The Non-Uniform Nature of the Chemical Composition and Physical Properties of CGM Environments

Joseph Ribaudo1, Brittany Vanderhoof2, Nicolas Lehner3, & J. Christopher Howk3 1Utica College, 2Rochester Institute of Technology, 3University of Notre Dame

HE0439+5254   Comp.  I   Comp.  II   Comp.  III  Velocity  (km/s)   -­‐100   0   +140  log  U   [-­‐2.56,-­‐2.18]   -­‐2.66   [-­‐2.64,-­‐2.62]  [X/H]   [-­‐0.10,+0.30]   -­‐0.30   -­‐0.60  [C/O]   -­‐0.15   0.0   -­‐0.6  Temperature  (kK)   [5.0,10.1]   11.2   14.4  Size  (kpc)   [0.01,0.08]   0.86   0.40  

Abstract: We present a detailed investigation of CGM environments through the analysis of three Lyman‐limit Systems, identified in HST/COS QSO spectra, that show extended multi‐component absorption structure. In each of the three absorption systems, we are unable to model the individual absorbing components with either uniform metallicity or ionization conditions. Rather, the non‐uniform nature of the chemical composition and physical properties of these multi‐component absorbers highlights the dynamic and complex nature of the CGM, providing insight into the processes driving the circulation of gas throughout the CGM. In each of these CGM environments, individual components are found to be consistent with infalling metal‐poor gas, outflowing or recycled metal‐enriched gas, and in one case, potentially a mixture of the two.

Figure 1: An example of the final output from the Voigt-profile, multi-component fitting routine used to estimate column density, b-value, and velocity centroid for each ion detected in our study. Shown is the final fit for HI detected along the SBS1122+594 sightline, the fit derived from fitting all transitions shown in the panel. Similar fits were performed on all ions/transitions detected in each of the three sightlines. For HI, the inclusion of the shorter wavelength transitions of the Lyman-series in the fitting routine allow for constraints on the HI column density that are typically diff icult to achieve due to saturation in lines such as Lyα or Lyβ. Using the column densities derived from the fitting routine, we modeled each component using the photoionization code, Cloudy (Ferland   et   al.   2013).   The  physical   condiOons   and   chemical  properOes   of   each   absorpOon  component   are   shown   in   Tables   1,  2,  &  3  in  the  next  panels.

Panels 2, 3, & 4: Each panel contains a stack of plots showing cut-outs of spectra for each ion/transition probed with the HST/COS QSO data for sightlines SBS1122+594, HE0439+5254, and J1619+3342 from Lehner et al. (2013). The shaded vertical bars correspond to the individual absorption components analyzed with the multi-component Voigt-profile fitting routine and modeled with Cloudy (color indicating consistency with other components). The individual component models are shown in the middle of the panel, with the model output consistent with the column densities measured from the profile fitting shown with the filled in circles. The physical conditions and chemical properties of the absorbers determined from the models are listed in the Tables below the plots.  

J1619+3342   Comp.  I   Comp.  II  Velocity  (km/s)   0   +130  log  U   [-­‐2.92,-­‐2.80]   [-­‐2.92,-­‐2.68]  [X/H]   [-­‐1.60,-­‐1.50]   [-­‐0.60,-­‐0.20]  [C/O]   -­‐0.3   -­‐0.1  Temperature  (kK)   [12.5,13.8]   [9.4,14.0]  Size  (kpc)   [1.6,2.0]   [0.02,0.07]  

SBS1122+594   Comp.  I   Comp.  II   Comp.  III  Velocity  (km/s)   -­‐125   0   +60  log  U   [-­‐2.40,-­‐2.36]   [-­‐3.16,-­‐3.08]   -­‐3.00  [X/H]   [-­‐0.40,-­‐0.30]   [-­‐1.10,-­‐1.00]   -­‐1.10  [C/O]   0.0   -­‐0.7   -­‐0.6  Temperature  (kK)   [12.5,13.8]   [14.2,14.9]   15.2  Size  (kpc)   [1.6,2.0]   [0.10,0.15]   0.13  

Analysis: HE0439+5254 – three absorption components with distinct physical and chemical properties. Comp. I with properties consistent with near solar gas, Comp. III with properties consistent with metal-poor gas, and Comp. II with possibly the mixture of the former two components. J1619+3342 – two components with distinct physical and chemical properties. Comp. I with properties consistent with extremely metal-poor gas and Comp. II with properties consistent with slightly sub-solar gas. SBS1122+594 – three components, consistent with two distinct physical and chemical properties. Comp. I with properties consistent with slightly sub-solar gas and Comps. II and III consistent with metal-poor gas.  

Concluding Remarks: Through our detailed analysis we have identified evidence of multiple absorbing structures within the same CGM environment, but with distinct physical conditions and chemical properties – suggesting we are detecting gas being driven by several different physical processes and originating from disparate cosmic environments. It is not yet clear if these complex CGM systems are rare or representative of a large portion of CGM environments. However, these systems at z ~ 0.5 share similar characteristics with the high-velocity clouds identified in the halo of the Milky Way and other galaxy environments in the local universe and provide insight into the dynamic and complex gas flows throughout the CGM over a significant fraction of cosmic time.  

References: Lehner et al. 2013, ApJ, 770, 138 Ferland et al. 2013, RMxAA, 49, 137 Table 1: Physical conditions and chemical properties of HE0439+5254.  

Table 2: Physical conditions and chemical properties of J1619+3342.  

Table 3: Physical conditions and chemical properties of SBS1122+594.