We present Keck Planet Imager and Characterizer (KPIC) high-resolution (
Sub-Neptunes are common among the discovered exoplanets. However, lack of knowledge on the state of matter in
- NSF-PAR ID:
- 10145528
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 117
- Issue:
- 18
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- p. 9747-9754
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract R ∼35,000)K -band thermal emission spectroscopy of the ultrahot Jupiter WASP-33b. The use of KPIC’s single-mode fibers greatly improves both blaze and line-spread stabilities relative to slit spectrographs, enhancing the cross-correlation detection strength. We retrieve the dayside emission spectrum with a nested-sampling pipeline, which fits for orbital parameters, the atmospheric pressure–temperature profile, and the molecular abundances. We strongly detect the thermally inverted dayside and measure mass-mixing ratios for CO ( ), H2O ( ), and OH ( ), suggesting near-complete dayside photodissociation of H2O. The retrieved abundances suggest a carbon- and possibly metal-enriched atmosphere, with a gas-phase C/O ratio of , consistent with the accretion of high-metallicity gas near the CO2snow line and post-disk migration or with accretion between the soot and H2O snow lines. We also find tentative evidence for12CO/13CO ∼ 50, consistent with values expected in protoplanetary disks, as well as tentative evidence for a metal-enriched atmosphere (2–15 × solar). These observations demonstrate KPIC’s ability to characterize close-in planets and the utility of KPIC’s improved instrumental stability for cross-correlation techniques. -
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 We present new estimates on the fraction of heavily X-ray-obscured, Compton-thick (CT) active galactic nuclei (AGNs) out to a redshift of
z ≤ 0.8. From a sample of 540 AGNs selected by mid-infrared (MIR) properties in observed X-ray survey fields, we forward model the observed-to-intrinsic X-ray luminosity ratio ( ) with a Markov Chain Monte Carlo simulation to estimate the total fraction of CT AGNs (f CT), many of which are missed in typical X-ray observations. We create modelN Hdistributions and convert these to using a set of X-ray spectral models. We probe the posterior distribution of our models to infer the population of X-ray-nondetected sources. From our simulation we estimate a CT fraction off CT= . We perform an X-ray stacking analysis for sources in Chandra X-ray Observatory fields and find that the expected soft (0.5–2 keV) and hard (2–7 keV) observed fluxes drawn from our model to be within 0.48 and 0.12 dex of our stacked fluxes, respectively. Our results suggests at least 50% of all MIR-selected AGNs, possibly more, are CT (N H≳ 1024cm−2), which is in excellent agreement with other recent work using independent methods. This work indicates that the total number of AGNs is higher than can be identified using X-ray observations alone, highlighting the importance of a multiwavelength approach. A highf CTalso has implications for black hole (BH) accretion physics and supports models of BH and galaxy coevolution that include periods of heavy obscuration. -
Abstract We present a Keck/MOSFIRE rest-optical composite spectrum of 16 typical gravitationally lensed star-forming dwarf galaxies at 1.7 ≲
z ≲ 2.6 (z mean= 2.30), all chosen independent of emission-line strength. These galaxies have a median stellar mass of and a median star formation rate of . We measure the faint electron-temperature-sensitive [Oiii ]λ 4363 emission line at 2.5σ (4.1σ ) significance when considering a bootstrapped (statistical-only) uncertainty spectrum. This yields a direct-method oxygen abundance of ( ). We investigate the applicability at highz of locally calibrated oxygen-based strong-line metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strong-line ratio. At fixedM *, our composite is well represented by thez ∼ 2.3 direct-method stellar mass—gas-phase metallicity relation (MZR) of Sanders et al. When comparing to predicted MZRs from the IllustrisTNG and FIRE simulations, having recalculated our stellar masses with more realistic nonparametric star formation histories , we find excellent agreement with the FIRE MZR. Our composite is consistent with no metallicity evolution, at fixedM *and SFR, of the locally defined fundamental metallicity relation. We measure the doublet ratio [Oii ]λ 3729/[Oii ]λ 3726 = 1.56 ± 0.32 (1.51 ± 0.12) and a corresponding electron density of ( ) when considering the bootstrapped (statistical-only) error spectrum. This result suggests that lower-mass galaxies have lower densities than higher-mass galaxies atz ∼ 2. -
Abstract Cosmic reionization was the last major phase transition of hydrogen from neutral to highly ionized in the intergalactic medium (IGM). Current observations show that the IGM is significantly neutral at
z > 7 and largely ionized byz ∼ 5.5. However, most methods to measure the IGM neutral fraction are highly model dependent and are limited to when the volume-averaged neutral fraction of the IGM is either relatively low ( ) or close to unity ( ). In particular, the neutral fraction evolution of the IGM at the critical redshift range ofz = 6–7 is poorly constrained. We present new constraints on atz ∼ 5.1–6.8 by analyzing deep optical spectra of 53 quasars at 5.73 <z < 7.09. We derive model-independent upper limits on the neutral hydrogen fraction based on the fraction of “dark” pixels identified in the Lyα and Lyβ forests, without any assumptions on the IGM model or the intrinsic shape of the quasar continuum. They are the first model-independent constraints on the IGM neutral hydrogen fraction atz ∼ 6.2–6.8 using quasar absorption measurements. Our results give upper limits of (1σ ), (1σ ), and (1σ ). The dark pixel fractions atz > 6.1 are consistent with the redshift evolution of the neutral fraction of the IGM derived from Planck 2018.