Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAGN are cooler than you think: the intrinsic far-IR emission from QSOs
274
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present an intrinsic AGN SED extending from the optical to the submm, derived with a sample of unobscured, optically luminous (vLv(5100)>10^43.5 erg/s) QSOs at z<0.18 from the Palomar Green survey. The intrinsic AGN SED was computed by removing the contribution from stars using the 11.3um polycyclic aromatic hydrocarbon (PAH) feature in the QSOs mid-IR spectra; the 1sigma uncertainty on the SED ranges between 12 and 45 per cent as a function of wavelength and is a combination of PAH flux measurement errors and the uncertainties related to the conversion between PAH luminosity and star-forming luminosity. Longwards of 20um the shape of the intrinsic AGN SED is independent of the AGN power indicating that our template should be applicable to all systems hosting luminous AGN (vLv(5100) or L_X(2-10keV) > 10^43.5 erg/s). We note that for our sample of luminous QSOs, the average AGN emission is at least as high as, and mostly higher than, the total stellar powered emission at all wavelengths from the optical to the submm. This implies that in many galaxies hosting powerful AGN, there is no `safe broadband photometric observation (at lambda<1000um) which can be used in calculating star-formation rates without subtracting the AGN contribution. Roughly, the AGN contribution may be ignored only if the intrinsic AGN luminosity at 5100 Ang is at least a factor of 4 smaller than the total infrared luminosity (L_IR; 8-1000um) of the galaxy. Finally, we examine the implication of our work in statistical studies of star-formation in AGN host galaxies.
rate research
Read More
Context. Extinction and emission of dust models need for observational constraints to be validated. The coreshine phenomenon has already shown the importance of scattering in the 3 to 5 micron range and its ability to validate dust properties for dense cores. Aims. We want to investigate whether scattering can also play a role at longer wavelengths and to place even tighter constraints on the dust properties. Methods. We analyze the inversion of the Spitzer 8 micron map of the dense molecular cloud L183, to examine the importance of scattering as a potential contributor to the line-of-sight extinction. Results. The column density deduced from the inversion of the 8 micron map, when we neglect scattering, disagrees with all the other column density measurements of the same region. Modeling confirms that scattering at 8 microns is not negligible with an intensity of several hundred kJy per sr. This demonstrates the need of efficiently scattering dust grains at MIR wavelengths up to 8 microns. Coagulated aggregates are good candidates and might also explain the discrepancy at high extinction between E(J-K) et tau(9.7) toward dense molecular clouds. Further investigation requires considering efficiently scattering dust grains including ices as realistic dust models.
We investigate the intrinsic spectral energy distribution (SED) of active galactic nuclei (AGNs) at infrared (IR) bands with 42 $z < 0.5$ optically luminous Palomar Green survey quasars through SED decomposition. We decompose the SEDs of the 42 quasars by combining an AGN IR template library Siebenmorgen2015 that covers a wide range of the AGN parameter space with three commonly used galaxy template libraries. We determine the median AGN SED from the best-fitting results. The far-IR (FIR) contribution of our median AGN SED is significantly smaller than that of Symeonidis et al. 2016, but roughly consistent with that of Lyu et al. 2017. The AGN IR SED becomes cooler with increasing bolometric luminosity, which might be due to that more luminous AGNs might have stronger radiative feedback to change torus structures and/or their tori might have higher metallicities. Our conclusions do not depend on the choice of galaxy template libraries. However, since the predicted polycyclic aromatic hydrocarbon (PAH) emission line flux is galaxy template-dependent, cautions should be taken on deriving galaxy FIR contribution from PAH fluxes.
Measuring the star-forming properties of AGN hosts is key to our understanding of galaxy formation and evolution. However, this topic remains debated, partly due to the difficulties in separating the infrared (i.e. 1--1000 $mu$m) emission into AGN and star-forming components. Taking advantage of archival far-infrared data from Herschel, we present a new set of AGN and galaxy infrared templates, and introduce the spectral energy distribution fitting code IRAGNSEP. Both can be used to measure infrared host galaxy properties, free of AGN contamination. To build these, we used a sample of 100 local ($z$ < 0.3), low-to-high luminosity AGNs (i.e. $L_{rm bol}~sim~10^{42--46}~rm erg~s^{-1}$), selected from the 105-month Swift - BAT X-ray survey, which have archival Spitzer - IRS spectra and Herschel photometry. We first built a set of seven galaxy templates using a sample of 55 star-forming galaxies selected via infrared diagnostics. Using these templates, combined with a flexible model for the AGN contribution, we extracted the intrinsic infrared emission of our AGN sample. We further demonstrate that we can reduce the diversity in the intrinsic shapes of AGN spectral energy distributions down to a set of three AGN templates, of which two represent AGN continuum, and one represents silicate emission. Our results indicate that, on average, the contribution of AGNs to the far-infrared ($lambda~gtrsim$ 50 $mu$m) is not as high as suggested by some recent work. We further show that the need for two infrared AGN continuum templates could be related to nuclear obscuration, where one of our templates appears dominated by the emission of the extended polar dust.
We used the 1.4 GHz NVSS to study radio sources in two color-selected QSO samples: a volume-limited sample of 1313 QSOs defined by M_i < -23 in the redshift range 0.2 < z < 0.45 and a magnitude-limited sample of 2471 QSOs with m_r < 18.5 and 1.8 < z < 2.5. About 10% were detected above the 2.4 mJy NVSS catalog limit and are powered primarily by AGNs. The space density of the low-redshift QSOs evolves as rho proportional to (1+z)^6. In both redshift ranges the flux-density distributions and luminosity functions of QSOs stronger than 2.4 mJy are power laws, with no features to suggest more than one kind of radio source. Extrapolating the power laws to lower luminosities predicts the remaining QSOs should be extremely radio quiet, but they are not. Most were detected statistically on the NVSS images with median peak flux densities S_p(mJy/beam) ~ 0.3 and 0.05 in the low- and high-redshift samples, corresponding to 1.4 GHz spectral luminosities log[L(W/Hz)] ~ 22.7$ and 24.1, respectively. We suggest that the faint radio sources are powered by star formation at rates ~20 M_sun per year in the moderate luminosity (median M_i ~ -23.4) low-redshift QSOs and ~500 M_sun per year in the very luminous (M_i} ~ -27.5) high-redshift QSOs. Such luminous starbursts [ log(L / L_sun) ~ 11.2 and 12.6, respectively] are consistent with quasar mode accretion in which cold gas flows fuel both AGN and starburst.
Using photometry of NGC 1097 from the Herschel PACS (Photodetector Array Camera and Spectrometer) instrument, we study the resolved properties of thermal dust continuum emission from a circumnuclear starburst ring with a radius ~ 900 pc. These observations are the first to resolve the structure of a circumnuclear ring at wavelengths that probe the peak (i.e. lambda ~ 100 micron) of the dust spectral energy distribution. The ring dominates the far-infrared (far-IR) emission from the galaxy - the high angular resolution of PACS allows us to isolate the rings contribution and we find it is responsible for 75, 60 and 55% of the total flux of NGC 1097 at 70, 100 and 160 micron, respectively. We compare the far-IR structure of the ring to what is seen at other wavelengths and identify a sequence of far-IR bright knots that correspond to those seen in radio and mid-IR images. The mid- and far-IR band ratios in the ring vary by less than +/- 20% azimuthally, indicating modest variation in the radiation field heating the dust on ~ 600 pc scales. We explore various explanations for the azimuthal uniformity in the far-IR colors of the ring including a lack of well-defined age gradients in the young stellar cluster population, a dominant contribution to the far-IR emission from dust heated by older (> 10 Myr) stars and/or a quick smoothing of local enhancements in dust temperature due to the short orbital period of the ring. Finally, we improve previous limits on the far-IR flux from the inner ~ 600 pc of NGC 1097 by an order of magnitude, providing a better estimate of the total bolometric emission arising from the active galactic nucleus and its associated central starburst.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
