Context.
The AGN bolometric correction is a key element for understanding black hole (BH) demographics and computing accurate BH accretion histories from AGN luminosities. However, current estimates ...still differ from each other by up to a factor of two to three, and rely on extrapolations at the lowest and highest luminosities.
Aims.
Here we revisit this fundamental question by presenting general hard X-ray (
K
X
) and optical (
K
O
) bolometric corrections, computed by combining several AGN samples spanning the widest (about 7 dex) luminosity range ever used for this type of studies.
Methods.
We analysed a total of ∼1000 type 1 and type 2 AGN for which we performed a dedicated SED-fitting.
Results.
We provide a bolometric correction separately for type 1 and type 2 AGN; the two bolometric corrections agree in the overlapping luminosity range. Based on this we computed for the first time a universal bolometric correction for the whole AGN sample (both type 1 and type 2). We found that
K
X
is fairly constant at log(
L
BOL
/
L
⊙
) < 11, while it increases up to about one order of magnitude at log(
L
BOL
/
L
⊙
) ∼ 14.5. A similar increasing trend has been observed when its dependence on either the Eddington ratio or the BH mass is considered, while no dependence on redshift up to
z
∼ 3.5 has been found. In contrast, the optical bolometric correction appears to be fairly constant (i.e.
K
O
∼ 5) regardless of the independent variable. We also verified that our bolometric corrections correctly predict the AGN bolometric luminosity functions. According to this analysis, our bolometric corrections can be applied to the whole AGN population in a wide range of luminosity and redshift.
ABSTRACT
We present a VLT/X-Shooter spectroscopy of the Lyman continuum (LyC) emitting galaxy Ion2 at z = 3.2121 and compare it to that of the recently discovered strongly lensed LyC emitter at ...z = 2.37, known as the Sunburst arc. Three main results emerge from the X-Shooter spectrum: (a) the Ly α has three distinct peaks with the central one at the systemic redshift, indicating a ionized tunnel through which both Ly α and LyC radiation escape; (b) the large O32 oxygen index (O iii λλ4959, 5007/O ii λλ3727, 3729) of $9.18_{-1.32}^{+1.82}$ is compatible to those measured in local (z ∼0.4) LyC leakers; (c) there are narrow nebular high-ionization metal lines with σv < 20 km s−1, which confirms the presence of young hot, massive stars. The He iiλ1640 appears broad, consistent with a young stellar component including Wolf–Rayet stars. Similarly, the Sunburst LyC emitter shows a triple-peaked Ly α profile and from VLT/MUSE spectroscopy the presence of spectral features arising from young hot and massive stars. The strong lensing magnification, (μ > 20), suggests that this exceptional object is a gravitationally bound star cluster observed at a cosmological distance, with a stellar mass M ≲ 107 M⊙ and an effective radius smaller than 20 pc. Intriguingly, sources like Sunburst but without lensing magnification might appear as Ion2-like galaxies, in which unresolved massive star clusters dominate the ultraviolet emission. This work supports the idea that dense young star clusters can contribute to the ionization of the IGM through holes created by stellar feedback.
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.
•Direct absorption solar collectors (DASC) with nanofluids are simulated by CFD.•Nanofluid light absorption performance are experimentally measured.•Simulated design does not fully exploit ...theoretical advantages of DASC.•Optimization of DASC design is needed to foster their potential at low temperature.
Direct absorption solar collector (DASC) have recently attracted increasing interest in combination with some new absorbing fluids, obtained through the suspension of nanoparticles in water or other liquids (nanofluids). A volumetric direct absorption in a solar collector is in principle more convenient than a superficial indirect one, assuring a temperature distribution whose peak is internal to the fluid instead and not on the external surface, as in superficial one, thus promising lower heat losses. Nanofluids, i.e. fluids with a suspension of nanoparticles, such as the carbon nanohorns we choose as case study, can be considered a good and innovative family of absorbing fluids, due to their higher absorption coefficient than the pure base fluid and to their high stability under moderate temperature gradients. In this paper, we focus on the application of direct volumetric absorption by nanofluids for civil applications, which have a typical operative temperature lower than 100 °C. A DASC using nanofluids with different nanoparticle concentrations is compared to a commercially available indirect vacuum tube solar collector. The comparison is made between simulated performance of the DASC and the nominal performance of the commercial collector. The simulations are made with a CFD model, that leverages original experimental measurements of the optical properties of the considered nanofluid. It is shown that the DASC concept is more convenient in case of higher heat losses, i.e. in case of a high transmittance solar collector or of very high temperature of the heated fluid. It is also underlined the importance of balancing the heat absorption and heat transport function of the fluid. The simulations of the first considered design reveals, in fact, that the thermal field does not completely develop in the pipe, due to the large pipe diameter in relation to the flow and to the low heat losses, thus producing a low bulk temperature. The addition of a compound parabolic concentrator (CPC) and the adoption of an annular pipe (triple tube) improve the performance in terms of average bulk temperature, though not matching yet the surface reference collector in terms of efficiency.
We investigate the strongly lensed (
μ
≃ ×10 − 100) Lyman continuum (LyC) galaxy, dubbed Sunburst, at
z
= 2.37, taking advantage of a new accurate model of the lens. A characterization of the ...intrinsic (delensed) properties of the system yields a size of ≃3 sq. kpc, a luminosity of
M
UV
= −20.3, and a stellar mass of
M
≃ 10
9
M
⊙
; 16% of the ultraviolet light is located in a 3 Myr old gravitationally bound young massive star cluster (YMC), with an effective radius of ∼8 pc (corresponding to 1 milliarcsec without lensing) and a dynamical mass of ∼10
7
M
⊙
(similar to the stellar mass) – from which LyC radiation is detected (
λ
< 912 Å). The star formation rate and stellar mass surface densities for the YMC are Log
10
(Σ
SFR
M
⊙
yr
−1
kpc
−2
) ≃ 3.7 and Log
10
(Σ
M
M
⊙
pc
−2
) ≃ 4.1, with sSFR > 330 Gyr
−1
, consistent with the values observed in local young massive star clusters. The inferred outflowing gas velocity (> 300 km s
−1
) exceeds the escape velocity of the cluster. The resulting relative escape fraction of the ionizing radiation emerging from the entire galaxy is higher than 6−12%, whilst it is ≳46 − 93% if inferred from the YMC multiple line of sights. At least 12 additional unresolved star-forming knots with radii spanning the interval 3 − 20 pc (the majority of them likely gravitationally bound star clusters) are identified in the galaxy. A significant fraction (40−60%) of the ultraviolet light of the entire galaxy is located in such bound star clusters. In adopting a formation timescale of the star clusters of 20 Myr, a cluster formation efficiency Γ ≳ 30%. The star formation rate surface density of the Sunburst galaxy (Log
10
(Σ
SFR
) = 0.5
−0.2
+0.3
) is consistent with the high inferred Γ, as observed in local galaxies experiencing extreme gas physical conditions. Overall, the presence of a bursty event (i.e., the 3 Myr old YMC with large sSFR) significantly influences the morphology (nucleation), photometry (photometric jumps), and spectroscopic output (nebular emission) of the entire galaxy. Without lensing magnification, the YMC would be associated to an unresolved 0.5 kpc–size star-forming clump. The delensed LyC and UV magnitude
m
1600
(at 1600 Å) of the YMC are ≃30.6 and ≃26.9, whilst the entire galaxy has
m
1600
≃ 24.8. The Sunburst galaxy shows a relatively large rest-frame equivalent width of EW
rest
(H
β
+ O
III
λλ
4959, 5007) ≃ 450 Å, with the YMC contributing to ∼30% (having a local EW
rest
≃ 1100 Å) and ∼1% of the total stellar mass. If O-type (ionizing) stars are mainly forged in star clusters, then such engines were the key ionizing agents during reionization and the increasing occurrence of high equivalent width lines (H
β
+ O
III
) observed at
z
> 6.5 might be an indirect signature of a high frequency of forming massive star clusters (or high Γ) at reionization. Future facilities, which will perform at few tens milliarcsec resolution (e.g., VLT/MAVIS or ELT), will probe bound clusters on moderately magnified (
μ
< 5 − 10) galaxies across cosmic epochs up to reionization.
•Innovative method of detecting bacteria decorated with extra negative charge.•Zeta potential of L. pneumophila doubled with sodium dodecyl sulfide molecules.•Detection of L. pneumophila at 103 ...CFU/mL achieved with charge sensitive biosensor.•The method paves the way to enhanced detection of other charged biomolecules.
The net electric charge associated with a bacterial strain is primarily defined by the number of available functional groups at its surface and we observed that it can determine the limit of detection of a charge-sensing biosensor. We have investigated the dynamic range of bacterial electric charge variations through binding negatively charged sodium dodecyl sulphate (SDS) molecules, with the objective of improving the detection limit of a charge-sensing GaAs/AlGaAs nanoheterostructure biosensor designed for detection of Legionella pneumophila. A two-fold increased zeta potential of L. pneumophila was measured at pH 7.4 following the exposure of these bacteria to an SDS solution at 0.02 mg/mL. Subsequently, it was possible to detect SDS decorated and heat-inactivated L. pneumophila at 103 CFU/mL. This illustrates the fundamental role of the bacterial electric charge in the operation of photocorrosion-based III-V semiconductor biochips. We discuss the mechanisms of bacterial interaction with SDS, critical aspects of decorating bacteria with this anionic surfactant and the channels responsible for charge transfer.
Aims.
We study the coevolution between the black hole accretion rate (BHAR) and the star formation rate (SFR) in different phases of galaxy life: main-sequence star-forming galaxies, quiescent ...galaxies, and starburst galaxies at different cosmic epochs.
Methods.
We exploited the unique combination of depth and area in the COSMOS field and took advantage of the X-ray data from the
Chandra
COSMOS-Legacy survey and the extensive multiwavelength ancillary data presented in the COSMOS2015 catalog, including in particular the UVista Ultra-deep observations. These large datasets allowed us to perform an X-ray stacking analysis and combine it with detected sources in a broad redshift interval (0.1 <
z
< 3.5) with unprecedented statistics for normal star-forming, quiescent, and starburst galaxies. The X-ray luminosity was used to predict the black holeAR, and a similar stacking analysis on far-infrared
Herschel
maps was used to measure the corresponding obscured SFR for statistical samples of sources in different redshifts and stellar mass bins.
Results.
We focus on the evolution of the average SFR-stellar mass (
M
*
) relation and compare it with the BHAR-
M
*
relation. This extends previous works that pointed toward the existence of almost linear correlations in both cases. We find that the ratio between BHAR and SFR does not evolve with redshift, although it depends on stellar mass. For the star-forming populations, this dependence on
M
*
has a logarithmic slope of ∼0.6 and for the starburst sample, the slope is ∼0.4. These slopes are both at odds with quiescent sources, where the dependence remains constant (log(BHAR/SFR) ∼ −3.4). By studying the specific BHAR and specific SFR, we find signs of downsizing for
M
*
and black hole mass (
M
BH
) in galaxies in all evolutionary phases. The increase in black hole mass-doubling timescale was particularly fast for quiescents, whose super-massive black holes grew at very early times, while accretion in star-forming and starburst galaxies continued until more recent times.
Conclusions.
Our results support the idea that the same physical processes feed and sustain star formation and black hole accretion in star-forming galaxies while the starburst phase plays a lesser role in driving the growth of the supermassive black holes, especially at high redshift. Our integrated estimates of the
M
*
−
M
BH
relation at all redshifts are consistent with independent determinations of the local
M
*
−
M
BH
relation for samples of active galactic nuclei. This adds key evidence that the evolution in the BHAR/SFR is weak and its normalization is relatively lower than that of local dynamical
M
*
−
M
BH
relations.
Abstract We report on the serendipitous discovery of a z = 4.0, M1500 = −22.20 star-forming galaxy (Ion3) showing copious Lyman continuum (LyC) leakage (∼60 per cent escaping), a remarkable multiple ...peaked Ly α emission, and significant Ly α radiation directly emerging at the resonance frequency. This is the highest redshift confirmed LyC emitter in which the ionizing and Ly α radiation possibly share a common ionized channel (with NH I < 1017.2 cm−2). Ion3 is spatially resolved, it shows clear stellar winds signatures like the P-Cygni N vλ1240 profile, and has blue ultraviolet continuum (β = −2.5 ± 0.25, Fλ ∼ λβ) with weak low-ionization interstellar metal lines. Deep VLT/HAWKI Ks and Spitzer/IRAC 3.6 and 4.5μm imaging show a clear photometric signature of the H α line with equivalent width of 1000 Å rest-frame emerging over a flat continuum (Ks − 4.5μm ≃ 0). From the SED fitting, we derive a stellar mass of 1.5 × 109 M⊙, SFR of 140 M⊙ yr−1 and age of ∼10 Myr, with a low dust extinction, E(B − V) ≲ 0.1, placing the source in the starburst region of the SFR−M* plane. Ion3 shows similar properties of another LyC emitter previously discovered (z = 3.21, Ion2, Vanzella et al. 2016). Ion3 (and Ion2) represents ideal high-redshift reference cases to guide the search for reionizing sources at z > 6.5 with JWST.
We present the results of a 5–8 μm spectral analysis performed on the largest sample of local ultraluminous infrared galaxies (ULIRGs) selected so far, consisting of 164 objects up to a redshift of ...∼0.35. The unprecedented sensitivity of the Infrared Spectrograph onboard Spitzer allowed us to develop an effective diagnostic method to quantify the active galactic nucleus (AGN) and starburst (SB) contribution to this class of objects. The large AGN over SB brightness ratio at 5–8 μm and the sharp difference between the spectral properties of AGN and SB galaxies in this wavelength range make it possible to detect even faint or obscured nuclear activity, and disentangle its emission from that of star formation. By defining a simple model we are also able to estimate the intrinsic bolometric corrections for both the AGN and SB components, and obtain the relative AGN/SB contribution to the total luminosity of each source. Our main results are the following. The AGN detection rate among local ULIRGs amounts up to 70 per cent, with 113/164 convincing detections within our sample, while the global AGN/SB power balance is ∼1/3. A general agreement is found with optical classification; however, among the objects with no spectral signatures of nuclear activity, our IR diagnostics find a subclass of elusive, highly obscured AGN. We analyse the correlation between nuclear activity and IR luminosity, recovering the well-known trend of growing AGN significance as a function of the overall energy output of the system: the sources exclusively powered by star formation are mainly found at LIR < 1012.3 L⊙, while the average AGN contribution rises from ∼10 to ∼60 per cent across the ULIRG luminosity range. From a morphological point of view, we confirm that the AGN content is larger in compact systems, but the link between activity and evolutionary stage is rather loose. By analysing a control sample of IR-luminous galaxies around z∼ 1, we find evidence for only minor changes with redshift of the large-scale spectral properties of the AGN and SB components. This underlines the potential of our method as a straightforward and quantitative AGN/SB diagnostic tool for ULIRG-like systems at high redshift as well, and hints to possible photometric variants for fainter sources.
We investigated the interstellar medium (ISM) properties of the disc and outflowing gas in the central regions of nine nearby Seyfert galaxies, all characterised by prominent conical or biconical ...outflows. These objects are part of the Measuring Active Galactic Nuclei Under MUSE Microscope (MAGNUM) survey, which aims to probe their physical conditions and ionisation mechanism by exploiting the unprecedented sensitivity of the Multi Unit Spectroscopic Explorer (MUSE), combined with its spatial and spectral coverage. Specifically, we studied the different properties of the gas in the disc and in the outflow with spatially and kinematically resolved maps by dividing the strongest emission lines in velocity bins. We associated the core of the lines with the disc, consistent with the stellar velocity, and the redshifted and the blueshifted wings with the outflow. We measured the reddening, density, ionisation parameter, and dominant ionisation source of the emitting gas for both components in each galaxy. We find that the outflowing gas is characterised by higher values of density and ionisation parameter than the disc, which presents a higher dust extinction. Moreover, we distinguish high- and low-ionisation regions across the portion of spatially resolved narrow-line region (NLR) traced by the outflowing gas. The high-ionisation regions characterised by the lowest N II/Hα and S II/Hα line ratios generally trace the innermost parts along the axis of the emitting cones where the S III/S II line ratio is enhanced, while the low-ionisation regions follow the cone edges and/or the regions perpendicular to the axis of the outflows, also characterised by a higher O III velocity dispersion. A possible scenario to explain these features relies on the presence of two distinct populations of line emitting clouds: one is optically thin to the radiation and is characterised by the highest excitation, while the other is optically thick and is impinged by a filtered, and thus harder, radiation field which generates strong low-excitation lines. The highest values of N II/Hα and S II/Hα line ratios may be due to shocks and/or a hard filtered radiation field from the active galactic nucleus.
PDF
