Search for: All records

The recent detection of a stochastic gravitational wave background (SGWB) at nanohertz frequencies by pulsar timing arrays (PTAs) has sparked a flurry of interest. Beyond the standard interpretation that the progenitor is a network of supermassive black hole binaries, many exotic models have also been proposed, some of which can potentially offer a better fit to the data. We explore how the various connections between gravitational waves (GWs) and cosmic microwave background (CMB) spectral distortions (SDs) can be leveraged to help determine whether an SGWB was generated primordially or astrophysically. To this end, we present updated k-space window functions that can be used for distortion parameter estimation on enhancements to the primordial scalar power spectrum. These same enhancements can also source GWs directly at second order in perturbation theory, so-called scalar-induced GWs (SIGWs), and indirectly through the formation of primordial black holes (PBHs). We perform a mapping of scalar power spectrum constraints into limits on the GW parameter space of SIGWs for δ-function features. We highlight that broader features in the scalar spectrum can explain the PTA results while simultaneously producing an SD within reach of future experiments. We additionally update PBH constraints from μ- and y-type SDs. Refined treatments of the distortion window functions widen existing SD constraints, and we find that a future CMB spectrometer could play a pivotal role in unravelling the origin of GWs imprinted at or below CMB anisotropy scales.

 

The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is designed to detect and measure the redshifts of more than 1 million Lyαemitting galaxies (LAEs) 1.88 <z< 3.52. In addition to its cosmological measurements, these data enable studies of Lyαspectral profiles and the underlying radiative transfer. Using the roughly half a million LAEs in the HETDEX Data Release 3, we stack various subsets to obtain the typical Lyαprofile for thez∼ 2–3 epoch and to understand their physical properties. We find clear absorption wings around Lyαemission, which extend ∼2000 km s⁻¹both redward and blueward of the central line. Using far-UV spectra of nearby (0.002 <z< 0.182) LAEs in the COS Legacy Archive Spectroscopic Survey treasury and optical/near-IR spectra of 2.8 <z< 6.7 LAEs in the Multi Unit Spectroscopic-Wide survey, we observe absorption profiles in both redshift regimes. Dividing the sample by volume density shows that the troughs increase in higher-density regions. This trend suggests that the depth of the absorption is dependent on the local density of objects near the LAE, a geometry that is similar to damped Lyαsystems. Simple simulations of Lyαradiative transfer can produce similar troughs due to absorption of light from background sources by Higas surrounding the LAEs.

 

We present analysis using a citizen science campaign to improve the cosmological measures from the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the Hubble expansion rate,H(z), and angular diameter distance,D_A(z), atz= 2.4, each to percent-level accuracy. This accuracy is determined primarily from the total number of detected Lyαemitters (LAEs), the false positive rate due to noise, and the contamination due to [Oii] emitting galaxies. This paper presents the citizen science project, Dark Energy Explorers (https://www.zooniverse.org/projects/erinmc/dark-energy-explorers), with the goal of increasing the number of LAEs and decreasing the number of false positives due to noise and the [Oii] galaxies. Initial analysis shows that citizen science is an efficient and effective tool for classification most accurately done by the human eye, especially in combination with unsupervised machine learning. Three aspects from the citizen science campaign that have the most impact are (1) identifying individual problems with detections, (2) providing a clean sample with 100% visual identification above a signal-to-noise cut, and (3) providing labels for machine-learning efforts. Since the end of 2022, Dark Energy Explorers has collected over three and a half million classifications by 11,000 volunteers in over 85 different countries around the world. By incorporating the results of the Dark Energy Explorers, we expect to improve the accuracy on theD_A(z) andH(z) parameters atz= 2.″4 by 10%–30%. While the primary goal is to improve on HETDEX, Dark Energy Explorers has already proven to be a uniquely powerful tool for science advancement and increasing accessibility to science worldwide.

 

Abstract The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is an untargeted spectroscopic survey that aims to measure the expansion rate of the universe at z ∼ 2.4 to 1% precision for both H ( z ) and D A ( z ). HETDEX is in the process of mapping in excess of one million Ly α emitting (LAE) galaxies and a similar number of lower- z galaxies as a tracer of the large-scale structure. The success of the measurement is predicated on the post-observation separation of galaxies with Ly α emission from the lower- z interloping galaxies, primarily [O ii ], with low contamination and high recovery rates. The Emission Line eXplorer (ELiXer) is the principal classification tool for HETDEX, providing a tunable balance between contamination and completeness as dictated by science needs. By combining multiple selection criteria, ELiXer improves upon the 20 Å rest-frame equivalent width cut commonly used to distinguish LAEs from lower- z [O ii ] emitting galaxies. Despite a spectral resolving power, R ∼ 800, that cannot resolve the [O ii ] doublet, we demonstrate the ability to distinguish LAEs from foreground galaxies with 98.1% accuracy. We estimate a contamination rate of Ly α by [O ii ] of 1.2% and a Ly α recovery rate of 99.1% using the default ELiXer configuration. These rates meet the HETDEX science requirements. 

We describe the ensemble properties of the 1.9 <z< 3.5 Lyman alpha emitters (LAEs) found in the HETDEX survey’s first public data release, HETDEX Public Source Catalog 1. Stacking the low-resolution (R∼ 800) spectra greatly increases the signal-to-noise ratio (S/N), revealing spectral features otherwise hidden by noise, and we show that the stacked spectrum is representative of an average member of the set. The flux-limited, LyαS/N restricted stack of 50,000 HETDEX LAEs shows the ensemble biweightaveragez∼ 2.6 LAE to be a blue (UV continuum slope ∼ −2.4 andE(B – V)< 0.1), moderately bright (M_UV∼ −19.7) star-forming galaxy with strong Lyαemission (logL_Lyα∼ 42.8 andW_λ(Lyα) ∼ 114 Å), and potentially significant leakage of ionizing radiation. The rest-frame UV light is dominated by a young, metal-poor stellar population with an average age of 5–15 Myr and metallicity of 0.2–0.3Z_⊙.

 

We present the Lyαemission line luminosity function (LF) of the active galactic nuclei (AGN) in the first release of the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX) AGN catalog. The AGN are selected either by emission line pairs characteristic of AGN or by a single broad emission line, free of any photometric preselections (magnitude/color/morphology). The sample consists of 2346 AGN spanning 1.88 <z< 3.53, covering an effective area of 30.61 deg². Approximately 2.6% of the HETDEX AGN are not detected at >5σconfidence atr∼ 26 in the deepestr-band images we have searched. The Lyαline luminosity ranges from ∼10^42.3to 10^45.9erg s⁻¹. Our LyαLF shows a turnover luminosity with opposite slopes on the bright end and the faint end: The space density is highest at$L_{\text{Ly}\mathit{\text{α}}}^{\ast }={10}^{43.4}$erg s⁻¹. We explore the evolution of the AGN LF over a broader redshift range (0.8 <z< 3); constructing the rest-frame ultraviolet (UV) LF with the 1450 Å monochromatic luminosity of the power-law component of the continuum (M₁₄₅₀) fromM₁₄₅₀∼ −18 to −27.5. We divide the sample into three redshift bins (z∼ 1.5, 2.1, and 2.6). In all three redshift bins, our UV LFs indicate that the space density of AGN is highest at the turnover luminosity$M_{1450}^{*}$with opposite slopes on the bright end and the faint end. TheM₁₄₅₀LFs in the three redshift bins can be well fit with a luminosity evolution and density evolution model: the turnover luminosity ($M_{1450}^{*}$) increases, and the turnover density (Φ*) decreases with increasing redshift.

 

Abstract We present the first publicly released catalog of sources obtained from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). HETDEX is an integral field spectroscopic survey designed to measure the Hubble expansion parameter and angular diameter distance at 1.88 < z < 3.52 by using the spatial distribution of more than a million Ly α -emitting galaxies over a total target area of 540 deg 2 . The catalog comes from contiguous fiber spectra coverage of 25 deg 2 of sky from 2017 January through 2020 June, where object detection is performed through two complementary detection methods: one designed to search for line emission and the other a search for continuum emission. The HETDEX public release catalog is dominated by emission-line galaxies and includes 51,863 Ly α -emitting galaxy (LAE) identifications and 123,891 [O ii ]-emitting galaxies at z < 0.5. Also included in the catalog are 37,916 stars, 5274 low-redshift ( z < 0.5) galaxies without emission lines, and 4976 active galactic nuclei. The catalog provides sky coordinates, redshifts, line identifications, classification information, line fluxes, [O ii ] and Ly α line luminosities where applicable, and spectra for all identified sources processed by the HETDEX detection pipeline. Extensive testing demonstrates that HETDEX redshifts agree to within Δ z < 0.02, 96.1% of the time to those in external spectroscopic catalogs. We measure the photometric counterpart fraction in deep ancillary Hyper Suprime-Cam imaging and find that only 55.5% of the LAE sample has an r -band continuum counterpart down to a limiting magnitude of r ∼ 26.2 mag (AB) indicating that an LAE search of similar sensitivity to HETDEX with photometric preselection would miss nearly half of the HETDEX LAE catalog sample. Data access and details about the catalog can be found online at http://hetdex.org/ . A copy of the catalogs presented in this work (Version 3.2) is available to download at Zenodo doi: 10.5281/zenodo.7448504 . 

We present the first active galactic nuclei (AGN) catalog of the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX) observed between 2017 January and 2020 June. HETDEX is an ongoing spectroscopic survey (3500–5500 Å) with no target preselection based on magnitudes, colors or morphologies, enabling us to select AGN based solely on their spectral features. Both luminous quasars and low-luminosity Seyferts are found in our catalog. AGN candidates are selected with at least two significant AGN emission lines, such as the Lyαand Civλ1549 line pair, or with a single broad emission line with FWHM > 1000 km s⁻¹. Each source is further confirmed by visual inspections. This catalog contains 5322 AGN, covering an effective sky coverage of 30.61 deg². A total of 3733 of these AGN have secure redshifts, and we provide redshift estimates for the remaining 1589 single broad-line AGN with no crossmatched spectral redshifts from the Sloan Digital Sky Survey Data Release 14 of QSOs. The redshift range of the AGN catalog is 0.25 <z< 4.32, with a median ofz= 2.1. The bolometric luminosity range is 10⁹–10¹⁴L_☉with a median of 10¹²L_☉. The medianr-band magnitude of our AGN catalog is 21.6 mag, with 34% havingr> 22.5, and 2.6% reaching the detection limit atr∼ 26 mag of the deepest imaging surveys we searched. We also provide a composite spectrum of the AGN sample covering 700–4400 Å.