We investigate the intracluster light (ICL) in the six Hubble Frontier Field clusters at 0.3 < z < 0.6 . We employ a new method, which is free from any functional form of the ICL profile, and exploit ...the unprecedented depth of this Hubble Space Telescope imaging to map the ICL's diffuse light out to clustrocentric radii R ∼ 300 kpc ( ICL ∼ 27 mag arcsec−2). From these maps, we construct radial color and stellar mass profiles via SED fitting and find clear negative color gradients in all systems with increasing distance from the Brightest Cluster Galaxy (BCG). While this implies older/more metal-rich stellar components in the inner part of the ICL, we find that the ICL mostly consists of a 2 Gyr population, and plausibly originated with log M * M 10 cluster galaxies. Furthermore, we find that 10%-15% of the ICL's mass at large radii ( 150 kpc) lies in a younger/bluer stellar population (∼1 Gyr), a phenomenon not seen in local samples. We attribute this light to the higher fraction of star-forming/(post-)starburst galaxies in clusters at z ∼ 0.5 . Ultimately, we find the ICL's total mass to be log M * ICL M ∼ 11 -12, constituting 5%-20% of the clusters' total stellar mass, or about half of the value at z ∼ 0 . The above implies distinct formation histories for the ICL and BCGs/other massive cluster galaxies; i.e., the ICL at this epoch is still being constructed rapidly ( ∼ 40 M yr−1), while the BCGs have mostly completed their evolution. To be consistent with the ICL measurements of local massive clusters, such as Virgo, our data suggest mass acquisition mainly from quiescent cluster galaxies is the principal source of ICL material in the subsequent ∼5 Gyr of cosmic time.
Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP) program, we compare the integrated star formation rate-mass relation (SFR-M*) relation of 42 cluster galaxies ...undergoing ram-pressure stripping (RPS; "stripping galaxies") to that of 32 field and cluster undisturbed galaxies. Theoretical predictions have so far led to contradictory conclusions about whether or not ram pressure can enhance the star formation (SF) in the gas disks and tails, and until now a statistically significant observed sample of stripping galaxies was lacking. We find that stripping galaxies occupy the upper envelope of the control sample SFR-M* relation, showing a systematic enhancement of the SFR at any given mass. The star formation enhancement occurs in the disk (0.2 dex), and additional SF takes place in the tails. Our results suggest that strong RPS events can moderately enhance the SF also in the disk prior to gas removal.
GASP XIII. Star formation in gas outside galaxies Poggianti, Bianca M; Gullieuszik, Marco; Tonnesen, Stephanie ...
Monthly notices of the Royal Astronomical Society,
02/2019, Letnik:
482, Številka:
4
Journal Article
Abstract
It is well known that galaxies falling into clusters can experience gas stripping due to ram pressure by the intra-cluster medium. The most spectacular examples are galaxies with extended ...tails of optically bright stripped material known as ‘jellyfish’. We use the first large homogeneous compilation of jellyfish galaxies in clusters from the WINGS and OmegaWINGS surveys, and follow-up MUSE observations from the GASP MUSE programme to investigate the orbital histories of jellyfish galaxies in clusters and reconstruct their stripping history through position versus velocity phase-space diagrams. We construct analytic models to define the regions in phase-space where ram-pressure stripping is at play. We then study the distribution of cluster galaxies in phase-space and find that jellyfish galaxies have on average higher peculiar velocities (and higher cluster velocity dispersion) than the overall population of cluster galaxies at all cluster-centric radii, which is indicative of recent infall into the cluster and radial orbits. In particular, the jellyfish galaxies with the longest gas tails reside very near the cluster cores (in projection) and are moving at very high speeds, which coincides with the conditions of the most intense ram pressure. We conclude that many of the jellyfish galaxies seen in clusters likely formed via fast (∼1–2 Gyr), incremental, outside-in ram-pressure stripping during first infall into the cluster in highly radial orbits.
Abstract
We present the results of a first search for galaxy candidates at
z
∼ 9–15 on deep seven-band NIRCam imaging acquired as part of the GLASS-James Webb Space Telescope (JWST) Early Release ...Science Program on a flanking field of the Frontier Fields cluster A2744. Candidates are selected via two different renditions of the Lyman-break technique, isolating objects at
z
∼ 9–11, and
z
∼ 9–15, respectively, supplemented by photometric redshifts obtained with two independent codes. We find five color-selected candidates at
z
> 9, plus one additional candidate with photometric redshift
z
phot
≥ 9. In particular, we identify two bright candidates at
M
UV
≃ −21 that are unambiguously placed at
z
≃ 10.6 and
z
≃ 12.2, respectively. The total number of galaxies discovered at
z
> 9 is in line with the predictions of a nonevolving luminosity function. The two bright ones at
z
> 10 are unexpected given the survey volume, although cosmic variance and small number statistics limits general conclusions. This first search demonstrates the unique power of JWST to discover galaxies at the high-redshift frontier. The candidates are ideal targets for spectroscopic follow-up in Cycle-2.
ABSTRACT Knowledge of galaxy evolution rests on cross-sectional observations of different objects at different times. Understanding of galaxy evolution rests on longitudinal interpretations of how ...these data relate to individual objects moving through time. The connection between the two is often assumed to be clear, but we use a simple "physics-free" model to show that it is not and that exploring its nuances can yield new insights. Comprising nothing more than 2094 loosely constrained lognormal star formation histories (SFHs), the model faithfully reproduces the following data it was not designed to match: stellar mass functions at the slope of the star formation rate/stellar mass relation (the SFR "Main Sequence") at the mean of low-mass galaxies at "fast-" and "slow-track" quenching; downsizing; and a correlation between formation timescale and similar to results from simulations that provides a natural connection to bulge growth. We take these findings-which suggest that quenching is the natural downturn of all SFHs affecting galaxies at rates/times correlated with their densities-to mean that: (1) models in which galaxies are diversified on Hubble timescales by something like initial conditions rival the dominant grow-and-quench framework as good descriptions of the data; or (2) absent spatial information, many metrics of galaxy evolution are too undiscriminating-if not inherently misleading-to confirm a unique explanation. We outline future tests of our model but stress that, even if ultimately incorrect, it illustrates how exploring different paradigms can aid learning and, we hope, more detailed modeling efforts.
Large surveys of galaxy clusters with the Hubble Space Telescope (HST) and Spitzer, including the Cluster Lensing And Supernova survey with Hubble 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, described here. Our 188-orbit Hubble Treasury Program observed 41 clusters at 0.182 ≤ z ≤ 0.972 with Advanced Camera for Surveys (ACS) and WFC3/IR imaging spanning 0.4-1.7 m. We selected 21 of the most massive clusters known based on Planck PSZ2 estimates and 20 additional clusters based on observed or inferred lensing strength. RELICS observed 46 WFC3/IR pointings (∼200 arcmin2) each 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 over 300 z ∼ 6-10 candidates, including the brightest z ∼ 6 candidates known, and the most distant spatially resolved lensed arc known at z ∼ 10. Spitzer IRAC imaging (945 hr awarded, plus 100 archival, spanning 3.0-5.0 m) 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. Reduced HST images, catalogs, and lens models are available on MAST, and reduced Spitzer images are available on IRSA.
Within the GASP survey, aimed at studying the effect of ram pressure stripping on star formation quenching in cluster galaxies, we analyze here ALMA observations of the jellyfish galaxy JW100. We ...find an unexpected large amount of molecular gas (∼2.5 × 1010 ), 30% of which is located in the stripped gas tail out to ∼35 kpc from the galaxy center. The overall kinematics of the molecular gas is similar to the one shown by the ionized gas, but for clear signatures of double components along the stripping direction detected only out to 2 kpc from the disk. The line ratio r21 has a clumpy distribution and in the tail can reach large values (≥1), while its average value is low (0.58 with a 0.15 dispersion). All these evidence strongly suggest that the molecular gas in the tail is newly born from stripped H i gas or newly condensed from stripped diffuse molecular gas. The analysis of interferometric data at different scales reveals that a significant fraction (∼40%) of the molecular gas is extended over large scales (≥8 kpc) in the disk, and this fraction becomes predominant in the tail (∼70%). By comparing the molecular gas surface density with the star formation rate surface density derived from the H emission from MUSE data, we find that the depletion time on 1 kpc scale is particularly large (5-10 Gyr) both within the ram-pressure-disturbed region in the stellar disk and in the complexes along the tail.
With MUSE, Chandra, VLA, ALMA, and UVIT data from the GASP program, we study the multiphase baryonic components in a jellyfish galaxy (JW100) with a stellar mass 3.2 × 1011 M hosting an active ...galactic nucleus (AGN). We present its spectacular extraplanar tails of ionized and molecular gas, UV stellar light, and X-ray and radio continuum emission. This galaxy represents an excellent laboratory to study the interplay between different gas phases and star formation and the influence of gas stripping, gas heating, and AGNs. We analyze the physical origin of the emission at different wavelengths in the tail, in particular in situ star formation (related to H , CO, and UV emission), synchrotron emission from relativistic electrons (producing the radio continuum), and heating of the stripped interstellar medium (ISM; responsible for the X-ray emission). We show the similarities and differences of the spatial distributions of ionized gas, molecular gas, and UV light and argue that the mismatch on small scales (1 kpc) is due to different stages of the star formation process. We present the relation H -X-ray surface brightness, which is steeper for star-forming regions than for diffuse ionized gas regions with a high O i/H ratio. We propose that ISM heating due to interaction with the intracluster medium (either for mixing, thermal conduction, or shocks) is responsible for the X-ray tail, observed O i excess, and lack of star formation in the northern part of the tail. We also report the tentative discovery in the tail of the most distant (and among the brightest) currently known ULX, a pointlike ultraluminous X-ray source commonly originating in a binary stellar system powered by either an intermediate-mass black hole or a magnetized neutron star.
Massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. We present here ...the candidate high-redshift galaxies from the Reionization Lensing Cluster Survey (RELICS), a Hubble and Spitzer Space Telescope survey of 41 massive galaxy clusters spanning an area of 200 arcmin2. These clusters were selected to be excellent lenses, and we find similar high-redshift sample sizes and magnitude distributions as the Cluster Lensing And Supernova survey with Hubble (CLASH). We discover 257, 57, and eight candidate galaxies at z ∼ 6, 7, and 8 respectively, (322 in total). The observed (lensed) magnitudes of the z ∼ 6 candidates are as bright as AB mag ∼23, making them among the brightest known at these redshifts, comparable with discoveries from much wider, blank-field surveys. RELICS demonstrates the efficiency of using strong gravitational lenses to produce high-redshift samples in the epoch of reionization. These brightly observed galaxies are excellent targets for follow-up study with current and future observatories, including the James Webb Space Telescope.
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