A. Humphrey

VIMOS-VLT spectroscopy of the giant Lyα nebulae associated with three z ∼ 2.5 radio galaxies

The morphological and spectroscopic properties of the giant (>60 kpc) Lyα nebulae associated with three radio galaxies at z ∼ 2.5 (MRC 1558‐003, 2025‐218 and 0140‐257) have been investigated using integral field spectroscopic data obtained with the Visible Multi-Object Spectrograph (VIMOS) on VLT. The morphologies are varied. The nebula of one source has a centrally peaked, rounded appearance. In the other two objects, it consists of two spatial components. The three nebulae are aligned with the radio axis within � 30 ◦ . The total Lyα luminosities are in the range (0.3‐3.4) × 10 44 erg s −1 . The Lyα spectral profile shows strong variation through the nebulae, with full width at half-maximum (FWHM) values in the range ∼400‐1500 km s −1 and velocity shifts Voffset ∼ 120‐600 km s −1 . We present an infall model that can successfully explain the morphology, size, surface brightness distribution and the velocity field of the Lyα nebula associated with MRC 1558‐ 003. It can also explain why Lyα is redshifted relative to other emission lines and the FWHM values of the non-resonant He II line. This adds further support to our previous conclusion that the quiescent giant nebulae associated with this and other high-redshift powerful radio galaxies are in infall. A problem for this model is the difficulty to reproduce the large Lyα FWHM values, which might be the consequence of a different mechanism. We have discovered a giant (∼85 kpc) Lyα nebula associated with the radio galaxy MRC 0140‐257 at z = 2.64. It shows strikingly relaxed kinematics (FWHM < 300 km s −1 and Voffset � 120 km s −1 ), unique among high-z (� 2) radio galaxies.

Jet–gas interactions in z∼ 2.5 radio galaxies: evolution of the ultraviolet line and continuum emission with radio morphology

We present an investigation into the nature of the jet‐gas interactions in a sample of 10 radio galaxies at 2.3 < z < 2.9 using deep spectroscopy of the ultraviolet (UV) line and continuum emission obtained at Keck II and the Very Large Telescope. Kinematically perturbed gas, which we have shown to be within the radio structure in previous publications, is always blueshifted with respect to the kinematically quiescent gas, is usually spatially extended, and is usually detected on both sides of the nucleus. In the three objects from this sample for which we are able to measure line ratios for both the perturbed and quiescent gases, we suggest that the former has a lower ionization state than the latter. We propose that the perturbed gas is part of a jet-induced outflow, with dust obscuring the outflowing gas that lies on the far side of the object. The spatial extent of the blueshifted perturbed gas, typically ∼35 kpc, implies that the dust is spatially extended at least on similar spatial scales. We also find interesting interrelationships between UV line, UV continuum and radio continuum properties of this sample.

Interactions, star formation and extended nebulae in SDSS type 2 quasars at 0.3 ≤ z ≤ 0.6*

We present long-slit spectroscopy and imaging data obtained with FORS2 on the Very Large Telescope of 13 optically selected type 2 quasars at z �0.3-0.6 from the original sample of Zakamska et al. (2003). The sample is likely to be affected by different selection biases. We investigate the evidence for: a) mergers/interactions b) star formation activity in the neighborhood of the quasars and c) extended emission line regions and their nature. Evidence for mergers/interactions is found in 5/13 objects. This is a lower limit for our sample, given the shallowness of most of our continuum images. Although AGN photoionization cannot be totally discarded, line ratios consistent with stellar photoionization are found in general in companion galaxies/knots/nuclei near these same objects. On the contrary, the gas in the neighborhood of the quasar nucleus shows line ratios inconsistent with HII galaxies and typical of AGN photoionized nebulae. A natural scenario to explain the observations is that star formation is ongoing in companion galaxies/knots/nuclei, possibly triggered by the interactions. These systems are, therefore, composite in their emission line properties showing a combination of AGN and star formation features. Extended emission line regions (EELRs) have been found in 7/13 objects, although this fraction might be higher if a complete spatial coverage around the quasars was performed. The sizes vary between few and up to 64 kpc. In general, the EELRs apparently consist of an extended nebula associated with the quasar. In at least one case the EELR is associated with ionized tidal features.

VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter

We present long-slit spectroscopy, continuum and [OIII]�5007 imaging data obtained with the Very Large Telescope and the Gran Telescopio Canarias of the type 2 quasar SDSS J0123+00 at z =0.399. The quasar lies in a complex, gas-rich environment. It appears to be physically connected by a tidal bridge to another galaxy at a projected distance of �100 kpc, which suggests this is an interacting system. Ionized gas is detected to a distance of at least �133 kpc from the nucleus. The nebula has a total extension of �180 kpc. This is one of the largest ionized nebulae ever detected associated with an active galaxy. Based on the environmental properties, we propose that the origin of the nebula is tidal debris from a galactic encounter, which could as well be the triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that giant, luminous ionized nebulae can exist associated with type 2 quasars of low radio luminosities, contrary to expectations based on type 1 quasar studies.

Emission‐line activity in type 2 quasars from the Sloan Digital Sky Survey

We have compared the optical emission line ratios of type 2 quasars from Zakamska et al. with standard AGN photoionization model predictions, Seyfert 2s, HII galaxies, and narrow line FRII radio galaxies. Moderate to high ionization narrow line radio galaxies and Seyfert 2s are indistinguishable from type 2 quasars based on their optical line ratios. The standard AGN photoionization models, widely discussed for other type 2 AGNs, can reproduce successfully the loci and trends of type 2 quasars in some of the main diagnostic diagrams. These models are not exempt of problems and the discrepancies with the data are the same encountered for other type 2 AGNs. As for these, realistic models must take into account a range of cloud properties, as widely demonstrated in the literature. The Zakamska et al. sample is strongly biased towards objects with high line luminosities (L[OIII]>10 42 erg s 1 ). We have found that stellar photoionization is obvious in a fraction of objects (3 out of 50) which are characterized by low [OIII] luminosities compared with most type 2 quasars in the sample. We suggest that if the sample were expanded towards lower line luminosities (�10 40 42 erg s 1 ) stellar photoionization might be evident much more frequently. We explore an alternative scenario to pure AGN photoionization in which a varying contribution of stellar ionized gas contributes to the line flux es. Although the models presented here are rather simplistic and not strong quantitative resu lts can be extracted regarding the relative contribution of stellar vs. AGN photoionization, our results suggest that adding a varying contribution of stellar photoionized gas works in the right direction to solve most of the problems affecting the standard AGN photoionization models. The “temperature problem”, on the other hand remains.

Energy Distribution of Individual Quasars from Far-Ultraviolet to X-Rays. I. Intrinsic Ultraviolet Hardness and Dust Opacities

Using Chandra and HST archival data, we have studied the individual SED of 11 quasars at redshifts 0.3 < z < 1.8. All UV spectra show a spectral break around 1100 ?. Five X-ray spectra showed the presence of a soft excess, and seven spectra showed an intrinsic absorption. We found that for most quasars a simple extrapolation of the far-UV power law into the X-ray domain generally lies below the X-ray data and that the big blue bump and the soft X-ray excess do not share a common physical origin. We explore the issue of whether the observed SED might be dust absorbed in the far- and near-UV. We fit the UV break, assuming a power law that is absorbed by cubic nanodiamond dust grains. We then explore the possibility of a universal SED (with a unique spectral index) by including further absorption from SMC-like extinction. Using this approach, satisfactory fits to the spectra can be obtained. The hydrogen column densities required by either nanodiamonds or amorphous dust models are all consistent, except for one object, with the columns deduced by our X-ray analysis, provided that the C depletion is ~0.6. Because dust absorption implies a flux recovery in the EUV (<700 ?), our modeling opens the possibility that the intrinsic quasar SED is much harder and more luminous in the EUV than inferred from the near-UV data, as required by photoionization models of the broad emission line region. We conclude that the intrinsic UV SED must undergo a sharp turnover before the X-ray domain.

Spatially extended absorption around the z= 2.63 radio galaxy MRC 2025−218: outflow or infall?

We present an investigation into the absorber in front of the z = 2.63 radio galaxy MRC 2025−218, using integral field spectroscopy obtained at the Very Large Telescope, and longslit spectroscopy obtained at the Keck II telescope. The properties of MRC 2025−218 are particularly conducive to study the nature of the absorbing gas, i.e. this galaxy shows bright and spatially extended Lyα emission, along with bright continuum emission from the active nucleus. Lyα absorption is detected across ∼40 × 30 kpc 2 , has a covering factor of ∼1, and shows remarkably little variation in its properties across its entire spatial extent. This absorber is kinematically detached from the extended emission line region (EELR). Its properties suggest that the absorber is outside of the EELR. We derive lower limits to the H I ,H II and H column densities for this absorber of 3 × 10 16 ,7 × 10 17 and 2 × 10 18 cm −2 , respectively. Moreover, the relatively bright emission from the active nucleus has allowed us to measure a number of metal absorption lines: C I ,C II ,C IV ,N V ,O I ,S iII ,S iIV ,A lII and Al III. The column density ratios are most naturally explained using photoionization by a hard continuum, with an ionization parameter U ∼ 0.0005–0.005. Shocks or photoionization by young stars cannot reproduce satisfactorily the measured column ratios. Using the ratio between the Si II ∗ and Si II column densities, we derive a lower limit of ≥10 cm −3 for the electron density of the absorber. The data do not allow useful constraints to be placed on the metallicity of the absorber. We consider two possibilities for the nature of this absorber: the cosmological infall of gas, and an outflow driven by supernovae or the radio jets. We find it plausible that the absorber around 2025−218 is in outflow. We also find good agreement between the observed properties of the H I absorber and the properties of the H I absorption expected from the cosmological infall model of Barkana & Loeb.

Interactions, star formation and extended nebulae in SDSS type 2 quasars at ★: VLT-FORS2 observations of SDSS type 2 quasars

We present long-slit spectroscopy and imaging data obtained with FORS2 on the Very Large Telescope of 13 optically selected type 2 quasars at z �0.3-0.6 from the original sample of Zakamska et al. (2003). The sample is likely to be affected by different selection biases. We investigate the evidence for: a) mergers/interactions b) star formation activity in the neighborhood of the quasars and c) extended emission line regions and their nature. Evidence for mergers/interactions is found in 5/13 objects. This is a lower limit for our sample, given the shallowness of most of our continuum images. Although AGN photoionization cannot be totally discarded, line ratios consistent with stellar photoionization are found in general in companion galaxies/knots/nuclei near these same objects. On the contrary, the gas in the neighborhood of the quasar nucleus shows line ratios inconsistent with HII galaxies and typical of AGN photoionized nebulae. A natural scenario to explain the observations is that star formation is ongoing in companion galaxies/knots/nuclei, possibly triggered by the interactions. These systems are, therefore, composite in their emission line properties showing a combination of AGN and star formation features. Extended emission line regions (EELRs) have been found in 7/13 objects, although this fraction might be higher if a complete spatial coverage around the quasars was performed. The sizes vary between few and up to 64 kpc. In general, the EELRs apparently consist of an extended nebula associated with the quasar. In at least one case the EELR is associated with ionized tidal features.

Giant quiescent haloes associated with high redshift radio galaxies

Abstract We present a summary of the results from the kinematic study of the extended gas in a sample of 10 high redshift radio galaxies (z∼2.5) based on high S/N Keck spectroscopy. We find that, in addition to the typical high surface brightness kinematically perturbed regions, giant low surface brightness quiescent haloes are detected in all objects. We suggest that we have resolved kinematically the emission from ambient non-shocked gas (the quiescent haloes) and the emission from (jet induced) shocked gas. The haloes often extend for more than 100 kpc and sometimes beyond the radio structures. The quasar continuum is the dominant source for the ionization of this very extended gas. The kinematic properties are consistent with gravitational motions and are similar to those seen in low redshift radio galaxies. They are enriched with heavy elements at tens of kpc from the active nucleus. The discovery of the giant quiescent haloes in all objects suggests that they are a common ingredient of high redshift radio galaxies. Although the nature of the haloes—be they disks, spherical envelopes or cooling flow nebulae—is not clear, they are giant gaseous reservoirs within which the radio galaxy is embedded. The giant elliptical galaxy might have grown (or still be growing) from the giant halo.

UV and optical emission lines from the z∼ 2.6 radio galaxy 0828+193: spatially resolved measurements

We present an investigation into the spatial variation of the rest-frame ultraviolet (UV) and optical line and continuum emission along the radio axis of the z ∼ 2.6 radio galaxy 0828+193, using long-slit spectra from the Keck II and Subaru telescopes. Line brightnesses, line ratios and electron temperatures are examined, and their relationship with the arm-length asymmetry of the radio source is also investigated. We find that on the side of the nucleus with the shortest radio lobe, the gas covering factor is higher, and the ionization parameter is lower. The contrasts in environmental density required to explain the asymmetries in the line brightness and the radio arm-length asymmetries are in fair agreement with each other. These results add further weight to the conclusion of McCarthy, van Breugel & Kapahi ‐ lobe distance asymmetries in powerful radio sources are the result of an asymmetry in the environmental density. We also note that the brightness of both the UV and optical continuum emission shows a similar spatial asymmetry to that shown by the line emission. While the UV continuum asymmetry can be wholly explained by the expected asymmetry in the nebular continuum, the optical continuum asymmetry cannot. We argue that, at least at optical wavelengths, the starlight and/or the scattered light must also be strongly spatially asymmetric.