arXiv subjects

A. Trudeau

Publications and source records attributed to A. Trudeau.

6 recordsLinked to original sources

arXiv2026

Euclid: A blue galaxy population and a brightest cluster galaxy in the making in a $z\sim1.74$ MaDCoWS2 galaxy cluster candidate

We present an example cluster follow-up study with Euclid. Our target, a $z\sim 1.74$ candidate cluster nicknamed the 'Puddle', was initially discovered by the Massive and Distant Clusters of WISE Survey 2 as a $z_\mathrm{phot}\sim 1.65$ candidate cluster. It was also detected independently as a $z_\mathrm{phot}\sim 1.5$ candidate with the two cluster-finding algorithms in Euclid Quick Release 1 (Q1). A Keck MOSFIRE spectrum shows the brightest nucleus is at $z=1.74$ and is dominated by an active galactic nucleus. Our analysis focused on the galaxy population and the brightest cluster galaxy (BCG), and is based on Euclid and ancillary photometry. Compared to similar fields, we measured an overdensity of $110\pm 14$ galaxies with $H_\mathrm{E}\leq 22.25$ in a 2' radius around the BCG. About $18\pm 4$% of the completeness-corrected galaxy population is red, which is consistent with some clusters at $z>1.5$ but lower than others. Euclid imaging revealed that six or seven galaxies appear to be assembling to form the future BCG. Spectral energy distribution fitting suggests that the merging BCG has a stellar mass of $5.7\pm 0.3\times 10^{11}\,M_\odot$ and that it experienced a short burst of star formation $\sim 300\,$Myr ago. Its morphology and star-formation history suggest that the proto-BCG is a more evolved version of the merging core of SPT2349$-$56. These systems indicate that multiobject mergers might be a common BCG formation process. Assuming a similar density of mergers in the Euclid Wide Survey, we expect that Euclid will discover approximately 400 assembling BCGs by the end of its mission.

astro-ph.GA↗

arXiv2026

The Massive and Distant Clusters of WISE Survey 2: Detection of splashback radii in galaxy cluster total light stacks

The splashback radius, the radius of the apocenter of the first orbit of infalling material, is a measurable quantity marking the boundary between a galaxy cluster and its infalling region. We report detections of splashback radii in total light stacks, i.e. image stacks centered on the cores of galaxy clusters. Our analysis uses Wide-field Infrared Survey Explorer (WISE) W1 and W2 images of 83,345 candidate clusters at $0.5 \lesssim z \lesssim 1.9$ from the Massive and Distant Clusters of WISE Survey 2 (MaDCoWS2). The clusters are organized in stacks by redshift and signal-to-noise ($S\slash N$) ratios. We adopt a statistical approach, using 1000 bootstrap realizations to determine the median projected splashback radius and its confidence interval in a given bin. We compare our splashback radii with the measurements made by K. Thongkham et al. on a similar sample of MaDCoWS2 clusters using galaxy-cluster cross-correlation and find that they are consistent, although our method yields larger error bars. Our main systematic error is the accuracy of the background subtraction, but its impact remains small: the consistency of K. Thongkham et al. and our results suggests that neither method suffers from large systematics. The sensitivity of total light stacking to the contribution of faint galaxies can be advantageous to locate splashback radii when only the brightest galaxies are detected in individual images, such as at high redshifts. We present a potential application of this new technique to probe the evolution of the stellar mass in cluster infalling regions.

astro-ph.CO↗

arXiv2024

The Massive and Distant Clusters of WISE Survey 2: A Stacking Analysis Investigating the Evolution of Star Formation Rates and Stellar Masses in Groups and Clusters

The evolution of galaxies depends on their masses and local environments; understanding when and how environmental quenching starts to operate remains a challenge. Furthermore, studies of the high-redshift regime have been limited to massive cluster members, owing to sensitivity limits or small fields of views when the sensitivity is sufficient, intrinsically biasing the picture of cluster evolution. In this work, we use stacking to investigate the average star formation history of more than 10,000 groups and clusters drawn from the Massive and Distant Clusters of WISE Survey 2 (MaDCoWS2). Our analysis covers near ultraviolet to far infrared wavelengths, for galaxy overdensities at $0.5 \lesssim z \lesssim 2.54$. We employ SED fitting to measure the specific star formation rates (sSFR) in four annular apertures with radii between 0 and 1000 kpc. At $z \gtrsim 1.6$, the average sSFR evolves similarly to the field in both the core and the cluster outskirts. Between $\overline{z} = 1.60$ and $\overline{z} = 1.35$, the sSFR in the core drops sharply, and continues to fall relative to the field sSFR at lower redshifts. We interpret this change as evidence that the impact of environmental quenching dramatically increases at $z \sim 1.5$, with the short time span of the transition suggesting that the environmental quenching mechanism dominant at this redshift operates on a rapid timescale. We find indications that the sSFR may decrease with increasing host halo mass, but lower-scatter mass tracers than the signal-to-noise ratio (S/N) are needed to confirm this relationship.

astro-ph.GA↗

arXiv2022

The XXL survey. XLIX. Linking the members star formation histories to the cluster mass assembly in the z=1.98 galaxy cluster XLSSC 122

The most massive protoclusters virialize to become clusters at $z\sim 2$, which is also a critical epoch for the evolution of their member galaxies. XLSSC 122 is a $z=1.98$ galaxy cluster with 37 spectroscopically confirmed members. We aim to characterize their star formation histories and to put them in the context of the cluster accretion history. We measure their photometry in 12 bands and create a PSF-matched catalogue of the cluster members. We employ BAGPIPES to fit star formation histories characterized by exponentially decreasing star-forming rates. Stellar masses, metal and dust contents are also treated as free parameters. The oldest stars in the red-sequence galaxies display a range of ages, from 0.5 Gyr to over $\sim$3 Gyrs. Characteristic times are between $\sim$0.1 and $\sim$0.3 Gyr, and the oldest members present the longest times. Using MultiDark Planck 2 dark matter simulations, we calculate the assembly of XLSSC 122-like haloes, weighted by the age posteriors of the oldest members. We found that 74% of these haloes were less than 10% assembled at the onset of star formation, declining to 67% of haloes when such galaxies had formed 50% of their z=1.98 stellar masses. When 90% of their stellar masses were formed, 75% of the haloes were less than 30% assembled. The star formation histories of the red-sequence galaxies seem consistent with episodes of star formation with short characteristic times. Onset and cessation of star formation in the oldest galaxies are both likely to precede XLSSC 122 virialization.

astro-ph.GA↗

arXiv2020

The XXL survey: XLII. Detection and characterization of the galaxy population of distant galaxy clusters in the XXL-N/VIDEO field: A tale of variety

Context. Distant galaxy clusters provide an effective laboratory in which to study galaxy evolution in dense environments and at early cosmic times. Aims. We aim to identify distant galaxy clusters as extended X-ray sources coincident with overdensities of characteristically bright galaxies. Methods. We use optical and near-infrared (NIR) data from the Hyper Suprime-Cam (HSC) and VISTA Deep Extragalactic Observations (VIDEO) surveys to identify distant galaxy clusters as overdensities of bright, $z_{phot}\geq 0.8$ galaxies associated with extended X-ray sources detected in the ultimate XMM extragalactic survey (XXL). Results. We identify a sample of 35 candidate clusters at $0.80\leq z\leq 1.93$ from an approximately 4.5 deg$^2$ sky area. This sample includes 15 newly discovered candidate clusters, ten previously detected but unconfirmed clusters, and ten spectroscopically confirmed clusters. Although these clusters host galaxy populations that display a wide variety of quenching levels, they exhibit well-defined relations between quenching, cluster-centric distance, and galaxy luminosity. The brightest cluster galaxies (BCGs) within our sample display colours consistent with a bimodal population composed of an old and red subsample together with a bluer, more diverse subsample. Conclusions. The relation between galaxy masses and quenching seem to be already in place at $z\sim 1$, although there is no significant variation of the quenching fraction with the cluster-centric radius. The BCG bimodality might be explained by the presence of a younger stellar component in some BCGs but additional data are needed to confirm this scenario.

astro-ph.CO↗

arXiv2020

Evidence of runaway gas cooling in the absence of supermassive black hole feedback at the epoch of cluster formation

Cosmological simulations, as well as mounting evidence from observations, have shown that supermassive black holes play a fundamental role in regulating the formation of stars throughout cosmic time. This has been clearly demonstrated in the case of galaxy clusters in which powerful feedback from the central black hole is preventing the hot intracluster gas from cooling catastrophically, thus reducing the expected star formation rates by orders of magnitude. These conclusions have however been almost entirely based on nearby clusters. Based on new Chandra X-ray observations, we present the first observational evidence for massive, runaway cooling occurring in the absence of supermassive black hole feedback in the high-redshift galaxy cluster SpARCS104922.6+564032.5 ($z=1.709$). The hot intracluster gas appears to be fueling a massive burst of star formation ($\approx900$~M$_\odot$yr$^{-1}$) that is offset by dozens of kpc from the central galaxy. The burst is co-spatial with the coolest intracluster gas but not associated with any galaxy in the cluster. In less than 100 million years, such runaway cooling can form the same amount of stars as in the Milky Way. Intracluster stars are therefore not only produced by tidal stripping and the disruption of cluster galaxies, but can also be produced by runaway cooling of hot intracluster gas at early times. Overall, these observations show the dramatic impact when supermassive black hole feedback fails to operate in clusters. They indicate that in the highest overdensities such as clusters and proto-clusters, runaway cooling may be a new and important mechanism for fueling massive bursts of star formation in the early universe.

astro-ph.GA↗