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Below is a brief introduction to the research projects (published or submitted) I have led. For a complete list of all the published projects I've been involved in, please click here.
Below is a brief introduction to the research projects (published or submitted) I have led. For a complete list of all the published projects I've been involved in, please click here.
Linking nuclear winds to galactic-scale outflows remains a major observational challenge in understanding the multiscale physics of AGN feedback. To bridge this gap, we present a multi-wavelength kinematic analysis of the z ~ 1 quasar PKS 0352-0711, combining VLT/KMOS integral-field spectroscopy, SDSS and HST/COS observations.
By integrating UV mini-broad-absorption-line (mini BAL) data with optical [O III] emission properties, we trace an outflow structure across three orders of magnitude in spatial scale (from 10 pc to 10 kpc). We identify an inner, constant-velocity wind expanding at ~ -3800 km/s in both absorption (~ 9 pc, S2) and emission (≳ 40 pc, C). At intermediate scales (~ 500 pc, S1), the outflow decelerates to ~ -2100 km/s consistent with mass-loading from the ISM. Finally, we capture the gas breaking out of the inner galaxy as a wide-angle blueshifted outflow (~ -1000 km/s, B) propogating beyond 8 kpc.
Despite the three orders of magnitude variation in spatial scale, and a factor-of-four deceleration, the momentum fluxes remain consistent within uncertainties across all scales. These kinematics strongly support a unified evolutionary scenario where the distinct spatial components reflect the integrated history of a sustained AGN feedback cycle from nuclear to galactic scales.
Spatially resolved kinematics of the extended [O III] emission around PKS 0352. The blue and green components trace a large-scale rotating disk (~ 13 kpc) and a wide-angle blue-shifted outflow (~ 10 kpc), respectively. The narrow profile in R6 and R7 traces a potential tidal feature.
Evolution of the outflowing gas as traced by the multiscale components in PKS 0352.
We propose a new method to determine the dark matter density profile in the vicinity of distant supermassive black holes (SMBH) using reverberation mapping (RM) measurements of active galactic nuclei (AGN). The mapping of multiple emission lines allows the measurement of the enclosed mass within different radii from the central SMBH, which can be used to infer or constrain the dark matter density profile on sub-parsec scales. We apply a toy model based on this method to a sample of fourteen AGN to test its feasibility based on current measurements.
We find that for five objects, the observed enclosed mass does grow with radii, hinting towards the presence of a dark matter component at the 1-2 𝜎 level. For these sources, we find global evidence for a universal dark matter profile with a preferred radial steepness of index 𝛾∼1.6, consistent with the scenario expected for a dark matter spike mildly relaxed by stellar heating processes. The enclosed dark matter mass, however, is found to be significantly larger than expected. We show that the current RM based mass measurements suffer from large systematic uncertainties, that limit the effectiveness of our method. Our work emphasizes the importance of applying the recent developments in mass determination techniques to target multiple emission lines with future RM and interferometry campaigns. This provides the most direct way of constraining the dark matter density in the sub-parsec regions around extragalactic SMBHs, which is crucial to our understanding of the dynamics and nature of dark matter.
RM based measurements of the enclosed mass within different radii for 3C 390 (gray points). The best-fit DM model and constant mass profile are shown in purple and dashed-pink, respectively.
Confidence contours on the dark matter profile parameters—density and radial slope. In horizontal markings the expected profile indexes for different theoretical expectations are shown.
Quasar outflows can play a crucial role in the evolution of their host galaxies through various feedback processes. This effect is expected to be particularly important when the universe was only 2-3 billion years old, during the period known as cosmic noon. By utilizing existing observations from the Dark Energy Spectroscopy Instrument (DESI), we conduct a survey of high-ionization quasar outflows at cosmic noon, with the aim of doubling the current sample of such outflows with distance and energetics determination.
The detected outflows show complex kinematic structures with a wide range in blueshifted velocities (100 - 4600 km/s). We locate five outflows at distances between 240 - 5500 pc away from the central source, while only upper limits could be obtained for two outflows, placing them closer than 100 and 900 pc. From the combined sample of 15 high-ionization S IV outflows at cosmic noon, we find a high fraction (up to 46%) of them to be powerful enough to contribute significantly to multi-stage AGN feedback processes. Their energetics are also found to be consistent with spatially resolved emission outflows in a luminosity and redshift matched sample of quasars.
Mass outflow rates as a function of the AGN bolometric luminosity (adapted from Fig. 9 of Carniani et. al. 2015, with permission). The teal stars represent our combined S IV sample seen in absorption. The open and filled circles represent the mass outflow rates for ionized outflows determined from [O III] and Hβ emission lines, respectively. The squares denote molecular outflows.
Observational signatures of quasar outflows are studied using two main techniques: (a) Line of sight (Absorption) Spectroscopy and (b) Integral Field (Emission) Spectroscopy (IFS). However, they have never been used together to study the same outflow phase in a quasar, and thus we do not know if these techniques even trace the same gas.
This work (along with its companion paper: Zhao. et. al. 2025) presents the results of applying both these analysis methods to the same quasar outflow. For the first time ever, we verify the indirect distance determination from absorption spectroscopy (VLT/XShooter) by a direct spatially resolved IFS observation (VLT/SINFONI). In addition, the velocities (and energetics) from the IFS and absorption data are also found to be consistent, demonstrating that these are two manifestations of the same outflow.
This finding provides the long missing link needed to combine the strengths of the two methods and develop a deeper understanding of quasar outflows and their impact on the host galaxies.
Indirect distance determination based on the population ratio of the Si II/II* troughs shown in the inset.
Median velocity map of the blueshifted component of the ionized outflow seen in emission.
In this work, we analyse the high-resolution VLT/UVES spectrum of SDSS J0932+0840 and identify several narrow and broad outflow components in absorption, with multiple ionization species including Fe II (singly ionized Iron), which puts it among a rare class of outflows known as FeLoBALs.
We present detailed photoionization modeling of one of the outflow components with a velocity of ~ -700 km/s. We study the internal physical structure of the outflow and constrain its total hydrogen column density and ionization parameter. We model the electron and hydrogen number densities separately and demonstrate a dramatic departure from the common assumption of fully ionized plasma.
Finally, we compare epochs separated by 2.4 years in the quasar rest-frame and report interesting patterns of variability in the outflowing troughs that are explained in terms of a possible change in the ionization state of the gas.
Left: Photoionization modeling of the population ratios for different excited states of Fe II.
Right: Variability in the absorption troughs observed roughly 8 years apart by SDSS.
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