arXiv subjects

R. Morganti

Publications and source records attributed to R. Morganti.

At least 181 records · Page 10Linked to original sources

arXiv2005

Outflows and shocks in compact radio sources

We report some key results from the optical emission line study of a complete sample of compact radio sources. We find strong evidence for jet-driven outflows in the circum-nuclear emission line gas namely: 1) highly broadened and blueshifted emission line components (up to 2000 km/s), 2) shock ionised gas (broader, shifted components), 3) consistency in the scales of the emission line gas and the radio source and 4) trends between the maximum outflow velocity and radio source size (and orientation). Full details can be found in Holt (2005).

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arXiv2005

Merger-origin of radio galaxies investigated with H I observations

We present results of an HI study of a complete sample of nearby radio galaxies. Our goal is to investigate whether merger or interaction events could be at the origin of the radio-AGN activity. Around five of our radio galaxies, hosted mainly by early-type galaxies, we detect extended HI in emission. In most cases this HI is distributed in large (up to 190 kpc) and massive (up to M(HI) ~ 10^10 M(sun)) disk- or ring-like structures, that show fairly regular rotation around the host galaxy. This suggests that in these systems a major merger did occur, but at least several Gyr ago. For the HI-rich radio galaxy B2 0648+27 we confirm such a merger origin through the detection of a post-starburst stellar population that dominates the visible light throughout this system. The timescale of the current episode of radio-AGN activity in our HI-rich radio galaxies is many orders of magnitude smaller than the merger timescales. Therefore the radio-AGN activity either started late in the lifetime of the merger event, or is not directly related to the merger event at all. Another intriguing result is that the HI-rich (> 10^9 M(sun)) radio galaxies in our sample all have compact radio sources, while none of the extended radio sources contain these amounts of extended HI. This strongly suggests that there is a relation between the size of the radio jet and the presence of large amounts of neutral gas associated with the host galaxy.

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arXiv2005

A dark jet dominates the power output of the stellar black hole Cygnus X-1

Accreting black holes are thought to emit the bulk of their power in the X-ray band by releasing the gravitational potential energy of the infalling matter. At the same time, they are capable of producing highly collimated jets of energy and particles flowing out of the system with relativistic velocities. Here we show that the 10 solar mass black hole in the X-ray binary Cygnus X-1 is surrounded by a large-scale (about 5 pc in diameter) ring-like structure that appears to be inflated by the inner radio jet. We estimate that in order to sustain the observed emission of the ring, the jet of Cygnus X-1 has to carry a kinetic power that can be as high as the bolometric X-ray luminosity of the binary system. This result may imply that low-luminosity stellar mass black holes as a whole dissipate the bulk of the liberated accretion power in the form of `dark', radiatively inefficient relativistic outflows, rather than locally in the X-ray emitting inflow.

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arXiv2005

A jet-induced outflow of warm gas in 3C 293

Using long slit emission-line spectra we detect a fast outflow of ionized gas, with velocities up to 1000 km/s, in the nearby powerful radio galaxy 3C 293 (z = 0.045). The fast outflow is located about 1 kpc east of the nucleus, in a region of enhanced radio emission due to the presence of a distorted radio jet. We present results that indicate that this fast outflow is caused by a jet-ISM interaction. The kinematics of the outflowing ionized gas are very similar to those of a fast outflow of neutral hydrogen gas in this galaxy, suggesting that both outflows are the result of the same driving mechanism. While the mass of the outflowing ionized gas is about 1 x 10e5 M_sun, the total HI mass involved in the neutral outflow is about 100 times higher (10e7 M_sun). This shows that, despite the high energies that must be involved in driving the outflow, most of the gas remains, or becomes again, neutral. Other outflows of ionized gas, although not as pronounced as in the region of the enhanced radio emission, are also seen in various other regions along the axis of the inner radio jets. The regular kinematics of the emission-line gas along the major axis of the host galaxy reveal a rotating ionized gas disk 30 kpc in extent.

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arXiv2005

Fast outflow of neutral and ionized gas from the radio galaxy 3C 293

We detect a fast outflow of neutral and ionized gas with velocities up to about 1000 km/s from the central region of radio galaxy 3C 293. With optical spectroscopy we locate the bulk of the ionized gas outflow at the position of a bright radio hot-spot in the inner radio jet, about 1 kpc east of the nucleus. Given the presence of large amounts of cold gas and the distorted morphology of the radio jet in this region, we argue that the ISM is pushed out by a severe interaction with the radio plasma. The similarity of the outflow of HI with the ionized gas outflow that we see at the position of the radio hot-spot suggests that despite the high energies involved in the jet-ISM interaction, part of the gas stays, or becomes again, neutral. In this paper we also present the detection of HI emission in three nearby companions of 3C 293.

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arXiv2005

Are radio galaxies and quiescent galaxies different? Results from the analysis of HST brightness profiles

We present a study of the optical brightness profiles of early type galaxies, using a number of samples of radio galaxies and optically selected elliptical galaxies. For the radio galaxy samples--B2 of Fanaroff-Riley type I and 3C of Fanaroff-Riley type II-- we determined a number of parameters that describe a "Nuker-law" profile, which were compared with those already known for the optically selected objects. We find that radio active galaxies are always of the "core" type (i.e. an inner Nuker law slope gamma < 0.3). However, there are core-type galaxies which harbor no significant radio source and which are indistinguishable from the radio active galaxies. We do not find any radio detected galaxy with a power law profile (gamma > 0.5). This difference is not due to any effect with absolute magnitude, since in a region of overlap in magnitude the dichotomy between radio active and radio quiescent galaxies remains. We speculate that core-type objects represent the galaxies that have been, are, or may become, radio active at some stage in their lives; active and non-active core-type galaxies are therefore identical in all respects except their eventual radio-activity: on HST scales we do not find any relationship between boxiness and radio-activity. There is a fundamental plane, defined by the parameters of the core (break radius r_b and break brightness mu_b), which is seen in the strong correlation between r_b and mu_b. The break radius is also linearly proportional to the optical Luminosity in the $I$ band. Moreover, for the few galaxies with an independently measured black hole mass, the break radius turns out to be tightly correlated with M_{BH}. The black hole mass correlates even better with the combination of fundamental plane parameters r_b and mu_b, which represents the central velocity dispersion.

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arXiv2005

The location of the broad HI absorption in 3C305: clear evidence for a jet-accelerated neutral outflow

We present high-spatial resolution 21-cm HI VLA observations of the radio galaxy 3C305 (z=0.041). These new high-resolution data show that the ~1000 km/s broad HI absorption, earlier detected in low-resolution WSRT observations, is occurring against the bright, eastern radio lobe, about 1.6 kpc from the nucleus. We use new optical spectra taken with the WHT to make a detailed comparison of the kinematics of the neutral hydrogen with that of the ionised gas. The striking similarity between the complex kinematics of the two gas phases suggests that both the ionised gas and the neutral gas are part of the same outflow. Earlier studies of the ionised gas had already found evidence for a strong interaction between the radio jet and the interstellar medium at the location of the eastern radio lobe. Our results show that the fast outflow produced by this interaction also contains a component of neutral atomic hydrogen. The most likely interpretation is that the radio jet ionises the ISM and accelerates it to the high outflow velocities observed. Our observations demonstrate that, following this strong jet-cloud interaction, not all gas clouds are destroyed and that part of the gas can cool and become neutral. The mass outflow rate measured in 3C~305 is comparable, although at the lower end of the distribution, to that found in Ultra-Luminous IR galaxies. This suggests that AGN-driven outflows, and in particular jet-driven outflows, can have a similar impact on the evolution of a galaxy as starburst-driven superwinds.

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arXiv2005

HST/STIS low dispersion spectroscopy of three Compact Steep Spectrum sources Evidence for jet-cloud interaction

We present Hubble Space Telescope Imaging Spectrograph long-slit spectroscopy of the emission line nebulae in the compact steep spectrum radio sources 3C 67, 3C 277.1, and 3C 303.1. We derive BPT (Baldwin- Philips-Terlevich; Baldwin et al. 1981) diagnostic emission line ratios for the nebulae which are consistent with a mix of shock excitation and photoionization in the extended gas. In addition, line ratios indicative of lower ionization gas are found to be associated with higher gas velocities. The results are consistent with a picture in which these galaxy scale radio sources interact with dense clouds in the interstellar medium of the host galaxies, shocking the clouds thereby ionizing and accelerating them.

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arXiv2005

Discovering the microJy Radio VLBI Sky via "Full-beam" Self-calibration

We demonstrate that at 1.4 GHz the combined response of sources detected serendipitously in deep, wide-field VLBI images is sufficient to permit self-calibration techniques to be employed. This technique of "full-beam" VLBI self-calibration permits coherent VLBI observations to be successfully conducted in any random direction on the sky, thereby enabling very faint radio sources to be detected. Via full-beam self-calibration, Global VLBI observations can equal and indeed surpass the level of sensitivity achieved by connected arrays. This technique will enable large-scale VLBI surveys of the faint radio source population to be conducted, in addition to targeted observations of faint sources of special interest (e.g. GRBs, SNe, SNR and low-luminosity AGN).

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arXiv2004

Spitzer 24 micron imaging of Faint Radio Sources in the FLSv: a new radio-loud, Mid-IR/optically obscured population?

Data from the Spitzer Space Telescope (the First Look Survey - FLS) have recently been made public. We have compared the 24 micron images with very deep WSRT 1.4 GHz observations (Morganti et al. 2004), centred on the FLS verification strip (FLSv). Approximately 75% of the radio sources have corresponding 24 micron identifications. Such a close correspondence is expected, especially at the fainter radio flux density levels, where star forming galaxies are thought to dominate both the radio and mid-IR source counts. Spitzer detects many sources that have no counter-part in the radio. However, a significant fraction of radio sources detected by the WSRT (about 25%) have no mid-IR identification in the FLSv (implying a 24 micron flux density less than 100 microJy). The fraction of radio sources without a counterpart in the mid-IR appears to increase with increasing radio flux density, perhaps indicating that some fraction of the AGN population may be detected more readily at radio than Mid-IR wavelenghts. We present initial results on the nature of the radio sources without Spitzer identification, using data from various multi-waveband instruments, including the publicly available R-band data from the Kitt Peak 4-m telescope.

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arXiv2004

The nature of the Mid-IR faint radio sources from the Spitzer First Look Survey

Data from the Spitzer Space Telescope (the First Look Survey - FLS) have recently been made public. We have compared the 24 micron images with very deep WSRT 1.4 GHz observations, centred on the FLS verification strip (FLSv). Approximately 75% of the radio sources have corresponding 24 micron identifications. Such a close correspondence is expected, especially at the fainter radio flux density levels, where star forming galaxies are thought to dominate both the radio and mid-IR source counts. However, a significant fraction of radio sources detected by WSRT (25%) have no mid-IR detection in the FLSv (implying a 24 micron flux density less than 0.1 mJy). We present initial results on the nature of the radio sources without Spitzer identification, using data from various multi-waveband instruments, including the publicly available R-band data from the Kitt Peak 4-m telescope.

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arXiv2004

Outflows of neutral (and ionized) gas in radio galaxies

Outflows up to 1500 km/s of atomic neutral hydrogen are detected in a growing number of radio galaxies. Outflows with similar velocities are also detected in ionized gas, suggesting a common origin for the extreme kinematics of these two phases of the gas. The high detection rate ofsuch outflows in young (or restarted) radio sources appears to be related to the existence of a dense ISM around these objects. Such a dense ISM can have important consequences for the evolution of the radio source and the galaxy as a whole. Here we summarize the recent results obtained and the characteristics derived so far for these outflows. We also discuss possible mechanisms (e.g. interaction between the radio plasma and the ISM and adiabatically expanding broad emission lines clouds) that can be at the origin of these phenomena.

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arXiv2004

Deep VLBI Imaging of Faint Radio Sources in the NOAO Bootes Field

We have conducted a deep, very long baseline interferometry (VLBI) observation at 1.4 GHz of an area of sky located within the NOAO Bootes field, using the NRAO VLBA and 100-m Green Bank Telescope. Applying wide-field VLBI techniques, a total of 61 sources, selected from a WSRT image, were surveyed simultaneously with a range of different sensitivities and resolutions. The inner 0-2', of the field reached an unprecedented 1-sigma rms noise level ~ 9 uJy/beam and yielded 2 detections. A further 7 sources were detected in the rest of the field. All of the sources have a brightness temperature in excess of 10^5 K; suggesting they are AGN. Optical identifications are available for 8 of the 9 VLBI detections - only VLBI J142906.6095 remains unidentified (I > 25.6m). Two sources are not detected in K-band (K > 18.5m) suggesting that some significant fraction of these compact radio sources may be located at z > 1. The VLBI detection rate for sub-mJy radio sources is 8^{+4}_{-5} %. The VLBI detection rate for mJy sources is higher, 29^{+11}_{-12}%. This trend is expected if the radio emission associated with fainter sub-mJy and microJy sources increasingly arises from extended regions of star formation. The 9 VLBI detections pin-point the precise location of AGN or candidate AGN, and their VLBI positions can help to anchor the NOAO Bootes field to the ICRF. The simultaneous detection of several sub-mJy and mJy radio sources, in a single observation, suggest that their combined response may be used to self-calibrate wide-field VLBI data. Future VLBI observations of faint sub-mJy and microJy radio sources can take full advantage of this "full-beam" calibration technique.

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arXiv2004

Starbursts and the triggering of the activity in nearby powerful radio galaxies

We present high quality long-slit spectra for three nearby powerful radio galaxies 3C293, 3C305, PKS1345+12. These were taken with the aim of characterising the young stellar populations (YSP), and thereby investigating the evolution of the host galaxies, as well as the events that triggered the activity. Isochrone spectral synthesis modelling of the wide wavelength coverage spectra of nuclear and off-nuclear continuum-emitting regions have been used to estimate the ages, masses and luminosities of the YSP component, taking full account of reddening effects and potential contamination by activity-related components. We find that the YSP make a substantial contribution to the continuum flux in the off-nuclear regions on a radial scale of 1 - 20kpc in all three objects. Moreover, in two objects we find evidence for reddened post-starburst stellar populations in the near-nuclear regions of the host galaxies. The YSP are relatively old (0.1- 2Gyr), massive and make up a large proportion (~1 - 50%) of the total stellar mass in the regions of galaxies sampled by the observations. Overall, these results are consistent with the idea that AGN activity in some radio galaxies is triggered by major gas-rich mergers. Therefore, these radio galaxies form part of the subset of early-type galaxies that is evolving most rapidly in the local universe. Intriguingly, the results also suggest that the radio jets are triggered relatively late in the merger sequence, and that there is an evolutionary link between radio galaxies and luminous/ultra-luminous infrared galaxies.

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arXiv2004

Disks, Tori, and Cocoons: Emission and Absorption Diagnostics of AGN Environments

One of the most important problems in the study of active galaxies is understanding the detailed geometry, physics, and evolution of the central engines and their environments. The leading models involve an accretion disk and torus structure around a central dense object, thought to be a supermassive black hole. Gas found in the environment of AGN is associated with different structures: molecular accretion disks, larger scale atomic tori, ionized and neutral "cocoons" in which the nuclear regions can be embedded. All of them can be studied at radio wavelengths by various means. Here, we summarize the work that has been done to date in the radio band to characterize these structures. Much has been learned about the central few parsecs of AGN in the last few decades with contemporary instruments but the picture remains incomplete. In order to be able to define a more accurate model of this region, significant advances in sensitivity, spectral and angular resolution, and bandpass stability are required. The necessary advances will only be provided by the Square Kilometer Array and we discuss the possibilities that these dramatic improvements will open for the study of the gas in the central region of AGN.

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arXiv2004

Anomalous HI kinematics in Centaurus A: evidence for jet-induced star formation

We present new 21-cm HI observations performed with ATCA of the large HI filament located about 15 kpc NE from the centre of Centaurus A and discovered by Schiminovich et al.(1994). This HI cloud is situated (in projection) near the radio jet of Centaurus A, as well as near a large filament of ionised gas of high excitation and turbulent velocities and near regions with young stars. The higher velocity and spatial resolution of the new data reveals that, apart from the smooth velocity gradient corresponding to the overall rotation of the cloud around Centaurus A, HI with anomalous velocities of about 100 km/s is present at the southern tip of this cloud. This is interpreted as evidence for an ongoing interaction between the radio jet and the HI cloud. Gas stripped from the HI cloud gives rise to the large filament of ionised gas and the star formation regions that are found downstream from the location of the interaction. The implied flow velocities are very similar to the observed anomalous HI velocities. Given the amount of HI with anomalous kinematics and the current star formation rate, the efficiency of jet-induced star formation is at most of the order of a percent.

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arXiv2004

Infrared Properties of Radio-Selected Submillimeter Galaxies in the Spitzer First Look Survey Verification Field

We report on submillimeter and infrared observations of 28 radio-selected galaxies in the Spitzer First Look Survey Verification field (FLSV). All of the radio-selected galaxies that show evidence for emission at 850um with SCUBA have Spitzer counterparts at 24um, while only half of the radio-selected galaxies without 850um emission have detectable counterparts at 24um. The data show a wide range of infrared colors (S70/S24 < 5--30, S8/S3.6 < 0.3--4), indicative of a mixture of infrared-warm AGN and cooler starburst dominated sources. The galaxies showing 850um emission have Spitzer flux densities and flux density ratios consistent with the range of values expected for high-redshift (z=1--4) ultraluminous infrared galaxies.

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arXiv2004

The unfriendly ISM in the radio galaxy 4C12.50 (PKS 1345+12)

The radio source 4C12.50 has often been suggested to be a prime candidate for the link between ultraluminous infrared galaxies and young radio galaxies. A VLBI study of the neutral hydrogen in the nuclear regions of this object shows that most of the gas detected close to the systemic velocity is associated with an off-nuclear cloud (~50 to 100 pc from the radio core) with a column density of ~10^22 T_spin/100 K) cm^(-2) and an HI mass of a few times 10^5 to 10^6 M_sun. We consider a number of possibilities to explain the results. In particular, we discus the possibility that this cloud indicates the presence of a rich and clumpy interstellar medium in the centre, likely left over from the merger that triggered the activity and that this medium influences the growth of the radio source. The location of the cloud -- at the edge of the northern radio jet/lobe -- suggests that the radio jet might be interacting with a gas cloud. This interaction could be responsible for bending the young radio jet. The velocity profile of the gas is relatively broad (~150$ km/s) and we interpret this as kinematical evidence for interaction of the radio plasma with the cloud. We also consider the model where the cloud is part of a broader circumnuclear structure. Only a limited region of this structure would have sufficient background radio brightness and large enough column depth in neutral gas to obtain detectable HI absorption against the counterjet. The VLBI study of the neutral hydrogen in 4C12.50 suggests that HI detected near the systemic velocity (as it is often the case in radio galaxies) may not necessarily be connected with a circumnuclear disk or torus (as is very often assumed) but instead could be a tracer of the large-scale medium that surrounds the active nucleus and that may influence the growth of the young radio source.

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