Giant Lyα Nebulae Associated with High‐Redshift Radio Galaxies

Monthly Notices of the Royal Astronomical Society, 2012

Monthly Notices of the Royal Astronomical Society, 2007

The Astrophysical Journal Supplement Series, 2008

We present HST/WFPC2 Linear Ramp Filter images of high surface brightness emission lines (either [OII], [OIII], or Hα+[NII]) in 80 3CR radio sources. We overlay the emission line images on high resolution VLA radio images (eight of which are new reductions of archival data) in order to examine the spatial relationship between the optical and radio emission. We confirm that the radio and optical emission line structures are consistent with weak alignment at low redshift (z < 0.6) except in the Compact Steep Spectrum (CSS) radio galaxies where both the radio source and the emission line nebulae are on galactic scales and strong alignment is seen at all redshifts. There are weak trends for the aligned emission line nebulae to be more luminous, and for the emission line nebula size to increase with redshift and/or radio power. The combination of these results suggests that there is a limited but real capacity for the radio source to influence the properties of the emission line nebulae at these low redshifts (z < 0.6). Our results are consistent with previous suggestions that both mechanical and radiant energy are responsible for generating alignment between the radio source and emission line gas.

The Astrophysical Journal, 2006

We selected 40 candidate Lyman Alpha Emitting galaxies (LAEs) at z ≃ 3.1 with observed frame equivalent widths >150Å and inferred emission line fluxes > 2.5 × 10 −17 ergs cm −2 s −1 from deep narrow-band and broadband MUSYC images of the Extended Chandra Deep Field South. Covering 992 arcmin 2 , this is the largest "blank field" surveyed for LAEs at z ∼ 3, allowing an improved estimate of the space density of this population of 3 ± 1 × 10 −4 h 3 70 Mpc −3 . Spectroscopic follow-up of 23 candidates yielded 18 redshifts, all at z ≃ 3.1. Over 80% of the LAEs are dimmer in continuum magnitude than the typical Lyman break galaxy spectroscopic limit of R = 25.5 (AB), with a median continuum magnitude R ≃ 27 and very blue continuum colors, (V − z) ≃ 0. Over 80% of the LAEs have the right UV R colors to be selected as Lyman break galaxies, but only 10% also have R ≤ 25.5. Stacking the UBV RIzJK fluxes reveals that LAEs have stellar masses ≃ 5 × 10 8 h −2 70 M ⊙ and minimal dust extinction, A V 0.1. Inferred star formation rates are ≃6h −2 70 M ⊙ yr −1 , yielding a cosmic star formation rate density of 2 × 10 −3 h 70 M ⊙ yr −1 Mpc −3 . None of our LAE candidates show evidence for restframe emission line equivalent widths EW rest >240Å which might imply a non-standard IMF. One candidate is detected by Chandra, implying an AGN fraction of 2 ± 2% for LAE candidate samples. In summary, LAEs at z ∼ 3 have rapid star formation, low stellar mass, little dust obscuration and no evidence for a substantial AGN component. 1

The Astrophysical Journal, 2001

We present Hubble Space T elescope and ground-based observations of a pair of galaxies at a redshift of 2.38, which are collectively known as 2142[4420 B1. Both galaxies are luminous extremely red objects (EROs) and are separated by They are embedded within a 100 kpc scale di †use Lya nebula 0A .8. (or blob) of luminosity D1044 ergs s~1. The radial proÐles and colors of both red objects are most naturally explained if they are young elliptical galaxies, the most distant galaxies of this type found to date. It is not possible, however, to rule out a model in which they are abnormally compact, extremely dusty starbursting disk galaxies. If they are elliptical galaxies, their stellar populations have inferred masses of D1011 and ages of D7 ] 108 yr. Both galaxies have color gradients : their centers are signiÐcantly M _ bluer than their outer regions. The surface brightness of both galaxies is roughly 1 order of magnitude greater than would be predicted by the Kormendy relation. A chain of di †use star formation extending 1A from the galaxies may be evidence that they are interacting or merging. The Lya nebula surrounding the galaxies shows apparent velocity substructure of amplitude D700 km s~1. We propose that the Lya emission from this nebula may be produced by fast shocks that are powered either by a galactic superwind or by the release of gravitational potential energy.

The Astrophysical Journal, 2009

We present a study of an extended Lyα nebula located in a known overdensity at z ∼ 2.38. The data include multiwavelength photometry covering the rest-frame spectral range from 0.1 to 250µm, and deep optical spectra of the sources associated with the extended emission. Two galaxies are associated with the Lyα nebula. One of them is a dust enshrouded AGN, while the other is a powerful starburst, forming stars at ∼ 600M ⊙ yr −1. We detect the He II emission line at 1640Å in the spectrum of the obscured AGN, but detect no emission from other highly ionized metals (C IV or N V) as is expected from an AGN. One scenario that simultaneously reproduces the width of the detected emission lines, the lack of C IV emission, and the geometry of the emitting gas, is that the He II and the Lyα emission are the result of cooling gas that is being accreted on the dark matter halo of the two galaxies, Ly1 and Ly2. Given the complexity of the environment associated with our Lyα nebula it is possible that various mechanisms of excitation are at work simultaneously.

The Astrophysical Journal, 2003

We present the results of a high resolution UV 2-D spectroscopic survey of star forming galaxies observed with HST-STIS. Our main aim was to map the Lyα profiles to learn about the gas kinematics and its relation with the escape of Lyα photons and to detect extended Lyα emission due to scattering in gaseous halos. We have combined our data with previously obtained UV spectroscopy on other three star-forming galaxies. We find that the P-Cygni profile is spatially extended, smooth and spans several kiloparsecs covering a region much larger than the starburst itself. We propose a scenario whereby an expanding supershell is generated by the interaction of the combined stellar winds and supernova ejecta from the young starbursts, with an extended low density halo. The variety of observed Lyα profiles both in our sample and in high redshift starbursts is explained as phases in the time evolution of the super-shell expanding into the disk and halo of the host galaxy. The observed shapes, widths and velocities are in excellent agreement with the super-shell scenario predictions and represent a time sequence. We confirm that among the many intrinsic parameters of a star forming region that can affect the properties of the observed Lyα profiles, velocity and density distributions of neutral gas along the line of sight are by far the dominant ones, while the amount of dust will determine the intensity of the emission line, if any.

Astronomy & Astrophysics

We study the nearby lenticular galaxy NGC 3998. This galaxy is known to host a low-power radio AGN with a kpc-size one-sided jet and a large, nearly polar H i disc. It is therefore a good system to study to understand the relation between the availability of cold-gas and the triggering of AGNs in galaxies. Our new WSRT data reveal two faint, S-shaped radio lobes extending out to ∼10 kpc from the galaxy centre. Remarkably, we find that the inner H i disc warps back towards the stellar mid-plane in a way that mirrors the warping of the radio lobes. We suggest that the polar H i disc was accreted through a minor merger, and that the torques causing it to warp in the inner regions are also responsible for feeding the AGN. The "S" shape of the radio lobes would then be due to the radio jets adapting to the changing angular momentum of the accreted gas. The extended radio jets are likely poorly collimated, which would explain their quick fading and, therefore, their rarity in galaxies similar to NGC 3998. The fuelling of the central super-massive black hole is likely occurring via "discrete events", suggested by the observed variability of the radio core and the extremely high core dominance, which we attribute to the formation and ejection of a new jet resulting from a recent fuelling event.

2006

We present the results of an optical and near-IR spectroscopic study of giant nebular emission line halos associated with three z > 3 radio galaxies, 4C 41.17, 4C 60.07 and B2 0902+34. Previous deep narrow band Lyα imaging had revealed complex morphologies with sizes up to 100 kpc), possibly connected to outflows and AGN feedback from the central regions. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s −1 , and velocity shears that can mostly be interpreted as being due to rotation. The inner regions show shocked cocoons of gas closely associated with the radio lobes. These display disturbed kinematics and have expansion velocities and/or velocity dispersions >1000 km s −1 . The core region is chemically evolved, and we also find spectroscopic evidence for the ejection of enriched material in 4C 41.17 up to a distance of ≈60 kpc along the radio-axis. The dynamical structures traced in the Lyα line are, in most cases, closely echoed in the Carbon and Oxygen lines. This shows that the Lyα line is produced in a highly clumped medium of small filling factor, and can therefore be used as a tracer of the dynamics of HzRGs. We conclude that these HzRGs are undergoing a final jet-induced phase of star formation with ejection of most of their interstellar medium before becoming "red and dead" Elliptical galaxies.

Monthly Notices of the Royal Astronomical Society, 2017

We present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the Very Large Telescope in a quasar field that hosts a high column density damped Lyα absorber (DLA) at z ≈ 3.25. We detect Lyα emission from a nebula at the redshift of the DLA with line luminosity (27 ± 1) × 10 41 erg s −1 , which extends over 37 ± 1 kpc above a surface brightness limit of 6 × 10 −19 erg s −1 cm −2 arcsec −2 at a projected distance of 30.5 ± 0.5 kpc from the quasar sightline. Two clumps lie inside this nebula, both with Lyα rest-frame equivalent width >50 Å and with relative line-of-sight velocities aligned with two main absorption components seen in the DLA spectrum. In addition, we identify a compact galaxy at a projected distance of 19.1 ± 0.5 kpc from the quasar sightline. The galaxy spectrum is noisy but consistent with that of a star-forming galaxy at the DLA redshift. We argue that the Lyα nebula is ionized by radiation from star formation inside the two clumps, or by radiation from the compact galaxy. In either case, these data imply the presence of a structure with size 50 kpc inside which galaxies are assembling, a picture consistent with galaxy formation in groups and filaments as predicted by cosmological simulations such as the EAGLE simulations.