arXiv subjects

Jia-Sheng Huang

Publications and source records attributed to Jia-Sheng Huang.

At least 19 recordsLinked to original sources

arXiv2026

HI Depletion Begins Well Beyond the Virial Radius: A FAST Stacking Study of 36 Galaxy Clusters to 5R200

We present a stacking study of the neutral atomic hydrogen (HI) content in and around 36 local galaxy clusters at $z<0.07$, using a combination of the FAST all sky HI survey (FASHI) and the extensive spectroscopic catalog mainly from the Dark Energy Spectroscopic Instrument (DESI). We employ spectral stacking techniques to probe the average HI mass and HI-to-stellar mass ratio ($M_{\rm HI}/M_*$) for member galaxies down to stellar masses of $M_*\sim 10^9M_\odot$, spanning a projected cluster-centric distance to $5R_{200}$. Our analysis reveals a pronounced environmental effect: both $M_{\rm HI}$ and $M_{\rm HI}/M_*$ decrease steadily towards the cluster center, dropping by $\sim 0.5$ dex on average from the outskirts to the core. Crucially, we find that $M_{\rm HI}/M_*$ of galaxies remain lower than the field galaxies even at the $5R_{200}$. This provides direct, statistical evidence for substantial gas stripping and pre-processing in the cluster outskirts, likely occurring in infalling groups and large-scale filaments. By further splitting the sample by $g-r$ color, we show that the HI deficiency persists at fixed galaxy color: even the bluest cluster members exhibit $\sim 0.5$~dex lower $M_{\rm HI}/M_*$ than field galaxies of similar color, reflecting environmental effects on the cold gas reservoir prior to full optical transformation. The total HI mass within clusters and their outskirts agrees broadly with predictions from cosmological simulation. Our results underscore the critical role of the extended cluster environment in quenching galaxies by depleting their cold gas reservoirs well before they enter the dense cluster core.

astro-ph.GA↗

arXiv2026

Ly$α$ Escape in JWST/NIRCam F430M-Selected H$α$ Emitters at $z\simeq5.5$

We study the Ly$α$ escape fraction ($f_{\rm esc}$) in an H$α$-selected sample of star-forming galaxies at $z\simeq5.5$, identified via JWST/NIRCam F430M excess and covered by archival VLT/MUSE data. By anchoring the intrinsic Ly$α$ production to H$α$ emission, our approach provides a direct and Ly$α$-unbiased probe of the escape of Ly$α$ photons in galaxies with SFR $\gtrsim 0.1\,M_\odot\,{\rm yr^{-1}}$ at this epoch. Ly$α$ emission is detected in 3 out of 12 galaxies covered by VLT/MUSE. Combining detections and upper limits, we place a conservative upper bound of $\langle f_{\rm esc}^{\rm Lyα} \rangle < 0.32$ on the population-averaged Ly$α$ escape fraction. We find that Ly$α$ detections are preferentially associated with nearly dust-free systems, while no clear correlation between SFR and $f_{\rm esc}$, suggesting a stochastic picture of Ly$α$ escape. Interestingly, three of the four Ly$α$-detected galaxies reside within a known overdense structure, suggesting that local environment may further facilitate Ly$α$ photons escape. Our H$α$-selected approach establishes a general and scalable framework for probing Ly$α$ escape by combining JWST medium- or narrow-band imaging with ground-based spectroscopic data, enabling systematic and less biased studies of Ly$α$ visibility in typical star-forming galaxies during the post-reionization era.

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arXiv2026

COSMOS-3D: Dense Circumnuclear Gas across Black Hole Growth Phases at z ~ 3

We report the discovery of two broad-line X-ray AGNs (cid_414 and cid_947) at z ~ 3 identified in the JWST Cycle 3 COSMOS-3D program using NIRCam F444W grism spectroscopy. Both exhibit prominent HeI+Pa$γ$ emission and absorption, indicative of circumnuclear dense gas that is traced in these systems. Complementary UV and optical spectroscopy in the COSMOS field provides Ly$α$, Si IV, and C IV measurements. Both sources are detected in MIRI F1000W, and cid_414 is also detected in F2100W, indicating hot dust emission. The two AGNs show distinct black hole and obscuration properties. The source cid_414 displays little red dots (LRD)-like V-shape spectra energy distribution (SED) shape with a turnover near the Balmer 4000 Å break, and a narrow Ly$α$ line with $\log L_{\rm Lyα}=42.49\pm0.01~\mathrm{erg\ s^{-1}}$, with no additional metal lines detected. In contrast, cid_947 exhibits a higher HeI absorption column density, larger X-ray--inferred $N_{\rm H}$, lower intrinsic 2--10 keV luminosity, and strong blueshifted features in He I, Si IV, and C IV absorption with velocity offsets exceeding $5000~\mathrm{km\ s^{-1}}$. Photoionization modeling implies gas densities of $\sim10^{9-10} \mathrm{cm^{-3}}$ and sizes comparable to the broad-line region, consistent with dense gas envelopes predicted for LRDs. Together with previous detections of HeI absorption in compact little red dots, these results suggest that dense circumnuclear gas is likely prevalent at high redshift and may regulate obscuration and black hole--host co-evolution across AGN types.

astro-ph.GA↗

arXiv2026

An Archival Optical Counterpart Search for Extragalactic Fast X-Ray Transients Discovered by Einstein Probe

Extragalactic fast X-ray transients (eFXTs) represent a rapidly growing class of high-energy phenomena, whose physical origins remain poorly understood. With its wide-field, sensitive all-sky monitoring, the Einstein Probe (EP) has greatly increased the discovery rate of eFXTs. The search and identification of the optical counterparts of eFXT are vital for understanding their classification and constraining their physical origin. Yet, a considerable fraction of eFXTs still lack secure classifications due to the absence of timely follow-up observations. We carry out a systematic search of publicly available optical survey data and transient databases (including the Zwicky Transient Facility, ZTF, and the Transient Name Server, TNS) for optical counterparts to eFXT candidates detected by EP. In this paper, we describe our ongoing program and report the first results. Specifically, we identified the eFXT EP240506a to be associated with a UV/optical counterpart, AT 2024ofs. Spectroscopy of its host galaxy with VLT yields a redshift of $z = 0.120 \pm 0.002$. By combining archival survey data with early-time multiwavelength observations, we find that the luminosity and light-curve evolution of AT~2024ofs are consistent with a core-collapse supernova origin. From detectability simulations, we estimate a local event rate density $ρ_{0}=8.8^{+21.2}_{-3.9}\ \mathrm{yr^{-1}\, Gpc^{-3}}$ for EP240506a-like events, and completeness-corrected rate of about $36$--$78\ \mathrm{yr^{-1}\ Gpc^{-3}}$ for EP-detected X-ray transients associated with supernovae. Our results demonstrate the potential of EP to uncover prompt high-energy emission from core-collapse supernovae and underscore the critical importance of timely follow-up of future eFXT events.

astro-ph.HE↗

arXiv2026

PEARLS: 21 Transients Found in the Three-Epoch NIRCam Observations in the Continuous Viewing Zone of the James Webb Space Telescope

We present 21 transients from our three-epoch, four-band NIRCam observations covering 14.16 arcmin^2 in the Spitzer IRAC Dark Field (IDF), taken by the JWST Prime Extragalactic Areas for Reionization and Lensing Science program with a time cadence of ~6 months. A separate Hubble Space Telescope program provided Advanced Camera for Surveys optical imaging contemporaneous with the second and third epochs of the NIRCam observations. The NIRSpec spectroscopy on three transients confirmed a Type Ia supernova at z=1.63 and the host galaxies of the other two at z=2.64 and 1.90, respectively. Combining these with the photometric redshifts (z_ph) of the host galaxies in the rest of the sample, we find that the transients are in either a "mid-z" group at z>1.6 with M_V < -16.0 mag or a "low-z" group at z < 0.4 with M_H > -14.0 mag. The mid-z transients are consistent with supernovae. In contrast, the low-z transients' luminosities fall in the range of the so-called "gap transients" between supernovae and novae. However, this latter conclusion is only tentative due to possible catastrophic failures in z_ph that could bias them to low-z. Conversely, if they are indeed at z < 0.4, it would be worth studying similar transients in the future. Our work further demonstrates the power of NIRCam in transient science and also shows that it would be more fruitful to carry out a long-term monitoring program with more passbands, a higher cadence and prompt follw-up spectroscopy. Being in the continuous viewing zone of the JWST, the IDF is an ideal field for this purpose.

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arXiv2025

HI-detected Dwarf Galaxies in the FASHI Survey: Insights from Single- and Double-Peaked Emission-Line Samples

We present a sample of low HI mass dwarf galaxies ($M_{\rm HI} < 10^8 M_\odot$) detected by The FAST All Sky HI Survey (FASHI) project. Due to the faint and irregular morphology of these galaxies, the default photometry is often inaccurate. Therefore, we utilized The Dark Energy Camera Legacy Survey (DECaLS) data to perform careful photometric measurements, and find that the low HI mass galaxies have similar stellar mass densities to dwarf elliptical (dE) galaxies. Compared to other dwarf galaxy populations, the HI-selected dwarfs exhibit higher stellar mass densities than ultradiffuse galaxies, and similar densities to HI-selected low-surface-brightness galaxies, albeit with lower stellar masses, suggesting a possible evolutionary connection among these populations. By classifying the galaxies according to their HI spectral-line profiles, we show that the double-peaked sources conform closely to the Tully-Fisher relation, whereas the single-peaked sources follow the Faber-Jackson relation but with large scatter. This indicates that the single-peaked systems are likely dispersion dominated and that the relationship between stellar mass and halo mass in such systems may remain consistent across both low- and high-mass regimes. These findings suggest that HI-selected dwarf galaxies with single-peaked HI profiles may share a similar dynamical state with massive ellipticals, offering new insights into their structural evolution and the diversity of formation pathways for low-mass galaxies.

astro-ph.GA↗

arXiv2025

Evolution of the Physical Properties of the Most Massive Galaxies in Clusters and their Protohalos

We investigated the evolution of the physical properties of the brightest galaxies in clusters and their protohalos from $z = 4$ to $z = 0$. Galaxy clusters and groups are identified using a halo-based group finder applied to the COSMOS2020 galaxy catalog. We construct evolution chains from low redshift clusters to higher redshift groups via the abundance matching method. The region of protohalos corresponding to clusters is defined on the basis of a characteristic radius. Our analysis encompasses a wide range of physical properties, including stellar mass, luminosity, star formation rate (SFR), specific star formation rate (sSFR), color ($g - r$), and stellar age. The evolution trends of the most massive galaxies (MMGs) in higher redshift groups and their corresponding protohalos are generally consistent. The stellar mass of MMGs shows an increasing trend across the entire redshift range. By considering the stellar mass growth as in-situ and ex-situ components, we find that in-situ star formation is efficient at $z \sim 2$, while ex-situ accretion becomes the primary growth channel at later times. At $z \gtrsim 2$, MMGs undergo an intense star formation phase of approximately $10^{2}\ \rm M_{\odot}yr^{-1}$, but are generally quenched at lower redshifts. Stellar age analysis suggests that most stars in MMGs formed at $z > 2$. Our results present a coherent picture of MMG evolution across cosmic epochs, which is broadly consistent with the current theoretical framework of galaxy formation and evolution. Moreover, our work provides an intriguing way to trace galaxy evolution through the construction of cluster evolutionary chains in observations.

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arXiv2025

Probing Obscured Star Formation in Galaxy Clusters Using JWST Medium Band Images: 3.3$μ\rm m$ PAH Emitter Sample in Abell 2744

Star-forming galaxies in galaxy clusters play a crucial role in understanding the advanced stages of galaxy evolution within dense environments. We present a sample of 3.3$μ$m PAH-bright galaxies in the Abell 2744 (A2744) galaxy cluster. Using F430M medium band images, we select PAH emitters in the galaxy cluster, which capture the 3.3$μ$m PAH emission at the redshift of A2744. Our multi-wavelength study demonstrates consistent star formation rates (SFRs) derived from PAH emission and SED fitting, indicating the 3.3 $μ$m PAH flux estimated from medium band image alone can reveal the entirety of star formation, immune to dust obscuration. We find that the PAH emitters are located in relatively low mass surface density regions of A2744, with SFRs aligning with the field star-forming main sequence at $z=0.3$. The PAH emission morphologies show more asymmetry than that of the F444W image when asymmetry index $> 0.4$. With these results, we suggest that these star-forming galaxies in A2744 are in the stage of falling into the cluster from the field, and have not been quenched yet. We further explore a potential link between these galaxies and cosmic filaments being accreted onto the cluster, which may channel gas inflows to fuel star formation. JWST medium-band imaging provides a powerful new tool for identifying heavily dust-obscured star-forming populations. Future HI and low-J CO observations should be prioritized to resolve the cold gas kinematics and star formation processes in these systems, which would directly test the role of environmental stripping versus filamentary gas supply.

astro-ph.GA↗

arXiv2025

An H$α$ Cloud in the HI Tail: Recent Star Formation in the Outskirts of NGC 4258 Revealed by Nanshan 1-m Telescope

We present first-light deep H$α$ imaging taken with the Nanshan 1-meter wide-field telescope on the local galaxy NGC 4258, alongside archival data from Hubble Space telescope (HST), Westerbork Synthesis Radio Telescope, and The Dark Energy Camera Legacy Survey. The H$α$ image shows ongoing star formation not only inside the galaxy but also in an HI cloud in the eastern HI tail, which is roughly 16 kpc away from the main galaxy. The HST images reveal several ultra-blue compact objects ($\rm F555W - F814W <-0.5 mag,\, FWHM\sim 0.2''$) in the H$α$ bright region, aligned with the HI tail, suggesting the presence of young open cluster candidate in the HI tail. Our results suggest that wide field H$α$ imaging is a valuable tool for investigating recent star formation in the extended regions of NGC 4258. Furthermore, the star formation in diffuse HI tails could highlight an potential aspect of galaxy stellar halo formation, warranting further investigation of the impact of star formation in halos on galaxy evolution.

astro-ph.GA↗

arXiv2025

Starburst Galaxies in Their Last Billion Years: An H$δ$ Absorption Line Selected Sample

In this paper, we focus on the study of starburst galaxies in their final billion years. Our galaxy selection is based solely on the presence of the H$δ$ absorption line, which permits tracing the later evolution of starburst galaxies, coinciding with the emergence of A-type stars in these galaxies. We propose a novel method that utilizes star formation rate and UVJ colors to classify galaxies in the sample, and use the spectral features to mark their evolution stages. Our in-depth analysis of the MgII line indicates the substantial increasing of F- and G-type stars when a galaxy evolves from star forming to quiescent phase. Furthermore, we identify AGNs in this sample to explore their roles in the later stage of galaxy star formation history.

astro-ph.GA↗

arXiv2025

Comparison of Global HI and H$α$ Line Profiles in MaNGA Galaxy Pairs with FAST

We present case studies comparing the global HI and H$α$ emission line profiles of six galaxy pairs. The six pairs are selected to have different nuclear activities, with two hosting an active galactic nucleus, and in different merging stages (two of each from pre-merging, merging, and post-merger stages). We observe their global HI spectra with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), achieving a noise level of about 0.5 mJy. Five out of the six pair systems have secure detections of HI emissions (signal-to-noise ratio > 10). The HI fraction and star formation efficiency of the six pairs do not deviate from isolated galaxies. For the HI line profiles, common unique asymmetry is observed, indicating disturbances on the atomic gas from the galaxy interaction. The global H$α$ spectra of the merger systems are constructed from the optical integral field spectroscopic observations, by integrating the flux in corresponding line-of-sight velocity bins. The H$α$ spectra tend to show multiple components in the pre-merger phase, and single component line profiles in the post-merger systems, while all HI spectra show single component line profiles regardless of merger stages. The HI and H$α$ spectra show offsets in the central velocities, which appear to decrease from >100 km/s in the pre-merger pair to <10 km/s in post-merger pairs. This trend is consistent with the scenario that, despite the significantly different distribution and kinematics of the atomic and ionized gases, the merging process may contribute to the mixing and eventually align various gas contents.

astro-ph.GA↗

arXiv2024

A first measurement of galaxy merger rate increasing in dynamically colder protoclusters at cosmic noon

The process of galaxy cluster formation likely leaves an imprint on the properties of its individual member galaxies. Understanding this process is essential for uncovering the evolutionary connections between galaxies and cosmic structures. Here we study a sample of ten protoclusters at z~2-3 in different dynamical states that we estimate based on spectroscopic data of their members. We combine the dynamical information with HST imaging to measure galaxy sizes and pair fractions. Our analysis reveals a clear anti-correlation between the velocity dispersion of the protocluster and its galaxy pair fractions (indicative of merger rates). The velocity dispersion also anti-correlates with the dispersion in size among of the member galaxies. These correlations may be explained by protoclusters in colder dynamical states maintaining a velocity dispersion and galaxy number density that boosts galaxy mergers, which in turn contributes to the structural expansion and compaction of galaxies. Our findings offer constraints for cosmological models regarding the evolution of galaxy morphology across different stages in the assembly of protoclusters.

astro-ph.GA↗

arXiv2024

A Complete 16 $μ$m selected Galaxy Sample at $z \sim 1$. II: Morphological Analysis

We present morphological analysis of the 16$μ$m flux-density-limited galaxy sample at 0.8$<z<$1.3 from arXiv:2103.04585. At the targeted redshift, the 16$μ$m emission corresponds to the Polycyclic aromatic hydrocarbon (PAH) feature from intense star formation, or dust heated by AGN (Active galactic nuclei). Our sample of 479 galaxies are dominated by Luminous Infrared Galaxies (LIRGs, 67\%) in three CANDLES fields (EGS, GOODS-N, and GOODS-S), and are further divided into AGN dominated, star-forming dominated, composite, and blue compact galaxies by their spectral energy distribution (SED) types. The majority of our sample (71\%) have disky morphologies, with the few AGN dominated galaxies being more bulge-dominanted than the star-forming dominated and composite galaxies. The distribution of our sample on the Gini vs. M$_{\text{20}}$ plane is consistent with previous studies, where the Sérsic index $n$ shows an increasing trend towards the smaller M$_{\text{20}}$ and higher Gini region below the dividing line for mergers. The subsample of ULIRGs follow a steep size-mass relation that is closer to the early-type galaxies. In addition, as the 4.5 $μ$m luminosity excess ($L_{4.5}^{Exc}$, proxy for AGN strength) increases, our sample appear to be more bulge-dominated (i.e. higher $n$). Based on the sSFR and compactness ($log_{10}Σ_{1.5}, Σ_{1.5}=M_*/R_e^{1.5}$) diagram, the majority of our LIRG-dominated galaxy sample follow a secular evolution track, and their distribution can be explained without involving any merging activities. Out of the 16 ULIRGs in our sample, six are compact with strong AGN contributions, likely evolving along the fast-track from more violent activities.

astro-ph.GA↗

arXiv2024

A Close Look at Ly$α$ Emitters with JWST/NIRCam at $z\approx3.1$

We study 10 spectroscopically confirmed Ly$α$ emitters (LAEs) at $z\approx3.1$ in the UDS field, covered by JWST/NIRCam in the PRIMER program. All LAEs are detected in all NIRCam bands from F090W to F444W, corresponding to restframe 2200Å--1.2$\mathrm{μm}$. Based on morphological analysis of the F200W images, three out of the 10 targets are resolved into pair-like systems with separations of $<0.9''$, and another three show asymmetric structures. We then construct the spectral energy distributions (SEDs) of these LAEs. All sources, including the pairs, show similar SED shapes, with a prominent flux excess in the F200W band, corresponding to extremely strong [O III]+H$β$ emission lines (${\rm EW_{rest}}=740$--$6500\,$Å). The median effective radii, stellar mass, and UV slope of our sample are 0.36$\,$kpc, $3.8\times10^7\,M_\odot$, and --2.48, respectively. The average burst age, estimated by stellar mass over star formation rate, is $<40\,$Myr. These measurements reveal an intriguing starbursting dwarf galaxy population lying off the extrapolations of the $z \sim 3$ scaling relations to the low-mass end: $\sim 0.7$ dex above the star-forming main sequence, $\sim 0.35$ dex below the mass--size relation, and bluer in the UV slope than typical high-z galaxies at similar UV luminosities. We speculate that these numbers may require a larger main sequence scatter or tail in the dwarf galaxy regime towards the starburst outliers.

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arXiv2024

Close Major-merger Pairs at $z=0$: Star-forming Galaxies with Pseudobulges

We present a study of star-forming galaxies (SFGs) with pseudobulges (bulges with Sérsic index $\rm n < 2$) in a local close major-merger galaxy pair sample (H-KPAIR). With data from new aperture photometries in the optical and near-infrared bands (aperture size of 7\;kpc) and from the literature, we find that the mean Age of central stellar populations in Spirals with pseudobulges is consistent with that of disky galaxies and is nearly constant against the bulge-to-total ratio (B/T). Paired Spirals have a slightly lower fraction of pure disk galaxies ($\rm B/T \leq 0.1$) than their counterparts in the control sample. Compared to SFGs with classical bulges, those with pseudobulges have a higher ($>2\;σ$) mean of specific star formation rate (sSFR) enhancement ($\rm sSFR_{enh} = 0.33\pm0.07$ vs $\rm sSFR_{enh} = 0.12\pm0.06$) and broader scatter (by $\sim 1$\;dex). The eight SFGs that have the highest $\rm sSFR_{enh}$ in the sample all have pseudobulges. A majority (69\%) of paired SFGs with strong enhancement (having sSFR more than 5 times the median of the control galaxies) have pseudobulges. The Spitzer data show that the pseudobulges in these galaxies are tightly linked to nuclear/circum-nuclear starbursts. Pseudobulge SFGs in S+S and in S+E pairs have significantly ($>3\;σ$) different sSFR enhancement, with the means of $\rm sSFR_{enh} = 0.45\pm0.08$ and $-0.04\pm0.11$, respectively. We find a decrease in the sSFR enhancements with the density of the environment for SFGs with pseudobulges. Since a high fraction (5/11) of pseudobulge SFGs in S+E pairs are in rich groups/clusters (local density $\rm N_{1Mpc} \geq 7$), the dense environment might be the cause for their low $\rm sSFR_{enh}$.

astro-ph.GA↗

arXiv2024

Dust and Cold Gas Properties of Starburst HyLIRG-Quasars at $z \sim 2.5$

Some high-z active galactic nuclei (AGNs) are found to reside in extreme star-forming galaxies, such as hyper-luminous infrared galaxies (HyLIRGs), with AGN-removed $L_{\rm{IR}}$ of $>10^{13} L_{\rm{\odot}}$. In this paper, we report NOEMA observations of six apparent starburst HyLIRGs associated with optical quasars at $z\sim2-3$ in the Stripe 82 field, to study their dust and molecular CO properties. Five out of the six candidates are detected with CO(4-3) or CO(5-4) emission, and four in 2mm dust continuum. Based on the linewidth-$L'_{\rm{CO(1-0)}}$ diagnostics, we find that four galaxies are likely unlensed or weakly lensed sources. The molecular gas mass is in the range of $μM_{\rm{H_2}} \sim0.8-9.7\times10^{10} M_{\odot}$ (with $α= 0.8 M_{\odot} (\rm{K km s^{-1} pc^2})^{-1}$ and $μ$ is the unknown possible gravitational magnification factor). We fit their SEDs, after including the observed 2mm fluxes and upper limits, and estimate their apparent (uncorrected for possible lensing effect) star formation rates ($μ$SFRs) to be $\sim400-2500$ $M_{\rm{\odot}} \rm{yr^{-1}}$ with depletion time of $\sim20-110$ Myr. We notice interesting offsets, of $\sim10-40$ kpc spatially or $\sim1000-2000$ km s$^{-1}$ spectroscopically, between the optical quasar and the mm continuum or CO emissions. The observed velocity shift is likely related to the blueshifted broad-emission-line region of quasars, though mergers or recoiling black holes are also possible causes, which can explain the spatial offset and the high intrinsic SFRs in the HyLIRG-quasar systems.

astro-ph.GA↗

arXiv2024

Active Galactic Nuclei in a Mid-Infrared Selected Galaxy Sample at z>0.13: [Ne V]3426 Line Emission as a Benchmark

We present a 24 um-selected spectroscopic sample z > 0.13 (median z = 0.41) in the Lockman Hole field, consisting of 4035 spectra. Our aim is to identify AGNs and determine their fraction in this mid-infrared selected sample. In this work, we use the [Ne V]3426 emission line to spectroscopically identify AGNs. Combined with broad-line Type I AGNs selected in our previous study, our sample consists of 887 (22%) spectroscopically confirmed AGNs. We perform a stacking analysis on the remaining spectra, and find that in various MIR-wedge-selected AGN candidates, the stacked spectra still show significant [Ne V]3426 emission, In contrast, no clear [Ne V]3426 signal is detected in non-AGN candidates falling outside the wedges. Assuming a range of AGN mid-IR SED slope of 0.3< alpha <0.7, and an average star-forming relation derived from 65 star-forming templates, we develop a robust method to separate the AGN and star-forming contributions to the mid-IR SEDs using the rest-frame L12 /L1.6 vs L4.5 /L1.6 diagram. We separate the objects into bins of L12 , and find that AGN fraction increases with increasing L12. We also find that the stacked [Ne V]3426 strength scales with L12 . The pure AGN luminosity at 12 um exhibits a positive correlation with the star formation rates, indicating possible co-evolution and common gas supply between the AGN and their host galaxies. Varying population properties across the redshift range explored contribute to the observed correlation.

astro-ph.GA↗

arXiv2023

Detection of TiO and VO in the atmosphere of WASP-121b and Evidence for its temporal variation

We report the transit observations of the ultra hot Jupiter WASP-121b using the Goodman High Throughput Spectrograph (GHTS) at the 4-meter ground-based telescope Southern Astrophysical Research Telescope (SOAR), covering the wavelength range $502-900$ nm. By dividing the target and reference star into 19 spectroscopic passbands and applying differential spectrophotometry, we derive spectroscopic transit light curves and fit them using Gaussian process framework to determine transit depths for every passbands. The obtained optical transmission spectrum shows a steep increased slope toward the blue wavelength, which seems to be too steep to be accounted for by the Rayleigh scattering alone. We note that the transmission spectrum from this work and other works differ obviously from each other, which was pointed out previously by \citet{Wilson2021} as evidence for temporal atmospheric variation. We perform a free chemistry retrieval analysis on the optical transmission spectra from this work and the literature HST/WFC3 NIR spectrum. We determine TiO, VO and H$_{2}$O with abundances of $-5.95_{-0.42}^{+0.47}$ dex, $-6.72_{-1.79}^{+0.51}$ dex, and $-4.13_{-0.46}^{+0.63}$ dex, respectively. We compare the abundances of all these three molecules derived from this work and previous works, and find that they are not consistent with each other, indicating the chemical compositions of the terminator region may change over long timescales. Future multi-epoch and high-precision transit observations are required to further confirm this phenomena. We note that when combining the transmission spectra in the optical and in NIR in retrieval analysis, the abundances of V and VO, the NIR-to-optical offset and the cloud deck pressure may be coupled with each other.

astro-ph.EP↗