The molecular Kennicutt-Schmidt (mK-S) Law has been key for understanding star formation (SF) in galaxies across all redshifts. However, recent sub-kpc observations of nearby galaxies reveal deviations from the nearly unity slope (N) obtained with disk-averaged measurements. We study SF and molecular gas (MG) distribution in the early-stage luminous infrared galaxy merger Arp240 (NGC5257-8). Using VLA radio continuum (RC) and ALMA CO(2-1) observations with a uniform grid analysis, we estimate SF rates and MG surface densities ($\Sigma_{\mathrm{SFR}}$ and $\Sigma_{\mathrm{H_2}}$, respectively). In Arp 240, N is sub-linear at 0.52 $\pm$ 0.17. For NGC 5257 and NGC 5258, N is 0.52 $\pm$ 0.16 and 0.75 $\pm$ 0.15, respectively. We identify two SF regimes: high surface brightness (HSB) regions in RC with N $\sim$1, and low surface brightness (LSB) regions with shallow N (ranging 0.15 $\pm$ 0.09 to 0.48 $\pm$ 0.04). Median CO(2-1) linewidth and MG turbulent pressure (P$_{\mathrm{turb}}$) are 25 km s$^{-1}$ and 9 $\times$10$^{5}$ K cm$^{-3}$. No significant correlation was found between $\Sigma_{\mathrm{SFR}}$ and CO(2-1) linewidth. However, $\Sigma_{\mathrm{SFR}}$ correlates with P$_{\mathrm{turb}}$, particularly in HSB regions ($\rho >$0.60). In contrast, SF efficiency moderately anti-correlates with P$_{\mathrm{turb}}$ in LSB regions but shows no correlation in HSB regions. Additionally, we identify regions where peaks in SF and MG are decoupled, yielding a shallow N ($\leq$ 0.28 $\pm$ 0.18). Overall, the range of N reflects distinct physical properties and distribution of both the SF and MG, which can be masked by disk-averaged measurements.

We present the analysis of similar to 100 pc scale compact radio continuum sources detected in 63 local (ultra)luminous infrared galaxies (U/LIRGs; L-IR >= 10(11) L-circle dot), using FWHM less than or similar to 0 ''.1-0 ''.2 resolution 15 and 33 GHz observations with the Karl G. Jansky Very Large Array. We identify a total of 133 compact radio sources with effective radii of 8-170 pc, which are classified into four main categories-"AGN" (active galactic nuclei), "AGN/SBnuc" (AGN-starburst composite nucleus), "SBnuc" (starburst nucleus), and "SF" (star-forming clumps)-based on ancillary data sets and the literature. We find that "AGN" and "AGN/SBnuc" more frequently occur in late-stage mergers and have up to 3 dex higher 33 GHz luminosities and surface densities compared with "SBnuc" and "SF," which may be attributed to extreme nuclear starburst and/or AGN activity in the former. Star formation rates (SFRs) and surface densities (Sigma(SFR)) are measured for "SF" and "SBnuc" using both the total 33 GHz continuum emission (SFR similar to 0.14-13 M-circle dot yr(-1), Sigma(SFR) similar to 13-1600 M-circle dot yr(-1) kpc(-2)) and the thermal free-free emission from H ii regions (median SFRth similar to 0.4 M-circle dot yr(-1), Sigma(SFR)(th) similar to 44 M-circle dot yr(-)(1) kpc(-2)). These values are 1-2 dex higher than those measured for similar-sized clumps in nearby normal (non-U/LIRGs). The latter also have a much flatter median 15-33 GHz spectral index (similar to-0.08) compared with "SBnuc" and "SF" (similar to-0.46), which may reflect higher nonthermal contribution from supernovae and/or interstellar medium densities in local U/LIRGs that directly result from and/or lead to their extreme star-forming activities on 100 pc scales.

Nuclear rings are excellent laboratories for studying intense star formation. We present results from a study of nuclear star-forming rings in five nearby normal galaxies from the Star Formation in Radio Survey (SFRS) and four local LIRGs from the Great Observatories All-sky LIRG Survey at sub-kiloparsec resolutions using Very Large Array high-frequency radio continuum observations. We find that nuclear ring star formation (NRSF) contributes 49%–60% of the total star formation of the LIRGs, compared to 7%–40% for the normal galaxies. We characterize a total of 57 individual star-forming regions in these rings, and find that with measured sizes of 10–200 pc, NRSF regions in the LIRGs have star formation rate (SFR) and ΣSFR up to 1.7 M ⊙ yr−1 and 402 M ⊙ yr−1 kpc−2, respectively, which are about 10 times higher than in NRSF regions in the normal galaxies with similar sizes, and comparable to lensed high-z star-forming regions. At ∼100–300 pc scales, we estimate low contributions (<50%) of thermal free–free emission to total radio continuum emission at 33 GHz in the NRSF regions in the LIRGs, but large variations possibly exist at smaller physical scales. Finally, using archival sub-kiloparsec resolution CO (J = 1–0) data of nuclear rings in the normal galaxies and NGC 7469 (LIRG), we find a large scatter in gas depletion times at similar molecular gas surface densities, which tentatively points to a multimodal star formation relation on sub-kiloparsec scales.

We present results of 3 mm observations of SiO maser sources in the Galactic Centre (GC) from observations with the Australia Telescope Compact Array between $2010-2014$, along the transitions of the SiO molecule at $v = 1, J = 2-1$ at 86.243 GHz and $v = 2, J = 2-1$ at 85.640 GHz. We also present the results of the 3 mm observations with Atacama Large Millimeter/Submillimeter Array (ALMA). We detected 5 maser sources from the ATCA data, IRS 7, IRS 9, IRS 10EE, IRS 12N, and IRS 28; and 20 sources from the ALMA data including 4 new sources. These sources are predominantly late-type giants or emission line stars with strong circumstellar maser emission. We analyse these sources and calculate their proper motions. We also study the variability of the maser emission. IRS 7, IRS 12N and IRS 28 exhibit long period variability of the order of $1 - 2$ years, while other sources show steady increase or decrease in flux density and irregular variability over observation timescales. This behaviour is consistent with the previous observations.

We study the environment of Sgr A* using spectral and continuum observations with the ALMA and VLA. Our analysis of sub-arcsecond H30alpha, H39alpha, H52alpha and H56alpha line emission towards Sgr A* confirm the recently published broad peak ~500 km/s~spectrum toward Sgr~A*. We also detect emission at more extreme radial velocities peaking near -2500 and 4000 km/s, within 0.2''. We then present broad band radio continuum images at multiple frequencies on scales from arcseconds to arcminutes. A number of elongated continuum structures lie parallel to the Galactic plane, extending from ~0.4'' to 10'. We note a nonthermal elongated structure on an arcminute scale emanating from Sgr A* at low frequencies between 1 and 1.4 GHz where thermal emission from the mini-spiral is depressed by optical depth effects. The position angle of this elongated structure and the sense of motion of ionized features with respect to Sgr A* suggest a symmetric, collimated jet emerging from Sgr A* with an opening angle of ~30deg and a position angle of ~60deg punching through the medium before accelerating a significant fraction of the orbiting ionized gas to high velocities. The jet with estimated mass flow rate ~1.4x10^{-5} solar mass/yr emerges perpendicular to the equatorial plane of the accretion flow near the event horizon of Sgr A* and runs along the Galactic plane. To explain a number of east-west features near Sgr A*, we also consider the possibility of an outflow component with a wider-angle launched from the accretion flow at larger radii.

We have used the capabilities of ALMA to probe the ionized gas towards the Galactic center with the H30alpha mm hydrogen recombination line within 30'' of the Galaxy's dynamical center. The observations are made with spatial and spectral resolutions of 0.46'' X 0.35'' and 3 km/s, respectively. Multiple compact and extended sources are detected in the mini-cavity region with extreme negative radial velocities ranging from -480 to -300 km/s, 2-3'' (0.08-0.12 pc) from Sgr A*. This is the highest radial velocity of ionized gas detected beyond the inner 1'' of Sgr A*. This new component is kinematically isolated from the orbiting ionized gas. The detected gas has a velocity gradient ranging from -50 to -200 km/s per arcsecond located to the southwest of Sgr A* at a position angle of roughly -160 degrees. Previous proper motion measurements in the immediate vicinity of these extreme high-velocity ionized components have been measured and show transverse velocities that range from 313 - 865 km/s. If we assume that they are associated with each other, then the total velocity implies these components are gravitationally unbound. In addition, we report the kinematics of cometary radio and infrared sources. These sources are diagonally distributed with a position angle of roughly 50 degrees within 14'' of Sgr A*. We interpret the highly blue-shifted features to the SW where the mini-cavity is located and red-shifted cometary sources to the NE in terms of the interaction of a collimated outflow with an opening angle of roughly 30 degrees. An expected mass outflow rate of 2E-7 or 4E-5 solar mass per yr is estimated by a relativistic jet-driven outflow or collimated stellar winds, respectively.

Magnetic null points can develop near the ergosphere boundary of a rotating black hole through the combined effects of strong gravitational field and the frame-dragging mechanism. The electric component does not vanish in the magnetic null, and an efficient process or particle acceleration can occur. The situation is relevant to starving (low-accretion-rate, such as the Milky Way's supermassive black hole [SMBH]) nuclei of some galaxies that exhibit only episodic accretion events. The presence of the magnetic field of external origin is an important aspect. We propose that such conditions can develop when a magnetized neutron star approaches the SMBH during late stages of its inspiral motion. The field lines of the neutron star dipole thread the black hole's event horizon and rapidly change their connectivity. We compare the case of a dipole-type magnetic field of a sinking and orbiting star near a nonrotating black hole and the near-horizon structure of an asymptotically uniform magnetic field of a distant source near a fast-rotating black hole. Although the two cases are qualitatively different from each other, they both develop magnetically neutral null points near the event horizon.

Bright Active Galactic Nuclei are powered by accretion of mass onto the super massive black holes at the centers of the host galaxies. For fainter objects star formation may significantly contribute to the luminosity. We summarize experimental indicators of the accretion processes in Active Galactic Nuclei (AGN), i.e., observable activity indicators that allow us to conclude on the nature of accretion. The Galactic Center is the closest galactic nucleus that can be studied with unprecedented angular resolution and sensitivity. Therefore, here we also include the presentation of recent observational results on Sagittarius A* and the conditions for star formation in the central stellar cluster. We cover results across the electromagnetic spectrum and find that the Sagittarius A* (SgrA*) system is well ordered with respect to its geometrical orientation and its emission processes of which we assume to reflect the accretion process onto the super massive black hole.

Broad Emission Lines are the most characteristic features of active galaxies but the mechanism of the line formation is still under debate. In 2011 we proposed that the H beta lines are formed in a Failed Radiatively Accelerated Dusty Outflow (FRADO). In this paper we investigate this mechanism in more detail. We calculated the motion of dusty clouds taking into account the dust evaporation which arises when they are additionally illuminated by the central source. Our model explains the location and extension of the Broad Line Region as well as its large turbulent motion superimposed on Keplerian rotation. However, an enhancement of the dust opacity or additional mechanisms are necessary to push the material high enough above the disk.

Accretion onto black holes often proceeds via an accretion disk or a temporary disk-like pattern. Variability features observed in light curves as well as theoretical models of accretion flows suggest that accretion disks tend to be inhomogeneous variety of substructures (clumps) emerge within the flow. Rapid orbital motion of individual clumps then modulates the observed signal in X-rays. Furthermore, changes of spectral lines and polarization properties of the observed signal (or the absence of changes) constrain the models and reveal information about general relativity (GR) effects. In this write-up we summarize the basic equations that have been employed to study light propagation near black holes and to derive the radiation signal that can be expected at a detector within the framework of geometrical optics approximation.

In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.

A. Eckart 1 ∗,2†, M. Valencia-S. , B. Shahzamanian , M. Zajacek 2,1, L. Moser 1,3, G. Busch , M. Parsa 2,1, M. Subroweit , F. Peissker , N. Sabha , S.E. Hosseini 1,2, M. Horrobin , C. Straubmeier , N. Fazeli , A. Borkar , D. Kunneriath 4,6, V. Karas , C. Rauch , S. Britzen , A. Zensus , M. García-Marín , Y.E. Rashed 7 1) I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany; 2) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany; 3) Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany 4) Astronomical Institute of the Czech Academy of Sciences, Bocni II 1401, CZ-14100 Prague, Czech Republic 5) European Space Agency (ESA/STScI), 3700 San Martin Drive, Baltimore, MD 21218, USA 6) North American ALMA Science Centre, NRAO, Edgemont Road, Charlottesville, VA 22903, USA 7) Department of Astronomy, Faculty of Science, University of Baghdad, 10071 Baghdad Aljadirya, Iraq

Black holes cannot support their own internal magnetic field like, for example, compact stars can. Despite this fact observations indicate that event horizons of supermassive black holes (SMBH) are threaded by field lines along which plasma streams flow. Various magnetohydrodynamical mechanisms have been suggested to generate turbulent magnetic fields on small scales, however, the origin of the large-scale component is unclear. In this write-up we describe our progress in an on-going work and discuss the possibility of dipole-type magnetic fields being brought onto SMBH by magnetized neutron stars, which are expected to drift inward from a hidden population in the Nuclear Star Cluster. This can contribute to an organised component of the magnetic field on the characteristic length-scale of the stellar size, which thread the horizon during the final stages of the magnetized star plunge into or its close flyby around SMBH. Because of mass--size scaling relations for black holes, the effect is more important for lower-mass SMBH.

We study the conditions for the onset of Thermal Instability in the innermost regions of compact galactic nuclei, where the properties of the interstellar environment are governed by the interplay of quasi-spherical accretion onto a supermassive black hole (SMBH) and the heating/cooling processes of gas in a dense nuclear star cluster. Stellar winds are the source of material for radiatively inefficient (quasi-spherical, non-magnetised) inflow/outflow onto the central SMBH, where a stagnation point develops within the Bondi type accretion. We study the local thermal equilibrium to determine the parameter space which allows cold and hot phases in mutual contact to co-exist. We include the effects of mechanical heating by stellar winds and radiative cooling/heating by the ambient field of the dense star cluster. We consider two examples: the Nuclear Star Cluster (NSC) in the Milky Way central region (including the gaseous Mini-spiral of Sgr~A*), and the Ultra-Compact Dwarf galaxy M60-UCD1. We find that the two systems behave in different ways because they are placed in different areas of parameter space in the instability diagram: gas temperature vs. dynamical ionization parameter. In the case of Sgr~A*, stellar heating prevents the spontaneous formation of cold clouds. The plasma from stellar winds joins the hot X-ray emitting phase and forms an outflow. In M60-UCD1 our model predicts spontaneous formation of cold clouds in the inner part of the galaxy. These cold clouds may survive since the cooling timescale is shorter than the inflow/outflow timescale.

We present 44 and 226 GHz observations of the Galactic Centre within 20 arcsec of Sgr A*. Millimetre continuum emission at 226 GHz is detected from eight stars that have previously been identified at near-IR and radio wavelengths. We also detect a 5.8 mJy source at 226 GHz coincident with the magnetar SGR J1745-29 located 2.39 arcsec SE of Sgr A* and identify a new 2.5 arcsec x 1.5 arcsec halo of mm emission centred on Sgr A*. The X-ray emission from this halo has been detected previously and is interpreted in terms of a radiatively inefficient accretion flow. The mm halo surrounds an EW linear feature that appears to arise from Sgr A* and coincides with the diffuse X-ray emission and a minimum in the near-IR extinction. We argue that the millimetre emission is produced by synchrotron emission from relativistic electrons in equipartition with an similar to 1.5 mG magnetic field. The origin of this is unclear but its coexistence with hot gas supports scenarios in which the gas is produced by the interaction of winds either from the fast moving S-stars, the photoevaporation of low-mass YSO discs or by a jet-driven outflow from Sgr A*. The spatial anti-correlation of the X-ray, radio and mm emission from the halo and the low near-IR extinction provides a compelling evidence of an outflow sweeping up the interstellar material, creating a dust cavity within 2 arcsec of Sgr A*. Finally, the radio and mm counterparts to eight near-IR identified stars within similar to 10 arcsec of Sgr A* provide accurate astrometry to determine the positional shift between the peak emission at 44 and 226 GHz.

1) I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany; 2) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany; 3) Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany 4) Astronomical Institute of the Czech Academy of Sciences, Bocni II 1401, CZ-14100 Prague, Czech Republic 5) European Space Agency (ESA/STScI), 3700 San Martin Drive, Baltimore, MD 21218, USA 6) North American ALMA Science Centre, NRAO, Edgemont Road, Charlottesville, VA 22903, USA 7) Department of Astronomy, Faculty of Science, University of Baghdad, 10071 Baghdad Aljadirya, Iraq