Galaxy formation and evolution

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.