The bright quasar 3C 273

In synthetic jet actuators with an orifice diameter typically less than 1 mm (termed as small-scale synthetic jet actuators), the compressibility and viscosity effects often become significant causing them behave differently from large-scale synthetic jets. In this paper, a numerical study of the synthetic jet from an orifice diameter of 0.5 mm is undertaken and the results are compared with the synthetic jet from an orifice diameter of 5 mm. The results reveal that, given the same dimensionless parameters L and Re L , the appearance and circulation of vortex rings produced from synthetic jets of different scales are identical in the near field. It is also found that although the linear relationships between (L and Re L ) and actuator operating conditions observed for large-scale synthetic jets are no longer valid for small-scale synthetic jets, the linear relationships between the dimensionless jet performance parameters and (L and Re L ) still exist. This finding is very useful to support the development of low-dimensional predictions models.Key wordsSynthetic jetCFD simulation

Axion-Like Particles (ALPs), if exist in nature, are expected to mix with photons in the presence of an external magnetic field. The energy range of photons which undergo strong mixing with ALPs depends on the ALP mass, on its coupling with photons as well as on the external magnetic field and particle density configurations. Recent observations of blazars by the Fermi Gamma-Ray Space Telescope in the 0.1–300 GeV energy range show a break in their spectra in the 1–10 GeV range. We have modeled this spectral feature for the flat-spectrum radio quasar 3C454.3 during its November 2010 outburst, assuming that a significant fraction of the gamma rays convert to ALPs in the large scale jet of this blazar. Using theoretically motivated models for the magnetic field and particle density configurations in the kiloparsec scale jet, outside the broad-line region, we find an ALP mass ma ∼ (1−3)⋅10−7 eV and coupling gaγ ∼ (1−3)⋅10−10 GeV−1 after performing an illustrative statistical analysis of spectral data in four different epochs of emission. The precise values of ma and gaγ depend weakly on the assumed particle density configuration and are consistent with the current experimental bounds on these quantities. We apply this method and ALP parameters found from fitting 3C454.3 data to another flat-spectrum radio quasar PKS1222+216 (4C+21.35) data up to 400 GeV, as a consistency check, and found good fit. We find that the ALP-photon mixing effect on the GeV spectra may not be washed out for any reasonable estimate of the magnetic field in the intergalactic media.

We perform a spectral energy distribution fitting analysis on a COSMOS photometric sample covering the ultra-violet up to the far-infrared wavelengths and including emission lines from the Fiber Multi-Object Spectrograph survey. The sample consists of 182 objects with Hαand [OIII]λ5007 emission line measurements lying in a redshift range of 1.40 < z < 1.68. We obtain robust estimates of the stellar mass and star-formation rate spanning over a range of 109.5 − 1011.5M⊙and 101 − 103M⊙yr−1from the Bayesian analysis performed with CIGALE and using continuum photometry and Hαfluxes. Combining photometry and spectroscopy gives secure estimations of the amount of dust attenuation for both continuum and line emissions. We obtain a median attenuation ofAHα = 1.16 ± 0.19 mag andA[OIII] = 1.41 ± 0.22 mag. Hαand [OIII]λ5007 attenuations are found to increase with stellar mass, confirming previous findings with Hα. A difference of 57% in the attenuation experienced by emission lines and continuum is found to be in agreement with the emission lines being more attenuated than the continuum emission. Implementation of new CLOUDY HII-region models in CIGALE enables good fits of the Hα, Hβ, [OIII]λ5007 emission lines with discrepancies smaller than 0.2 dex in the predicted fluxes. Fitting the [NII]λ6584 line is found challenging due to well-known discrepancies in the locus of galaxies in the [NII]-BPT diagram at intermediate and high redshifts. We find a positive correlation between SFR andL[OIII]λ5007 after correcting for dust attenuation and we derive the linear relation log10(SFR/M⊙yr−1)=log10(L[OIII]/ergs s−1)−(41.20 ± 0.02). Leaving the slope as a free parameter leads to log10(SFR/M⊙yr−1)=(0.83 ± 0.06)log10(L[OIII]/ergs s−1)−(34.01 ± 2.63). The spread in the relation is driven by differences in the gas-phase metallicity and ionization parameter accounting for a 0.24 dex and 1.1 dex of the dispersion, respectively. We report an average value of logU ≈ −2.85 for this sample of galaxies. Including HII-region models to fit simultaneously photometric data and emission line fluxes is paramount to analyses of upcoming data sets from large spectroscopic surveys of the future, such as MOONS and PFS.

The MEGA project: Science goals and hardware development

We propose a method for estimating the composition, i.e. the relative amounts of leptons and protons, of extragalactic jets which exhibit X-ray bright knots in their kpc scale jets. The method relies on measuring, or setting upper limits on, the component of the Cosmic Microwave Background (CMB) radiation that is bulk-Comptonized by cold electrons in the relativistically flowing jet. These measurements, along with modeling of the broadband knot emission that constrain the bulk Lorentz factor of the jets, can yield estimates of the jet power carried by protons and leptons. We provide an explicit calculation of the spectrum of the bulk-Comptonized (BC) CMB component and apply these results to PKS 0637--752 and 3C 273, two superluminal quasars with Chandra-detected large scale jets. What makes these sources particularly suited for such a procedure is the absence of significant non-thermal jet emission in the `bridge', the region between the core and the first bright jet knot, which guarantees that most of the electrons are cold there, leaving the BC scattered CMB radiation as the only significant source of photons in this region. At lambda=3.6-8.0 microns the most likely band to observe the BC scattered CMB emission, the Spitzer angular resolution (~ 1''-3) is considerably smaller than the `bridges' of these jets (~10''), making it possible to both measure and resolve this emission.

Influence of initial conditions on the evolution towards similarity of passive scalar in turbulent round jets

Irradiated accretion disks around massive black holes are expected to produce part of the line spectrum of AGN, but most of the disk emission must be thermal, observed at UV wavelengths. The two emission components, lines and continuum, are fitted by a unique accretion-disk model that gives the mass of the black hole and the inclination of the disk. The distribution of the disk inclination in a complete sample of Seyfert 1 galaxies suggests that their nuclei are orientation-selected, affected by strong absorption at low disk latitudes. The black-hole masses in the same sample confirm the long-standing non-linearity between M and L for AGN and the non-causal relationship between nearby Seyfert 1 galaxies and distant quasars (i.e., pure luminosity evolution is ruled out).Irradiated accretion disks are also combined with the relativistic jet model in order to constrain the orientation and the Lorentz factor of 14 superluminal radio sources. At least for a few objects, the line and the radio data are inconsistent with both models, unless a new parameter (jet bending, a second emission-line component, etc.), is also involved. Despite this inconsistency and the ambiguous evidence for combined disk and jet fits in the remaining superluminal sources, a successful merger of these two models might address questions about the nature of AGN and also constrain the Hubble constant.

Sequences of spectra of the nova-like cataclysmic variable (CV) BZ Cam were acquired on nine nights in 2005-2006 in order to study the time development of episodes of wind activity known to occur frequently in this star. We confirm the results of Ringwald & Naylor that the P-Cygni absorption components of the lines mostly evolve from higher expansion velocity to lower velocity as an episode progresses. We also commonly find blueshifted emission components in the H? line profile, whose velocities and durations strongly suggest that they are also due to the wind. Curiously, Ringwald & Naylor reported common occurrences of redshifted H? emission components in their BZ Cam spectra. We have attributed these emission components in H? to occasions when gas concentrations in the bipolar wind (both front side and back side) become manifested as emission lines as they move beyond the disk's outer edge. We also suggest, based on changes in the P-Cygni profiles during an episode, that the progression from larger to smaller expansion velocities is due to the higher velocity portions of a wind concentration moving beyond the edge of the continuum light of the disk first, leaving a net redward shift of the remaining absorption profile. We derive a new orbital ephemeris for BZ Cam, using the radial velocity of the core of the He I ?5876 line, finding P = 0.15353(4). Using this period, the wind episodes in BZ Cam are found to be concentrated near the inferior conjunction of the emission line source. This result helps confirm that the winds in nova-like CVs are often phase dependent, in spite of the puzzling implication that such winds lack axisymmetry. We argue that the radiation-driven wind in BZ Cam receives an initial boost by acting on gas that has been lifted above the disk by the interaction of the accretion stream with the disk, thereby imposing flickering timescales onto the wind events, as well as leading to an orbital modulation of the wind due to the non-axisymmetric nature of the stream/disk interaction. Simultaneous photometry and spectroscopy were acquired on three nights in order to test the possible connection between flickering continuum light and the strength of the front-side wind. We found strong agreement on one night, some agreement on another, and no agreement on the third. We suggest that some flickering events lead to only back-side winds which will not have associated P-Cygni profiles.

Flow and mixing characteristics of dual parallel plane jets subject to acoustic excitation

We present JWST/NIRSpec IFU observations of the $z=7.152$ galaxy system B14-65666, as part of the GA-NIFS survey. Line and continuum emission in this massive system ($\log _{10}(M_*/{\rm M}_{\odot })=9.8\pm 0.2$) is resolved into two strong cores surrounded by diffuse emission, as seen in recent JWST/NIRCam imaging. Our data set contains detections of [O ii]$\lambda \lambda 3726{,}3729$, [Ne iii]$\lambda \lambda 3869{,}3968$, Balmer lines, [O iii]$\lambda \lambda 4959{,}5007$, He i$\lambda 5875$, and weak [O iii]$\lambda 4363$. Each spectrum is fit with a model that consistently incorporates interstellar medium conditions (i.e. electron temperature, $T_{\rm e}$, electron density, $n_{\rm e}$, and colour excess, $E(B-V)$). The resulting line fluxes are used to constrain the gas-phase metallicity ($Z_{\rm g}\sim 0.2\mathrm{ -}0.3$ solar) and H$\beta$-based star formation rate for each region. Common line ratio diagrams (O32–R23, R3–R2, Ne3O2–R23) reveal that each line-emitting region lies at the intersection of low- and high-redshift galaxies, suggesting low ionization and higher metallicity compared to the predominantly lower-mass galaxies studied with the JWST/NIRSpec IFU so far at $z\gt 5.5$. Spaxel-by-spaxel fits reveal evidence for both narrow (FWHM $\lt 400$ km s$^{-1}$) and broad (FWHM $\gt 500$ km s$^{-1}$) line emission, the latter of which likely represents tidal interaction or outflows. Comparison to ALMA [C ii]158$\mu$m and [O iii]88$\mu$ m data shows a similar velocity structure, and we explore optical-far infrared diagnostics. The two core galaxies both lie on the mass-metallicity relation at $z\gt 4$, but show contrasting properties (e.g. $M_*$, $Z_{\rm g}$), suggesting distinct evolutionary pathways. Combining the NIRSpec IFU and ALMA data sets, our analysis opens new windows into the merging system B14-65666.

Jet scale affects the mixing and combustion of fuel and inflow. With the increase in the scale of scramjet combustors, the study of large-scale jets is particularly significant. The effects of jet scale on flame stability in scramjet combustors were studied by direct-connect combustion experiments. In this paper, the flame distribution characteristics of different jet scales were compared by using similar jet/inflow momentum ratios. The inflow Mach numbers were 2.4 and 3.0, and the total temperature was 1265 K and 1600 K, respectively. The results show that, when the equivalence ratio increases, the combustion intensity increases. Under the condition of same momentum ratio, the increase of jet scale is conducive to fuel injection into the core mainstream, increasing heat release, and the flame stabilization mode will change from cavity stabilization mode to jet-wake stabilization mode. Increasing the distance between jet orifices is not beneficial to combustion, and may even lead to blowoff.

Context. The study of molecular line emission is crucial to unveil the kinematics and the physical conditions of gas in star-forming regions. We use data from the ALMAGAL survey, which provides an unprecedentedly large statistical sample of high-mass star-forming clumps that helps us to remove bias and reduce noise (e.g., due to source peculiarities, selection, or environmental effects) to determine how well individual molecular species trace continuum emission. Aims. Our aim is to quantify whether individual molecular transitions can be used reliably to derive the physical properties of the bulk of the H2 gas, by considering morphological correlations in their overall integrated molecular line emission with the cold dust. We selected transitions of H2CO, CH3OH, DCN, HC3N, CH3CN, CH3OCHO, SO, and SiO and compared them with the 1.38 mm dust continuum emission at different spatial scales in the ALMAGAL sample. We included two transitions of H2CO to understand whether the validity of the results depends on the excitation condition of the selected transition of a molecular species. The ALMAGAL project observed more than 1000 candidate high-mass star-forming clumps in ALMA band 6 at a spatial resolution down to 1000 au. We analyzed a total of 1013 targets that cover all evolutionary stages of the high-mass star formation process and different conditions of clump fragmentation. Methods. For the first time, we used the method called histogram of oriented gradients (HOG) as implemented in the tool astroHOG on a large statistical sample to compare the morphology of integrated line emission with maps of the 1.38 mm dust continuum emission. For each clump, we defined two masks: the first mask covered the extended more diffuse continuum emission, and the second smaller mask that only contained the compact sources. We selected these two masks to study whether and how the correlation among the selected molecules changes with the spatial scale of the emission, from extended more diffuse gas in the clumps to denser gas in compact fragments (cores). Moreover, we calculated the Spearman correlation coefficient and compared it with our astroHOG results. Results. Only H2CO, CH3OH, and SO of the molecular species we analyzed show emission on spatial scales that are comparable with the diffuse 1.38 mm dust continuum emission. However, according the HOG method, the median correlation of the emission of each of these species with the continuum is only ~24–29%. In comparison with the dusty dense fragments, these molecular species still have low correlation values that are below 45% on average. The weak morphological correlation suggests that these molecular lines likely trace the clump medium or outer layers around dense fragments on average (in some cases, this might be due to optical depth effects) or also trace the inner parts of outflows at this scale. On the other hand DCN, HC3N, CH3CN3 and CH3OCHO are well correlated with the dense dust fragments at above 60%. The lowest correlation is seen with SiO for the extended continuum emission and for compact sources. Moreover, unlike other outflow tracers, in a large fraction of the sources, SiO does not cover the area of the extended continuum emission well. This and the results of the astroHOG analysis reveal that SiO and SO do not trace the same gas, in contrast to what was previously thought. From the comparison of the results of the HOG method and the Spearman correlation coefficient, the HOG method gives much more reliable results than the intensity-based coefficient when the level of similarity of the emission morphology is estimated.

This paper presents accretion disc fits to the UV continuum and Hβ emission line in a complete sample of broad-emission-line AGN sources. Disc fits to the UV continuum emission leave an ambiguity between the central mass and the orientation of the disc in that more massive black holes mimic more edge-on discs. The opposite dependence between mass and orientation is derived from disc fits to the broad-line profile. Fitting both continuum shape and line profile consistently can thus lead to a unique determination of the two parameters. Models consistent with the two emission components have a low inclination (with means equal to ∼2500B0 and 35° for extreme Kerr and Schwarzschild black holes respectively), supporting orientation-dependent unification schemes. The derived masses confirm the non-linearity between mass and luminosity for AGN, and rule out a pure luminosity evolution of distant quasars to nearby Seyfert 1 nuclei. Finally, the disc irradiation and the size of the Hβ emission region are estimated.

To unravel the dominant cause of the weak emission line in a subset of optically selected radio-quiet ‘weak emission line quasars’ (WLQs), we have investigated the possibility of an underdeveloped broad line region (BLR). For this, we have modelled spectral energy distributions (SED) of 61 WLQs by using their optical and infrared (IR) photometric observations from Sloan Digital Sky Survey (SDSS) and WISE, respectively. SED fit consists of various emission components, including the luminosity from the dusty torus (Ltor). For comparison with the normal quasar, we have used a control sample of 55 Quasi-Stellar Objects (QSOs) for each WLQ matching in emission redshift and SDSS r-band. Based on our measurement of Ltor, we found a decrement of 42 ± 2 per cent in IR luminosity in WLQs with respect to the control sample of normal QSOs. Using Ltor/Lbol as the measure of torus covering factor (CFtor), we found a similar decrement in WLQ covering factor, with their CFtor distribution being significantly different with respect to the normal QSOs with a KS test Pnull of 4.27 × 10−14. As dusty torus and BLR covering factors are expected to be of a similar order in active galactic nucleus (AGN), our results suggest that the BLR in the WLQs is underdeveloped and could be a dominant cause of the weakness of their emission line. As a result, our analysis gives support to the models of WLQs based on the evolution scenario being in an early stage of AGNs.

An additional Hα emission component in LS I +61°303: Further evidence for the Hα emission related to the neutron star