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MG II absorption in the spectra of high and low redshift QSOs

1988; IOP Publishing; Volume: 334; Linguagem: Inglês

10.1086/166814

1538-4357

W. L. W. Sargent, Charles C. Steidel, A. Boksenberg,

Astrophysics and Star Formation Studies

view Abstract Citations (111) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS MG II Absorption in the Spectra of High and Low Redshift QSOs Sargent, Wallace L. W. ; Steidel, Charles C. ; Boksenberg, A. Abstract We present a sample of 40 Mg II absorption redshifts found in the spectra of a new, uniform sample of 55 QSOs with emission redshifts in the range 1.8 <= z_em_ <= 3.56 published elsewhere. The Mg II redshifts lie in the range 0.24 <= z_abs_ <= 1.46. This sample is augmented by new spectra of nine QSOs with emission redshifts in the range 0.6 <= z_em_ <= 1.42 which yielded one Mg II absorption system. The new data are analyzed in conjunction with samples recently published by Lanzetta, Turnshek, and Wolfe and by Tytler et al. In total, we have 71 Mg II absorption systems, of which 37 constitute a complete sample of independent systems with a well-defined rest equivalent width cutoff W_0_(λ2796) > 0.6 A. It is found that: 1. The distribution of number of absorption systems per QSO accurately follows a Poisson distribution, as is expected for randomly distributed intervening absorbers. An application of the second Bahcall-Peebles test is also consistent with this hypothesis. 2. The density of Mg II absorption in a given observed absorption redshift range does not depend significantly on the emission redshift of the QSO; 3. The variation of Mg II system density with redshift, expressed as a power law, follows the relationship N(z) is proportional to ^ (1 + z)^1.45+/-0.63 over the redshift range 0.16 <= z_abs_ <= 2.14, consistent within the errors with a constant comoving density of absorbers in a Friedmann universe with q_0_ = 0, and possibly inconsistent if q_0_ = 1/2. If the results for Mg II are combined with those for C IV obtained by Sargent, Boksenberg, and Steidel, a qualitative picture emerges in which the density of absorbers increases rapidly until z_abs_ ~ 1, then flattens off, and finally declines beyond z_abs_ ~ 2.5. This is interpreted as being due to the combined effects of cosmological expansion and the chemical evolution of the absorbers. 4. There is no significant correlation of either the Mg II doublet ratio or the mean Mg II rest equivalent width with redshift; 5. The Mg II redshifts are significantly clustered on a scale {DELTA}v <= 200 km s^-1^. Both the enormous amplitude of the two-point correlation function and direct observations of the absorbing galaxy imply that the apparent clustering is due to the relative motions of clouds within galaxies. There is insufficient information to say anything about clustering on larger scales. The newly discovered Mg II redshifts significantly increase the sample available for searches for the absorbing galaxy. Publication: The Astrophysical Journal Pub Date: November 1988 DOI: 10.1086/166814 Bibcode: 1988ApJ...334...22S Keywords: Absorption Spectra; Magnesium; Quasars; Red Shift; Density Distribution; Metallicity; Space Density; Astronomy; COSMOLOGY; QUASARS full text sources ADS | data products SIMBAD (48) NED (48)