Galaxy formation and evolution

Abstract:

Abstract A key question in extragalactic astronomy is how the star-formation rate density (SFRD) evolves over cosmic time. A powerful way of addressing this question is using radio-continuum observations, where the radio waves are unaffected by dust and are able to reach sufficient resolution to resolve individual galaxies. We present an investigation of the 1.4 GHz radio luminosity functions (RLFs) of star-forming galaxies (SFGs) and Active Galactic Nuclei (AGN) using deep radio continuum observations in the COSMOS and XMM–LSS fields, covering a combined area of ∼4 deg2. These data enable the most accurate measurement of the evolution in the SFRD from mid-frequency radio continuum observations. We model the total RLF as the sum of evolving SFG and AGN components, negating the need for individual source classification. We find that the SFGs have systematically higher space densities at fixed luminosity than found in previous radio studies, but consistent with more recent studies with MeerKAT. We attribute this to the excellent low-surface brightness sensitivity of MeerKAT. We then determine the evolution of the SFRD. Adopting the far-infrared – radio correlation results in a significantly higher SFRD at z > 1, compared to combined UV and far-infrared measurements. However, using more recent relations for the correlation between star-formation rate and radio luminosity, based on full spectral energy distribution modelling, can resolve this apparent discrepancy. Thus radio observations provide a powerful method of determining the total SFRD, in the absence of dust-sensitive far-infrared data.

Abstract:

Abstract Studying samples of young star-forming regions allows us to statistically examine the evolution of their natal gas and dust along with the associated timescales in the volatile early stages of their lives. With the PHANGS survey data, we analyze the diversity of spectral energy distributions (SEDs) for the rich sample of massive star-forming regions found in NGC 1365. By combining unique detections across a variety of datasets from HST, JWST, and ALMA images, we produce a catalog of 85 star-forming regions located in the central starbursting region of NGC 1365. Prior to analysis, we observe clear saturation effects in our four JWST/MIRI images, and implement a saturation-correction method which allows us to recover data for 23 of 32 saturation-affected regions in these images. We then perform photometry in 13 HST & JWST images which are convolved to match the resolution of MIRI/F2100W (~64pc), allowing us to probe star clusters as well as their immediate surroundings. Upon deriving their properties from SED-fitting using CIGALE, we observe that regions selected with progressively redder wavebands are younger and generally more reddened. We also identify three SED features correlated with age: 1) sources with a positive near-infrared slope ((F300W+F360M)/(2×F200W)) are by median half the age of those with negative near-infrared slopes; turnover occurs around 6 Myr, 2) the relative strength of dust emission (F2100W/F200W) and 3) PAH emission (F335M/F300M) both show that larger such ratios correlate with younger ages. Considering our working resolution, these features are robust to the inclusion of nearby emission surrounding star clusters.

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.