arXiv subjects

Kameswara B. Mantha

Publications and source records attributed to Kameswara B. Mantha.

5 recordsLinked to original sources

arXiv2026

The Ly$α$ and Continuum Origins Survey. III. Investigating the Link between Galaxy Morphology, Merger Properties and LyC Escape

Characterizing the mechanisms and galaxy properties conducive to the emission and escape of ionizing (LyC) emission is necessary to accurately model the Epoch of Reionization, and identify the sources that powered it. The Ly$α$ and Continuum Origins Survey (LaCOS) is the first program to obtain uniform, multi-wavelength subkiloparsec imaging for a large sample (42) of galaxies observed in LyC and enable statistically robust studies between LyC and resolved galaxy properties. Here, we characterize the morphology and galaxy merger properties of LaCOS galaxies and investigate their connection with the escape fraction of LyC emission $f_{esc}^{LyC}$. We find strong anticorrelations between $f_{esc}^{LyC}$ and size ($r_{20}$, $r_{50}$, and $r_{80}$) measured in filters containing emission from star-forming regions, and with the asymmetry and clumpiness in F150LP, the bluest filter in our dataset, tracing UV continuum and Ly$α$. We find that $\geq48\%$ of LaCOS galaxies, and $\geq41\%$ of LaCOS LyC-emitters are visually classified as galaxy mergers. Galaxies robustly identified as mergers in LaCOS are at advanced stages of interaction, close to coalescence. The $f_{esc}^{LyC}$ properties of robust mergers and low-probability mergers cannot be differentiated statistically, and we only find significant difference between the two populations in terms of their of their sizes and LyC luminosity: robust mergers having larger values. We conclude that (i) $f_{esc}^{LyC}$ tends to be larger in galaxies with a small number of compact, centrally-located, UV-emitting star-forming regions, (ii) at advanced stages of interaction represent a sizable fraction of LyC-emitting samples at $z\sim0.3$, $z\sim0$, and (iii) mergers can facilitate the escape of LyC photons from galaxies.

astro-ph.GA↗

arXiv2026

Investigating quenching in Recently Quenched Elliptical galaxies with HI studies

Recently Quenched Elliptical galaxies (RQEs) represent a critical phase in the transition from star-forming to quiescent galaxies. However, the mechanisms driving their quenching remain elusive. We conduct a multi-wavelength analysis of 155 RQEs, along with their precursors (preRQEs) and descendants (postRQEs), focusing on their neutral hydrogen (HI) content and star formation properties. Contrary to conventional quenching models emphasizing gas depletion, RQEs retain substantial HI reservoirs ($f_{\text{gas}} \geq 17\%$), suggesting that quenching is not primarily driven by gas exhaustion. We identify a critical halo mass threshold at $\log M_{\text{halo}} = 12.1 M_{\odot}$, delineating different evolutionary pathways for RQEs. This threshold aligns with the transition from cold-mode to hot-mode gas accretion in theoretical models. RQEs in lower-mass halos ($\log M_{\text{halo}} < 12.1 M_{\odot}$) likely experience rapid quenching, possibly initiated by major mergers, followed by brief AGN activity and sustained LINER emission. We propose two evolutionary pathways: (a) rapid quenching via major mergers followed by AGN/LINER activity and passive evolution, and (b) rapid quenching followed by rejuvenation through minor mergers before evolving into more massive, long-term quenched ellipticals. These results challenge the conventional understanding of galaxy quenching, especially in low-density environments where RQEs typically reside. Our findings suggest that while RQEs may follow a rapid quenching pathway, their evolution is influenced by interactions between gas accretion modes, feedback mechanisms, and environmental factors. Future observations with advanced radio interferometers like SKA will be crucial for elucidating the quenching mechanisms in RQEs and their role in galaxy evolution.

astro-ph.GA↗

arXiv2025

Challenging the LyC-Ly$α$ relation: strong Ly$α$ emitters without LyC leakage at z $\sim$ 2.3

The escape fraction of LyC ionizing radiation ($f_{lyc}$) is crucial for understanding reionization, yet difficult to measure at $z \gtrsim 4$. Recently, studies have focused on calibrating indirect indicators of $f_{lyc}$ at $z \sim 0.3$, finding that $Lyα$ is closely linked to it. What is still unclear is whether the LyC $-$ $Lyα$ relation evolves with redshift, and if $Lyα$ is truly applicable as an $f_{lyc}$ indicator during the reionization epoch. In this study, we investigate seven $-21 \lesssim M_{UV} \lesssim-19$ gravitationally lensed galaxies from the BELLS GALLERY Survey at $z\sim2.3$. Our targets have rest-frame $Lyα$ equivalent widths between 40 Å and 200 Å and low dust content ($-2.4 \lesssim β\lesssim -2.0$), both indicative of high LyC escape. Surprisingly, direct estimates of $f_{lyc}$ using Hubble Space Telescope imaging with F275W and F225W reveal that our targets are not LyC emitters, with an absolute $f_{lyc} < 13 \%$ (assuming the median IGM transmission). The low $f_{lyc}$, coupled with the high $Lyα$ equivalent width and escape fraction, could potentially be attributed to the redshift evolution of the neutral hydrogen column density and dust content, as well as covering fractions of optically thick gas below 1 in high redshift galaxies. Additionally, our analysis suggests that the emission for each lensed component is uniformly absorbed. Our results challenge the validity of the extrapolation of $z\sim0$ Ly$α$-based LyC indirect estimators into the reionization epoch.

astro-ph.GA↗

arXiv2021

On the Nature of AGN and Star Formation Enhancement in the $z = 3.1$ SSA22 Protocluster: The HST WFC3 IR View

We examine possible environmental sources of the enhanced star formation and active galactic nucleus (AGN) activity in the $z = 3.09$ SSA22 protocluster using Hubble WFC3 F160W ($\sim1.6\ \rm μm$) observations of the SSA22 field, including new observations centered on eight X-ray selected protocluster AGN. To investigate the role of mergers in the observed AGN and star formation enhancement, we apply both quantitative (Sérsic-fit and Gini-$M_{20}$) and visual morphological classifications to F160W images of protocluster Lyman break galaxies (LBGs) in the fields of the X-ray AGN and $z \sim 3$ field LBGs in SSA22 and GOODS-N. We find no statistically significant differences between the morphologies and merger fractions of protocluster and field LBGs, though we are limited by small number statistics in the protocluster. We also fit the UV-to-near-IR spectral energy distributions (SED) of F160W-detected protocluster and field LBGs to characterize their stellar masses and star formation histories (SFH). We find that the mean protocluster LBG is by a factor of $\sim2$ times more massive and more attenuated than the mean $z \sim 3$ field LBG. We take our results to suggest that ongoing mergers are not more common among protocluster LBGs than field LBGs, though protocluster LBGs appear to be more massive. We speculate that the larger mass of the protocluster LBGs contributes to the enhancement of SMBH mass and accretion rate in the protocluster, which in turn drives the observed protocluster AGN enhancement.

astro-ph.GA↗

arXiv2019

Observational constraints on the merger history of galaxies since $z\approx6$: Probabilistic galaxy pair counts in the CANDELS fields

Galaxy mergers are expected to have a significant role in the mass assembly of galaxies in the early Universe, but there are very few observational constraints on the merger history of galaxies at $z>2$. We present the first study of galaxy major mergers (mass ratios $>$ 1:4) in mass-selected samples out to $z\approx6$. Using all five fields of the HST/CANDELS survey and a probabilistic pair count methodology that incorporates the full photometric redshift posteriors and corrections for stellar mass completeness, we measure galaxy pair-counts for projected separations between 5 and 30 kpc in stellar mass selected samples at $9.7 < \log_{10}(\rm{M}_{*}/\rm{M}_{\odot}) < 10.3$ and $\log_{10}(\rm{M}_{*}/\rm{M}_{\odot}) > 10.3$. We find that the major merger pair fraction rises with redshift to $z\approx6$ proportional to $(1+z)^{m}$, with $m = 0.8\pm0.2$ ($m = 1.8\pm0.2$) for $\log_{10}(\rm{M}_{*} / \rm{M}_{\odot}) > 10.3$ ($9.7 < \log_{10}(\rm{M}_{*}/\rm{M}_{\odot}) < 10.3$). Investigating the pair fraction as a function of mass ratio between 1:20 and 1:1, we find no evidence for a strong evolution in the relative numbers of minor to major mergers out to $z<3$. Using evolving merger timescales we find that the merger rate per galaxy ($\mathcal{R}$) rises rapidly from $0.07\pm 0.01$ Gyr$^{-1}$ at $z < 1$ to $7.6\pm 2.7$ Gyr$^{-1}$ at $z = 6$ for galaxies at $\log_{10}(\rm{M}_{*}/\rm{M}_{\odot}) > 10.3$. The corresponding co-moving major merger rate density remains roughly constant during this time, with rates of $Γ\approx 10^{-4}$ Gyr$^{-1}$ Mpc$^{-3}$. Based on the observed merger rates per galaxy, we infer specific mass accretion rates from major mergers that are comparable to the specific star-formation rates for the same mass galaxies at $z>3$ - observational evidence that mergers are as important a mechanism for building up mass at high redshift as in-situ star-formation.

astro-ph.GA↗