arXiv subjects

Luigi Spinoglio

Publications and source records attributed to Luigi Spinoglio.

47 records · Page 3Linked to original sources

arXiv2007

High-excitation OH and H_2O lines in Markarian 231: the molecular signatures of compact far-infrared continuum sources

The ISO/LWS far-infrared spectrum of the ultraluminous galaxy Mkn 231 shows OH and H_2O lines in absorption from energy levels up to 300 K above the ground state, and emission in the [O I] 63 micron and [C II] 158 micron lines. Our analysis shows that OH and H_2O are radiatively pumped by the far-infrared continuum emission of the galaxy. The absorptions in the high-excitation lines require high far-infrared radiation densities, allowing us to constrain the properties of the underlying continuum source. The bulk of the far-infrared continuum arises from a warm (T_dust=70-100 K), optically thick (tau_100micron=1-2) medium of effective diameter 200-400 pc. In our best-fit model of total luminosity L_IR, the observed OH and H2O high-lying lines arise from a luminous (L/L_IR~0.56) region with radius ~100 pc. The high surface brightness of this component suggests that its infrared emission is dominated by the AGN. The derived column densities N(OH)>~10^{17} cm^{-2} and N(H_2O)>~6x10^{16} cm^{-2} may indicate XDR chemistry, although significant starburst chemistry cannot be ruled out. The lower-lying OH, [C II] 158 micron, and [O I] 63 micron lines arise from a more extended (~350 pc) starburst region. We show that the [C II] deficit in Mkn 231 is compatible with a high average abundance of C+ because of an extreme overall luminosity to gas mass ratio. Therefore, a [C II] deficit may indicate a significant contribution to the luminosity by an AGN, and/or by extremely efficient star formation.

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arXiv2007

Spitzer-IRS high resolution spectroscopy of the 12μm Seyfert galaxies: I. First results

The first high resolution Spitzer IRS 9-37um spectra of 29 Seyfert galaxies (about one quarter) of the 12um Active Galaxy Sample are presented and discussed. The high resolution spectroscopy was obtained with corresponding off-source observations. This allows excellent background subtraction, so that the continuum levels and strengths of weak emission lines are accurately measured. The result is several new combinations of emission line ratios, line/continuum and continuum/continuum ratios that turn out to be effective diagnostics of the strength of the AGN component in the IR emission of these galaxies. The line ratios [NeV]/[NeII], [OIV]/[NeII], already known, but also [NeIII]/[NeII] and [NeV]/[SiII] can all be effectively used to measure the dominance of the AGN. We extend the analysis, already done using the 6.2um PAH emission feature, to the equivalent width of the 11.25um PAH feature, which also anti-correlates with the dominance of the AGN. We measure that the 11.25um PAH feature has a constant ratio with the H_2 S(1) irrespective of Seyfert type, approximately 10 to 1. Using the ratio of accurate flux measurements at about 19um with the two spectrometer channels, having aperture areas differing by a factor 4, we measured the source extendness and correlated it with the emission line and PAH feature equivalent widths. The extendness of the source gives another measure of the AGN dominance and correlates both with the EWs of [NeII] and PAH emission. Using the rotational transitions of H$_2$ we were able to estimate temperatures (200-300K) and masses (1-10 x 10^6 M_sun), or significant limits on them, for the warm molecular component in the galaxies observed.

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arXiv2007

Infrared spectroscopic diagnostics for Active Galactic Nuclei

Infrared spectroscopy in the mid- and far-infrared provides powerful diagnostics for studying the emission regions in active galaxies. The large variety of ionic fine structure lines can probe gas conditions in a variety of physical conditions, from highly ionized gas excited by photons originated by black hole accretion to gas photoionized by young stellar systems. The critical density and the ionization potential of these transitions allow to fully cover the density-ionization parameter space. Some examples of line ratios diagrams using both mid-infrared and far-infrared ionic fine structure lines are presented. The upcoming space observatory Herschel will be able to observe the far-infrared spectra of large samples of local active galaxies. Based on the observed near-to-far infrared emission line spectrum of the template galaxy NGC1068, are presented the predictions for the line fluxes expected for galaxies at high redshift. To observe spectroscopically large samples of distant galaxies, we will have to wait fot the future space missions, like SPICA and, ultimately, FIRI.

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arXiv2006

Potential programs for high sensitivity FIR spectroscopy with SPICA

We discuss the potential of high sensitivity mid-IR and far-IR spectroscopy to proof the physical properties of active nuclei and starburst regions of local and distant galaxies. For local galaxies, it will be possible to map the discs and ISM through the low ionization ionic lines and a variety of molecular tracers, such as OH, H2O and high-J CO. At increasing distance, most of the ionic nebular lines (typical of stars and AGNs) are shifted into the FIR, making possible to compare the observed spectra with those predicted by different evolutionary scenarios. At the very high redshift of 10-15, sensitive mid-to-far-IR spectrometers, such as those planned to be at the focal plane of the future SPICA mision, could be adequate to detect the H recombination lines excited in the HII regions around population III stars, if these stars happened to reside in large clusters of more than 10^5 members.

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arXiv2006

A Herschel survey of local galaxies activity (HERLOGA)

The key project HERLOGA to be proposed for the Herschel mission is aimed to provide an homogeneous data set on local active galaxies that could be the reference for further studies on the interplay between star formation processes and accretion onto massive black holes in galactic nuclei. The selected sample will be the overlap between the 12 micron sample and an all-sky hard-X ray selected sample of AGNs. The Herschel data will follow extensive observational work that is already available from radio to X-rays frequencies and will provide the baseline of zero-redshift objects for comparison with the high redshift Universe which will be revealed by the Herschel cosmological surveys.

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arXiv2005

The far-infrared emission line and continuum spectrum of the Seyfert galaxy NGC 1068

The first complete far-infrared spectrum (43-197um) of the Seyfert 2 galaxy NGC 1068 as observed with the LWS onboard ISO is reported. In addition to the expected ionic fine structure emission lines, the OH rotational lines at 79, 119 and 163um were all detected in emission. The line intensities were modelled together with ISO SWS and optical and UV line intensities from the literature, considering two independent emission components: the AGN component and the starburst component in the circumnuclear ring of 3 kpc in size. Using the UV to mid-IR emission line spectrum to constrain the nuclear ionizing continuum, we have confirmed previous results: a canonical power-law ionizing spectrum is a poorer fit than one with a deep absorption trough, while the presence of a big blue bump is ruled out. Based on starburst synthesis models, we were able to fit the mid- and far-infrared fine-structure line emission, with a low ionization parameter (logU=-3.5) and low densities (n=100 cm^-3). Combining AGN and starburst components, we succeeded in modeling the overall UV to far-IR atomic spectrum of NGC1068, reproducing the line fluxes to within a factor 2.0 on average with a standard deviation of 1.3 and the overall continuum as the sum of the contribution of the thermal dust emission in the ionized and neutral components. TheOH 119 um emission indicates that the line is collisionally excited and arises in a warm and dense region. The OH emission has been modeled using spherically symmetric, non-local, non-LTE radiative transfer models. The models indicate that the bulk of the emission arises from the nuclear region, although some extended contribution from the starburst is not ruled out. The OH abundance in the nuclear region is expected to be $\sim10^{-5}$, characteristic of X-ray dominated regions.

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arXiv2003

The ISO-LWS far-infrared spectra of pre-Main Sequence objects

The Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO) satellite has allowed for the first time to investigate the whole far infrared (FIR) part of the spectrum (from 43 to 197 um), inaccessible from the ground. The FIR spectrum is crucial for the study of the early phases of protostellar evolution since the peak of the continuum emission of the protostars falls around 100 um and many molecular species emit in this range. In this paper we review the main results of the spectroscopic observations carried out with the LWS on a sample of pre-Main Sequence objects in different evolutionary stages. The FIR spectra are characterized by a strong continuum with superimposed atomic and molecular emission lines. The fine structure lines emitted by the OI and CII atoms are present in all the objects of our sample while emission from molecular species (CO, H_2O and OH) dominate the spectrum of the younger and more embedded objects; lines of highly ionized atoms (OIII, NIII, NII) are present only in high luminosity sources. We will show how both the FIR continuum and the emission lines are powerful indicators of the evolutionary status of young embedded objects. The analysis of the LWS spectra has allowed to study only the average properties of the young stellar objects, due to the large field of view (~ 80 arcsec), the limited sensitivity and the poor spectral resolution (~ 200) of the instrument in its grating mode. The higher spatial and spectral resolutions of the instruments on board the Herschel satellite will allow to address in deeper detail the scientific problems highlighted by the ISO results.

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arXiv2003

How many active galaxies and QSOs will future Space Missions detect?

Averaged spectral energy distributions (SEDs) of active and starburst galaxies from the 12 micron sample in the Local Universe and Quasars, from an optically selected sample at a mean redshift =0.7, are built from optical/near-IR/far-IR (IRAS & ISO) photometric observations. These SEDs are then used to predict at various redshifts the number of Seyfert type 1 and type 2, starburst, normal galaxies, and quasars, that will be detected by future Space Missions dedicated to far-infrared and submillimeter astronomy, like SIRTF and Herschel. These predictions are then compared with the expected capabilities and detection limits of future deep far-IR surveys. Possible ways to identify AGN candidates on far-IR colour-colour plots for follow-up observations are then explored.

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arXiv2002

The far-infrared energy distributions of Seyfert and starburst galaxies in the Local Universe: ISO photometry of the 12 micron active galaxy sample

New far-infrared photometry with ISOPHOT, onboard the Infrared Space Observatory, is presented for 58 galaxies with homogeneous published data for another 32 galaxies all belonging to the 12 micron galaxy sample. In total 29 Seyfert 1's, 35 Seyfert 2's and 12 starburst galaxies, about half of the 12 micron active galaxy sample, plus 14 normal galaxies for comparison. The ISO and the IRAS data are used to define color-color diagrams and spectral energy distributions (SED). Thermal dust emission at two temperatures (one cold at 15-30K and one warm at 50-70K) can fit the 60-200 micron SED, with a dust emissivity law proportional to the inverse square of the wavelength. Seyfert 1's and Seyfert 2's are indistinguishable longward of 100 micron, while, as already seen by IRAS, the former have flatter SEDs shortward of 60 micron. A mild anti-correlation is found between the [200 - 100] color and the "60 micron excess". We infer that this is due to the fact that galaxies with a strong starburst component, and thus a strong 60 micron flux, have a steeper far-infrared turnover. In non-Seyfert galaxies, increasing the luminosity corresponds to increasing the star formation rate, that enhances the 25 and 60 micron emission. This shifts the peak emission from around 150 micron in the most quiescent spirals to shorter than 60 micron in the strongest starburst galaxies.

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arXiv2000

A Shock-Induced PDR in the HH 80/81 Flow. Far Infrared Spectroscopy

The two spectrometers on board the Infrared Space Observatory were used to observe the Herbig-Haro objects HH 80, 81 and 80N, as well as their candidate exciting source IRAS 18162-2048. The fine structure lines of [OI]63um, [OI]145um and [CII]158um are detected everywhere, while [NII]122um and [OIII]88um are only detected toward the HH objects; line ratios confirm for the first time the collisionally excited HH nature of HH 80N. No molecular line is detected in any of the observed positions. We use a full shock code to diagnose shock velocities vs~100 km/s toward the HH objects, as expected from the optical spectroscopy. Since proper motions suggest velocities in excess of 600 km/s, the HH objects probably represent the interface between two flow components with velocity differing by ~vs. Aside from the flow exciting source, the [CII]158um line is everywhere brighter than the [OI]63um line, indicating the presence of a Photo-Dissociation Region (PDR) all along the flow. Continuum emission from the HH objects and from other positions along the flow is only detected longword of ~50 micron, and its proportionality to the [CII]158um line flux suggests it is PDR in origin. We propose that the FUV continuum irradiated by the HH objects and the jet is responsible for the generation of a PDR at the walls of the flow cavity. We develop a very simple model which strengthens the plausibility of this hypothesis.

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arXiv1995

Multiwavelength Energy Distributions and Bolometric Luminosities of the 12--Micron Galaxy Sample

Aperture photometry from our own observations and the literature is presented for the 12\um\ Galaxies in the near infrared J, H and K bands and, in some cases, in the L band. These data are corrected to ``total'' near--infrared magnitudes, (with a typical uncertainty of 0.3 magnitudes) for a direct comparison with our IRAS fluxes which apply to the entire galaxy. The corrected data are used to derive integrated total NIR and FIR luminosities. We then combine these with blue photometry and an estimate of the flux contribution from cold dust at wavelengths longward of 100\um\ to derive the first {\it bolometric\/} luminosities for a large sample of galaxies. We use multiwavelength correlations to identify several combinations of infrared colors which discriminate between Seyfert~1 and~2 galaxies, LINERs, and ultraluminous starbursts. We find that bolometric luminosity is more closely proportional to 12-micron luminosity than to 60-micron, 25-micron or optical luminosity.

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