arXiv subjects

Jaclyn Champagne

Publications and source records attributed to Jaclyn Champagne.

7 recordsLinked to original sources

arXiv2025

Lyman-Break Galaxies in the Mpc-Scale Environments Around Three $z\sim7.5$ Quasars With JWST Imaging

We study the Mpc-scale environments of the three highest redshift luminous quasars at $z\geq 7.5$ (J031343.84-180636.40, J134208.11+092838.61, and J100758.27+211529.21) to understand their connection to large-scale structure. Cosmological simulations show that these early supermassive black holes (SMBHs) are expected to form in the most massive dark matter halos. Therefore, it is expected that they are anchors of galaxy overdensities if luminous matter traces the underlying dark matter structure of the Universe. Using JWST NIRCam (F090W/F115W/F250M/F360M/F430M) imaging, we observe the large-scale structure out to $\sim13$ comoving Mpc around these quasars. We select F090W-dropout Lyman Break galaxies (LBGs) and F430M-excess [OIII] emitters in the three fields. We find 18, 21, and 6 LBG candidates in the fields of J0313, J1342, and J1007, respectively, resulting in a wide range of overdensities ($1+δ\sim 19,\,24,$ and $7$). The photometric redshifts indicate serendipitous foreground and background overdensities in the J0313 field. The joint angular autocorrelation of the combined LBG sample shows significant clustering on $<1.8$ comoving Mpc scales, demonstrating that the selected galaxies are likely associated with the large-scale structure surrounding the quasars. This first systematic study of $z\sim 7.5$ quasars shows a diverse set of quasar environments at the onset of their formation, providing empirical data to help constrain theoretical predictions of early structure formation.

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arXiv2024

Large Scale Overdensity of Lyman Break Galaxies Around the z=6.3 Ultraluminous Quasar J0100+2802

We study the environment of the z=6.33 ultraluminous quasar SDSS J010013.02+280225.8 (J0100) to understand its association with large-scale structure. Theoretical models propose high-redshift quasars as markers of galaxy overdensities residing in the most massive dark matter halos (DMHs) in the early universe. J0100 is an ultraluminous quasar with the most massive black hole known at z>6, suggesting a high likelihood of residing in a massive DMH. We present wide-field ($\sim$522 square arcminute) imaging in the r-, i-, and z-bands from the Large Binocular Camera on the Large Binocular Telescope, with Y- and J-band imaging from the Wide-field Infrared Camera on the Canada-France-Hawaii Telescope, centered on J0100. Applying color selections, we identify 23 objects as i-droput Lyman Break Galaxy (LBG) candidates in the J0100 field. We use the deep photometric catalog in the 1.27 square degree COSMOS field to calculate the density of LBGs in a blank field, and to estimate the selection completeness and purity. The observed surface density of LBG candidates in the J0100 field corresponds to a galaxy overdensity of $δ$=4 (at 8.4$σ$). This large-scale overdensity suggests that the $\sim$ 22 square arcminute overdensity found by Kashino et al. using JWST data extends out to much larger scales. We calculate the angular auto-correlation function of the candidates and find a positive correlation on $\lesssim$ 10 arcminute scales as well as evidence of asymmetries in their spatial distribution, further suggesting a direct detection of large-scale structure around the ultra-luminous quasar J0100.

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arXiv2023

COALAS II. Extended molecular gas reservoirs are common in a distant, forming galaxy cluster

This paper presents the results of 475 hours of interferometric observations with the Australia Telescope Compact Array towards the Spiderweb protocluster at $z=2.16$. We search for large, extended molecular gas reservoirs among 46 previously detected CO(1-0) emitters, employing a customised method we developed. Based on the CO emission images and position-velocity diagrams, as well as the ranking of sources using a binary weighting of six different criteria, we have identified 14 robust and 7 tentative candidates that exhibit large extended molecular gas reservoirs. These extended reservoirs are defined as having sizes greater than 40 kpc or super-galactic scale. This result suggests a high frequency of extended gas reservoirs, comprising at least $30 \%$ of our CO-selected sample. An environmental study of the candidates is carried out based on N-th nearest neighbour and we find that the large molecular gas reservoirs tend to exist in denser regions. The spatial distribution of our candidates is mainly centred on the core region of the Spiderweb protocluster. The performance and adaptability of our method are discussed. We found 13 (potentially) extended gas reservoirs located in nine galaxy (proto)clusters from the literature. We noticed that large extended molecular gas reservoirs surrounding (normal) star-forming galaxies in protoclusters are rare. This may be attributable to the lack of observations low-J CO transitions and the lack of quantitative analyses of molecular gas morphologies. The large gas reservoirs in the Spiderweb protocluster are a potential source of the intracluster medium seen in low redshift Virgo- or Coma-like galaxy clusters.

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arXiv2022

Missing Giants: Predictions on Dust-Obscured Galaxy Stellar Mass Assembly Throughout Cosmic Time

Due to their extremely dust-obscured nature, much uncertainty still exists surrounding the stellar mass growth and content in dusty, star-forming galaxies (DSFGs) at $z>1$. In this work, we present a numerical model built using empirical data on DSFGs to estimate their stellar mass contributions across the first $\sim$10 Gyr of cosmic time. We generate a dust-obscured stellar mass function that extends beyond the mass limit of star-forming stellar mass functions in the literature, and predict that massive DSFGs constitute as much as $50-100\%$ of all star-forming galaxies with M $\ge10^{11}$M$_\odot$ at $z>1$. We predict the number density of massive DSFGs and find general agreement with observations, although more data is needed to narrow wide observational uncertainties. We forward model mock massive DSFGs to their quiescent descendants and find remarkable agreement with observations from the literature demonstrating that, to first order, massive DSFGs are a sufficient ancestral population to describe the prevalence of massive quiescent galaxies at $z>1$. We predict that massive DSFGs and their descendants contribute as much as $25-60\%$ to the cosmic stellar mass density during the peak of cosmic star formation, and predict an intense epoch of population growth during the $\sim1$ Gyr from $z=6$ to 3 during which the majority of the most massive galaxies at high-$z$ grow and then quench. Future studies seeking to understand massive galaxy growth and evolution in the early Universe should strategize synergies with data from the latest observatories (e.g. JWST and ALMA) to better include the heavily dust-obscured galaxy population.

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arXiv2022

Probing cold gas in a massive, compact star-forming galaxy at z=6

Observations of low order CO transitions represent the most direct way to study galaxies' cold molecular gas, the fuel of star formation. Here we present the first detection of CO(2-1) in a galaxy lying on the main-sequence of star-forming galaxies at z>6. Our target, G09-83808 at z=6.03, has a short depletion time-scale of T_dep~50Myr and a relatively low gas fraction of M_gas/M_star=0.30 that contrasts with those measured for lower redshift main-sequence galaxies. We conclude that this galaxy is undergoing a starburst episode with a high star formation efficiency that might be the result of gas compression within its compact rotating disk. Its starburst-like nature is further supported by its high star formation rate surface density, thus favoring the use of the Kennicutt-Schmidt relation as a more precise diagnostic diagram for starbursts. Without further significant gas accretion, this galaxy would become a compact, massive quiescent galaxy at z~5.5. In addition, we find that the calibration for estimating ISM masses from dust continuum emission satisfactorily reproduces the gas mass derived from the CO(2-1) transition (within a factor of ~2). This is in line with previous studies claiming a small redshift evolution in the gas-to-dust ratio of massive, metal-rich galaxies. In the absence of gravitational amplification, this detection would have required of order ~1000h of observing time. The detection of cold molecular gas in unlensed star-forming galaxies at high redshifts is thus prohibitive with current facilities and requires a ten-fold improvement in sensitivity, such as that envisaged for the ngVLA.

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arXiv2019

Taking Census of Massive, Star-Forming Galaxies formed <1 Gyr After the Big Bang

Two decades of effort have been poured into both single-dish and interferometric millimeter-wave surveys of the sky to infer the volume density of dusty star-forming galaxies (DSFGs, with SFR>100M$_\odot$ yr$^{-1}$) over cosmic time. Though obscured galaxies dominate cosmic star-formation near its peak at $z\sim2$, the contribution of such heavily obscured galaxies to cosmic star-formation is unknown beyond $z\sim2.5$ in contrast to the well-studied population of Lyman-break galaxies (LBGs) studied through deep, space- and ground-based pencil beam surveys in the near-infrared. Unlocking the volume density of DSFGs beyond $z>3$, particularly within the first 1 Gyr after the Big Bang is critical to resolving key open questions about early Universe galaxy formation: (1) What is the integrated star-formation rate density of the Universe in the first few Gyr and how is it distributed among low-mass galaxies (e.g. Lyman-break galaxies) and high-mass galaxies (e.g. DSFGs and quasar host galaxies)? (2) How and where do the first massive galaxies assemble? (3) What can the most extreme DSFGs teach us about the mechanisms of dust production (e.g. supernovae, AGB stars, grain growth in the ISM) <1 Gyr after the Big Bang? We summarize the types of observations needed in the next decade to address these questions.

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arXiv2018

Science with an ngVLA: Imaging Cold Gas to 1 kpc Scales in High-Redshift Galaxies with the ngVLA

The next generation Very Large Array (ngVLA) will revolutionize our understanding of the distant Universe via the detection of cold molecular gas in the first galaxies. Its impact on studies of galaxy characterization via detailed gas dynamics will provide crucial insight on dominant physical drivers for star-formation in high redshift galaxies, including the exchange of gas from scales of the circumgalactic medium down to resolved clouds on mass scales of $\sim10^{5}\,M_\odot$. In this study, we employ a series of high-resolution, cosmological, hydrodynamic zoom simulations from the MUFASA simulation suite and a CASA simulator to generate mock ngVLA observations of a $z\sim4.5$ gas rich star-forming galaxy. Using the DESPOTIC radiative transfer code that encompasses simultaneous thermal, chemical, and statistical equilibrium in calculating the molecular and atomic level transitions of CO from ALMA for comparison. We find that observations of CO(1-0) are especially important for tracing the systemic redshift of the galaxy and the total mass of the well-shielded molecular gas reservoir, while even CO(2-1) can predominantly trace denser gas regions distinct from CO(1-0). The factor of 100 times improvement in mapping speed for the ngVLA beyond the Jansky VLA and the proposed ALMA Band 1 will make these detailed, high-resolution imaging and kinematic studies of CO(1-0) routine at $z\sim2-5$.

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