The astro-ph electronic preprint archive has had a large impact on our field by greatly increasing the accessibility of preprints and making them instantly available around the world. It also provides a convenient way of tracking the latest developments. Here I mention a few highlights gleaned from postings to astro-ph in the last year and from other sources.
The Most Luminous.
Irwin et al. (1998)
reported the discovery
of APM 08279 + 5255, a broad-absorption line quasar
with z = 3.87 and R = 15.2 mag. The object is coincident
with an IRAS FSC source, and the estimated luminosity is
5 ×
1015
L
, making it
the intrinsically most luminous object known. There is evidence that
the source is gravitationally lensed, which amplifies the true emitted
luminosity.
The Most Distant.
Weymann et al. (1998)
find from Keck spectroscopy
an emission line in the galaxy HDF4-473.0 that, if identified with
Ly
, yields a redshift of
z = 5.60. The galaxy is in the Hubble
Deep Field and is the most distant object with slit spectroscopy that
has yet been identified. It is not a quasar or AGN, and the absence of
quasars with z > 4.9, despite continuing surveys for them,
is beginning to appear
significant in view of the increasing number of confirmed and candidate
galaxies with z > 5.
The Smallest. Kedziora-Chudczer et al. (1998) observed significant radio variability on timescales less than an hour in the radio quasar PKS 0405 - 385, which would make it the smallest extragalactic source observed. They attribute the variation to interstellar scintillation of a source with an angular size smaller than 5 microarcsec. The inferred brightness temperature is well above the inverse Compton limit. If interpreted as steady relativistic beaming, the Lorentz factor would be 1000.
The first FIRST gravitational lens. Schechter et al. (1998) found that the quasar FBQ 0951 + 2635, with V = 16.9 mag and z = 1.24, from the FIRST radio survey, is a gravitational lens with two images separated by 1.1 arcsec.
Update to the Verón-Cetty and Verón Catalog. Verón-Cetty and Verón released the 8th edition of their catalog during the year. It contains entries for 11,358 quasars, 357 BL Lac objects, and 3334 AGNs and is available electronically at http://www.obs-hp.fr/www/catalogues/veron2_9/veron2_8.html. Such catalogs continue to be an vital resource for the community, especially as new surveys yield so many new quasars and AGNs. Also, the electronic availability of the catalogue makes it even more accessible and valuable than it was previously.