High Specific Star Formation Rate Research Articles

Integral Field Spectroscopy of the cometary starburst galaxy NGC 4861

ABSTRACT Using the PMAS Integral Field Unit on the Calar Alto 3.5 m telescope, we observed the southern component (Markarian 59) of the ‘cometary’ starburst galaxy NGC 4861. Mrk 59 is centred on a giant nebula and concentration of stars 1 kpc in diameter. Strong $\rm H\,\alpha$ emission points to a star-formation rate (SFR) at least 0.47 $\rm M_{\odot }\, yr^{-1}$. Mrk 59 has a very high [O iii] $\rm \lambda 5007/H\,\beta$ ratio, reaching 7.35 in the central nebula, with a second peak at a star-forming hotspot further north. Fast outflows are not detected but nebular motion and galaxy rotation produce relative velocities up to 40 km $\rm s^{-1}$. Spectral analysis of different regions with ‘Fitting Analysis using Differential evolution Optimization’ (FADO) finds that the stars in the central and ‘spur’ nebulae are very young, $\rm \le 125~Myr$ with a large $\rm \lt 10~Myr$ contribution. Older stars ($\rm \sim 1~Gyr$) make up the northern disk component, while the other regions show mixtures of 1 Gyr age with very young stars. This and the high specific SFR $\rm \sim 3.5~Gyr^{-1}$ imply a bimodal star formation history, with Mrk 59 formed in ongoing starbursts fuelled by a huge gas inflow, turning the galaxy into an asymmetric ‘green pea’ or blue compact dwarf. We map the He ii λ4686 emission, and identify a broad component from the central nebula, consistent with the emission of ∼300 Wolf–Rayet stars. About a third of the He ii λ4686 flux is a narrow line emitted from a more extended area covering the central and spur nebulae, and may have a different origin.

Evolution of the UV LF from z ∼ 15 to z ∼ 8 using new JWST NIRCam medium-band observations over the HUDF/XDF

ABSTRACT We present the first constraints on the prevalence of z > 10 galaxies in the Hubble Ultra Deep Field (HUDF) leveraging new NIRCam observations from JEMS (JWST Extragalactic Medium-band Survey). These NIRCam observations probe redward of 1.6 μm, beyond the wavelength limit of HST, allowing us to search for galaxies to z > 10. These observations indicate that the highest redshift candidate identified in the HUDF09 data with HST, UDFj-39546284, has a redshift of z > 11.5, as had been suggested in analyses of the HUDF12/XDF data. This has now been confirmed with JWST NIRSpec. This source is thus the most distant galaxy discovered by HST in its >30 yr of operation. Additionally, we identify nine other z ∼ 8–13 candidate galaxies over the HUDF, two of which are new discoveries that appear to lie at z ∼ 11–12. We use these results to characterize the evolution of the UV luminosity function (LF) from z ∼ 15 to z ∼ 8.7. While our LF results at z ∼ 8.7 and z ∼ 10.5 are consistent with previous findings over the HUDF, our new LF estimates at z ∼ 12.6 are higher than other results in the literature, potentially pointing to a milder evolution in the UV luminosity density from z ∼ 12.6. We emphasize that our LF results are uncertain given the small number of z ∼ 12.6 sources and limited volume probed. The new NIRCam data also indicate that the faint z ∼ 8–13 galaxies in the HUDF/XDF show blue UV-continuum slopes β ∼ −2.7, high specific star formation rates ∼24.5 Gyr−1, and high EW (∼1300 Å) [O iii] + H β emission, with two z ∼ 8.5 sources showing [O iii] + H β EWs of ∼2300 Å.

The production of ionizing photons in UV-faint z ∼ 3–7 galaxies

Aims. The demographics of the production and escape of ionizing photons from UV-faint early galaxies is a key unknown that has hindered attempts to discover the primary drivers of reionization. With the advent of JWST, it is finally possible to observe the rest-frame optical nebular emission from individual sub-L*z > 3 galaxies to measure the production rate of ionizing photons, ξion. Methods. Here we study a sample of 370 z ∼ 3 − 7 galaxies spanning −23 < MUV < −15.5 (median MUV ≈ −18) with deep multiband HST and JWST/NIRCam photometry that covers the rest-UV to the optical from the GLASS and UNCOVER JWST surveys. Our sample includes 102 galaxies with Lyman-alpha emission detected in MUSE spectroscopy. We used Hα fluxes inferred from NIRCam photometry to estimate the production rate of ionizing photons that do not escape these galaxies, ξion(1 − fesc). Results. We find median log10ξion(1 − fesc) = 25.33 ± 0.47, with a broad intrinsic scatter of 0.42 dex, which implies a broad range of galaxy properties and ages in our UV-faint sample. Galaxies detected with Lyman-alpha have ∼0.1 dex higher ξion(1 − fesc), which is explained by their higher Hα equivalent width distribution; this implies younger ages and higher specific star formation rates and, thus, more O/B stars. We find significant trends of increasing ξion(1 − fesc) with increasing Hα equivalent width, decreasing UV luminosity, and decreasing UV slope; this implies that the production of ionizing photons is enhanced in young galaxies with assumed low metallicities. We find no significant evidence for sources with very high ionizing escape fractions (fesc > 0.5) in our sample based on their photometric properties, even amongst the Lyman-alpha-selected galaxies. Conclusions. This work demonstrates that considering the full distribution of ξion across galaxy properties is important for assessing the primary drivers of reionization.

Properties and evolution of dual and offset AGN in the ASTRID simulation at z ∼ 2

ABSTRACT We examine the dual [both black hole (BH) active] and offset (one BH active and in distinct galaxies) active galactic nucleus (AGN) population (comprising ∼ 2000 pairs at $0.5\, \text{kpc}\lesssim \Delta r\lt 30\, \text{kpc}$) at z = 2 ∼ 3 in the ASTRID simulation covering (360 cMpc)3. The dual (offset) AGN make up 3.0(0.5) per cent of all AGN at z = 2. The dual fraction is roughly constant while the offset fraction increases by a factor of 10 from z = 4 ∼ 2. Compared with the full AGN population, duals are characterized by low MBH/M* ratios, high specific star formation rates (sSFR) of $\sim 1\, \text{Gyr}^{-1}$, and high Eddington ratios (∼0.05, double that of single AGN). Dual AGNs are formed in major galaxy mergers (typically involving $M_\text{halo}\lt 10^{13}\, M_\odot$), with simular-mass BHs. At small separations (when host galaxies are in the late phase of the merger), duals become 2 ∼ 8 times brighter (albeit more obscured) than at larger separations. 80 per cent of the bright, close duals would merge within $\sim 500\, \text{Myr}$. Notably, the initially less-massive BHs in duals frequently become the brighter AGN during galaxy mergers. In offset AGN, the active BH is typically ≳ 10 times more massive than its non-active counterpart and than most BHs in duals. Offsets are predominantly formed in minor galaxy mergers with the active BH residing in the centre of massive haloes ($M_\text{ halo}\sim 10^{13-14}\, \mathrm{M}_\odot$). In these deep potentials, gas stripping is common and the secondary quickly deactivates. The stripping also leads to inefficient orbital decay amongst offsets, which stall at $\Delta r\sim 5\, \text{kpc}$ for a few hundred Myrs.

A Preview of JWST Metallicity Studies at Cosmic Noon: The First Detection of Auroral [O ii] Emission at High Redshift* *The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made

We present ultradeep Keck/MOSFIRE rest-optical spectra of two star-forming galaxies at z = 2.18 in the COSMOS field with bright emission lines, representing more than 20 hr of total integration. The fidelity of these spectra enabled the detection of more than 20 unique emission lines for each galaxy, including the first detection of the auroral [O ii]λλ7322, 7332 lines at high redshift. We use these measurements to calculate the electron temperature in the low-ionization O+ zone of the ionized interstellar medium and derive abundance ratios of O/H, N/H, and N/O using the direct method. The N/O and α/Fe abundance patterns of these galaxies are consistent with rapid formation timescales and ongoing strong starbursts, in accord with their high specific star formation rates. These results demonstrate the feasibility of using auroral [O ii] measurements for accurate metallicity studies at high redshift in a higher-metallicity and lower-excitation regime previously unexplored with the direct method in distant galaxies. These results also highlight the difficulty in obtaining the measurements required for direct-method metallicities from the ground. We emphasize the advantages that the JWST/NIRSpec instrument will bring to high-redshift metallicity studies, where the combination of increased sensitivity and uninterrupted wavelength coverage will yield more than an order of magnitude increase in efficiency for multiplexed auroral-line surveys relative to current ground-based facilities. Consequently, the advent of JWST promises to be the beginning of a new era of precision chemical abundance studies of the early universe at a level of detail rivaling that of local galaxy studies.

Central concentration of asymmetric features in post-starburst galaxies at z ∼ 0.8

ABSTRACT We present morphological analyses of post-starburst galaxies (PSBs) at 0.7 < z < 0.9 in the COSMOS field. We fitted ultraviolet to mid-infrared multiband photometry of objects with i < 24 from COSMOS2020 catalogue with population synthesis models assuming non-parametric, piece-wise constant function of star formation history, and selected 94 of those galaxies that have high specific star formation rates (SSFRs) of more than 10−9.5 yr−1 in 321–1000 Myr before observation and an order-of-magnitude lower SSFRs within recent 321 Myr. We devised a new non-parametric morphological index which quantifies concentration of asymmetric features, CA, and measured it as well as concentration C and asymmetry A on the Hubble Space Telescope/Advanced Camera for Surveys IF814W-band images. While relatively high C and low A values of PSBs are similar to those of quiescent galaxies rather than star-forming galaxies, we found that PSBs show systematically higher values of CA than both quiescent and star-forming galaxies; 36 per cent of PSBs have log CA > 0.8, while only 16 per cent (2 per cent) of quiescent (star-forming) galaxies show such high CA values. Those PSBs with high CA have relatively low overall asymmetry of A ∼ 0.1, but show remarkable asymmetric features near the centre. The fraction of those PSBs with high CA increases with increasing SSFR in 321–1000 Myr before observation rather than residual ongoing star formation. These results and their high surface stellar mass densities suggest that those galaxies experienced a nuclear starburst in the recent past, and processes that cause such starbursts could lead to the quenching of star formation through rapid gas consumption, supernova/active galactic nucleus feedback, and so on.

A Selection of Hα Emitters at z = 2.1–2.5 Using the K s -band Photometry of ZFOURGE

Large and less-biased samples of star-forming galaxies are essential to investigate galaxy evolution. Hα emission line is one of the most reliable tracers of star-forming galaxies because its strength is directly related to recent star formation. However, it is observationally expensive to construct large samples of Hα emitters by spectroscopic or narrowband imaging survey at high redshifts. In this work, we demonstrate a method to extract Hα fluxes of galaxies at z = 2.1–2.5 from K s broadband photometry of ZFOURGE catalog. Combined with 25–39 other filters, we estimate the emission-line fluxes by SED fitting with stellar population models that incorporate emission-line strengths. 2005 galaxies are selected as Hα emitters by our method and their fluxes show good agreement with previous measurements in the literature. On the other hand, there are more Hα luminous galaxies than previously reported. The discrepancy can be explained by extended Hα profiles of massive galaxies and a luminosity dependence of dust attenuation, which are not taken into account in the previous work. We also find that there are a large number of low-mass galaxies with a much higher specific star formation rate (sSFR) than expected from the extrapolated star formation main sequence. Such low-mass galaxies exhibit larger ratios between Hα and UV fluxes compared to more massive high sSFR galaxies. This result implies that a “starburst” mode may differ among galaxies: low-mass galaxies appear to assemble their stellar mass via short-duration bursts, while more massive galaxies tend to experience longer-duration (>10 Myr) bursts.

Massive-Star Feedback at Low Metallicity

AbstractEarly cosmic epochs are characterized by low metallicity and high specific star-formation rates. These conditions are dominated by massive-star feedback that may be dramatically different than the traditional model dominated by hot, thermal superwinds driven by supernova explosions. Instead, metal-poor feedback from massive stars may be radiation-dominated, with weak mechanical feedback, possibly aiding the escape of Lyα and Lyman continuum radiation. I will describe our understanding that is emerging from observations of starburst galaxies in the local universe.

CLASSY IV. Exploring UV Diagnostics of the Interstellar Medium in Local High-z Analogs at the Dawn of the JWST Era* *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

The Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY (CLASSY) provides the first high-resolution spectral catalog of 45 local high-z analogs in the ultraviolet (UV; 1200–2000 Å) to investigate their stellar and gas properties. Here we present a toolkit of UV interstellar medium (ISM) diagnostics, analyzing the main emission lines of CLASSY spectra (N iv] λ λ1483,87, C iv λλ1548,51, He ii λ1640, O iii]λ λ1661,6, Si iii] λλ1883,92, C iii] λ1907,9). Specifically, our aim is to provide accurate diagnostics for the reddening E(B − V), electron density n e , electron temperature T e , metallicity 12+log(O/H), and ionization parameter log(U), taking the different ISM ionization zones into account. We calibrate our UV toolkit using well-known optical diagnostics, analyzing archival optical spectra for all CLASSY targets. We find that UV density diagnostics estimate n e values that are ∼1–2 dex higher (e.g., n e (C iii]λ λ1907,9) ∼ 104 cm−3) than those inferred from their optical counterparts (e.g., n e ([S ii]λ λ6717,31) ∼ 102 cm−3; n e ([Ar iv]λ λ4714,41) ∼ 103 cm−3). T e derived from the hybrid ratio [O iii] λ1666/λ5007 proves to be reliable, implying differences in determining 12+log(O/H) compared to the optical counterpart O iii] λ4363/[O iii] λ5007 within ∼ ±0.3 dex. We also investigate the relation between the stellar and gas E(B − V), finding consistent values at high specific star formation rates (sSFRs; yr−1), while at low sSFRs we confirmed an excess of dust attenuation in the gas. Finally, we investigate UV line ratios and equivalent widths to provide correlations with 12+log(O/H) and log(U), but note that there are degeneracies between the two. With this suite of UV-based diagnostics, we illustrate the pivotal role CLASSY plays in understanding the chemical and physical properties of high-z systems that JWST can observe in the rest-frame UV.

Warped Disk Galaxies. I. Linking U-type Warps in Groups/Clusters to Jellyfish Galaxies

Warped disk galaxies are classified into two morphologies: S and U types. Conventional theories routinely attribute both types to galactic tidal interaction and/or gas accretion, but reproducing U types in simulations is extremely challenging. Here we investigate whether both types are governed by the same mechanisms using the most extensive sample of ∼8000 nearby (0.02 < z < 0.06) massive (M */M ⊙ > 109) edge-on disks from the Sloan Digital Sky Survey. We find that U types show on average bluer optical colors and a higher specific star formation rate (sSFR) than S types, with more strongly warped U types having a higher sSFR. We also find that while the S-type warp properties correlate with the tidal force by the nearest neighbor regardless of the environment, there is no such correlation for U types in groups/clusters, suggesting a nontidal mechanism could be at play for U types, such as ram pressure stripping (RPS). Indeed, U types are more common in groups/clusters than in fields and they have stellar mass, gas fraction, sSFR enhancement, and phase-space distribution closely analogous to RPS-induced jellyfish galaxies in clusters. We furthermore show that the stellar disks of most RPS galaxies in the IllustrisTNG simulation are warped in a U shape and bent in the opposite direction of stripped gas tails, satisfying theoretical expectations for stellar warps embedded in jellyfishes. We therefore suggest that despite the majority of U types that live in fields being still less explained, RPS can be an alternative origin for those in groups/clusters.

Elevated Hot Gas and High-mass X-Ray Binary Emission in Low-metallicity Galaxies: Implications for Nebular Ionization and Intergalactic Medium Heating in the Early Universe

High-energy emission associated with star formation has been proposed as a significant source of interstellar medium (ISM) ionization in low-metallicity starbursts and an important contributor to the heating of the intergalactic medium (IGM) in the high-redshift (z ≳ 8) universe. Using Chandra observations of a sample of 30 galaxies at D ≈ 200–450 Mpc that have high specific star formation rates of 3–9 Gyr−1 and metallicities near Z ≈ 0.3Z ⊙, we provide new measurements of the average 0.5–8 keV spectral shape and normalization per unit star formation rate (SFR). We model the sample-combined X-ray spectrum as a combination of hot gas and high-mass X-ray binary (HMXB) populations and constrain their relative contributions. We derive scaling relations of /SFR = 40.19 ± 0.06 and /SFR significantly elevated compared to local relations. The HMXB scaling is also somewhat higher than –SFR-Z relations presented in the literature, potentially due to our galaxies having relatively low HMXB obscuration and young and X-ray luminous stellar populations. The elevation of the hot gas scaling relation is at the level expected for diminished attenuation due to a reduction of metals; however, we cannot conclude that an –SFR-Z relation is driven solely by changes in ISM metal content. Finally, we present SFR-scaled spectral models (both emergent and intrinsic) that span the X-ray-to-IR band, providing new benchmarks for studies of the impact of ISM ionization and IGM heating in the early universe.

The molecular gas resolved by ALMA in the low-metallicity merging dwarf galaxy Haro 11

Context.The physical mechanisms driving starbursts and quenching in less massive (M* ≤ 1010 M⊙) galaxies are unclear. The merger is one of the inescapable processes referred to as both starburst and quenching in massive galaxies. However, the effects of the merger on star formation in dwarf galaxies and their evolution are still uncertain.Aims.We aim to explore how star formation in dwarf galaxies is both triggered and quenched by studying metal-poor gas-rich dwarf mergers based on multi-band observations at a spatial resolution of ∼460 pc.Methods.We use archival data of Atacama Large Millimetre Array (Band 3 and 8) and Very Large Telescope/Multi Unit Spectroscopic Explorer to map CO(J = 1–0), [CI](3P1–3P0), and Hαemission in one of the most extreme merging starburst dwarf galaxies, Haro 11.Results.We find the molecular gas is assembled around the central two star-forming regions (knots B and C). The molecular and ionized gas and stellar components show complex kinematics, indicating that the gas is probably at a combined stage of collision of clouds and feedback from star formation. The peak location and distribution of [CI](1–0) closely coincide with the CO(1–0) emission, meaning that it might trace the same molecular gas as CO in such a dwarf merger starburst galaxy. The enhancement of line ratios (∼0.5) of [CI]/CO around knot C is probably generated by the dissociation of CO molecules by cosmic rays and far-ultraviolet photons. Globally, Haro 11 and its star-forming regions share similar star formation efficiency (SFE) to the high-zstarburst galaxies or the clumps in nearby ultraluminous infrared galaxies.Conclusions.Given the high SFE, the high specific star formation rate, small stellar mass, low metallicity, and deficient HI gas, Haro 11 could be an analog of a high-zdwarf starburst and the potential progenitor of the nearby less massive elliptical galaxies. The significantly smaller turbulent pressure and viral parameter is probably triggering the intense starbursts. We predict that Haro 11 will quench atM* ≤ 8.5 × 109 M⊙.

The eROSITA Final Equatorial-Depth Survey (eFEDS)

Context.The eROSITA Final Equatorial Depth Survey (eFEDS), completed in survey mode during the calibration and performance verification phase of the eROSITA instrument on Spectrum Roentgen Gamma, delivers data at and beyond the final depth of the 4-yr eROSITA all-sky survey (eRASS:8),f0.5–2 keV= 1.1 × 10−14erg s−1cm−2, over 140 deg2. It provides the first view of normal galaxy X-ray emission from X-ray binaries (XRBs) and the hot interstellar medium at the full depth of eRASS:8.Aims.We used the Heraklion Extragalactic Catalogue (HECATE) of galaxies to correlate with eFEDS X-ray sources and identify X-ray detected normal galaxies. This flux-limited X-ray survey is relatively free from selection effects and enables the study of integrated normal galaxy X-ray emission and its relation to galaxy parameters such as the stellar mass, star formation rate (SFR), and metallicity.Methods.We cross-correlated 32 646 eFEDS X-ray sources to 1181 HECATE normal galaxies and obtained 94 matches. We classified galaxies as star-forming, early-type, composite, and active galactic nuclei (AGN) using Sloan Digital Sky Survey (SDSS) and Six-degree Field (6dF) optical spectroscopy.Results.The eFEDS field harbours 37 normal galaxies: 36 late-type (star-forming) galaxies and one early-type galaxy. There are 1.9 times as many normal galaxies as predicted by scaling relations via simulations, with an overabundance of late-type galaxies and a dearth of early-type galaxies. When compared with empirical relations, eFEDS dwarf galaxies with a high specific SFR have elevatedLX/SFR at a fixed specific SFR and metallicity, indicating an increase in XRB emission due to low metallicity. We expect that eRASS:8 will detect 12 500 normal galaxies, the majority of which will be star-forming, with the caveat that there are unclassified sources in eFEDS and galaxy catalogue incompleteness issues that could increase the actual number of detected galaxies over these current estimates.Conclusions.eFEDS observations detected a rare population of galaxies – the metal-poor dwarf starbursts – that do not follow known scaling relations. eRASS is expected to discover significant numbers of these high-redshift analogues, which are important for studying the heating of the intergalactic medium at high redshift. Further investigation of the hot gas emission from normal galaxies and stochastic effects in the dwarf galaxy population are required to constrain their X-ray output.

EMPRESS. VI. Outflows Investigated in Low-mass Galaxies with M ∗ = 104–107 M ⊙: Weak Feedback in Low-mass Galaxies?

We study emission line profiles of 21 nearby low-mass (M * = 104–107 M ⊙) galaxies in deep medium-high resolution spectra taken with Magellan/MagE. These low-mass galaxies are actively star-forming systems with high specific star formation rates of ∼100–1000 Gyr−1 that are well above the star formation main sequence and its extrapolation. We identify broad-line components of Hα and [O iii]λ5007 emission in 14 out of the 21 galaxies that cannot be explained by the MagE instrumental profile or the natural broadening of line emission. We conduct double-Gaussian profile fitting to the emission of the 14 galaxies, and find that the broad-line components have line widths significantly larger than those of the narrow-line components, indicative of galactic outflows. The broad-line components have moderately large line widths of ∼100 km s−1. We estimate the maximum outflow velocities v max and obtain values of ≃60–200 km s−1, which are found to be comparable to or slightly larger than the escape velocities. Positive correlations of v max with star formation rates, stellar masses, and circular velocities extend down into this low-mass regime. Broad- to narrow-line flux ratios (BNRs) are generally found to be smaller than those of massive galaxies. The small v max and BNRs suggest that the mass-loading factors η can be as small as 0.1–1 or below, in contrast to the large η of energy-driven outflows predicted by numerical simulations.

Blue Rest-frame UV-optical Colors in z ∼ 8 Galaxies from GREATS: Very Young Stellar Populations at ∼650 Myr of Cosmic Time

Abstract Deep rest-optical observations are required to accurately constrain the stellar populations of z ∼ 8 galaxies. Due to significant limitations in the availability of such data for statistically complete samples, observational results have been limited to modest numbers of bright or lensed sources. To revolutionize the present characterization of z ∼ 8 galaxies, we exploit the ultradeep (∼27 mag, 3σ) Spitzer/Infrared Array Camera (IRAC) 3.6 and 4.5 μm data, probing the rest-frame optical at z ∼ 8, over ∼200 arcmin2 of the GOODS fields from the recently completed GOODS Re-ionization Era wide-Area Treasury from Spitzer program (GREATS), combined with observations in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)/Ultra Deep Survey (UDS) and CANDELS/Cosmic Evolution Survey (COSMOS) fields. We stacked ≳100 z ∼ 8 Lyman-break galaxies in four bins of UV luminosity (M UV ∼ −20.7 to −18.4 mag) and study their H 160 − [3.6] and [3.6]–[4.5] colors. We find young ages (≲100 Myr) for the three faintest stacks, inferred from their blue H 160 − [3.6] ∼ 0 mag colors, consistent with a negative Balmer break. Meanwhile, the redder H 160 − [3.6] color seen in the brightest stack is suggestive of slightly older ages. We explored the existence of a correlation between the UV luminosity and age, and find either no trend or fainter galaxies being younger. The stacked SEDs also exhibit very red [3.6]–[4.5] ∼ 0.5 mag colors, indicative of intense [O iii]+Hβ nebular emission and star formation rate (SFR). The correspondingly high specific SFRs, sSFR ≳10 Gyr−1, are consistent with recent determinations at similar redshifts and higher luminosities, and support the coevolution between the sSFR and the specific halo mass accretion rate.

Accretion mode versus radio morphology in the LOFAR Deep Fields

ABSTRACT Radio-loud active galaxies have two accretion modes [radiatively inefficient (RI) and radiatively efficient (RE)], with distinct optical and infrared signatures, and two jet dynamical behaviours, which in arcsec- to arcmin-resolution radio surveys manifest primarily as centre- or edge-brightened structures [Fanaroff–Riley (FR) class I and II]. The nature of the relationship between accretion mode and radio morphology (FR class) has been the subject of long debate. We present a comprehensive investigation of this relationship for a sample of 286 well-resolved radio galaxies in the LOFAR Two-metre Sky Survey Deep Fields (LoTSS-Deep) first data release, for which robust morphological and accretion mode classifications have been made. We find that two-thirds of luminous FRII radio galaxies are RI, and identify no significant differences in the visual appearance or source dynamic range (peak/mean surface brightness) of the RI and RE FRIIs, demonstrating that both RI and RE systems can produce FRII structures. We also find a significant population of low-luminosity FRIIs (predominantly RI), supporting our earlier conclusion that FRII radio structures can be produced at all radio luminosities. We demonstrate that in the luminosity range where both morphologies are present, the probability of producing FRI or FRII radio morphology is directly linked to stellar mass, while across all morphologies and luminosities, RE accretion occurs in systems with high specific star formation rate, presumably because this traces fuel availability. In summary, the relationship between accretion mode and radio morphology is very indirect, with host-galaxy environment controlling these two key parameters in different ways.

Finite-resolution Deconvolution of Multiwavelength Imaging of 20,000 Galaxies in the COSMOS Field: The Evolution of Clumpy Galaxies over Cosmic Time

Abstract Compact star-forming clumps observed in distant galaxies are often suggested to play a crucial role in galaxy assembly. In this paper, we use a novel approach of applying finite-resolution deconvolution on ground-based images of the COSMOS field to resolve 20,185 star-forming galaxies (SFGs) at 0.5 &lt; z &lt; 2 to an angular resolution of 0.″3 and study their clump fractions. A comparison between the deconvolved images and HST images across four different filters shows good agreement and validates image deconvolution. We model spectral energy distributions using the deconvolved 14-band images to provide resolved surface brightness and stellar-mass density maps for these galaxies. We find that the fraction of clumpy galaxies decreases with increasing stellar masses and with increasing redshift: from ∼30% at z ∼ 0.7 to ∼50% at z ∼ 1.7. Using abundance matching, we also trace the progenitors for galaxies at z ∼ 0.7 and measure the fractional mass contribution of clumps toward their total mass budget. Clumps are observed to have a higher fractional mass contribution toward galaxies at higher redshift: increasing from ∼1% at z ∼ 0.7 to ∼5% at z ∼ 1.7. Finally, the majority of clumpy SFGs have higher specific star formation rates (sSFR) compared to the average SFGs at fixed stellar mass. We discuss the implication of this result for in situ clump formation due to disk instability.

What is Important? Morphological Asymmetries are Useful Predictors of Star Formation Rates of Star-forming Galaxies in SDSS Stripe 82

Abstract The morphology and structure of galaxies reflect their star formation and assembly histories. We use the framework of mutual information (MI) to quantify the interdependence among several structural variables and to rank them according to their relevance for predicting the specific star formation rate (SSFR) by comparing the MI of the predictor variables with the SSFR and penalizing variables that are redundant. We apply this framework to study ∼3700 face-on star-forming galaxies (SFGs) with varying degrees of bulge dominance and central concentration and with stellar mass M ⋆ ≈ 109 M ⊙−5 × 1011 M ⊙ at redshift z = 0.02–0.12. We use the Sloan Digital Sky Survey (SDSS) Stripe 82 deep i-band imaging data, which improve measurements of asymmetry and bulge dominance indicators. We find that star-forming galaxies are a multiparameter family. In addition to M ⋆, asymmetry emerges as the most powerful predictor of SSFR residuals of SFGs, followed by bulge prominence/concentration. Star-forming galaxies with higher asymmetry and stronger bulges have higher SSFR at a given M ⋆. The asymmetry reflects both irregular spiral arms and lopsidedness in seemingly isolated SFGs and structural perturbations by galaxy interactions or mergers.

A Catalog of Host Galaxies for WISE-selected AGN: Connecting Host Properties with Nuclear Activity and Identifying Contaminants

Abstract We present a catalog of physical properties for galaxies hosting active galactic nuclei (AGN) detected by the Wide-field Infrared Survey Explorer (WISE). By fitting broadband spectral energy distributions of sources in the WISE AGN Catalog with empirical galaxy and AGN templates, we derive photometric redshifts, AGN bolometric luminosities, measures of AGN obscuration, host galaxy stellar masses, and host galaxy star formation rates (SFRs) for 695,273 WISE AGN. The wide-area nature of this catalog significantly augments the known number of obscured AGN out to redshifts z ∼ 3 and will be useful for studies focused on AGN or their host galaxy physical properties. We first show that the most likely non-AGN contaminants are galaxies at redshifts z = 0.2–0.3, with relatively blue W1–W2 colors, and with high specific SFRs for which the dust continuum emission is elevated in the W2 filter. Toward increasingly lower redshifts, WISE AGN host galaxies have systematically lower specific SFRs relative to those of normal star-forming galaxies, likely due to decreased cold gas fractions and the time delay between global star formation and AGN triggering. Finally, WISE AGN obscuration is not strongly correlated with AGN bolometric luminosity but shows a significant negative correlation with the Eddington ratio. This result is consistent with a version of the receding torus model in which the obscuring material is located within the supermassive black hole gravitational sphere of influence and the dust inner radius increases due to radiation pressure.

Spiral Structure Boosts Star Formation in Disk Galaxies

Abstract We investigate the impact of spiral structure on global star formation using a sample of 2226 nearby bright disk galaxies. Examining the relationship between spiral arms, star formation rate (SFR), and stellar mass, we find that arm strength correlates well with the variation of SFR as a function of stellar mass. Arms are stronger above the star-forming galaxy main sequence (MS) and weaker below it: arm strength increases with higher log ( SFR / SFR MS ) , where SFRMS is the SFR along the MS. Likewise, stronger arms are associated with higher specific SFR. We confirm this trend using the optical colors of a larger sample of 4378 disk galaxies, whose position on the blue cloud also depends systematically on spiral arm strength. This link is independent of other galaxy structural parameters. For the subset of galaxies with cold gas measurements, arm strength positively correlates with H i and H2 mass fraction, even after removing the mutual dependence on log ( SFR / SFR MS ) , consistent with the notion that spiral arms are maintained by dynamical cooling provided by gas damping. For a given gas fraction, stronger arms lead to higher log ( SFR / SFR MS ) , resulting in a trend of increasing arm strength with shorter gas depletion time. We suggest a physical picture in which the dissipation process provided by gas damping maintains spiral structure, which, in turn, boosts the star formation efficiency of the gas reservoir.