On the Size and Mass of Photo-ionized Clouds in Extended Spiral Galaxy Halos

Abstract

The size and mass of two circum-galactic medium (CGM) clouds in the halo (impact parameter = 65 kpc) of a nearby late-type galaxy, MGC-01-04-005 ($cz=1865$ km/s), are investigated using a close triplet of QSO sight lines (the "LBQS Triplet"; Crighton et al. 2010). Far ultraviolet spectra obtained with the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope (HST) find two velocity components in Lyman $\alpha$ at $\sim 1830$ and 1900 km/s in two of these sight lines, requiring minimum transverse cloud sizes of $\ge 10$ kpc. A plausible, but not conclusive, detection of CIV 1548 Å absorption at the higher velocity in the third sight line suggests an even larger lower limit of $\ge 23$ kpc for that cloud. Using various combinations of constraints, including photo-ionization modeling for one absorber, lower limits on masses of these two clouds of $\ge 10^6$ M_Sun are obtained. Ground-based imaging and long-slit spectroscopy of MCG -01-04-005 obtained at the Apache Point Observatory (APO) 3.5m telescope find it to be a relatively normal late-type galaxy with a current star formation rate (SFR) of $\sim 0.01$ M_Sun per year. Galaxy Evolution Explorer (GALEX) photometry finds an SFR only a few times higher over the last $10^8$ yrs. We conclude that the CGM clouds probed by these spectra are typical in being at impact parameters of 0.4-0.5 R_vir from a rather typical, non-starbursting late-type galaxy so that these size and mass results should be generic for this class. Therefore, at least some CGM clouds are exceptionally large and massive.

10 pages, 2 tables, 5 figures, Accepted to ApJ Jul 29 2015

References in corpus (5)

• The COS-Halos Survey: Physical Conditions and Baryonic Mass in the Low-Redshift Circumgalactic Medium
• Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy
• The COS-Dwarfs Survey: The Carbon Reservoir Around sub-L* Galaxies
• The Properties of Low Redshift Intergalactic O VI Absorbers Determined from High S/N Observations of 14 QSOs with the Cosmic Origins Spectrograph
• Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy

Cited by in corpus (3)

• Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy: II. Methods and Models
• Column Density Profiles of Multi-Phase Gaseous Halos
• Outskirts of Distant Galaxies In Absorption