[論文レビュー] GA-NIFS: Black hole and host galaxy properties of two z$\simeq$6.8 quasars from the NIRSpec IFU

Madeline A. Marshall, Michele Perna+21 more|arXiv (Cornell University)|Feb 9, 2023

Galaxies: Formation, Evolution, Phenomena参考文献 5被引用数 10

ひとこと要約

本論文は JWST/NIRSpec IFU 観測を用いて z~6.8 の2つのクエーサーから黒穴質量を Hβ および Hα から堅牢に推定し、クエーサーと宿主星系の放出を分解し、伴星-合体の特徴を同定し、宿主/伴星の特性と電離性アウトフローを測定する。

ABSTRACT

Integral Field Spectroscopy (IFS) with JWST NIRSpec will significantly improve our understanding of the first quasars, by providing spatially resolved, infrared spectroscopic capabilities which cover key rest-frame optical emission lines that have been previously unobservable. Here we present our results from the first two z>6 quasars observed as a part of the Galaxy Assembly with NIRSpec IFS (GA-NIFS) GTO program, DELS J0411-0907 at z=6.82 and VDES J0020-3653 at z=6.86. By observing the H$β$, [OIII], and H$α$ emission lines in these high-z quasars for the first time, we measure accurate black hole masses, $M_{ m{BH}}=1.85e9$ and $2.9e9$M$_\odot$, corresponding to Eddington ratios of $λ_{ m{Edd}}=0.8$ and 0.4 for DELS J0411-0907 and VDES J0020-3653 respectively. These provide a key comparison for existing estimates from the more uncertain MgII line. We perform quasar-host decomposition using models of the quasars' broad lines to measure the underlying host galaxies. We also discover multiple emission line regions surrounding each of the host galaxies, which are likely companion galaxies undergoing mergers with these hosts. We measure the star formation rates, excitation mechanisms, and dynamical masses of the hosts and companions, measuring the $M_{ m{BH}}/M_{ m{dyn}}$ ratios at high-z using these estimators for the first time. DELS J0411-0907 and VDES J0020-3653 both lie above the local black hole--host mass relation, and are consistent with the existing observations of $z\gtrsim6$ quasar host galaxies with ALMA. We detect ionized outflows in [OIII] and H$β$ from both quasars, with mass outflow rates of 58 and 525 M$_{\odot}$/yr for DELS J0411-0907 and VDES J0020-3653, much larger than their host star formation rates of <33 and <54 M$_\odot$/yr. This work highlights the exceptional capabilities of the JWST NIRSpec IFU for observing quasars in the early Universe.

研究の動機と目的

• JWST/NIRSpec で観測可能な rest-frame の Hβ および Hα 線を用いて、 z~6.8 の2つのクエーサーについて正確な黒穴質量とエディントン比を決定する。
• クエーサーとホスト星系の分解を実施して宿主銀河の発光を回復し、星形成、ISM特性、およびダイナミクスを評価する。
• 周囲の発光線領域を潜在的な合併伴星として同定・特徴づけ、宿主のダイナミクスへの影響を測定する。
• 電離ガスからのアウトフロー特性を定量化し、ブラックホール–ホストのスケーリングを高赤方偏移時の局所関係と比較する。

提案手法

• 3"×3" の視野と波長域 2.87–5.27 μm (R~2700) を持つ2つのクエーサー: DELS J0411−0907 および VDES J0020−3653 に対する観測。
• Quasar spectrum fitting with QubeSpec using a broken power-law for BLR lines and Gaussian components for GN/GB lines to model Hβ, [O III], and Hα regions.
• Decomposition of quasar and host emission using QDeblend3D to model the PSF from broad-line regions and subtract unresolved emission in two wavelength regimes (blueward of detector gap using Hβ and redward using Hα).
• Continuum subtraction per spaxel using selected rest-frame continuum windows to aid spatially resolved line analysis.
• Extraction of integrated spectra within optimized apertures and correction factors to recover total flux.
• Measurement of line kinematics (V_r, FWHM) and line luminosities for GN, GB, and BLR components; calculation of black hole masses and Eddington ratios from Hβ and Hα.

実験結果

リサーチクエスチョン

• RQ1 What are the black hole masses and Eddington ratios for two z~6.8 quasars when using rest-frame Hβ and Hα?
• RQ2 What are the properties of the quasar host galaxies (SFR, dynamics, masses) and their surrounding emission-line regions?
• RQ3 Do the hosts lie above the local M_BH–M_dyn relation at high redshift, and what does this imply for SMBH growth?
• RQ4 Are there visible signatures of interactions or mergers (companion galaxies) and how do they influence host properties and outflows?
• RQ5 What are the ionized outflow properties and how do their mass outflow rates compare to host SFRs?

主な発見

• Measured black hole masses: DELS J0411−0907 = 1.85^{+2}_{-0.8}×10^9 M_sun and VDES J0020−3653 = 2.9^{+3.5}_{-1.3}×10^9 M_sun.
• Eddington ratios: λ_Edd = 0.8^{+0.7}_{-0.4} for DELS J0411−0907 and λ_Edd = 0.4^{+0.3}_{-0.2} for VDES J0020−3653.
• Joint quasar–host decomposition reveals host galaxy emission and multiple surrounding emission-line regions likely representing merging companions.
• Outflows detected in [O III] and Hβ with mass outflow rates of 58^{+44}_{-37} M_sun/yr (DELS J0411−0907) and 525^{+75}_{-92} M_sun/yr (VDES J0020−3653), exceeding the hosts’ SFRs (<33 and <54 M_sun/yr respectively).
• Both quasars lie above the local black hole–host mass relation, consistent with other z>6 quasar host studies (ALMA trends).
• Demonstrates JWST NIRSpec IFU capabilities for obtaining spatially resolved rest-frame optical diagnostics in the early universe.