We report the discovery of a candidate dual QSO at
Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher.
Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?
Some links on this page may take you to non-federal websites. Their policies may differ from this site.
-
Abstract z = 1.889, a redshift that is in the era known as “cosmic noon” where most of the universe’s black hole and stellar mass growth occurred. The source was identified in Hubble Space Telescope WFC3/IR images of a dust-reddened QSO that showed two closely separated point sources at a projected distance of 0.″26, or 2.2 kpc. This red QSO was targeted for imaging to explore whether red QSOs are hosted by merging galaxies. We subsequently obtained a spatially resolved Space Telescope Imaging Spectrograph spectrum of the system, covering the visible spectral range, and verifying the presence of two distinct QSO components. We also obtained high-resolution radio continuum observations with the Very Long Baseline Array at 1.4 GHz (21 cmL band) and found two sources coincident with the optical positions. The sources have similar black hole masses, bolometric luminosities, and radio-loudness parameters. However, their colors and reddenings differ significantly. The redder QSO has a higher Eddington ratio, consistent with previous findings. We consider the possibility of gravitational lensing and find that it would require extreme and unlikely conditions. If confirmed as a bona fide dual QSO, this system would link dust reddening to galaxy and supermassive black hole mergers, opening up a new population in which to search for samples of dual active galactic nuclei. -
Abstract This study addresses how the incidence rate of strong O
vi absorbers in a galaxy’s circumgalactic medium (CGM) depends on galaxy mass and, independently, on the amount of star formation in the galaxy. We use Hubble Space Telescope/Cosmic Origins Spectrograph absorption spectroscopy of quasars to measure Ovi absorption within 400 projected kpc and 300 km s−1of 52 galaxies withM *∼ 3 × 1010M ⊙. The galaxies have redshifts 0.12 <z < 0.6, stellar masses 1010.1M ⊙<M *< 1010.9M ⊙, and spectroscopic classifications as star-forming or passive. We compare the incidence rates of high column density Ovi absorption (N OVI ≥ 1014.3cm−2) near star-forming and passive galaxies in two narrow ranges of stellar mass and, separately, in a matched range of halo mass. In all three mass ranges, the Ovi covering fraction within 150 kpc is higher around star-forming galaxies than around passive galaxies with greater than 3σ -equivalent statistical significance. On average, the CGM of star-forming galaxies withM *∼ 3 × 1010M ⊙contains more Ovi than the CGM of passive galaxies with the same mass. This difference is evidence for a CGM transformation that happens together with galaxy quenching and is not driven primarily by halo mass. -
Abstract We combine data sets from the CGM2and CASBaH surveys to model a transition point,
R cross, between circumgalactic and intergalactic media (CGM and IGM, respectively). In total, our data consist of 7244 galaxies atz < 0.5 with precisely measured spectroscopic redshifts, all having impact parameters of 0.01–20 comoving Mpc from 28 QSO sightlines with high-resolution UV spectra that cover Hi Lyα . Our best-fitting model is a two-component model that combines a 3D absorber–galaxy cross-correlation function with a simple Gaussian profile at inner radii to represent the CGM. By design, this model gives rise to a determination ofR crossas a function of galaxy stellar mass, which can be interpreted as the boundary between the CGM and IGM. For galaxies with 108≤M ⋆/M ⊙≤ 1010.5, we find thatR cross(M ⋆) ≈ 2.0 ± 0.6R vir. Additionally, we find excellent agreement betweenR cross(M ⋆) and the theoretically determined splashback radius for galaxies in this mass range. Overall, our results favor models of galaxy evolution atz < 0.5 that distributeT ≈ 104K gas to distances beyond the virial radius. -
Abstract The circumgalactic medium (CGM) plays a vital role in the formation and evolution of galaxies, acting as a lifeline between galaxies and the surrounding intergalactic medium. In this study, we leverage a unique sample of quasar pairs to investigate the properties of the CGM with absorption line tomography. We present a new sample of medium-resolution Keck/ESI, Magellan/MagE, and VLT/XSHOOTER spectra of 29 quasar pairs at redshift 2 <
z < 3. We supplement the sample with additional spectra of 32 pairs from the literature, creating a catalog of 61 quasar pairs with angular separations between 1.″7 and 132.″9 and projected physical separations (r ⊥) between 14 kpc and 887 kpc. We construct a catalog of 906 metal-line absorption doublets of Civ (λλ 1548, 1550) with equivalent widths ranging from 6 m Å ≤W r ,1550≤ 2053 m Å. The best-fit linear model to the log-space equivalent width frequency distribution ( ) of the sample yields coefficients ofm = −1.44 ± 0.16 andb = −0.43 ± 0.16. To constrain the projected extent of Civ , we calculate the transverse autocorrelation function. The flattening of the autocorrelation function at lowr ⊥provides a lower limit for the coherence length of the metal enriched CGM—on the order of 200h −1comoving kpc. This physical size constraint allows us to refine our understanding of the metals in the CGM, where the extent of Civ in the CGM depends on gas flows, feedback, timescale of metal injection and mixing, and the mass of the host galaxies. -
Abstract We use medium-resolution Keck/Echellette Spectrograph and Imager spectroscopy of bright quasars to study cool gas traced by Ca
ii λλ 3934, 3969 and Nai λλ 5891, 5897 absorption in the interstellar/circumgalactic media of 21 foreground star-forming galaxies at redshifts 0.03 <z < 0.20 with stellar masses 7.4 ≤ logM */M ⊙≤ 10.6. The quasar–galaxy pairs were drawn from a unique sample of Sloan Digital Sky Survey quasar spectra with intervening nebular emission, and thus have exceptionally close impact parameters (R ⊥< 13 kpc). The strength of this line emission implies that the galaxies’ star formation rates (SFRs) span a broad range, with several lying well above the star-forming sequence. We use Voigt profile modeling to derive column densities and component velocities for each absorber, finding that column densitiesN (Caii ) > 1012.5cm−2(N (Nai ) > 1012.0cm−2) occur with an incidencef C(Caii ) = 0.63+0.10−0.11(f C(Nai ) = 0.57+0.10−0.11). We find no evidence for a dependence off Cor the rest-frame equivalent widthsW r (Caii K) orW r (Nai 5891) onR ⊥orM *. Instead,W r (Caii K) is correlated with local SFR at >3σ significance, suggesting that Caii traces star formation-driven outflows. While most of the absorbers have velocities within ±50 km s−1of the host redshift, their velocity widths (characterized by Δv 90) are universally 30–177 km s−1larger than that implied by tilted-ring modeling of the velocities of interstellar material. These kinematics must trace galactic fountain flows and demonstrate that they persist atR ⊥> 5 kpc. Finally, we assess the relationship between dust reddening andW r (Caii K) (W r (Nai 5891)), finding that 33% (24%) of the absorbers are inconsistent with the best-fit Milky WayE (B −V)-W r relations at >3σ significance. -
Abstract We present the KODIAQ-Z survey aimed to characterize the cool, photoionized gas at 2.2 ≲
z ≲ 3.6 in 202 Hi -selected absorbers with 14.6 ≤ < 20 that probe the interface between galaxies and the intergalactic medium (IGM). We find that gas with at 2.2 ≲z ≲ 3.6 can be metal-rich (−1.6 ≲ [X/H] ≲ − 0.2) as seen in damped Lyα absorbers (DLAs); it can also be very metal-poor ([X/H] < − 2.4) or even pristine ([X/H] < − 3.8), which is not observed in DLAs but is common in the IGM. For absorbers, the frequency of pristine absorbers is about 1%–10%, while for absorbers it is 10%–20%, similar to the diffuse IGM. Supersolar gas is extremely rare (<1%) at these redshifts. The factor of several thousand spread from the lowest to highest metallicities and large metallicity variations (a factor of a few to >100) between absorbers separated by less than Δv < 500 km s−1imply that the metals are poorly mixed in gas. We show that these photoionized absorbers contribute to about 14% of the cosmic baryons and 45% of the cosmic metals at 2.2 ≲z ≲ 3.6. We find that the mean metallicity increases withN Hi , consistent with what is found inz < 1 gas. The metallicity of gas in this column density regime has increased by a factor ∼8 from 2.2 ≲z ≲ 3.6 toz < 1, but the contribution of the absorbers to the total metal budget of the universe atz < 1 is a quarter of that at 2.2 ≲z ≲ 3.6. We show that FOGGIE cosmological zoom-in simulations have a similar evolution of [X/H] withN Hi , which is not observed in lower-resolution simulations. In these simulations, very metal-poor absorbers with [X/H] < − 2.4 atz ∼ 2–3 are tracers of inflows, while higher-metallicity absorbers are a mixture of inflows and outflows. -
Abstract The bimodal absorption system imaging campaign (BASIC) aims to characterize the galaxy environments of a sample of 36 H
i -selected partial Lyman limit systems (pLLSs) and Lyman limit systems (LLSs) in 23 QSO fields atz ≲ 1. These pLLSs/LLSs provide a unique sample of absorbers with unbiased and well-constrained metallicities, allowing us to explore the origins of metal-rich and low-metallicity circumgalactic medium (CGM) atz < 1. Here we present Keck/KCWI and Very Large Telescope/MUSE observations of 11 of these QSO fields (19 pLLSs) that we combine with Hubble Space Telescope/Advanced Camera for Surveys imaging to identify and characterize the absorber-associated galaxies at 0.16 ≲z ≲ 0.84. We find 23 unique absorber-associated galaxies, with an average of one associated galaxy per absorber. For seven absorbers, all with <10% solar metallicities, we find no associated galaxies with withinρ /R virand ∣Δv ∣/v esc≤ 1.5 with respect to the absorber. We do not find any strong correlations between the metallicities or Hi column densities of the gas and most of the galaxy properties, except for the stellar mass of the galaxies: the low-metallicity ([X/H] ≤ −1.4) systems have a probability of for having a host galaxy with withinρ /R vir≤ 1.5, while the higher metallicity absorbers have a probability of . This implies metal-enriched pLLSs/LLSs atz < 1 are typically associated with the CGM of galaxies with , whereas low-metallicity pLLSs/LLSs are found in more diverse locations, with one population arising in the CGM of galaxies and another more broadly distributed in overdense regions of the universe. Using absorbers not associated with galaxies, we estimate the unweighted geometric mean metallicity of the intergalactic medium to be [X/H] ≲ −2.1 atz < 1, which is lower than previously estimated. -
ABSTRACT Quasar absorption systems encode a wealth of information about the abundances, ionization structure, and physical conditions in intergalactic and circumgalactic media. Simple (often single-phase) photoionization models are frequently used to decode such data. Using five discrete absorbers from the COS Absorption Survey of Baryon Harbors (CASBaH) that exhibit a wide range of detected ions (e.g. Mg ii, S ii – S vi, O ii – O vi, Ne viii), we show several examples where single-phase ionization models cannot reproduce the full set of measured column densities. To explore models that can self-consistently explain the measurements and kinematic alignment of disparate ions, we develop a Bayesian multiphase ionization modelling framework that characterizes discrete phases by their unique physical conditions and also investigates variations in the shape of the UV flux field, metallicity, and relative abundances. Our models require at least two (but favour three) distinct ionization phases ranging from T ≈ 104 K photoionized gas to warm-hot phases at T ≲ 105.8 K. For some ions, an apparently single absorption ‘component' includes contributions from more than one phase, and up to 30 per cent of the H i is not from the lowest ionization phase. If we assume that all of the phases are photoionized, we cannot find solutions in thermal pressure equilibrium. By introducing hotter, collisionally ionized phases, however, we can achieve balanced pressures. The best models indicate moderate metallicities, often with subsolar N/α, and, in two cases, ionizing flux fields that are softer and brighter than the fiducial Haardt & Madau UV background model.more » « less
-
Abstract We combine 126 new galaxy-O
vi absorber pairs from the CGM2survey with 123 pairs drawn from the literature to examine the simultaneous dependence of the column density of Ovi absorbers (N O VI) on galaxy stellar mass, star-formation rate, and impact parameter. The combined sample consists of 249 galaxy-Ovi absorber pairs coveringz = 0–0.6, with host galaxy stellar massesM *= 107.8–1011.2M ⊙and galaxy-absorber impact parametersR ⊥= 0–400 proper kiloparsecs. In this work, we focus on the variation ofN O VIwith galaxy mass and impact parameter among the star-forming galaxies in the sample. We find that the averageN O VIwithin one virial radius of a star-forming galaxy is greatest for star-forming galaxies withM *= 109.2–1010M ⊙. Star-forming galaxies withM *between 108and 1011.2M ⊙can explain most Ovi systems with column densities greater than 1013.5cm−2. Sixty percent of the Ovi mass associated with a star-forming galaxy is found within one virial radius, and 35% is found between one and two virial radii. In general, we find that some departure from hydrostatic equilibrium in the CGM is necessary to reproduce the observed Ovi amount, galaxy mass dependence, and extent. Our measurements serve as a test set for CGM models over a broad range of host galaxy masses.