Roberto Decarli

SDSSJ092712.65+294344.0: a candidate massive black hole binary

In this Letter, we explore the hypothesis that the quasar SDSSJ092712.65+294344.0 is hosting a massive black hole binary embedded in a circumbinary disc. The lightest, secondary black hole is active, and gas orbiting around it is responsible for the blue-shifted broad emission lines with velocity off-set of 2650 km s −1 , relative to the galaxy rest frame. As the tidal interaction of the binary with the outer disc is expected to excavate a gap, the blue-shifted narrow emission lines are consistent with being emitted from the low-density inhomogeneous gas of the hollow region. From the observations, we infer a binary mass ratio q ≈ 0.3, a mass for the primary of M 1 ≈ 2 × 10 9 M� , and a semimajor axis of 0.34 pc, corresponding to an orbital period of 370 years. We use the results of cosmological merger trees to estimate the likelihood of observing SDSSJ092712.65+294344.0 as recoiling black hole or as a binary. We find that the binary hypothesis is preferred being 100 times more probable than the ejection hypothesis. If SDSSJ092712.65+294344.0 hosts a binary, it would be the one closest massive black hole binary system ever discovered.

On the geometry of broad emission region in quasars

We study the geometry of the Hβ broad emission region by comparing the M BH values derived from Hβ through the virial relation with those obtained from the host galaxy luminosity in a sample of 36 low-redshift (z ∼ 0.3) quasars. This comparison lets us infer the geometrical factor f needed to deproject the line-of-sight velocity component of the emitting gas. The wide range off values we found, together with the strong dependence off on the observed linewidth, suggests that a disc-like model for the broad-line region is preferable to an isotropic model, both for radio-loud and radio-quiet quasars. We examined similar observations of the C iv line and found no correlation in the width of the two lines. Our results indicate that an inflated disc broad-line region, in which the Carbon line is emitted in a flat disc while Hβ is produced in a geometrically thick region, can account for the observed differences in the width and shape of the two emission lines.

The quasar relation through cosmic time – I. Data set and black hole masses

We study the MBH–Mhost relation as a function of cosmic time in a sample of 96 quasars from z = 3 to the present epoch. In this paper, we describe the sample, the data sources and the new spectroscopic observations. We then illustrate how we derive MBH from single-epoch spectra, pointing out the uncertainties in the procedure. In a companion paper, we address the dependence of the ratio between the black hole mass and the host-galaxy luminosity and mass on cosmic time.

Downsizing of supermassive black holes from the SDSS quasar survey

Starting from the ∼50 000 quasars of the Sloan Digital Sky Survey for which Mg II line width and 3000 A monochromatic flux are available, we aim to study the dependence of the mass of active black holes on redshift. We focus on the observed distribution in the full width at half-maximum-nuclear luminosity plane, which can be reproduced at all redshifts assuming a limiting M BH , a maximum Eddington ratio and a minimum luminosity (due to the survey flux limit). We study the z-dependence of the best-fitting parameters of assumed distributions at increasing redshift and find that the maximum mass of the quasar population evolves as log (M BH(max) /M ⊙ ) ∼ 0.3z + 9, while the maximum Eddington ratio (∼0.45) is practically independent of cosmic time. These results are unaffected by the Malmquist bias.

EUROPEAN SOUTHERN OBSERVATORY VERY LARGE TELESCOPE OPTICAL SPECTROSCOPY OF BL LACERTAE OBJECTS. III. AN EXTENSION OF THE SAMPLE

We present results of an ongoing program at the European Southern Observatory Very Large Telescope for spectroscopy of BL Lac objects (BLLs) lacking a firm redshift estimate, and here we report on 15 objects. For 11 sources we confirm the BL Lac classification, and determine new redshifts for three objects, one with weak emission lines (PKS 1057 – 79, z = 0.569) and two with absorptions from the host galaxy (RBS 1752, z = 0.449; RBS 1915, z = 0.243); moreover, a subdamped Lyα system is detected in the direction of the BL Lac PKS 0823 – 223 (z ≥ 0.911). For the remaining eight BLLs, from the very absence of absorption lines of the host galaxy, lower limits to the redshift are deduced with z min in the interval 0.20-0.80. The remaining three sources are reclassified as a FSRQ (PKS 1145 – 676, z = 0.210; TXS 2346+052, z = 0.419) and a misclassified galactic star (PMNJ 1323 – 3652).

Search for sub-parsec massive binary black holes through line diagnosis - II: Observational signatures of sub-pc binary BHs

Massive black hole binaries at sub-parsec separations may display in their spectra anomalously small flux ratios between the MgII and CIV broad emission lines, i.e. F_MgII/F_CIV <~ 0.1, due to the erosion of the broad line region around the active, secondary black hole, by the tidal field of the primary. In Paper I by Montuori et al. (2011), we focussed on broad lines emitted by gas bound to the lighter accreting member of a binary when the binary is at the center of a hollow density region (the gap) inside a circum-binary disc. The main aim of this new study is at exploring the potential contribution to the broad line emission by the circum-binary disc and by gaseous streams flowing toward the black hole through the gap. We carry out a post-process analysis of data extracted from a SPH simulation of a circum-binary disc around a black hole binary. Our main result is that the MgII to CIV flux ratio can be reduced to ~ 0.1 within an interval of sub-pc binary separations of the order of a ~ (0.01-0.2)(f_Edd/0.1)^(1/2) pc corresponding to orbital periods of ~ (20-200) (f_Edd/0.1)^(3/4) years for a secondary BH mass in the range M_2 ~ 10^7-10^9 M_sun and a binary mass ratio of 0.3. At even closer separations this ratio returns to increase to values that are indistinguishable from the case of a single AGN (typically F_MgII/F_CIV ~ 0.3-0.4) because of the contribution to the MgII line from gas in the circum-binary disc.Massive black hole binaries at sub-parsec separations may display in their spectra anomalously small flux ratios between the MgII and CIV broad emission lines, i.e. FMgII/FCIV ∼ 0.1, due to the erosion of the broad line region around the active, secondary black hole, by the tidal field of the primary. In Paper I by Montuori et al. (2011), we focussed on broad lines emitted by gas bound to the lighter accreting member of a binary when the binary is at the center of a hollow density region (the gap) inside a circum-binary disc. The main aim of this new study is at exploring the potential contribution to the broad line emission by the circum-binary disc and by gaseous streams flowing toward the black hole through the gap. We carry out a post-process analysis of data extracted from a SPH simulation of a circum-binary disc around a black hole binary. Our main result is that the MgII to CIV flux ratio can be reduced to ∼ 0.1 within an interval of sub-pc binary separations of the order of a ∼ (0.01 − 0.2)(fEdd/0.1) pc corresponding to orbital periods of ∼ (20−200)(fEdd/0.1) years for a secondary BH mass in the range M2 ∼ 10−10 M and a binary mass ratio of 0.3. At even closer separations this ratio returns to increase to values that are indistinguishable from the case of a single AGN (typically FMgII/FCIV ∼ 0.3 − 0.4) because of the contribution to the MgII line from gas in the circum-binary disc.

A quasar companion to the puzzling quasar SDSS J0927+2943

We report the discovery of a quasar close to SDSS J0927+2943 (z = 0.713), which is a massive binary / recoiling black hole candidate. The companion quasar is at a projected distance of 125 h_70^{-1} kpc and exhibits a radial velocity difference of ~1400 km/s with respect to the known quasar. We discuss the nature of this peculiar quasar pair and the properties of its environment. We propose that the overall system is caught in the process of ongoing structure formation.

Coevolution of supermassive black holes and their host galaxies

Accretion onto a supermassive black hole (BH) is the most viable explanation for the huge emitted luminosity in active galaxies. Nowadays a wealth of observations have shown the presence of a BH in many nearby inactive bulges, suggesting that all massive spheroids harbor a BH. Moreover, at low redshift, fundamental correlations have been found between the BH mass and the luminosity (mass) and the central velocity dispersion of the host galaxy bulge. These correlations underline the important fact that there must be a strong relationship between the formation and evolution of massive bulges and their central BH. We discuss our ongoing program to investigate the cosmic evolution of this relationship. Optical (rest‐frame UV) spectroscopy is used to determine the virial BH masses of a large sample of high redshift quasars for which the host galaxy luminosity is reliably determined from our previous VLT imaging.