Environments of strong / ultrastrong, ultraviolet Fe II emitting quasars
Monthly Notices of the Royal Astronomical Society (2013), 433, 2467.
Environments of strong / ultrastrong, ultraviolet FeII emitting quasars
Roger G. Clowes1, Srinivasan Raghunathan2, Ilona K. Söchting3, Matthew J. Graham4, Luis E. Campusano2
1 Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
2 Observatorio Astronómico Cerro Calán, Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
3 Astrophysics, Denys Wilkinson Building, Keble Road, University of Oxford, Oxford OX1 3RH, UK
4 California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
UV FeII emission is stronger in LQG quasars. Quasars in LQGs in general, and including the Huge-LQG (Clowes et al. 2013a), have recently been discovered to have statistically stronger UV FeII emission, with the strongest FeII emitters – the ultrastrong emitters – also showing evidence for a preferred nearest-neighbour scale to other quasars (Clowes et al. 2013b; Harris et al. 2012; Harris 2011). We use the Weymann et al. (1991) W2400 equivalent width, defined between the rest-frame continuum windows 2240-2255 and 2665-2695 Å, as the measure of the UV FeII emission. We find a significant shift of the W2400 distribution to higher values for quasars within LQGs, predominantly for those LQGs with 1.1 ≤ <zLQG> ≤ 1.5. There is a tentative indication that the shift to higher values increases with the quasar i magnitude. We find evidence that within LQGs the ultrastrong emitters with W2400 ≥ 45 Å (more precisely, ultrastrong-plus with W2400 ≥ 44 Å) have preferred nearest-neighbour separations of ∼ 30-50 Mpc to the adjacent quasar of any W2400 strength. No such effect is seen for the ultrastrong emitters that are not in LQGs. The possibilities for increasing the strength of the FeII emission appear to be iron abundance, Lyα fluorescence and microturbulence, and probably all of these operate. The dense environment of the LQGs may have led to an increased rate of star formation and an enhanced abundance of iron in the nuclei of galaxies. Similarly, the dense environment may have led to more active blackholes and increased Lyα fluorescence. The preferred nearest-neighbour separation for the stronger emitters would appear to suggest a dynamical component, such as microturbulence.
Figure 1. MMT / Hectospec spectrum (rest-frame) of an ultrastrong UV FeII emitting quasar. Note the FeII emission between ~ 2255-2650 Å.
Figure 2. The distribution of the rest-frame equivalent width, W2400, is shown for the 75 LQGs with 1.1 ≤ <zLQG> ≤ 1.5 as the solid blue histogram (1778 quasars). The distribution for the matched control sample (matched in i magnitude and redshift) is shown as the hatched red histogram (1778 quasars). Both are density histograms. Both are for i ≤ 19.1 and 1.0 ≤ z ≤ 1.8, with the condition 1.1 ≤ <zLQG> ≤ 1.5 applied to the LQGs. The bin size is 5 Å.
The shift to higher W2400 appears to be strongly concentrated in the 75 LQGs having 1.1 ≤ <zLQG> ≤ 1.5 (one-sided Mann-Whitney p-value = 0.0042, shift = 0.97 Å), and it appears to be a stronger effect at fainter magnitudes 18.0 ≤ i ≤ 19.1 (p-value = 0.00054, shift = 1.31 Å).
Figure 3. The distribution of the nearest-neighbour separations (present epoch) for the members of the 75 LQGs with 1.1 ≤ <zLQG> ≤ 1.5 and for W2400 ≥ 44 Å (post-hoc adjustment) is shown as the solid blue histogram (160 quasars), with mean 57.40 ± 1.60 Mpc. The distribution for the members of the LQGs with W2400 < 30 Å is shown as the hatched red histogram (1152 quasars), with mean 59.65 ± 0.63 Mpc. Both are density histograms. Both are for i ≤ 19.1 and 1.0 ≤ z ≤ 1.8. The bin size is 5 Mpc. Note that the LQG finding algorithm restricts separations to ≤100 Mpc.
Note the apparent preference of the W2400 ≥ 44 Å quasars for separations in the range 30-50 Mpc (one-sided Kolmogorov-Smirnov p-value = 0.0197).
Figure 4. Visualisation of the location of the seven ultrastrong-plus emitters (W2400 ≥ 44 Å) within the Huge-LQG (Clowes et al. 2013a). The Huge-LQG has 73 members: 66 of the members are represented by blue spheres of radius that corresponds to 33 Mpc (present epoch). The seven ultrastrong-plus quasars are represented by slightly larger red spheres of radius that corresponds to 40 Mpc. The long dimension of the surrounding box corresponds to approximately 1000 Mpc. Six of the seven strongest emitters very obviously form three pairings within the total of 73 members.
This work has used the SDSS DR7QSO catalogue (Schneider et al. 2010) and the SDSS spectra.
Clowes R.G., Harris K.A., Raghunathan S., Campusano L.E., Söchting I.K., Graham M.J., 2013a, MNRAS, 429, 2910
Clowes R.G., Raghunathan S., Söchting I.K., Graham M.J., Campusano L.E., 2013b, MNRAS, 433, 2467
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