Discovery of CWISE J052306.42−015355.4, an Extreme T Subdwarf Candidate

We present the discovery of CWISE J052306.42−015355.4, which was found as a faint, significant proper-motion object (0.″52 ± 0.″08 yr−1) using machine-learning tools on the unWISE re-processing of time series images from the Wide-field Infrared Survey Explorer. Using the CatWISE2020 W1 and W2 magnitudes along with a J-band detection from the VISTA Hemisphere Survey, the location of CWISE J052306.42−015355.4 on the W1 − W2 versus J − W2 diagram best matches that of other known, or suspected, extreme T subdwarfs. As there is currently very little knowledge concerning extreme T subdwarfs we estimate a rough distance of ≤68 pc, which results in a tangential velocity of ≤167 km s−1, both of which are tentative. A measured parallax is greatly needed to test these values. We also estimate a metallicity of −1.5 < [M/H] < −0.5 using theoretical predictions.

A Census of the Circumstellar Disk Populations in the Sco-Cen Complex*

I have used mid-infrared (IR) photometry from the Wide-field Infrared Survey Explorer (WISE) to perform a census of circumstellar disks among ∼10,000 candidate members of the Sco-Cen complex that were recently identified with data from the Gaia mission. IR excesses are detected for more than 1200 of the WISE counterparts that are within the commonly adopted boundary for Sco-Cen, ∼400 of which are newly reported in this work. The richest population in Sco-Cen, UCL/LCC, contains the largest available sample of disks (>500) for any population near its age (∼20 Myr). UCL/LCC also provides the tightest statistical constraints to date on the disk fractions of low-mass stars for any single age beyond that of Upper Sco (∼11 Myr). For Upper Sco and UCL/LCC, I have measured the disk fractions as a function of spectral type. The disk fraction in Upper Sco is higher at later spectral types, which is consistent with the results for previous samples of candidate members. In UCL/LCC, that trend has become more pronounced; the disk fractions in UCL/LCC are lower than those in Upper Sco by factors of ∼10, 5.7, and 2.5 at B7–K5.5, K6–M3.5, and M3.75–M6, respectively. The data in UCL/LCC also demonstrate that the disk fraction for low-mass stars remains nonnegligible at an age of 20 Myr (0.09 ± 0.01). Finally, I find no significant differences in the ages of disk-bearing and diskless low-mass stars in Upper Sco and UCL/LCC based on their positions in color–magnitude diagrams.

A Census of the Stellar Populations in the Sco-Cen Complex*

I have used high-precision photometry and astrometry from the early installment of the third data release of Gaia (EDR3) to perform a survey for members of the stellar populations within the Sco-Cen complex, which consist of Upper Sco, UCL/LCC, the V1062 Sco group, Ophiuchus, and Lupus. Among Gaia sources with σ π < 1 mas, I have identified 10,509 candidate members of those populations. I have compiled previous measurements of spectral types, Li equivalent widths, and radial velocities for the candidates, which are available for 3169, 1420, and 1740 objects, respectively. In a subset of candidates selected to minimize field star contamination, I estimate that the contamination is ≲1% and the completeness is ∼90% at spectral types of ≲M6–M7 for the populations with low extinction (Upper Sco, V1062 Sco, UCL/LCC). I have used that cleaner sample to characterize the stellar populations in Sco-Cen in terms of their initial mass functions, ages, and space velocities. For instance, all of the populations in Sco-Cen have histograms of spectral types that peak near M4–M5, which indicates that they share similar characteristic masses for their initial mass functions (∼0.15–0.2 M ⊙). After accounting for incompleteness, I estimate that the Sco-Cen complex contains nearly 10,000 members with masses above ∼0.01 M ⊙. Finally, I also present new estimates for the intrinsic colors of young stars and brown dwarfs (≲20 Myr) in bands from Gaia EDR3, the Two Micron All Sky Survey, the Wide-field Infrared Survey Explorer, and the Spitzer Space Telescope.

The nature and likely redshift of GLEAM J0917–0012

We previously reported a putative detection of a radio galaxy at $z=10.15$ , selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The redshift of this source, GLEAM J0917–0012, was based on three weakly detected molecular emission lines observed with the Atacama Large Millimetre Array (ALMA). In order to confirm this result, we conducted deep spectroscopic follow-up observations with ALMA and the Karl Jansky Very Large Array (VLA). The ALMA observations targeted the same CO lines previously reported in Band 3 (84–115 GHz) and the VLA targeted the CO(4-3) and [CI(1-0)] lines for an independent confirmation in Q-band (41 and 44 GHz). Neither observation detected any emission lines, removing support for our original interpretation. Adding publicly available optical data from the Hyper Suprime-Cam survey, Widefield Infrared Survey Explorer (WISE), and Herschel Space Observatory in the infrared, as well as $<$ 10 GHz polarisation and 162 MHz inter-planetary scintillation observations, we model the physical and observational characteristics of GLEAM J0917–0012 as a function of redshift. Comparing these predictions and observational relations to the data, we are able to constrain its nature and distance. We argue that if GLEAM J0917–0012 is at $z<3,$ then it has an extremely unusual nature, and that the more likely solution is that the source lies above $z=7$ .

Lyman-α emission from a WISE-selected optically faint powerful radio galaxy M151304.72-252439.7 at z = 3.132*

We report the detection of a large (∼90 kpc) and luminous Lyα nebula [LLyα = (6.80±0.08) × 1044 $\rm {\, erg\, s^{-1}}$] around an optically faint (r&gt;23 mag) radio galaxy M1513-2524 at zem=3.132. The double-lobed radio emission has an extent of 184 kpc, but the radio core, i.e., emission associated with the active galactic nucleus (AGN) itself, is barely detected. This object was found as part of our survey to identify high-z quasars based on Wide-field Infrared Survey Explorer (WISE) colors. The optical spectrum has revealed Lyα, N v, C iv and He ii emission lines with a very weak continuum. Based on long-slit spectroscopy and narrow band imaging centered on the Lyα emission, we identify two spatial components: a “compact component” with high velocity dispersion (∼1500 km s−1) seen in all three lines, and an “extended component”, having low velocity dispersion (i.e., 700-1000 km s−1). The emission line ratios are consistent with the compact component being in photoionization equilibrium with an AGN. We also detect spatially extended associated Lyα absorption, which is blue-shifted within 250-400 km s−1 of the Lyα peak. The probability of Lyα absorption detection in such large radio sources is found to be low (∼10%) in the literature. M1513-2524 belongs to the top few percent of the population in terms of Lyα and radio luminosities. Deep integral field spectroscopy is essential for probing this interesting source and its surroundings in more detail.

Strong Hα emission in the young planetary mass companion 2MASS J0249−0557 c

Aims. Our objective is the optical and near-infrared spectroscopic characterisation of 2MASS J0249−0557 c, a recently discovered young planetary mass companion to the β Pictoris (~25 Myr) member 2MASS J0249−0557. Methods. Using the Visible and Infrared Survey Telescope for Astronomy Hemisphere Survey and the Two Micron All Sky Survey (2MASS) data, we independently identified the companion 2MASS J0249−0557 c. We also obtained low-resolution optical spectroscopy of this object using the Optical System for Imaging and low-intermediate-Resolution Integrated Spectroscopy spectrograph at the Gran Telescopio Canarias, and near-infrared spectroscopy using the Son of Isaac spectrograph on the New Technology Telescope. Results. We classified 2MASS J0249−0557 c with a spectral type of L2.5 ± 0.5 in the optical and L3 ± 1 in the near-infrared. We identified several spectroscopic indicators of youth both in the optical and in the near-infrared that are compatible with the age of the β Pictoris moving group: strong absorption due to oxides, weak alkaline atomic lines, and a triangular shape of the H-band pseudo-continuum. We also detect a strong Hα emission, with a pseudo-equivalent width (pEW) of −90−40+20 Å, which seems persistent at timescales from several days to a few years. This indicates strong chromospheric activity or disk accretion. Although many M-type brown dwarfs have strong Hα emission, this target is one of the very few L-type planetary mass objects in which this strong Hα emission has been detected. Lithium absorption at 6708 Å is observed with pEW ≲5 Å. We also computed the binding energy of 2MASS J0249−0557 c and obtained an (absolute) upper limit of U = (−8.8 ± 4.4) × 1032 J. Conclusions. Similarly to other young brown dwarfs and isolated planetary mass objects, strong Hα emission due to accretion or chromospheric activity is also present in young planetary mass companions at ages of some dozen million years. We also found that 2MASS J0249−0557 c is one of the wide substellar companions with the lowest binding energy known to date.