A Large Reservoir of Ionized Gas in the Galactic Halo: Ionized Silicon in High-Velocity and Intermediate-Velocity Clouds

Details A Large Reservoir of Ionized Gas in the Galactic Halo: Ionized Silicon in High-Velocity and Intermediate-Velocity Clouds A Large Reservoir of Ionized Gas in the Galactic Halo: Ionized Silicon in High-Velocity and Intermediate-Velocity Clouds

2009-04-30

arxiv.org/abs/0904.4901v2

Astrophys.J.699:754-767,2009

Astronomy and Astrophysics

Astrophysics

Galaxy Astrophysics

Accepted for July 10th ApJ, Vol 700, 16 pages, 6 figures, 3 tables (v2: several small clarifications including updated abstrac

Scientific paper

10.1088/0004-637X/699/1/754

The low Galactic halo is enveloped by a sheath of ionized, low-metallicity gas, which can provide a substantial (1 M_sun/yr) cooling inflow to replenish star formation in the disk. Using absorption spectra from the HST and FUSE toward 37 active galactic nuclei at high latitude, we detect widespread interstellar SiIII 1206.5 absorption: 61 high-velocity clouds (HVCs) along 30 sight lines and 22 intermediate-velocity clouds (IVCs) along 20 sight lines. We find a segregation of redshifted and blueshifted absorbers across the Galactic rotation axis at l=180, consistent with a lag in the rotation velocity above the Galactic plane. The HVC sky coverage is large (81+-5% for 30/37 directions) with SiIII optical depth typically 4-5 times that of OVI 1032. The mean HVC column density per sight line, =13.42+-0.21, corresponds to total column density N_HII~6x10^18)/(Z_Si/0.2Z_sun) of ionized low-metallicity gas, similar to that inferred in OVI. This reservoir could total 10^8 M_sun and produce a mass infall rate ~1 M_sun/yr. By modeling SiII, SiIII, SiIV, and HI in a subset of absorbers, we constrain the mean photoionization parameter in the low halo, = -3.0 (+0.3,-0.4), approximately ten times lower than observed in the low-redshift intergalactic medium. The metallicities in some HVCs, derived from [SiII/HI], are 10-30% solar, whereas values found from all three silicon ions are lower in the pure-photoionization models. Thse formally lower metallicities are highly uncertain, since some of the higher ions may be collisionally ionized. The mean Si metallicities, = -2.1(+1.1,-0.3) in 17 HVCs and -1.0(+0.6,-1.0) in 19 IVCs, are somewhat uncertain owing to ionization modeling, but consistent with the median photometric metallicity, [Fe/H]=-1.46+-0.30, for ~2e5 halo F/G stars in SDSS.

Affiliated with

Also associated with

No associations

Rating

A Large Reservoir of Ionized Gas in the Galactic Halo: Ionized Silicon in High-Velocity and Intermediate-Velocity Clouds does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with A Large Reservoir of Ionized Gas in the Galactic Halo: Ionized Silicon in High-Velocity and Intermediate-Velocity Clouds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Large Reservoir of Ionized Gas in the Galactic Halo: Ionized Silicon in High-Velocity and Intermediate-Velocity Clouds will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-443956