arXiv subjects

Oğuzhan Çakır

Publications and source records attributed to Oğuzhan Çakır.

5 recordsLinked to original sources

arXiv2026

Hector Galaxy Survey: Falling in Between - Infalling Galaxies in the Midst of the Abell 3667 Merger

Whether cluster mergers enhance ram pressure stripping (RPS) and accelerate member galaxy evolution remains an open question. Here, we investigate galaxy populations in the nearby merging cluster Abell 3667 ($z\simeq0.0553$) using spatially resolved data from the Hector Galaxy Survey. We define an RPS sample combining Hector-selected galaxies with ionised gas disturbances (e.g., asymmetric tails or truncated disks) and supplementary, optically identified jellyfish galaxies lacking Hector data. Most of the RPS sample ($\sim 71^{+10}_{-7}\%$; 20/28) lies within $R_{200}$, where the merger impact is greater. Most asymmetric galaxies ($\sim 73^{+14}_{-8}\%$; 11/15), especially those with extreme RPS signatures, are concentrated in the inner cluster ($R \lesssim 0.6\, R_{200}$), along the merger axis between two shock-tracing radio relics. These central asymmetric galaxies show two spatial and kinematic groups: one at the North-West (NW) subcluster, downstream of its radio relic in a region of high-velocity intracluster medium (ICM) bulk motion, with blueshifted line-of-sight velocities; and a mostly redshifted population near the main cluster (MC), which also shows a turbulent ICM. Despite their projected association with the MC core and NW substructure, both samples' velocities indicate they are not bound to them. Tail orientations give insight into orbital histories: NW tails point away from the cluster centre and often align with the merger axis, suggesting merger-driven stripping, while MC tails show neither pattern clearly. Tails are broadly westward, with MC tails tracing due west and NW tails shifted northwest, pointing to two distinct filamentary accretion events for the NW and MC populations. Together, our results indicate enhanced RPS in the heart of A3667, driven mainly by infalling galaxies accreted along nearby filaments interacting with the merger-driven turbulent environment.

astro-ph.GA↗

arXiv2026

Hector Galaxy Survey: Optical IFU and Chandra Reveal a Low-Luminosity AGN Behind Extended LINER Emission

We present evidence that the Hector Galaxy Survey galaxy C901005481609968 ($z_{\rm cl}=0.0553$), which exhibits spatially extended LINER-like emission in optical integral-field spectroscopy (IFS), hosts a low-luminosity active galactic nucleus (LLAGN) that contributes substantially to its ionization budget. Although the galaxy is not selected as an AGN by mid-infrared AGN color criteria, archival Chandra data reveal a compact nuclear X-ray source with $\log L_{\rm X}\approx41.46$ erg/s, supporting the presence of an LLAGN. Spatially resolved emission-line diagnostics show LINER-like line ratios across most spaxels with $\mathrm{S/N} \geq 3$, while spatially resolved $τ$ maps ($τ\equiv Q_{\rm pAGB}/Q_{\rm req}$) indicate a widespread photon deficit ($\logτ<0$ over most of the mapped region), even under the most optimistic pAGB normalizations, the nuclear region remains at $τ< 1$. Line-ratio--kinematic tests find no evidence for shock-dominated excitation as the primary driver of the extended emission, although a localized or sub-dominant shock contribution cannot be ruled out with the present data. We use this galaxy as a pilot case because the combination of Hector IFS and an independent nuclear X-ray constraint provides a stringent validation of the spatially resolved photon-budget framework. Our results indicate that evolved stellar populations alone cannot account for the observed emission, that an additional nuclear ionizing source is required at least in the inner region, and that a weak LLAGN likely contributes to the ionizing budget, particularly in the inner region. Our results demonstrate that extended LINER-like emission can conceal a substantial LLAGN contribution even when traditional optical and infrared AGN indicators are weak, and that spatially resolved photon-budget tests combined with X-ray constraints can effectively reveal such hidden activity.

astro-ph.GA↗

arXiv2026

The SAMI Galaxy Survey: Quenching of Star Formation in Clusters III. Ram-Pressure-Affected Galaxy Populations

Cluster environments influence galaxy evolution by curtailing star formation activity, notably through ram-pressure stripping (RPS). In this study, using spatially resolved spectroscopic data from the SAMI Galaxy Survey, we identify galaxies undergoing or recently affected by RPS in eight nearby clusters ($0.029 < z < 0.058$), through a visual classification scheme based on the ionised gas ($\rm Hα+ [NII]λ6584$) morphologies, split into unperturbed, asymmetric, and truncated. The projected phase-space analysis shows that asymmetric galaxies are found in a narrow region in cluster-centric distance ($\rm 0.1 < R/R_{200} < 0.6$) and have a larger dispersion in line-of-sight velocity ($σ(|v_{pec}|)_\mathrm{Asym} = 0.71^{+0.09}_{-0.07}\ σ_{200}$) compared to the truncated and unperturbed samples. In terms of star formation activity, RPS candidates yield a much steeper resolved star-forming main sequence (rSFMS; $Σ_\mathrm{SFR} - Σ_\ast$) relation compared to the unperturbed counterparts, primarily emerging from having lower $Σ_\mathrm{SFR}$ values for the low mass density regime, with the steepest gradient deriving from the truncated sample. Moreover, radial star formation profiles reveal that star formation in RPS candidates is suppressed in the outskirts relative to unperturbed galaxies and is more prominent for the truncated sample. In contrast, central ($\rm r/r_{eff}<0.5$) star formation activity in RPS candidates is comparable with that in their unperturbed and field counterparts, suggesting no elevated activity. Taken together, this suggests an evolutionary trend linked to the RPS stage, where unperturbed galaxies likely represent recently accreted systems (pre-RPS), while asymmetric and truncated galaxies may correspond to populations undergoing RPS and post-RPS phases, respectively, favouring outside-in quenching.

astro-ph.GA↗

arXiv2025

The Impact of Cluster Mergers on Galaxy Properties

The impact of galaxy cluster mergers on the properties of the resident galaxies remains poorly understood. In this paper, we investigate the effects of merging environments on star formation (SF) activity in nearby clusters ($0.04<z<0.06$) from the SAMI Galaxy Survey - A168, A2399, A3380, and EDCC 0442 - which exhibit different dynamical activity. Using single-fibre spectroscopy from the SAMI Cluster Redshift Survey and Sloan Digital Sky Survey, we trace SF activity across the cluster sample by identifying the star-forming galaxy (SFG) population based on spectral features. We find a mild enhancement in the star-forming galaxy fraction ($f_{SFG}$) in merging clusters, although not statistically significant. The spatial and projected phase-space distributions show that SFGs in merging clusters are well-mixed with the passive population, while galaxy populations exhibit a clear segregation in the relaxed clusters. Analysis of the equivalent width of the $\rm Hα$ line, as a tracer of recent SF activity, does not reveal strong evidence of triggered SF activity as a function of dynamical state for both the global cluster environment and subsamples of galaxies selected near possible merger features. This suggests that the increase in $f_{SFG}$ is due to the mixing of galaxies in dynamically complex, young merging systems that are still forming, unlike their older, relaxed counterparts that have had longer to quench.

astro-ph.GA↗

arXiv2025

Cluster passage driving galaxy kinematic and structural evolution in the SAMI Galaxy Survey

The cluster environment can have a significant impact on galaxy evolution. We study the impact that passage through a cluster has on stellar and ionised gas kinematics for galaxies within the Sydney-AAO Multi Integral field (SAMI) Galaxy Survey. We compute the kinematic asymmetry $v_{\rm asym}$ in the line-of-sight stellar and ionsied gas velocity maps to quantify how the cluster environment disturbs the kinematics of the stars and ionised gas. We find a significantly higher fraction of galaxies with elevated gas asymmetries in clusters compared to non-cluster environments (17$^{+2}_{-3}$\%, 26/154 vs. 11$^{+1}_{-1}$\%, 72/751), with these galaxies most likely being recent infallers passage based on their position in projected-phase-space. Compared to cluster galaxies without elevated gas asymmetries, cluster galaxies with elevated gas asymmetries have, on average, more centrally concentrated star-formation. Finally, we find the highest fraction of galaxies with elevated gas asymmetries in clusters likely to host significant substructure or be dynamically complex. Our findings are consistent with the scenario of galaxies falling into clusters, either individually or in groups, and undergoing disk-fading and a redistribution of gas, due to ram pressure stripping experienced during pericentre passage.

astro-ph.GA↗