E. Sani

The Spitzer/IRAC view of black hole–bulge scaling relations

We present a mid-infrared investigation of the scaling relations between supermassive black hole masses (M BH ) and the structural parameters of the host spheroids in local galaxies. This work is based on 2D bulge-disc decompositions of Spitzer/IRAC 3.6 μm images of 57 galaxies with M BH estimates. We first verify the accuracy of our decomposition by examining the Fundamental Plane (FP) of spheroids at 3.6 μm. Our estimates of effective radii (R e ) and average surface brightnesses, combined with velocity dispersions from the literature, define a FP relation consistent with previous determinations but doubling the observed range in R e . None of our galaxies is an outlier of the FP, demonstrating the accuracy of our bulge-disc decomposition which also allows us to independently identify pseudo-bulges in our sample. We calibrate M/L at 3.6 μm by using the tight M dyn ―L bul relation (∼0.1 dex intrinsic dispersion) and find that no colour corrections are required to estimate the stellar mass. The 3.6 μm luminosity is thus the best tracer of stellar mass yet studied. We then explore the connection between M BH and bulge structural parameters (luminosity, mass, effective radius). We find tight correlations of M BH with both 3.6 μm bulge luminosity and dynamical mass (M BH /M dyn ∼ 1/1000), with intrinsic dispersions of ∼0.35 dex, similar to the M BH ―σ relation. Our results are consistent with previous determinations at shorter wavelengths. By using our calibrated M/L, we rescale M BH ―L bul to obtain the M BH ―M * relation, which can be used as the local reference for high-z studies which probe the cosmic evolution of M BH ―galaxy relations and where the stellar mass is inferred directly from luminosity measurements. The analysis of pseudo-bulges shows that four out of nine lie on the scaling relations within the observed scatter, while those with small M BH are significantly displaced. We explore the different origins for such behaviour while considering the possibility of nuclear morphological components not reproduced by our 2D decomposition.

Spectral decomposition of starbursts and active galactic nuclei in 5–8 μm Spitzer-IRS spectra of local ultraluminous infrared galaxies

We present an analysis of the 5–8 μm Spitzer -IRS spectra of a sample of 68 local Ultraluminous Infrared Galaxies (ULIRGs). Our diagnostic technique allows a clear separation of the active galactic nucleus (AGN) and starburst (SB) components in the observed mid-IR emission, and a simple analytic model provides a quantitative estimate of the AGN/starburst contribution to the bolometric luminosity. We show that AGNs are ∼ 30 times brighter at 6 μm than starbursts with the same bolometric luminosity, so that even faint AGNs can be detected. Star formation events are confirmed as the dominant power source for extreme infrared activity, since ∼ 85% of ULIRG luminosity arises from the SB component. Nonetheless an AGN is present in the majority (46/68) of our sources.

Unveiling the nature of Ultraluminous Infrared Galaxies with 3–4 μm spectroscopy

We present the results of L-band spectroscopical observations of local bright Ultraluminous Infrared Galaxies (ULIRGs), performed with the Infrared Spectrometer And Array Camera (ISAAC) at the Very Large Telescope. The excellent sensitivity of the telescope and of the instrument provided spectra of unprecedented quality for this class of objects, which allowed a detailed study of the active galactic nucleus (AGN)/starburst contribution to the energy output, and of the composition of the circumnuclear absorber. We discuss the L-band spectral features of seven single sources, and the statistical properties of a complete sample of 15 sources obtained combining our observations with other published 3–4 μm spectra. Our main results are as follows. (i)  When a spectral indicator suggesting the presence of an AGN (low equivalent width of the 3.3-μm emission line, steep λ–fλ spectrum, presence of an absorption feature at 3.4 μm) is found, the AGN is always confirmed by independent analysis at other wavelengths. Conversely, in all known AGNs at least one of the above indicators is present. (ii)  Two new diagnostic diagrams are proposed combining the above indicators, in which starbursts and AGNs are clearly and completely separated. (iii)  The above diagnostic techniques are possible with spectra of relatively low quality, which can be obtained for several tens of ULIRGs with currently available telescopes. This makes L-band spectroscopy the current best tool to disentangle AGN and starburst contributions in ULIRGs. (iv)  The L-band properties of ULIRGs are heterogeneous. However, we show that all the spectral differences among ULIRGs can be reproduced starting from pure intrinsic AGN and starburst spectra and two varying parameters: the amount of dust extinction of the AGN component, and the relative AGN/starburst contribution to the bolometric luminosity. (v)  Using the above decomposition model, we show that AGNs in ULIRGs have a low dust-to-gas ratio and a dust extinction curve different from Galactic. (vi)  The estimate of the presence and contribution of AGNs in a complete sample shows that AGNs are hosted by approximately two-thirds of ULIRGs, but their energetic contribution is relevant (>30 per cent of the bolometric luminosity) only in ∼20 per cent of the sample.

Exploring the active galactic nucleus and starburst content of local ultraluminous infrared galaxies through 5–8 μm spectroscopy

We present a 5-8 μm analysis of the Spitzer spectra of 71 ultraluminous infrared galaxies (ULIRGs) with redshift z < 0.15, devoted to the study of the role of active galactic nuclei (AGN) and starbursts (SBs) as the power source of the extreme infrared emission. Around ∼5 μm, an AGN is much brighter (by a factor of ≈30) than an SB of equal bolometric luminosity. This allows us to detect the presence of even faint accretion-driven cores inside ULIRGs: signatures of AGN activity are found in ∼70 per cent of our sample (50/71 sources). Through a simple analytical model, we are also able to obtain a quantitative estimate of the AGN/SB contribution to the overall energy output of each source. Although the main fraction of ULIRG luminosity is confirmed to arise from star formation events, the AGN contribution is non-negligible (∼23 per cent) and is shown to increase with luminosity. The existence of a rather heterogeneous pattern in the composition and geometrical structure of the dust among ULIRGs is newly supported by the comparison between individual absorption features and continuum extinction.

A quantitative determination of the AGN content in local ULIRGs through L-band spectroscopy

We present a quantitative estimate of the relative active galactic nucleus (AGN)/starburst content in a sample of 59 nearby (z 85 per cent of the observed infrared luminosity. The subsample of sources optically classified as low-ionization nuclear emission-line regions (LINERs; 31 objects) shows a similar AGN/starburst distribution as the whole sample, indicating a composite nature for this class of objects. We also show that a few ULIRGs, optically classified as starbursts, have L-band spectral features suggesting the presence of a buried AGN.

The double active galactic nucleus in NGC 6240 revealed through 3-5 μm spectroscopy

We present 3-5 micron spectroscopy of the interacting system NGC 6240, showing the presence of two active galactic nuclei. The brightest (southern) nucleus shows up with a starburst-like emission, with a prominent 3.3 micron emission feature. However, the presence of an AGN is revealed by the detection of a broad Br alpha emission line, with a width of ~1,800 km/s. The spectrum of the faintest (northern) nucleus shows typical AGN features, such as a steep continuum and broad absorption features in the M-band. We discuss the physical properties of the dusty absorbers/emitters, and show that in both nuclei the AGN is dominant in the 3-5 micron band, but its contribution to the total luminosity is small (a few percent of the starburst emission).We present 3-5 μm spectroscopy of the interacting system NGC 6240, revealing the presence of two active galactic nuclei (AGNs). The brightest (southern) nucleus shows up with a starburst-like emission, with a prominent 3.3 μm emission feature. However, the presence of an AGN is revealed by the detection of a broad Brα emission line, with a width of ~1800 km s-1. The spectrum of the faintest (northern) nucleus shows typical AGN features, such as a steep continuum and broad absorption features in the M band. We discuss the physical properties of the dusty absorbers/emitters, and we show that in both nuclei, the AGN is dominant in the 3-5 μm band but that its contribution to the total luminosity is small (a few percent of the starburst emission).

Detection of faint broad emission lines in type 2 AGN – II. On the measurement of the black hole mass of type 2 AGN and the unified model

We report the virial measurements of the BH mass of a sample of 17 type 2 AGN, drawn from the Swift/BAT 70-month 14-195 keV hard X-ray catalogue, where a faint BLR component has been measured via deep NIR (0.8-2.5

The active galactic nuclei/starburst content in high-redshift ultraluminous infrared galaxies

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The WISSH quasars project IV. Broad line region versus kiloparsec-scale winds

m) spectroscopy. We compared the type 2 AGN with a control sample of 33 type 1 AGN. We find that the type 2 AGN BH masses span the 5

MAGNUM survey: A MUSE-Chandra resolved view on ionized outflows and photoionization in the Seyfert galaxy NGC 1365

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