ALBERT

Description: In the low-redshift Universe, the most powerful radio sources are often associated with gas-rich galaxy mergers or interactions. We here present evidence for an advanced, gas-rich (‘wet’) merger associated with a powerful radio galaxy at a redshift of z  ~ 2. This radio galaxy, MRC 0152-209, is the most infrared-luminous high-redshift radio galaxy known in the Southern hemisphere. Using the Australia Telescope Compact Array, we obtained high-resolution CO(1–0) data of cold molecular gas, which we complement with Hubble Space Telescope ( HST )/ Wide Field Planetary Camera 2 ( WFPC 2) imaging and William Herschel Telescope long-slit spectroscopy. We find that, while roughly M H2  ~ 2 10 10  M of molecular gas coincides with the central host galaxy, another M H2  ~ 3 10 10  M is spread across a total extent of ~60 kpc. Most of this widespread CO(1–0) appears to follow prominent tidal features visible in the rest-frame near-UV HST / WFPC 2 imaging. Lyα emission shows an excess over He II, but a deficiency over L IR , which is likely the result of photoionization by enhanced but very obscured star formation that was triggered by the merger. In terms of feedback, the radio source is aligned with widespread CO(1–0) emission, which suggests that there is a physical link between the propagating radio jets and the presence of cold molecular gas on scales of the galaxy's halo. Its optical appearance, combined with the transformational stage at which we witness the evolution of MRC 0152-209, leads us to adopt the name ‘Dragonfly Galaxy’.

Description: Fast outflows of gas, driven by the interaction between the radio jets and interstellar medium (ISM) of the host galaxy, are being observed in an increasing number of galaxies. One such example is the nearby radio galaxy 3C 293. In this paper we present integral field unit observations taken with OASIS on the William Herschel Telescope, enabling us to map the spatial extent of the ionized gas outflows across the central regions of the galaxy. The jet-driven outflow in 3C 293 is detected along the inner radio lobes with a mass outflow rate ranging from ~0.05 to 0.17 M  yr –1 (in ionized gas) and corresponding kinetic power of ~0.5–3.5  x  10 40  erg s –1 . Investigating the kinematics of the gas surrounding the radio jets (i.e. not directly associated with the outflow), we find linewidths broader than 300 km s –1 up to 5 kpc in the radial direction from the nucleus (corresponding to 3.5 kpc in the direction perpendicular to the radio axis at maximum extent). Along the axis of the radio jet linewidths 〉400 km s –1 are detected out to 7 kpc from the nucleus and linewidths of 〉500 km s –1 at a distance of 12 kpc from the nucleus, indicating that the disturbed kinematics clearly extend well beyond the high surface brightness radio structures of the jets. This is suggestive of the cocoon structure seen in simulations of jet–ISM interaction and implies that the radio jets are capable of disturbing the gas throughout the central regions of the host galaxy in all directions.

Description: A significant minority of high-redshift radio galaxy (HzRG) candidates show extremely red broad-band colours and remain undetected in emission lines after optical ‘discovery’ spectroscopy. In this paper, we present deep GTC optical imaging and spectroscopy of one such radio galaxy, 5C 7.245, with the aim of better understanding the nature of these enigmatic objects. Our g -band image shows no significant emission coincident with the stellar emission of the host galaxy, but does reveal faint emission offset by ~3 arcsec (26 kpc) therefrom along a similar position angle to that of the radio jets, reminiscent of the ‘alignment effect’ often seen in the optically luminous HzRGs. This offset g -band source is also detected in several UV emission lines, giving it a redshift of 1.609, with emission line flux ratios inconsistent with photoionization by young stars or an AGN, but consistent with ionization by fast shocks. Based on its unusual gas geometry, we argue that in 5C 7.245 we are witnessing a rare (or rarely observed) phase in the evolution of quasar hosts when stellar mass assembly, accretion on to the back hole, and powerful feedback activity has eradicated its cold gas from the central ~20 kpc, but is still in the process of cleansing cold gas from its extended halo.

Description: We report the detection of molecular CO(1–0) gas in F00183-7111, one of the most extreme ultraluminous infrared galaxies (ULIRGs) known, with the Australia Telescope Compact Array. We measure a redshift of 0.3292 for F00183-7111 from the CO(1–0) line and estimate the mass of the molecular gas in 00183 to be 1 10 10 M . We find that F00183-7111 is predominately powered by the active galactic nucleus (AGN) and only ~14 per cent of the total luminosity is contributed by star formation (SFR ~220 M  yr –1 ). We also present an optical image of F00183-7111, which shows an extension to the east. We searched for star formation in this extension using radio continuum observations but do not detect any. This suggests that the star formation is likely to be predominately nuclear. These observations provide additional support for a model in which the radio emission from ULIRGs is powered by an intense burst of star formation and by a radio-loud AGN embedded in its nucleus, both triggered by a merger of gas-rich galaxies.

Description: We present a CO(1–0) survey for cold molecular gas in a representative sample of 13 high- z radio galaxies (HzRGs) at 1.4 〈 z 〈 2.8, using the Australia Telescope Compact Array. We detect CO(1–0) emission associated with five sources: MRC 0114-211, MRC 0152-209, MRC 0156-252, MRC 1138-262 and MRC 2048-272. The CO(1–0) luminosities are in the range $L^{\prime }_{\rm CO} \sim (5\hbox{--}9) \times 10^{10}$ K km s –1 pc 2 . For MRC 0152-209 and MRC 1138-262, part of the CO(1–0) emission coincides with the radio galaxy, while part is spread on scales of tens of kpc and likely associated with galaxy mergers. The molecular gas mass derived for these two systems is M H2  ~ 6 10 10 M ( M H2 / $L^{\prime }_{\rm CO}$  = 0.8). For the remaining three CO-detected sources, the CO(1–0) emission is located in the halo (~50-kpc) environment. These three HzRGs are among the fainter far-IR emitters in our sample, suggesting that similar reservoirs of cold molecular halo gas may have been missed in earlier studies due to pre-selection of IR-bright sources. In all three cases, the CO(1–0) is aligned along the radio axis and found beyond the brightest radio hotspot, in a region devoid of 4.5 μm emission in Spitzer imaging. The CO(1–0) profiles are broad, with velocity widths of ~1000–3600 km s –1 . We discuss several possible scenarios to explain these halo reservoirs of CO(1–0). Following these results, we complement our CO(1–0) study with detections of extended CO from the literature and find at marginal statistical significance (95 per cent level) that CO in HzRGs is preferentially aligned towards the radio jet axis. For the eight sources in which we do not detect CO(1–0), we set realistic upper limits of $L^{\prime }_{\rm CO} \sim 3\hbox{--}4 \times 10^{10}$ K km s –1 pc 2 . Our survey reveals a CO(1–0) detection rate of 38 per cent, allowing us to compare the CO(1–0) content of HzRGs with that of other types of high- z galaxies.

Description: We have identified ionized outflows in the narrow-line region of all but one Sloan Digital Sky Survey type 2 quasars (QSO2) at z 0.1 (20/21, detection rate 95 per cent), implying that this is a ubiquitous phenomenon in this object class also at the lowest z . The outflowing gas has high densities ( n e 1000 cm –3 ) and covers a region the size of a few kpc. This implies ionized outflow masses M outf  ~ (0.3–2.4) 10 6 M and mass outflow rates M〈 few M yr –1 . The triggering mechanism of the outflows is related to the nuclear activity. The QSO2 can be classified into two groups according to the behaviour and properties of the outflowing gas. QSO2 in Group 1 (5/20 objects) show the most extreme turbulence; they have on average higher radio luminosities and higher excess of radio emission. QSO2 in Group 2 (15/20 objects) show less extreme turbulence; they have lower radio luminosities and, on average, lower or no radio excess. We propose that two competing outflow mechanisms are at work: radio jets and accretion disc winds. Radio jet induced outflows are dominant in Group 1, while disc winds dominate in Group 2. We find that the radio jet mode is capable of producing more extreme outflows. To test this interpretation, we predict that (1) high resolution radio imaging will reveal the presence of jets in Group 1 QSO2; (2) the morphology of their extended ionized nebulae must be more highly collimated and kinematically perturbed.

Description: We investigate the presence of extended ionized outflows in 18 luminous type 2 AGNs (11 quasars and 7 high-luminosity Seyfert 2s) at 0.3 〈 z 〈 0.6 based on VLT-FORS2 spectroscopy. We infer typical lower limits on the radial sizes of the outflows R o several x 100 pc and upper limits R o 1–2 kpc. Our results are inconsistent with related studies which suggest that large scale ( R o ~ several-15 kpc) are ubiquitous in QSO2. We study the possible causes of discrepancy and propose that seeing smearing is the cause of the large inferred sizes. The implications in our understanding of the feedback phenomenon are important since the mass M o (through the density), mass injection $\skew3\dot{M}_{\rm o}$ and energy injection $\dot{E}_{\rm o}$ rates of the outflows become highly uncertain. One conclusion seems unavoidable: M o , $\skew3\dot{M}_{\rm o}$ and $\dot{E}_{\rm o}$ are modest or low compared with previous estimations. We obtain typically M o (0.4–22) x 10 6 M (median 1.1 x 10 6 M ) assuming n = 1000 cm –3 . These are ~10 2 –10 4 times lower than values reported in the literature. Even under the most favourable assumptions, we obtain $\skew3\dot{M}_{\rm o}\lesssim$ 10 M  yr –1 in general, 100–1000 times lower than claimed in related studies. Although the uncertainties are large, it is probable that these are lower than typical star-forming rates. In conclusion, no evidence is found supporting that typical outflows can affect the interstellar medium of the host galaxies across spatial scales 1–2 kpc.

Description: Using data obtained with the Australia Telescope Compact Array (ATCA), we have characterized the amount, spatial distribution and kinematics of the molecular gas in the merging, double-nucleus type 2 quasar (QSO) SDSS J002531.46–104022.2 (hereafter SDSS J0025–10) at z  = 0.30 using the CO(1–0) transition. This is one of the scarce examples of quasar host galaxies where the CO emission has been resolved spatially at any redshift. We infer a molecular gas mass $M_{\rm H_2}=(6\pm 1)\times 10^9$ M , which is distributed in two main reservoirs separated by ~9 kpc. It has been found that ~60 per cent of the gas is in the central region, associated with the QSO nucleus and/or the intermediate region between the two nuclei. The other 40 per cent is associated with the northern tidal tail and is therefore unsettled. With its high infrared (IR) luminosity L IR  = (1.1 ± 0.3)  x 10 12 L , SDSS J0025–10 is an analogue of local luminous infrared galaxies (LIRGs with high L IR 〉 several x 10 11 L ) and ultraluminous infrared galaxies (ULIRGs). The clear evidence for an ongoing major merger of two gas-rich progenitors, the high L IR dominated by a starburst, the massive reservoir of molecular gas, with a large fraction still unsettled, and the quasar activity are all properties consistent with a transition phase in the (U)LIRG–optical QSO evolutionary scenario. We propose that we are observing the system during a particular transient phase, prior to more advanced mergers where the nuclei have already coalesced. We argue that a fraction of the molecular gas reservoir is associated with a tidal dwarf galaxy identified in the optical Hubble Space Telescope image at the tip of the northern tidal tail. The formation of such structures is predicted by simulations of colliding galaxies.

Description: We present newly reduced archival radio observations of SN 1996cr in the Circinus Galaxy from the Australia Telescope Compact Array and the Molonglo Observatory Synthesis Telescope, and attempt to model its radio light curves using recent hydrodynamical simulations of the interaction between the supernova (SN) ejecta and the circumstellar material (CSM) at X-ray wavelengths. The radio data within the first 1000 d show clear signs of free–free absorption (FFA), which decreases gradually and is minimal above 1.4 GHz after day ~3000. Constraints on the FFA optical depth provide estimates of the CSM free electron density, which allows insight into the ionization of SN 1996cr's CSM and offers a test on the density distribution adopted by the hydrodynamical simulation. The intrinsic spectral index of the radiation shows evidence for spectral flattening, which is characterized by α = 0.852 ± 0.002 at day 3000 and a decay rate of α = –0.014 ± 0.001 yr –1 . The striking similarity in the spectral flattening of SN 1987A, SN 1993J and SN 1996cr suggests this may be a relatively common feature of SNe/CSM shocks. We adopt this spectral index variation to model the synchrotron radio emission of the shock, and consider several scalings that relate the parameters of the hydrodynamical simulation to the magnetic field and electron distribution. The simulated light curves match the large-scale features of the observed light curves, but fail to match certain tightly constraining sections. This suggests that simple energy density scalings may not be able to account for the complexities of the true physical processes at work, or alternatively, that the parameters of the simulation require modification in order to accurately represent the surroundings of SN 1996cr.

Description: We present the detection of 12 CO(2–1) in the z  = 4.44 submillimetre galaxy ALESS65.1 using the Australia Telescope Compact Array. A previous Atacama Large Millimeter/submillimeter Array study of submillimetre galaxies (SMGs) in the Extended Chandra Deep Field South determined the redshift of this optically and near-infrared undetected source through the measurement of [C  ii ] 157.74 μm emission. Using the luminosity of the 12 CO(2–1) emission, we estimate the gas mass to be M gas  ~ 1.7 10 10 M . The gas depletion time-scale of ALESS65.1 is ~ 25 Myr, similar to other high-redshift SMGs and consistent with z  〉 4 SMGs being the progenitors of massive ‘red-and-dead’ galaxies at z  〉 2. The ratio of the [C ii ], 12 CO and far-infrared luminosities implies a strong far-ultraviolet field of G 0  ~ 10 3.25 , which is at the high end of the far-ultraviolet fields seen in local starbursts, but weaker than the far-ultraviolet fields of most nearby ultraluminous infrared galaxies (ULIRGs). The high ratio of $L_{\rm [{\rm C\,\small {II}}]}/L_{\rm FIR} = 1.0 \times 10^{-3}$ observed in ALESS65.1, combined with $L_{\rm [{\rm C\,\small {II}}]}/L_{\rm CO} \sim 2300$ , is consistent with ALESS65.1 having more extended regions of intense star formation than local ULIRGs.