Spatially mapping the metal-enriched absorbing CGM of a massive galaxy at z~4.5

Wuji Wang 1 , Dominika Wylezalek 1 , Joël Vernet 2 , Carlos De Breuck 2

  • 1 Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Heidelberg
  • 2 European Southern Observatory, Garching

Abstract

High-redshift radio galaxies (HzRGs) are hosted by some of the most massive galaxies known at any redshift and are unique markers of concomitant powerful active galactic nuclei (AGN) activity and extreme starbursts. Their energetic radio jets, high star formation rates and black hole accretion rates place them amongst the most active sources at and near Cosmic Noon. Their extended gaseous environments of HzRGs are disturbed by outflows and inflows and show signs of significant jet-gas interactions making them unique objects in which quasar-mode feedback, radio-mode feedback and the host galaxies can be studied simultaneously.

I will present Multi Unit Spectroscopic Explorer (MUSE) integral field unit spectroscopic observations of the 70 x 30 kpc² Lyα halo around a massive (M_stellar ~ 10^11.5 M_sun) z ~ 4.5 radio galaxy. I will present our detailed spatially resolved spectral analysis of the complex Lyα profile in which we identify and measure the signatures (kinematics and column densities) of eight neutral gas absorbing systems at -3500 < Δv < 0 km/s. The strongest absorber at v ~ 0 km/s has a high covering fraction being detected across the extent of the Lyα halo, a significant column density gradient along the south to north direction and a velocity gradient along the radio jet axis. The absorber is also observed in CIV and NV absorption, and very likely represents an outflowing metal-enriched shell driven by a previous AGN or star formation episode within the galaxy and is now caught up by the radio jet leading to jet-gas interactions. These observations provide evidence that feedback from AGN in some of the most massive galaxies in the early Universe may take an important part in re-distributing material and metals in their environments.

This work is part of larger sample of similarly massive HzRGs, and I will present the future plans for this unique sample of massive high-z galaxies hosting powerful AGN. JWST will be transformative for these galaxies as it will allow a detailed investigation on how radio- and quasar-mode feedback work together in the early Universe.

1. Background

Galaxy evolution & feedback at Cosmic Noon
  • Feedback from active galaxies is essential part in the formation and evolution of their hosts through which the galaxy exchanges energy and material with the environment.
  • The epoch at z~2--3 (Cosmic Noon) which marks the peak of both star formation and quasar activity is a key period to study the feedback processes.
High-redshift Radio Galaxies (HzRGs)
  • HzRGs are the only kind of object where one can study the quasar-mode feedback, radio-mode feedback and host galaxies simultaneously.
  • HzRGs have extended gaseous halos (many with >100 kpc) around , well into the circumgalactic medium (CGM). The halos are often metal enriched with deep extended absorbers.
  • We have a sample of eight HzRGs with MUSE observations (~4h each). In this work, we perform a pilot study to map the absorption gas around one HzRG, 4C04.11 at z ~4.5.

This poster is based on Wang et al. (submitted).

3. Line fitting -- Ly-alpha, Nv, CIV and HeII

Fig. 2 The fitting result of the 1D Ly-alpha emission line. The dark magenta line is the best-fit model. The black vertical bars represent the positions of eight HI absorbers. The bottom panel shows the spectrum noise which is used as fitting weight and skyline tracer. 

We preform the MCMC fitting to the Ly-alpha, CIV+HeII and Nv lines.

  • For Ly-alpha (Fig. 2), we identify 8 HI absorbers with column densities around 1014.8 cm-2.
  • For CIV (Fig. 3), we infer the detection of 2 absorbers for which we believed are associated with HI absorber #1 and #4 (numbers are the same in the figures). The CIV absorbers #2 and #3 are not well constrained which are marked with dashed bars in Fig. 3.
  • We obtain the systemic redshift, z=4.5077 (uncertainty 0.0001), of the radio galaxy from the brightest non-resonant line, HeII.
  • For Nv (Fig. 4), we infer the presence of the Nv absorber #1.

Fig. 3 The fitting result of the 1D CIV+HeII emission lines. The dark magenta line is the best-fit model. The green (red) vertical bars represent the positions of CIV absorbers on top of CIV1548 (CIV1551) line. The bottom panel shows the spectrum noise which is used as fitting weight and skyline tracer. 

Fig. 4 The fitting result of the 1D Nv emission lines. The dark magenta line is the best-fit model. The green (red) vertical bars represent the positions of Nv absorbers on top of Nv1239 (Nv1243) line. The bottom panel shows the spectrum noise which is used as fitting weight and skyline tracer. 

2. Methods

Fig. 1 The narrow band Ly-alpha emission image (left) and spatial binning map (right).

  • We extract 1D spectrum from the 1 arcsec radius aperture (red circle on the left panel) to perform the fit of Ly-alpha (Fig. 2), Nv (Fig. 4) and CIV+HeII (Fig. 3).
  • We perform the spatial binning to the green square region and obtain 64 tessellations. From each of the bins, we fit the Ly-alpha line and map the properties of the HI absorption (Section 4). 

4. Spatial mapping

Fig. 5 The spatial mapping results from the fitting. (a) The intrinsic Ly-alpha surface brightness map. (b) The W80 map of Ly-alpha emission (non-parametric measurement of the line width). (c) The column density maps for HI absorber #1. (d) The velocity shift maps for HI absorber #1. The black contours are the Ly-alpha emission profile and the green ones are the radio jet.

  • The W80 profile (Fig. 5 b) may suggest a tentative signature of jet-gas interaction in the south where the jet hotsopt is detected as approaching.
  • We observe a column density gradient along the SW-NE (increasing of 1 dex in 24kpc) for HI absorber #1 (Fig. 5 c). There is also a small velocity gradient for absorber #1 (Fig. 5 d) along the radio jet axis. We prose a model to explain the scenario in Secion 5.
  • Our observation is not deep and sensitive enough to probe the spatial details of absorber #2-#8.

5. Ejected shell model for HI absorber #1

Fig. 6 The cross-section schematic presentation of the proposed outflowing shell model. The figure is not to scale.

  • We propose the absorber #1 (seen on 30*20 kpc2) is a giant gaseous shell (dark green in Fig. 6) expelled by wind in early AGN/SF activitives.  The absorber #1 is metal enriched (detected CIV and Nv) which could be a hint of its inner origin.
  • The absorbing cloud traveled 10s kpc before it was caught up by a later launched jet. Jet hotsopts are shown in Fig. 6 with blue and orange for approaching and receeding ones, respectively.
  • The column density gradient could be explained by the geometry setup that the line of sight of observer passes longer length in the north and have higher absorbing column density. The continue decreasing in the south could be explained by the jet-gas interaction which disturbs the gaseous shell.

6. Summary & Future

Summary
  • We detected 8 HI absorbers with column densities around 1014.8 cm-2. The presence of CIV absorbers are also inferred associated with HI absorber #1 and #4. Nv absorption is inferred in absorber #1.
  • A spatial column density gradient for HI absorber #1 is detected along SW-NE direction with increasing of 1 dex in 24 kpc. We propose that this could be explained by a metal-enriched expelled gaseous shell that is disturbed by the jet which was launched later.
  • Our observations suggest that we are observing the enrichment and re-distribution of metals in and of the ISM and even the CGM driven by a powerful AGN in a massive galaxy near Cosmic Noon in action.
Future work
  • We will perform the similar analysis to our full sample of eight HzRGs with 2.9<z<4.6 and SFR span a wide range (84-626 Msun yr-1).
  • Four of our sample target around z~3.5 will be observed in JWST Cycle 1 under the program ID 1970 (PI:Wang). This will offer us a zoom-in view (FOV 3*3 arc2, resolution ~0.1 arc) of the ISM and stellar population of the host galaxies in the rest-frame optical wavelngth.