arXiv subjects

E. Oliva

Publications and source records attributed to E. Oliva.

At least 73 records · Page 4Linked to original sources

arXiv2002

Mid-Infrared line diagnostics of Active Galaxies -- A spectroscopic AGN survey with ISO-SWS

We present medium resolution (R approx. 1500) ISO-SWS 2.4--45 micron spectra of a sample of 29 galaxies with active nuclei. This data set is rich in fine structure emission lines tracing the narrow line regions and (circum-)nuclear star formation regions, and it provides a coherent spectroscopic reference for future extragalactic studies in the mid-infrared. We use the data set to briefly discuss the physical conditions in the narrow line regions (density, temperature, excitation, line profiles) and to test for possible differences between AGN sub-types. Our main focus is on new tools for determining the propertibes of dusty galaxies and on the AGN-starburst connection. We present mid-IR line ratio diagrams which can be used to identify composite (starburst + AGN) sources and to distinguish between emission excited by active nuclei and emission from (circum-nuclear) star forming regions. For instance, line ratios of high to low excitation lines like [O IV]25.9um/[Ne II]12.8um, that have been used to probe for AGNs in dusty objects, can be examined in more detail and with better statistics now. In addition, we present two-dimensional diagnostic diagrams that are fully analogous to classical optical diagnostic diagrams, but better suited for objects with high extinction. Finally, we discuss correlations of mid-infrared line fluxes to the mid- and far-infrared continuum. We compare these relations to similar relations in starburst galaxies in order to examine the contribution of AGNs to the bolometric luminosities of their host galaxies. The spectra are available in electronic form from the authors.

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arXiv2002

A Young Very Low-Mass Object surrounded by warm dust

We present a complete low-resolution (R~100) near-infrared spectrum of the substellar object GY11, member of the rho-Ophiuchi young association. The object is remarkable because of its low estimated mass and age and because it is associated with a mid-infrared source, an indication of a surrounding dusty disk. Based on the comparison of our spectrum with similar spectra of field M-dwarfs and atmospheric models, we obtain revised estimates of the spectral type, effective temperature and luminosity of the central object. These parameters are used to place the object on a Hertzprung-Russell diagram and to compare with the prediction of pre-main sequence evolutionary models. Our analysis suggests that the central object has a very low mass, probably below the deuterium burning limit and in the range 8-12MJupiter, and a young age, less than 1Myr. The infrared excess is shown to be consistent with the emission of a flared, irradiated disk similar to those found in more massive brown dwarf and TTauri systems. This result suggests that substellar objects, even the so-called isolated planetary mass objects, found in young stellar associations are produced in a similar fashion as stars, by core contraction and gravitational collapse.

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arXiv2002

Transmission curves and effective refraction indices of MKO near infrared consortium filters at cryogenic temperatures

We report transmission measurements at cryogenic temperatures for 4 broad-band filters of the Mauna Kea Observatories (MKO) near-infrared filter set and 5 narrow-band filters. The spectral scans were collected using the multi-mode IR instrument of the TNG telescope (NICS) in which these filters are permanently mounted and commonly used for astronomical observations. We determined the transmission curves at a temperature of 78K and found no significant red-leak up to 2.6 microns, the data are available in electronic form on the TNG web page. We also estimated the variation of the wavelength response with the incidence angle and found it compatible with an effective refractive index of about 2.

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arXiv2001

The relative abundances of ellipticals and starbursts among the Extremely Red Galaxies

We present J band observations of a complete sample of 57 red galaxies selected to have K<20 and R-K>5.3. We use the Pozzetti and Mannucci (2000) prescriptions, based on the R-K and J-K colours, to separate the two dominant populations, old ellipticals and dusty starbursts. We find that both populations are present in the current sample and have similar abundances, and discuss the uncertainties in this result. Galactic stars comprise about 9% of the objects. The starburst galaxies of the present sample are found to give a contribution to the cosmic star formation density similar to the Lyman-break galaxies.

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arXiv2001

The TNG Near Infrared Camera Spectrometer

NICS (acronym for Near Infrared Camera Spectrometer) is the near-infrared cooled camera-spectrometer that has been developed by the Arcetri Infrared Group at the Arcetri Astrophysical Observatory, in collaboration with the CAISMI-CNR for the TNG (the Italian National Telescope Galileo at La Palma, Canary Islands, Spain). As NICS is in its scientific commissioning phase, we report its observing capabilities in the near-infrared bands at the TNG, along with the measured performance and the limiting magnitudes. We also describe some technical details of the project, such as cryogenics, mechanics, and the system which executes data acquisition and control, along with the related software.

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arXiv2001

NICS-TNG infrared spectroscopy of trans-neptunian objects 2000 EB173 and 2000 WR106

We report complete near-infrared (0.9-2.4 $μ$m) spectral observations of trans-neptunian objects (TNOs) 2000 EB173 and 2000 WR106 collected using the new Near Infrared Camera Spectrometer (NICS) attached to the 3.56m Telescopio Nazionale Galileo (TNG). Both spectra are very red and with a quite strong and broad drop extending throughout the K band. However, while 2000 EB173 does not show any evidence of narrow absorption features, the spectrum of 2000 WR106 has quite deep water ice absorption at 1.5 and 2.0 $μ$m. Moreover, the latter object is significantly less red than the former indicating, therefore, that the surface of 2000 WR106 is ``cleaner'' (i.e. less processed by particle irradiation) than that of 2000 EB173.

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arXiv2001

Discovery of strong CIV absorption in the highest redshift quasar

We report the near-IR detection of a prominent CIV absorption in the rest-frame UV spectrum of the most distant known QSO, SDSS J104433.04-012502.2, at z=5.80. This QSO was recently observed with XMM-Newton and it was found to be notably X-ray weak. The equivalent width of the CIV absorption feature (~10 A) strongly supports the idea that the X-ray faintness of this QSO is due to heavy absorption by gas with a column density N_H > 10^{24} cm^-2. The shape of the CIV feature suggests that this is a Broad Absorption Line QSO. Although absorbed by a huge column of gas, the observed continuum in the 0.9-2.4um range (~1300-3500 A rest frame) exactly matches the template of unabsorbed QSOs without invoking any reddening (E(B-V)<0.08 mag), indicating that dust in the absorbing gas is either absent or composed of large grains.

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arXiv2001

NICS-TNG low-resolution 0.85-2.45um spectra of L-Dwarfs: a near-infrared spectral classification scheme for faint dwarfs

We present complete near-infrared (0.85-2.45 um), low-resolution (~100) spectra of a sample of 26 disk L-dwarfs with reliable optical spectral type classification. The observations have been obtained with NICS at the TNG using a prism-based optical element (the Amici device) that provides a complete spectrum of the source on the detector. Our observations show that low-resolution near-infrared spectroscopy can be used to determine the spectral classification of L-dwarfs in a fast but accurate way. We present a library of spectra that can be used as templates for spectral classification of faint dwarfs. We also discuss a set of near-infrared spectral indices well correlated with the optical spectral types that can be used to accurately classify L-dwarfs earlier than L6.

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arXiv2001

NICS-TNG infrared spectroscopy of NGC1068: the first extragalactic measurement of [PII] and a new tool to constrain the origin of [FeII] line emission in galaxies

We report 0.9-1.4 micron spectroscopic observations of NGC1068 collected during the commissioning phase of the near infrared camera spectrometer (NICS) of the Telescopio Nazionale Galileo (TNG). These yielded the first extragalactic measurement of [PII] (1.188 micron) line emission. In the central 0.75"x2" the [FeII]/[PII] line-intensity ratio is close to unity, similar to that measured in the Orion bar and a factor of about 20 smaller than in supernova remnants. This indicates that most of iron is locked into grains and, therefore, argues against shock excitation being the primary origin of [FeII] line emission in the central regions of NGC1068. We propose the [FeII]/[PII] ratio as a simple and effective tool to study and perhaps resolve the long debated questions related to the origin of [FeII] line emission and, more generally, to constrain the role of shock excitation in active galaxies.

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arXiv2000

Dust in active nuclei. II. Powder or gravel?

In a companion paper, Maiolino et al. (2000) presented various observational evidences for "anomalous" dust properties in the circumnuclear region of AGNs and, in particular, the reduced E(B-V)/N_H and Av/N_H ratios, the absence of the silicate absorption feature in mid-IR spectra of Sy2s and the absence of the carbon dip in UV spectra of reddened Sy1s. In this paper we discuss various explanations for these facts. The observational constraints favor a scenario where coagulation, catalyzed by the high densities in the circumnuclear region, yields to the formation of large grains. The resulting extinction curve is featureless, flatter than Galactic and the E(B-V)/N_H and Av/N_H ratios are significantly reduced. These results should warn about an unappropriate use of the standard Galactic extinction curve and Av/N_H ratio when dealing with the extreme gas conditions typical of the circumnuclear clouds of AGNs. We also investigated alternative scenarios for the observed anomalous properties of dust in AGNs. Some of these scenarios might explain some of the observed properties for a few objects, but they generally fail to account for all of the observational constraints obtained for the large sample of AGNs studied in these works.

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arXiv2000

Is the [CO] index an age indicator for star forming galaxies?

The classical [CO] index, i.e. the strength of the CO first overtone absorption bands starting at 2.29 micron, is sometimes used to constrain the maximum age of star formation events in galaxies. In this paper we critically analyze - theoretical models which could predict either a factor of >2 drop or a pronounced increase of [CO] at ages older than 100 Myr, depending on the evolutionary tracks one adopts - observational data for young clusters in the LMC which do not show any strong relationship between the CO index and cluster age. The above scenario indicates that the value of [CO] does not provide a reliable tool for estimating the age of stellar populations older than about 10 Myr, i.e. after the first red supergiants have been formed. The contradictory results of theoretical models reflect problems in treating the evolution along the Asymptotic Giant Branch (AGB). In particular, those evolutionary synthesis models using stellar tracks which do not include the thermal pulsing AGB phase produce too weak CO features at 100-1000 Myr, i.e. in the range of ages when the near infrared emission is dominated by thermal pulsing AGB stars.

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arXiv2000

The Elusive Active Nucleus of NGC 4945

We present new HST NICMOS observations of NGC 4945, a starburst galaxy hosting a highly obscured active nucleus that is one of the brightest extragalactic sources at 100 keV. The HST data are complemented with ground based [FeII] line and mid--IR observations. A 100pc-scale starburst ring is detected in Pa alpha, while H_2 traces the walls of a super bubble opened by supernova-driven winds. The conically shaped cavity is particularly prominent in Pa alpha equivalent width and in the Pa alpha/H_2 ratio. Continuum images are heavily affected by dust extinction and the nucleus of the galaxy is located in a highly reddened region with an elongated, disk-like morphology. No manifestation of the active nucleus is found, neither a strong point source nor dilution in CO stellar features, which are expected tracers of AGN activity. Even if no AGN traces are detected in the near-IR, with the currently available data it is still not possible to establish whether the bolometric luminosity of the object is powered by the AGN or by the starburst: we demonstrate that the two scenarios constitute equally viable alternatives. However, the absence of any signature other than in the hard X-rays implies that, in both scenarios, the AGN is non-standard: if it dominates, it must be obscured in all directions, conversely, if the starburst dominates, the AGN must lack UV photons with respect to X-rays. An important conclusion is that powerful AGNs can be hidden even at mid-infrared wavelengths and, therefore, the nature of luminous dusty galaxies cannot be always characterized by long-wavelength data alone but must be complemented with sensitive hard X-ray observations.

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arXiv1999

New Clues on the Nature of Extremely Red Galaxies

We present near-infrared VLT-UT1+ISAAC spectroscopy of a sample of 9 extremely red galaxies (ERGs) with R-K>5 and K<19.0. Neither strong emission lines (F_lim<1-5 10^{-16} erg s^{-1}cm^{-2}) nor continuum breaks are detected. From near-infrared spectrophotometry, complemented with broad-band optical and near-IR photometry, we estimate ``spectro-photometric'' redshifts to be in the range of 0.8 0.8. We discuss the general implications of our findings in relation with the problem of the formation of early type galaxies.

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arXiv1999

The density of methane brown dwarfs: observational and theoretical constraints

Methane brown dwarfs, i.e. objects similar to the low mass star Gliese 229B, are characterized by very unusual colours: J-K<~0 and I-J>~5. An analysis of the ESO public images, which cover an area of 37 sq. arcmin in the three filters, yields one clear methane dwarf candidate with J=20.2 and two fainter sources with J~=23. The resulting observed density of methane dwarfs ranges from ~100 to ~500 objects per sq. degree with J<23.1, quite high but compatible, within the errors, with what we derive from simulations of the stellar population of brown dwarfs in the disk of the Galaxy adopting reasonable (although still speculative) hypotheses on the evolution of BD colours with cooling. The predictions presented here can be useful in constraining the results from future searches of these objects in the infrared. Deep imaging of several sq. degrees of sky down to J~=22, K~=22 and I>~27 are necessary to significantly improve the observational database.

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arXiv1999

Infrared instrumentation for large telescopes: an alternative approach

I very briefly describe the latest generation near infrared (1-2.5 micron) instruments which are available on, or under development for `large' (D>=3.5 m) telescopes. Most of the imagers under construction are limited to relatively small fields, while the spectrometers aim at quite high resolving powers. The alternative instruments which I discuss here are - WIDE, a relatively low-cost instrument for the prime focus of LBT and/or of TNG optimized for deep imaging of very large fields (12'x12' on LBT and 26'x26' on TNG) through the 1 micron, J, H, K' broad-band filters. - AMICI, an ultra-high efficiency, low resolution disperser optimized for collecting complete 0.9-2.5 micron spectra of very faint objects. This device is mounted in NICS (the IR instrument for TNG) and should soon deliver spectra with quality comparable to that obtained with instruments on 8m class telescopes with similar integration times.

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arXiv1999

Starbursts in active galaxy nuclei: observational constraints from IR stellar absorption lines

High quality infrared spectra of active galaxies including the stellar absorption features of Si at 1.59 um, CO(6,3) at 1.62 um, and CO(2,0) at 2.29 um are used to measure the stellar mass to light ratio at 1.65 um (M_H/L) and investigate the occurrence circum--nuclear starbursts. We find that old and powerful starbursts are relatively common in obscured AGNs (5 objects out of 13) while absent in genuine Seyfert 1's (0 objects out of 8). The data are also used to derive the non-stellar continuum which is very red and compatible with emission from warm (~1000 K) dust even in bare Sy1's, thus indicating that the near IR nuclear continuum is reprocessed radiation. Hot dust (~800 K) emission is also detected in a few obscured AGNs, including the Seyfert 2 prototype NGC1068. The observed non-stellar flux is too high to be accounted for by scattered light and therefore indicates that the material obscuring the AGN must have a quite small (<~1 pc) projected size.

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arXiv1999

Infrared spectroscopy of young supernova remnants heavily interacting with the interstellar medium

ISO spectral observations of the supernova remnant RCW103 are presented. This object is the prototype of relatively young remnants with fast shocks interacting with dense interstellar medium. The spectrum is dominated by prominent lines of [NeII], [SiII], [FeII] and other low excitation species which provide, for the first time, a simple and reliable estimate of the gas abundances of refractory (Si, Fe, Ni) and non-refractory (Ne, P, S, Cl, Ar) species. Apart from nickel, all the derived abundances are close to solar, confirming that the shock has destroyed all dust grains. Like the optical nickel lines, [NiII] 6.64micron yields Ni abundances a factor ~10 solar which we propose results from a large underestimation of the computed Ni+ collision strengths. The observed intensities and velocity widths of ionic lines are compatible with emission from the post-shock region alone with only a very small (if any) contribution from the photoionized precursor. This result does not agree with shock models which predict that the precursor should emit powerful line emission, especially from highly ionized species. The possible consequence of this on the modelling of Seyfert spectra is briefly discussed.

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arXiv1998

ISO-SWS spectroscopy of IC443 and the origin of the IRAS 12 and 25 micron emission from radiative supernova remnants

ISO-SWS spectral observations of the supernova remnant IC443 are presented. Like other radiative SNRs, this object is characterized by prominent line-emitting filaments and relatively strong IRAS 12 and 25 micron emission which is commonly interpreted as thermal radiation from very small grains stochastically heated by collisions with the hot plasma behind the shock front. This interpretation is challenged by the data presented in this Letter which indicate that most of the 12 and 25 micron IRAS flux is accounted for by ionized line emission (mainly [NeII] and [FeII]). This result also seems to hold for other radiative SNRs. We also discuss the possible contribution of H_2 lines to the IRAS 12 micron flux from the southern rim of IC443 and briefly analyze the element abundances derived from the observed ionic lines.

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