arXiv subjects

P. Sawant

Publications and source records attributed to P. Sawant.

7 recordsLinked to original sources

arXiv2026

Stellar mass growth in COSMOS-Web: a mass-complete main sequence to z ~ 8 and its consistency with GSMF evolution

The star-forming main sequence (MS) links the instantaneous star-formation rate of galaxies to their stellar-mass growth and therefore to the evolution of the galaxy stellar mass function (GSMF). We determine a mass-complete MS in COSMOS-Web out to z=8 and test whether its mass and redshift dependence is consistent with the observed evolution of the GSMF. We stacked 251,462 star-forming galaxies in Herschel and JCMT maps and corrected the far-infrared fluxes for blending using forward-modeled maps. We combined the resulting infrared luminosities with the unobscured ultraviolet emission to derive total star-formation rates and fitted a redshift-dependent MS. We independently measured the quiescent fraction and evolved the observed z=8 COSMOS-Web GSMF forward within a continuity-equation framework including stellar-mass return, suppression of in-situ growth by the quiescent fraction, and mergers. The MS is well described by a power law at low masses with a redshift-dependent turnover toward high masses. We measure a low-mass slope of gamma=1.215+/-0.028, implying a mildly increasing specific star-formation rate with stellar mass. The GSMF evolved using this relation follows the observed progressive flattening of the low-mass end substantially better than the literature MS prescriptions considered here. Mergers change the low-mass number densities by <=0.2 dex by z~0.65 and have little effect on the slope. Small differences in MS normalization also accumulate strongly, producing large differences in the evolved GSMF after several Gyr. The observed GSMF evolution provides an independent integral test of the MS. Our results favor a mildly super-linear low-mass MS and show that both its slope and normalization must be measured accurately to reproduce the buildup of the galaxy stellar-mass distribution.

astro-ph.GA↗

arXiv2026

Multiphase images of a powerful supernova-driven wind in the early Universe

Galactic winds are considered a likely driver of rapid quenching in early massive galaxies, but until now there has been no direct evidence that such systems drive winds powerful enough to meaningfully suppress their star-formation. We present resolved cold gas and ionized gas observations of a powerful supernova-driven wind in a massive galaxy 1.1 billion years after the Big Bang (at $z$=5.3). The outflow, likely triggered by ongoing merger activity, is removing gas at twice the rate of star-formation and could plausibly eject all the cold gas from the galaxy within 100 Myr. Our results suggest that powerful merger-driven outflows may be a key mechanism to produce abundant massive quiescent galaxies in the early Universe when a large fraction of massive galaxies are interacting. The mass and energetics of this distant outflow are consistent with nearby starburst-driven superwinds, suggesting that the efficiency of stellar feedback has remained relatively constant over the last 12 billion years of cosmic history.

astro-ph.GA↗

arXiv2025

The ALPINE-CRISTAL-JWST Survey: JWST/IFU Optical Observations for 18 Main-Sequence Galaxies at z=4-6

To fully characterize the formation and evolution of galaxies, we need to observe their stars, gas, and dust on resolved spatial scales. We present the ALPINE-CRISTAL-JWST survey, which combines kpc-resolved imaging and spectroscopy from HST, JWST, and ALMA for 18 representative main-sequence galaxies at z=4-6 and log(M/$M_\odot$) > 9.5 to study their star formation, chemical properties, and extended gas reservoirs. The co-spatial measurements resolving the ionized gas, molecular gas, stars, and dust on 1-2 kpc scales make this a unique benchmark sample for the study of galaxy formation and evolution at $z\sim5$, connecting the Epoch of Reionization with the cosmic noon. In this paper, we outline the survey goals and sample selection, and present a summary of the available data for the 18 galaxies. In addition, we measure spatially integrated quantities (such as global gas metallicity), test different star formation rate indicators, and quantify the presence of H$\alpha$ halos. Our targeted galaxies are relatively metal rich (10-70% solar), complementary to JWST samples at lower stellar mass, and there is broad agreement between different star formation indicators. One galaxy has the signature of an active galactic nuclei (AGN) based on its emission line ratios. Six show broad H$\alpha$~emission suggesting type 1 AGN candidates. We conclude with an outlook on the exciting science that will be pursued with this unique sample in forthcoming papers.

astro-ph.GA↗

arXiv2025

The ALPINE-CRISTAL-JWST survey: spatially resolved star formation relations at $z\sim5$

Star formation governs galaxy evolution, shaping stellar mass assembly and gas consumption across cosmic time. The Kennicutt-Schmidt (KS) relation, linking star formation rate (SFR) and gas surface densities, is fundamental to understand star formation regulation, yet remains poorly constrained at $z > 2$ due to observational limitations and uncertainties in locally calibrated gas tracers. The [CII] $158 {\rm \mu m}$ line has recently emerged as a key probe of the cold ISM and star formation in the early Universe. We investigate whether the resolved [CII]-SFR and KS relations established at low redshift remain valid at $4 < z < 6$ by analysing 13 main-sequence galaxies from the ALPINE and CRISTAL surveys, using multi-wavelength data (HST, JWST, ALMA) at $\sim2$ kpc resolution. We perform pixel-by-pixel spectral energy distribution (SED) modelling with CIGALE on resolution-homogenised images. We develop a statistical framework to fit the [CII]-SFR relation that accounts for pixel covariance and compare our results to classical fitting methods. We test two [CII]-to-gas conversion prescriptions to assess their impact on inferred gas surface densities and depletion times. We find a resolved [CII]-SFR relation with a slope of $0.87 \pm 0.15$ and intrinsic scatter of $0.19 \pm 0.03$ dex, which is shallower and tighter than previous studies at $z\sim5$. The resolved KS relation is highly sensitive to the [CII]-to-gas conversion factor: using a fixed global $\alpha_{\rm [CII]}$ yields depletion times of $0.5$-$1$ Gyr, while a surface brightness-dependent $W_{\rm [CII]}$, places some galaxies with high gas density in the starburst regime ($<0.1$ Gyr). Future inputs from both simulations and observations are required to better understand how the [CII]-to-gas conversion factor depends on local ISM properties. We need to break this fundamental limit to properly study the KS relation at $z\gtrsim4$.

astro-ph.GA↗

arXiv2024

The ALPINE-ALMA [CII] Survey: Unveiling the baryon evolution in the ISM of $z\sim5$ star-forming galaxies

Recent observations reveal a rapid dust build-up in high-redshift galaxies (z > 4), challenging current models of galaxy formation. While our understanding of dust production and destruction in the interstellar medium (ISM) is advancing, probing baryonic processes in the early Universe remains a complex task. We characterize the evolution of 98 z~5 star-forming galaxies observed as part of the ALPINE survey by constraining the physical processes underpinning the gas and dust production, consumption, and destruction in their ISM. We make use of chemical evolution models to simultaneously reproduce the observed dust and gas content. For each galaxy, we estimate initial gas mass, inflows and outflows, and efficiencies of dust growth and destruction. We test the models with the canonical Chabrier and top-heavy initial mass functions (IMFs), with the latter enabling rapid dust production on shorter timescales. Our models successfully reproduce gas and dust content in older galaxies (> 600 Myr) regardless of the IMF, with Type II SNe as the primary dust source and no dust growth in ISM with moderate inflow of primordial gas. In case of intermediate-age galaxies (300 - 600 Myr), we reproduce the gas and dust content through Type II SNe and dust growth in ISM, though we observe an over-prediction of dust mass in older galaxies, potentially indicating an unaccounted dust destruction mechanism and/or an overestimation of the observed dust masses. The number of young galaxies (< 300 Myr) reproduced, increases for models assuming top-heavy IMF but with maximal prescriptions of dust production. Galactic outflows are necessary to reproduce observed gas and dust masses. The Chabrier IMF models reproduce 65% of galaxies, while top-heavy IMF models improve this to 93%, easing tensions with observations. Upcoming JWST data will refine these models by resolving degeneracies in intrinsic galaxy properties.

astro-ph.GA↗

arXiv2024

Evidence of extended [CII] and dust emission in local dwarf galaxies

The evolution of dwarf galaxies is dramatically affected by gaseous and dusty outflows, which can easily deprive their interstellar medium of the material needed for the formation of new stars, simultaneously enriching their surrounding circumgalactic medium (CGM). In this letter, we present the first evidence of extended [CII] 158 $μ$m line and dust continuum emission in local dwarf galaxies hosting star-formation-driven outflows. By stacking the [CII], far-infrared, and near-UV (NUV) emission obtained from Herschel and GALEX data, we derived the average radial profiles, and compared the spatial extension of gas, dust, and stellar activity in dwarf galaxies. We find that [CII] and dust emissions are comparable to each other, and more extended than the NUV continuum. The [CII] size is in agreement with that measured for $z>4$ star-forming galaxies, suggesting that similar mechanisms could be at the origin of the observed atomic carbon reservoir around local and high-$z$ sources. The cold dust follows the [CII] emission, going beyond the stellar continuum as opposed to what is typically observed in the early Universe where measurements can be affected by the poor sensitivity and faintness of dust emission in the CGM of high-$z$ galaxies. We attribute the extended [CII] and dust continuum emission to the presence of galactic outflows. As local dwarf galaxies are considered analogs of primordial sources, we expect that comparable feedback processes can be at the origin of the observed [CII] halos at $z>4$, dominating over other possible formation mechanisms.

astro-ph.GA↗

arXiv2023

Shedding Light on Low Surface Brightness Galaxies in Dark Energy Survey with Transformers

Low surface brightness galaxies (LSBGs) which are defined as galaxies that are fainter than the night sky, play a crucial role in understanding galaxy evolution and cosmological models. Upcoming large-scale surveys like Rubin Observatory Legacy Survey of Space and Time (LSST) and Euclid are expected to observe billions of astronomical objects. In this context, using semi-automatic methods to identify LSBGs would be a highly challenging and time-consuming process and demand automated or machine learning-based methods to overcome this challenge. We study the use of transformer models in separating LSBGs from artefacts in the data from the Dark Energy Survey (DES) data release 1. Using the transformer models, we then search for new LSBGs from the DES that the previous searches may have missed. Properties of the newly found LSBGs are investigated, along with an analysis of the properties of the total LSBG sample in DES. We identified 4,083 new LSBGs in DES, adding an additional $\sim17\% $ to the LSBGs already known in DES. This also increased the number density of LSBGs in DES to 5.5 deg$^{-2}$. We performed a clustering analysis of the LSBGs in DES using an angular two-point auto-correlation function and found that LSBGs cluster more strongly than their high surface brightness counterparts. We associated 1310 LSBGs with galaxy clusters and identified 317 among them as ultra-diffuse galaxies (UDGs). We found that these cluster LSBGs are getting bluer and larger in size towards the edge of the clusters when compared with those in the centre. Transformer models have the potential to be on par with convolutional neural networks as state-of-the-art algorithms in analysing astronomical data.

astro-ph.GA↗