arXiv subjects

A. Vayner

Publications and source records attributed to A. Vayner.

3 recordsLinked to original sources

arXiv2026

A cosmic collision in the making: JWST/NIRISS reveals a merging and maturing protocluster core at z~3 around a red quasar

We report the discovery of ``The Step'', a dense protocluster at z=3 revealed by JWST/NIRISS Wide-Field Slitless Spectroscopy (WFSS) of the field around the luminous quasar and starburst SDSSJ165202.64+172852.3. The protocluster contains at least 18 member galaxies and exhibits two substructures in the 3D position-velocity space - notably a distinctive step-like distribution, from which the nickname derives. We propose that the Step may be undergoing a merger of two haloes, which could also explain the large velocity span (700-850km/s) between galaxies along the densest line of sight. This sightline contains seven galaxies within 70 projected kpc from the quasar, consistent with a remarkably dense protocluster core. We derive a galaxy overdensity of a factor >100 in the core and >15 within 1 Mpc$^2$, making it one of the densest structures known at this redshift, and a very massive halo of $13.1 < log M_{\rm halo}/ M_\odot < 13.8$, which suggests the structure could potentially evolve into a massive, Coma-like cluster at z=0. Compared to the field, the star-forming galaxies in the Step show slightly elevated levels of star formation. Yet, we find two quiescent galaxies with strong D4000 breaks and no evidence for ongoing star formation. Compared to other z=3 protoclusters, the Step exhibits similar or slightly suppressed star-forming activity. We also identify two new AGN candidates and find tentative evidence for an enhanced AGN fraction (10-20%) compared to the field. The protocluster constitutes one of the emerging handful of maturing structures at 2 < z < 4 that host both star-forming and quenched galaxies. This redshift regime may thus be a key transitional epoch for cluster studies, where overdensities transition from being the most active sites of star formation in the early Universe towards shaping the massive passive ellipticals seen in the cores of today's clusters.

astro-ph.GA↗

arXiv2026

Scattering from Dusty Outflows in Hot Dust-Obscured Galaxies with Blue Excess Emission

(Context) Hot Dust-Obscured Galaxies (Hot DOGs) are a population of hyper-luminous quasars heavily obscured by dust and gas. While most have rest UV/optical SEDs dominated by their host galaxy emission, a small fraction shows blue emission in excess of what is expected for star-formation. Detailed multi-wavelength studies from X-rays to the far-IR of these Blue Excess Hot DOGs (BHDs) have concluded the most likely origin of this blue excess is scattered light from the central engine. This scenario was confirmed by previous studies for the BHDs W0116-0505 and W0204-0506 which found highly polarized UV emission, a key signature of scattered light. (Aims) In this article we investigate this scattered light scenario in three other BHDs and further constrain the properties of the scattering material in W0116-0505. (Methods) We analyze new VLT/FORS2 imaging polarimetry observations in the $R_{\rm Special}$-band of three BHDs and additional observations of W0116-0505 in the $v_{\rm High}$- and $I_{Bessel}$-bands. (Results) We find spatially integrated polarization fractions in all three BHDs observed in the $R_{\rm Special}$-band ranging from about 6% to 15%. This confirms that their blue excess emission is due to AGN scattered light. We also find that the polarization fraction has a significant dependence with rest-frame wavelength in W0116-0505 and that it cannot be explained by Thomson scattering or by an AGN shining onto a smooth ISM. We find that a dusty bi-conical outflow acting as the scatterer can successfully explain the observations as long as the dust is dominated by graphites. This may be due to the high temperatures of the outflowing gas and the higher sublimation temperature of graphites compared to silicates.

astro-ph.GA↗

arXiv2023

First results from the JWST Early Release Science Program Q3D: Benchmark Comparison of Optical and Mid-IR Tracers of a Dusty, Ionized Red Quasar Wind at z=0.435

The [OIII] 5007 A emission line is the most common tracer of warm, ionized outflows in active galactic nuclei across cosmic time. JWST newly allows us to use mid-infrared spectral features at both high spatial and spectral resolution to probe these same winds. Here we present a comparison of ground-based, seeing-limited [OIII] and space-based, diffraction-limited [SIV] 10.51 micron maps of the powerful, kiloparsec-scale outflow in the Type 1 red quasar SDSS J110648.32+480712.3. The JWST data are from the Mid-InfraRed Instrument (MIRI). There is a close match in resolution between the datasets (0."6), in ionization potential of the O$^{+2}$ and S$^{+3}$ ions (35 eV), and in line sensitivity (1e-17 to 2e-17 erg/s/cm$^2$/arcsec$^2$). The [OIII] and [SIV] line shapes match in velocity and linewidth over much of the 20 kpc outflowing nebula, and [SIV] is the brightest line in the rest-frame 3.5-19.5 micron range, demonstrating its usefulness as a mid-IR probe of quasar outflows. [OIII] is nevertheless intriniscally brighter and provides better contrast with the point-source continuum, which is strong in the mid-IR. There is a strong anticorrelation of [OIII]/[SIV] with average velocity, which is consistent with a scenario of differential obscuration between the approaching (blueshifted) and receding (redshifted) sides of the flow. The dust in the wind may also obscure the central quasar, consistent with models that attribute red quasar extinction to dusty winds.

astro-ph.GA↗