We investigate the ideas that a sizable fraction of the interferometrically unresolved infrared emission of the nucleus of NGC 1068 might originate from other processes than thermal dust emission from the torus. We examine the contribution of free-free or synchrotron emissions to the central mid- and near-IR parsec-scale emitting region of NGC 1068. Each mechanism is constrained with parsec scale radio data available for NGC 1068 in the 10^9 - 10^11 Hz regime, and compared to the highest-resolution interferometric data available in the mid-infrared. It is shown that the unresolved emission in the interferometric observation (<~1pc) is still dominatedd by dust emission and not by contributions from synchrotron or free-free emission. As recent studies suggest, the interferometric observations prefer a clumpy structure of the dust distribution. Extrapolation of the radio free-free or synchrotron emission to the IR indicates that their contribution is <20% even for the unresolved fraction of the interferometric flux. The slope of the available radio data is consistent with a power law exponent alpha = 0.29 +/- 0.07 which we interprete in terms of either free-free emission or synchrotron radiation from quasi-monochromatic electrons. We apply emission models for both mechanisms in order to obtain physical parameters. (abridged)
We describe a method of disentangling the composite,0.12-5 microns continuum of symbiotic binaries.The observed SED is determined by the IUE/HST archival spectra and flux-points corresponding to the optical UBVRI and infrared JHKLM photometric measurements. The modeled SED is given by superposition of fluxes from the cool giant, hot stellar source and nebula including the effect of the Rayleigh scattering process and considering influence of the iron curtain absorptions.We applied this method to 21 S-type symbiotic stars during quiescence, activity and eclipses.
We determine the nuclear spectral energy distribution (SED) from the radio to the gamma-ray band for the FR I radio galaxy NGC6251, by using both data from the literature and analyzing HST and X-ray archival data. In the Log nu - Log nu F(nu) representation, the SED has two broad peaks, and it is remarkably similar to those of blazars. We show that the low-energy peak can be explained in terms of synchrotron radiation, while the high energy peak is most plausibly produced by inverse Compton scattering. This brings direct support to the FR I-BL Lacs unification model. We model the overall emiss…
We discuss the interpretation of the dust SED from the mid-infrared to the millimeter range of NGC 1569. The model developed by Désert et al. (1990) including three dust components (Polyaromatic Hydrocarbons, Very Small Grains and big grains) can explain the data using a realistic interstellar radiation field and adopting an enhanced abundance of VSGs. A simple three-temperature model is also able to reproduce the data but requires a very low dust temperature which is considered to be unlikely in this low-metallicity starburst galaxy. The high abundance of Very Small Grains might be due to lar…
Results of submillimeter (450 micron and 850 micron) observations of a nearby dwarf irregular galaxy NGC 4214 with SCUBA on JCMT are presented. We aimed at examining the far-infrared to submillimeter spectral energy distribution (SED) and properties of dust thermal emission in a low metallicity environment by choosing NGC 4214 of which gas metallicity (log O/H + 12) is 8.34. We found that the SED is quite similar to those of IRAS bright galaxies sample (IBGS) which are local bright star-forming galaxies with metallicity comparable to the solar abundance. A dust temperature and an emissivity in…
We present the spectral energy distribution (SED) between 10 and 200 micron obtained for the prototype Narrow-Line X-Ray Galaxy NGC 7582 with ISOPHOT, the photometer on board the Infrared Space Observatory. The emission is spatially extended and we separated for the first time the nuclear and extranuclear infrared SEDs. The nuclear luminosity is dominated by cold (T ~ 32 K) dust emission mainly due to star formation activity; warm (T ~ 122 K) dust emission is also present and is probably related to the active nucleus. In addition to a cold component of 30 K, the extranuclear SED shows emission…
We present the results of a double analysis of the ionizing cluster in NGC 588, a giant HII region (GHR) in the outskirts of the nearby galaxy M33. For this purpose, we obtained ground based long-slit spectroscopy and combined it with archival ground based and space borne imaging and spectroscopy, in the wavelength range 1100-9800 A. A first modeling of the cluster was performed using integrated properties, such as the spectral energy distribution (SED), broad band colors, nebular emission Hbeta equivalent width, the main ultraviolet resonance lines, and the presence of Wolf-Rayet star feature…
We present X-ray (ROSAT), infrared, and radio observations of NGC 4395, which harbors the optically least luminous type 1 Seyfert nucleus discovered thus far. In combination with published optical and ultraviolet spectra, we have used these data to assemble the broadband spectral energy distribution (SED) of the galaxy's nucleus. Interestingly, the SED of NGC 4395 differs markedly from the SEDs of both quasars and typical low-luminosity active galactic nuclei, which may be a manifestation of the different physical conditions (i.e., black hole masses, accretion rates, and/or accretion modes) th…
A multi-cloud model is presented which explains the soft X-ray excess in NGC 4051 and, consistently, the optical line spectrum and the SED of the continuum. The clouds are heated and ionized by the photoionizing flux from the active center and by shocks. Diffuse radiation, partly absorbed throughout the clouds, nicely fits the bump in the soft X-ray domain, while bremsstrahlung radiation from the gaseous clouds contribute to the fit of the continuum SED. Debris of high density fragmented clouds are necessary to explain the absorption oxygen throats observed at 0.87 keV and 0.74 keV. The debris…
Images obtained with the CFHTIR camera on the Canada-France-Hawaii Telescope are used to investigate the near-infrared photometric properties of the star-forming M81 group galaxy NGC 3077. The spectral-energy distribution (SED) of the near-infrared light within 10 arcsec of the nucleus is consistent with the 2um light being dominated by hot young (log(t_{yr}) < 6.8) stars reddened by A_V = 3 - 4, with A_V < 8 mag in some regions. A population like that near the center of NGC 205 likely contributes only a modest fraction of the light near 2um. A number of candidate star clusters are detected in…
We describe a new tool for the analysis of the UV to the sub-millimeter (sub-mm) spectral energy distribution (SED) of spiral galaxies. We use a consistent treatment of grain heating and emission, solve the radiation transfer problem for a finite disk and bulge, and self-consistently calculate the stochastic heating of grains placed in the resulting radiation field. We use this tool to analyse the well-studied nearby edge-on spiral galaxy NGC891. First we investigate whether the old stellar population in NGC891, along with a reasonable assumption about the young stellar population, can account…
We present new 450 and 850 microns SCUBA data of the dwarf galaxy NGC 1569. We construct the mid-infrared to millimeter SED of NGC 1569, using ISOCAM, ISOPHOT, IRAS, KAO, SCUBA and MAMBO data, and model the SED in order to explore the nature of the dust in low metallicity environments. The detailed modeling is performed in a self-consistent way, synthesizing the global ISRF of the galaxy using an evolutionary synthesis model with further constraints provided by the observed MIR ionic lines and a photoionisation model. Our results show that the dust properties are different in this low metallic…
We present a model for the accretion flow around the supermassive black hole in the LINER nucleus of NGC 1097 which fits the optical to X-ray spectral energy distribution (SED). The X-ray segment of the SED is based on observations with the Chandra X-Ray Observatory, which are reported here for the first time. The inner part of the flow is modeled as a radiatively inefficient accretion flow (RIAF) and the outer part as a standard thin disk. The value of the transition radius (~225 Schwarzschild radii) between the RIAF and outer thin disk was obtained from our previous fitting of the double-pea…
Using tools previously described and applied to the prototype galaxy NGC 891, we model the optical to far-infrared spectral energy distributions (SED) of four additional edge-on spiral galaxies, namely NGC 5907, NGC 4013, UGC 1082 and UGC 2048. Comparing the model predictions with IRAS and, where available, sub-millimeter and millimeter observations, we determine the respective roles of the old and young stellar populations in grain heating. In all cases, the young population dominates, with the contribution of the old stellar population being at most 40%, as previously found for NGC 891. Afte…
We report on XMM-Newton spectroscopy of the low-luminosity active galaxies (LLAGN) M81 and NGC4579 both of which have known black hole masses and well-sampled spectral energy distributions (SED). The iron Kalpha line profiles from both the LLAGN can be described in terms of two components - a narrow line at 6.4 keV and a moderately broad line (FWHM = 20000 km/s) arising from highly ionized, He-like or H-like species (E \sim 6.8 keV). We interpret the broad lines arising from an accretion disk the inner edge of which is restricted to large radii (r_{in} \sim 100 r_g). However, the Eddington rat…
We present the results of a 10 ks XMM-Newton observation of NGC 3998, a ``type-I'' LINER galaxy. Our goal is to test the extent to which radiatively-inefficient accretion flow (RIAF) models and/or scaled-down AGN models are consistent with the observed properties of NGC 3998. The upper-limit for narrow Fe-K emission derived from a combined fit of the XMM-Newton and BeppoSAX spectra is 25 eV, which is one of the strictest limits to date for any AGN. This significantly rules out Fe-K emission as is expected to be observed in typical Seyfert 1 galaxies. The lack of any reflection features suggest…
We present the Spitzer IRS spectra for 33 young stars in Tr 37 and NGC 7160. The sample includes the high- and intermediate-mass stars with MIPS 24 microns excess, the only known active accretor in the 12 Myr-old cluster NGC 7160, and 19 low-mass stars with disks in the 4 Myr-old cluster Tr 37. We examine the 10 microns silicate feature, present in the whole sample of low-mass star and in 3 of the high- and intermediate-mass targets, and we find that PAH emission is detectable only in the Herbig Be star. We analyze the composition and size of the warm photospheric silicate grains by fitting th…
We present a new scheme for modeling the broad line region in active galactic nuclei (AGNs). It involves photoionization calculations of a large number of clouds, in several pre-determined geometries, and a comparison of the calculated line intensities with observed emission line light curves. Fitting several observed light curves simultaneously provides strong constraints on model parameters such as the run of density and column density across the nucleus, the shape of the ionizing continuum, and the radial distribution of the emission line clouds. When applying the model to the Seyfert 1 gal…
Very Large Telescope adaptive optics images of NGC 253 with resolutions down to 200 mas resolve the central 300 pc of this galaxy in ~ 37 infrared (IR) bright knots, a factor of 3 larger than previously reported, and extended diffuse emission. The angular resolution, comparable to that of available Very Large Array 2 cm maps, permits us a very accurate IR-radio registration. Eight radio sources are found to have an IR counterpart. The knots have Hαequivalent width of about 80 angstroms, sizes of ~ 3 pc, magnitudes in L-band of about 12 mag and relatively high extinction, Av ~ 7 mag. Their spec…
We present the results of high-resolution mid-infrared observations of the source NGC 3576 IRS 1. Near diffraction-limited images were taken at the Gemini South Observatory through OSCIR's filters N, 7.9, 9.8, 12.5 and IHW18. The source IRS 1 was resolved into 3 sources for the first time at mid-infrared wavelengths. For each source we constructed the SED from 1.25 to 18 microns, as well the color temperature and the spatial distribution of the dust in the region. The optical depth of the silicate absorption feature at 9.8 microns is presented also.
We present mid-infrared spectra of the nearby, Ultraluminous Infrared Galaxy NGC 6240 taken with the IRS on Spitzer. The spectrum of NGC 6240 is dominated by strong fine-structure lines, rotational H2 lines, and PAH emission features. The H2 line fluxes suggest molecular gas at a variety of temperatures. A simple two-temperature fit to the S(0) through S(7) lines implies a mass of 6.7E6 solar masses at T=957K and 1.6E9 solar masses at T=164K, or about 15% of the total molecular gas mass in this system. Noteably, we have detected the [NeV] 14.3 micron emission line, with a flux of 5E-14 erg/cm^…
We have analyzed the total and nuclear SED for NGC 4261 and find that the dominant process for the mid- and far-infrared emission in this object is non-thermal emission from the active nucleus. Modeling the emission from the optically detected 300 pc dust disk yields no significant disk contribution at any wavelength. To explain the observations, either the disk has an inflated inner region which partly absorbs the core, or the intrinsic core spectrum is curved. The inner 10 pc of the disk can potentially be conceived as an obscuring torus, albeit with optical depth around unity.
We obtained low-resolution, long-slit 5300--9100 A spectroscopy of NGC4826 (a nearby galaxy with an absorbing dust lane (DL) asymmetrically placed across its bulge, associated with several HII regions) with a slit encompassing its bulge, positioned across its nucleus. The wavelength-dependent effects of absorption and scattering by dust in the lane are evident when comparing the observed stellar SEDs of pairs of positions symmetrically located with respect to the nucleus, one on the DL side and one on the opposite side of the bulge, by assuming that the intrinsic ISRF is axi-symmetric. We anal…
The central region of the Seyfert 2 galaxy NGC 1068 is imaged in the mid infrared (MIR) using the Mid-Infrared Test Observation System on the 8.2 m Subaru Telescope. The oversampling pixel scale associated with shift-and-add method shows 0.1 arcsec resolution images with a high dynamic range after deconvolution. Along with an extended structure at a position angle (P.A.) of -10 degrees with higher surface brightness, another structure extends wider with lower surface brightness at a P.A. of 20 degrees. The central peak elongates north-south with FWHM of 0.3 x 0.2 arcsec. Spectral energy distri…
We have modelled the low luminosity AGN NGC 4579 by explaining both the continuum and the line spectra. It was found that the nuclear emission is dominated by an AGN. However, a young starburst, an older starburst with age of 4.5 Myr, and shock dominated clouds with velocities of 100, 300, and 500 km/s also contribute. HII regions appear in the the extended regions (about 1 kpc), where radiation and shock dominated clouds with Vs=100 km/s prevail. The continuum SED of NGC 4579 is characterized by the strong flux from an old stellar population. Emissions in the radio range show synchrotron radi…
