arXiv subjects

Angelo George

Publications and source records attributed to Angelo George.

6 recordsLinked to original sources

arXiv2026

Size-Mass Relation Shows Its Colours: Contrasting Physical Imprints of Galaxy Evolution in Rest-Frame UV and Optical

The galaxy size-mass relation (SMR) is a key scaling relation used to constrain the physical processes that build galaxy structure, yet it is almost always measured in a single rest-frame optical band, where the light traces the bulk of the old stellar mass. Tracing younger populations with flux-weighted ages of ~100-500 Myr and low-metallicity stars, the rest-frame near-ultraviolet opens a new stellar window on this scaling relation. Because each process redistributes the light of young and old stars differently, the same mechanism shifts the slope and zero point of the SMR by different amounts in the two wavelength regimes. Here we review and synthesize the effects of main physical processes on the form of the SMR for star-forming and quiescent galaxies in the rest-UV and optical. For each process, we start from its underlying physics, the galaxy stellar masses it affects, and the light it adds/removes/rearranges, anchoring the predictions to observations and simulations. We validate the predicted imprints with forward Monte Carlo modelling. The two-wavelength view breaks several degeneracies that single-band analyses cannot, most notably between minor mergers, dry major mergers, and adiabatic expansion. These results motivate joint rest-UV and optical SMR measurements with current and upcoming wide-field imaging surveys.

astro-ph.GA↗

arXiv2026

The Role of Cluster Environments in Quiescent Galaxy Stellar Halo Assembly

External interactions drive galaxy stellar mass growth and morphological evolution. As stellar haloes-assembled largely via hierarchical accretion-preserve signatures of these processes, their growth probes how environment regulates galaxy evolution. We investigate how cluster environments influence quiescent galaxy (QG) stellar halo assembly over 0.1 $\leq$ $z$ $\leq$ 1.0 in a sample of 2,168 cluster and 94,479 field QGs of $\log M_{\star} \geq 9.66$. Extended emission is traced via rest-frame $g$-band surface brightness ($\mu_g$) profiles extracted from deep HSC-SSP $grizy$ imaging. We study stellar halo assembly trends by linking median $\mu_g$ profile evolution to the underlying mass growth in galaxy subpopulations. Over 0.1 $\leq$ $z$ $\leq$ 1.0, cluster QGs build up stellar haloes faster than field QGs, with a $\sim23\%$ and $\sim40\%$ larger increase in integrated stellar halo luminosity ($L_{halo}$) in the low-mass ($9.66 \leq \log M_{\star} < 10.5$) and high-mass ($\log M_{\star} \geq 10.5$) samples, respectively. High-mass cluster QGs host more luminous stellar haloes than the field (mean cluster-to-field $L_{halo}$ ratio of $\sim1.2$), while low-mass cluster QGs host less luminous stellar haloes (mean ratio of $\sim0.87$). Among cluster QGs of $\log M_{\star} \geq 10$, $L_{halo}$ increases with host cluster mass, but decreases for cluster QGs of $\log M_{\star} < 10$. These results suggest higher-mass cluster QGs ($\log M_{\star} \geq 10$) experience enhanced stellar halo growth over 0.1 $\leq$ $z$ $\leq$ 1.0 fueled by increased merger-driven accretion, likely from minor mergers in cluster outskirts or in pre-infall group and filament environments. Lower-mass cluster QGs ($9.66 \leq \log M_{\star} < 10$) instead have suppressed stellar halo growth in clusters and likely lose outer stellar material to environmental stripping or accretion by high-mass galaxies during mergers.

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arXiv2025

Effects of Environment on the Size Evolution of Quiescent Galaxies: Comparing Galaxies in Clusters and in the Field at Two Rest-frame Wavelengths

We investigate the impact of environment on quiescent galaxy (QG) size evolution using the CLAUDS+HSC imaging covering 18.6~deg$^2$ in five broad filters ($Ugriz$) and the effective radius of a single-S\'{e}rsic fit as a proxy for galaxy size. We estimate sizes in two rest-frame wavelengths -- 3000\r{A} (UV) and 5000\r{A} (optical) -- for $\sim86,000$ massive ($M_*>10^{9.5}$M$_\odot$) field QGs and for $1,000$ of their similarly massive counterparts from 47 clusters at $0.1<z<0.85$. We fit the size-mass relation (SMR) for field and cluster QGs in five $\Delta z=0.15$ redshift bins and use the characteristic size of $M_*=5\times10^{10}$M$_\odot$ QGs (SMR's zero point) to trace the change in galaxy size over cosmic time and in two types of environment. Sizes of QGs are larger in the rest-frame UV than in the rest-frame optical in both clusters and the field, and this difference is more prominent in the field sample. However, QGs in clusters are systematically smaller than the field QGs, and this difference is significantly more pronounced if measured in the rest-frame UV light. Modeling of the redshift evolution in the characteristic QG size as $R_e\varpropto(1+z)^{\beta}$ shows that the cluster QGs ($\beta=-1.02$ in UV and $\beta= -1.00$ in optical) grow in size as fast as the field QGs ($\beta=-0.95$ in UV and $-1.22$ in optical). This fast growth of cluster QGs is consistent with size increase driven by the accretion of two subpopulations onto clusters: a) field QGs that are larger than their quiescent counterparts in clusters, and b) environmentally quenched galaxies (newcomers) that are larger than the rest of the quiescent population.

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arXiv2024

The Growth of Galaxy Stellar Haloes Over $0.2 \leq z \leq 1.1$

Galaxies are predicted to assemble their stellar haloes through the accretion of stellar material from interactions with their cosmic environment. Observations that trace stellar halo buildup probe the processes that drive galaxy size and stellar mass growth. We investigate stellar halo assembly over $0.2 \leq z \leq 1.1$ in a mass-complete ($M_{\star} \geq 10^{9.5}M_{\odot}$) sample of 242,456 star-forming and 88,421 quiescent galaxies (SFGs and QGs) from the CLAUDS and HSC-SSP surveys. We extract galaxy rest-frame $g$-band surface brightness ($\mu_g$) profiles to study faint, extended emission in galaxy outskirts. We examine trends in galaxy assembly by analyzing the median $\mu_g$ profiles in different SFG and QG \msS ranges with decreasing redshift and connecting evolution in galaxy $\mu_g$ profiles with the underlying stellar mass growth in galaxies. Since $z=1.1$, the majority of evolution in the median $\mu_g$ profiles of galaxies ($\sim$64$\%$ in SFGs and $\sim$71$\%$ in QGs) occurs throughout their stellar halo regions (2-10$R_e$). More massive galaxies assemble stellar halo material more rapidly at $0.2 \leq z \leq 1.1$. Over this period, QGs grow a larger fraction of their stellar haloes than SFGs at fixed $M_{\star}$ (factor of $\sim$1.2). Although star formation can account for the stellar halo growth observed in low-mass SFGs ($10^{9.5}M_\odot \leq M_\star < 10^{10.5}M_\odot$), high-mass SFGs ($M_\star \geq 10^{10.5}M_\odot$) and both low- and high-mass QGs require an additional assembly mechanism. Our results suggest accretion via minor mergers drives additional stellar halo growth in these galaxies. The contribution from accretion is larger in more massive galaxies (over $M_{\star} \geq 10^{9.5}M_{\odot}$), and QGs exhibit larger fractional increases to their ex-situ fractions over $0.2 \leq z \leq 1.1$ than SFGs at fixed $M_{\star}$.

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arXiv2024

Two rest-frame wavelength measurements of galaxy sizes at $z<1$: the evolutionary effects of emerging bulges and quenched newcomers

We analyze the size evolution of $16000$ star-forming galaxies (SFGs) and $5000$ quiescent galaxies (QGs) with mass $M_*>10^{9.5}M_\odot$ at $0.1 9$ are red and only QGs have $\log{\Sigma}_1>9.7$. The size of $M_*=M_0$ QGs grows by $50\%$ ($110\%$) in the UV (visible) light. Up to $\sim20\%$ of this increase in size of massive QGs is due to newcomers (recently quenched galaxies). However, newcomers cannot explain the observed pace in the size growth of QGs; that trend has to be dominated by processes affecting individual galaxies, such as minor mergers and accretion.

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arXiv2021

Hyper Suprime-Cam Subaru Strategic Program: A Mass-Dependent Slope of the Galaxy Size-Mass Relation at $z<1$

We present the galaxy size-mass ($R_{e}-M_{\ast}$) distributions using a stellar-mass complete sample of $\sim1.5$ million galaxies, covering $\sim100$ deg$^2$, with $\log(M_{\ast}/M_{\odot})>10.2~(9.2)$ over the redshift range $0.2<z<1.0$ $(z<0.6)$ from the second public data release of the Hyper Suprime-Cam Subaru Strategic Program. We confirm that, at fixed redshift and stellar mass over the range of $\log(M_{\ast}/M_{\odot})<11$, star-forming galaxies are on average larger than quiescent galaxies. The large sample of galaxies with accurate size measurements, thanks to the excellent imaging quality, also enables us to demonstrate that the $R_{e}-M_{\ast}$ relations of both populations have a form of broken power-law, with a clear change of slopes at a pivot stellar mass $M_{p}$. For quiescent galaxies, below an (evolving) pivot mass of $\log(M_{p}/M_{\odot})=10.2-10.6$ the relation follows $R_{e}\propto M_{\ast}^{0.1}$; above $M_{p}$ the relation is steeper and follows $R_{e}\propto M_{\ast}^{0.6-0.7}$. For star-forming galaxies, below $\log(M_{p}/M_{\odot})\sim10.7$ the relation follows $R_{e}\propto M_{\ast}^{0.2}$; above $M_{p}$ the relation evolves with redshift and follows $R_{e}\propto M_{\ast}^{0.3-0.6}$. The shallow power-law slope for quiescent galaxies below $M_{p}$ indicates that large low-mass quiescent galaxies have sizes similar to those of their counterpart star-forming galaxies. We take this as evidence that large low-mass quiescent galaxies have been recently quenched (presumably through environment-specific process) without significant structural transformation. Interestingly, the pivot stellar mass of the $R_{e}-M_{\ast}$ relations coincides with mass at which half of the galaxy population is quiescent, implied that the pivot mass represents the transition of galaxy growth from being dominated by in-situ star formation to being dominated by (dry) mergers.

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