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The incidence of X-ray AGN and non-AGN galaxies in the far-infrared: Insights into host galaxy properties and AGN obscuration

Mountrichas, G., Carrera, F. J., Georgantopoulos, I., Mateos, S., Ruiz, A., Corral, A., Astronomy and Astrophysics

We investigate the far-infrared (far-IR) incidence of X-ray-selected active galactic nuclei (AGNs) and galaxies that do not host an AGN (non-AGNs) as a function of the stellar mass (M_*), star formation rate (SFR), and specific black hole accretion rate (λ_sBHAR), using data from five well-characterized extragalactic fields (COSMOS, XMM-LSS, Stripe82, ELAIS-S1, and CDFS-SWIRE). We constructed spectral energy distributions (SEDs) using optical-to-far-IR photometry to derive host galaxy properties and assess AGN obscuration, while X-ray absorption was quantified using the 4XMM-DR11s catalogue. Our final sample comprises 172 697 non-AGN galaxies (53% Herschel-detected) and 2417 X-ray AGNs (73% Herschel-detected), with 10 < log [M_*/M_⊙]< 12 and 0 < z < 2. We find that X-ray AGNs exhibit a relatively flat far-IR detection rate across stellar mass and specific SFR (sSFR = SFR/M_*), unlike non-AGN galaxies, where detection correlates strongly with star formation. Far-IR detection among AGNs decreases with increasing λ_sBHAR, even as their SFR rises. Our results suggest that X-ray AGNs are preferentially found in gas-rich environments, where both star formation and black hole accretion are fuelled by the presence of cold gas. The far-IR incidence of X-ray AGNs remains high across all sSFR bins, indicating that these AGNs can coexist with ongoing star formation for extended periods, in line with a scenario in which AGNs feedback regulates rather than abruptly quenches star formation. We also find that comparing AGNs and non-AGN SFRs without separating Herschel-detected from non-detected sources introduces biases. Obscured AGNs show 10% higher far-IR detection rates than unobscured ones, yet at similar λ_sBHAR, unobscured AGNs tend to have higher SFR. This may indicate that obscured AGNs reside in dustier environments where moderate star formation still contributes to far-IR emission. Our results support a scenario in which AGNs and star formation coexist in gas-rich galaxies, with AGNs feedback acting as a regulatory process over extended timescales and not necessarily quenching.

Deep Reinforcement Learning for Efficient Scheduling of Ground-based Astronomical Observations

Cao, Hai, Hu, Shaoming, Du, Junju, Chen, Xu, Liu, Shuqi, Feng, Shuai, Zhang, Bo, Jiang, Yuchen, The Astronomical Journal

Ground-based astronomical observations face inherent challenges from weather changes, target visibility window constraints, and observational requirements. Enhancing the efficiency and effectiveness of telescope operations has long been a key objective for many observatories because of the high cost of observational resources. In this study, we formalize observation scheduling as a time-dependent combinatorial optimization problem. To achieve this, we implement a pointer network with temporal attention that is capable of planning observations while accounting for time-varying factors such as moonlight interference, target altitude, and air mass, which impact the exposure time and image quality. To support the training of the deep neural network, we propose a scoring mechanism to evaluate the effectiveness of the observations, which is optimized through a refined REINFORCE algorithm with a baseline. Furthermore, an exposure time calculator and an equipment kinematic model are incorporated to dynamically estimate the time costs during the decision-making process. The simulation results demonstrated that the trained model significantly outperformed both manual scheduling and a greedy algorithm in terms of theoretical reward scores and the total number of scheduled targets. Observation experiments conducted using a dual-telescope system at Muztaga observatory further validated the superiority of our approach, demonstrating a 45.8% enhancement in the total signal-to-noise ratio across all observed targets and a 24.1% increase in the number of completed tasks under the same observing conditions.

Traces of the evolution of cosmic void galaxies: An integral field spectroscopy-based analysis

Rodríguez-Medrano, Agustín M., Paz, Dante J., Mast, Damián, Stasyszyn, Federico A., Ruiz, Andrés N., Astronomy and Astrophysics

Context. Galaxies in the most underdense regions of the Universe, known as cosmic voids, exhibit astrophysical properties that suggest a distinct evolutionary path compared to galaxies in denser environments. Numerical simulations indicate that the assembly of void galaxies occurs later, leading to galaxies with younger stellar populations, low metallicities, and high gas content in their halos, which provides the fuel to sustain elevated star formation activity. Aims. Our objective in this work is to test these numerical predictions using observational data by comparing galaxies in voids with galaxies in non-void environments. Methods. We used voids identified in the SDSS data and selected galaxies from the MaNGA survey, which offers integral field spectroscopy (IFS) for each galaxy. This IFS data allows for state-of-the-art modeling of their stellar populations. We separated the galaxies into void and non-void samples, mimicked the magnitude distribution, and compared their integrated astrophysical properties, as well as the metallicity and age profiles, through a stacking technique. We analyzed early-type galaxies (ETGs) and late-type galaxies (LTGs) separately. Results. We find that void galaxies tend to host younger and less metal-rich stellar populations. This trend is observed both as a function of mass and in samples with matched magnitude distributions. With respect to the gas mass, we do not find differences across environments. When dividing galaxies into ETGs and LTGs, we observe that ETGs show negative gradients in both age and metallicity, with void galaxies consistently appearing younger and less metal-rich. For LTGs, age gradients are also negative, indicating younger populations in void galaxies. However, we do not find statistically significant differences in the stellar metallicity gradients between void and non-void environments. Conclusions. Our results show how the astrophysical properties of galaxies in voids differ from those of galaxies in the rest of the Universe. This suggests that the void environment plays a role in the evolution of its galaxies, delaying their assembly and growth.

Nature or Nurture: LMC-like Dust in the Solar Metallicity Galaxy M31

Clayton, Geoffrey C., Yanchulova Merica-Jones, Petia, Gordon, Karl D., Decleir, Marjorie, Murray, Claire E., Bohlin, Ralph, Bianchi, Luciana, Massey, Philip, Wolff, Michael J., The Astrophysical Journal

Using the Hubble Space Telescope/Space Telescope Imaging Spectrograph, ultraviolet (UV) extinction curves have been measured in M31 along 13 new sight lines, increasing the M31 sample to 17. This sample covers a wide area of M31, having galactocentric distances of 5─16 kpc, enabling the analysis of UV extinction curve variations over a large region of an external galaxy similar to the Milky Way with global galactic characteristics such as metallicity for the first time. No correlation is found between the extinction parameters and galactocentric distance, which might be expected if there is a radial metallicity gradient in M31. Most of the new UV extinction curves presented here are significantly different from the average extinction curves of the Milky Way, Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC), but the average M31 extinction curve is similar to the average extinction curve in the 30 Dor region of the LMC. The wide range of extinction curves seen in each individual Local Group galaxy suggests that global galactic properties such as metallicity may be less important than the local environmental conditions, such as density, UV radiation field, and shocks along each sight line. The combined behavior of the Milky Way, LMC, SMC, and now M31 UV extinction curves supports the idea that there is a family of curves in the Local Group with overlapping dust grain properties between different galaxies.

The Epoch of Giant Planet Migration Planet Search Program. III. The Occurrence Rate of Young Giant Planets inside the Water Ice Line

Tran, Quang H., Bowler, Brendan P., Cochran, William D., Bender, Chad F., Halverson, Samuel, Mahadevan, Suvrath, Ninan, Joe P., Robertson, Paul, Roy, Arpita, Stefánsson, Guðmundur, Terrien, Ryan C., The Astronomical Journal

We present statistical results from the Epoch of Giant Planet Migration RV planet search program. This survey was designed to measure the occurrence rate of giant planets interior to the water ice line of young Sun-like stars, compare this to the prevalence of giant planets at older ages, and provide constraints on the timescale and dominant inward migration mechanism of giant planets. Our final sample amounts to 85 single young (20─200 Myr) G and K dwarfs that we target across a 4 yr time baseline with the near-infrared Habitable-zone Planet Finder spectrograph at McDonald Observatory's Hobby-Eberly Telescope. As part of this survey, we discovered the young hot Jupiter HS Psc b. We characterize survey detection completeness with realistic injection-recovery tests and measure an occurrence rate of 1.9−1.4+2.6 % for intermediate-age giant planets ( 0.3MJ<msini<13MJ ) within 2.5 au. This is lower than the field age occurrence rate for the same planet masses and separations and favors an increase in the prevalence of giant planets over time from ∼100 Myr to several Gyr, although our results cannot rule out a constant rate. A decaying planet occurrence rate is, however, strongly excluded. This suggests that giant planets located inside the water ice line originate from a combination of in situ formation or early migration coupled with longer-term inward scattering. The completeness-corrected prevalence of young hot Jupiters in our sample is 1.5−1.1+2.2 % —similar to the rate for field stars—and the 95% upper limit for young brown dwarfs within 5000 days is <3.6% . ^*Based on observations obtained with the Hobby-Eberly Telescope (HET), which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximillians-Universitaet Muenchen, and Georg-August Universitaet Goettingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.