分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yu-Ching Chen
Xin Liu
Adi Foord
Yue Shen
Nianyi Chen
Miguel Holgado
Tiziana Di Matteo
Masamune Oguri
Hsiang-Chih Hwang
Nadia Zakamska
摘要： Most local massive galaxies, if not all, are believed to harbor a supermassive black hole (SMBH) at the center. Galaxy mergers have long been thought to drive strong gas inflows and accretion onto one or both central SMBH, triggering single or dual quasars as a natural stage of the hierarchical galaxy and SMBH evolution. While many dual active galactic nuclei -- the low-luminosity counterparts of quasars -- have been observed at low redshift, no unambiguous dual quasar is known at cosmic noon (z>~2) when both quasar activity and global star formation density peaked. While a handful of dual quasar candidates were known at z>1, competing explanations remained. Here we report multi-wavelength observations of SDSS J0749+2255 as the first kpc-scale dual quasar confirmed to be hosted by a galaxy merger at cosmic noon. Hubble Space Telescope NIR imaging reveals extended host galaxies underlying the compact double nuclei (separated by 0.46" or 3.8 kpc) and tidal features as evidence for galactic interactions. We also present new multi-wavelength observations, all lending support to the dual quasar hypothesis. Unlike the low-redshift low-luminosity counterparts, the high-redshift dual quasar is hosted by two massive compact disk-dominated galaxies, which may be critical for efficient gas fueling onto the SMBHs in the early-stage merger. The apparent lack of stellar bulges and that SDSS J0749+2255 already follows the local SMBH mass-host stellar mass relation are at odds with the canonical SMBH-host co-evolution picture and suggest that at least some SMBHs may have formed before their host stellar bulges. While still at kpc-scale separations where the host-galaxy gravitational potential dominates, the SMBHs may evolve into a gravitationally bound binary system in ~0.22 Gyr. The merger products at low redshift are expected to be gravitational wave sources for pulsar-timing arrays (abridged).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yue Shen
Hsiang-Chih Hwang
Masamune Oguri
Nianyi Chen
Tiziana Di Matteo
Yueying Ni
Simeon Bird
Nadia Zakamska
Xin Liu
Yu-Ching Chen
Kaitlin M. Kratter
摘要： The statistics of galactic-scale quasar pairs can elucidate our understanding
of the dynamical evolution of supermassive black hole (SMBH) pairs, the duty
cycles of quasar activity in mergers, or even the nature of dark matter, but
have been challenging to measure at cosmic noon, the prime epoch of massive
galaxy and SMBH formation. Here we measure a double quasar fraction of $\sim
6.2\pm0.5\times 10^{-4}$ integrated over $\sim 0.3-3$ arcsec separations
(projected physical separations of $\sim 3-30\,{\rm kpc}$ at $z\sim 2$) in
luminous ($L_{\rm bol}>10^{45.8}\,{\rm erg\,s^{-1}}$) unobscured quasars at
$1.5
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yue Shen
Yu-Ching Chen
Hsiang-Chih Hwang
Xin Liu
Nadia Zakamska
Masamune Oguri
Jennifer I-Hsiu Li
Joseph Lazio
Peter Breiding
摘要： Galaxy mergers occur frequently in the early universe and bring multiple supermassive black holes (SMBHs) into the nucleus, where they may eventually coalesce. Identifying post-merger-scale (i.e., 2, but critical to constraining the progenitors of SMBH mergers. The redshift z~2 also marks the epoch of peak activity of luminous quasars, hence probing this spatial regime at high redshift is of particular significance in understanding the evolution of quasars. However, given stringent resolution requirements, there is currently no confirmed 2. Here we report two sub-arcsec double quasars at z>2 discovered from a targeted search with a novel astrometric technique, demonstrating a high success rate (~50%) in this systematic approach. These high-redshift double quasars could be the long-sought kpc-scale dual SMBHs, or sub-arcsec gravitationally-lensed quasar images. One of these double quasars (at z=2.95) was spatially resolved with optical spectroscopy, and slightly favors the scenario of a physical quasar pair with a projected separation of 3.5 kpc (0.46"). Follow-up observations of double quasars discovered by this targeted approach will be able to provide the first observational constraints on kpc-scale dual SMBHs at z>2.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： CSS1603+19 is a cataclysmic variable (CV) with an orbital period of 81.96 min, near the minimal period of cataclysmic variables. It is unusual in having a strong mid-infrared excess inconsistent with thermal emission from a brown dwarf companion. Here we present time-resolved multi-wavelength observations of this system. WISE photometry indicates that the mid-infrared excess displays a one-magnitude eclipsing-like variability during the orbit. We obtained near-infrared and optical spectroscopy using Gemini, MDM and APO telescopes. Near-infrared spectra show possible cyclotron features indicating that the white dwarf has a magnetic field of about 5MG. Optical and near-infrared spectra display double-peaked emission lines, with both components showing strong radial velocity variations during the orbital period and with the broad component leading the narrow component stably by about 0.2 of the orbital phase. We construct a physical model informed by existing observations of the system and determine that one component likely originates from the accretion column onto the magnetized white dwarf in synchronous rotation with the orbital motion and the other from the Roche overflow point. This allows us to constrain the masses of the binary components to be $M_1>0.24 M_{\odot}$ for the white dwarf accretor and $M_2=0.0644\pm0.0074 M_\odot$ for the donor. We classify the system as an AM Herculis star, or a polar. It has likely completed its stint on the period gap, but has not yet gone through the period bounce.
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