Galaxy formation and evolution

Abstract:

Combining Atacama Large Millimeter/submillimeter Array CO(2–1) mapping and JWST near- and mid-infrared imaging, we characterize the relationship between CO(2–1) and polycyclic aromatic hydrocarbon (PAH) emission at ≈100 pc resolution in 70 nearby star-forming galaxies. Leveraging a new Cycle 2 JWST Treasury program targeting nearby galaxies, we expand the sample size by more than an order of magnitude compared to previous ≈100 pc resolution CO–PAH comparisons. In regions of galaxies where most of the gas is likely to be molecular, we find strong correlations between CO(2–1) and 3.3 μm, 7.7 μm, and 11.3 μm PAH emission, estimated from JWST’s F335M, F770W, and F1130W filters. We derive power-law relations between CO(2–1) and PAH emission, with indices in the range 0.8–1.3, implying relatively weak variations in the observed CO-to-PAH ratios across our sample. We find that CO-to-PAH ratios and scaling relationships near H ii regions are similar to those in diffuse sight lines. The main difference between the two types of regions is that sight lines near H ii regions show higher intensities in all tracers. Galaxy centers show higher overall intensities and enhanced CO-to-PAH ratios compared to galaxy disks. Individual galaxies show 0.19 dex scatter in the normalization of CO at fixed IPAH, and this normalization anticorrelates with specific star formation rate and correlates with stellar mass. We provide a prescription that accounts for galaxy-to-galaxy variations, representing our best current empirical predictor to estimate CO(2–1) intensity from PAH emission, allowing one to take advantage of JWST’s excellent sensitivity and resolution to trace cold gas.

Abstract:

This paper presents the first effort to Extend the Investigation of Stellar Populations In RElics (E-INSPIRE). We present a catalogue of 430 spectroscopically confirmed ultra-compact massive galaxies (UCMGs) from the Sloan Digital Sky Survey at redshifts . This increases the original INSPIRE sample eightfold, bridging the gap with the local Universe. For each object, we compute integrated stellar velocity dispersion, age, metallicity, and [Mg/Fe] through spectroscopic stellar population analysis. We infer star formation histories (SFHs), metallicity evolution histories (MEHs) and compute the Degree of Relicness (DoR) of each object. The UCMGs, covering a wide range of DoR from 0.05 to 0.88, can be divided into three groups, according to how extreme their SFH was. The first group consists of 81 extreme relics () that have formed the totality of their stellar mass by and have super-solar metallicities at all cosmic epochs. The second group () contains 293 objects also characterized by peaked SFHs but with a small percentage of later-formed stars and with a variety of MEHs. The third group (), has 56 objects that cannot be considered relics since they have extended SFHs and formed a non-negligible fraction ( per cent) of their stellar mass at . We conclude that the most efficient method of finding relics is to select UCMGs with a combination of large velocity dispersion values (as already found by INSPIRE), super-solar metallicities and high [Mg/Fe].