Characterization of exoplanets from their formation III: The statistics of planetary luminosities

This paper continues a series in which we predict the main observable characteristics of exoplanets based on their formation. In Paper I we described our global planet formation and evolution model. In Paper II we studied the planetary mass-radius relationship. Here we present an extensive study of the statistics of planetary luminosities during both formation and evolution. Our results can be compared with individual directly imaged (proto)planets as well as statistical results from surveys. We calculated three synthetic planet populations assuming different efficiencies of the accretional heating by gas and planetesimals. We describe the temporal evolution of the planetary mass-luminosity relation. We study the shock and internal luminosity during formation. We predict a statistical version of the post-formation mass versus entropy "tuning fork" diagram. We find high nominal post-formation luminosities for hot and cold gas accretion. Individual formation histories can still lead to a factor of a few spread in the post-formation luminosity at a given mass. However, if the gas and planetesimal accretional heating is unknown, the post-formation luminosity may exhibit a spread of as much as 2-3 orders of magnitude at a fixed mass covering cold, warm, and hot states. As a key result we predict a flat log-luminosity distribution for giant planets, and a steep increase towards lower luminosities due to the higher occurrence rate of low-mass planets. Future surveys may detect this upturn. During formation an estimate of the planet mass may be possible for cold gas accretion if the gas accretion rate can be estimated. Due to the "core-mass effect" planets that underwent cold gas accretion can still have high post-formation entropies. Once the number of directly imaged exoplanets with known ages and luminosities increases, the observed distributions may be compared with our predictions.Comment: 44 pages, 26 figures (journal format). A&A in print. Language correction only relative to V

The influence of infall on the properties of protoplanetary discs : Statistics of masses, sizes, lifetimes, and fragmentation

Context. The properties of protoplanetary discs determine the conditions for planet formation. In addition, planets can already form during the early stages of infall. Aims. We constrain physical quantities such as the mass, radius, lifetime, and gravitational stability of protoplanetary discs by studying their evolution from formation to dispersal. Methods. We perform a population synthesis of protoplanetary discs with a total of 50 000 simulations using a 1D vertically integrated viscous evolution code, studying a parameter space of final stellar mass from 0.05 to 5 Msol . Each star-and-disc system is set up shortly after the formation of the protostar and fed by infalling material from the parent molecular cloud core. Initial conditions and infall locations are chosen based on the results from a radiation-hydrodynamic population synthesis of circumstellar discs. We also consider a different infall prescription based on a magnetohydrodynamic (MHD) collapse simulation in order to assess the influence of magnetic fields on disc formation. The duration of the infall phase is chosen to produce a stellar mass distribution in agreement with the observationally determined stellar initial mass function. Results. We find that protoplanetary discs are very massive early in their lives. When averaged over the entire stellar population, the discs have masses of ∼0.3 and 0.1 Msol for systems based on hydrodynamic or MHD initial conditions, respectively. In systems characterised by a final stellar mass ∼1 Msol , we find disc masses of ∼0.7 Msol for the “hydro” case and ∼0.2 Msol for the “MHD” case at the end of the infall phase. Furthermore, the inferred total disc lifetimes are long, ≈5–7 Myr on average. This is despite our choice of a high value of 10^-2 for the background viscosity α-parameter. In addition, we find that fragmentation is common in systems that are simulated using hydrodynamic cloud collapse, with more fragments of larger mass formed in more massive systems. In contrast, if disc formation is limited by magnetic fields, fragmentation may be suppressed entirely. Conclusions. Our work draws a picture quite different from the one often assumed in planet formation studies: protoplanetary discs are more massive and live longer. This means that more mass is available for planet formation. Additionally, when fragmentation occurs, it can affect the disc’s evolution by transporting large amounts of mass radially. We suggest that the early phases in the lives of protoplanetary discs should be included in studies of planet formation. Furthermore, the evolution of the central star, including its accretion history, should be taken into account when comparing theoretical predictions of disc lifetimes with observations

The Nature of the Halo Population of NGC 5128 Resolved with NICMOS on the Hubble Space Telescope

We present the first infrared color-magnitude diagram (CMD) for the halo of a giant elliptical galaxy. The CMD for the stars in the halo of NGC 5128 (Centaurus A) was constructed from HST NICMOS observations of the WFPC2 CHIP-3 field of Soria et al. (1996) to a 50% completeness magnitude limit of [F160W]=23.8. This field is located at a distance of 08'50" (~9 kpc) south of the center of the galaxy. The luminosity function (LF) shows a marked discontinuity at [F160W]=20.0. This is 1-2 mag above the tip of the red giant branch (TRGB) expected for an old population (~12 Gyr) at the distance modulus of NGC 5128. We propose that the majority of stars above the TRGB have intermediate ages (~2 Gyr), in agreement with the WFPC2 observations of Soria et al. (1996). Five stars with magnitudes brighter than the LF discontinuity are most probably due to Galactic contamination. The weighted average of the mean giant branch color above our 50% completeness limit is [F110W]-[F160W]=1.22+-0.08 with a dispersion of 0.19 mag. From our artificial-star experiments we determine that the observed spread in color is real, suggesting a real spread in metallicity. We estimate the lower and upper bounds of the stellar metallicity range by comparisons with observations of Galactic star clusters and theoretical isochrones. Assuming an old population, we find that, in the halo field of NGC 5128 we surveyed, stars have metallicities ranging from roughly 1% of solar at the blue end of the color spread to roughly solar at the red end, with a mean of [Fe/H]=-0.76 and a dispersion of 0.44 dex.Comment: Accepted for publication in AJ, 23 pages of text, 13 figures, uses aastex v5.

Characterization of Extragalactic 24micron Sources in the Spitzer First Look Survey

In this Letter, we present the initial characterization of extragalactic 24um sources in the Spitzer First Look Survey (FLS) by examining their counterparts at 8um and R-band. The color-color diagram of 24-to-8 vs. 24-to-0.7um is populated with 18,734 sources brighter than the 3sigma flux limit of 110uJy, over an area of 3.7sq.degrees. The 24-to-0.7um colors of these sources span almost 4 orders of magnitudes, while the 24-to-8um colors distribute at least over 2 orders of magnitudes. In addition to identifying ~30% of the total sample with infrared quiescent, mostly low redshift galaxies, we also found that: (1) 23% of the 24um sources (~1200/sq.degrees) have very red 24-to-8 and 24-to-0.7 colors and are probably infrared luminous starbursts with L(IR)>3x10^(11)Lsun at z>1. In particular, 13% of the sample (660/sq.degrees) are 24um detected only, with no detectable emission in either 8um or R-band. These sources are the candidates for being ULIRGs at z>2. (2) 2% of the sample (85/sq.degrees) have colors similar to dust reddened AGNs, like Mrk231 at z~0.6-3. (3) We anticipate that some of these sources with extremely red colors may be new types of sources, since they can not be modelled with any familiar type of spectral energy distribution. We find that 17% of the 24um sources have no detectable optical counterparts brighter than R limit of 25.5mag. Optical spectroscopy of these optical extremely faint 24um sources would be very difficult, and mid-infrared spectroscopy from the Spitzer would be critical for understanding their physical nature (Abridged).Comment: Accepted for publication in ApJ (Spitzer Special Issue

Radial Velocity Survey for Planets around Young stars (RVSPY) A transiting warm super-Jovian planet around HD 114082, a young star with a debris disk

Aiming to detect planetary companions to young stars with debris disks via the radial velocity method, we observed HD114082 during April 2018 - August 2022 as one of the targets of our RVSPY program (Radial Velocity Survey for Planets around Young stars). We used the FEROS spectrograph, mounted to the MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs). Additionally, we analyzed archival HARPS spectra and TESS photometric data. We used the CERES, CERES++ and SERVAL pipelines to derive RVs and activity indicators and ExoStriker for the independent and combined analysis of the RVs and TESS photometry. We report the discovery of a warm super-Jovian companion around HD114082 based on a 109.8$\pm$0.4 day signal in the combined RV data from FEROS and HARPS, and on one transit event in the TESS photometry. The best-fit model indicates a 8.0$\pm$1.0 Mjup companion with a radius of 1.00$\pm$0.03 Rjup in an orbit with a semi-major axis of 0.51$\pm$0.01 au and an eccentricity of 0.4$\pm$0.04. The companions orbit is in agreement with the known near edge-on debris disk located at about 28 au. HD114082b is possibly the youngest (15$\pm$6 Myr), and one of only three younger than 100 Myr giant planetary companions for which both their mass and radius have been determined observationally. It is probably the first properly model-constraining giant planet that allows distinguishing between hot and cold-start models. It is significantly more compatible with the cold-start model.Comment: 10 pages, 9 figures, 5 tables; Accepted for publication in A&A Letter

Obscured and unobscured active galactic nuclei in the Spitzer Space Telescope First Look Survey

Selection of active galactic nuclei (AGN) in the infrared allows the discovery of AGN whose optical emission is extinguished by dust. In this paper, we use the Spitzer Space Telescope First Look Survey (FLS) to assess what fraction of AGN with mid-infrared luminosities comparable to quasars are missed in optical quasar surveys due to dust obscuration. We begin by using the Sloan Digital Sky Survey (SDSS) database to identify 54 quasars within the 4 deg^2 extragalactic FLS. These quasars occupy a distinct region in mid-infrared color space by virtue of their strong, red, continua. This has allowed us to define a mid-infrared color criterion for selecting AGN candidates. About 2000 FLS objects have colors consistent with them being AGN, but most are much fainter in the mid-infrared than the SDSS quasars, which typically have 8 micron flux densities, S(8.0), ~1 mJy. We have investigated the properties of the 43 objects with S(8.0) >= 1 mJy satisfying our AGN color selection. This sample should contain both unobscured quasars, and AGN which are absent from the SDSS survey due to extinction in the optical. After removing 16 known quasars, three probable normal quasars, and eight spurious or confused objects from the initial sample of 43, we are left with 16 objects which are likely to be obscured quasars or luminous Seyfert-2 galaxies. This suggests the numbers of obscured and unobscured AGN are similar in samples selected in the mid-infrared at S(8.0)~1 mJy.Comment: To appear in the ApJS Spitzer Special Issu

Near-Infrared Accretion Signatures from the Circumbinary Planetary-Mass Companion Delorme 1 (ab)b

Accretion signatures from bound brown dwarf and protoplanetary companions provide evidence for ongoing planet formation, and accreting substellar objects have enabled new avenues to study the astrophysical mechanisms controlling the formation and accretion processes. Delorme 1 (AB)b, a ?1/430-45 Myr circumbinary planetary-mass companion, was recently discovered to exhibit strong Hα emission. This suggests ongoing accretion from a circumplanetary disk, somewhat surprising given canonical gas disk dispersal timescales of 5-10 Myr. Here, we present the first NIR detection of accretion from the companion in Paβ, Pa?3, and Br?3 emission lines from SOAR/TripleSpec 4.1, confirming and further informing its accreting nature. The companion shows strong line emission, with L line ≈ 1-6 × 10-8 L ? across lines and epochs, while the binary host system shows no NIR hydrogen line emission (L line \u3c 0.32-11 × 10-7 L ?). Observed NIR hydrogen line ratios are more consistent with a planetary accretion shock than with local line excitation models commonly used to interpret stellar magnetospheric accretion. Using planetary accretion shock models, we derive mass accretion rate estimates of Ṁpla?1/43 -4 × 10-8 M J yr-1, somewhat higher than expected under the standard star formation paradigm. Delorme 1 (AB)b\u27s high accretion rate is perhaps more consistent with formation via disk fragmentation. Delorme 1 (AB)b is the first protoplanet candidate with clear (signal-to-noise ratio ?1/45) NIR hydrogen line emission