COSMIC ORIGINS SPECTROGRAPH AND FUSE OBSERVATIONS OF T {approx} 10{sup 5} K GAS IN A NEARBY GALAXY FILAMENT

Journal Article · Fri Oct 01 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/721/2/960· OSTI ID:21464803

Narayanan, Anand; Wakker, Bart P; Savage, Blair D ^[1]; Keeney, Brian A; Shull, J Michael; Stocke, John T ^[2]

---

1. Department of Astronomy, University of Wisconsin-Madison, 5534 Sterling Hall, 475 N. Charter Street, Madison WI 53706-1582 (United States)
2. CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389-UCB, Boulder, CO 80309 (United States)

We present a clear detection of a broad Ly{alpha} absorber (BLA) with a matching O VI line in the nearby universe. The BLA is detected at z(Ly{alpha})=0.01028 in the high signal-to-noise ratio spectrum of Mrk 290 obtained using the Cosmic Origins Spectrograph. The Ly{alpha} absorption has two components, with b(H i) = 55{+-}1 km s{sup -1} and b(H i) = 33{+-}1 km s{sup -1}, separated in velocity by v {approx} 115 km s{sup -1}. The O VI, detected by the Far-Ultraviolet Spectroscopic Explorer at z(O vi) = 0.01027, has a b(O vi) = 29{+-}3 km s{sup -1} and is kinematically well aligned with the broader H I component. The non-detection of other ions such as C II, Si II, Fe II, C III, Si III, C IV, Si IV, and N V at the same velocity as the BLA and the O VI implies that the absorber is tracing highly ionized gas. The different line widths of the BLA and O VI suggest a temperature of T = 1.4 x 10{sup 5} K in the absorber. Photoionization, collisional ionization equilibrium as well as non-equilibrium collisional ionization models do not explain the ion ratios at this temperature. The observed line strength ratios and line widths favor an ionization scenario in which both ion-electron collisions and UV photons contribute to the ionization in the gas. Such a model requires a low metallicity of {approx}-1.7 dex, ionization parameter of log U {approx} -1.4, a large total hydrogen column density of N(H) {approx} 4 x 10{sup 19} cm{sup -2}, and a path length of {approx}400 kpc. The line of sight to Mrk 290 intercepts at the redshift of the absorber, a megaparsec scale filamentary structure extending over {approx}20{sup 0} in the sky, with several luminous galaxies distributed within {approx}1.5 h {sup -1} Mpc projected distance from the absorber. The collisionally ionized gas phase of this absorber is most likely tracing a shock-heated gaseous structure, consistent with a few different scenarios for the origin including an overdense region of the warm-hot intergalactic medium in the galaxy filament or highly ionized gas in the extended halo of one of the galaxies in the filament. In general, BLAs with metals provide an efficient means to study T {approx} 10{sup 5}-10{sup 6} K gas in galaxy halos and in the intergalactic medium. A substantial fraction of the baryons missing from the present universe is predicted to be in such environments in the form of highly ionized plasma.

• OSTI ID: 21464803
• Journal Information: Astrophysical Journal, Vol. 721, Issue 2; Other Information: DOI: 10.1088/0004-637X/721/2/960; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABSORPTION
ELECTRON-ION COLLISIONS
FAR ULTRAVIOLET RADIATION
GALAXIES
GALAXY CLUSTERS
HYDROGEN
LINE WIDTHS
PHOTOIONIZATION
PHOTONS
QUASARS
RED SHIFT
SIGNAL-TO-NOISE RATIO
UNIVERSE
BOSONS
COLLISIONS
COSMIC RADIO SOURCES
DIMENSIONLESS NUMBERS
ELECTROMAGNETIC RADIATION
ELECTRON COLLISIONS
ELEMENTARY PARTICLES
ELEMENTS
ION COLLISIONS
IONIZATION
MASSLESS PARTICLES
NONMETALS
RADIATIONS
SORPTION
ULTRAVIOLET RADIATION