arXiv subjects

L. R. Ivey

Publications and source records attributed to L. R. Ivey.

6 recordsLinked to original sources

arXiv2026

GA-NIFS: The interplay between feedback and star formation at 3 < z < 9 probed by JWST/NIRSpec IFU

The study of starburst- and AGN-driven feedback is fundamental for understanding the processes that shape galaxy growth, quench star formation, and drive the co-evolution of galaxies and their central black holes. We present a spatially resolved study of six galaxies at $3 < z < 9$, including starburst- and AGN-dominated systems, observed with JWST/NIRSpec IFU in low- ($R \sim 100$) and high-resolution ($R \sim 2700$) mode. Previous analysis of $R \sim 2700$ data revealed ionized outflows in all these galaxies. We explore possible links between outflows and stellar population properties to assess the mechanisms driving galaxy evolution at early epochs. Combining the spatially resolved stellar population analysis with the outflow properties, we find that the most massive galaxies ($M_\star > 5 \times 10^{10} M_\odot$) with strong AGN-driven ionized outflows show evidence of past quenching episodes occurring within the last $\sim 100$--$300$ Myr, mainly in the nuclear regions ($r < 3$ kpc). In contrast, higher-redshift ($z > 5$) and less massive ($M_\star < 10^{10} M_\odot$) starburst galaxies with powerful (starburst-driven) outflows appear to have experienced continuous growth, with no clear sign of quenching. Massive galaxies with weaker outflows do not show evidence of quenching in their history. One massive AGN host (GS20936) shows evidence for a recent ($10$--$30$ Myr) rejuvenation phase, likely fueled by a recent major merger. These results suggest that (AGN-driven) outflows can already play a key role in shaping the SFHs of massive galaxies at early cosmic epochs.

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arXiv2026

Little Red and Blue Dots: simply stratified Broad Line Regions

It has been claimed that a fraction of the so-called Little Red Dots (LRDs) are characterised by exponential broad line profiles, which have been ascribed to broadening from electron scattering by an ionised cocoon. In this work, we investigate the H$α$ broad line profiles of 32 AGN, including Little Red Dots (LRDs), Little Blue Dots (LBDs), and X-ray detected sources, using high SNR and resolution spectroscopy. We find that while single Gaussian models are statistically rejected, the exponential model is not universally preferred. Lorentzian and multi-Gaussian profiles provide equally good or superior fits for the majority of the sample, with no statistical preference for exponential profiles in $\sim$60% of cases across all AGN subtypes. There are indications that exponential profiles are preferred more frequently among LBDs, indicating that exponential profiles are not a prerogative of LRDs, which actually seem to more often favour Lorentzian profiles. Furthermore, we demonstrate that exponential wings can emerge naturally from the stratification of BLR clouds in virial motion, without invoking any scattering process. More generally, we also show that stacking multiple broad lines (either from multiple objects, as done in previous works, or from different BLR components within the same object) generally yields an exponential profile, even if none of the individual profiles are exponential. Explaining the exponential profiles in terms of BLR stratification solves various observational tensions with the electron scattering interpretation. While electron scattering may play a role, there is no evidence that it dominates the line profiles and that it significantly affects the inferred black hole masses.

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arXiv2026

The Little Blue and Red Dots Rosetta Stones: Non-Gaussian broad lines, hot dust, and X-ray weakness

The population of Active Galactic Nuclei (AGN) newly discovered by the James Webb Space Telescope (JWST) exhibits peculiar properties that distinguish it from both local type I AGN and high-redshift quasars. Most of these sources are compact, appearing as 'little dots': among them, the sub-class (10-30% of the total) characterized by significantly red optical colors has been named 'Little Red Dots' (LRDs), while here we analogously introduce the term 'Little Blue Dots' (LBDs) for the remaining, bluer sources (70-90%). We then present a comparative analysis of the prototypical representatives ('Rosetta Stones') of the two classes: GN-28074 at z=2.26, the Red Rosetta Stone, and GS-3073 at z=5.55, the Blue Rosetta Stone. In both Rosetta Stones the broad Balmer lines are better described by exponential profiles rather than single Gaussians, similarly to normal low-redshift type I AGN, indicating that exponential profiles are not unique to LRDs. They are both extremely X-ray weak, show strong auroral [OIII] 4363 emission, weak hot dust mid-IR emission, and no time variability. However, they differ in terms of excitation diagnostics: the HeII 4686 line is undetected in the Red Rosetta but strongly detected in the Blue Rosetta in both narrow and broad components, with the latter much broader than hydrogen Balmer lines. This supports BLR stratification and disfavors the cocoon electron-scattering scenario. An additional difference is the presence of prominent Balmer absorption in the Red Rosetta -- indicative of extremely dense gas along the line of sight -- but absent in the Blue Rosetta. Taken together, these results suggest that LRDs and LBDs share the same central engine as standard type I AGN, while differing in the amount and geometry of dense gas surrounding the accretion disk, and/or in their accretion properties.

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arXiv2025

Exploring Spatially-Resolved Metallicities, Dynamics and Outflows in Low-Mass Galaxies at $z \sim 7.6$

A majority of JWST/NIRSpec/IFU studies at high redshifts to date have focused on UV-bright or massive objects, while our understanding of low-mass galaxies at early cosmic times remains limited. In this work, we present NIRSpec/IFS high-resolution observations of two low-mass ($M_* < 10^9 \ M_\odot$), low-metallicity ($[12 + \log(\text{O/H})] < 8$) galaxies at $z \sim 7.66$, one of which we identify as hosting a Type-II AGN. We measure flat strong-line metallicity gradients, suggestive of ISM redistribution by outflows or past merging, but also identify tension with the direct-$T_\text{e}$ metallicity gradient in one galaxy. We measure $v_\text{rot}/σ< 1$ in both galaxies, consistent with observations of lower rotational support at early cosmic times. We identify broad kinematical components decoupled from galactic rotation with velocities of $\sim 250 - 500 \ \text{km} \ \text{s}^{-1}$ and argue these components trace outflows, for which we infer outflow rates of $\sim 8 - 14 \ M_\odot \ \text{yr}^{-1}$ with $v_\text{out}/v_\text{esc} \sim 1$. We compare our findings to results from the new large-volume AESOPICA simulations, which fully incorporate different models of black hole growth and AGN feedback. We find that our observational results of $v_\text{out}/v_\text{esc}$ are consistent with the simulated dwarf AGN population, hinting AGN-driven feedback may contribute to quenching both in our systems and in a wider population of low-mass galaxies in the early Universe. This novel study illustrates the necessity of deep IFU observations to decompose the complex kinematics and morphology of high-$z$ galaxies, trace outflows, and constrain the effect of feedback in the early Universe.

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arXiv2024

Hidden Cooling Flows in Elliptical Galaxies

The radiative cooling time of hot gas in the cool cores of many galaxy clusters and massive elliptical galaxies drops in the centre to below 100 million years. The mass cooling rates inferred from simple modelling of X-ray observations of these objects are very low, indicating that either AGN feedback is tightly balanced or that soft X-rays from cooling gas are somehow hidden from view. An intrinsic absorption model developed for application to galaxy clusters is used here to search for hidden cooling flows (HCFs) in seven nearby elliptical galaxies. Mass cooling rates of 0.5-8 solar masses per year are found in each galaxy. The absorbed cooling flow luminosity is in agreement with the observed Far Infrared (FIR) luminosity in each case, indicating absorbed emission is energetically capable of emerging in the FIR band. An observed lack of agreement between HCF rates and normal star formation rates suggests the cooled material must have an alternative fate, with low-mass star formation considered as the primary outcome.

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arXiv2024

Hidden Cooling Flows IV: More Details on Centaurus and the Efficiency of AGN Feedback in Clusters

Cooling flows are common in galaxy clusters which have cool cores. The soft X-ray emission below 1 keV from the flows is mostly absorbed by cold dusty gas within the central cooling sites. Further evidence for this process is presented here through a more detailed analysis of the nearby Centaurus cluster and some additional clusters. Predictions of JWST near and mid-infrared spectra from cooling gas are presented. [NeVI] emission at 7.65 micron should be an important diagnostic of gas cooling between 6 and 1.5 times 10^5 K. The emerging overall picture of hidden cooling flows is explored. The efficiency of AGN feedback in reducing the total cooling rate in cool cores is shown to be above 50 percent for many clusters but is rarely above 90 per cent. The reduction is mostly in outer gas. Cooling dominates in elliptical galaxies and galaxy groups which have mass flow rates below about 15M/yr and in some massive clusters where rates can exceed 1000M/yr.

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