arXiv subjects

Gauri Sharma

Publications and source records attributed to Gauri Sharma.

At least 19 recordsLinked to original sources

arXiv2026

The MAGPI survey: Stellar population radial trends and mass assembly in star-forming galaxies at z~0.3

The evolution of galaxies from cosmic noon to the present day provides a key window to probe the balance between early, rapid bulge formation and prolonged disk growth. The epoch at $z \sim 0.3$ marks a crucial transitional phase between the peak of cosmic star formation and the predominantly quiescent local Universe. In this work, we examine the spatially resolved stellar populations of 34 galaxies at $z \sim 0.3$ to quantify radial gradients in age, stellar metallicity, and star formation activity, and disentangle the distinct evolutionary pathways of inner and outer galactic components. We utilise MUSE integral-field spectroscopy data cubes from the MAGPI survey at redshifts of $0.28 < z < 0.35$. Stellar population properties are derived using the spectral synthesis codes FADO and Starlight, and radial profiles are constructed by fitting isophotal annuli to the galaxy continuum emission. We further reconstruct star formation histories and cumulative mass assembly curves for inner and outer regions. We find pronounced negative radial gradients in age and negative to flat gradients in stellar metallicity. Inner regions are systematically older and more metal-rich than their surrounding outskirts, with age differences up to 3-4 Gyr in the most massive systems. H$\alpha$ equivalent width profiles reveal centrally suppressed specific star formation in most galaxies. Star formation histories and mass assembly curves demonstrate that galaxy cores formed $80\%$ of their stellar mass rapidly, within the first 2-3 Gyr of cosmic time; while areas outside $\mathrm{1\,R_{eff}}$ assembled more gradually and sustained star formation to later epochs. Outskirts evolve primarily through extended, secular star formation, establishing the centrally concentrated quenching and inside-out growth that link high-redshift systems to the quiescent galaxies of the local Universe.

astro-ph.GA↗

arXiv2026

How Supply Chain Dependencies Complicate Bias Measurement and Accountability Attribution in AI Hiring Applications

The increasing adoption of AI systems in hiring has raised concerns about algorithmic bias and accountability, prompting regulatory responses including the EU AI Act, NYC Local Law 144, and Colorado's AI Act. While existing research examines bias through technical or regulatory lenses, both perspectives overlook a fundamental challenge: modern AI hiring systems operate within complex supply chains where responsibility fragments across data vendors, model developers, platform providers, and deploying organizations. This paper investigates how these dependency chains complicate bias evaluation and accountability attribution. Drawing on literature review and regulatory analysis, we demonstrate that fragmented responsibilities create two critical problems. First, bias emerges from component interactions rather than isolated elements, yet proprietary configurations prevent integrated evaluation. A resume parser may function without bias independently but contribute to discrimination when integrated with specific ranking algorithms and filtering thresholds. Second, information asymmetries mean deploying organizations bear legal responsibility without technical visibility into vendor-supplied algorithms, while vendors control implementations without meaningful disclosure requirements. Each stakeholder may believe they are compliant; nevertheless, the integrated system may produce biased outcomes. Analysis of implementation ambiguities reveals these challenges in practice. We propose multi-layered interventions including system-level audits, vendor guidelines, continuous monitoring mechanisms, and documentation across dependency chains. Our findings reveal that effective governance requires coordinated action across technical, organizational, and regulatory domains to establish meaningful accountability in distributed development environments.

cs.CY↗

arXiv2026

MIDST Challenge at SaTML 2025: Membership Inference over Diffusion-models-based Synthetic Tabular data

Synthetic data is often perceived as a silver-bullet solution to data anonymization and privacy-preserving data publishing. Drawn from generative models like diffusion models, synthetic data is expected to preserve the statistical properties of the original dataset while remaining resilient to privacy attacks. Recent developments of diffusion models have been effective on a wide range of data types, but their privacy resilience, particularly for tabular formats, remains largely unexplored. MIDST challenge sought a quantitative evaluation of the privacy gain of synthetic tabular data generated by diffusion models, with a specific focus on its resistance to membership inference attacks (MIAs). Given the heterogeneity and complexity of tabular data, multiple target models were explored for MIAs, including diffusion models for single tables of mixed data types and multi-relational tables with interconnected constraints. MIDST inspired the development of novel black-box and white-box MIAs tailored to these target diffusion models as a key outcome, enabling a comprehensive evaluation of their privacy efficacy. The MIDST GitHub repository is available at https://github.com/VectorInstitute/MIDST

cs.LG↗

arXiv2026

Glance: A Comprehensive Framework for Galactic Archaeology

A central topic in extragalactic astronomy is understanding the formation and evolutionary histories of galaxies. These systems often comprise multiple structural components with distinct physical and dynamical properties, making it challenging to disentangle their individual contributions. Aiming at investigating the true structure of the inner stellar disk, we have developed a comprehensive pipeline for the chronochemical and dynamical analysis of galaxies (Glance: Galactic archaeoLogy via chronochemicAl & dyNamiCal modElling). The presented pipeline employs several state-of-the-art techniques by integrating them into a single, automated pipeline, enabling streamlined analysis of integral-field spectroscopy data, by allowing users to easily and directly extract valuable information on stellar populations, kinematics, dynamics, and gas properties. It automates multiple analysis techniques, including stellar population synthesis (Fado, Starlight, post-processing with RemoveYoung, kinematic extraction (pPXF, Bayes-LOSVD), and dynamical modelling (Dynamite). It handles tasks such as Galactic extinction correction, de-redshifting, Voronoi binning, and nebular continuum correction, while offering extensive customization options. Parallel processing significantly reduces computational time. When applied to MUSE data sampling the central region of NGC 1566, this methodology reveals that its stellar disk significantly deviates from the conventional exponential model, challenging the assumption of universality in disk morphology. In summary, this work presents a powerful, publicly available pipeline for conducting galactic archaeology, designed to advance our understanding of the formation and evolution of galaxies.

astro-ph.GA↗

arXiv2026

MIGHTEE HI observations of low surface brightness and ultra-diffuse galaxies in the XMM-LSS field

Untargeted neutral hydrogen (HI) surveys are well suited to identifying low surface brightness galaxies (LSBGs) that are gas rich, and they offer a complementary view to optically selected populations. We examined the LSBG population as identified via stellar and gaseous content using the MIGHTEE HI XMM-LSS early science data and the publicly available catalogs of optically identified LSBGs. There is currently little overlap between these datasets, with only three galaxies commonly detected. We performed surface brightness photometry of selected MIGHTEE HI detections to find 29 LSBGs, and 26 of these meet the size requirement (R_eff > 1.5 kpc) to be ultra-diffuse galaxies (UDGs). Furthermore, we extracted HI spectra at the location of all optically identified galaxies, placing upper limits on the HI-to-stellar mass ratio in these systems. While the HI-identified population overall tends toward bluer colors, the HI-identified and the optically selected samples mostly overlap in mean effective surface brightness, effective radii, and color. Although it is not straightforward to discern why the HI-identified LSBGs were missed in optical searches, this work highlights the utility of HI surveys in finding these faint systems. The HI-identified LSBGs are gas rich compared to the general HI-selected population. Furthermore, three out of four HI-selected UDGs with available kinematics show no systematic offset from the baryonic Tully-Fisher relation, although we are biased away from sources with low rotational velocities due to the low spectral resolution of the data. This work demonstrates the utility of HI observations for finding and characterizing the low surface brightness Universe.

astro-ph.GA↗

arXiv2026

The MAGPI Survey: co-evolution of baryons and dark matter in star-forming disk-like galaxies at $0.1 \lesssim z \lesssim 0.85$

We present a comprehensive analysis of the dark matter (DM) content and its structural dependence in star-forming disk-like galaxies at intermediate redshifts ($0.1 \lesssim z \lesssim 0.85$), utilizing spatially resolved kinematic data from the MAGPI survey. We report the following: (1) Low stellar mass galaxies ($M_{\rm star} < 10^{9.5}\, M_\odot$) are strongly DM dominated across all radii, with average $\langle f_{_{\rm DM}} \rangle \sim 0.85$, while high-mass ($M_{\rm star} > 10^{10.5}\, M_\odot$) systems exhibit relatively low DM fractions in their inner regions ($\langle f_{_{\rm DM}} \rangle \sim 0.47$) which is equivalent to local massive disk galaxies (e.g., Milky Way and Andromeda). This suggests a mass-dependent structural dichotomy, most-likely governed by a combination of internal galactic processes and environmental influences. (2) A tight inverse correlation between $f_{_{\rm DM}}$ and baryon mass surface density ($\Sigma_{\rm bar}$), with intrinsic scatter of $\sim 0.11$ dex. This is consistent with an inside-out baryon assembly scenario and suggests that the fundamental structural correlations of galaxies were already established by $z\sim 0.85$. (3) No significant evolution in $f_{_{\rm DM}}$ with redshift across the MAGPI window, and when combined with higher-redshift ($0.6 \leq z \leq 1.5$) data from Sharma et al. 2025, we quantitatively show that the reported decline in $f_{_{\rm DM}}(z)$ is most-likely due to observational biases against low-mass systems at $z > 1$. These results offer empirical evidence for a scenario in which disk-like galaxies evolve through a co-regulated build-up of baryonic and DM components, preserving internal structural regularities (such as the total mass distribution and rotation-curve shape) throughout cosmic time.

astro-ph.GA↗

arXiv2025

Echoes of Human Malice in Agents: Benchmarking LLMs for Multi-Turn Online Harassment Attacks

Large Language Model (LLM) agents are powering a growing share of interactive web applications, yet remain vulnerable to misuse and harm. Prior jailbreak research has largely focused on single-turn prompts, whereas real harassment often unfolds over multi-turn interactions. In this work, we present the Online Harassment Agentic Benchmark consisting of: (i) a synthetic multi-turn harassment conversation dataset, (ii) a multi-agent (e.g., harasser, victim) simulation informed by repeated game theory, (iii) three jailbreak methods attacking agents across memory, planning, and fine-tuning, and (iv) a mixed-methods evaluation framework. We utilize two prominent LLMs, LLaMA-3.1-8B-Instruct (open-source) and Gemini-2.0-flash (closed-source). Our results show that jailbreak tuning makes harassment nearly guaranteed with an attack success rate of 95.78--96.89% vs. 57.25--64.19% without tuning in Llama, and 99.33% vs. 98.46% without tuning in Gemini, while sharply reducing refusal rate to 1-2% in both models. The most prevalent toxic behaviors are Insult with 84.9--87.8% vs. 44.2--50.8% without tuning, and Flaming with 81.2--85.1% vs. 31.5--38.8% without tuning, indicating weaker guardrails compared to sensitive categories such as sexual or racial harassment. Qualitative evaluation further reveals that attacked agents reproduce human-like aggression profiles, such as Machiavellian/psychopathic patterns under planning, and narcissistic tendencies with memory. Counterintuitively, closed-source and open-source models exhibit distinct escalation trajectories across turns, with closed-source models showing significant vulnerability. Overall, our findings show that multi-turn and theory-grounded attacks not only succeed at high rates but also mimic human-like harassment dynamics, motivating the development of robust safety guardrails to ultimately keep online platforms safe and responsible.

cs.AI↗

arXiv2025

Towards Unifying Quantitative Security Benchmarking for Multi Agent Systems

Evolving AI systems increasingly deploy multi-agent architectures where autonomous agents collaborate, share information, and delegate tasks through developing protocols. This connectivity, while powerful, introduces novel security risks. One such risk is a cascading risk: a breach in one agent can cascade through the system, compromising others by exploiting inter-agent trust. In tandem with OWASP's initiative for an Agentic AI Vulnerability Scoring System we define an attack vector, Agent Cascading Injection, analogous to Agent Impact Chain and Blast Radius, operating across networks of agents. In an ACI attack, a malicious input or tool exploit injected at one agent leads to cascading compromises and amplified downstream effects across agents that trust its outputs. We formalize this attack with an adversarial goal equation and key variables (compromised agent, injected exploit, polluted observations, etc.), capturing how a localized vulnerability can escalate into system-wide failure. We then analyze ACI's properties -- propagation chains, amplification factors, and inter-agent compound effects -- and map these to OWASP's emerging Agentic AI risk categories (e.g. Impact Chain and Orchestration Exploits). Finally, we argue that ACI highlights a critical need for quantitative benchmarking frameworks to evaluate the security of agent-to-agent communication protocols. We outline a methodology for stress-testing multi-agent systems (using architectures such as Google's A2A and Anthropic's MCP) against cascading trust failures, developing upon groundwork for measurable, standardized agent-to-agent security evaluation. Our work provides the necessary apparatus for engineers to benchmark system resilience, make data-driven architectural trade-offs, and develop robust defenses against a new generation of agentic threats.

cs.CR↗

arXiv2025

MIGHTEE-HI: The direct detection of neutral hydrogen in galaxies at $z>0.25$

Atomic hydrogen constitutes the gas reservoir from which molecular gas and star formation in galaxies emerges. However, the weakness of the line means it has been difficult to directly detect in all but the very local Universe. Here we present results from the first search using the MeerKAT International Tiered Extragalactic Exploration (MIGHTEE) Survey for high-redshift ($z>0.25$) H{\sc i} emission from individual galaxies. By searching for 21-cm emission centered on the position and redshift of optically-selected emission-line galaxies we overcome difficulties that hinder untargeted searches. We detect 11 galaxies at $z>0.25$, forming the first sample of $z>0.25$ detections with an interferometer, with the highest redshift detection at $z = 0.3841$. We find they have much larger H{\sc i} masses than their low-redshift H{\sc i}-selected counterparts for a given stellar mass. This can be explained by the much larger cosmological volume probed at these high redshifts, and does not require any evolution of the H{\sc i} mass function. We make the first-ever measurement of the baryonic Tully-Fisher relation (bTFr) with H{\sc i} at $z>0.25$ and find consistency with the local bTFr, but with tentative evidence of a flattening in the relation at these redshifts for higher-mass objects. This may signify evolution, in line with predictions from hydrodynamic simulations, or that the molecular gas mass in these high-mass galaxies could be significant. This study paves the way for future studies of H{\sc i} beyond the local Universe, using both searches targeted at known objects and via pure H{\sc i} selection.

astro-ph.GA↗

arXiv2025

The MAGPI Survey: the subtle role of environment and not-so-subtle impact of generations of stars on galaxy dynamics

The stellar age and mass of galaxies have been suggested as the primary determinants for the dynamical state of galaxies, with environment seemingly playing no or only a very minor role. We use a sample of 77 galaxies at intermediate redshift (z~0.3) in the Middle-Ages Galaxies Properties with Integral field spectroscopy (MAGPI) Survey to study the subtle impact of environment on galaxy dynamics. We use a combination of statistical techniques (simple and partial correlations and principal component analysis) to isolate the contribution of environment on galaxy dynamics, while explicitly accounting for known factors such as stellar age, star formation histories and stellar masses. We consider these dynamical parameters: high-order kinematics of the line-of-sight velocity distribution (parametrised by the Gauss-Hermite coefficients $h_3$ and $h_4$), kinematic asymmetries $V_{\rm asym}$ derived using kinemetry and the observational spin parameter proxy $\lambda_{R_e}$. Of these, the mean $h_4$ is the only parameter found to have a significant correlation with environment as parametrised by group dynamical mass. This correlation exists even after accounting for age and stellar mass trends. Finally, we confirm that variations in the spin parameter $\lambda_{R_e}$ are most strongly (anti-)correlated with age as seen in local studies, and show that this dependence is well-established by z~0.3.

astro-ph.GA↗

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$\sigma$. 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.

astro-ph.GA↗

arXiv2024

Measures of luminous and dark matter in galaxies across time

Dark matter is one of the pillars of the current standard model of structure formation: it is assumed to constitute most of the matter in the Universe. However, it can so far only be probed indirectly through its gravitational effects, and its nature remains elusive. In this focus meeting, we discussed different methods used to estimate galaxies' visible and dark matter masses in the nearby and distant Universe. We reviewed successes of the standard model relying on cold dark matter, confronted observations with simulations, and highlighted inconsistencies between the two. We discussed how robust mass measurements can help plan, perform, and refine particle dark matter searches. We further exchanged about alternatives to cold dark matter, such as warm, self-interacting, and fuzzy dark matter, as well as modified gravity. Finally, we discussed prospects and strategies that could be implemented to reveal the nature of this crucial component of the Universe.

astro-ph.GA↗

arXiv2024

The MAGPI Survey: Orbital distributions, intrinsic shapes, and mass profiles for MAGPI-like Eagle galaxies using Schwarzschild dynamical models

Schwarzschild dynamical models are now regularly employed in large surveys of galaxies in the local and distant Universe to derive information on galaxies' intrinsic properties such as their orbital structure and their (dark matter and stellar) mass distribution. Comparing the internal orbital structures and mass distributions of galaxies in the distant Universe with simulations is key to understanding what physical processes are responsible for shaping galaxy properties. However it is first crucial to understand whether observationally derived properties are directly comparable with intrinsic ones in simulations. To assess this, we build Schwarzschild dynamical models for MUSE-like IFS cubes (constructed to be like those obtained by the MAGPI survey) of 75 galaxies at z ~ 0.3 from the Eagle simulations. We compare the true particle-derived properties with the galaxies' model-derived properties. In general, we find that the models can recover the true galaxy properties qualitatively well, with the exception of the enclosed dark matter, where we find a median offset of 48%, which is due to the assumed NFW profile not being able to reproduce the dark matter distribution in the inner region of the galaxies. We then compare our model-derived properties with Schwarzschild models-derived properties of observed MAGPI galaxies and find good agreement between MAGPI and Eagle: the majority of our galaxies (57%) have non-oblate shapes within 1 effective radius. More triaxial galaxies show higher fractions of hot orbits in their inner regions and tend to be more radially anisotropic.

astro-ph.GA↗

arXiv2024

Tully-Fisher Relation of Late-type Galaxies at $0.6 \leq z \leq 2.5$

We present a study of the stellar and baryonic Tully-Fisher relation within the redshift range of $0.6 \leq z \leq 2.5$ utilizing observations of \sfgs. This dataset, as explored in \citet{GS23}, comprises of disk-like galaxies spanning a stellar mass range of $8.89 \leq \log(M_{star} \ [\mathrm{M_\odot}]) \leq 11.5$, baryonic mass range of $9.0 \leq \log(M_{bar} [\mathrm{M_\odot}]) \leq 11.5$, and circular velocity range of $1.65 \leq \log(V_c \ [{\rm km/s}]) \leq 2.85$. Stellar masses of these objects are estimated using spectral energy distribution fitting techniques, while gas masses are determined via scaling relations. Circular velocities are directly derived from the Rotation Curves (RCs), after meticulously correcting for beam smearing and pressure support. Our analysis confirms that our sample adheres to the fundamental mass-size relations of galaxies and reflects the evolution of velocity dispersion in galaxies, in line with previous findings. This reaffirms the reliability of our photometric and kinematic parameters (i.e., $M_{star}$ and $V_c$), thereby enabling a comprehensive examination of the Tully-Fisher relation. To attain robust results, we employed a novel orthogonal likelihood fitting technique designed to minimize intrinsic scatter around the best-fit line, as required at \hz. For the STFR, we obtained a slope of $\alpha=3.03\pm 0.25$, an offset of $\beta = 3.34\pm 0.53$, and an intrinsic scatter of $\zeta_{int}=0.08$ dex. Correspondingly, the BTFR yielded $\alpha=3.21\pm 0.28$, $\beta=3.16\pm 0.61$, and $\zeta_{int}=0.09$ dex. Our findings suggest a subtle deviation in the stellar and baryonic Tully-Fisher relation with respect to local studies, which is most-likely due to the evolutionary processes governing disk formation.

astro-ph.GA↗

arXiv2024

Equity in Healthcare: Analyzing Disparities in Machine Learning Predictions of Diabetic Patient Readmissions

This study investigates how machine learning (ML) models can predict hospital readmissions for diabetic patients fairly and accurately across different demographics (age, gender, race). We compared models like Deep Learning, Generalized Linear Models, Gradient Boosting Machines (GBM), and Naive Bayes. GBM stood out with an F1-score of 84.3% and accuracy of 82.2%, accurately predicting readmissions across demographics. A fairness analysis was conducted across all the models. GBM minimized disparities in predictions, achieving balanced results across genders and races. It showed low False Discovery Rates (FDR) (6-7%) and False Positive Rates (FPR) (5%) for both genders. Additionally, FDRs remained low for racial groups, such as African Americans (8%) and Asians (7%). Similarly, FPRs were consistent across age groups (4%) for both patients under 40 and those above 40, indicating its precision and ability to reduce bias. These findings emphasize the importance of choosing ML models carefully to ensure both accuracy and fairness for all patients. By showcasing effectiveness of various models with fairness metrics, this study promotes personalized medicine and the need for fair ML algorithms in healthcare. This can ultimately reduce disparities and improve outcomes for diabetic patients of all backgrounds.

cs.LG↗

arXiv2024

Radial Tully-Fisher relation and the local variance of Hubble parameter

Utilizing the well-established Radial Tully-Fisher (RTF) relation observed in a `large' (843) sample of local galaxies, we report the maximum allowed variance in the Hubble parameter, $H_0$. We estimate the total intrinsic scatter in the magnitude of the RTF relation(s) implementing a cosmological model-independent cosmographic expansion. We find that the maximum allowed local variation in our baseline analysis, using 4 RTF relations in the galaxy sample is $\Delta H_0/H_0 \lesssim 3 \%$ at a $95\%$ C.L. significance. Which is implied form a constraint of $\Delta H_0/H_0 = 0.54^{+1.32}_{-1.37} \%$ estimated at $D_{\rm{L}}\sim 10\, [\rm{Mpc}]$. Using only one `best-constrained' radial bin we report a conservative $95\%$ C.L. limit of $\Delta H_0/H_0 \lesssim 4 \%$. Through our estimate of maximum variation, we propose a novel method to validate several late-time/local modifications put forth to alleviate the $H_0$ tension. We find that within the range of the current galaxy sample redshift distribution $10 \, [\rm{Mpc}] \le D_{\rm{L}} \le 140\, [\rm{Mpc}]$, it is highly unlikely to obtain a variation of $\Delta H_0/H_0 \sim 9\%$, necessary to alleviate the $H_0$-tension. However, we also elaborate on the possible alternative inferences when the innermost radial bin is included in the analysis. Alongside the primary analysis of fitting the individual RTF relations independently, we propose and perform a joint analysis of the RTF relations useful to create a pseudo-standardizable sample of galaxies. We also test for the spatial variation of $H_0$, finding that the current samples' galaxies distributed only in the southern hemisphere support the null hypothesis of isotropy, within the allowed noise levels.

astro-ph.CO↗

arXiv2024

MIGHTEE-HI: HI galaxy properties in the large scale structure environment at z~0.37 from a stacking experiment

We present the first measurement of HI mass of star-forming galaxies in different large scale structure environments from a blind survey at $z\sim 0.37$. In particular, we carry out a spectral line stacking analysis considering $2875$ spectra of colour-selected star-forming galaxies undetected in HI at $0.23 < z < 0.49$ in the COSMOS field, extracted from the MIGHTEE-HI Early Science datacubes, acquired with the MeerKAT radio telescope. We stack galaxies belonging to different subsamples depending on three different definitions of large scale structure environment: local galaxy overdensity, position inside the host dark matter halo (central, satellite, or isolated), and cosmic web type (field, filament, or knot). We first stack the full star-forming galaxy sample and find a robust HI detection yielding an average galaxy HI mass of $M_{\rm HI}=(8.12\pm 0.75)\times 10^9\, {\rm M}_\odot$ at $\sim 11.8\sigma$. Next, we investigate the different subsamples finding a negligible difference in $M_{\rm HI}$ as a function of the galaxy overdensity. We report an HI excess compared to the full sample in satellite galaxies ($M_{\rm HI}=(11.31\pm1.22)\times 10^9$, at $\sim 10.2 \sigma$) and in filaments ($M_{\rm HI}=(11.62\pm 0.90)\times 10^9$. Conversely, we report non-detections for the central and knot galaxies subsamples, which appear to be HI-deficient. We find the same qualitative results also when stacking in units of HI fraction ($f_{\rm HI}$). We conclude that the HI amount in star-forming galaxies at the studied redshifts correlates with the large scale structure environment.

astro-ph.GA↗

arXiv2023

The MAGPI Survey: Effects of Spiral Arms on Different Tracers of the Interstellar Medium and Stellar Populations at z~0.3

Spiral structures are important drivers of the secular evolution of disc galaxies, however, the origin of spiral arms and their effects on the development of galaxies remain mysterious. In this work, we present two three-armed spiral galaxies at z~0.3 in the Middle Age Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey. Taking advantage of the high spatial resolution (~0.6'') of the Multi-Unit Spectroscopic Unit (MUSE), we investigate the two-dimensional distributions of different spectral parameters: Halpha, gas-phase metallicity, and D4000. We notice significant offsets in Halpha (~0.2 dex) as well as gas-phase metallicities (~0.05 dex) among the spiral arms, downstream and upstream of MAGPI1202197197 (SG1202). This observational signature suggests the spiral structure in SG1202 is consistent with arising from density wave theory. No azimuthal variation in Halpha or gas-phase metallicities is observed in MAGPI1204198199 (SG1204), which can be attributed to the tighter spiral arms in SG1204 than SG1202, coming with stronger mixing effects in the disc. The absence of azimuthal D4000 variation in both galaxies suggests the stars at different ages are well-mixed between the spiral arms and distributed around the disc regions. The different azimuthal distributions in Halpha and D4000 highlight the importance of time scales traced by various spectral parameters when studying 2D distributions in spiral galaxies. This work demonstrates the feasibility of constraining spiral structures by tracing interstellar medium (ISM) and stellar population at z~0.3, with a plan to expand the study to the full MAGPI survey.

astro-ph.GA↗