arXiv subjects

Matteo Fossati

Publications and source records attributed to Matteo Fossati.

At least 37 records · Page 2Linked to original sources

arXiv2025

The impact of ram pressure on cluster galaxies, insights from GAEA and TNG

Ram pressure stripping (RPS) has a non-negligible impact on the gas content of cluster galaxies. We use the semi-analytic model GAEA and the hydro-simulation TNG to investigate whether cluster galaxies suffer a strong RPS that is sufficient to remove a significant fraction of their gas during the first pericentric passage. We estimate that a ram pressure of $10^{-10.5}$, $10^{-12} $, $10^{-13.5} $ $g cm^{-1} s^{-2}$ can remove at most $90\%$, $50\%$, and $20\%$ of the cold gas reservoir from low-mass galaxies with $9<\log M_{\star}/{\rm M}_{\odot} <9.5$, assuming the gas can be stripped instantaneously. We then use this information to divide the phase space diagram into `strong', `moderate', `weak', and `no' RPS zones. By tracing the orbit of galaxies since $2.5R_{vir}$, we find in both GAEA and TNG that about half of the galaxies in Virgo-like halos ($\log M_h / M_{\odot} \sim 14 $) did not suffer strong RPS during the first pericentric passage. In Coma-like halos ($\log M_h / M_{\odot} \sim 15$), almost all galaxies have suffered strong RPS during the first pericentric passage, which can remove all gas from low-mass galaxies but is insufficient to significantly reduce the gas content of more massive galaxies. In general, results from TNG and GAEA are consistent, with the RPS being only slightly stronger in TNG than in GAEA. Our findings suggest that most cluster galaxies will maintain a notable fraction of their gas and continue forming stars after the first pericentric passage, except for those with low stellar mass ($\log M_{\star}/{\rm M}_{\odot} <9.5$) in very massive halos ($\log M_{h}/{\rm M}_{\odot} > 15$).

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arXiv2025

The MUSE Ultra Deep Field: A 5 Mpc stretch of the z $\approx$ 4 cosmic web revealed in emission

We detect Ly$α$ emission from a ~5 Mpc-long (comoving) portion of the cosmic web hosting an overdensity ($δ\approx 25$) of 19 Ly$α$ emitters (LAEs) at $z\approx 4$ within the MUSE Ultra Deep Field (MUDF), reaching an average surface brightness (SB) of $5\times 10^{-20}~\rm{erg~s^{-1}~ cm^{-2}~arcsec^{-2}}$. This large-scale structure has an average SB similar to the filament across the two MUDF quasars at $z\approx 3.22$. However, deep multiwavelength data do not show a clear presence of active galactic nuclei, suggesting that the emission is mainly regulated by the underlying gas density. We find $\approx 0.2$ dex higher star formation compared to control samples and a remarkable predominance (5/7) of blue-peaked emission lines in the spectra of the embedded LAEs, indicative of favorable conditions for gas accretion. Lastly, we quantify the contribution of intragalactic gas to the Ly$α$ SB profile at large distances from LAEs. By studying samples of filaments detected in emission within diverse environments, we are finally gaining new insight into the physics of gas accretion within the cosmic web.

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arXiv2025

High-definition imaging of a filamentary connection between a close quasar pair at z=3

Filaments connecting halos are a long-standing prediction of cold dark matter theories. We present a detection of the cosmic web emission connecting two quasar-host galaxies at redshift z ~3.22 in the MUSE Ultra Deep Field (MUDF). The very deep observations unlock a high-definition view of the filament morphology, a measure of the transition radius between the intergalactic and circumgalactic medium, and the characterization of the surface brightness profiles along the filament and in the transverse direction. Through systematic comparisons with simulations, we validate the filaments' typical density predicted in the current cold dark-matter model. Our analysis of the MUDF field, an excellent laboratory for quantitatively studying filaments in emission, opens a new avenue to constrain the physical properties of the cosmic web and to trace the distribution of dark matter on large scales.

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arXiv2024

Modeling Mg II resonance doublet spectra from galaxy haloes at z $\sim$ 1

We investigate the properties of cold gas at $10^4~\rm K$ around star-forming galaxies at $z~\sim~1$ using Mg II spectra through radiative transfer modeling. We utilize a comprehensive dataset of 624 galaxies from the MAGG and MUDF programs. We focus on Mg II emission from galaxies and their outskirts to explore the cold gas within galaxies and the circumgalactic medium (CGM). We model Mg II spectra for 167 individual galaxies and stacked data for different stellar mass bins. The Mg II spectrum and surface brightness vary significantly with stellar mass. In low-mass galaxies ($M_*/M_\odot<10^9$), Mg II emission is observed in both core ($R_{\rm p}<$ 10 kpc) and halo regions (10 kpc $ 10^{10}$), strong core absorption and more extended halo emission are prominent. This indicates that more massive galaxies have more cold gas. Radiative transfer modeling allows us to investigate key parameters such as the Mg II column density $N_{\rm MgII}$ and the outflow velocity $v_{\rm exp}$. We identify a negative correlation between $N_{\rm MgII}$ and $v_{\rm exp}$. Since higher stellar mass galaxies exhibit a higher $N_{\rm MgII}$ and lower $v_{\rm exp}$, this suggests an abundance of slowly moving cold gas in massive galaxies. In addition, the fitting results of halo spectra indicate the presence of intrinsic Mg II absorption and strong anisotropy of the cold gas distribution around massive galaxies. This study is not only a proof-of-concept of modeling spatially varying Mg II spectra but also enhances our understanding of the CGM and provides insights into the mass-dependent properties of cold gas in and around galaxies.

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arXiv2024

Baryonic Ecosystem in Galaxies (BEINGMgII). Host Galaxies of Ultra-strong MgII Absorbers in Subaru Hyper Suprime-Cam Survey

We study the galaxies hosting ultra-strong MgII (USMgII) absorbers at small impact parameters of $\sim$2" (5 - 20 kpc), spanning a redshift range of $0.4 \le z \le 1.7$, using deep, high-resolution images from Hyper Suprime-Cam Subaru Strategic Survey and spectra from SDSS survey. From a total of 418 USMgII absorbers with $W_{2796}\ \ge 3 \mathring{A}$, along 412 quasar sightlines, we detect 50 galaxies based on [O II] $λλ$3727,3729 nebular emission detected at $\ge 2σ$ level. Utilizing the [O II] emission from the stacked spectrum and employing the best-fit galaxy SED template, we further identify 86 galaxies, leading to a total of 136 bona fide USMgII galaxies. With a prerequisite of having a minimum of four HSC passbands available, we find a detection rate of $\sim$38% at an average impact parameter of 11.4 kpc. We find that galaxies hosting USMgII systems are typically star-forming main sequence galaxies, with 21% exhibiting a starburst nature. The non-zero [O II] emission along the `clear' sightlines, with no stellar counterpart, hints that the USMgII absorbers may likely emanate from the unseen faint galaxies near the quasar. The USMgII absorbers preferentially align along the major and minor axes of the galaxy, which suggests that they originate in the disk or large-scale wind. We show that the distribution of $W_{2796}$ as a function of impact parameter indicates a discernible radial dependence for the `disk' and `wind' subsets, with the observed large scatter in $W_{2796}$ potentially attributed to large-scale outflows. The quasar sightline hosting USMgII systems show a factor three higher galaxy surface density at impact parameters of $\lesssim 50$kpc, highlights the multiple pathways giving rise to USMgII absorption.

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arXiv2024

Can AGN activity be enhanced by ram pressure stripping? -- X-ray perspective

Ram pressure stripping (RPS) is an important process that plays a significant role in shaping the evolution of cluster galaxies and their surrounding environment. Despite its recognized significance, the potential connection between RPS and AGN activity in cluster galaxies remains poorly understood. Recent claims, based on optical emission line diagnostics, have suggested such a connection. Here, we investigate this relationship from an X-ray perspective using a sample of galaxies undergoing RPS in four nearby galaxy clusters - A1656, A1367, A426, and A3627. This study is the first to test such a connection from an X-ray standpoint. Our analysis reveals no signs of enhanced X-ray AGN activity in our sample, with most RPS galaxies ($\sim$ $90\%$) showing X-ray luminosities below $10^{41}$ erg s$^{-1}$ in their central point sources. Moreover, there is no noticeable difference in X-ray AGN activity among RPS galaxies compared to a control sample of non-RPS galaxies, as demonstrated by similar X-ray luminosities observed in their central point sources. While the most luminous X-ray AGN in our sample is found in ESO 137-002, a galaxy undergoing RPS in A3627, there is no evidence for a widespread enhancement of X-ray AGN activity due to RPS. Given the limited sample size of our study, this could also indicate that either the X-ray AGN enhancement from RPS is at most weak, or the timescale for the X-ray AGN enhancement is short. This emphasizes the need for further investigations with larger X-ray samples to better understand the impact of RPS on AGN activity in cluster galaxies.

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arXiv2024

A Giant Disk Galaxy Two Billion Years After The Big Bang

Observational studies showed that galaxy disks are already in place in the first few billion years of the universe. The early disks detected so far, with typical half-light radii of 3 kiloparsecs at stellar masses around 10^11 M_sun for redshift z~3, are significantly smaller than today's disks with similar masses, in agreement with expectations from current galaxy models. Here, we report observations of a giant disk at z=3.25, when the universe was only 2 billion years old, with a half-light radius of 9.6 kiloparsecs and stellar mass of 3.7^+2.6_-2.2x10^11 M_sun. This galaxy is larger than any other kinematically-confirmed disks at similar epochs and surprisingly similar to today's largest disks regarding size and mass. JWST imaging and spectroscopy reveal its spiral morphology and a rotational velocity consistent with local Tully-Fisher relation. Multi-wavelength observations show that it lies in an exceptionally dense environment, where the galaxy number density is over ten times higher than the cosmic average and mergers are frequent. The discovery of such a giant disk suggests the presence of favorable physical conditions for large-disk formation in dense environments in the early universe, which may include efficient accretion of gas carrying coherent angular momentum and non-destructive mergers between exceptionally gas-rich progenitor galaxies.

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arXiv2024

The stellar population of a $z\sim3.25$ Ly$α$ emitting group associated with a damped Ly$α$ absorber

We present near-infrared observations, acquired with the Wide Field Camera 3 (WFC3) on board of the Hubble Space Telescope (HST), of a Ly$α$ double-clumped emitting nebula at $z \approx 3.25$ associated with a damped Ly$α$ absorber (DLA). With the WFC3/F160W data we observe the stellar continuum around $3600$ $\mathring{\rm A}$ in the rest frame for a galaxy embedded in the West clump of the nebula, $G_{\rm W}$, for which we estimate a star formation rate SFR$_{G_{\rm W}} = 5.0 \pm 0.4$ M$_\odot$ yr$^{-1}$ and maximum stellar mass M$_{G_{\rm W}} < 9.9 \pm 0.7 \times 10^9$ M$_\odot$. With the enhanced spatial resolution of HST, we discover the presence of an additional faint source, $G_{\rm E}$, in the center of the East clump, with a star formation rate of SFR$_{G_{\rm E}} = 0.70 \pm 0.20$ M$_\odot$ yr$^{-1}$ and maximum stellar mass M$_{G_{\rm E}} < 1.4 \pm 0.4 \times 10^9$ M$_\odot$. We show that the Ly$α$ emission in the two clumps can be explained by recombination following in-situ photoionization by the two galaxies, assuming escape fractions of ionizing photons of $\lesssim 0.24$ for $G_{\rm W}$ and $\lesssim 0.34$ for $G_{\rm E}$. The fact that $G_{\rm W}$ is offset by $\approx 8$ kpc from the West clump does not fully rule out the presence of additional fainter star-forming sources that would further contribute to the photon budget inside this $\approx 10^{12}$ M$_\odot$ galaxy group that extends over a region encompassing over $30 \times 50$ kpc.

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arXiv2024

Metal line emission around z<1 galaxies

We characterize, for the first time, the average extended emission in multiple lines ([OII], [OIII], and Hbeta) around a statistical sample of 560 galaxies at z~0.25-0.85. By stacking the Multi Unit Spectroscopic Explorer (MUSE) 3D data from two large surveys, the MUSE Analysis of Gas around Galaxies (MAGG) and the MUSE Ultra Deep Field (MUDF), we detect significant [OII] emission out to ~40 kpc, while [OIII] and Hbeta emission is detected out to ~30 kpc. Via comparisons with the nearby average stellar continuum emission, we find that the line emission at 20-30 kpc likely arises from the disk-halo interface. Combining our results with that of our previous study at z~1, we find that the average [OII] surface brightness increases independently with redshift over z~0.4-1.3 and with stellar mass over M* ~10^{6-12} Msun, which is likely driven by the star formation rate as well as the physical conditions of the gas. By comparing the observed line fluxes with photoionization models, we find that the ionization parameter declines with distance, going from log q (cm/s) ~7.7 at <=5 kpc to ~7.3 at 20-30 kpc, which reflects a weaker radiation field in the outer regions of galaxies. The gas-phase metallicity shows no significant variation over 30 kpc, with a metallicity gradient of ~0.003 dex/kpc, which indicates an efficient mixing of metals on these scales. Alternatively, there could be a significant contribution from shocks and diffuse ionized gas to the line emission in the outer regions.

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arXiv2024

The MUSE Ultra Deep Field (MUDF). VI. The relationship between galaxy properties and metals in the circumgalactic medium

We present intial results associating galaxies in the MUSE Ultra Deep Field (MUDF) with gas seen in absorption along the line-of-sight to two bright quasars in this field, to explore the dependence of metals in the circumgalactic medium (CGM) on galaxy properties. The MUDF includes $\sim$140h of VLT/MUSE data and 90 orbits of HST/G141M grism observations alongside VLT/UVES spectroscopy of the two quasars and several bands of HST imaging. We compare the metal absorption around galaxies in this field as a function of impact parameter, azimuthal angle and galaxy metallicity across redshifts 0.5 $<$ z $<$ 3.2. Due to the depth of our data and a large field-of-view, our analysis extends to low stellar masses ($<$ $10^{7}$ M$_{\odot}$) and high impact parameters ($>$ 600 kpc). We find a correlation between absorber equivalent width and number of nearby galaxies, but do not detect a significant anti-correlation with impact parameter. Our full sample does not show any significant change in absorber incidence as a function of azimuthal angle. However, we do find a bimodality in the azimuthal angle distribution of absorption at small impact parameters ($<$2 r$_{vir}$) and around highly-star-forming galaxies, possibly indicating disk-like accretion and biconical outflows. Finally, we do not detect any systematic deviation from the fundamental metallicity relation (FMR) among galaxies with detected absorption. This work is limited by gaps in the wavelength coverage of our current data; broader-wavelength observations with JWST will allow us to unlock the full potential of the MUDF for studying the CGM.

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arXiv2024

MUSE Analysis of Gas around Galaxies (MAGG) -- VI. The cool and enriched gas environment of z$\gtrsim$3 Ly$α$ emitters

We present a novel dataset that extends our view of the cosmic gas around z$\approx$3-4 Ly$α$ emitting galaxies (LAEs) in the Muse Analysis of Gas around Galaxies (MAGG) survey by tracing a cool and enriched gas phase through 47 MgII absorbers identified in newly-obtained VLT/XSHOOTER near-infrared quasar spectra. Jointly with the more ionized gas traced by CIV systems and the neutral HI from previous work, we find that LAEs are distributed inside cosmic structures that contain multiphase gas in composition and temperature. All gas phases are a strong function of the large-scale galaxy environment: the MgII and the CIV strength and kinematics positively correlate with the number of associated galaxies, and it is $\approx$3-4 times more likely to detect metal absorbers around group than isolated LAEs. Exploring the redshift evolution, the covering factor of MgII around group and isolated LAEs remains approximately constant from z$\approx$3-4 to z<2, but the one of CIV around group galaxies drops by z<2. Adding the cool enriched gas traced by the MgII absorbers to the results we obtained for the HI and CIV gas, we put forward a picture in which LAEs lie along gas filaments that contain high column-density HI systems and are enriched by strong CIV and MgII absorbers. While the MgII gas appears to be more centrally concentrated near LAEs, weaker CIV systems trace instead a more diffuse gas phase extended up to larger distances around the galaxies.

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arXiv2024

The MUSE Ultra Deep Field (MUDF). V. Characterizing the Mass-Metallicity Relation for Low Mass Galaxies at $z\sim 1$-$2$

Using more than 100 galaxies in the MUSE Ultra Deep Field with spectroscopy from the Hubble Space Telescope's Wide Field Camera 3 and the Very Large Telescope's Multi Unit Spectroscopic Explorer, we extend the gas-phase mass-metallicity relation (MZR) at $z\approx\,$1$\,$-$\,$2 down to stellar masses of M$_{\star}$ $\approx$ 10$^{7.5}$ M$_{\odot}$. The sample reaches six times lower in stellar mass and star formation rate (SFR) than previous HST studies at these redshifts, and we find that galaxy metallicities decrease to log(O/H) + 12 $\approx$ 7.8 $\pm$ 0.1 (15% solar) at log(M$_{\star}$/M$_{\odot}$) $\approx$ 7.5, without evidence of a turnover in the shape of the MZR at low masses. We validate our strong-line metallicities using the direct method for sources with [O III] $λ$4363 and [O III] $λ$1666 detections, and find excellent agreement between the techniques. The [O III] $λ$1666-based metallicities double existing measurements with S/N $\geq$ 5 for unlensed sources at $z~>$ 1, validating the strong-line calibrations up to $z \sim$2.5. We confirm that the MZR resides $\sim$0.3 dex lower in metallicity than local galaxies and is consistent with the fundamental metallicity relation (FMR) if the low mass slope varies with SFR. At lower redshifts ($z\sim$0.5) our sample reaches $\sim$0.5 dex lower in SFR than current calibrations and we find enhanced metallicities that are consistent with extrapolating the MZR to lower SFRs. Finally, we detect only a $\sim$0.1 dex difference in the metallicities of galaxies in groups versus isolated environments. These results are based on robust calibrations and reach the lowest masses and SFRs that are accessible with HST, providing a critical foundation for studies with the Webb and Roman Space Telescopes.

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arXiv2024

Probing coherence in metal absorption towards multiple images of strong gravitationally lensed quasars

We present a tomographic analysis of metal absorption lines arising from the circumgalactic medium (CGM) of galaxies at z~0.5-2, using Multi Unit Spectroscopic Explorer (MUSE) observations of two background quasars at z~2.2 and 2.8, which are two of the few currently known quasars with multiple images due to strong gravitational lensing by galaxy clusters at z~0.6 and 0.5, respectively. The angular separations between different pairs of quasar multiple images enable us to probe the absorption over transverse physical separations of ~0.4-150 kpc, which are based on strong lensing models exploiting MUSE observations. The fractional difference in rest-frame equivalent width (Delta Wr) of MgII, FeII, CIV absorption increases on average with physical separation, indicating that the metal-enriched gaseous structures become less coherent with distance, with a likely coherence length scale of ~10 kpc. However, Delta Wr for all the ions vary considerably over ~0.08-0.9, indicating a clumpy CGM over the full range of length scales probed. At the same time, paired MgII absorption is detected across ~100-150 kpc at similar line-of-sight velocities, which could be probing cool gas clouds within the same halo. No significant dependence of Delta Wr is found on the equivalent width and redshift of the absorbing gas and on the galaxy environment associated with the absorption. The high-ionization gas phase traced by CIV shows a higher degree of coherence than the low-ionization gas phase traced by MgII, with ~90 percent of CIV systems exhibiting Delta Wr <=0.5 at separations <=10 kpc compared to ~50 percent of MgII systems.

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arXiv2023

The MUSE Ultra Deep Field (MUDF). IV. A pair of X-ray weak quasars at the heart of two extended Lyα nebulae

We present the results obtained from follow-up observations of the MUSE Ultra Deep Field (MUDF) at X-ray energies with XMM-Newton. The MUDF is centred on a unique field with two bright, physically associated quasars at $z\simeq3.23$, separated by $\sim$500 kpc in projection. Both quasars are embedded within extended Ly$α$ nebulae ($\gtrsim 100~\rm kpc$ at a surface brightness flux level of $\approx 6\times 10^{-19} \rm erg~s^{-1}~cm^{-2}~arcsec^{-2}$), whose elongated morphology is suggestive of an extended filament connecting the quasar haloes. The new X-ray observations presented here allow us to characterise the physical properties (e.g. X-ray slope, luminosities, gas column densities) in the innermost region of the MUDF quasars. We find that both quasars are X-ray underluminous compared to objects at similar ultraviolet luminosities. Based on our X-ray spectral analysis, absorbing columns of $N_H(z)\gtrsim$ 10$^{23}$ cm$^{-2}$ appear unlikely, therefore such a weakness is possibly intrinsic. When also including literature data, we do not observe any detectable trend between the area of the nebulae and nuclear luminosities at both the rest-frame 2 keV and 2500 $\rm \mathring{A}$. The area is also not correlated with the X-ray photon index nor with the integrated band flux in the hard band (2$-$10 keV). We also do not find any trend between the extended Ly$α$ emission of the nebulae and the nuclear X-ray luminosity. Finally, the properties of the MUDF quasars' nebulae are consistent with the observed relation between the Ly$α$ integrated luminosity of the nebulae and their area. Our results suggest that the quasar ionization power is not a strong driver of the morphology and size of the nebulae.

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arXiv2023

Resolving the physics of Quasar Ly$α$ Nebulae (RePhyNe): I. Constraining Quasar host halo masses through Circumgalactic Medium kinematics

Ly$α$ nebulae ubiquitously found around z>2 quasars can supply unique constraints on the properties of the Circumgalactic Medium, such as its density distribution, provided the quasar halo mass is known. We present a new method to constrain quasar halo masses based on the line-of-sight velocity dispersion maps of Ly$α$ nebulae. By using MUSE-like mock observations obtained from cosmological hydrodynamic simulations under the assumption of maximal quasar fluorescence, we show that the velocity dispersion radial profiles of Ly$α$-emitting gas are strongly determined by gravity and that they are thus self-similar with respect to halo mass when rescaled by the virial radius. Through simple analytical arguments and by exploiting the kinematics of HeII1640Ȧ emission for a set of observed nebulae, we show that Ly$α$ radiative transfer effects plausibly do not change the shape of the velocity dispersion profiles but only their normalisation without breaking their self-similarity. Taking advantage of these results, we define the variable $η^{140-200}_{40-100}$ as the ratio of the median velocity dispersion in two specifically selected annuli and derive an analytical relation between $η^{140-200}_{40-100}$ and the halo mass which can be directly applied to observations. We apply our method to 37 observed quasar Ly$α$ nebulae at 3<z<4.7 and find that their associated quasars are typically hosted by ~$10^{12.16 \pm 0.14}$ M$_{\odot}$ haloes independent of redshift within the explored range. This measurement, which is completely independent of clustering methods, is consistent with the lowest mass estimates based on quasar auto-correlation clustering at z~3 and with quasar-galaxies cross-correlation results.

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arXiv2023

Towards an automatic approach to modelling the circumgalactic medium: new tools for mock making and fitting of metal profiles in large surveys

We present two new tools for studying and modelling metal absorption lines in the circumgalactic medium. The first tool, dubbed ``NMF Profile Maker'' (NMF$-$PM), uses a non-negative matrix factorization (NMF) method and provides a robust means to generate large libraries of realistic metal absorption profiles. The method is trained and tested on 650 unsaturated metal absorbers in the redshift interval $z=0.9-4.2$ with column densities between $11.2 \le \log{(\mathrm{N/cm^{-2}})} \le 16.3$, obtained from high-resolution ($R> 4000$) and high signal-to-noise ratio ($S/N \ge 10$) quasar spectroscopy. To avoid spurious features, we train on infinite $S/N$ Voigt models of the observed line profiles derived using the code ``Monte-Carlo Absorption Line Fitter'' (MC$-$ALF), a novel automatic Bayesian fitting code that is the second tool we present in this work. MC$-$ALF is a Monte Carlo code based on nested sampling that, without the need for any prior guess or human intervention, can decompose metal lines into individual Voigt components. Both MC$-$ALF and NMF$-$PM are made publicly available to allow the community to produce large libraries of synthetic metal profiles and to reconstruct Voigt models of absorption lines in an automatic fashion. Both tools contribute to the scientific effort of simulating and analysing metal absorbers in very large spectroscopic surveys of quasars like the ongoing Dark Energy Spectroscopic Instrument (DESI), the 4-meter Multi-Object Spectroscopic Telescope (4MOST), and the WHT Enhanced Area Velocity Explorer (WEAVE) surveys.

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arXiv2023

JCMT/SCUBA-2 uncovers an excess of $850μ$m counts on megaparsec scales around high-redshift quasars. Characterization of the overdensities and their alignment with the quasars' Ly$α$ nebulae

We conducted a systematic survey of the environment of high-z quasars at submillimeter wavelengths to unveil and characterize the surrounding distribution of dusty submillimeter galaxies (SMGs). We took sensitive JCMT/SCUBA-2 observations for 3 enormous Lyman-alpha nebulae (ELANe) and 17 quasar fields in the redshift range 2 4 or detected in both bands at S/N>3. We ran Monte Carlo simulations to construct 850$μ$m number counts and unveil an excess of sources in 75% of the targeted fields. Overall, regions around ELANe and quasars are overabundant with respect to blank fields by a factor of $3.4\pm0.4$ and $2.5\pm0.2$, respectively. Therefore, the excess of SMGs is likely part of the Mpc-scale environment around these systems. By combining all fields and repeating the count analysis in radial apertures, we find a decrease in the overdensity factor from >3 within $\sim 2$ cMpc to $\sim2$ at the edge of the surveyed field ($\sim10$ cMpc), suggesting that the physical extent of the overdensities is larger than our maps. We computed preferred directions for the overdensities of SMGs from the positions of the sources and used them to orient and create stacked maps of source densities for the quasars' environment. This stacking unveils an elongated structure reminiscent of a large-scale filament with a scale width of $\approx 3$ cMpc. Finally, the directions of the overdensities are roughly aligned with the major axis of the Ly$α$ nebulae, suggesting that the latter trace, on hundreds of kpc, the central regions of the projected large-scale structure described by the SMGs on Mpc scales. Confirming member associations of the SMGs is required to further characterize their spatial and kinematic distribution around ELANe and quasars.

astro-ph.GA↗

arXiv2023

HST viewing of spectacular star-forming trails behind ESO 137-001

We present the results from the HST WFC3 and ACS data on an archetypal galaxy undergoing ram pressure stripping (RPS), ESO 137-001, in the nearby cluster Abell 3627. ESO 137-001 is known to host a prominent stripped tail detected in many bands from X-rays, Halpha to CO. The HST data reveal significant features indicative of RPS such as asymmetric dust distribution and surface brightness as well as many blue young star complexes in the tail. We study the correlation between the blue young star complexes from HST, HII regions from Halpha (MUSE) and dense molecular clouds from CO (ALMA). The correlation between the HST blue star clusters and the HII regions is very good, while their correlation with the dense CO clumps are typically not good, presumably due in part to evolutionary effects. In comparison to the Starburst99+Cloudy model, many blue regions are found to be young (< 10 Myr) and the total star formation (SF) rate in the tail is 0.3 - 0.6 M_Sun/yr for sources measured with ages less than 100 Myr, about 40% of the SF rate in the galaxy. We trace SF over at least 100 Myr and give a full picture of the recent SF history in the tail. We also demonstrate the importance of including nebular emissions and a nebular to stellar extinction correction factor when comparing the model to the broadband data. Our work on ESO 137-001 demonstrates the importance of HST data for constraining the SF history in stripped tails.

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