Hα Imaging of Nearby Seyfert Host Galaxies

We used narrowband (Δλ = 70 Å) interference filters with the CCD imaging camera on the Nickel 1.0 m telescope at Lick Observatory to observe 31 nearby (z 67%) their H ii region emission. Only the most luminous AGNs (log(L_(Hα) /erg s^(−1)) > 41.5) would still be identified as such at z ~ 0.3

Predicting Lyα Emission from Galaxies via Empirical Markers of Production and Escape in the KBSS

Lyα emission is widely used to detect and confirm high-redshift galaxies and characterize the evolution of the intergalactic medium (IGM). However, many galaxies do not display Lyα emission in typical spectroscopic observations, and intrinsic Lyα emitters represent a potentially biased set of high-redshift galaxies. In this work, we analyze a set of 703 galaxies at 2 ≾ z ≾ 3 with both Lyα spectroscopy and measurements of other rest-frame ultraviolet and optical properties in order to develop an empirical model for Lyα emission from galaxies and understand how the probability of Lyα emission depends on other observables. We consider several empirical proxies for the efficiency of Lyα photon production, as well as the subsequent escape of these photons through their local interstellar medium. We find that the equivalent width of metal-line absorption and the O3 ratio of rest-frame optical nebular lines are advantageous empirical proxies for Lyα escape and production, respectively. We develop a new quantity, X_(LIS)^(O3), that combines these two properties into a single predictor of net Lyα emission, which we find describes ~90% of the observed variance in Lyα equivalent width when accounting for our observational uncertainties. We also construct conditional probability distributions demonstrating that galaxy selection based on measurements of galaxy properties yield samples of galaxies with widely varying probabilities of net Lyα emission. The application of the empirical models and probability distributions described here may be used to infer the selection biases of current galaxy surveys and evaluate the significance of high-redshift Lyα (non)detections in studies of reionization and the IGM

Dust Attenuation, Star Formation, and Metallicity in z ~ 2-3 Galaxies from KBSS-MOSFIRE

We present a detailed analysis of 317 2.0 ≤ z ≤ 2.7 star-forming galaxies from the Keck Baryonic Structure Survey. Using complementary spectroscopic observations with Keck/LRIS and Keck/MOSFIRE, as well as spectral energy distribution (SED) fits to broadband photometry, we examine the joint rest-UV and rest-optical properties of the same galaxies, including stellar and nebular dust attenuation, metallicity, and star formation rate (SFR). The inferred parameters of the stellar population (reddening, age, SFR, and stellar mass) are strongly dependent on the details of the assumed stellar population model and the shape of the attenuation curve. Nebular reddening is generally larger than continuum reddening, but with large scatter. Compared to local galaxies, high-redshift galaxies have lower gas-phase metallicities (and/or higher nebular excitation) at fixed nebular reddening, and higher nebular reddening at fixed stellar mass, consistent with gas fractions that increase with redshift. We find that continuum reddening is correlated with 12 + log(O/H)_(O3N2) at 3.0σ significance, whereas nebular reddening is correlated with only 1.1σ significance. This may reflect the dependence of both continuum reddening and O3N2 on the shape of the ionizing radiation field produced by the massive stars. Finally, we show that Hα-based and SED-based estimates of SFR exhibit significant scatter relative to one another, and on average agree only for particular combinations of spectral synthesis models and attenuation curves. We find that the SMC extinction curve predicts consistent SFRs if we assume the subsolar (0.14 Z⊙) binary star models that are favored for high-redshift galaxies

Predicting Lyα Emission from Galaxies via Empirical Markers of Production and Escape in the KBSS

Lyα emission is widely used to detect and confirm high-redshift galaxies and characterize the evolution of the intergalactic medium (IGM). However, many galaxies do not display Lyα emission in typical spectroscopic observations, and intrinsic Lyα emitters represent a potentially biased set of high-redshift galaxies. In this work, we analyze a set of 703 galaxies at 2 ≾ z ≾ 3 with both Lyα spectroscopy and measurements of other rest-frame ultraviolet and optical properties in order to develop an empirical model for Lyα emission from galaxies and understand how the probability of Lyα emission depends on other observables. We consider several empirical proxies for the efficiency of Lyα photon production, as well as the subsequent escape of these photons through their local interstellar medium. We find that the equivalent width of metal-line absorption and the O3 ratio of rest-frame optical nebular lines are advantageous empirical proxies for Lyα escape and production, respectively. We develop a new quantity, X_(LIS)^(O3), that combines these two properties into a single predictor of net Lyα emission, which we find describes ~90% of the observed variance in Lyα equivalent width when accounting for our observational uncertainties. We also construct conditional probability distributions demonstrating that galaxy selection based on measurements of galaxy properties yield samples of galaxies with widely varying probabilities of net Lyα emission. The application of the empirical models and probability distributions described here may be used to infer the selection biases of current galaxy surveys and evaluate the significance of high-redshift Lyα (non)detections in studies of reionization and the IGM

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

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 〈z_(fg)〉 = 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 HI Lyα optical depth relative to the intergalactic mean as a function of projected galactocentric distance (20 ≲ D_(tran)/pkpc ≲ 4000) and line-of-sight velocity. We obtain accurate galaxy systemic redshifts, providing significant information on the line-of-sight kinematics of HI gas as a function of projected distance D_(tran). 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 HI. The best-fitting model suggests that galaxy-scale outflows with initial velocity v_(out) ≃ 600 km s⁻¹ dominate the kinematics of circumgalactic HI out to D_(tran) ≃ 50 kpc, while HI at D_(tran) ≳ 100 kpc is dominated by infall with characteristic v_(in) ≲ circular velocity. Over the impact parameter range 80 ≲ D_(tran)/pkpc ≲ 200, the HI line-of-sight velocity range reaches a minimum, with a corresponding flattening in the rest-frame Lyα equivalent width. These observations can be naturally explained as the transition between outflow-dominated and accretion-dominated flows. Beyond D_(tran) ≃ 300 pkpc (∼1 cMpc), the line-of-sight kinematics are dominated by Hubble expansion

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

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 +/- 0.4 from the Keck Baryonic Structure Survey (KBSS), 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 = 2.23 and = 2.57. The ensemble of sightlines and foreground galaxies is used to construct a 2D map of the mean excess Ly$\alpha$ optical depth relative to the intergalactic mean as a function of projected galactocentric distance (20 < $D_{tran}$/pkpc < 4000) and line-of-sight velocity. We provide information on the line-of-sight kinematics of H I gas as a function of projected distance $D_{tran}$. 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 H I. The best-fitting model suggests that galaxy-scale outflows with initial velocity $v_{out}$ ~ 600 km/s dominate the kinematics of circumgalactic H I out to $D_{tran}$ ~ 50 kpc, while H I at $D_{tran}$ > 100 kpc is dominated by infall with characteristic $v_{in}$ < $v_c$, where $v_c$ is the circular velocity of the host halo ($M_h$ ~ $10^{12} M_\odot$). Over the impact parameter range 80 < $D_{tran}$/pkpc < 200, the H I line-of-sight velocity range reaches a minimum, with a corresponding flattening in the rest-frame Ly$\alpha$ equivalent width. These observations can be naturally explained as the transition between outflow-dominated and accretion-dominated flows. Beyond $D_{tran}$ ~ 300 kpc, the line of sight kinematics are dominated by Hubble expansion.Comment: 27 pages, 24 figures, 3 tables, accepted by MNRAS. Additional data at http://ramekin.caltech.edu/KBSS

H alpha IMAGING OF NEARBY SEYFERT HOST GALAXIES

We used narrowband interference filters with the CCD imaging camera on the Nickel 1.0 meter telescope at Lick Observatory to observe 31 nearby (z &lt; 0.03) Seyfert galaxies in the 12 {\mu}m Active Galaxy Sample. We obtained pure emission line images of each galaxy in order to separate H{\alpha} emission from the nucleus from that of the host galaxy. The extended H{\alpha} emission is expected to be powered by newly formed hot stars, and correlates well with other indicators of current star formation in these galaxies: 7.7 {\mu}m PAH, far-infrared, and radio luminosity. Relative to what would be expected from recent star formation, there is a 0.8 dex excess of radio emission in our Seyfert galaxies. The nuclear H{\alpha} luminosity is dominated by the AGN, and is correlated with the hard X-ray luminosity. There is an upward offset of 1 dex in this correlation for the Seyfert 1s due to a strong contribution from the Broad Line Region. We found a correlation between star formation rate and AGN luminosity. In spite of selection effects, we concluded that the absence of bright Seyfert nuclei in galaxies with low SFRs is real, albeit only weakly significant. We used our measured spatial distributions of H{\alpha} emission to determine what these Seyfert galaxies would look like when observed through fixed apertures at high redshifts. Although all would be detectable emission line galaxies at any redshift, most would appear dominated by HII region emission. Only the most luminous AGN would still be identified at z~0.3