More Like this

1. The Keck Baryonic Structure Survey: using foreground/background galaxy pairs to trace the structure and kinematics of circumgalactic neutral hydrogen at z ∼ 2

   https://doi.org/10.1093/mnras/staa2808  

   Chen; Steidel, Charles C; Hummels, Cameron B; Rudie, Gwen C; Dong; Trainor, Ryan F; Bogosavljević, Milan; Erb, Dawn K; Pettini, Max; Reddy, Naveen A; et al (October 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present new measurements of the spatial distribution and kinematics of neutral hydrogen in the circumgalactic and intergalactic medium surrounding star-forming galaxies at z ∼ 2. Using the spectra of ≃3000 galaxies with redshifts 〈z〉 = 2.3 ± 0.4 from the Keck Baryonic Structure Survey, we assemble a sample of more than 200 000 distinct foreground-background pairs with projected angular separations of 3–500 arcsec and spectroscopic redshifts, with 〈zfg〉 = 2.23 and 〈zbg〉 = 2.57 (foreground, background redshifts, respectively.) The ensemble of sightlines and foreground galaxies is used to construct a 2D map of the mean excess $$\rm{H\,{\small I}}$$\rm Ly\,\alpha$$ optical depth relative to the intergalactic mean as a function of projected galactocentric distance (20 ≲ Dtran/pkpc ≲ 4000) and line-of-sight velocity. We obtain accurate galaxy systemic redshifts, providing significant information on the line-of-sight kinematics of $$\rm{H\,{\small I}}$$ gas as a function of projected distance Dtran. We compare the map with cosmological zoom-in simulation, finding qualitative agreement between them. A simple two-component (accretion, outflow) analytical model generally reproduces the observed line-of-sight kinematics and projected spatial distribution of $$\rm{H\,{\small I}}$$. The best-fitting model suggests that galaxy-scale outflows with initial velocity vout ≃ 600 km s$$^{-1}\,$$ dominate the kinematics of circumgalactic $$\rm{H\,{\small I}}$$ out to Dtran ≃ 50 kpc, while $$\rm{H\,{\small I}}$$ at Dtran ≳ 100 kpc is dominated by infall with characteristic vin ≲ circular velocity. Over the impact parameter range 80 ≲ Dtran/pkpc ≲ 200, the $$\rm{H\,{\small I}}$$ line-of-sight velocity range reaches a minimum, with a corresponding flattening in the rest-frame $$\rm Ly\,\alpha$$ equivalent width. These observations can be naturally explained as the transition between outflow-dominated and accretion-dominated flows. Beyond Dtran ≃ 300 pkpc (∼1 cMpc), the line-of-sight kinematics are dominated by Hubble expansion. 

   more » « less
2. The size and pervasiveness of Ly α–UV spatial offsets in star-forming galaxies at z ∼ 6

   https://doi.org/10.1093/mnras/stab924  

   Lemaux, B C; Fuller, S; Bradač, M; Pentericci, L; Hoag, A; Strait, V; Treu, T; Alvarez, C; Bolan, P; Gandhi, P J; et al (May 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We study the projected spatial offset between the ultraviolet continuum and Ly α emission for 65 lensed and unlensed galaxies in the Epoch of Reionization (5 ≤ z ≤ 7), the first such study at these redshifts, in order to understand the potential for these offsets to confuse estimates of the Ly α properties of galaxies observed in slit spectroscopy. While we find that ∼40 per cent of galaxies in our sample show significant projected spatial offsets ($$|\Delta _{\rm {Ly}\alpha -\rm {UV}}|$$), we find a relatively modest average projected offset of $$|\widetilde{\Delta }_{\rm {Ly}\alpha -\rm {UV}}|$$  = 0.61 ± 0.08 proper kpc for the entire sample. A small fraction of our sample, ∼10 per cent, exhibit offsets in excess of 2 proper kpc, with offsets seen up to ∼4 proper kpc, sizes that are considerably larger than the effective radii of typical galaxies at these redshifts. An internal comparison and a comparison to studies at lower redshift yielded no significant evidence of evolution of $$|\Delta _{\rm {Ly}\alpha -\rm {UV}}|$$ with redshift. In our sample, ultraviolet (UV)-bright galaxies ($$\widetilde{L_{\mathrm{ UV}}}/L^{\ast }_{\mathrm{ UV}}=0.67$$) showed offsets a factor of three greater than their fainter counterparts ($$\widetilde{L_{\mathrm{ UV}}}/L^{\ast }_{\mathrm{ UV}}=0.10$$), 0.89 ± 0.18 versus 0.27 ± 0.05 proper kpc, respectively. The presence of companion galaxies and early stage merging activity appeared to be unlikely causes of these offsets. Rather, these offsets appear consistent with a scenario in which internal anisotropic processes resulting from stellar feedback, which is stronger in UV-brighter galaxies, facilitate Ly α fluorescence and/or backscattering from nearby or outflowing gas. The reduction in the Ly α flux due to offsets was quantified. It was found that the differential loss of Ly α photons for galaxies with average offsets is not, if corrected for, a limiting factor for all but the narrowest slit widths (<0.4 arcsec). However, for the largest offsets, if they are mostly perpendicular to the slit major axis, slit losses were found to be extremely severe in cases where slit widths of ≤1 arcsec were employed, such as those planned for James Webb Space Telescope/NIRSpec observations. 

   more » « less
3. An uncontaminated measurement of the escaping Lyman continuum at z ∼ 3

   https://doi.org/10.1093/mnras/stab1374  

   Pahl, Anthony J; Shapley, Alice; Steidel, Charles C; Chen, Yuguang; Reddy, Naveen A (June 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Observations of reionization-era analogues at z ∼ 3 are a powerful tool for constraining reionization. Rest-ultraviolet observations are particularly useful, in which both direct and indirect tracers of ionizing-photon production and escape can be observed. We analyse a sample of 124 z ∼ 3 galaxies from the Keck Lyman Continuum Spectroscopic Survey, with sensitive spectroscopic measurements of the Lyman continuum region. We present a method of removing foreground contamination from our sample using high-resolution, multiband Hubble Space Telescope imaging. We re-measure the global properties of the cleaned sample of 13 individually detected Lyman continuum sources and 107 individually undetected sources, including a sample-averaged absolute escape fraction of fesc, abs = 0.06 ± 0.01 and a sample-averaged ratio of ionizing to non-ionizing ultraviolet flux density of 〈f900/f1500〉out = 0.040 ± 0.006, corrected for attenuation from the intergalactic and circumgalactic media. Based on composite spectra, we also recover a strong positive correlation between 〈f900/f1500〉out and Lyα equivalent width (Wλ(Ly$$\rm \alpha$$)) and a negative correlation between 〈f900/f1500〉out and UV luminosity. As in previous work, we interpret the relationship between 〈f900/f1500〉out and Wλ(Ly$$\rm \alpha$$) in terms of the modulation of the escape of ionizing radiation from star-forming galaxies based on the covering fraction of neutral gas. We also use a Wλ(Ly$$\rm \alpha$$)-weighted 〈f900/f1500〉out to estimate an ionizing emissivity from star-forming galaxies at z ∼ 3 as ϵLyC ≃ 5.5 × 1024 erg s−1 Hz−1 Mpc−3. This estimate, evaluated using the uncontaminated sample of this work, affirms that the contribution of galaxies to the ionizing background at z ∼ 3 is comparable to that of active galactic nuclei. 

   more » « less
4. H i Lyα Emission from a Metal-poor Cool Stream Fueling an Early Dusty Starburst

   https://doi.org/10.3847/1538-4357/ad4601  

   Hall, Kevin; Fu, Hai (June 2024, The Astrophysical Journal)

   Abstract The GAMA J0913−0107 system is a rare conjunction of a submillimeter galaxy (SMG) atz≈ 2.7 and two background QSOs with projected separations <200 kpc. Previous high-resolution QSO absorption-line spectroscopy has revealed high Hicolumn density, extremely metal-poor (∼1% solar) gas streams in the circumgalactic medium of the SMG. Here we present deep optical integral-field spectroscopy of the system with the Keck Cosmic Web Imager (KCWI). Reaching a 2σsurface brightness limit ≈10⁻¹⁹erg s⁻¹cm⁻²arcsec⁻²with ∼2 hr of integration time, we detect a filamentary Lyαnebula stretching ∼180 kpc from the SMG intercepting both QSO sightlines. This Lyαfilament may correspond to the same cool gas stream penetrating through the hot halo seen in the absorption. In contrast to Lyαnebulae around QSOs, there is no obvious local source for photoionization due to the massive dust content. While uncertain, we consider the possibility that the nebula is ionized by shocks induced by the infall, obscured star formation, and/or a boosted UV background. The SMG–QSOs conjunction multiplied the efficiency of the KCWI observations, allowing a direct comparison of Lyαnebulae in two distinct environments. We find that the nebulae around the QSOs are much brighter and show steeper surface brightness profiles than the SMG nebula. This is consistent with the additional photoionization and Lyαscattering provided by the QSOs. While illustrating the challenges of detecting Lyαnebulae around SMGs, our work also demonstrates that important insights can be gained from comparative studies of high-zLyαnebulae. 

   more » « less
5. Resolved galactic superwinds reconstructed around their host galaxies at z > 3

   https://doi.org/10.1093/mnras/stab1041  

   Chen, Mandy C; Chen, Hsiao-Wen; Gronke, Max; Rauch, Michael; Broadhurst, Tom (May 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT This paper presents a detailed analysis of two giant Lyman-alpha (Ly α) arcs detected near galaxies at z = 3.038 and z = 3.754 lensed by the massive cluster MACS 1206−0847 (z = 0.44). The Ly α nebulae revealed in deep MUSE observations exhibit a double-peaked profile with a dominant red peak, indicating expansion/outflowing motions. One of the arcs stretches over 1 arcmin around the cluster Einstein radius, resolving the velocity field of the line-emitting gas on kpc scales around three star-forming galaxies of 0.3–$$1.6\, L_*$$ at z = 3.038. The second arc spans 15 arcsec in size, roughly centred around two low-mass Ly α emitters of $$\approx 0.03\, L_*$$ at z = 3.754. All three galaxies in the z = 3.038 group exhibit prominent damped Ly α absorption (DLA) and several metal absorption lines, in addition to nebular emission lines such as $$\hbox{He ii}$$\lambda \, 1640$$ and C iii]λλ1906, 1908. Extended Ly α emission appears to emerge from star-forming regions with suppressed surface brightness at the centre of each galaxy. Significant spatial variations in the Ly α line profile are observed which, when unaccounted for in the integrated line, leads to biased constraints for the underlying gas kinematics. The observed spatial variations indicate the presence of a steep velocity gradient in a continuous flow of high column density gas from star-forming regions into a low-density halo environment. A detailed inspection of available galaxy spectra shows no evidence of AGN activity in the galaxies, and the observed Ly α signals are primarily explained by resonant scattering. The study presented in this paper shows that spatially resolved imaging spectroscopy provides the most detailed insights yet into the kinematics of galactic superwinds associated with star-forming galaxies. 

   more » « less