Exploring the line-of-sight environment to a quasar with Gemini/GMOS.

1. Exploring the line-of-sight environment to a quasar with Gemini/GMOS. Matthew Whiting (UNSW) Rachel Webster (U. Melbourne) Paul Francis (ANU)

2. PKS 2126-158 • Very luminous flat-spectrum radio quasar at redshift of 3.2663. • MV=-29.8, L5GHz= 2.5x1028 W/Hz, L1keV=1039 W • Optical SED dominated by blue power law up to the Ly-a emission line. • Spectrum shows many Ly-a and metal-line absorption systems at redshifts from 2.3941 – 3.2165, as well as one at z~0.6631: • zabs = 0.66247, 0.66282, 0.66344, 0.66374, with MgII, MgI and CaII components. A quasar's line-of-sight environment with Gemini/GMOS

3. z = 0.21 Surrounding field of 2126-158 • Quasar is surrounded by a collection of objects, typical colours of R-K>3.5 • Colours from short exposure images of Francis et al. (2000), taken with ANU 2.3m telescope • Only one had a known redshift (Veron et al. 1990), with bluer colours than the rest of the nearby objects. • What/Where are they? • Is lensing important? • Are they associated with any of the absorption systems? K band image from IRIS, AAT A quasar's line-of-sight environment with Gemini/GMOS

4. GMOS observations • Pre-imaging done in i’ band – 20 minute exposure. • Use GMOS on Gemini South in MOS mode. Slits placed on objects pre-identified from near-IR images and pre-imaging. • Grating R150, filter GG455, 0.75 arcsec slits. • Total of 2 hours exposure time over two nights. • Not all nearby sources could have slit placed on them, as we only had time for one mask setting. Got around this problem by placing multiple objects in slits. A quasar's line-of-sight environment with Gemini/GMOS

5. Slit positions near quasar A quasar's line-of-sight environment with Gemini/GMOS

6. Sample targets and spectra • b=170kpc • Mi’=-22 • L=4.1x1010 L • b=60kpc • Mi’=-22.2 • L=4.8x1010 L • b=160kpc • Mi’=-21.6 • L=2.7x1010 L

7. Positions and redshifts A quasar's line-of-sight environment with Gemini/GMOS

8. 2126-158: is lensing important? • 2126-158 is a very luminous quasar – is this luminosity intrinsic, or is it being magnified? • No multiple images, but single-image magnification is possible – are we seeing it here? • Is the amount of matter along the line of sight sufficient to greatly magnify the quasar flux? • Our observations show that there is no large cluster in front of the quasar, but rather several smaller groups at different redshifts. Hard to tell if there is strong magnification present from current data. • Statistical properties of high-z radio quasars may be more useful in determining importance of lensing • ie. are most high-z quasars surrounded by groups of galaxies? A quasar's line-of-sight environment with Gemini/GMOS

9.      ?   ?    ? Association with absorbing system • We find at least 5 (possibly 7) confirmed galaxies at z~0.664 close to the quasar (within ~170 kpc), with a few further away. • The nearest galaxy is 50kpc from the quasar line-of-sight. Possibly an interacting system? (Very close in redshift and spatial directions.) • There may be closer galaxies in the same system, based on their colours, but these have unknown redshifts. One may be a star, rather than a galaxy. Q A quasar's line-of-sight environment with Gemini/GMOS

10. Origin of absorbing gas • Absorber has metal-bearing gas, with column densities up to 1017 cm-2 in MgII. Where is the gas located? • Could originate in outer halo of nearby galaxy. Nearest confirmed galaxy is 50kpc from line-of-sight, so quasar is likely to be still in the halo. • This displacement is comparable to that seen with other galaxies associated with MgII absorbers. Redshift slightly different though. • Closest possible galaxy is ~20kpc, but is fainter (hence smaller). • Could originate in stripped gas, that may result from tidal stripping. • From formation of large ellipticals in a group environment? • Due to interaction between two large galaxies? • Other observations, such as HI absorption or emission, would be useful to constrain these models. A quasar's line-of-sight environment with Gemini/GMOS

11. Possible interacting system • Possible interaction? Velocity difference of ~500 km/s, which seems large for an interaction within a group. • An interaction could lead to extra gas being ejected from galaxies, increasing the column density towards the quasar. • No sign of strong interaction in either spectrum, eg star formation tracers. Unclear from isophotes if there is any surrounding envelope. A quasar's line-of-sight environment with Gemini/GMOS

12. Summary • We used GMOS-South to measure redshifts of many red galaxies around PKS 2126-158. • We find a group of galaxies close to the line-of-sight to the quasar at the same redshift as a metal-line absorption system in the quasar spectrum. • Still unclear as to origin of absorbing gas. • We also find several other lower-redshift features in redshift-space in the field surrounding the quasar. • The relatively dense line-of-sight may help magnify the quasar flux, without multiple lensing, partly accounting for its high apparent luminosity. A quasar's line-of-sight environment with Gemini/GMOS