arXiv subjects

Brian Welch

Publications and source records attributed to Brian Welch.

41 records · Page 3Linked to original sources

arXiv2021

Galaxy Science with ORCAS: Faint Star-Forming Clumps to AB$\leq$31 mag and r$_e$$\geq$ 0.01"

The NASA concept mission ORCAS (Orbiting Configurable Artificial Star) aims to provide near diffraction-limited angular resolution at visible and near-infrared wavelengths using laser signals from space-based cubesats as Adaptive Optics beacons for ground-based 8-30 meter telescopes, in particular the 10 meter Keck Telescopes. When built as designed, ORCAS+Keck would deliver images of ~0.01-0.02" FWHM at 0.5-1.2 micron wavelength that reach AB<31 mag for point sources in a few hours over a 5x5" FOV that includes IFU capabilities. We summarize the potential of high-resolution faint galaxy science with ORCAS. We show that the ability to detect optical-near-IR point sources with r_e>0.01" FWHM to AB<31 mag will yield about 5.0x10^6 faint star-forming (SF) clumps per square degree, or ~0.4 per arcsec^2. From recent HST lensing data, the typical intrinsic (unlensed) sizes of SF clumps at z~1-7 will be r_e ~1-80 m.a.s. to AB<31 mag, with intrinsic (unmagnified) fluxes as faint as AB<35-36 mag when searching with ORCAS around the critical curves of lensing clusters imaged with HST and JWST. About half of these SF clumps will have sizes below the ORCAS diffraction limit, and the other half will be slightly resolved, but still mostly above the ORCAS surface brightness (SB) limits. ORCAS will address how galaxies assemble from smaller clumps to stable disks by measuring ages, metallicities, and gradients of clumps within galaxies. ORCAS can monitor caustic transits of individual stars in SF clumps at z>1-2 that have been detected with HST, and those that may be detected with JWST at z>6 at extreme magnifications (mu>10^3-10^5) for the first stars and their stellar mass black hole accretion disks. ORCAS provides a unique opportunity to obtain a statistical census of individual stars at cosmological distances, leveraging the largest telescopes only available on the ground.

astro-ph.GA↗

arXiv2020

RELICS: A Very Large ($θ_{E}\sim40"$) Cluster Lens -- RXC J0032.1+1808

Extensive surveys with the \textit{Hubble Space Telescope} (HST) over the past decade, targeting some of the most massive clusters in the sky, have uncovered dozens of galaxy-cluster strong lenses. The massive cluster strong-lens scale is typically $θ_{E}\sim10\arcsec$ to $\sim30-35\arcsec$, with only a handful of clusters known with Einstein radii $θ_{E}\sim40\arcsec$ or above (for $z_{source}=2$, nominally). Here we report another very large cluster lens, RXC J0032.1+1808 ($z=0.3956$), the second richest cluster in the redMapper cluster catalog and the 85th most massive cluster in the Planck Sunyaev-Zel'dovich catalog. With our Light-Traces-Mass and fully parametric (dPIEeNFW) approaches, we construct strong lensing models based on 18 multiple images of 5 background galaxies newly identified in the \textit{Hubble} data mainly from the \textit{Reionization Lensing Cluster Survey} (RELICS), in addition to a known sextuply imaged system in this cluster. Furthermore, we compare these models to Lenstool and GLAFIC models that were produced independently as part of the RELICS program. All models reveal a large effective Einstein radius of $θ_{E}\simeq40\arcsec$ ($z_{source}=2$), owing to the obvious concentration of substructures near the cluster center. Although RXC J0032.1+1808 has a very large critical area and high lensing strength, only three magnified high-redshift candidates are found within the field targeted by RELICS. Nevertheless, we expect many more high-redshift candidates will be seen in wider and deeper observations with \textit{Hubble} or \emph{JWST}. Finally, the comparison between several algorithms demonstrates that the total error budget is largely dominated by systematic uncertainties.

astro-ph.CO↗

arXiv2020

Galaxy Cluster Contribution to the Diffuse Extragalactic Ultraviolet Background

The diffuse ultraviolet background radiation has been mapped over most of the sky with 2\arcmin \ resolution using data from the \textit{GALEX} survey. We utilize this map to study the correlation between the UV background and clusters of galaxies discovered via the Sunyaev-Zeldovich effect in the \textit{Planck} survey. We use only high Galactic latitude ($|b| > 60^{\circ} $) galaxy clusters to avoid contamination by Galactic foregrounds, and we only analyze clusters with a measured redshift. This leaves us with a sample of 142 clusters over the redshift range $0.02 \leq z \leq 0.72$, which we further subdivide into four redshift bins. In analysing our stacked samples binned by redshift, we find evidence for a central excess of UV background light compared to local backgrounds for clusters with $z<0.3$. We then stacked these $z<0.3$ clusters to find a statistically significant excess of $12 \pm 2.3$ photon cm$^{-2}$ s${-1}$ sr$^{-1}$ Å$^{-1}$ \ over the median of $\sim 380$ photon cm$^{-2}$ s${-1}$ sr$^{-1}$ Å$^{-1}$ \ measured around random blank fields. We measure the stacked radial profile of these clusters, and find that the excess UV radiation decays to the level of the background at a radius of $\sim 1$ Mpc, roughly consistent with the maximum radial extent of the clusters. Analysis of possible physical processes contributing to the excess UV brightness indicates that non-thermal emission from relativistic electrons in the intracluster medium and faint, unresolved UV emission from cluster member galaxies and intracluster light are likely the dominant contributors.

astro-ph.GA↗

arXiv2019

RELICS: Reionization Lensing Cluster Survey

Large surveys of galaxy clusters with the Hubble and Spitzer Space Telescopes, including CLASH and the Frontier Fields, have demonstrated the power of strong gravitational lensing to efficiently deliver large samples of high-redshift galaxies. We extend this strategy through a wider, shallower survey named RELICS, the Reionization Lensing Cluster Survey. This survey, described here, was designed primarily to deliver the best and brightest high-redshift candidates from the first billion years after the Big Bang. RELICS observed 41 massive galaxy clusters with Hubble and Spitzer at 0.4-1.7um and 3.0-5.0um, respectively. We selected 21 clusters based on Planck PSZ2 mass estimates and the other 20 based on observed or inferred lensing strength. Our 188-orbit Hubble Treasury Program obtained the first high-resolution near-infrared images of these clusters to efficiently search for lensed high-redshift galaxies. We observed 46 WFC3/IR pointings (~200 arcmin^2) with two orbits divided among four filters (F105W, F125W, F140W, and F160W) and ACS imaging as needed to achieve single-orbit depth in each of three filters (F435W, F606W, and F814W). As previously reported by Salmon et al., we discovered 322 z ~ 6 - 10 candidates, including the brightest known at z ~ 6, and the most distant spatially-resolved lensed arc known at z ~ 10. Spitzer IRAC imaging (945 hours awarded, plus 100 archival) has crucially enabled us to distinguish z ~ 10 candidates from z ~ 2 interlopers. For each cluster, two HST observing epochs were staggered by about a month, enabling us to discover 11 supernovae, including 3 lensed supernovae, which we followed up with 20 orbits from our program. We delivered reduced HST images and catalogs of all clusters to the public via MAST and reduced Spitzer images via IRSA. We have also begun delivering lens models of all clusters, to be completed before the JWST GO call for proposals.

astro-ph.GA↗

arXiv2018

Weak-lensing calibration of a stellar mass-based mass proxy for redMaPPer and Voronoi Tessellation clusters in SDSS Stripe 82

We present the first weak lensing calibration of $μ_{\star}$, a new galaxy cluster mass proxy corresponding to the total stellar mass of red and blue members, in two cluster samples selected from the SDSS Stripe 82 data: 230 redMaPPer clusters at redshift $0.1\leq z<0.33$ and 136 Voronoi Tessellation (VT) clusters at $0.1 \leq z < 0.6$. We use the CS82 shear catalog and stack the clusters in $μ_{\star}$ bins to measure a mass-observable power law relation. For redMaPPer clusters we obtain $M_0 = (1.77 \pm 0.36) \times 10^{14}h^{-1} M_{\odot}$, $α= 1.74 \pm 0.62$. For VT clusters, we find $M_0 = (4.31 \pm 0.89) \times 10^{14}h^{-1} M_{\odot}$, $α= 0.59 \pm 0.54$ and $M_0 = (3.67 \pm 0.56) \times 10^{14}h^{-1} M_{\odot}$, $α= 0.68 \pm 0.49$ for a low and a high redshift bin, respectively. Our results are consistent, internally and with the literature, indicating that our method can be applied to any cluster finding algorithm. In particular, we recommend that $μ_{\star}$ be used as the mass proxy for VT clusters. Catalogs including $μ_{\star}$ measurements will enable its use in studies of galaxy evolution in clusters and cluster cosmology.

astro-ph.CO↗