arXiv subjects

Mahan Mirza Khanlari

Publications and source records attributed to Mahan Mirza Khanlari.

5 recordsLinked to original sources

arXiv2026

Population III Host Candidates at $z\sim2$: Strong He II $\lambda1640$ and Absent UV Metal Lines in HETDEX Ly$α$ Emitters

Population III (Pop III) stars are expected to produce extremely hard ionizing spectra, yet direct evidence for their signature--strong narrow He II $\lambda1640$ emission with weak or absent metal lines--remains elusive. Although Pop III formation peaks at $z\gtrsim10$, models predict that nearly pristine gas pockets can survive to later times, making intermediate-redshift searches a probe of metal mixing across cosmic time. We search 109,545 high-confidence Ly$α$-emitting galaxies at $1.9<z<2.3$ in the Hobby--Eberly Telescope Dark Energy Experiment's database for systems with strong He II $\lambda1640$ and no detected UV metal lines, recovering eight candidates and a first-order, tentative comoving number density of $\sim30$ Gpc$^{-3}$. The eight-object stack yields a rest-frame He II equivalent width of $28.7\pm6.7$ Angstrom, He II/Ly$α=0.354\pm0.094$, and a resolution-corrected He II FWHM of $449\pm105$ km s$^{-1}$. We find no significant N V, C IV, or O III] emission; using the He II width to set the scale, we derive $3σ$ upper limits of N V/He II $<0.167$, C IV/He II $<0.128$, and O III]/He II $<0.140$. This combination of strong He II, elevated He II/Ly$α$, moderate line width, and weak metal lines is difficult to reproduce with metal-enriched stellar populations, AGN narrow-line regions, shocks, or classical Wolf--Rayet features. We interpret the sample as candidates for very metal-poor or Pop III-like ionizing sources at $z\sim2$. Definitive confirmation requires deeper rest-UV spectroscopy to measure He II and metal-line limits in individual objects, followed by rest-optical spectroscopy of H$β$, [O III] $\lambda4959,\lambda5007$, [O II] $\lambda3727$, and H$α$ to constrain gas-phase metallicity, ionization conditions, and AGN activity.

astro-ph.GA↗

arXiv2026

HETDEX Public Data Release 1: Source Catalog 2 and Data Cubes from ~90 sq deg of Integral-Field Optical Spectroscopy

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is a wide-field, integral-field spectroscopic survey designed to map the large-scale distribution of Lyman-alpha emitting galaxies (LAEs) at 1.88 < z < 3.52 and constrain dark energy at cosmic noon. Using the 10-m Hobby-Eberly Telescope and the Visible Integral-Field Replicable Unit (IFU) Spectrograph, HETDEX obtains >35,000 spectra per exposure over 3500-5500 Å at R~800 with ~1.8 arcsec image quality, enabling an untargeted census of emission-line galaxies across 540 sq deg. We present HETDEX Public Data Release 1 (PDR1), comprising 431,713 IFU observations covering 86.67 sq deg of noncontiguous sky in the Spring (13h, +51°) and Fall (1.5h, 0°) fields, along with legacy regions (COSMOS, GOODS-N, NEP, SA22). PDR1 includes the HETDEX Public Source Catalog 2 (HPSC2), an expanded and reprocessed version of Mentuch Cooper et al. (2023) incorporating four additional years of data, improved quality control, and new machine learning classifiers. HPSC2 contains 426,654 LAEs, 491,411 [O II] emitters, 19,457 low-z galaxies, 18,303 active galactic nuclei, and 150,608 stars, providing coordinates, redshifts or stellar velocities, and 1D spectra for each source. Because the data cubes use local sky subtraction optimized for faint emission-line detection, they are not suited for absolute surface-brightness measurements or very extended nearby galaxies. Appendix materials include the full detection catalog, the 1.6 million-candidate LAE sample, and raw detection databases. All products are publicly accessible through the HETDEX data portal (https://hetdex.org/data-results/), including access to a public JupyterLab. HPSC2 is also publicly available via Zenodo (DOI: 10.5281/zenodo.19581262).

astro-ph.GA↗

arXiv2025

The HETDEX Survey: Probing neutral hydrogen in the circumgalactic medium of ~88,000 Lyman Alpha Emitters

We explore the neutral hydrogen (H I) gas around 1.9 < z < 3.5 Lyman Alpha Emitters (LAEs) from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) using faint Ly$α$ absorption. This absorption is the result of H I in the halo of the LAE scattering Ly$α$ photons from the integrated light of background galaxies along the line of sight. We stack millions of spectra from regions around ~88,000 LAEs to focus on the physics of the gas at large radii. The extensive number of fiber spectra contributing to the stacks ensures significant signal-to-noise ratio (S/N) to detect the faint Ly$α$ absorption which would otherwise be buried within the noise. We detect absorption out to a projected ~350 kpc around an average LAE at z~2.5. We use these results to create an empirical radial $W_λ$(Ly$α$) profile around LAEs. Comparison with numerical simulations reveals a profile similar to the empirical one within this region. Compared to previous studies, the profile is similar but modestly higher. We also outline a simple physical picture motivated by the observed trends in the data. We plan to quantify this radial profile as a function of redshift, local density, and Ly$α$ luminosity to explore the relationship between LAE environments and H I distribution.

astro-ph.GA↗

arXiv2025

Using Lyman Alpha Absorption to Measure the Intensity and Variability of $z \sim 2.4$ Ultraviolet Background Light

We present measurements of $z \sim 2.4$ ultraviolet background light using Lya absorption from galaxies at $z \sim 2-3$ in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) database. Thanks to the wide area of this survey, we also measure the variability of this light across the sky. The data suggest an asymmetric geometry where integrated ultraviolet light from background galaxies is absorbed by \ion{H}{1} within the halo of a foreground galaxy, in a configuration similar to damped Lya systems. Using stacking analyses of over 400,000 HETDEX LAE spectra, we argue that this background absorption is detectable in our data. We also argue that the absorption signal becomes negative due to HETDEX's sky subtraction procedure. The amount that the absorption is over-subtracted is representative of the $z \sim 2.4$ UV contribution to the overall extragalactic background light (EBL) at Lya. Using this method, we determine an average intensity (in $νJ_ν$ units) of $12.9 \pm 3.7$ nW m$^{-2}$ sr$^{-1}$ at a median observed wavelength of 4134 angstroms, or a rest-frame UV background intensity of $508 \pm 145$ nW m$^{-2}$ sr$^{-1}$ at $z\sim2.4$. We find that this flux varies significantly depending on the density of galaxies in the field of observation. Our estimates are consistent with direct measurements of the overall EBL.

astro-ph.GA↗

arXiv2024

Absorption Troughs of Lyman Alpha Emitters in HETDEX

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is designed to detect and measure the redshifts of more than one million Ly$α$ emitting galaxies (LAEs) between $1.88 < z < 3.52$. In addition to its cosmological measurements, these data enable studies of Ly$α$ spectral 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 Ly$α$ profile for the $z \sim 2-3$ epoch and to understand their physical properties. We find clear absorption wings around Ly$α$ emission, which extend $\sim 2000$ km $\mathrm{s}^{-1}$ both redward and blueward of the central line. Using far-UV spectra of nearby ($0.002 < z < 0.182$) LAEs in the CLASSY treasury and optical/near-IR spectra of $2.8 < z < 6.7$ LAEs in the MUSE-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 Lyman-$α$ systems. Simple simulations of Ly$α$ radiative transfer can produce similar troughs due to absorption of light from background sources by HI gas surrounding the LAEs.

astro-ph.GA↗