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We investigated the stellar population properties of a sample of 1858 massive compact galaxies (MCGs) extracted from the Sloan Digital Sky Survey (SDSS). Motivated by previous results showing that older compact galaxies tend to have larger velocity dispersion at fixed stellar mass, we used the distance to the σe versus R e and M ⋆ versus σe relations as selection criteria. We found that MCGs are old (≳10 Gyr), α-enhanced ([α/Fe] ∼ 0.2), and have solar to supersolar stellar metallicities. Metallicity increases with σe, while age and [α/Fe] do not vary significantly. Moreover, at fixed σe, metallicity and stellar mass are correlated. Compared with a control sample of typical quiescent galaxies, MCGs have, on average, lower metallicities than control sample galaxies (CSGs) of similar σe. For σe ≲ 225 km s−1, MCGs are older and more α-enhanced than CSGs, while for higher σe ages and α-enhancement are similar. The differences in age and α-enhancement can be explained by lower σe CSGs being an amalgam of quiescent galaxies with a variety of ages. The origin of the differences in metallicity, however, is not clear. Lastly, we compared the stellar mass within the region probed by the SDSS fibre finding that, at fixed fibre velocity dispersion, MCGs have lower stellar masses on average. Since the velocity dispersion is a tracer of the dynamical mass, this raises the possibility that MCGs have, on average, a bottom-heavier initial mass function or a larger dark matter fraction within the inner ∼1−2 kpc. [ABSTRACT FROM AUTHOR]

We investigate the formation and evolution of z = 0 massive compact galaxies (MCGs) in the IllustrisTNG cosmological simulation. We found that, as in observations, MCGs are mainly old (median age ∼10.8 Gyr), have supersolar metallicities (median log  Z /Z⊙ ∼ 0.35), and are α-enhanced (median [α/Fe] ∼ 0.25). The age distribution extends to younger ages, however, and a few MCGs are as young as ∼7 Gyr. In general, MCGs assemble their mass early and accrete low angular momentum gas, significantly increasing their mass while growing their size much slower. A small fraction of MCGs follow another evolutionary path, going through a compaction event, with their sizes shrinking by 40 per cent or more. The accretion of low angular momentum gas leads to enhanced supermassive black hole (SMBH) growth, and MCGs reach the threshold SMBH mass of |$\log M_\mathrm{BH}\sim 10^{8.5}\ \mathrm{ M}_\odot$| – when kinetic active galactic nucleus feedback kicks in and quenches the galaxy – earlier than non-compact galaxies. Comparing MCGs to a sample of median-sized quiescent galaxies matched in effective velocity dispersion, we find that their accretion histories are very different. 71 per cent of MCGs do not merge after quenching compared to 37 per cent of median-sized quiescent galaxies. Moreover, tracing these populations back in time, we find that at least a third of median-sized quiescent galaxies do not have a compact progenitor, underscoring that both dry mergers and progenitor bias effects are responsible for the differences in the kinematics and stellar population properties of MCGs and median-sized quiescent galaxies. [ABSTRACT FROM AUTHOR]

We characterized the kinematics, morphology, and stellar population (SP) properties of a sample of massive compact quiescent galaxies (MCGs, |$10\, \lesssim \, \log M_\star$| /M |$_\odot \, \lesssim \, 11$| and r e ∼ 1–3 kpc) in the MaNGA Survey, with the goal of constraining their formation, assembly history, and assessing their relation with non-compact quiescent galaxies. We compared their properties with those of a control sample of median-sized quiescent galaxies (r e ∼ 4–8 kpc) with similar effective velocity dispersions. MCGs have elevated rotational support, as evidenced by a strong anticorrelation between the Gauss–Hermite moment h 3 and V / σ. In contrast, 30 |${{\ \rm per\ cent}}$| of control sample galaxies (CSGs) are slow rotators, and fast-rotating CSGs generally show a weak h 3– V / σ anticorrelation. MCGs and CSGs have similar ages, but MCGs are more metal-rich and α -enhanced. Both MCGs and CSGs have shallow negative metallicity gradients and flat [ α /Fe] gradients. On average, MCGs and CSGs have flat age gradients, but CSGs have a significantly larger dispersion of gradient values. The kinematics and SP properties of MCGs suggest that they experienced highly dissipative gas-rich events, such as mergers, followed by an intense, short, and centrally concentrated burst of star formation, between 4 and 10 Gyr ago (z ∼ 0.4–2), and had a quiet accretion history since then. This sequence of events might be analogous to, although less extreme than, the compaction events that formed compact quiescent galaxies at z  ∼ 2. The small sizes of MCGs, and the high efficiency and short duration of their last star formation episode suggest that they are descendants of compact post-starburst galaxies. [ABSTRACT FROM AUTHOR]

Compact groups of dwarf galaxies (CGDs) have been observed at low redshifts (z < 0.1) and are direct evidence of hierarchical assembly at low masses. To understand the formation of CGDs and the galaxy assembly in the low-mass regime, we search for analogues of compact (radius ≤100 kpc) groups of dwarfs (7 ≤ log [ M */M⊙] ≤ 9.5) in the IllustrisTNG highest resolution simulation. Our analysis shows that TNG50-1 can successfully produce CGDs at z  = 0 with realistic total and stellar masses. We also find that the CGD number density decreases towards the present, especially at z ≲ 0.26, reaching |$n \approx 10^{-3.5} \ \rm cMpc^{-3}$| at z  = 0. This prediction can be tested observationally with upcoming surveys targeting the faint end of the galaxy population and is essential to constrain galaxy evolution models in the dwarf regime. The majority of simulated groups at z ∼ 0 formed recently (⁠|$\lesssim 1.5 \ \rm Gyr$|⁠), and CGDs identified at z ≤ 0.5 commonly take more than 1 Gyr to merge completely, giving origin to low- to intermediate-mass (8 ≤ log [ M */M⊙] ≤ 10) normally star-forming galaxies at z  = 0. We find that haloes hosting CGDs at z  = 0 formed later when compared to haloes of similar mass, having lower stellar masses and higher total gas fractions. The simulations suggest that CGDs observed at z ∼ 0 arise from a late hierarchical assembly in the last ∼3 Gyr, producing rapid growth in total mass relative to stellar mass and creating dwarf groups with median halo masses of |$\sim 10^{11.3} \ \rm M_\odot$| and B -band mass-to-light ratios mostly in the range 10 ≲ M / L ≲ 100, in agreement with previous theoretical and observational studies. [ABSTRACT FROM AUTHOR]

We analyse optical data cubes of the inner kiloparsec of 30 local (z ≤ 0.02) active galactic nucleus (AGN) hosts that our research group, AGNIFS, has collected over the past decade via observations with the integral field units of the Gemini Multi-Object Spectrographs. Spatial resolutions range between 50 and 300 pc and spectral coverage is from 4800 or 5600 to 7000 Å, at velocity resolutions of ≈50  |$\rm ~km~s^{-1}$|⁠. We derive maps of the gas excitation and kinematics, and determine the AGN ionization axis – which has random orientation relative to the galaxy – and the kinematic major axes of the emitting gas. We find that rotation dominates the gas kinematics in most cases, but is disturbed by the presence of inflows and outflows. Outflows have been found in 21 nuclei, usually along the ionization axis. The gas velocity dispersion is traced by W 80 (velocity width encompassing 80 per cent of the line flux), adopted as a tracer of outflows. In seven sources, W 80 is enhanced perpendicularly to the ionization axis, indicating lateral expansion of the outflow. We have estimated mass-outflow rates |$\dot{M}$| and powers |$\dot{E}$|⁠ , finding median values of |$\log \, [\dot{M}/({\rm \, M_\odot \, yr^{-1}})]=-2.1_{-1.0}^{+1.6}$| and |$\log \, [\dot{E}/({\rm \, erg\, s^{-1}})]=38.5_{-0.9}^{+1.8}$|⁠ , respectively. Both quantities show a mild correlation with the AGN luminosity (L AGN). |$\dot{E}$| is of the order of 0.01 L AGN for four sources, but much lower for the majority (nine) of the sources, with a median value of |$\log \, [\dot{E}/L_{\rm AGN} ]=-5.34_{-0.9}^{+3.2}$|⁠ , indicating that typical outflows in the local Universe are unlikely to significantly impact their host galaxy evolution. [ABSTRACT FROM AUTHOR]

In order to gauge the role that active galactic nuclei play in the evolution of galaxies via the effect of kinetic feedback in nearby QSO 2's (z ∼ 0.3), we observed eight such objects with bolometric luminosities |$L_{bol} \sim 10^{46}\rm {erg\, s^{-1}}$| using Gemini Multi-Object Spectrograph-integral field units. The emission lines were fitted with at least two Gaussian curves, the broadest of which we attributed to gas kinetically disturbed by an outflow. We found that the maximum extent of the outflow ranges from ∼1 to 8 kpc, being |${\sim }\, 0.5\, {\pm }\, 0.3$| times the extent of the [ |$\mathrm{O\,{\small III}}$| ] ionized gas region. Our ' default ' assumptions for the gas density (obtained from the [ |$\mathrm{S\,{\small II}}$| ] doublet) and outflow velocities resulted in peak mass outflow rates of |$\dot{M}_{\mathrm{ out}}^{{\tt def}}\sim$|  3–30  |$\rm {M_{\odot }}\, yr^{-1}$| and outflow power of |$\dot{E}_{\mathrm{ out}}^{{\tt \mathrm{ def}}}\sim \, 10^{41}$| – |$10^{43}\, \mathrm{erg\, s^{-1}}$|⁠. The corresponding kinetic coupling efficiencies are |$\varepsilon _f^{{\tt def}}=\dot{E}_{\mathrm{ out}}^{{\tt def}}/L_{\mathrm{ bol}}\, \sim 7\times 10^{-4}$| –0.5 per cent, with the average efficiency being only 0.06 per cent (0.01 per cent median), implying little feedback powers from ionized gas outflows in the host galaxies. We investigated the effects of varying assumptions and calculations on |$\dot{M}_{\mathrm{ out}}$| and |$\dot{E}_{\mathrm{ out}}$| regarding the ionized gas densities, velocities, masses, and inclinations of the outflow relative to the plane of the sky, resulting in average uncertainties of 1 dex. In particular, we found that better indicators of the [ |$\mathrm{O\,{\small III}}$| ] emitting gas density than the default [ |$\mathrm{S\,{\small II}}$| ] line ratio, such as the [ |$\mathrm{Ar\,{\small IV}}$| ] λλ4711,40 line ratio, result in almost an order of magnitude decrease in the ε f . [ABSTRACT FROM AUTHOR]