Rubin-LSST

Abstract:

Abstract We analyse black hole scaling relations for disk-dominated galaxies, and present evidence for secularly driven galaxy-black hole co-evolution. We do this observationally by looking at “bulgeless” galaxies, where the lack of a stellar bulge suggests a quiet merger history. We first compose a sample of 2,435 disk-dominated galaxies hosting optical broad line active galactic nuclei (AGN) from DESI data, and find a $M_{\mathrm{BH}^{}}$–$M_{*}^{}$ scaling relation of log (MBH) $= - 3.7^{+0.3}_{-0.3} + 1.00^{+0.03}_{-0.03} \log (M_*)$. From these, we identify 546 bulgeless galaxies hosting AGN, a factor of ≳ 5 larger than pre-existing samples, and find they follow the same $M_{\mathrm{BH}^{}}$-$M_{*}^{}$ relation as the general disk galaxy sample. Comparing the bulgeless galaxies to those with some bulge component, we find good agreement in the $M_{\mathrm{BH}^{}}$–$M_{*}^{}$ relation (within 3σ), but disagreement in the $M_{\mathrm{BH}^{}}$–$M_{\mathrm{*,bulge}}^{}$ relation (at >7σ). This is the opposite of what is expected from merger-driven co-evolution, suggesting secular growth is significant in establishing observed $M_{\mathrm{BH}^{}}$–$M_{*}^{}$ scaling relations. Furthermore, in a control sample of early-type galaxies we find tentative evidence of increased AGN luminosity compared to the bulgeless sample, but no statistical difference in black hole mass. This suggests the assumed merger-dominated evolutionary history of early-type galaxies does not lead to significantly increased long-term BH growth. These results support numerous recent observational and theoretical studies which suggest secular processes fuel significant supermassive black hole growth and galaxy-black hole co-evolution.

Abstract:

Abstract In this second paper of the E-INSPIRE series, we train a machine-learning-based regression on ~430 nearby (z < 0.5) ultra-compact massive galaxies (UCMGs) with spectroscopically inferred kinematics, stellar population parameters and a measured “degree of relicness” (DoR). Our goal is to investigate how robustly the spectroscopically inferred DoR can be statistically reconstructed from observable galaxy properties, and to explore the potential applicability of this framework to future wide-area surveys. We test several regression algorithms finding that Support Vector Regression (SVR) provides the best performance. We explore multiple input feature configurations, from a minimal set including only age and metallicity to more comprehensive ones incorporating stellar population parameters, kinematics, structural properties, and the associated uncertainties. All tested models achieve similarly high performance on the training set (R2 ≥ 0.81), except for the minimal configuration (R2 ~ 0.78). When evaluated on an independent INSPIRE sample of 52 UCMGs, the predictive power remains robust, although with increased model-to-model variation. The DoR distribution shows three regimes, with low (DoR<0.3) and high (DoR>0.6) values sparsely populated, leading to mild regression shrinkage toward intermediate values. However, this behaviour enables a conservative selection strategy: galaxies with predicted DoR≥0.6 are strongly biased toward genuine extreme relics, making them prime targets for follow-up observations. This proof-of-concept confirms that the spectroscopically inferred DoR is robustly connected to observable stellar population and kinematical properties, and provides a first step toward future relic-candidate selection strategies in large photometric and spectroscopic surveys.