Jacob McLane | Searcharxiv

arXiv2026

Near-Infrared Spectroscopy of Low-Redshift Palomar-Green Quasars and Composite Spectra

The Palomar-Green (PG) Quasars have been used extensively to establish the spectral properties of luminous active galactic nuclei (AGNs) at low redshifts in many wavebands, but not the near-infrared (NIR). We present NIR spectra of all 87 PG quasars with z < 0.5 observed with the Apache Point Observatory 3.5-m telescope and the TripleSpec spectrograph in standard cross-dispersed mode. Here we employ our data set to construct a NIR composite quasar spectrum spanning rest-frame wavelengths from approximately 8800-22000 angstroms reaching a signal-to-noise ratio of several hundred in the H-band for 4 angstrom pixels. We characterize the continuum and emission-line properties of this composite. Additionally, we construct composite spectra as a function of luminosity and Eddington ratio, finding some differences, not entirely unexpected. In particular, more luminous composite NIR spectra grow increasingly red at long wavelengths, consistent with relatively stronger dust emission at higher temperatures.

astro-ph.GA↗

arXiv2016

Planets Around Low-Mass Stars (PALMS). VI. Discovery of a Remarkably Red Planetary-Mass Companion to the AB Dor Moving Group Candidate 2MASS J22362452+4751425

We report the discovery of an extremely red planetary-mass companion to 2MASS J22362452+4751425, a $\approx$0.6 $M_{\odot}$ late-K dwarf likely belonging to the $\sim$120 Myr AB Doradus moving group. 2M2236+4751 b was identified in multi-epoch NIRC2 adaptive optics imaging at Keck Observatory at a separation of 3.7$"$, or 230 $\pm$ 20 AU in projection at the kinematic distance of 63 $\pm$ 5 pc to its host star. Assuming membership in the AB Dor group, as suggested from its kinematics, the inferred mass of 2M2236+4751 b is 11-14 $M_\mathrm{Jup}$. Follow-up Keck/OSIRIS $K$-band spectroscopy of the companion reveals strong CO absorption similar to other faint red L dwarfs and lacks signs of methane absorption despite having an effective temperature of $\approx$900-1200 K. With a ($J$-$K$)$_\mathrm{MKO}$ color of 2.69 $\pm$ 0.12 mag, the near-infrared slope of 2M2236+4751 b is redder than all of the HR 8799 planets and instead resembles the $\approx$23 Myr isolated planetary-mass object PSO J318.5-22, implying that similarly thick photospheric clouds can persist in the atmospheres of giant planets at ages beyond 100 Myr. In near-infrared color-magnitude diagrams, 2M2236+4751 b is located at the tip of the red L dwarf sequence and appears to define the "elbow" of the AB Dor substellar isochrone separating low-gravity L dwarfs from the cooler young T dwarf track. 2M2236+4751 b is the reddest substellar companion to a star and will be a valuable benchmark to study the shared atmospheric properties of young low-mass brown dwarfs and extrasolar giant planets.

astro-ph.EP↗