Galaxy formation and evolution

Abstract:

Abstract Radio emission during X-ray binary outbursts is dominated by synchrotron radiation from relativistic jets, but is usually studied through total-intensity diagnostics such as flux density, spectra, variability, and proper motion. Radio spectropolarimetry provides a complementary probe of the magneto-ionic plasma through Faraday rotation and depolarisation. When the Faraday rotating material is local to the source, these effects can constrain the jet plasma composition and mass content, but this approach is rarely applied to transient jetted sources. We present MeerKAT L-band spectropolarimetry of the black hole X-ray binary Swift J1727 during its 2023 outburst, focusing on the brightest radio flaring interval, when relativistic jets were being launched intermittently. Using multiple spectropolarimetric techniques, we identify transient Faraday-complex structure coincident with the major radio flares. The close temporal association with the flaring activity, together with the stability of the foreground Faraday screen, favours an origin local to the jet rather than in the ISM or in a separate local screen external to the emitting plasma. Since internal Faraday rotation is suppressed in a pure electron–positron plasma, the data favour a dominant electron–proton component. Interpreting the characteristic Faraday thickness as internal rotation, and anchoring the magnetic-field and size scales with synchrotron self-absorption arguments, we infer a characteristic Faraday-rotating mass of order Mrot ~ 1021 g, corresponding to only a small fraction, frot ~ 10−3, of the accreted mass available during the flare. These results show that time-domain spectropolarimetry can turn transient Faraday complexity into a diagnostic of jet composition, mass loading, and plasma evolution in X-ray binary outbursts, and potentially other transient jetted sources.

Abstract:

We analyze H i 21 cm observations of the Local Group dwarf galaxy Wolf–Lundmark–Melotte (WLM) from the Local Group L-Band Survey to search for evidence of ram pressure stripping. While previous MeerKAT-16 observations of WLM showed evidence for off-galaxy atomic gas emission with a geometry suggestive of ram pressure stripping, our observations find no evidence for this stripped gas. We demonstrate that our observations would be sensitive to the claimed detections and suggest that an uncorrected observational flaw with the MeerKAT data led to the apparent off-galaxy emission. The lack of off-galaxy emission obviates the need for uncharacteristically high values of the density of the intergalactic medium in this region.

Abstract:

Dynamical modelling can be used to constrain the masses of central black holes, but it is challenging to model massive galaxies because of their complex kinematics. We report six new measurements of supermassive black hole masses of massive early-type galaxies from stellar kinematics, which were extracted from adaptive-optics-assisted SINFONI and MUSE observations. We combined the stellar kinematics with HST photometry to build triaxial Schwarzschild orbit-superposition models. Our Schwarzschild models can recover the complex triaxial features of the galaxies and constrain the black hole masses of all six galaxies. We found that strong triaxial kinematic features can bias the mass measurements and corrected for this effect. The derived black hole masses are $(1.14^ DYNAMITE +0.41 _ -0.63 ) _ 10^9$ M_⊙ for NGC 3706, $(1.19^ +1.34 -0.80 ) _ 10^9$ M_⊙ for NGC 3923, $(1.14^ +1.08 -0.95 ) _ 10^9$ M_⊙ for NGC 4261, $(4.68^ +2.99 -4.26 ) _ 10^8$ M_⊙ for NGC 4636, $(3.51^ +3.37 -2.57 ) _ 10^9$ M_⊙ for IC 4296, and $(2.43^ +1.53 -1.65 ) 10^9$ M_⊙ for IC 4329 at a confidence level of 3σ. We compared our measurements with published results from axisymmetric Schwarzschild modelling and with our JAM Jeans Anisotropic models and obtained mostly consistent black hole masses. Most of our black hole mass estimates can be well constrained using MUSE observations alone. All of our mass measurements agree with local black hole scaling relations.

Abstract:

Context. Hubble Space Telescope (HST) images are used to study the structure of the central regions of the luminous infrared galaxy (LIRG) IC 860. IC 860 is of special interest as a system with an extreme central concentration of molecular gas cloaking its compact obscured nucleus (CON). The CON provides most of the 1.5 × 10 11 L ⊙ luminosity in IC 860 from an undetermined combination of stellar and active galactic nucleus power sources. Aims. We mapped and photometered the central molecular zone (CMZ) of IC 860 motivated by a previous detection of a luminous compact nuclear source. Our objective was to study the properties of the CMZ and its relationship to the CON, which we identified as an opaque central region in archival near-infrared (NIR) images. Methods. We measured the coordinates of the compact NIR source, IC860-a, from HST coordinates calibrated with Gaia positions. The photometry of the HST images yielded magnitudes, colors, and high V-band dust optical depths based on foreground screen dust models. Photometry corrected for dimming by dust yielded NIR luminosities of IC860-a and the CMZ. Results. IC 860 has distinct compact central luminosity sources. Most of the NIR luminosity is from the CMZ, while the LIRG-CON is an obscured region centered in the CMZ. IC860-a, on the northeastern side of the CMZ, is offset by ≈0.2″ from the CON, has a luminosity of ∼10 9 L ⊙ , and may be a massive young stellar complex or intruding nucleus. Conclusions. The inner CMZ in IC 860 contains two luminous compact objects. The CON is identified for the first time as an obscured central source, while the structure of the CMZ+CON is complicated by the presence of IC860-a, compact object and possibly a massive young stellar system or second nucleus. The presence of IC 860-a in combination with the CON is a further signature of the unusual evolution of the gas-rich IC 860 CMZ.