AN HST /COS OBSERVATION OF BROAD Lyα EMISSION AND ASSOCIATED ABSORPTION LINES OF THE BL LACERTAE OBJECT H 2356-309

Weak spectral features in BL Lacertae objects (BL Lacs) often provide a unique opportunity to probe the inner region of this rare type of active galactic nucleus. We present a Hubble Space Telescope/Cosmic Origins Spectrograph observation of the BL Lac H 2356-309. A weak Ly alpha emission line was d...

Full description

Saved in:
Bibliographic Details
Published in:The Astrophysical journal 2014-11, Vol.795 (1), p.1-6, Article 57
Main Authors: Fang, Taotao, Danforth, Charles W, Buote, David A, Stocke, John T, Shull, J Michael, Canizares, Claude R, Gastaldello, Fabio
Format: Article
Language:English
Subjects:
ABSORPTION
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BL LACERTAE OBJECTS
Clouds
DENSITY
DETECTION
ELEMENT ABUNDANCE
EMISSION
GALAXIES
GALAXY NUCLEI
Hubble Space Telescope
HYDROGEN
Ionization
Lorentz factor
LYMAN LINES
OXYGEN
PHOTOIONIZATION
PHOTONS
RELATIVISTIC RANGE
SPACE
TELESCOPES
Ultraviolet
ULTRAVIOLET RADIATION
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Weak spectral features in BL Lacertae objects (BL Lacs) often provide a unique opportunity to probe the inner region of this rare type of active galactic nucleus. We present a Hubble Space Telescope/Cosmic Origins Spectrograph observation of the BL Lac H 2356-309. A weak Ly alpha emission line was detected. This is the fourth detection of a weak Ly alpha emission feature in the ultraviolet (UV) band in the so-called high-energy peaked BL Lacs, after Stocke et al. Assuming the line-emitting gas is located in the broad line region (BLR) and the ionizing source is the off-axis jet emission, we constrain the Lorentz factor ([Gamma]) of the relativistic jet to be [> or =, slanted]8.1 with a maximum viewing angle of 3[degrees].6. The derived [Gamma] is somewhat larger than previous measurements of [Gamma] approximately 3-5, implying a covering factor of ~3% of the line-emitting gas. Alternatively, the BLR clouds could be optically thin, in which case we constrain the BLR warm gas to be ~10 super(-5) M sub([middot in circle]). We also detected two HI and one OVI absorption lines that are within | Delta [upsilon]| < 150 km s super(-1) of the BL Lac object. The OVI and one of the HI absorbers likely coexist due to their nearly identical velocities. We discuss several ionization models and find a photoionization model where the ionizing photon source is the BL Lac object that can fit the observed ion column densities with reasonable physical parameters. This absorber can either be located in the interstellar medium of the host galaxy or in the BLR.
ISSN:0004-637X
1538-4357
1538-4357
DOI:10.1088/0004-637X/795/1/57