Hα Emission from High‐Velocity Clouds and Their Distances

Putman, Mary E.; Bland-Hawthorn, Joss; Veilleux, Sylvain; Gibson, Brad K.; Freeman, K. C.; Maloney, P. R.

doi:10.1086/378555

Cited by 181 publications

(237 citation statements)

References 41 publications

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“…In addition, the strong radiation field should ionise the part of the CHVCs being exposed to the radiation. This should result in high Hα intensities which are not consistent with the faint Hα emission found by Tufte et al (2002) and Putman et al (2003).…”

Section: Evidence Of Ram-pressure Interactioncontrasting

confidence: 66%

Effelsberg H I observations of compact high-velocity clouds

Westmeier¹,

Brüns²,

Kerp³

2005

A&A

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Abstract. We have mapped 11 compact high-velocity clouds (CHVCs) in the 21-cm line emission of neutral, atomic hydrogen, using the Effelsberg 100-m radio telescope. The aim of our observations was to study the overall distribution of the warm neutral medium of CHVCs with high sensitivity. The achieved baseline rms of σ rms ≈ 50 mK at the original 2.6 km s −1 velocity resolution allows us to search for evidence of ram-pressure interaction with the ambient medium. In addition, we have obtained spectra along an appropriate axis across each CHVC with longer integration times and denser angular sampling. These deep slices with σ rms ≈ 25 . . . 35 mK allow us to determine the column density profile in greater detail as well as the velocity and line width gradient across each cloud.The most outstanding result of our observations is the complexity of the H  column density distribution and the line profiles of the investigated CHVCs. We have found only one cloud with a spherically-symmetric appearance. Among the remaining clouds we observe head-tail structures, bow-shock shapes, and objects with irregular shapes. These complex morphologies in combination with the obtained physical parameters suggest that ram-pressure interactions with an ambient medium may play a significant role in shaping some of the CHVCs from our sample. These results are consistent with a circumgalactic distribution of CHVCs with typical distances of the order of 100 kpc. The pressure of the ambient medium might also stabilise CHVCs in addition to their own gravitational potential.

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Section: Evidence Of Ram-pressure Interactioncontrasting

confidence: 66%

Effelsberg H I observations of compact high-velocity clouds

Westmeier¹,

Brüns²,

Kerp³

2005

A&A

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“…Bouwens et al (2010) estimate that an escape fraction of 20% (60%) is required for consistency with the WMAP results at the 2σ (1σ ) level. This is much higher than the escape fraction of 1-2% measured for the Milky Way (Putman et al 2003).…”

Section: Introductioncontrasting

confidence: 55%

Extreme Feedback and the Epoch of Reionization: Clues in the Local Universe

Heckman

Borthakur

Overzier

et al. 2011

ApJ

291

405

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The source responsible for reionizing the universe at z > 6 remains uncertain. While an energetically adequate population of star-forming galaxies may be in place, it is unknown whether a large enough fraction of their ionizing radiation can escape into the intergalactic medium. Attempts to measure this escape fraction in intensely star-forming galaxies at lower redshifts have largely yielded upper limits. In this paper, we present new Hubble Space Telescope Cosmic Origins Spectrograph and archival Far-Ultraviolet Spectroscopic Explorer (FUSE) far-UV spectroscopy of a sample of 11 Lyman Break Analogs (LBAs), a rare population of local galaxies that strongly resemble the high-z Lyman Break galaxies. We combine these data with Sloan Digital Sky Survey optical spectra and Spitzer photometry. We also analyze archival FUSE observations of 15 typical UV-bright local starbursts. We find evidence of small covering factors for optically thick neutral gas in three cases. This is based on two independent pieces of evidence: a significant residual intensity in the cores of the strongest interstellar absorption-lines tracing neutral gas and a small ratio of extinction-corrected Hα to UV plus far-IR luminosities. These objects represent three of the four LBAs that contain a young, very compact (∼10 2 pc), and highly massive (∼10 9 M ) dominant central object (DCO). These three objects also differ from the other galaxies in showing a significant amount of blueshifted Lyα emission, which may be related to the low covering factor of neutral gas. All four LBAs with DCOs in our sample show extremely high velocity outflows of interstellar gas, with line centroids blueshifted by about 700 km s −1 and maximum outflow velocities reaching at least 1500 km s −1 . We show that these properties are consistent with an outflow driven by a powerful starburst that is exceptionally compact. We speculate that such extreme feedback may be required to enable the escape of ionizing radiation from star-forming galaxies.

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“…Tumlinson et al (2011) give a relation to derive the contribution of star-forming regions to the UV background, as a function of escape fraction, distance and SFR. At a distance of d > 95 kpc and SFR = 0.33 ± 0.04 Myr, star formation contributes to the ionization field at the level of a few percent for reasonable values of the escape fraction of ionizing photons (i.e., f esc < 0.04; Putman et al 2003a;Chen et al 2007). Note also that photoionization of O v to O vi requires photons with energies of 114 eV or greater, which cannot be supplied by star formation.…”

Section: Metal-poor Cloud At V = +365 Km S −1mentioning

confidence: 98%

THE GAS–GALAXY CONNECTION ATz_abs= 0.35: O VI AND H I ABSORPTION TOWARD J 0943+0531

Thom

Werk

Tumlinson

et al. 2011

ApJ

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We present observations of H i and O vi absorption systems proximate to a galaxy at z gal = 0.3529. The absorption was detected serendipitously in Cosmic Origins Spectrograph observations of the low-z QSO J 0943+0531 (z qso = 0.564). The data show two separate clouds along the sightline at an impact parameter of 95 kpc from the galaxy. The first is likely low-metallicity gas falling onto the galaxy. This assessment is based on the high velocity offset of the cloud from the galaxy (Δv = 365 km s −1 ) and the weak metal line absorption, combined with photoionization modeling. The second cloud, with only a modest velocity separation from the galaxy (Δv = 85 km s −1 ), exhibits very strong O vi absorption qualitatively similar to O vi absorption seen in the Milky Way halo. Collisional ionization equilibrium models are ruled out by the metal line column density ratios. Photoionization modeling implies a length scale for the O vi cloud of ∼0.1-1.2 Mpc, which indicates the absorbing gas most likely resides within the local filamentary structure. This system emphasizes that kinematic association alone is not sufficient to establish a physical connection to galaxies, even at small impact parameters and velocity separations. Observations such as these, connecting galaxies with their gaseous environments, are becoming increasingly important for understanding of galaxy evolution and provide constraints for cosmological simulations.

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Hα Emission from High‐Velocity Clouds and Their Distances

Cited by 181 publications

References 41 publications

Effelsberg H I observations of compact high-velocity clouds

Effelsberg H I observations of compact high-velocity clouds

Extreme Feedback and the Epoch of Reionization: Clues in the Local Universe

THE GAS–GALAXY CONNECTION ATz_abs= 0.35: O VI AND H I ABSORPTION TOWARD J 0943+0531

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Hα Emission from High‐Velocity Clouds and Their Distances

Cited by 181 publications

References 41 publications

Effelsberg H I observations of compact high-velocity clouds

Effelsberg H I observations of compact high-velocity clouds

Extreme Feedback and the Epoch of Reionization: Clues in the Local Universe

THE GAS–GALAXY CONNECTION ATzabs= 0.35: O VI AND H I ABSORPTION TOWARD J 0943+0531

Contact Info

Product

Resources

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THE GAS–GALAXY CONNECTION ATz_abs= 0.35: O VI AND H I ABSORPTION TOWARD J 0943+0531