arXiv subjects

Tianmu Gao

Publications and source records attributed to Tianmu Gao.

10 recordsLinked to original sources

arXiv2026

Deciphering The Launching of Multi-phase AGN-driven Outflows and Their (Spatially Resolved) Multi-scale Impact

Beyond deepening our understanding of the formation, growth, and evolution of supermassive black holes, it is crucial to uncover the role of feeding and feedback processes from growing black holes (i.e., active galactic nucleus; AGN) in shaping the cosmic ecosystem. Such studies include understanding the dynamics of gas flows in the interstellar (ISM), circumgalactic (CGM), intracluster (ICM), and intergalactic media (IGM). As the output of a sub-group in Habitable Worlds Observatory (HWO) AGN Working Group, this Science Case Development Document (SCDD) proposes to use future HWO observations to solve the following questions. Which mechanism is dominant in triggering inflows/outflows through feedback? How is AGN activity triggered, and is it associated with circumnuclear star formation and what is the overall effect of AGN feedback on star formation (SF)? In AGN feedback, which mode is more influential and does AGN feedback operate similarly or differently in the local universe and at high redshift? To answer these questions, this SCDD proposes to use potential HWO observations as follows. Resolve and characterize the spatial distribution of ionized and cold/warm molecular gas, especially those in inflows/outflows; Explore the spatial coupling and potential stratification of multi-phase inflows/outflows on different physical scales and their resolved and global correlations with AGN and/or SF activities; Investigate whether corresponding outflows/jets induce shocks and/or fluctuations that trigger or suppress the formation of molecular clouds and hence new stars. Specifically, HWO's capabilities will enable us to achieve the above scientific goals while existing facilities lack the required combination of high-throughput ultraviolet (UV) and near-infrared (NIR) integral field unit (IFU) capabilities with simultaneously sufficient spatial resolution and sensitivity.

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arXiv2026

KCWI Discovery of a Spatially Resolved Kpc-Scale Ionized Outflow in NGC 1275

We present new Keck Cosmic Web Imager observations of the central few kiloparsecs of NGC 1275, the brightest cluster galaxy of the Perseus Cluster. These integral field spectroscopic data reveal a warm-ionized outflow traced by H$β$ and the [O III] doublet extending out to $\sim2.5$ kpc from the nucleus. The warm-ionized outflow has an [O III]-derived $v_{50}$ of up to $\sim570$ km/s, $w_{80}$ of up to $3780$ km/s, and H$β$-derived outflowing mass of $(2.7 \pm 0.3)\times 10^6$ M$_\odot$. Our H$β$-derived warm-ionized outflowing mass rate of 2.7$\pm$0.7 M$_\odot$ yr$^{-1}$ is comparable to the estimated cold molecular disk accretion rate of 1$-$10 M$_\odot$ yr$^{-1}$, which could be a sign of self-regulation between the pc-scale cold gas feeding the active galactic nucleus (AGN) and the warm wind accelerated out to kpc scales. In the host galaxy, we detect an enhancement in the [O III] / H$β$ ratio in the direction of the receding jet, which may imply jet interaction with the host interstellar medium. The outflow component also shows a clear enhancement of [O III] / H$β$ that positively correlates with $w_{80}$ and $v_{50}$, indicative of AGN influence and/or fast shocks. Both the outflow and host galaxy [O III] / H$β$ ratio decrease with increasing distance from the center, showing that the influence of the AGN is confined to the central $\sim2$ kpc. These results are the first resolved measurements of a kpc-scale ionized wind in NGC 1275 and provide a view into how both jets and winds contribute to the feedback cycles in complex cool core cluster systems.

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arXiv2026

Clumpy Disk, Interloper, or Merger? Nature of a Distant Galaxy Pair at 5 kpc Projected Separation

We present the morphological, photometric, and spectroscopic properties of a z ~ 1 galaxy, "lil gal", serendipitously detected in JWST Mid Infrared Instrument (MIRI) images of nearby galaxy VV 340. In the MIRI F560W and F770W images, we identify what appears to be a spiral galaxy with a central bulge. However, in the F1500W image, a second peak appears ~0.7" northwest (NW) from the central bulge, calling into question the nature of this source as a clumpy disk, a high-redshift interloper, or a galaxy merger. Multi-band analyses of the three MIRI and four Hubble Space Telescope (HST) images suggest a photometric redshift of ~0.92. Spectroscopic analyses of data from the Keck Near-Infrared Echellette Spectrometer (NIRES) reveal two sets of [N II] and H-alpha emission lines corresponding to the two observed sources. A redshift of z = 0.9248 is identified for the NW companion. Fainter emission lines are identified from the underlying galaxy at z = 0.9225, suggesting a merging galaxy pair at a projected separation of ~5 kpc. From the emission line ratios from Keck NIRES and Keck Cosmic Web Imager (KCWI) spectra, we classify the system as hosting regions of active star formation, likely attributed to merger-induced starburst activity. The results demonstrate the necessity of resolved, spectroscopic follow-up analyses of galaxies found in deep JWST images to disentangle the role of galaxy mergers from clumpy disk galaxies at z ~ 1 to cosmic noon and beyond.

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arXiv2026

A precessing jet from an active galactic nucleus drives gas outflow from a disk galaxy

To reproduce observed galaxy properties, cosmological simulations require that massive galaxies experience feedback from active galactic nuclei, which regulates star formation within those galaxies. However, the energetics and timescales of these feedback processes are poorly constrained. We combine optical, infrared, sub-millimeter and radio observations of the active galaxy VV 340a, hosting a low-power jet launched from a supermassive black hole at its center. We find that the jet undergoes precession, with a period of (8.2 $\pm~$5.5) $\times~$10$^5$ years, and drives an outflow of gas at a rate of 19.4 $\pm~$7.9 solar masses per year. The jet shocks the gas, producing highly ionized plasma extending several kiloparsecs from the nucleus. The outflow ejects sufficient gas from the galaxy to influence its star formation rate.

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arXiv2025

The MAGPI Survey: forward modelled gas-phase metallicity gradients in galaxies at $z\sim 0.3$

We measure the seeing-deconvolved gas-phase metallicity gradients of 70 star-forming galaxies at $z\sim 0.3$ from the MAGPI survey and investigate their relationship with galaxy properties to understand the mechanisms that influence the distribution of metals and shape the evolution of the galaxies. We use a Bayesian modelling technique, Blobby3D, which accounts for seeing effects (beam smearing) and can model the substructures of the flux distribution. The median metallicity gradient of our sample is $\nabla \mathrm{[O/H]}=-0.013^{+0.059}_{-0.033}$ dex/kpc. Among the galaxies in our sample, 32.9% have negative metallicity gradients (2$σ$ significance), 10.0% have positive gradients and 57.1% have flat gradients. The $\nabla \mathrm{[O/H]}$-$M_*$ relation of the MAGPI galaxies generally agrees with theoretical predictions, where a combination of stellar feedback, gas transport, and accretion shapes the metallicity profile, with the dominant processes varying with galaxy mass. We find a positive correlation between $\nabla \mathrm{[O/H]}$ and gas velocity dispersion ($r=0.36$), indicating that stronger gas turbulence is associated with flatter or inverted metallicity gradients, likely due to enhanced gas mixing. Additionally, smaller galaxies tend to have flatter or positive gradients, suggesting that metal dilution by gas accretion or removal via feedback-driven winds may outweigh metal enrichment in small galaxies.

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arXiv2025

The influence of external environment at cosmic noon on the subsequent evolution of galaxy stellar mass

Connecting high-redshift galaxies to their low-redshift descendants is one of the most important and challenging tasks of galaxy evolution studies. In this work, we investigate whether incorporating high-redshift environmental factors improves the accuracy of matching high-redshift galaxies to their $z\sim0$ descendants, using data from the EAGLE and MAGNETICUM simulations. Using random forest regression, we evaluate the relative importance of a set of environmental metrics at $z\sim3$ in determining the stellar mass of descendant galaxies at $z\sim0$. We identify the spherical overdensity within 1 cMpc ($δ_{1,\mathrm{sp}}$) as the most important environmental predictor. Tracking galaxies at $z\sim3$ with similar initial stellar masses but different $δ_{1,\mathrm{sp}}$ values, we find that, across all mass bins in both simulations, high-density environments produce $z\sim0$ descendants with median stellar masses up to eight times higher than the descendants of galaxies in low-density environments. For galaxies with $M_{*}\lesssim10^{10}M_{\odot}$, the difference is attributable to more merger-induced mass growth in high-density environments, whereas for higher-mass galaxies, it results from a combination of enhanced in-situ star formation and greater external mass accretion. By assessing the importance of overdensity across multiple scales and redshifts, we find that at $z\gtrsim2$, environmental factors become as important as stellar mass in predicting the stellar mass of $z\sim0$ descendants. Compared to using stellar mass at $z\sim3$ alone, incorporating $δ_{1,\mathrm{sp}}$ reduces the scatter in the residuals between the predicted and actual stellar masses by approximately 20% in EAGLE and 35% in MAGNETICUM.

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arXiv2025

Shockingly Effective: Cluster Winds as Engines of Feedback in Starburst Galaxy VV 114

We present high-resolution Keck Cosmic Web Imager (KCWI) and MUSE IFU spectroscopy of VV 114, a local infrared-luminous merger undergoing a vigorous starburst and showing evidence of galactic-scale feedback. The high-resolution data allow for spectral deblending of the optical emission lines and reveal a broad emission line component ($σ_{\rm{broad}} \sim$~100--300 km s$^{-1}$) with line ratios and kinematics consistent with a mixture of ionization by stars and radiative shocks. The shock fraction (percent ionization due to shocks) in the high velocity gas is anticorrelated with projected surface number density of resolved star clusters, and we find radial density profiles around clusters are well fit by models of adiabatically expanding cluster winds driven by massive stellar winds and supernovae (SNe). The total kinetic power estimated from the cluster wind models matches the wind+SNe mechanical energy deposition rate estimated from the soft band X-ray luminosity, indicating that at least 70\% of the shock luminosity in the galaxy is driven by the star clusters. \emph{Hubble Space Telescope} narrow band near-infrared imaging reveals embedded shocks in the dust-buried infrared nucleus of VV 114E. Most of the shocked gas is blueshifted with respect to the quiescent medium, and there is a close spatial correspondence between the shock map and the \emph{Chandra} soft band X-ray image, implying the presence of a galactic superwind. The energy budget of the superwind is in close agreement with the total kinetic power of the cluster winds, confirming the superwind is driven by the starburst.

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arXiv2025

Nuclear Spectral Energy Distributions of Luminous Infrared Galaxies

We present nuclear (100-150 pc) spectral energy distributions (SEDs) for a sample of 23 nearby luminous infrared galaxies hosting a total of 28 nuclei. We gather aperture photometry from high-resolution X-ray to submillimeter data for each nuclear region localized by ALMA observations of the dust continuum. We model the broadband SEDs using X-CIGALE. Binning the merging systems by interaction class, we find that the AGN fraction (fraction of AGN infrared luminosity to total infrared luminosity) appears enhanced in the late- and post-merger stages compared to early-stage mergers. Examining the relationship between X-ray emission and infrared emission of the nuclear regions, we find that the infrared emission in the nucleus is dominated by dust and AGN, with minimal contribution from stars. We also find that nuclear regions have higher X-ray hardness ratios than the host galaxies globally among both the AGN and non-AGN population. We highlight the similarities and differences in the SEDs of dual nuclei in five closely separated late-stage merging systems: Arp 220 ($d_\mathrm{nuc} \sim$ 0.5 kpc), NGC 6240 ($d_\mathrm{nuc} \sim$ 1 kpc), IRAS 07251-0248 ($d_\mathrm{nuc} \sim$ 2 kpc), IRAS F12112+0305 ($d_\mathrm{nuc} \sim$ 4 kpc), and IRAS F14348+1447 ($d_\mathrm{nuc} \sim$ 6 kpc). The SEDs for these resolved pairs are distinct, suggesting that the AGN state is much more susceptible to the stellar and dust content within the immediate circumnuclear ($<$150 pc) environment than to the host's global infrared luminosity or merger stage.

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arXiv2024

The MAGPI Survey: radial trends in star formation across different cosmological simulations in comparison with observations at $z \sim$ 0.3

We investigate the internal and external mechanisms that regulate and quench star formation (SF) in galaxies at $z \sim 0.3$ using MAGPI observations and the EAGLE, Magneticum, and IllustrisTNG cosmological simulations. Using SimSpin to generate mock observations of simulated galaxies, we match detection/resolution limits in star formation rates and stellar mass, along with MAGPI observational details including the average point spread function and pixel scale. While we find a good agreement in the slope of the global star-forming main sequence (SFMS) between MAGPI observations and all three simulations, the slope of the resolved SFMS does not agree within 1 $-$ 2$σ$. Furthermore, in radial SF trends, good agreement between observations and simulations exists only for galaxies far below the SFMS, where we capture evidence for inside-out quenching. The simulations overall agree with each other between $\sim1.5-4 \ R_{\rm e}$ but show varying central suppression within $R \sim 1.5 \ R_{\rm e}$ for galaxies on and below the SFMS, attributable to different AGN feedback prescriptions. All three simulations show similar dependencies of SF radial trends with environment. Central galaxies are subject to both internal and external mechanisms, showing increased SF suppression in the centre with increasing halo mass, indicating AGN feedback. Satellite galaxies display increasing suppression in the outskirts as halo mass increases, indicative of environmental processes. These results demonstrate the power of spatially resolved studies of galaxies; while global properties align, radial profiles reveal discrepancies between observations and simulations and their underlying physics.

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arXiv2022

GOALS-JWST: Resolving the Circumnuclear Gas Dynamics in NGC 7469 in the Mid-Infrared

The nearby, luminous infrared galaxy (LIRG) NGC 7469 hosts a Seyfert nucleus with a circumnuclear star-forming ring and is thus the ideal local laboratory for investigating the starburst--AGN connection in detail. We present integral-field observations of the central 1.3 kpc region in NGC 7469 obtained with the JWST Mid-InfraRed Instrument. Molecular and ionized gas distributions and kinematics at a resolution of {\sim}100 pc over the 4.9 - 7.6μm region are examined to study gas dynamics influenced by the central AGN. The low-ionization [Fe II] λ5.34μm and [Ar II] λ6.99μm lines are bright on the nucleus and in the starburst ring, as opposed to H2 S(5) λ6.91μm which is strongly peaked at the center and surrounding ISM. The high-ionization [Mg V] line is resolved and shows a broad, blueshifted component associated with the outflow. It has a nearly face-on geometry that is strongly peaked on the nucleus, where it reaches a maximum velocity of -650 km/s, and extends about 400 pc to the East. Regions of enhanced velocity dispersion in H2 and [Fe II] {\sim}180 pc from the AGN that also show high L(H2)/L(PAH) and L([Fe II])/L(Pfα) ratios to the W and N of the nucleus pinpoint regions where the ionized outflow is depositing energy, via shocks, into the dense interstellar medium between the nucleus and the starburst ring. These resolved mid-infrared observations of the nuclear gas dynamics demonstrate the power of JWST and its high-sensitivity integral-field spectroscopic capability to resolve feedback processes around supermassive black holes in the dusty cores of nearby LIRGs.

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