Galaxy formation and evolution

Abstract:

We present JWST observations of the radio galaxy TGSSJ1530+1049, spectroscopically confirmed at $z=4.0$ . NIRCam images and NIRSpec/IFU spectroscopy ( $R=2700$ ) show that TGSSJ1530+1049 is part of one of the densest-known structures of continuum and line-emitting objects found at these redshifts. NIRCam images show a number of distinct continuum objects and evidence of interactions traced by diffuse emission, and the NIRSpec IFU cube reveals further strong line emitting regions. We identify six continuum and four additional strong Halpha emitting sources with weaker or no underlying continuum within the 3’‘x3’’ IFU field. From spatial alignment with high-resolution radio data and emission line profiles, the radio AGN host galaxy is clearly identified. The bright Halpha emission (but not the optical components) is distributed remarkably linearly along the radio axis, suggestive of a biconical illumination zone by a central obscured AGN. The emission line kinematics indicate jet-gas interactions on scales of a few kpc. However, due to large relative velocities and presence of underlying continuum, the alignment with the radio structure appears to be, at least partly, caused by a particular configuration of interacting galaxies. At least four objects within a 10x10 (projected) kpc area which includes the radio source have high stellar masses (log( $M_{\star }/M_{\odot })>10.3$ ) and star formation rates in the range 70-163 $M_{\odot }$ yr. Using a stellar mass-based analysis, we predict a total dark matter halo mass of $\approx {10}^{13}{M}_{\odot }$ . Based on the physical separations and velocity differences between the galaxies, it is expected that these galaxies will merge to form a massive galaxy within a few Gyr. The system qualitatively resembles the forming brightest cluster galaxies in cosmological simulations that form early through a rapid succession of mergers.

Abstract:

With the rise of integral field spectroscopy (IFS), we are currently dealing with large amounts of spatially resolved data, whose analysis has become challenging, especially when observing complex objects such as nearby galaxies. We aim to develop a method of automatically separating regions with different physical properties (ionisation, kinematics, etc.) within the central parts (1" ∼ 160,pc, on average) of galaxies. This could allow us to better understand the systems and provide an initial characterisation of the main ionisation sources affecting its evolution. We developed an unsupervised hierarchical clustering algorithm to analyse data cubes based on spectral similarity. It clusters spaxels together with similar spectra, which is useful to disentangle regions affected by different processes, such as ionisation sources. We applied this method to a sample of 15 nearby (distances $<100,Mpc) galaxies: 7 from the Galaxy Activity, Torus, and Outflow Survey (GATOS) and 8 archival sources, all observed with the medium-resolution spectrometer (MRS) of the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST). The sample spans sources of various morphologies, active galactic nucleus (AGN) types, and/or starbursts. From the clusters, we computed their median spectrum and measured the line and continuum properties. We used these measurements to train random forest models and create several empirical mid-IR diagnostic diagrams for the MRS channel 3 wavelength range, ranging from 11.5 to 18μ$m, which includes among others the bright Ne,II , Ne,III , and Ne,V lines, several H_2 transitions, and PAH features. The clustering technique allows one to differentiate emission coming from an AGN, a nuclear starburst, the disc and star-forming (SF) regions in the galaxies, and other composite regions, potentially ionised by several sources simultaneously. This is supported by the results from the empirical diagnostic diagrams, which are indeed able to separate physically distinct regions. This innovative method serves as a tool to identify regions of interest in any data cube prior to an in-depth analysis of the sources. In a future work, we shall explore other wavelength ranges and a larger sample that would help us to obtain statistically significant conclusions.

Abstract:

Supermassive black hole (SMBH) masses can be measured using molecular gas kinematics. Here we present high-angular-resolution (0.12 arcsec or pc) Atacama Large Millimeter/submillimeter Array observations of the CO(2–1) line emission of the early-type galaxy NGC 1387. The observations reveal a face-on, regularly rotating central molecular gas disc with a diameter of arcsec ( kpc) and a central depression slightly larger than the SMBH sphere of influence. We forward model the CO data cube in a Bayesian framework with the Kinematic Molecular Simulation code, and use Hubble Space Telescope data to constrain the stellar gravitational potential contribution to the molecular gas kinematics. We infer an SMBH mass of M and an F160W-filter stellar mass-to-light ratio of M/L. This SMBH mass is consistent with the SMBH mass–stellar velocity dispersion relation.