Browsing by Author "Hu, W."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- ItemA lack of Lyman α emitters within 5 Mpc of a luminous quasar in an overdensity at z=6.9: Potential evidence of negative quasar feedback at protocluster scales(2024) Lambert, Trystan S.; Assef, R. J.; Mazzucchelli, C.; Banados, E.; Aravena, M.; Barrientos, F.; Gonzalez-Lopez, J.; Hu, W.; Infante, L.; Malhotra, S.; Moya-Sierralta, C.; Rhoads, J.; Valdes, F.; Wang, J.; Wold, I. G. B.; Zheng, Z.High-redshift quasars are thought to live in the densest regions of space, which should be made evident by an overdensity of galaxies around them. However, campaigns to identify these overdensities by searching for Lyman-break galaxies (LBGs) and Lyman alpha emitters (LAEs) have had mixed results. These may be explained by either the small field of view of some of the experiments, the broad redshift ranges targeted by LBG searches, and the inherently high uncertainty of quasar redshifts estimated from ultraviolet emission lines, which makes it difficult to place the Ly-alpha emission line within a narrowband filter. Here, we present a 3 square degree search (similar to 1000 pMpc(2)) for LAEs around the z = 6.9 quasar VIK J2348-3054 using the Dark Energy CAMera (DECam) housed on the 4m Blanco telescope, finding 38 LAEs. The systemic redshift of VIK J2348-3054 is known from ALMA [CII] observations and places the Ly-alpha emission line of companions within the NB964 narrowband of DECam. This is the largest field-of-view LAE search around a z > 6 quasar conducted to date. We find that this field is similar to ten times more overdense than Chandra Deep-Field South, observed previously with the same instrumental setup as well as several combined blank fields. This is strong evidence that VIK J2348-3054 resides in an overdensity of LAEs over several Mpc. Surprisingly, we find a lack of LAEs within 5 physical Mpc of the quasar and take this to most likely be evidence of quasar-suppressing star formation in its immediate vicinity. This result highlights the importance of performing overdensity searches over large areas to properly assess the density of those regions of the Universe.
- ItemA large, deep 3 deg2 survey of H α, [O iii], and [O ii] emitters from LAGER: constraining luminosity functions(OUP, 2020) Khostovan, A. A.; Malhotra, S.; Rhoads, J. E.; Jiang, C.; Wang, J.; Wold, I.; Zheng, Z. Y.; Barrientos, Luis Felipe; Coughlin, A.; Harish, S.; Hu, W.; Infante Lira, Leopoldo; Perez, L. A.; Pharo, J.; Valdes, F.; Walker, A. R.; Yan, H.We present our measurements of the H α, [O iii], and [O ii] luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 z = 0.47 H α-, 3933 z = 0.93 [O iii]-, and 5367 z = 1.59 [O ii]-selected emission line galaxies in a 3 deg 2 single, CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5σ depths of 8.2 × 10 −18 erg s −1 cm −2 and comoving volumes of (1−7) × 10 5 Mpc 3 making our survey one of the deepest narrow-band surveys. We select our emission line galaxies via spectroscopic confirmation, photometric redshifts, and colour–colour selections. We measure the observed luminosity functions for each sample and find best fits of ϕ⋆=10−3.16+0.09−0.09 Mpc −3 and L⋆=1041.72+0.09−0.09 erg s −1 for H α, ϕ⋆=10−2.16+0.10−0.12 Mpc −3 and L⋆=1041.38+0.07−0.06 erg s −1 for [O iii], and ϕ⋆=10−1.97+0.07−0.07 Mpc −3 and L⋆=1041.66+0.03−0.03 erg s −1 for [O ii], with α fixed to −1.75, −1.6, and −1.3, respectively. An excess of bright >10 42 erg s −1 [O iii] emitters is observed and may be due to active galactic nucleus (AGN) contamination. Corrections for dust attenuation are applied assuming A Hα = 1 mag. We also design our own empirical rest-frame g − r calibration using SDSS DR12 data, test it against our z = 0.47 H α emitters with zCOSMOS 1D spectra, and calibrate it for (g − r) between −0.8 and 1.3 mag. Dust and AGN-corrected star formation rate densities (SFRDs) are measured as log 10 ρ SFR /(M ⊙ yr −1 Mpc −3 ) = −1.63 ± 0.04, −1.07 ± 0.06, and −0.90 ± 0.10 for H α, [O iii], and [O ii], respectively. We find our [O iii] and [O ii] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multiwavelength SFRDs, while the H α sample traces ∼70 per cent of the total z = 0.47 SFRD.
- ItemA resolved Lyman α profile with doubly peaked emission at z∼7(EDP Sciences, 2024) Moya Sierralta, Cristobal; González López, Jorge; Infante Lira Leopoldo; Barrientos Parra, Luis Felipe; Hu, W.; Malhotra, S.; Rhoads, J.; Wang, J.; Wold, I.; Zheng, Z.© The Authors 2024.Context. The epoch of reionization is a landmark in structure formation and galaxy evolution. How it happened is still not clear, especially regarding which population of objects was responsible for contributing the bulk of ionizing photons to this process. Doubly peaked Lyman-alpha profiles in this epoch are of particular interest since they hold information about the escape of ionizing radiation and the environment surrounding the source. Aims. We wish to understand the escape mechanisms of ionizing radiation in Lyα emitters during this time and the origin of a doubly peaked Lyman-alpha profile. We also wish to estimate the size of a potential ionized bubble. Methods. Using radiative transfer models, we fit the line profile of a bright Lyα emitter at z-≈-6.9 using various gas geometries. The line modeling reveals significant radiation escape from this system. Results. The studied source shows significant escape (fesc(Lyα) ≈ 0.8, as predicted by the best fitting radiative transfer model) and appears to inhabit an ionized bubble of radius Rb-0.8-0.3+0.5-pMpc(tage/108)1/3. Radiative transfer modeling predicts the line to be completely redward of the systemic redshift. We suggest the line morphology is produced by inflows, by multiple components emitting Lyα, or by an absorbing component in the red wing. Conclusions. We propose that CDFS-1-s profile has two red peaks produced by winds within the system. Its high fesc(Lyα) and the low-velocity offset from the systemic redshift suggest that the source is an active ionizing agent. Future observations will reveal whether a peak is present blueward of the systemic redshift or if multiple components produce the profile.
- ItemCorrelations between H α equivalent width and galaxy properties at z = 0.47: Physical or selection-driven?(2021) Khostovan, A. A.; Malhotra, S.; Rhoads, J. E.; Harish, S.; Jiang, C.; Wang, J.; Wold, I.; Zheng, Z. -Y.; Barrientos, L. F.; Coughlin, A.; Hu, W.; Infante, L.; Perez, L. A.; Pharo, J.; Valdes, F.; Walker, A. R.The H alpha equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H alpha EW strongly anticorrelates with stellar mass as M-0.25 similar to the sSFR - stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H alpha EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H alpha emitters from the Ly alpha Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg(2) area of COSMOS with a survey comoving volume of 1.1 x 10(5) Mpc(3). We assume an intrinsic EW distribution to form mock samples of H alpha emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find that H alpha EW intrinsically correlates with stellar mass as W-0 proportional to M-0.16 +/- 0.03 and decreases by a factor of similar to 3 from 10(7) M-circle dot to 10(10) M-circle dot, while not correcting for selection effects steepens the correlation as M-025 +/- 0.04, We find low-mass H alpha emitters to be similar to 320 times more likely to have rest-frame EW > 200 angstrom compared to high-mass H alpha emitters. Combining the intrinsic W-0-stellar mass correlation with an observed stellar mass function correctly reproduces the observed H alpha luminosity function, while not correcting for selection effects underestimates the number of bright emitters. This suggests that the W-0-stellar mass correlation when corrected for selection effects is physically significant and reproduces three statistical distributions of galaxy populations (line luminosity function, stellar mass function, EW distribution). At lower stellar masses, we find there are more high-EW outliers compared to high stellar masses, even after we take into account selection effects. Our results suggest that high sSFR outliers indicative of bursty star formation activity are intrinsically more prevalent in low-mass H alpha emitters and not a byproduct of selection effects.
- ItemThe effect of size on the strength of coarse rock aggregates and large rockfill samples through experimental data(2014) Ovalle Ortega, Carlos Enrique; Frossard, E.; Dano, C.; Hu, W.; Maiolino, S.; Hicher, P.