Morphological properties of z∼ 0.5 absorption-selected galaxies: the role of galaxy inclination

Abstract

We have used Galaxy IMage 2D (GIM2D) to quantify the morphological properties of 40 intermediate‐redshift Mg ii absorption‐selected galaxies [0.03 ≤ Wr(2796) ≤ 2.9 Å], imaged with WFPC‐2/Hubble Space Telescope (HST), and compared them to the halo gas properties measured from HIRES/Keck and UVES/VLT quasar spectra. We find that as the quasar–galaxy separation, D, increases the Mg ii equivalent decreases with large scatter, implying that D is not the only physical parameter affecting the distribution and quantity of halo gas. Our main result shows that inclination correlates with Mg ii absorption properties after normalizing out the relationship (and scatter) between the absorption properties and D. We find a 4.3σ correlation between Wr(2796) and galaxy inclination, normalized by impact parameter, i/D. Other measures of absorption optical depth also correlate with i/D at greater than 3.2σ significance. Overall, this result suggests that Mg ii gas has a co‐planer geometry, not necessarily disc‐like, that is coupled to the galaxy inclination. It is plausible that the absorbing gas arises from tidal streams, satellites, filaments, etc., which tend to have somewhat co‐planer distributions. This result does not support a picture in which Mg ii absorbers with Wr(2796) ≲ 1 Å are predominantly produced by star formation driven winds. We further find that: (1) Mg ii host galaxies have quantitatively similar bulge and disc scalelength distribution to field galaxies at similar redshifts and have a mean disc and bulge scalelength of 3.8 and 2.5 kpc, respectively; (2) Galaxy colour and luminosity do not correlate strongly with absorption properties, implying a lack of a connection between host galaxy star formation rates and absorption strength; and (3) parameters such as scalelengths and bulge‐to‐total ratios do not significantly correlate with the absorption parameters, suggesting that the absorption is independent of galaxy size or mass.

Nature of the absorbing gas associated with a galaxy group at z∼0.4

“…The inclination is sin i=0.87±0.01, i.e. slightly higher than the one reported by Kacprzak et al (2011) from a GIM2D modelling of HST observations (sin i=0.75±0.05). These results are collected in Table 5.…”

“…This was the first spectroscopic confirmation of a galaxy associated with a quasar absorber. Kacprzak et al (2011) used HST/WFPC2 F702W archival data shown in Figure 3 and reported a B-band absolute magnitude MB = −20.32 and a corresponding luminosity of 0.46L * . They further studied the morphological properties of the object using GIM2D modelling (Simard et al 2002) (Pettini & Pagel 2004).…”

Unusual quasars from the Sloan Digital Sky Survey selected by means of Kohonen self-organising maps

“…One of the easiest species to detect is the Mg ii λλ2796, 2804 doublet, which is frequently in combination with Fe ii λλ2587, 2600, Fe ii λλ2374, 2382, Fe ii λ2344, and Mg i λ2853. While the origin of the absorbing gas remains unclear, a direct association with galaxies is suggested by several studies (e.g., Bahcall & Spitzer 1969;Steidel et al 1997;Bowen & Chelouche 2011;Kacprzak et al 2011). Dust embedded in foreground absorber systems along the line of sight is expected to absorb and scatter the UV photons from the quasar and redden the quasar spectrum.…”

Bimodality of low-redshift circumgalactic O vi in non-equilibrium eagle zoom simulations

“…Several HST programs have exploited this new capability to investigate the gaseous environments of a sample of low-z haloes, including COS-Halos (Tumlinson et al 2013), COS-Dwarfs (Bordoloi et al 2014), and COS-GASS (Borthakur et al 2015). Other recent studies have also characterized the CGM relative to samples of galaxies, including Chen et al (2010), Bordoloi et al (2011), Kacprzak et al (2011Kacprzak et al ( , 2015, Borthakur et al (2013), Churchill et al (2013), , Stocke et al (2013), Liang & Chen (2014) at low-z and Turner et al (2014) at high-z.…”