HAQ 2225+0527
The red quasar HAQ2225+0527 (z = 2.33) observed with the ALFOSC instrument at the NOT in August 2014. The top panel shows with a black, solid line the grism 4 spectrum (R=400 covering the full optical range from 3700 Å to 9000 Å, 1200 sec exposure time) together with the SDSS and UKIDSS photometry (shown with red points). There is a damped Lyα absorber (DLA) at z = 2.13 in the blue end of the spectrum. The dashed, blue curve shows a normal quasar spectrum (a composite) and the red curve shows a reddened quasar composite spectrum assuming an SMC-like extinction with AV = 0.42 at the redshift of the foreground DLA. When we saw that this was a good candidate for a quasar reddened by a foreground DLA we secured further spectroscopy with grism 6 (R = 980, covering the UV region and up to about 5500 Å, 9000 sec exposure time) to measure the Hydrogen column density (the red line in the lower left panel shows a DLA fit with a column density of 5.2 x 1020 cm-2) and with grism 17 (R=5750, covering about 500 Å around Hα, 9000 sec exposure time) to measure the column density of Zn II [marked with a solid, vertical line in the lower right panel]. The metallicity measured from Zn II appears to be slightly larger than solar metallicity (but the error bar is substantial due to the low S/N of the NOT data, about 0.3 dex). The position of transitions from the strongly refractory element Cr are marked with dotted vertical lines. From the absence of Cr II lines we infer very strong depletion, ([Zn/Cr] ≳ 1.7). Furthermore, the system contains cold gas (strong C I absorption is detected in the grism 6 spectrum) which, based on our previous observations of C I absorbers, implies that it almost certainly will show molecular Hydrogen and possibly CO molecular absorption.
This quasar was subsequently observed with the intermediate resolution spectrograph X-Shooter at the Very Large Telescope (VLT) in Chile. The spectrum covers the wavelength range from 3200 to 25000 Å and allowed us to carry out a more detailed analysis of the dust reddening (see figure below). We were further able to model the physical conditions in the cloud using absorption lines from C I and its fine-structure transitions. This fine-structure analysis shows that the absorbing cloud giving rise to C I lines is very compact (less than 1 pc) and covers only part of the background quasar emission region. The details are presented by Krogager et al. (2016).
The observed X-shooter spectrum in black has been smoothed and the strong telluric absorption bands in the near-infrared have been masked out for visual clarity. The yellow squares marks the photometry from SDSS (u, g, r, i, z), UKIDSS (Y, J, H, K), and WISE (W1). The blue solid line shows the unreddened intrinsic quasar template. The red line shows the best-fit dust-reddened model including variations from iron emission lines. The dark blue dashed line shows the best-fit model without iron line variations included.
Created by Jens-Kristian Krogager
Dark Cosmology Centre, Copenhagen University
&
ESO, Santiago, Chile