arXiv subjects

M. Villar-Martin

Publications and source records attributed to M. Villar-Martin.

At least 55 records · Page 3Linked to original sources

arXiv2000

Radio galaxies at z~2.5: results from Keck spectropolarimetry

In classifying the ensemble of powerful extragalactic radio sources, considerable evidence has accumulated that radio galaxies and quasars are orientation-dependent manifestations of the same parent population: massive spheroidal galaxies containing correspondingly massive black holes. [...] In this study, we exploit the opportunity to eliminate the quasar glare by performing sensitive spectropolarimetry with the Keck II telescope of a sample of radio galaxies with redshifts around 2.5. [...] We show that dust-reflected quasar light generally dominates the restframe ultraviolet continuum of these sources and that a highly clumped scattering medium results in almost grey scattering of the active galactic nucleus photons. The observations, however, do not exclude a substantial star formation rate averaged over a Gyr of evolution. The sub-mm reradiation from the scattering dust is likely to represent only a small fraction (~10%) of the total far infrared luminosity. An analysis of the emission lines excited in the interstellar medium of the host galaxy by the hard quasar radiation field reveals evidence of a dramatic chemical evolution within the spheroid during this epoch. Secondary nitrogen production in intermediate mass stars produces a characteristic signature in the NV/CIV and NV/HeII line ratios which has been seen previously in the broad line region of quasars at similar redshifts. We find intriguing correlations between the strengths of the Ly alpha and NV emission lines and the degree of ultraviolet continuum polarization which may represent the dispersal of dust associated with the chemical enrichment of the spheroid.

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arXiv2000

Interpreting the kinematics of the extended gas in distant radiogalaxies from 8-10m telescope spectra

The nature of the extreme kinematics in the extended gas of distant radio galaxies (z>0.7) is still an open question. With the advent of the 8-10 m telescope generation and the development of NIR arrays we are in the position for the first time to develop a more detailed study by using lines other than Lya and [OII]3727 depending on redshift. In this paper we review the main sources of uncertainty in the interpretation of the emission line kinematics: the presence of several kinematic components, Lya absorption by neutral gas/dust and the contribution of scattered light to some of the lines. As an example, several kinematic components can produce apparent, false rotation curves. We propose methods to solve these uncertainties. We propose to extend the methods applied to low redshift radio galaxies to investigate the nature of the kinematics in distant radio galaxies: by means of the spectral decomposition of the strong optical emission lines (redshifted into the NIR) we can isolate the different kinematic components and study the emission line ratios for the individual components. If shocks are responsible for the extreme kinematics, we should be able to isolate a kinematic component (the shocked gas) with large FWHM (>900 km/s), low ionization level [OIII]5007/Hb~2-4 and weak HeII4686/Hb<0.07, together with a narrow component (~few hundred km/s) with higher ionization level and strong HeII emission (HeII/Hb~0.5)

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arXiv2000

Gas metallicities and early evolution of distant radiogalaxies

By modeling the rich emission line spectra of a sample of high redshift (HzRG, z\sim 2.5) radio galaxies we find that solar and supersolar metallicities are common in the extended gas of these objects. Our models and the comparison with high redshift quasars suggest that HzRG at z\sim 2.5 are associated with intense star formation activity. This is consistent with chemical evolution models for giant ellipticals and it supports the idea that distant powerful radio galaxies are progenitors of giant ellipticals. We might be witnessing different evolutive status in different objects.

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arXiv2000

Keck Observations of the Hidden Quasar IRAS P09104+4109

We present imaging and spectro- polarimetric observations of the ultraluminous infrared galaxy IRAS P09104+4109 using the Keck 10-m Telescope. We detect the clear presence of broad Hb, Hg, and MgII 2800 emission lines in the polarized flux spectra of the nucleus and of an extranuclear emission region ~ 4" away, confirming the presence of a hidden central quasar. The polarization of the broad Mg II emission line is high (~ 29%), consistent with the remarkably high polarization (~ 30%-40%) observed in the extended continuum emission. The narrow emission lines are polarized in a stratified fashion, with the high ionization lines being polarized 0.7%-1.7% and [O II] essentially unpolarized. The line polarizations are positively correlated with critical density, ionization potential, and velocity width of the emission lines. This indicates that the NLR may be partially shadowed by the putative torus, with the higher ionization lines originating closer to the nucleus. One notable characteristic of the extranuclear knot is that all species of Fe are markedly absent in its spectrum, while they appear prominently in the nucleus. Our favored interpretation is that there is a large amount of dust in the extranuclear regions, allowing gaseous refractory metals to deposit. The extended emission regions are most likely material shredded from nearby cluster members and not gas condensed from the cooling flow or expelled from the obscured quasar. Our data provide strong evidence for matter-bounded clouds in addition to ionization-bounded clouds in the NLR. Ionization by pure velocity shocks can be ruled out. Shocks with photoionizing precursors may be present, but are probably not a dominant contributor to the energy input.

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arXiv2000

A vestige low metallicity gas shell surrounding the radio galaxy 0943-242 at z=2.92

Observations are presented showing the doublet CIV 1550 absorption lines superimposed on the CIV emission in the radio galaxy 0943-242. Within the errors, the redshift of the absorption system that has a column density of N_CIV = 10^{14.5 +- 0.1} cm-2 coincides with that of the deep Ly-alpha absorption trough observed by Rottgering et al. (1995). The gas seen in absorption has a resolved spatial extent of at least 13 kpc (the size of the extended emission line region). We first model the absorption and emission gas as co-spatial components with the same metallicity and degree of excitation. Using the information provided by the emission and absorption line ratios of CIV and Ly-alpha, we find that the observed quantities are incompatible with photoionization or collisional ionization of cloudlets with uniform properties. We therefore reject the possibility that the absorption and emission phases are co-spatial and favour the explanation that the absorption gas has low metallicity and is located further away from the host galaxy (than the emission line gas). The estimated low metallicity for the absorption gas in 0943-242 (Z \~ 1% solar) and its proposed location -outer halo outside the radio cocoon- suggest that its existence preceeds the observed AGN phase and is a vestige of the initial starburst at the onset of formation of the parent galaxy.

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arXiv2000

The large scale distribution of warm ionized gas around nearby radio galaxies with jet-cloud interactions

Deep, narrow-band Halpha observations taken with the TAURUS Tunable Filter (TTF) on the 4.2m WHT telescope are presented for two nearby radio galaxies with strong jet-cloud interactions. Although the brightest emission line components are closely aligned with the radio jets --- providing nearby examples of the ``alignment effect'' most commonly observed in high redshift (z > 0.5) radio galaxies --- lower surface brightness emission line structures are detected at large distances (10's of kpc) from the radio jet axis. These latter structures cannot be reconciled with anisotropic illumination of the ISM by obscured quasar-like sources, since parts of the structures lay outside any plausible quasar ionization cones. Rather, the distribution of the emission lines around the fringes of the extended radio lobes suggests that the gas is ionized either by direct interaction with the radio components, or by the diffuse photoionizing radiation fields produced in the shocks generated in such interactions. These observations serve to emphasise that the ionizing effects of the radio components can extend far from the radio jet axes, and that deep emission line imaging observations are required to reveal the true distribution of warm gas in the host galaxies. We expect future deep imaging observations to reveal similar structures perpendicular to the radio axes in the high-z radio galaxies.

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arXiv1999

The radio structures of southern 2-Jy radio sources: new ATCA and VLA radio images

We present new radio images obtained with the Australia Telescope Compact Array (ATCA) and the Very Large Array (VLA) for a group of 14 galaxies belonging to the 2-Jy sample of radio sources. The new images improve the data already available on these objects and, in general, the database that we are building up on the sample. They will also be used for follow-up work where radio-optical comparison will be done. We briefly discuss the core dominance parameter (R) for the objects for which the new data have given new information and, in particular, for broad line radio galaxies (BLRG). One of the BLRG does not show a core, even at 3 cm, and this is at variance with the general tendency of BLRG to have relatively strong cores. The depolarization is also discussed for a group of small double-lobed radio galaxies.

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arXiv1999

UV rest frame spectroscopy of four high redshift (z>2) active galaxies

We present UV spectra of a small sample of high redshift active galaxies: the hyperluminous, gravitationally lensed system SMM J02399-0136 (z=2.8) and three powerful radio galaxies (z~2.5). Extended continuum and emission lines are detected in all objects. The three radio galaxies present typical spectra with dominant Lya and weaker CIV1550, HeII1640 and CIII]1909. The spectrum of SMM J02399-0136 is strikingly different, showing relatively weak Lya and HeII and strong NV1240 relative to the C lines. We find that the weakness of HeII can be explained if the intermediate density narrow line region (n~10^{5-6} cm^-3 dominates the emission line spectrum, rather than the more extended low density gas (n<100 cm^-3). The line ratios of MRC2025-218 suggest that this is also the case in this object. MRC2025-218 and SMM J02399-0136 show the largest NV/HeII and NV/CIV values found in high redshift radio galaxies. The failure of solar abundance models to explain these line ratios and studies of metal abundances in high redshift quasars and radio galaxies, suggest that nitrogen is overabundant in the ionized gas of these objects. Alternative possibilities which we discuss include NV emission from the broad line region and differential amplification by a gravitational lens. We report the discovery of a PCygni profile in the CIV line in the spectrum of MRC2025-218. We detect also CII1334.5 in absorption and PCygni profiles for the lines SiIV1393.8,1402.8. We do not detect any purely photospheric stellar lines. The nature of the absorption features is not clear. It could be due to stars or an associated absorption line system.

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arXiv1999

The nature of the extreme kinematics in the extended gas of high redshift radio galaxies

We present UV rest frame spectra of 3 powerful narrow line radio galaxies and the hyperluminous type 2 active galaxy SMM02399-0136, all at high redshift (z>2). We find high velocities (FWHM>1000, km/s) in the extended gas of all objects. A natural explanation is the interaction between the radio jet and the ambient gas, that drives shocks into the gas and accelerates the clouds. However, the existence of high velocities in regions where such interactions are not taking place implies that other processes can play a role. We discuss here several possible mechanisms.

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arXiv1999

PKS2250-41 and the role of jet-cloud interactions in powerful radio galaxies (full paper)

We present high resolution, long-slit spectra of the jet-cloud interaction in the powerful southern radio galaxy PKS2250-41. We have resolved the emission lines into two main kinematic components: a broad component (FWHM \geq 900 km/s) and a narrow component (FWHM \leq 150 km/s). While the broad component is characterized by a low ionization level (with particular ly weak HeII$λ$4686 emission) and is spatially associated with the radio lobe, the narrow component is characterized by a higher ionization level and extends well beyond the radio lobe. Crucially, we measure a higher electron temperature for the broad component (T \sim 30,000 K) than for the narrow component (T \sim 15,000 K). The general line ratios and physical conditions of the two components are consistent with a model in which the broad component r epresents gas cooling behind the shock front driven by the radio jets, while the narrow component represents the AGN- or shock-photoionized precursor gas. However, uncertainties remain about the gas acceleration mechanism behind the shock front: unless the radio components are expanding unusually fast in this source, it is likely that entrainment of the warm clouds in the hot post-shock wind or radio plasma is required. The similarities between the kinematic properties of PKS2250-41 and some high redshift radio galaxies suggest that the ambient and the shocked gas have also been resolved in the more distant objects. Given the evidence that the emission line processes are affected by the interactions between the radio and the optical structures, care must be taken when interpreting the UV spectra of high redshift radio galaxies.

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arXiv1999

PKS2250-41 and the role of jet-cloud interactions in powerful radio galaxies

We have studied the effects of the interaction between the radio jet and the ambient gas in the powerful radio galaxy PKS2250-41 (z=0.31). Our results show that the gas has been accelerated, compressed, heated and collisionally ionized by the shock. This study helps us to understand the processes which determine the observed properties of many high redshift radio galaxies.

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arXiv1999

The NV/CIV ratio in high redshift radio galaxies

Deep Keck spectropolarimetry has been obtained of a sample of powerful radio galaxies with $z \sim 2.5 \pm 1$. In addition to a clear 2200Ådust scattering/extinction signature and an inverse correlation between the degree of continuum polarization and the Lyman-αemission line strength (relative to C IV), we find an intriguing positive correlation between the N~V/C IV ratio and the polarization. The line ratio, which varies by almost a dex amongst objects having a very similar ionization state, is most likely to indicate an abundance ratio. We speculate that the correlation with polarization represents a connection between nitrogen enhancement and dust production following a major starburst event connected with the birth of the quasar.

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arXiv1998

The nature of the optical---radio correlations for powerful radio galaxies

The nature of the optical--radio correlations for powerful radio galaxies is investigated using spectroscopic observations of a complete sample of southern 2Jy radio sources. In line with previous work, we find that significant correlations exist between the luminosities of the [OIII]5007, [OII]3727 and Hbeta emission lines and the radio luminosity. However, our observations are not easily reconciled with the idea that these correlations are caused by the increase in the power of the photoionizing quasar as the jet power increases, with average ISM properties not changing appreciably with redshift or radio power: not only do we find that the scatter in the L_[OIII] vs. L_radio correlation is significantly larger than in L_[OII]} vs. L_radio and L_Hbeta vs. L_radio correlations, but the ionization state deduced from the emission lines does not increase with radio power as predicted by the simple, constant ISM, photionization model. We conclude that: (a) there exists a considerable range in the quasar ionizing luminosity at a given redshift; and (b) that the mean density of the emission line clouds is larger in the high redshift/high power radio sources. The latter density enhancement may either be a consequence of the increased importance of jet-cloud interactions or, alternatively, due to a higher pressure in the confining hot ISM, in the high redshift objects. Deep spectra show that many of the sources in our sample are broad line radio galaxies (BLRG). The fact that the BLRG are observed out the redshift limit of the survey, overlapping in redshift with the quasars, argues against the idea that BLRG are simply the low radio power counterparts of high power, high redshift quasars.

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arXiv1998

Optical continuum structure of Cygnus A

As a prerequisite for interpreting new observations of the most distant radio galaxies, we make an optical study of the closest powerful radio source, Cygnus A. Using Keck imaging- and spectro-polarimetry in conjunction with HST, WFPC2 broad and narrow band imaging, we are able to identify specific geometrical structures in the galaxy with optical continuum components distinguished by both colour and polarimetric properties. A 4 kpc diameter dusty ring of young stars forms the equator of a double ionization cone which is co-axial with the radio jets.

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arXiv1998

PKS 1932-464: a jet-cloud interaction in a radio galaxy?

We present optical and radio images, and long-slit spectra of the radio galaxy PKS 1932-464 (z=0.230). Our main goal is to determine whether the observed properties of the extended emission line nebulosity in this object show evidence for interactions between the radio jet and the extended ionized gas, or whether they can be explained in terms of the illumination of the extended gas by the active nucleus. Although the data do not show compelling evidence for jet-cloud interactions, the existence of two well distinguished emitting line regions with very different kinematics and ionization levels suggests the presence of such interactions. The large-scale gas distribution is complex and suggests a gravitational interaction between the host galaxy of PKS 1932-464 and a nearby companiongalaxy. The detection of a broad Ha emission line in the nuclear spectrum of the object provides evidence that this object is a broad line radio galaxy (BLRG) rather than a narrow line radio galaxy (NLRG) as previously supposed.

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arXiv1997

The ionization mechanism of the extended gas in high redshift radio galaxies:shocks or AGN photoionization?

We have compared the UV line ratios of a sample of very high redshift radio galaxies with shock and AGN photoionization models, with the goal of determining the balance between jet-induced shocks and AGN illumination in the extended emission line regions. We find that the UV line ratios cannot be explained in terms of photoionization of solar abundance gas by the classical power law of index $α=$-1.5, which successfully reproduces the general trends defined by the optical line ratios of low redshift radio galaxies. Pure shock models also provide a poor fit to the data. However, photoionization by a power law of index -1.0 provides an excellent fit to the UV line ratios. This suggests that the ionizing continuum spectral shape may depend on radio luminosity and/or redshift, such that it becomes harder as the radio power and/or redshift increase. However, an alternative possibility is that we are seeing the first signs of chemical evolution in these objects, since a power-law of index -1.5 with low metallicity also provides a good fit to the data. We further show that the UV line ratios provide a sensitive test of the ionization mechanism for the lower ionization conditions prevalent in some low redshift jet-cloud interaction candidates.

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arXiv1996

Ca depletion and the presence of dust in large scale nebulosities in radiogalaxies (II)

We investigate here the origin of the gas observed in extended emission line regions surrounding AGNs. We use the technique of calcium depletion as a test to prove or disprove the existence of dust in such a gas in order to discriminate between two main theories: (1) a cooling process from a hotter X-ray emitting phase surrounding the galaxy, (2) merging or tidal interaction between two or more components. We have obtained long slit spectroscopy of a sample of objects representative of different galaxy types although our main interest focus on radio galaxies. The spectral range was set to always includethe [CaII]$λλ$7291,7324 doublet. The faintness or absence of such lines is interpreted as due to the depletion of calcium onto the dust grains and, therefore, is a proof of the existence of dust mixed with the gas in the EELRs.

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arXiv1996

Dust and gas in active galaxies

There are strong evidences which favour the existence of dust in active galaxies. Understanding the way in which dust interacts with the radiation and influences the physical conditions of the gas is crucial if we want to learn about the nature of the central active nucleus and about the physical conditions of the ISM in such galaxies. Not taking into account such effects may lead us towards misleading interpretations. Many intriguing questions concerns to the nature and the existence of dust in active galaxies: for instance, under which conditions does the very hard ionizing continuum of an AGN allows the survival of dust grains? Is the composition and size distribution of the dust the same as in our local interstellar medium? How is dust distributed compared to the gas which is at least in part highly ionized by the central AGN? Does dust also exist in radio galaxies at very high redshifts? The work developed in this thesis tries to find answers to some of these questions, through a detailed theoretical and observational research of the mechanisms which control the interaction of dust with the radiation and with the ions. The observable effects of the dust on the emission line spectrum are also analyzed in detail. The final goal has been to give clues about more general questions: origin of the emitting gas, ionization mechanisms, geometry, connection between low and high redshift active galaxies or the validity of the unification scenario. This thesis tries, in summary, to provide a clearer understanding of active galaxies in general.

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