CO Emission in the Inner Disk Around Young Intermediate-Mass Stars

We present observations that indicate viscous heating contributes significantly to the surface heating of the inner disk region (0.1-5 AU) around young intermediate-mass stars, Herbig AeBe stars, when the inner disk is optically thick. Brgamma flux is known to scale with accretion rate around young stars. We find a trend between Brgamma and CO emissivity, a tracer 1, 500 K gas in the gaseous atmospheres of less evolved inner disk regions in a sample of 25 Herbig AeBe stars, the higher mass analog of T Tauri stars. Evolved Herbig circumstellar disks do not follow this trend as closely. A thermal chemical model of the inner disk region of T Tauri stars by \citet{gla04} explains the strength and line profiles of observed CO rovibrational emission by showing that accretion contributes significantly to heating the protoplanetary disk. This heating produces the required temperatures and column densities for CO emission in the disk. Our results are consistent with these prescribed disk characteristics. Determining conditions and processes in circumstellar disks around young stars will help inform evolutionary theory and constrain timescales of disk dissipation and planet formation

Investigating the growing population of massive quiescent galaxies at cosmic noon

We explore the build-up of quiescent galaxies using a sample of 28 469 massive (M⋆ ≥ 1011 M☉) galaxies at redshifts 1.5 < zz < 3.0, drawn from a 17.5 deg2 area (0.33 Gpc3 comoving volume at these redshifts). This allows for a robust study of the quiescent fraction as a function of mass at 1.5 < zz < 3.0 with a sample ∼40 times larger at log(M⋆/ M⊙)≥11.5M⊙)≥11.5 than previous studies. We derive the quiescent fraction using three methods: specific star formation rate, distance from the main sequence, and UVJ colour-colour selection. All three methods give similar values at 1.5 < zz < 2.0, however the results differ by up to a factor of 2 at 2.0 < zz < 3.0. At redshifts 1.5 < zz < 3.0, the quiescent fraction increases as a function of stellar mass. By zz = 2, only 3.3 Gyr after the big bang, the universe has quenched ∼25 per cent of M⋆ = 1011 M☉ galaxies and ∼45 per cent of M⋆ = 1012 M☉ galaxies. We discuss physical mechanisms across a range of epochs and environments that could explain our results. We compare our results with predictions from hydrodynamical simulations SIMBA and IllustrisTNG and semi-analytic models (SAMs) SAG, SAGE, and Galacticus. The quiescent fraction from IllustrisTNG is higher than our empirical result by a factor of 2-5, while those from SIMBA and the three SAMs are lower by a factor of 1.5-10 at 1.5 < zz < 3.0Fil: Sherman, Sydney. Department Of Astronomy; Estados UnidosFil: Jogee, Shardha. Department Of Astronomy; Estados UnidosFil: Florez, Jonathan. Department Of Astronomy; Estados UnidosFil: Stevans, Matthew L. Department Of Astronomy; Estados UnidosFil: Kawinwanichakij, Lalitwadee. Kavli Institute For The Physics And Mathematics Of The; JapónFil: Wold, Isak. Nasa Goddard Space Flight Center; Estados UnidosFil: Finkelstein, Steven L. Department Of Astronomy; Estados UnidosFil: Papovich, Casey. Department Of Physics And Astronomy; Estados UnidosFil: Ciardullo, Robin. Department Of Astronomy And Astrophysics; Estados UnidosFil: Gronwall, Caryl. Department Of Astronomy And Astrophysics; Estados UnidosFil: Cora, Sofia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Hough, Tomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Vega Martínez, Cristian Antonio. Instituto de Investigación Multidisciplinar En Ciencia; Chil