arXiv subjects

M. Almudena Prieto

Publications and source records attributed to M. Almudena Prieto.

26 records · Page 2Linked to original sources

arXiv2002

The IR spectral energy distribution of the Seyfert 2 prototype NGC 5252

The complete mid- to far- infrared continuum energy distribution collected with the Infrared Space Observatory of the Seyfert 2 prototype NGC 5252 is presented. ISOCAM images taken in the 3--15 micron range show a resolved central source that is consistent at all bands with a region of about 1.3 kpc in size. Due to the lack of on going star formation in the disk of the galaxy, this resolved emission is associated with either dust heated in the nuclear active region or with bremsstrahlung emission from the nuclear and extended ionised gas. The size of the mid-IR emission contrasts with the standard unification scenario envisaging a compact dusty structure surrounding and hiding the active nucleus and the broad-line region. The mid-IR data are complemented with ISOPHOT aperture photometry in the 25--200 micron range. The overall IR spectral energy distribution is dominated by a well-defined component peaking at about 100$ micron, a characteristic temperature of T ~20 K, and an associated dust mass of 2.5 x 10E7 Msun, which greatly dominates the total dust mass content of the galaxy. The heating mechanism of this dust is probably the interstellar radiation field. After subtracting the contribution of this cold dust component, the bulk of the residual emission is attributed to dust heated within the nuclear environment. Its luminosity consistently accounts for the reprocessing of the X-ray to UV emission derived for the nucleus of this galaxy. The comparison of NGC 5252 spectral energy distribution with current torus models favors large nuclear disk structure on the kiloparsec scale.

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arXiv2002

Particle Accelerators in the Hot Spots of the Radio Galaxy 3C445 Imaged With the VLT

Hot spots (HSs) are regions of enhanced radio emission produced by supersonic jets at the tip of the radio lobes of powerful radiosources. Obtained with the Very Large Telescope (VLT), images of the HSs in the radio galaxy 3C445 show bright knots embedded in diffuse optical emission distributed along the post shock region created by the impact of the jet into the intergalactic medium. The observations reported here confirm that relativistic electrons are accelerated by Fermi-I acceleration processes in HSs. Furthermore, both the diffuse emission tracing the rims of the front shock and the multiple knots demonstrate the presence of additional continuous re-acceleration processes of electrons (Fermi-II).

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arXiv2001

On the relation between the IR continuum and the active galactic nucleus in Seyfert galaxies

A sample of the brightest known Seyfert galaxies from the CfA sample is analyzed on the basis of ISO photometric and spectroscopic data. Regardless of the Seyfert type, the mid-IR continuum emission from these galaxies is found to be correlated with the coronal line emission arising in the nuclear active region. Conversely, the correlation degrades progressively when moving from the mid- to the far-IR emission, where it ends to vanish. It is concluded that the mid-IR emission is largely dominated by dust heated by processes associated with the active nucleus whereas the far-IR is a different component most probably unrelated with the active region. We suggest that the far-IR component is due to dust heated by the stellar population in the disks of these galaxies.

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arXiv2001

The origin of the mid- and far-infrared emission in AGN

The relation between the X-ray emission, the infrared emission and the coronal line emission in a sample of the brightest known Seyfert galaxies is analyzed. A close relationship between the absorption-corrected soft X-ray emission and both the mid-infrared and the coronal line emission is found among the Seyfert type 2 objects studied in this work. Being both the coronal line and the X-ray emissions main tracers of the AGN activity, their relation with the mid-infrared emission adds further support to the claim that the mid-infrared emission is primarily due to dust heated directly by the central AGN. No apparent relationship between the soft X-ray emission and the coronal line and/or the mid-infrared emissions is seen within Seyfert 1 objects, the number of objects of this class in the sample is comparatively smaller though. That discrepancy is partially due to the fact that the soft X-ray emission in the Seyfert 1s is systematically larger by at least one order of magnitude than that in their Seyfert 2 counterparts. Finally, the hard X-ray emission in both Seyfert types shows unrelated to the mid-infrared and coronal line emissions.

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arXiv2000

Discovery of a very luminous megamaser during a radio flare in the Seyfert 2 galaxy Mrk 348

We report the detection of a new H_2O megamaser in the Seyfert 2 galaxy Mrk 348 with the MPIfR 100 m telescope in Effelsberg. With an apparent isotropic luminosity of L_H2O ~ 420 L_sun the maser is the third most luminous maser discovered so far. The detected line is unusually broad (Delta v ~ 130 km/s), is redshifted by ~130 km/s from the systemic velocity, and is asymmetric with a pronounced blue wing. While evidence for obscuring material towards the nucleus of this galaxy was found earlier, this detection is the first direct observation of molecular material in the vicinity of the AGN. We also searched for absorption from ammonia (NH_3) and cyclopropenylidene (C_3H_2) against the bright radio nucleus. The H_2O line was only marginally detected in archival data indicating that the maser flared recently in conjunction with a huge radio continuum flare. Continuum and line flux density increased by a factor of three, suggesting an unsaturated maser. The radio continuum flare has made Mrk 348 the most radio luminous megamaser galaxy known. It is pointed out that megamaser galaxies contain a rather large fraction of galaxies with prominent radio cores and it is speculated that the flare in the maser emission in Mrk 348 is related to the flare in the nuclear jet.

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arXiv2000

Extended X-ray emission in the radio loud galaxy 3C 382

ROSAT/HRI observations of the powerful radio-loud galaxy 3C382 reveal extended X-ray emission associated with the source. On the basis of this new spatial component, a previous ROSAT/PSPC spectral analysis of the source is revised. Allowing for the presence of an additional thermal component in the PSPC spectrum, the non-thermal component is found to be compatible with the extrapolation of the well defined 3C382 - 2-10 keV - power-law spectrum into the soft X-rays. The thermal -extended- component would then account for the soft excess emission previously reported for this source. The origin of this thermal component is not clear. Its luminosity compares with that of rich Abell clusters; yet, the galaxy environment in 3C382 appears of moderate optical richness. An alternative is that it is due to a massive extended gaseous atmosphere sustained by the deep gravitational potential well of 3C382.

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arXiv1999

On the ionizing continuum in active galactic nuclei: clues from ISO

The ISO coronal line spectrum of the brightest Seyfert galaxies from the CfA sample is presented and modeled. ISO observations of [O IV] 25.9 $μ$, [Ne V] 14.3 $μ$, [Mg VIII] 3.02 $μ$ and [Si IX] 2.58 $μ$ lines are presented; their relationship with the soft part of the ionizing spectrum from 50 to 300 eV is investigated. Pure photoionization models reproduce the line ratios, setting ranges for the ionization parameter and the optical depth of the emitting clouds. On the basis of the available data alone it is not possible to distinguish between a power-law or a blackbody distribution as the intrinsic shape of the UV ionizing spectrum. However, for the brightest Seyferts analyzed, namely, NGC 1068, Circinus and NGC 4151, a black-body UV continuum is favored.

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arXiv1997

X-ray analysis of Abell 2634 and its central galaxy 3C465

An analysis of a ROSAT/PSPC observation of the galaxy cluster A2634 is presented. The cluster has a luminosity of $7.9\pm0.1\times10^{43}$erg/s in the ROSAT band (0.1-2.4 keV). The temperature profile decreases from about 3 keV in the outer parts to 1.2 keV in the centre. Within a radius of 1.5 Mpc the gas mass of the cluster is 0.51$\times 10^{14}\msol$ and the total mass amounts to $4.1^{+2.6}_{-1.8}\times 10^{14}\msol$. The X-ray morphology shows two peculiar features -- a strongly peaked emission in the centre and an excess emission in the south-west. The central emission probably originates from a weak cooling flow, the SW emission is possibly associated with higher density regions in pressure equilibrium with the intra-cluster medium. This region of excess emission is somewhat embraced by the wide-angle radio tails associated with 3C465 suggesting that the overpressure of the relativistic particles has displaced the thermal gas.

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