Hydrogen Emission from the Ionized Gaseous Halos of Low Redshift Galaxies

Abstract

Using a sample of nearly half million galaxies, intersected by over 7 million lines of sight from the Sloan Digital Sky Survey Data Release 12, we trace H$\alpha$ + [N{\small II}] emission from a galactocentric projected radius, $r_p$, of 5 kpc to more than 100 kpc. The emission flux surface brightness is $\propto r_p^{-1.9\pm 0.4}$. We obtain consistent results using only the H$\alpha$ or [N{\small II}] flux. We measure a stronger signal for the bluer half of the target sample than for the redder half on small scales, $r_p<$ 20 kpc. We obtain a $3\sigma$ detection of H$\alpha$ + [N{\small II}] emission in the 50 to 100 kpc $r_p$ bin. The mean emission flux within this bin is $(1.10\pm 0.35)\times 10^{-20}$ erg cm${}^{-2}$ s${}^{-1}$ Å${}^{-1}$, which corresponds to $1.87\times 10^{-20}$ erg cm${}^{-2}$ s${}^{-1}$ arcsec${}^{-2}$ or 0.0033 Rayleigh. This detection is 34 times fainter than a previous strict limit obtained using deep narrow-band imaging. The faintness of the signal demonstrates why it has been so difficult to trace recombination radiation out to large radii around galaxies. This signal, combined with published estimates of n${}_{\mathrm{H}}$, lead us to estimate the temperature of the gas to be 12,000 K, consistent with independent empirical estimates based on metal ion absorption lines and expectations from numerical simulations.

12 pages, 13 figures

References in corpus (5)

• The COS-Halos Survey: Physical Conditions and Baryonic Mass in the Low-Redshift Circumgalactic Medium
• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
• The properties of the cool circumgalactic gas probed with the SDSS, WISE and GALEX surveys
• The distribution of gas in the Local Group from constrained cosmological simulations: the case for Andromeda and the Milky Way galaxies
• Deep Fabry-Perot Halpha Observations of NGC 7793: a Very Extended Halpha Disk and a Truly Declining Rotation Curve

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• The AGORA High-resolution Galaxy Simulations Comparison Project. VI. Similarities and Differences in the Circumgalactic Medium
• Searching for MgII absorbers in and around galaxy clusters
• MusE GAs FLOw and Wind (MEGAFLOW) XIII. Cool gas traced by MgII around isolated galaxies
• H$\alpha$ emission in the outskirts of galaxies at z=0.4
• Mainly on the Plane: Observing the Extended, Ionized Disks of Milky Way Analogs in IllustrisTNG