Richard R. Mellon

Low- and High-Ionization Absorption Properties of Mg II Absorption-selected Galaxies at Intermediate Redshifts. II. Taxonomy, Kinematics, and Galaxies* **

We examine a sample of 45 Mg II absorption-selected systems over the redshift range 0.4-1.4 in order to better understand the range of physical conditions present in the interstellar and halo gas associated with intermediate redshift galaxies. Mg II and Fe II absorption profiles were observed at a resolution of 6 km s-1 with HIRES/Keck. Lyα and C IV data were measured in FOS spectra obtained from the Hubble Space Telescope archive (resolution 230 km s-1). We perform a multivariate analysis of Wr(Mg II), Wr(Fe II), Wr(C IV), and Wr(Lyα) (rest-frame equivalent widths) and the Mg II kinematic spread. There is a large range of high- to low-ionization properties and kinematics in intermediate-redshift absorbers, that we find can be organized into five categories: classic, C IV-deficient, single/weak, double, and damped Lyα/H I-rich. These categories arise, in part, because there is a strong connection between low-ionization kinematics and the location of an absorber on the Wr(C IV)-Wr(Mg II) plane. Using photoionization modeling, we infer that in most absorbers a significant fraction of the C IV arises in a phase separate from that giving rise to the Mg II. We show that many of the C IV profiles are resolved in the FOS spectra because of the velocity structure in the C IV gas. For 16 systems, the galaxy MK, MB, B-K, and impact parameters are measured. We compare the available absorption-line properties (taken from Paper I) to the galaxy properties but find no significant (greater than 3 σ) correlations, although several suggestive trends are apparent. We compare the locations of our intermediate redshift absorbers on the Wr(C IV)-Wr(Mg II) plane with those of lower and higher redshift data taken from the literature and find evidence for evolution that is connected with the Mg II kinematics seen in HIRES/Keck profiles of Mg II at z > 1.4. We discuss the potential of using the above categorizations of absorbers to understand the evolution in the underlying physical processes giving rise to the gas and governing its ionization phases and kinematics. We also discuss how the observed absorbing gas evolution has interesting parallels with scenarios of galaxy evolution in which mergers and the accretion of protogalactic clumps govern the gas physics and provide reservoirs for elevated star formation rates at high redshift. At intermediate and lower redshifts, the galaxy gaseous components and star formation rates may become interdependent and self-regulatory such that, at z ≤ 1, the kinematics and balance of high- and low-ionization gas may be related to the presence of star-forming regions in the host galaxy.

Low and high ionization absorption properties of mg II absorption-selected galaxies at intermediate redshifts. I. general properties

We present extensive metal-line absorption properties for 45 absorption systems that were selected by their Mg II absorption at redshifts between 0.4 and 1.4. For each system the properties of several chemical species are determined, including a wide range of ionization conditions. In the optical, the absorption systems have been observed at ~6 km s-1 resolution with HIRES/Keck, which covered Mg II, several Fe II transitions, Mg I, and in some cases (depending upon redshift) Ca II, Ti II, Mn II, and Al III. Ultraviolet, lower resolution (~230 km s-1) Faint Object Spectrograph data (1600-3275 ?) were obtained from the Hubble Space Telescope archive. These spectra covered Al II, Al III, Si II, Si III, Si IV, C II, C III, C IV, N V, O VI, and several Lyman series transitions, with coverage dependent upon the absorption system redshift. From these data, we infer that Mg II-absorbing galaxies at intermediate redshifts have multiphase gaseous structures.

Detection of Circular Polarization in M81

We report the detection of circular polarization in the compact radio jet of the nearby spiral galaxy M81 (M81*). The observations were made with the Very Large Array at 4.8 and 8.4 GHz, and circular polarization was detected at both frequencies. We estimate a value of mc = 0.54% ± 0.06% ± 0.07% at 8.4 GHz and mc = 0.27% ± 0.06% ± 0.07% at 4.8 GHz for the fractional circular polarization. The errors are separated into statistical and systematic terms. The spectrum of the circular polarization is possibly inverted, which would be unusual for active galactic nuclei. We also detected no linear polarization in M81* at a level of 0.1%, implying that the source has a very high circular-to-linear polarization ratio as found so far only in Sagittarius A*, the central radio source in our Galaxy. This further supports the idea that M81* is a scaled-up version of Sgr A* and suggests that the polarization properties are intrinsic to the two sources and are not caused by a foreground screen in the Galaxy.

A Radio Survey for Linear and Circular Polarization in Low-Luminosity Active Galactic Nuclei

We conducted a Very Large Array survey of 11 low-luminosity active galactic nuclei (LLAGNs) for linear and circular polarization at 8.4 GHz. We detected circular polarization in one source (M81*) and linear polarization in three sources. Sensitivity limits were ~0.1% for both modes of polarization in nine of 11 sources. The detections confirm the importance of nonthermal emission in LLAGNs. However, detection rates for circular and linear polarization are lower for these sources than for more powerful AGNs. Fractional linear polarization in detected sources is also lower than in more powerful AGNs. The weak linear polarization in the survey sources indicates their overall similarity to Sgr A*. Confusion with thermal sources, depolarization, and weaker, less extended jets may contribute to these differences. We detect a rotation measure 7 × 104 rad m-2 for NGC 4579. This may arise from magnetized plasma in the accretion, outflow, or interstellar regions. Inverted spectra are present in both M81* and Sgr A* and absent from all sources in which circular polarization is not detected. This suggests that optical depth effects are important in the creation of circular polarization.

The C [CLC][CSC]iv[/CSC][/CLC] Absorption–M[CLC]g[/CLC] [CLC][CSC]ii[/CSC][/CLC] Kinematics Connection in 〈[CLC][ITAL]z[/ITAL][/CLC]〉 ∼ 0.7 Galaxies

We have examined Faint Object Spectrograph data from the Hubble Space Telescope Archive for CIV 1548,1550 absorption associated with 40 MgII 2796,2803 absorption-selected galaxies at 0.4 color; if further data corroborate this trend, in view of the strong CIV-MgII kinematics correlation, it could imply a connection between stellar populations, star formation episodes, and the kinematics and ionization conditions of halo gas at z~1.

The C IV Absorption-Mg II Kinematics Connection in ⟨z⟩ ~ 0.7 Galaxies

We have examined Faint Object Spectrograph data from the Hubble Space Telescope Archive for CIV 1548,1550 absorption associated with 40 MgII 2796,2803 absorption-selected galaxies at 0.4 color; if further data corroborate this trend, in view of the strong CIV-MgII kinematics correlation, it could imply a connection between stellar populations, star formation episodes, and the kinematics and ionization conditions of halo gas at z~1.