Rest-frame Ultraviolet Spectra Research Articles

Gemini Near Infrared Spectrograph−Distant Quasar Survey: Rest-frame Ultraviolet−Optical Spectral Properties of Broad Absorption Line Quasars

We present the rest-frame ultraviolet−optical spectral properties of 65 broad absorption line (BAL) quasars from the Gemini Near Infrared Spectrograph−Distant Quasar Survey (GNIRS-DQS). These properties are compared with those of 195 non-BAL quasars from GNIRS-DQS in order to identify the drivers for the appearance of BALs in quasar spectra. In particular, we compare equivalent widths and velocity widths, as well as velocity offsets from systemic redshifts, of principal emission lines. In spite of the differences between their rest-frame ultraviolet spectra, we find that luminous BAL quasars are generally indistinguishable from their non-BAL counterparts in the rest-frame optical band at redshifts 1.55 ≲ z ≲ 3.50. We do not find any correlation between BAL trough properties and the Hβ-based supermassive black hole masses and normalized accretion rates in our sample. Considering the Sloan Digital Sky Survey quasar sample, which includes the GNIRS-DQS sample, we find that a monochromatic luminosity at rest-frame 2500 Å of ≳1045 erg s−1 is a necessary condition for launching BAL outflows in quasars. We compare our findings with other BAL quasar samples and discuss the roles that accretion rate and orientation play in the appearance of BAL troughs in quasar spectra.

A Giant Metrewave Radio Telescope survey of radio-loud broad absorption line quasars

ABSTRACT A substantial fraction of quasars display broad absorption lines (BALs) in their rest-frame ultraviolet spectra. While the origin of BALs is thought to be related to the accretion disc wind, it remains unclear whether the observed ratio of BAL to non-BAL quasars is a result of orientation. We conducted observations of 48 BAL quasars and the same number of non-BAL quasars at 322 MHz using the Giant Metrewave Radio Telescope. Combined with previous flux measurements ranging from MHz to GHz frequencies, we compared continuum radio spectra between the two quasar groups. These data offer insights into low-frequency radio properties that have been difficult to investigate with previous observations only at GHz frequencies. Our results show that 73 ± 13 per cent of the BAL quasars exhibit steep or peaked spectra, a higher proportion than the 44 ± 14 per cent observed in the non-BAL quasars. In contrast, there are no discernible differences between the two quasar groups in the radio luminosity, peak frequency, and spectral index distributions of sources with steep or peaked spectra and sources with flat or inverted spectra. Generally, as the jet axis and line of sight become closer to parallel, quasars exhibit flat or inverted spectra rather than steep or peaked spectra. Therefore, these results suggest that BAL quasars are more frequently observed farther from the jet axis than non-BAL quasars. However, given that a certain proportion of BAL quasars exhibit flat or inverted spectra, more than the simple orientation scenario is required to elucidate the radio properties of BAL quasars.

No redshift evolution in the rest-frame ultraviolet emission line properties of quasars from z = 1.5 to z = 4.0

ABSTRACT We analyse the rest-frame ultraviolet (UV) spectra of 2531 high-redshift (3.5 < z < 4.0) quasars from the Sloan Digital Sky Survey DR16Q catalogue. In combination with previous work, we study the redshift evolution of the rest-frame UV line properties across the entire redshift range, 1.5 < z < 4.0. We improve the systemic redshift estimates at z > 3.5 using a cross-correlation algorithm that employs high signal-to-noise template spectra spanning the full range in UV emission line properties. We then quantify the evolution of C iv and He ii emission line properties with redshift. The increase in C iv blueshifts with cosmological redshift can be fully explained by the higher luminosities of quasars observed at high redshifts. We recover broadly similar trends between the He ii equivalent width and C iv blueshift at both 1.5 < z < 2.65 and 3.5 < z < 4.0 suggesting that the blueshift depends systematically on the spectral energy density (SED) of the quasar and there is no evolution in the SED over the redshift range 1.5 < z < 4.0. C iv blueshifts are highest when L/L$_\text {Edd} \ge$ 0.2 and Mbh ≥ 109 M⊙ for the entire 1.5 < z < 4.0 sample. We find that luminosity matching samples as a means to explore the evolution of their rest-frame UV emission line properties is only viable if the samples are also matched in the Mbh–L/L$_\text {Edd}$ plane. Quasars at z ≥ 6 are on average less massive and have higher Eddington-scaled accretion rates than their luminosity-matched counterparts at 1.5 < z < 4.0, which could explain the observed evolution in their UV line properties.

The VANDELS survey: the ionizing properties of star-forming galaxies at 3 ≤ z ≤ 5 using deep rest-frame ultraviolet spectroscopy

ABSTRACT The physical properties of Epoch of Reionization (EoR) galaxies are still poorly constrained by observations. To better understand the ionizing properties of galaxies in the EoR, we investigate deep, rest-frame ultraviolet (UV) spectra of ≃500 star-forming galaxies at 3 ≤ z ≤ 5 selected from the public ESO-VANDELS spectroscopic survey. The absolute ionizing photon escape fraction ($f_{\rm esc}^{\rm abs}$, i.e. the ratio of leaking against produced ionizing photons) is derived by combining absorption line measurements with estimates of the UV attenuation. The ionizing production efficiency (ξion, i.e. the number of ionizing photons produced per non-ionizing UV luminosity) is calculated by fitting the far-UV (FUV) stellar continuum of the VANDELS galaxies. We find that the $f_{\rm esc}^{\rm abs}$ and ξion parameters increase towards low-mass, blue UV-continuum slopes and strong Ly α emitting galaxies, and both are slightly higher-than-average for the UV-faintest galaxies in the sample. Potential Lyman Continuum Emitters (LCEs, $f_{\rm esc}^{\rm abs} \ge 5{{\ \rm \, per\ cent}}$) and selected Lyman Alpha Emitters (LAEs, WLyα ≤ −20 Å) show systematically higher ξion (log ξion(Hz erg−1) ≈ 25.38, 25.41) than non-LCEs and non-LAEs (log ξion(Hz erg−1) ≈ 25.18, 25.14) at similar UV magnitudes. This indicates very young underlying stellar populations (≈10 Myr) at relatively low metallicities (≈0.2 Z⊙). The FUV non-ionizing spectra of potential LCEs is characterized by blue UV slopes (≤−2), enhanced Ly α emission (≤−25 Å), strong UV nebular lines (e.g. high ${\rm C\, \small {IV}}$1550/${\rm C\, \small {III}}$1908 ≥0.75 ratios), and weak absorption lines (≤1 Å). The latter suggests the existence of low gas-column-density channels in the interstellar medium, which enables the escape of ionizing photons. By comparing our VANDELS results against other surveys in the literature, our findings imply that the ionizing budget in the EoR was likely dominated by UV-faint, low-mass, and dustless galaxies.

A Generative Model for Quasar Spectra

We build a multi-output generative model for quasar spectra and the properties of their black hole engines, based on a Gaussian process latent-variable model. This model treats every quasar as a vector of latent properties such that the spectrum and all physical properties of the quasar are associated with non-linear functions of those latent parameters; the Gaussian process kernel functions define priors on the function space. Our generative model is trained with a justifiable likelihood function that allows us to treat heteroscedastic noise and missing data correctly, which is crucial for all astrophysical applications. It can simultaneously predict unobserved spectral regions and the physical properties of quasars in held-out test data. We apply the model to rest-frame ultraviolet and optical quasar spectra for which precise black hole masses (based on reverberation-mapping measurements) are available. Unlike reverberation-mapping studies that require multi-epoch data, our model predicts black hole masses from single-epoch spectra—even with limited spectral coverage. We demonstrate the capabilities of the model by predicting black hole masses and unobserved spectral regions. We find that we predict black hole masses at close to the best possible accuracy.

An X-ray fading, UV brightening QSO at z ≈ 6

Explaining the existence of super massive black holes (SMBHs) with MBH ≳ 108 M⊙ at z ≳ 6 is a persistent challenge to modern astrophysics. Multiwavelength observations of z ≳ 6 quasi-stellar objects (QSOs) reveal that, on average, their accretion physics is similar to that of their counterparts at lower redshift. However, QSOs showing properties that deviate from the general behavior can provide useful insights into the physical processes responsible for the rapid growth of SMBHs in the early universe. We present X-ray (XMM-Newton, 100 ks) follow-up observations of a z ≈ 6 QSO, J1641+3755, which was found to be remarkably X-ray bright in a 2018 Chandra dataset. J1641+3755 is not detected in the 2021 XMM-Newton observation, implying that its X-ray flux decreased by a factor ≳7 on a notably short timescale (i.e., ≈115 rest-frame days), making it the z > 4 QSO with the largest variability amplitude. We also obtained rest-frame ultraviolet (UV) spectroscopic and photometric data with the Large Binocular Telescope (LBT). Surprisingly, comparing our LBT photometry with archival data, we found that J1641+3755 became consistently brighter in the rest-frame UV band from 2003 to 2016, while no strong variation occurred from 2016 to 2021. Its rest-frame UV spectrum is consistent with the average spectrum of high-redshift QSOs. Multiple narrow absorption features are present, and several of them can be associated with an intervening system at z = 5.67. Several physical causes can explain the variability properties of J1641+3755, including intrinsic variations of the accretion rate, a small-scale obscuration event, gravitational lensing due to an intervening object, and an unrelated X-ray transient in a foreground galaxy in 2018. Accounting for all of the z > 6 QSOs with multiple X-ray observations separated by more that ten rest-frame days, we found an enhancement of strongly (i.e., by a factor > 3) X-ray variable objects compared to QSOs at later cosmic times. This finding may be related to the physics of fast accretion in high-redshift QSOs.

A peculiar Type II QSO identified via broad-band detection of extreme nebular line emission

ABSTRACT We present S82-20, an unusual redshift ≈3 object identified in SDSS-Stripe 82 broad-band images. The rest-frame ultraviolet spectrum of S82-20 shows emission lines from highly ionized species, including He ii λ1640, and the C iv λλ1548, 1550 and O vi λλ1032, 1038 doublets. The high Ly α luminosity (3.5 × 1044 erg s−1), the high emission line equivalent widths (>200 Å for Ly α), the full width at half-maximum of the emission lines (<800 km s−1), and the high ionization O vi line strongly support the interpretation that S82-20 is a Type II Quasi-Stellar Objects (QSOs). However, photoionization models using Type II QSO do not fully explain the measured C iv/He ii line ratio, which requires either some contribution from star formation or high velocity shocks. Additionally, S82-20 is not detected at wavelengths longer than 2 μm, in tension with the expectation of isotropically infrared emission of a luminous QSO. We consider the possibility that S82-20 is a rare example of a changing-look QSO, observed in a temporarily low state, where the broad line region has faded, while the narrow line region still emits emission line. Otherwise, it may be a rare case of the short phase of the life of a massive galaxy, in which active star formation and accretion on to a supermassive black hole coexist.

Probing the He ii re-Ionization ERa via Absorbing C iv Historical Yield (HIERACHY) I: A strong outflow from a z ∼ 4.7 quasar

ABSTRACT Outflows from supermassive black holes (SMBHs) play an important role in the co-evolution of themselves, their host galaxies, and the larger scale environments. Such outflows are often characterized by emission and absorption lines in various bands and in a wide velocity range blueshifted from the systematic redshift of the host quasar. In this paper, we report a strong broad line region (BLR) outflow from the z ≈ 4.7 quasar BR 1202-0725 based on the high-resolution optical spectrum taken with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph installed on the 6.5 m Magellan/Clay telescope, obtained from the ‘Probing the He ii re-Ionization ERa via Absorbing C iv Historical Yield’ (HIERACHY) project. This rest-frame ultraviolet (UV) spectrum is characterized by a few significantly blueshifted broad emission lines from high ions; the most significant one is the C iv line at a velocity of $\sim -6500$ km s−1 relative to the H α emission line, which is among the highest velocity BLR outflows in observed quasars at z > 4. The measured properties of UV emission lines from different ions, except for O i and Ly α, also follow a clear trend that higher ions tend to be broader and outflow at higher average velocities. There are multiple C iv and Si iv absorbing components identified on the blue wings of the corresponding emission lines, which may be produced by either the outflow or the intervening absorbers.

UV absorption lines and their potential for tracing the Lyman continuum escape fraction

Context. The neutral intergalactic medium above redshift ∼6 is opaque to ionizing radiation, and therefore indirect measurements of the escape fraction of ionizing photons are required from galaxies of this epoch. Low-ionization-state absorption lines are a common feature in the rest-frame ultraviolet (UV) spectrum of galaxies, showing a broad diversity of strengths and shapes. As these spectral features indicate the presence of neutral gas in front of UV-luminous stars, they have been proposed to carry information on the escape of ionizing radiation from galaxies. Aims. We aim to decipher the processes that are responsible for the shape of the absorption lines in order to better understand their origin. We also aim to explore whether the absorption lines can be used to predict the escape fraction of ionizing photons. Methods. Using a radiation-hydrodynamical cosmological zoom-in simulation and the radiative transfer postprocessing code RASCAS we generated mock C II λ1334 and Lyβ lines of a virtual galaxy at z = 3 with M1500 = −18.5 as seen from many directions of observation. We also computed the escape fraction of ionizing photons in those directions and looked for correlations between the escape fraction and properties of the absorption lines, in particular their residual flux. Results. We find that the resulting mock absorption lines are comparable to observations and that the lines and the escape fractions vary strongly depending on the direction of observation. The effect of infilling due to the scattering of the photons and the use of different apertures of observation both result in either strong or very mild changes of the absorption profile. Gas velocity and dust always affect the absorption profile significantly. We find no strong correlations between observable Lyβ or C II λ1334 properties and the escape fraction. After correcting the continuum for attenuation by dust to recover the intrinsic continuum, the residual flux of the C II λ1334 line correlates well with the escape fraction for directions with a dust-corrected residual flux larger than 30%. For other directions, the relations have a strong dispersion, and the residual flux overestimates the escape fraction for most cases. Concerning Lyβ, the residual flux after dust correction does not correlate with the escape fraction but can be used as a lower limit.

Fe iii emission in quasars: evidence for a dense turbulent medium

ABSTRACT Recent improvements to atomic energy-level data allow, for the first time, accurate predictions to be made for the Fe iii line emission strengths in the spectra of luminous, $L_\text{bol}\simeq 10^{46}\!-\!10^{48}\mbox{${\rm \, erg}{\rm \, s}^{-1}\, $}$, active galactic nuclei. The Fe iii emitting gas must be primarily photoionized, consistent with observations of line reverberation. We use cloudy models exploring a wide range of parameter space, together with ≃26 000 rest-frame ultraviolet spectra from the Sloan Digital Sky Survey, to constrain the physical conditions of the line emitting gas. The observed Fe iii emission is best accounted for by dense (nH ≃ 1014 cm−3) gas which is microturbulent, leading to smaller line optical depths and fluorescent excitation. Such high density gas appears to be present in the central regions of the majority of luminous quasars. Using our favoured model, we present theoretical predictions for the relative strengths of the Fe iii UV34 λλ1895, 1914, 1926 multiplet. This multiplet is blended with the Si iii] λ1892 and C iii] λ1909 emission lines and an accurate subtraction of UV34 is essential when using these lines to infer information about the physics of the broad line region in quasars.

Highly Structured Quasar Outflow in SDSS J010612.22+001920.1

Abstract Evidence for quasar outflows can be detected via blueshifted broad absorption lines (BALs) in rest-frame ultraviolet spectra of quasars. We have identified 18 narrow absorption line (NAL) systems in the BAL system of SDSS J010612.22+001920.1, indicating that this BAL outflow has achieved a high degree of clumpiness. Moreover, these NAL systems are highly structured in velocity space and separated from each other by the doublet spacings of multiple ionic species, including a sequence of 10 C iv doublets that form arithmetic progression with a common difference of ≈498 . Cases like J010612.22+001920.1 offer strong evidence for the dynamical process of radiative acceleration in quasar outflow, and open up a new way for the research of quasar outflow under the framework of the NAL complex.

Accretion disc winds in tidal disruption events: ultraviolet spectral lines as orientation indicators

ABSTRACT Some tidal disruption events (TDEs) exhibit blueshifted broad absorption lines (BALs) in their rest-frame ultraviolet (UV) spectra, while others display broad emission lines (BELs). Similar phenomenology is observed in quasars and accreting white dwarfs, where it can be interpreted as an orientation effect associated with line formation in an accretion disc wind. We propose and explore a similar unification scheme for TDEs. We present synthetic UV spectra for disc and wind-hosting TDEs, produced by a state-of-the-art Monte Carlo ionization and radiative transfer code. Our models cover a wide range of disc wind geometries and kinematics. Such winds naturally reproduce both BALs and BELs. In general, sightlines looking into the wind cone preferentially produce BALs, while other orientations preferentially produce BELs. We also study the effect of wind clumping and CNO-processed abundances on the observed spectra. Clumpy winds tend to produce stronger UV emission and absorption lines, because clumping increases both the emission measure and the abundances of the relevant ionic species, the latter by reducing the ionization state of the outflow. The main effect of adopting CNO-processed abundances is a weakening of C iv 1550 Å and an enhancement of N v 1240 Å in the spectra. We conclude that line formation in an accretion disc wind is a promising mechanism for explaining the diverse UV spectra of TDEs. If this is correct, the relative number of BAL and BEL TDEs can be used to estimate the covering factor of the outflow. The models in this work are publicly available online and upon request.

The ALPINE–ALMA [C ii] Survey: Multiwavelength Ancillary Data and Basic Physical Measurements

Abstract We present the ancillary data and basic physical measurements for the galaxies in the ALMA Large Program to Investigate C+ at Early Times (ALPINE) survey—the first large multiwavelength survey that aims at characterizing the gas and dust properties of 118 main-sequence galaxies at redshifts 4.4 < z < 5.9 via the measurement of [ ] emission at (64% at >3.5σ) and the surrounding far-infrared continuum in conjunction with a wealth of optical and near-infrared data. We outline in detail the spectroscopic data and selection of the galaxies as well as the ground- and space-based imaging products. In addition, we provide several basic measurements including stellar masses, star formation rates (SFR), rest-frame ultra-violet (UV) luminosities, UV continuum slopes (β), and absorption line redshifts, as well as Hα emission derived from Spitzer colors. We find that the ALPINE sample is representative of the 4 < z < 6 galaxy population selected by photometric methods and only slightly biased toward bluer colors (Δβ ∼ 0.2). Using [ ] as tracer of the systemic redshift (confirmed for one galaxy at z = 4.5 out of 118 for which we obtained optical [ ]λ3727Å emission), we confirm redshifted Lyα emission and blueshifted absorption lines similar to findings at lower redshifts. By stacking the rest-frame UV spectra in the [ ] rest frame, we find that the absorption lines in galaxies with high specific SFR are more blueshifted, which could be indicative of stronger winds and outflows.

The correlations between optical/UV broad lines and X-ray emission for a large sample of quasars

ABSTRACT We present Chandra observations of 2106 radio-quiet quasars in the redshift range 1.7 ≤ z ≤ 2.7 from the Sloan Digital Sky Survey (SDSS), through data release 14 (DR14), that do not contain broad absorption lines in their rest-frame ultraviolet (UV) spectra. This sample adds over a decade worth of SDSS and Chandra observations to our previously published sample of 139 quasars from SDSS DR5 that is still used to correlate X-ray and optical/UV emission in typical quasars. We fit the SDSS spectra for 753 of the quasars in our sample that have high-quality (exposure time ≥ 10 ks and off-axis observation angle ≤ 10 arcmin) X-ray observations, and analyse their X-ray-to-optical spectral energy distribution properties (αox and Δαox) with respect to the measured C iv and Mg ii emission-line rest-frame equivalent width (EW) and the C iv emission-line blueshift. We find significant correlations (at the ≥99.99 per cent level) between αox and these emission-line parameters, as well as between Δαox and $\rm{C \, \small{IV}}$ EW. Slight correlations are found between Δαox and $\rm{C \, \small{IV}}$ blueshift, $\rm{Mg \, \small{II}}$ EW, and the $\rm{C \, \small{IV}}$ EW to $\rm{Mg \, \small{II}}$ EW ratio. The best-fitting trend in each parameter space is used to compare the X-ray weakness (Δαox) and optical/UV emission properties of typical quasars and weak-line quasars (WLQs). The WLQs typically exhibit weaker X-ray emission than predicted by the typical quasar relationships. The best-fitting relationships for our typical quasars are consistent with predictions from the disc–wind quasar model. The behaviour of the WLQs compared to our typical quasars can be explained by an X-ray ‘shielding’ model.

Kinematics of C iv and [O iii] emission in luminous high-redshift quasars

We characterise ionised gas outflows using a large sample of ~330 high-luminosity (45.5 < log(L_bol/erg s^-1) < 49.0), high-redshift (1.5 < z < 4.0) quasars via their [OIII]4960,5008 emission. The median velocity width of the [OIII] emission line is 1540 kms^-1, increasing with increasing quasar luminosity. Broad, blue-shifted wings are seen in the [OIII] profiles of 42 per cent of the sample. Rest-frame ultraviolet spectra with well-characterised CIV 1550 emission line properties are available for more than 210 quasars, allowing an investigation of the relationship between the Broad Line Region (BLR) and Narrow Line Region (NLR) emission properties. The [OIII] blueshift is correlated with CIV blueshift, even when the dependence of both quantities on quasar luminosity has been taken into account. A strong anti-correlation between the [OIII] equivalent width (EW) and CIV blueshift also exists. Furthermore, [OIII] is very weak, with EW<1A, in ~10 per cent of the sample, a factor of 10 higher compared to quasars at lower luminosities and redshifts. If the [OIII] emission originates in an extended NLR, the observations suggest that quasar-driven winds are capable of influencing the host-galaxy environment out to kilo-parsec scales. The mean kinetic power of the ionised gas outflows is then 10^44.7 erg s^-1, which is ~0.15 per cent of the bolometric luminosity of the quasar. These outflow efficiencies are broadly consistent with those invoked in current active galactic nuclei feedback models.

Quenching by gas compression and consumption

The objective of this work is to study how active galactic nuclei (AGN) influence star formation in host galaxies. We present a detailed investigation of the star-formation history and conditions of a z = 2.57 massive radio galaxy based on VLT/X-shooter and ALMA observations. The deep rest-frame ultraviolet spectrum contains photospheric absorption lines and wind features indicating the presence of OB-type stars. The most significantly detected photospheric features are used to characterize the recent star formation: neither instantaneous nor continuous star-formation history is consistent with the relative strength of the Si IIλ1485 and S Vλ1502 absorption. Rather, at least two bursts of star formation took place in the recent past, at 6+1-2 Myr and ≳20 Myr ago, respectively. We deduce a molecular H2 gas mass of (3.9 ± 1.0) × 1010 M⊙ based on ALMA observations of the [C I] 3P2−3P1 emission. The molecular gas mass is only 13% of its stellar mass. Combined with its high star-formation rate of (1020-170+190 M⊙ yr-1, this implies a high star-formation efficiency of (26 ± 8) Gyr−1 and a short depletion time of (38 ± 12) Myr. We attribute the efficient star formation to compressive gas motions in order to explain the modest velocity dispersions (⩽55 km s−1) of the photospheric lines and of the star-forming gas traced by [C I]. Because of the likely very young age of the radio source, our findings suggest that vigorous star formation consumes much of the gas and works in concert with the AGN to remove any residual molecular gas, and eventually quenching star formation in massive galaxies.

The mass-metallicity relation of high-z type-2 active galactic nuclei

The mass-metallicity relation (MZR) of type-2 active galactic nuclei (AGNs) at 1.2 &lt; z &lt; 4.0 is investigated by using high-z radio galaxies (HzRGs) and X-ray selected radio-quiet AGNs. We combine new rest-frame ultraviolet (UV) spectra of two radio-quiet type-2 AGNs obtained with FOCAS on the Subaru Telescope with existing rest-frame UV emission lines, i.e., C IVλ1549, He IIλ1640, and C IIIλ1909, of a sample of 16 HzRGs and 6 additional X-ray selected type-2 AGNs, whose host stellar masses have been estimated in literature. We divided our sample in three stellar mass bins and calculated averaged emission-line flux ratios of C IVλ1549/He IIλ1640 and C IIIλ1909/C IVλ1549. Comparing observed emission-line flux ratios with photoionization model predictions, we estimated narrow line region (NLR) metallicities for each mass bin. We found that there is a positive correlation between NLR metallicities and stellar masses of type-2 AGNs at z ~ 3. This is the first indication that AGN metallicities are related to their hosts, i.e., stellar mass. Since NLR metallicities and stellar masses follow a similar relation as the MZR in star-forming galaxies at similar redshifts, our results indicate that NLR metallicities are related to those of the host galaxies. This study highlights the importance of considering lower-mass X-ray selected AGNs in addition to radio galaxies to explore the metallicity properties of NLRs at high redshift.

Calibration and Limitations of the Mg ii Line-based Black Hole Masses

Abstract We present single-epoch black hole mass ( ) calibrations based on the rest-frame ultraviolet (UV) and optical measurements of Mg ii 2798 Å and Hβ 4861 Å lines and the active galactic nucleus (AGN) continuum, using a sample of 52 moderate-luminosity AGNs at z ∼ 0.4 and z ∼ 0.6 with high-quality Keck spectra. We combine this sample with a large number of luminous AGNs from the Sloan Digital Sky Survey to increase the dynamic range for a better comparison of UV and optical velocity and luminosity measurements. With respect to the reference based on the line dispersion of Hβ and continuum luminosity at 5100 Å, we calibrate the UV and optical mass estimators by determining the best-fit values of the coefficients in the mass equation. By investigating whether the UV estimators show a systematic trend with Eddington ratio, FWHM of Hβ, Fe ii strength, or UV/optical slope, we find no significant bias except for the slope. By fitting the systematic difference of Mg ii-based and Hβ-based masses with the L 3000/L 5100 ratio, we provide a correction term as a function of the spectral index as ΔC = 0.24 (1 + α λ ) + 0.17, which can be added to the Mg ii-based mass estimators if the spectral slope can be well determined. The derived UV mass estimators typically show &gt;∼0.2 dex intrinsic scatter with respect to the Hβ-based , suggesting that the UV-based mass has an additional uncertainty of ∼0.2 dex, even if high-quality rest-frame UV spectra are available.

The Strong Gravitationally Lensed Herschel Galaxy HLock01: Optical Spectroscopy Reveals a Close Galaxy Merger with Evidence of Inflowing Gas

Abstract The submillimeter galaxy (SMG) HERMES J105751.1+573027 (hereafter HLock01) at z = 2.9574 ± 0.0001 is one of the brightest gravitationally lensed sources discovered in the Herschel Multi-tiered Extragalactic Survey. Apart from the high flux densities in the far-infrared, it is also extremely bright in the rest-frame ultraviolet (UV), with a total apparent magnitude m UV ≃ 19.7 mag. We report here deep spectroscopic observations with the Gran Telescopio Canarias of the optically bright lensed images of HLock01. Our results suggest that HLock01 is a merger system composed of the Herschel-selected SMG and an optically bright Lyman break-like galaxy (LBG), separated by only 3.3 kpc in projection. While the SMG appears very massive (M * ≃ 5 × 1011 M ⊙), with a highly extinguished stellar component (A V ≃ 4.3 ), the LBG is a young, lower-mass (M * ≃ 1 × 1010 M ⊙), but still luminous ( ) satellite galaxy. Detailed analysis of the high signal-to-noise ratio (S/N) rest-frame UV spectrum of the LBG shows complex kinematics of the gas, exhibiting both blueshifted and redshifted absorption components. While the blueshifted component is associated with strong galactic outflows from the massive stars in the LBG, as is common in most star-forming galaxies, the redshifted component may be associated with gas inflow seen along a favorable sightline to the LBG. We also find evidence of an extended gas reservoir around HLock01 at an impact parameter of 110 kpc, through the detection of C ii λλ1334 absorption in the red wing of a bright Lyα emitter at z ≃ 3.327. The data presented here highlight the power of gravitational lensing in high S/N studies to probe deeply into the physics of high-z star-forming galaxies.

The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MegaSaura). II. Stacked Spectra

Abstract We stack the rest-frame ultraviolet spectra of N = 14 highly magnified gravitationally lensed galaxies at redshifts . The resulting new composite spans Å, with a peak signal-to-noise ratio (S/N) of 103 per spectral resolution element (∼100 km s−1). It is the highest S/N, highest spectral resolution composite spectrum of z ∼ 2–3 galaxies yet published. The composite reveals numerous weak nebular emission lines and stellar photospheric absorption lines that can serve as new physical diagnostics, particularly at high redshift with the James Webb Space Telescope (JWST). We report equivalent widths to aid in proposing for and interpreting JWST spectra. We examine the velocity profiles of strong absorption features in the composite, and in a matched composite of COS/HST galaxy spectra. We find remarkable similarity in the velocity profiles at and , suggesting that similar physical processes control the outflows across cosmic time. While the maximum outflow velocity depends strongly on ionization potential, the absorption-weighted mean velocity does not. As such, the bulk of the high-ionization absorption traces the low-ionization gas, with an additional blueshifted absorption tail extending to at least −2000 km s−1. We interpret this tail as arising from the stellar wind and photospheres of massive stars. Starburst99 models are able to replicate this high-velocity absorption tail. However, these theoretical models poorly reproduce several of the photospheric absorption features, indicating that improvements are needed to match observational constraints on the massive stellar content of star-forming galaxies at . We publicly release our composite spectra.