skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: (Nearly) Model-independent Constraints on the Neutral Hydrogen Fraction in the Intergalactic Medium at z ∼ 5–7 Using Dark Pixel Fractions in Lyα and Lyβ Forests
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 atz> 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 ( x ¯ H I 10 3 ) or close to unity ( x ¯ H I 1 ). 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 x ¯ H I 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 Lyαand Lyβforests, 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 x ¯ H I ( z = 6.3 ) < 0.79 ± 0.04 (1σ), x ¯ H I ( z = 6.5 ) < 0.87 ± 0.03 (1σ), and x ¯ H I ( z = 6.7 ) < 0.94 0.09 + 0.06 (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.  more » « less
Award ID(s):
1908284
PAR ID:
10390899
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
942
Issue:
2
ISSN:
0004-637X
Format(s):
Medium: X Size: Article No. 59
Size(s):
Article No. 59
Sponsoring Org:
National Science Foundation
More Like this
  1. 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 ≤ log N H I < 20 that probe the interface between galaxies and the intergalactic medium (IGM). We find that gas with 14.6 log N H I < 20 at 2.2 ≲z≲ 3.6 can be metal-rich (−1.6 ≲ [X/H] ≲ − 0.2) as seen in damped Lyαabsorbers (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 16 < log N H I < 20 absorbers, the frequency of pristine absorbers is about 1%–10%, while for 14.6 log N H I 16 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 14.6 log N H I < 20 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 withNHi, 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 14.6 log N H I < 19 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] withNHi, 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. 
    more » « less
  2. Abstract We present a detection of 21 cm emission from large-scale structure (LSS) between redshift 0.78 and 1.43 made with the Canadian Hydrogen Intensity Mapping Experiment. Radio observations acquired over 102 nights are used to construct maps that are foreground filtered and stacked on the angular and spectral locations of luminous red galaxies (LRGs), emission-line galaxies (ELGs), and quasars (QSOs) from the eBOSS clustering catalogs. We find decisive evidence for a detection when stacking on all three tracers of LSS, with the logarithm of the Bayes factor equal to 18.9 (LRG), 10.8 (ELG), and 56.3 (QSO). An alternative frequentist interpretation, based on the likelihood ratio test, yields a detection significance of 7.1σ(LRG), 5.7σ(ELG), and 11.1σ(QSO). These are the first 21 cm intensity mapping measurements made with an interferometer. We constrain the effective clustering amplitude of neutral hydrogen (Hi), defined as H I 10 3 Ω H I b H I + f μ 2 , where ΩHiis the cosmic abundance of Hi,bHiis the linear bias of Hi, and 〈fμ2〉 = 0.552 encodes the effect of redshift-space distortions at linear order. We find H I = 1.51 0.97 + 3.60 for LRGs (z= 0.84), H I = 6.76 3.79 + 9.04 for ELGs (z= 0.96), and H I = 1.68 0.67 + 1.10 for QSOs (z= 1.20), with constraints limited by modeling uncertainties at nonlinear scales. We are also sensitive to bias in the spectroscopic redshifts of each tracer, and we find a nonzero bias Δv= − 66 ± 20 km s−1for the QSOs. We split the QSO catalog into three redshift bins and have a decisive detection in each, with the upper bin atz= 1.30 producing the highest-redshift 21 cm intensity mapping measurement thus far. 
    more » « less
  3. Abstract We measure the CO-to-H2conversion factor (αCO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofαCOfor CO (2–1) and (1–0), respectively. The mean values forαCO (2–1)andαCO (1–0)are 9.3 5.4 + 4.6 and 4.2 2.0 + 1.9 M pc 2 ( K km s 1 ) 1 , respectively. The CO-intensity-weighted mean is 5.69 forαCO (2–1)and 3.33 forαCO (1–0). We examine howαCOscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ( U ¯ ). Among them, U ¯ , ΣSFR, and the integrated CO intensity (WCO) have the strongest anticorrelation with spatially resolvedαCO. We provide linear regression results toαCOfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenαCOandWCO, metallicity, U ¯ , and ΣSFR. We also find thatαCOin each galaxy decreases with the stellar mass surface density (Σ) in high-surface-density regions (Σ≥ 100Mpc−2), following the power-law relations α CO ( 2 1 ) Σ 0.5 and α CO ( 1 0 ) Σ 0.2 . The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inαCOwith increasing Σas a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inαCO. The decrease inαCOat high Σis important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors. 
    more » « less
  4. Abstract We investigate the effectiveness of the statistical radio frequency interference (RFI) mitigation technique spectral kurtosis ( SK ^ ) in the face of simulated realistic RFI signals. SK ^ estimates the kurtosis of a collection ofMpower values in a single channel and provides a detection metric that is able to discern between human-made RFI and incoherent astronomical signals of interest. We test the ability of SK ^ to flag signals with various representative modulation types, data rates, duty cycles, and carrier frequencies. We flag with various accumulation lengthsMand implement multiscale SK ^ , which combines information from adjacent time-frequency bins to mitigate weaknesses in single-scale SK ^ . We find that signals with significant sidelobe emission from high data rates are harder to flag, as well as signals with a 50% effective duty cycle and weak signal-to-noise ratios. Multiscale SK ^ with at least one extra channel can detect both the center channel and sideband interference, flagging greater than 90% as long as the bin channel width is wider in frequency than the RFI. 
    more » « less
  5. Abstract We study a magnitude-limited sample of 36 broad-lined type Ic supernovae (SNe Ic-BL) from the Zwicky Transient Facility Bright Transient Survey (detected between 2018 March and 2021 August), which is the largest systematic study of SNe Ic-BL done in literature thus far. We present the light curves (LCs) for each of the SNe and analyze the shape of the LCs to derive empirical parameters, along with the explosion epochs for every event. The sample has an average absolute peak magnitude in therband of M ¯ r , max = 18.51 ± 0.15 mag. Using spectra obtained around peak light, we compute expansion velocities from the Feii5169 Å line for each event with high enough signal-to-noise ratio spectra, and find an average value of v ph ¯ = 16 , 100 ± 1100 km s−1. We also compute bolometric LCs, study the blackbody temperature and radii evolution over time, and derive the explosion properties of the SNe. The explosion properties of the sample have average values of M ¯ Ni = 0.37 0.06 + 0.08 M , M ¯ ej = 2.45 0.41 + 0.47 M , and E ¯ K = ( 4.02 1.00 + 1.37 ) × 10 51 erg. Thirteen events have radio observations from the Very Large Array, with eight detections and five non-detections. We find that the populations that have radio detections and radio non-detections are indistinct from one another with respect to their optically inferred explosion properties, and there are no statistically significant correlations present between the events’ radio luminosities and optically inferred explosion properties. This provides evidence that the explosion properties derived from optical data alone cannot give inferences about the radio properties of SNe Ic-BL and likely their relativistic jet formation mechanisms. 
    more » « less