, the average metallicity of galaxies in overdensities with M * ∼ 109.8 M ⊙, 1010.2 M ⊙, and 1010.8 M ⊙ is higher relative to their field counterparts by 0.094 ± 0.051, 0.068 ± 0.028, and 0.052 ± 0.043 dex, respectively. However, this metallicity enhancement does not exist at higher redshift, z ∼ 2.3, where, compared to the field galaxies, we find 0.056 ± 0.043, 0.056 ± 0.028, and 0.096 ± 0.034 dex lower metallicity for galaxies in overdense environments with M * ∼ 109.8 M ⊙, 1010.2 M ⊙ and 1010.7 M ⊙, respectively. Our results suggest that, at 1.37 ≤ z ≤ 2.61, the variation of mass–metallicity relation with local environment is small (&lt;0.1 dex), and reverses at z ∼ 2. Our results support the hypothesis that, at the early stages of cluster formation, owing to efficient gas cooling, galaxies residing in overdensities host a higher fraction of pristine gas with prominent primordial gas accretion, which lowers their gas-phase metallicity compared to their coeval field galaxies. However, as the universe evolves to lower redshifts (z ≲ 2), the shock-heated gas in overdensities cannot cool down efficiently, and galaxies become metal-rich rapidly due to the suppression of pristine gas inflow and re-accretion of metal-enriched outflows in overdensities.

Prescriptions for Correcting Ultraviolet-based Redshifts for Luminous Quasars at High Redshift

Abstract High-redshift quasars typically have their redshift determined from rest-frame ultraviolet (UV) emission lines. However, these lines, and more specifically the prominent C iv λ1549 emission line, are typically blueshifted yielding highly uncertain redshift estimates compared to redshifts determined from rest-frame optical emission lines. We present near-infrared spectroscopy of 18 luminous quasars at 2.15 &lt; z &lt; 3.70 that allows us to obtain reliable systemic redshifts for these sources. Together with near-infrared spectroscopy of an archival sample of 44 quasars with comparable luminosities and redshifts, we provide prescriptions for correcting UV-based redshifts. Our prescriptions reduce velocity offsets with respect to the systemic redshifts by ∼140 km s−1 and reduce the uncertainty on the UV-based redshift by ∼25% with respect to the best method currently used for determining such values. We also find that the redshifts determined from the Sloan Digital Sky Survey Pipeline for our sources suffer from significant uncertainties, which cannot be easily mitigated. We discuss the potential of our prescriptions to improve UV-based redshift corrections given a much larger sample of high-redshift quasars with near-infrared spectra.

Three Dusty Star-forming Galaxies at z ∼ 1.5: Mergers and Disks on the Main Sequence

Abstract The main sequence of galaxies, a correlation between the star formation rates (SFRs) and stellar masses of galaxies, has been observed out to z ∼ 4. Galaxies within the scatter of the correlation are typically interpreted to be secularly evolving while galaxies with SFRs elevated above the main sequence are interpreted to be undergoing interactions or to be Toomre-unstable disks with starbursting clumps. In this paper, we investigate the recent merger histories of three dusty star-forming galaxies, identified by their bright submillimeter emission at z ∼ 1.5. We analyze rest-frame optical and UV imaging, rest-frame optical emission line kinematics using slit spectra obtained with the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) on Keck I, and calculate Gini and M 20 statistics for each galaxy and conclude two are merger driven while the third is an isolated disk galaxy. The disk galaxy lies ∼4× above the main sequence, one merger lies within the scatter of the main sequence, and one merger lies ∼4× below the main sequence. This hints that the location of a galaxy with respect to the main sequence may not be a useful discriminator of the recent star formation history of high-M galaxies at z ∼ 1.

The Lyman Continuum Escape Survey. II. Ionizing Radiation as a Function of the [O iii]/[O ii] Line Ratio

Abstract We discuss the rest-frame optical emission line spectra of a large (∼50) sample of z ∼ 3.1 Lyα emitting galaxies (LAEs) whose physical properties suggest such sources are promising analogs of galaxies in the reionization era. Reliable Lyman continuum (LyC) escape fractions have now been determined for a large sample of such LAEs from the LymAn Continuum Escape Survey (LACES) undertaken via deep Hubble Space Telescope imaging in the SSA22 survey area reported in Fletcher et al. Using new measures of [O ii] emission secured from Keck MOSFIRE spectra we re-examine, for a larger sample, earlier claims that LyC leakages may correlate with the nebular emission line ratio [O iii]/[O ii] as expected for density-bound H ii regions. We find that a large [O iii]/[O ii] line ratio is indeed a necessary condition for LyC leakage, strengthening earlier claims made using smaller samples at various redshifts. However, not all LAEs with large [O iii]/[O ii] line ratios are leakers and leaking radiation appears not to be associated with differences in other spectral diagnostics. This suggests the detection of leaking radiation is modulated by an additional property, possibly the viewing angle for porous H ii regions. We discuss our new results in the context of the striking bimodality of LAE leakers and non-leakers found in the LACES program and the implications for the sources of cosmic reionization.

DEIMOS and MOSFIRE spectroscopy of star-forming galaxies in the AKARI NEP-Deep field

AbstractObserving high resolution optical to infrared spectra is crucial to understanding how energy is generated in galaxies. We present follow-up optical Keck-II/DEIMOS and infrared Keck-I/MOSFIRE spectra of ∼200 galaxies in the AKARI/North Ecliptic Pole Deep survey region at intermediate redshift. From rest-frame optical emission lines, we classify most of our objects as star-forming (53%), with the MIR selection favoring relatively massive galaxies (median log M/M⊙∼ 10.3). In addition, we combine our spectroscopic redshifts with UV to FIR photometry as inputs in order to model SEDs with CIGALE, and we measure the PAH 7.7 μm luminosity as an SFR indicator.