The BL Lac object PKS 0215 + 015 in a low state - Variable emission lines at z(e) = 1.72 and no dust signature from the system at z(a) = 1.345

Details The BL Lac object PKS 0215 + 015 in a low state - Variable emission lines at z(e) = 1.72 and no dust signature from the system at z(a) = 1.345 The BL Lac object PKS 0215 + 015 in a low state - Variable emission lines at z(e) = 1.72 and no dust signature from the system at z(a) = 1.345

Mar 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988a%26a...192....1b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 192, no. 1-2, March 1988, p. 1-8.

Astronomy and Astrophysics

Astrophysics

24

Bl Lacertae Objects, Cosmic Dust, Emission Spectra, Interstellar Matter, Line Spectra, Absorption Spectra, Opacity, Quasars, Red Shift

Scientific paper

We present high signal to noise low resolution spectra of the BL Lac object PKS 0215+015 obtained in September 1986. At that time this object had a red magnitude m(r)=18.9 and thus was 5 magnitudes fainter than two years earlier. Two broad emission lines, C IV and C III] are clearly detected at a redshift z = 1.721, very close to the estimate derived by Foltz and Chaffee (1987) from observations made in November 1986 of Lyα and C IV in emission. Within the 55 days which separate the two sets of observations, the equivalent width of the C IV emission doublet has decreased by a factor of 2.0 while the continuum has remained nearly constant. In this low state, the spectrum of PKS 0215+015 still does not resemble those of QSOs or Seyfert 1 galaxies. The continuum flux distribution is very well fitted by a power law spectrum Fy ∝ v-2.22, and there is no significant deviation in the wavelength range of the expected 2175 Å dust feature associated with the low ionization absorption system at Za = 1.345. Therefore the dust in the intervening material cannot be of galactic-type and should either have different properties and/or a lower dust to gas ratio. We briefly review results obtained for other absorption systems with H I column densities in excess of 1020 cm-2 In no case evidence for associated dust is found which raises the question of the composition of interstellar matter in high z galaxies. We also discuss the possible obscuration of high redshift QSOs by dust associated with intervening galaxies using the observed H I column density distribution of metal-rich absorption line systems. We have estimated the dust obscuration for various dust properties and for the presently available N(H I) distributions. We find that the obscuration expected from SMC-type dust is always small, Av <1, and consistent with the UV continua of very high redshift quasars. Thus dust from absorption systems cannot explain the rareness of z >3 QSOs.

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