arXiv subjects

Fakhri S. Zahedy

Publications and source records attributed to Fakhri S. Zahedy.

At least 19 recordsLinked to original sources

arXiv2026

A Comprehensive Study of Morphology and Kinematics in Extended Nebulae Around UV Luminous Quasars at $z\approx1$

Gas flows between galaxies and the circumgalactic medium (CGM) play a central role in galaxy evolution and can become observable as giant nebulae when illuminated by the quasars. We present an ensemble study of nebulae around 30 UV-luminous quasars at z=0.4-1.4 from the CUBS and MUSEQuBES surveys, 27 of which are detected in extended [O II] and/or [O III] emission. Based on a joint analysis of nebular morphology and surrounding galaxy environments, we introduce three morpho-kinematic classifications. We identify eleven irregular, large-scale (>50 kpc) systems, many of which are likely interaction-related; twelve compact host-galaxy-scale nebula, likely tracing CGM/ISM gas; and four systems with complex morphologies of uncertain origin. We introduce a quantitative measure of the spatial and kinematic association between nebulae and quasar-host group galaxies, finding a statistically significant association for ten nebulae, most of which are irregular, large-scale nebulae, consistent with qualitative analysis. Radio jets are detected in six systems, with no strong correlation found between radio activity and nebular emission. The [O II] nebulae are more asymmetric than their Ly$α$ counterparts at $z>2$, but bear more similarity to H I gas observed in 21 cm around local elliptical galaxies. Blueshifted-redshifted patterns, likely tracing gas rotation, are observed in roughly 30% of the systems, though disturbed kinematics suggest that feedback may also be important. These results show that giant quasar nebulae are not a uniform class of objects, but instead arise through multiple pathways shaped by host-galaxy gas, galaxy interactions, group environments, and quasar activity, with the most striking cases associated with galaxy interactions.

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arXiv2026

MUSEQuBES: Physical conditions, origins, and multi-element abundances of the circumgalactic medium of an isolated, star-forming dwarf galaxy at z=0.57

In dwarf galaxy models, outflows expel metal-enriched interstellar medium (ISM) into the circumgalactic medium (CGM) to reproduce their observed low metallicities, but measurements of dwarf CGM properties are scarce. We present a study of the CGM of an isolated dwarf at $z=0.5723$ with a stellar mass of $\approx5\times10^7\rm\,M_{\odot}$ and star-formation rate ($\approx0.05\,\rm M_\odot\,yr^{-1}$) and ISM metallicity ($\rm [O/H]\approx-0.9$) consistent with the star-forming main sequence and mass-metallicity relation. A background quasar sightline with archival UV spectra probes the dwarf's CGM at a projected distance of 28 kpc, corresponding to approximately half of the estimated virial radius. The dwarf's CGM is detected in \ion{H}{1}, intermediate metal ions of \ion{C}{3}, \ion{O}{3}, \ion{O}{4}, and \textcolor{black}{\ion{S}{5}}, and kinematically broader, highly-ionized \ion{O}{6}, but is undetected in \ion{N}{4} and \ion{Ne}{8}. Photoionization modeling of the intermediate ions indicates a modest volume-filling factor ($\sim 6\%$ along the sightline or $\sim 2\%$ globally), and a mass of $\sim2\times10^8 {\rm\,M_\odot}$, $\sim4\times$ higher than the dwarf's stellar mass, but $\sim10\times$ less than the highly ionized CGM. The \ion{O}{6} kinematics are comparable to the dwarf's estimated virial velocity, suggesting it is likely associated with cool, photoionized, and volume-filling CGM, with bulk motion or turbulence dominating over thermal pressure. The metallicity inferred for the intermediate ions is $\rm [O/H]=-0.6$, but with low relative abundances of $\rm [C/O]=-0.6$ and \textcolor{black}{$\rm [N/O]<-1.0$}. The [N/O] is below levels expected of the dwarf's ISM, but consistent with core-collapse supernova ejecta, suggesting that supernova-enriched gas escaped the dwarf without mixing significantly with ISM enriched in nitrogen from evolved, low-mass stars.

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arXiv2025

The Morphology and Kinematics of a Giant, Symmetric Nebula Around a Radio-Loud Quasar 3C$\,$57: Extended Rotating Gas or Biconical Outflows?

Gas flows between galaxies and the CGM play a crucial role in galaxy evolution. When ionized by a quasar, these gas flows can be directly traced as giant nebulae. We present a study of a giant nebula around a radio-loud quasar, 3C$\,$57 at $z\approx0.672$. Observations from MUSE reveal that the nebula is elongated with a major axis of $70 \, \rm kpc$ and a minor axis of $40 \, \rm kpc$. The nebula displays an approximately symmetric blueshifted-redshifted pattern along the major axis and multi-component emission features in its $\rm[O\,II]$ and $\rm [O\,III]$ profiles. The morphology and kinematics can be explained as rotating gas or biconical outflow, both of which qualitatively reproduce the observed position-velocity diagram. The 3C$\,$57 nebula is significantly more kinematically disturbed, with $\rm W_{80}$ (the line width encompassing 80$\%$ of the flux) of approximately $300{-}400\,\rm km\,s^{-1}$, compared to $\rm H\,I$ gas in local early-type galaxies, which typically shows $\rm W_{80} \approx 50\,\rm km\,s^{-1}$. This velocity dispersion is comparable to the gas in cool-core clusters despite originating in a group 100 times less massive. For biconical outflow models, the inferred $10{-}20^{\circ}$ inclination angle is in tension with the unobscured nature of the quasar, as the dusty torus is expected to be perpendicular to the outflow. Neither a quiescent rotating gas origin nor a biconical outflow fully reproduces the observed kinematics and morphology of the 3C$\,$57 nebula, suggesting a more intricate origin likely involving both rotation and AGN feedback.

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arXiv2024

The Circumgalactic Medium

Galaxies are part of a vast cosmic ecosystem, embedded in an extensive gaseous reservoir that regulates their growth by providing the necessary fuel for star formation while preserving a fossil record of past interactions, outflows, and feedback processes. The circumgalactic medium (CGM) contains multiphase gas spanning a broad dynamic range in spatial scale, density, and temperature, with its thermodynamic and chemical properties deeply linked to the star formation histories of galaxies. As a rich laboratory for studying gas physics, the CGM offers unique insights into the processes governing gas cooling, heating, and material transfer between galaxies and their surroundings. Chemical tagging, based on the relative abundances of multiple elements, serves as a powerful timing tool to trace the origin of the gas and connect the stars in the interstellar medium (ISM) to the diffuse CGM. Developing a complete understanding of the CGM and its cosmic evolution requires multi-wavelength observational tools, ranging from X-ray, UV/optical, and sub-mm to radio, to probe this diffuse gas in both absorption and emission.

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arXiv2024

The Cosmic Ultraviolet Baryon Survey (CUBS) IX: The enriched circumgalactic and intergalactic medium around star-forming field dwarf galaxies traced by O VI absorption

The shallow potential wells of star-forming dwarf galaxies make their surrounding circumgalactic and intergalactic medium (CGM/IGM) sensitive laboratories for studying the inflows and outflows thought to regulate galaxy evolution. We present new absorption-line measurements in quasar sightlines probing within projected distances of $<300$ kpc from 91 star-forming field dwarf galaxies with a median stellar mass of $\log{M_\star/\rm{M_\odot}} \approx 8.3$ at $0.077 < z < 0.73$ from the Cosmic Ultraviolet Baryon Survey (CUBS). In this redshift range, the CUBS quasar spectra cover a suite of transitions including H I, low and intermediate metal ions (e.g., C II, Si II, C III, and Si III), and highly ionized O VI. This CUBS-Dwarfs survey enables constraints with samples 9$\times$ larger than past dwarf CGM/IGM studies with similar ionic coverage. We find that low and intermediate ionization metal absorption is rare around dwarf galaxies, consistent with previous surveys of local dwarfs. In contrast, highly ionized O VI is commonly observed in sightlines that pass within the virial radius of a dwarf, and O VI detection rates are non-negligible at projected distances of 1$-$2$\times$ the virial radius. Based on these measurements, we estimate that the O VI-bearing phase of the CGM/IGM accounts for a dominant share of the metal budget of dwarf galaxies. The absorption kinematics suggest that a relatively modest fraction of the O VI-bearing gas is formally unbound. Together, these results imply that low-mass systems at $z\lesssim 1$ effectively retain a substantial fraction of their metals within the nearby CGM and IGM.

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arXiv2024

On the Nature of the C IV-bearing Circumgalactic Medium at z~1

This paper presents a detailed study of the physical properties of seven C IV absorbers identified at z_abs = 0.68-1.28 along the line of sight toward QSO PG 1522+101 (z_QSO = 1.330). The study leverages high-quality QSO spectra from HST COS and STIS, and Keck HIRES to resolve component structures and to constrain the gas density and elemental abundances of individual components. Under the assumption of photoionization equilibrium (PIE), five of the 12 C IV components require a mixture of high- and low-density phases to fully explain the observed relative abundances between low-, intermediate-, and high-ionization species. In addition, galaxy surveys carried out using VLT MUSE and Magellan LDSS3C are utilized to characterize the galaxy environments. The results of this analysis are summarized as follows: (1) no luminous galaxies (> 0.1 L*) are found within 100 kpc in projected distance from the C IV absorbers; (2) the C IV selection preferentially targets high-metallicity (near solar) and chemically-evolved gas (~ solar [C/O] elemental abundances) in galaxy halos; (3) the observed narrow line widths of individual C IV components, places a stringent limit on the gas temperature (< 5e4 K) and supports a photoionization origin; (4) additional local ionizing sources beyond the UV ionizing background may be necessary for at least one absorber based on the observed deficit of He I relative to H I; and (5) a PIE assumption may not apply when the gas metallicity exceeds the solar value and the component line width implies a warmer temperature than expected from PIE models.

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arXiv2024

Discovery of optically emitting circumgalactic nebulae around the majority of UV-luminous quasars at intermediate redshift

We report the discovery of large ionized, [O II] emitting circumgalactic nebulae around the majority of thirty UV luminous quasars at $z=0.4-1.4$ observed with deep, wide-field integral field spectroscopy (IFS) with the Multi-Unit Spectroscopy Explorer (MUSE) by the Cosmic Ultraviolet Baryon Survey (CUBS) and MUSE Quasar Blind Emitters Survey (MUSEQuBES). Among the 30 quasars, seven (23%) exhibit [O II] emitting nebulae with major axis sizes greater than 100 kpc, twenty greater than 50 kpc (67%), and 27 (90%) greater than 20 kpc. Such large, optically emitting nebulae indicate that cool, dense, and metal-enriched circumgalactic gas is common in the halos of luminous quasars at intermediate redshift. Several of the largest nebulae exhibit morphologies that suggest interaction-related origins. We detect no correlation between the sizes and cosmological dimming corrected surface brightnesses of the nebulae and quasar redshift, luminosity, black hole mass, or radio-loudness, but find a tentative correlation between the nebulae and rest-frame [O II] equivalent width in the quasar spectra. This potential trend suggests a relationship between ISM content and gas reservoirs on CGM scales. The [O II]-emitting nebulae around the $z\approx1$ quasars are smaller and less common than Ly$α$ nebulae around $z\approx3$ quasars. These smaller sizes can be explained if the outer regions of the Ly$α$ halos arise from scattering in more neutral gas, by evolution in the cool CGM content of quasar host halos, by lower-than-expected metallicities on $\gtrsim50$ kpc scales around $z\approx1$ quasars, or by changes in quasar episodic lifetimes between $z=3$ and $1$.

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arXiv2024

The Cosmic Ultraviolet Baryon Survey (CUBS) VIII: Group Environment of the Most Luminous Quasars at $z\approx1$

We investigate the group-scale environment of 15 luminous quasars (luminosity $L_{\rm 3000}>10^{46}$ erg s$^{-1}$) from the Cosmic Ultraviolet Baryon Survey (CUBS) at redshift $z\approx1$. Using the Multi Unit Spectroscopic Explorer (MUSE) integral field spectrograph on the Very Large Telescope (VLT), we conduct a deep galaxy redshift survey in the CUBS quasar fields to identify group members and measure the physical properties of individual galaxies and galaxy groups. We find that the CUBS quasars reside in diverse environments. The majority (11 out of 15) of the CUBS quasars reside in overdense environments with typical halo masses exceeding $10^{13}{\rm M}_{\odot}$, while the remaining quasars reside in moderate-size galaxy groups. No correlation is observed between overdensity and redshift, black hole (BH) mass, or luminosity. Radio-loud quasars (5 out of 15 CUBS quasars) are more likely to be in overdense environments than their radio-quiet counterparts in the sample, consistent with the mean trends from previous statistical observations and clustering analyses. Nonetheless, we also observe radio-loud quasars in moderate groups and radio-quiet quasars in overdense environments, indicating a large scatter in the connection between radio properties and environment. We find that the most UV luminous quasars might be outliers in the stellar mass-to-halo mass relations or may represent departures from the standard single-epoch BH relations.

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arXiv2024

The Cosmic Ultraviolet Baryon Survey (CUBS) VII: on the warm-hot circumgalactic medium probed by O VI and Ne VIII at 0.4 $\lesssim$ z $\lesssim$ 0.7

This paper presents a newly established sample of 103 unique galaxies or galaxy groups at $0.4\lesssim z\lesssim 0.7$ from the Cosmic Ultraviolet Baryon Survey (CUBS) for studying the warm-hot circumgalactic medium (CGM) probed by both O VI and Ne VIII absorption. The galaxies and associated neighbors are identified at $< 1$ physical Mpc from the sightlines toward 15 CUBS QSOs at $z_{\rm QSO}\gtrsim 0.8$. A total of 30 galaxies or galaxy groups exhibit associated O VI $λλ$ 1031, 1037 doublet absorption within a line-of-sight velocity interval of $\pm250$ km/s, while the rest show no trace of O VI to a detection limit of $\log N_{\rm OVI}/{\rm cm^{-2}}\approx13.7$. Meanwhile, only five galaxies or galaxy groups exhibit the Ne VIII $λλ$ 770,780 doublet absorption, down to a limiting column density of $\log N_{\rm NeVIII}/{\rm cm^{-2}}\approx14.0$. These O VI- and Ne VIII-bearing halos reside in different galaxy environments with stellar masses ranging from $\log M_{\rm star}/M_\odot \approx 8$ to $\approx11.5$. The warm-hot CGM around galaxies of different stellar masses and star formation rates exhibits different spatial profiles and kinematics. In particular, star-forming galaxies with $\log M_{\rm star}/M_\odot\approx9-11$ show a significant concentration of metal-enriched warm-hot CGM within the virial radius, while massive quiescent galaxies exhibit flatter radial profiles of both column densities and covering fractions. In addition, the velocity dispersion of O VI absorption is broad with $σ_v > 40$ km/s for galaxies of $\log M_{\rm star}/M_\odot>9$ within the virial radius, suggesting a more dynamic warm-hot halo around these galaxies. Finally, the warm-hot CGM probed by O VI and Ne VIII is suggested to be the dominant phase in sub-$L^*$ galaxies with $\log M_{\rm star}/M_\odot\approx9-10$ based on their high ionization fractions in the CGM.

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arXiv2024

An ensemble study of turbulence in extended QSO nebulae at $z\approx0.5$--1

Turbulent motions in the circumgalactic medium (CGM) play a critical role in regulating the evolution of galaxies, yet their detailed characterization remains elusive. Using two-dimensional velocity maps constructed from spatially-extended [OII] and [OIII] emission, Chen et al. (2023b) measured the velocity structure functions (VSFs) of four quasar nebulae at $z\approx\!0.5$--1.1. One of these exhibits a spectacular Kolmogorov relation. Here we carry out an ensemble study using an expanded sample incorporating four new nebulae from three additional QSO fields. The VSFs measured for all eight nebulae are best explained by subsonic turbulence revealed by the line-emitting gas, which in turn strongly suggests that the cool gas ($T\!\sim\!10^4$ K) is dynamically coupled to the hot ambient medium. Previous work demonstrates that the largest nebulae in our sample reside in group environments with clear signs of tidal interactions, suggesting that environmental effects are vital in seeding and enhancing turbulence within the gaseous halos, ultimately promoting the formation of the extended nebulae. No discernible differences are observed in the VSF properties between radio-loud and radio-quiet QSO fields. We estimate the turbulent heating rate per unit volume, $Q_{\rm turb}$, in the QSO nebulae to be $\sim 10^{-26}$--$10^{-22}$ erg cm$^{-3}$ s$^{-1}$ for the cool phase and $\sim 10^{-28}$--$10^{-25}$ erg cm$^{-3}$ s$^{-1}$ for the hot phase. This range aligns with measurements in the intracluster medium and star-forming molecular clouds but is $\sim10^3$ times higher than the $Q_{\rm turb}$ observed inside cool gas clumps on scales $\lesssim1$ kpc using absorption-line techniques. We discuss the prospect of bridging the gap between emission and absorption studies by pushing the emission-based VSF measurements to below $\approx\!10$ kpc.

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arXiv2023

The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

This paper reports the first measurement of the relationship between turbulent velocity and cloud size in the diffuse circumgalactic medium (CGM) in typical galaxy halos at redshift z~0.4-1. Through spectrally-resolved absorption profiles of a suite of ionic transitions paired with careful ionization analyses of individual components, cool clumps of size as small as l_cl~1 pc and density lower than nH = 0.001 cm^-3 are identified in galaxy halos. In addition, comparing the line widths between different elements for kinematically matched components provides robust empirical constraints on the thermal temperature T and the non-thermal motions bNT, independent of the ionization models. On average, bNT is found to increase with l_cl following bNT \propto l_cl^0.3 over three decades in spatial scale from l_cl~1 pc to l_cl~1 kpc. Attributing the observed bNT to turbulent motions internal to the clumps, the best-fit bNT-l_cl relation shows that the turbulence is consistent with Kolmogorov at <1 kpc with a roughly constant energy transfer rate per unit mass of epsilon~0.003 cm^2 s^-3 and a dissipation time scale of <~ 100 Myr. No significant difference is found between massive quiescent and star-forming halos in the sample on scales less than 1 kpc. While the inferred epsilon is comparable to what is found in CIV absorbers at high redshift, it is considerably smaller than observed in star-forming gas or in extended line-emitting nebulae around distant quasars. A brief discussion of possible sources to drive the observed turbulence in the cool CGM is presented.

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arXiv2023

The Cosmic Ultraviolet Baryon Survey (CUBS) VI: Connecting Physical Properties of the Cool Circumgalactic Medium to Galaxies at $z\approx 1$

This paper presents a new sample of 19 unique galaxies and galaxy groups at $z\approx1$ from the CUBS program, which is designated as the CUBSz1 sample. In this CUBSz1 sample, nine galaxies or galaxy groups show absorption features, while ten systems do not have detectable absorption with 2-$σ$ upper limits of log$N$(HeI)/cm$^{-2}\lesssim 13.5$ and log$N$(OV)/cm$^{-2}\lesssim 13.3$. Environmental properties of the galaxies, including galaxy overdensities, the total stellar mass and gravitational potential summed over all nearby neighbors, and the presence of local ionizing sources, are found to have a significant impact on the observed CGM absorption properties. Specifically, massive galaxies and galaxies in overdense regions exhibit a higher rate of incidence of absorption. At the same time, the observed CGM absorption properties in galaxy groups appear to be driven by the galaxy closest to the QSO sightline, rather than by the most massive galaxy or by mass-weighted properties. We introduce a total projected gravitational potential $ψ$, defined as $-ψ/G =\sum M_{\rm halo}/d_{\rm proj}$ summed over all group members, to characterize the overall galaxy environment. This projected gravitational potential correlates linearly with the maximum density detected in each sightline, consistent with higher-pressure gas being confined in deeper gravitational potential wells. In addition, we find that the radial profile of cool gas density exhibits a general decline from the inner regions to the outskirts, being in pressure balance with the hot halo. Finally, we note that the ionizing flux from nearby galaxies can generate an elevated $N$(HI)/$N$(HeI) ratio, which in turn provides a unique diagnostic of possible local sources contributing to the ionizing radiation field.

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arXiv2022

Empirical constraints on the turbulence in QSO host nebulae from velocity structure function measurements

We present the first empirical constraints on the turbulent velocity field of the diffuse circumgalactic medium around four luminous QSOs at $z\!\approx\!0.5$--1.1. Spatially extended nebulae of $\approx\!50$--100 physical kpc in diameter centered on the QSOs are revealed in [OII]$λλ\,3727,3729$ and/or [OIII]$λ\,5008$ emission lines in integral field spectroscopic observations obtained using MUSE on the VLT. We measure the second- and third-order velocity structure functions (VSFs) over a range of scales, from $\lesssim\!5$ kpc to $\approx\!20$--50 kpc, to quantify the turbulent energy transfer between different scales in these nebulae. While no constraints on the energy injection and dissipation scales can be obtained from the current data, we show that robust constraints on the power-law slope of the VSFs can be determined after accounting for the effects of atmospheric seeing, spatial smoothing, and large-scale bulk flows. Out of the four QSO nebulae studied, one exhibits VSFs in spectacular agreement with the Kolmogorov law, expected for isotropic, homogeneous, and incompressible turbulent flows. The other three fields exhibit a shallower decline in the VSFs from large to small scales. However, with a limited dynamic range in the spatial scales in seeing-limited data, no constraints can be obtained for the VSF slopes of these three nebulae. For the QSO nebula consistent with the Kolmogorov law, we determine a turbulence energy cascade rate of $\approx\!0.2$ cm$^{2}$ s$^{-3}$. We discuss the implication of the observed VSFs in the context of QSO feeding and feedback in the circumgalactic medium.

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arXiv2022

The Cosmic Ultraviolet Baryon Survey (CUBS) V: On the Thermodynamic Properties of the Cool Circumgalactic Medium at $z < 1$

This paper presents a systematic study of the photoionization and thermodynamic properties of the cool circumgalactic medium (CGM) as traced by rest-frame ultraviolet absorption lines around 26 galaxies at redshift $z\lesssim1$. The study utilizes both high-quality far-ultraviolet and optical spectra of background QSOs and deep galaxy redshift surveys to characterize the gas density, temperature, and pressure of individual absorbing components and to resolve their internal non-thermal motions. The derived gas density spans more than three decades, from $\log (n_{\rm H}/{\rm cm^{-3}}) \approx -4$ to $-1$, while the temperature of the gas is confined in a narrow range of $\log (T/{\rm K})\approx 4.3\pm 0.3$. In addition, a weak anti-correlation between gas density and temperature is observed, consistent with the expectation of the gas being in photoionization equilibrium. Furthermore, decomposing the observed line widths into thermal and non-thermal contributions reveals that more than 30% of the components at $z\lesssim 1$ exhibit line widths driven by non-thermal motions, in comparison to $<20$% found at $z\approx 2$-3. Attributing the observed non-thermal line widths to intra-clump turbulence, we find that massive quenched galaxies on average exhibit higher non-thermal broadening/turbulent energy in their CGM compared to star-forming galaxies at $z\lesssim 1$. Finally, strong absorption features from multiple ions covering a wide range of ionization energy (e.g., from Mg II to O IV) can be present simultaneously in a single absorption system with kinematically aligned component structure, but the inferred pressure in different phases may differ by a factor of $\approx 10$.

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arXiv2022

EMPRESS. V. Metallicity Diagnostics of Galaxies over 12+log(O/H)=~6.9-8.9 Established by a Local Galaxy Census: Preparing for JWST Spectroscopy

We present optical-line gas metallicity diagnostics established by the combination of local SDSS galaxies and the largest compilation of extremely metal-poor galaxies (EMPGs) including new EMPGs identified by the Subaru EMPRESS survey. A total of 103 EMPGs are included that cover a large parameter space of magnitude (Mi=-19 to -7) and H-beta equivalent width (10-600 Ang), i.e., wide ranges of stellar mass and star-formation rate. Using reliable metallicity measurements of the direct method for these galaxies, we derive the relationships between strong optical-line ratios and gas-phase metallicity over the range of 12+log(O/H)=~6.9-8.9 corresponding to 0.02-2 solar metallicity Zsun. We confirm that R23-index, ([OIII]+[OII])/H-beta, is the most accurate metallicity indicator with the metallicity uncertainty of 0.14 dex over the range among various popular metallicity indicators. The other metallicity indicators show large scatters in the metal-poor range (<0.1 Zsun). It is explained by our CLOUDY photoionization modeling that, unlike R23-index, the other metallicity indicators do not use a sum of singly and doubly ionized lines and cannot trace both low and high ionization gas. We find that the accuracy of the metallicity indicators is significantly improved, if one uses H-beta equivalent width measurements that tightly correlate with ionization states. In this work, we also present the relation of physical properties with UV-continuum slope beta and ionization production rate xi_ion derived with GALEX data for the EMPGs, and provide local anchors of galaxy properties together with the optical-line metallicity indicators that are available in the form of ASCII table and useful for forthcoming JWST spectroscopic studies.

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arXiv2022

EMPRESS. VI. Outflows Investigated in Low-Mass Galaxies with $M_*=10^4-10^7~M_\odot$: Weak Feedback in Low-Mass Galaxies?

We study emission line profiles of 21 nearby low-mass ($M_*=10^4-10^7~M_\odot$) galaxies in deep medium-high resolution spectra taken with Magellan/MagE. These low-mass galaxies are actively star-forming systems with high specific star-formation rates of $\mathrm{sSFR}\sim100-1000~\mathrm{Gyr}^{-1}$ that are well above the star-formation main sequence and its extrapolation. We identify broad-line components of H$α$ and [OIII]$λ5007$ emission in 14 out of the 21 galaxies that cannot be explained by the MagE instrumental profile or the natural broadening of line emission. We conduct double Gaussian profile fitting to the emission of the 14 galaxies, and find that the broad-line components have line widths significantly larger than those of the narrow-line components, indicative of galactic outflows. The board-line components have moderately large line widths of $\sim 100$ km s$^{-1}$. We estimate the maximum outflow velocities $v_\mathrm{max}$ and obtain values of $\simeq 60-200$ km s$^{-1}$, which are found to be comparable to or slightly larger than the escape velocities. Positive correlations of $v_\mathrm{max}$ with star-formation rates, stellar masses, and circular velocities, extend down into this low-mass regime. Broad- to narrow-line flux ratios BNRs are generally found to be smaller than those of massive galaxies. The small $v_\mathrm{max}$ and BNRs suggest that the mass loading factors $η$ can be as small as 0.1 - 1 or below, in contrast to the large $η$ of energy-driven outflows predicted by numerical simulations.

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arXiv2022

Discovery of a damped Ly$α$ absorber originating in a spectacular interacting dwarf galaxy pair at $z = 0.026$

We present the discovery of neutral gas detected in both damped Ly$α$ absorption (DLA) and HI 21-cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an HI bridge connecting two interacting dwarf galaxies (log$(M_{\text{star}}/\text{M}_{\odot}) = 8.5 \pm 0.2$) that host a $z = 0.026$ DLA with log[$N$(HI)/cm$^{-2}$]$ = 20.60 \pm 0.05$ toward the QSO J2339-5523 ($z_{\text{QSO}} = 1.35$). At impact parameters of $d = 6$ and $33$ kpc, the dwarf galaxies have no companions more luminous than $\approx 0.05L_{*}$ within at least $Δv = \pm 300$ km s$^{-1}$ and $d \approx 350$ kpc. HI 21-cm emission is spatially coincident with the DLA at the 2-3$σ$ level per spectral channel over several adjacent beams. However, HI 21-cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with spin temperature to covering factor ratio $T_{s}/f_{c} > 1880$ K). VLT-MUSE observations demonstrate that the $α$-element abundance of the ionized ISM is consistent with the DLA ($\approx 10$% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf-dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and HI 21-cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.

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arXiv2021

The Cosmic Ultraviolet Baryon Survey (CUBS) IV: The Complex Multiphase Circumgalactic Medium as Revealed by Partial Lyman Limit Systems

We present a detailed study of two partial Lyman limit systems (pLLSs) of neutral hydrogen column density $N_\mathrm{H\,I}\approx(1-3)\times10^{16}\,\mathrm{cm}^{-2}$ discovered at $z=0.5$ in the Cosmic Ultraviolet Baryon Survey (CUBS). Available far-ultraviolet spectra from the Hubble Space Telescope Cosmic Origins Spectrograph and optical echelle spectra from MIKE on the Magellan Telescopes enable a comprehensive ionization analysis of diffuse circumgalactic gas based on resolved kinematics and abundance ratios of atomic species spanning five different ionization stages. These data provide unambiguous evidence of kinematically aligned multi-phase gas that masquerades as a single-phase structure and can only be resolved by simultaneous accounting of the full range of observed ionic species. Both systems are resolved into multiple components with inferred $α$-element abundance varying from $[α/\text{H}]\approx\!{-0.8}$ to near solar and densities spanning over two decades from $\log n_\mathrm{H}\mathrm{cm}^{-3}\approx\!-2.2$ to $<-4.3$. Available deep galaxy survey data from the CUBS program taken with VLT/MUSE, Magellan/LDSS3-C and Magellan/IMACS reveal that the $z=0.47$ system is located 55 kpc from a star-forming galaxy with prominent Balmer absorption of stellar mass $M_\star\approx2\times10^{10}M_\odot$, while the $z=0.54$ system resides in an over-dense environment of 11 galaxies within 750 kpc in projected distance, with the most massive being a luminous red galaxy of $M_\star\approx2\times10^{11}M_\odot$ at 375 kpc. The study of these two pLLSs adds to an emerging picture of the complex, multiphase circumgalactic gas that varies in chemical abundances and density on small spatial scales in diverse galaxy environments. The inhomogeneous nature of metal enrichment and density revealed in observations must be taken into account in theoretical models of diffuse halo gas.

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