Recent Star Formation Research Articles

Breaking Orion's Veil with fossil outflows

Context. The role of feedback in the self-regulation of star formation is a fundamental question in astrophysics. The Orion Nebula is the nearest site of ongoing and recent massive star formation. It is a unique laboratory for the study of stellar feedback. Recent SOFIA [C II] 158 μm observations have revealed an expanding bubble, the Veil shell, that is powered by stellar winds and ionization feedback. Aims. We have identified a protrusion-like substructure in the northwestern portion of the Orion Veil shell that may indicate additional, highly directional feedback mechanisms. Our goal is to investigate the origin of the protrusion by quantifying its possible driving mechanisms. Methods. We use the [C II] 158 μm map of the Orion Nebula obtained with the upGREAT instrument on board SOFIA. The spectral and spatial resolution of the observations are 0.3 km s−1 and 16", respectively. The velocity-resolved [C II] observations allow us to construct position-velocity (pv) diagrams to measure the morphology and the expansion velocity of the protrusion. For the morphology, we also use new observations of 12CO and 13CO J = 2-1 (to trace molecular gas), Spitzer 8 μm observations (to trace the far-ultraviolet-illuminated surfaces of photodissociation regions), and Hα observations (to trace ionized gas). For the kinematics, we perform a line-profile analysis of [C II], 13CO, and 12CO at 12 positions, covering the entire protrusion. To quantify the stellar feedback, we estimate the mass of the protrusion by fitting the dust thermal emission. We compare the kinetic energy with the stellar wind of θ1 Ori C and the momentum of the outflows of massive protostars to investigate the driving mechanism of the protrusion. Results. The pv diagrams reveal two half-shells expanding at velocities of +6 km s−1 and +12 km s−1. We find that the protrusion has a diameter of ~1.3 pc with a ~45 M⊙ shell expanding at +12 km s−1 at the northwestern rim of the Veil. The thickness of the expanding shell is ~0.1 pc. Using the mass in the limb-brightened shell and the maximum expansion velocity, we calculate the kinetic energy and the momentum of the protrusion to be ~7 × 1046 erg and 540 M⊙ km s−1, respectively. We consider three possible origins for this protrusion: fossil outflow cavities created by jets and outflows during the protostellar accretion phase, preexisting "clumpiness" in the OMC-1 core, and the stellar wind during the main-sequence phase. Based on the energetics and the morphology, we conclude that the northwestern part of the preexisting cloud was locally perturbed by outflows ejected from massive protostars in the Trapezium cluster. This suggests that the protrusion of the Veil is the result of mechanical rather than radiative feedback. Furthermore, we argue that the location of the protrusion is a suitable place to break Orion's Veil owing to the photo-ablation from the walls of the protrusion. Conclusions. We conclude that the outflows of massive protostars can influence the morphology of the future H II region and even cause breakages in the ionization front. Specifically, the interaction of stellar winds of main-sequence stars with the molecular core preprocessed by the protostellar jet is important.

Recent star formation history of the dwarf irregular galaxy Leo A

Context.Leo A is a gas-rich dwarf irregular galaxy of low stellar mass and metallicity. Its star formation history extends up to ∼10 Gyr. A few prominent H II regions indicate that star formation processes are active in the galaxy to this day. In the present epoch, Leo A is a highly isolated galaxy, which allows for it to be studied in a self-propagating star formation regime. Aims. Our aim is to study the recent star formation history of the Leo A galaxy over the last ∼300 Myr. Methods. We analysed populations of main sequence (MS) and blue helium-burning (BHeB – ‘blue loop’) stars using multi-colour photometry data obtained with the Subaru/Suprime-Cam (B, V, R, I, Hα) and the Hubble Space Telescope (HST) Advanced Camera for Surveys (F475W and F814W) cameras. We made use of colour-magnitude diagrams and stellar isochrones to determine individual ages of the BHeB stars, which enabled us to study the spatial distribution of these stars in different age bins. In addition, we used Hα emission and H I column density maps to study the relationship between young stellar populations and the surrounding interstellar medium. Results. We found that significant differences are visible in the morphology of stellar distributions represented by the BHeB and MS stars of different ages. We also studied a well-known H I hole in the Leo A galaxy and found that there is a noticeable difference in the surface number density of stars in the western and eastern parts of the hole. The bright young (< 20 Myr) MS stars residing in the western part of the hole indicate the recent star-forming activity in this region after the quiescent period of ∼300 Myr. Furthermore, there is a shock front (prominent in Hα) that closely resembles the shape of the western edge of the H I hole. This shock front could have been formed by the combined stellar feedback from the young MS stars or a Type II supernova located within the H I hole. Additionally, an analysis of the Suprime-Cam photometry in Hα and R passbands enabled us to identify 17 stars with a prominent Hα emission (Hα − R ≤ −0.06) which indicate the presence of early-type (Be, B[e], or A-shell) emission-line stars in the Leo A galaxy.

Ultraviolet to far infrared self-consistent analysis of the stellar populations of massive starburst galaxies at intermediate redshifts

ABSTRACT We study in detail the properties of the stellar populations of 111 massive [log (M⋆/M⊙) ≥ 10] dusty [far-infrared (FIR)-selected] starburst (SFR/SFRMS > 2) galaxies at 0.7 < z < 1.2. For that purpose, we use self-consistent methods that analyse the UV-to-FIR broad-band observations in terms of the stellar light and dust re-emission with energy-balance techniques. We find that the emission of our starburst galaxies can be interpreted as a recent star formation episode superimposed on a more evolved stellar population. On average, the burst age is ∼80 Myr and its attenuation ∼2.4 mag. Assuming our starburst galaxies at half their lifetimes, we infer a duration of the starburst phase of ∼160 Myr. The median stellar mass and star formation rate (SFR) are log (M⋆/M⊙) ∼ 10.6 and ∼220 M⊙yr−1. Assuming this SFR and the inferred duration of the starburst phase, the stellar mass added during this phase corresponds to ∼40 per cent the median stellar mass of our sample. The young-population age determines the position of our galaxies in the M⋆–SFR plane. Galaxies located at the largest distances of the MS present shorter young-population ages. The properties of the underlying stellar population cannot be constrained accurately with our broad-band data. We also discuss the impact of including the FIR data and energy-balance techniques in the analysis of the properties of the stellar populations in starburst galaxies.

The resolved chemical abundance properties within the interstellar medium of star-forming galaxies at z≈ 1.5

ABSTRACT We exploit the unprecedented depth of integral field data from the KMOS Ultra-deep Rotational Velocity Survey (KURVS) to analyse the strong (Hα) and forbidden ([N ii], [S ii]) emission line ratios in 22 main-sequence galaxies at $z\, \approx \, 1.5$. Using the [N ii]/Hα emission-line ratio, we confirm the presence of the stellar mass – gas-phase metallicity relation at this epoch, with galaxies exhibiting on average 0.13 ± 0.04 dex lower gas-phase metallicity (12 + log(O/H)M13 = 8.40 ± 0.03) for a given stellar mass (log10(M*[M⊙] = 10.1 ± 0.1) .than local main-sequence galaxies. We determine the galaxy-integrated [S ii] doublet ratio, with a median value of [S ii]λ6716/λ6731 = 1.26 ± 0.14 equivalent to an electron density of log10(ne[cm−3]) = 1.95 ± 0.12. Utilising CANDELS HST multi-band imaging we define the pixel surface-mass and star-formation rate density in each galaxy and spatially resolve the fundamental metallicity relation at $z\, \approx \, 1.5$, finding an evolution of 0.05 ± 0.01 dex compared to the local relation. We quantify the intrinsic gas-phase metallicity gradient within the galaxies using the [N ii]/Hα calibration, finding a median annuli-based gradient of ΔZ/ΔR = −0.015 ± 0.005 dex kpc−1. Finally, we examine the azimuthal variations in gas-phase metallicity, which show a negative correlation with the galaxy integrated star-formation rate surface density ($r_{\rm s}\,$ = −0.40, ps = 0.07) but no connection to the galaxies kinematic or morphological properties nor radial variations in stellar mass surface density or star formation rate surface density. This suggests both the radial and azimuthal variations in interstellar medium properties are connected to the galaxy integrated density of recent star formation.

Duality in spatially resolved star formation relations in local LIRGs

We analyse the star formation (SF) relations in a sample of 16 nearby luminous infrared galaxies (LIRGs) with more than 2800 regions defined on scales of 90 to 500 pc. We used ALMA to map the distribution of the cold molecular gas traced by the J = 2–1 line of CO and archival Paα HST/NICMOS imaging to trace the recent SF. In four objects we find two different branches in the Kennicutt-Schmidt relation at 90 pc scales, suggesting the existence of a duality in this relation. The two branches correspond to two different dynamical environments within each galaxy. One branch, which corresponds to the central region of these galaxies (90% of the regions are located at radii < 0.85 kpc), shows higher gas and SF rate surface densities with higher velocity dispersion. The other branch, which shows lower molecular gas and SF rate surface densities, corresponds to the more external disk regions (r ∼ 1 kpc). Despite the scatter, the SF efficiency of the galaxies with dual behaviour increases with increasing boundedness as measured by the b parameter (b≡ ΣH2/σ2 ∝ αvir−1). At larger spatial scales (250 and 500 pc), the duality disappears. The rest of the sample does not show evidence of this dual behaviour at any scale.

Spatially resolved evidence of the impact of quasar-driven outflows on recent star formation: the case of Mrk 34

ABSTRACT We present the results of our spatially resolved investigation into the interplay between the ages of the stellar populations and the kinematics of the warm ionized outflows in the well-studied type II quasar Markarian 34 (Mrk 34). Utilizing integral field spectroscopy data, we determine the spatial distribution of the young stellar population (YSP; tYSP < 100 Myr) using spectral synthesis modelling. We also employ the [O iii] λ5007 emission line as a tracer of the warm ionized gas kinematics. We demonstrate a spatial correlation between the outer edges of the blue side of the outflow and an enhancement in the proportion of the YSP flux, suggesting that the outflow is responsible for triggering star formation in this region. In regions with more highly disrupted gas kinematics, we find that the proportion of YSP flux is consistent with that found outside the outflow region, suggesting that the increased disruption is preventing a similar enhancement in star formation from occurring. Our analysis suggests that Mrk 34 is an example of quasar-driven outflows simultaneously producing both ‘positive’ and ‘preventive’ feedback, further demonstrating the complex nature of the relationship between quasars and their host galaxies.

The MUSE Extremely Deep Field: Evidence for SFR-induced cores in dark-matter dominated galaxies atz≃ 1

Context.Disc-halo decompositionsz = 1 − 2 star-forming galaxies (SFGs) atz > 1 are often limited to massive galaxies (M⋆ > 1010M⊙) and rely on either deep integral field spectroscopy data or stacking analyses.Aims.We present a study of the dark-matter (DM) content of ninez ≈ 1 SFGs selected among the brightest [O II] emitters in the deepest Multi-Unit Spectrograph Explorer (MUSE) field to date, namely the 140 h MUSE Extremely Deep Field. These SFGs have low stellar masses, ranging from 108.5to 1010.5 M⊙.Methods.We analyzed the kinematics with a 3D modeling approach, which allowed us to measure individual rotation curves to ≈3 times the half-light radiusRe. We performed disk-halo decompositions on their [O II] emission line with a 3D parametric model. The disk-halo decomposition includes a stellar, DM, gas, and occasionally a bulge component. The DM component primarily uses the generalizedα, β, γprofile or a Navarro-Frenk-White profile.Results.The disk stellar massesM⋆obtained from the [O II] disk-halo decomposition agree with the values inferred from the spectral energy distributions. While the rotation curves show diverse shapes, ranging from rising to declining at large radii, the DM fractions within the half-light radiusfDM(<Re) are found to be 60% to 95%, extending to lower masses (densities) recent results who found low DM fractions in SFGs withM⋆ > 1010M⊙. The DM halos show constant surface densities of ∼100M⊙pc−2. For isolated galaxies, half of the sample shows a strong preference for cored over cuspy DM profiles. The presence of DM cores appears to be related to galaxies with low stellar-to-halo mass ratio, logM⋆/Mvir ≈ −2.5. In addition, the cuspiness of the DM profiles is found to be a strong function of the recent star-formation activity.Conclusions.We measured the properties of DM halos on scales from 1 to 15 kpc, put constraints on thez > 0cvir − Mvirscaling relation, and unveiled the cored nature of DM halos in somez ≃ 1 SFGs. These results support feedback-induced core formation in the cold dark matter context.

Quenching of satellite galaxies of Milky Way analogues: reconciling theory and observations

ABSTRACT The vast majority of low-mass satellite galaxies around the Milky Way and M31 appear virtually devoid of cool gas and show no signs of recent or ongoing star formation. Cosmological simulations demonstrate that such quenching is expected and is due to the harsh environmental conditions that satellites face when joining the Local Group (LG). However, recent observations of Milky Way analogues in the SAGA survey present a very different picture, showing the majority of observed satellites to be actively forming stars, calling into question the realism of current simulations and the typicality of the LG. Here, we use the ARTEMIS suite of high-resolution cosmological hydrodynamical simulations to carry out a careful comparison with observations of dwarf satellites in the LG, SAGA, and the Local Volume (LV) survey. We show that differences between SAGA and the LG and LV surveys, as well as between SAGA and the ARTEMIS simulations, can be strongly reduced by considering differences in the host mass distributions and (more importantly) observational selection effects, specifically that low-mass satellites which have only recently been accreted are more likely to be star forming, have a higher optical surface brightness, and are therefore more likely to be included in the SAGA survey. This picture is confirmed using data from the deeper LV survey, which shows pronounced quenching at low masses, in accordance with the predictions of ΛCDM-based simulations.

Black-hole-triggered star formation in the dwarf galaxy Henize 2-10.

Black-hole-driven outflows have been observed in some dwarf galaxies with active galactic nuclei1, and probably play a role in heating and expelling gas (thereby suppressing star formation), as they do in larger galaxies2. The extent to which black-hole outflows can trigger star formation in dwarf galaxies is unclear, because work in this area has previously focused on massive galaxies and the observational evidence is scarce3-5. Henize 2-10 is a dwarf starburst galaxy previously reported to have a central massive black hole6-9, although that interpretation has been disputed because some aspects of the observational evidence are also consistent with a supernova remnant10,11. At a distance of approximately 9 Mpc, it presents an opportunity to resolve the central region and to determine if there is evidence for a black-hole outflow influencing star formation. Here we report optical observations of Henize 2-10 with a linear resolution of a few parsecs. We find an approximately 150-pc-long ionized filament connecting the region of the black hole with a site of recent star formation. Spectroscopy reveals a sinusoid-like position-velocity structure that is well described by a simple precessing bipolar outflow. We conclude that this black-hole outflow triggered the star formation.

The Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE)

Over the last decades, high-mass star formation research has concentrated on either the large-scale molecular cloud environments or on the smallscale hot dense molecular cores surrounding massive proto-stars/clusters and young stellar objects. However, questions regarding the gas flow from large to small scales, and how the gas is transferred via intermediate-scale filaments and clumps have so far been largely neglected. With “Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE)”, a part of the Max Planck IRAM Observatory Program (MIOP), we want to overcome this missing gap via studying one well-known molecular cloud complex with the IRAM NOEMA and 30m facilities from small to large scales, thereby connecting these important physical processes. In the nearby (1.4 kpc) luminous Cygnus X region, recent and on-going star formation combine to present a rich Northern hemisphere laboratory in which star formation and feedback processes can be studied globally as well as locally. Using the new and unique 4 mm capabilities of NOEMA, together with the IRAM 30m telescope, the flow of gas from cloudto core-scales is being probed with observations of large mosaics covering the ground state lines of many molecules, including their deuterium substituted isotopologs, with the unique large bandwidth only possible with this facility. Here a brief introduction into the program, together with initials results, is presented.

The Complete Local-Volume Groups Sample – IV. Star formation and gas content in group-dominant galaxies

ABSTRACT Using multiband data, we examine the star formation activity of the nearby group-dominant early-type galaxies of the Complete Local-volume Groups Sample (CLoGS) and the relation between star formation, gas content, and local environment. Only a small fraction of the galaxies (13 per cent; 6/47) are found to be far-ultraviolet (FUV) bright, with FUV to near-infrared colours indicative of recent active star formation (NGC 252, NGC 924, NGC 940, NGC 1106, NGC 7252, and ESO 507-25). These systems are lenticulars presenting the highest FUV-specific star formation rates in the sample (sSFRFUV > 5 × 1013 yr−1), significant cold gas reservoirs [M(H2) = 0.5-61 × 108 M⊙], reside in X-ray faint groups, and none hosts a powerful radio active galactic nucleus (AGN) (P$_{1.4\mathrm{ GHz}}\, \lt 10^{23}$ W Hz−1). The majority of the group-dominant galaxies (87 per cent; 41/47) are FUV faint, with no significant star formation, classified in most cases as spheroids based on their position on the infrared star-forming main sequence (87 per cent; 46/53). Examining the relationships between radio power, SFRFUV, and stellar mass, we find a lack of correlation that suggests a combination of origins for the cool gas in these galaxies, including stellar mass loss, cooling from the intra-group medium (IGrM) or galaxy halo, and acquisition through mergers or tidal interactions. X-ray bright systems, in addition to hosting radio powerful AGN, have a range of SFRs but, with the exception of NGC 315, do not rise to the highest rates seen in the FUV bright systems. We suggest that central group galaxy evolution is linked to gas mass availability, with star formation favoured in the absence of a group-scale X-ray halo, but AGN jet launching is more likely in systems with a cooling IGrM.

WALLABY pilot survey: H i gas disc truncation and star formation of galaxies falling into the Hydra I cluster

ABSTRACT We present results from our analysis of the Hydra I cluster observed in neutral atomic hydrogen (H i) as part of the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY). These WALLABY observations cover a 60-square-degree field of view with uniform sensitivity and a spatial resolution of 30 arcsec. We use these wide-field observations to investigate the effect of galaxy environment on H i gas removal and star formation quenching by comparing the properties of cluster, infall, and field galaxies extending up to ∼5R200 from the cluster centre. We find a sharp decrease in the H i-detected fraction of infalling galaxies at a projected distance of ∼1.5R200 from the cluster centre from $\sim 85{{\ \rm per\ cent}}$ to $\sim 35{{\ \rm per\ cent}}$. We see evidence for the environment removing gas from the outskirts of H i-detected cluster and infall galaxies through the decrease in the H i to r-band optical disc diameter ratio. These galaxies lie on the star-forming main sequence, indicating that gas removal is not yet affecting the inner star-forming discs and is limited to the galaxy outskirts. Although we do not detect galaxies undergoing galaxy-wide quenching, we do observe a reduction in recent star formation in the outer disc of cluster galaxies, which is likely due to the smaller gas reservoirs present beyond the optical radius in these galaxies. Stacking of H i non-detections with H i masses below $M_{\rm {HI}}\lesssim 10^{8.4}\, \rm {M}_{\odot }$ will be required to probe the H i of galaxies undergoing quenching at distances ≳60 Mpc with WALLABY.

The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. II. The Star-formation History of Andromeda I Derived from Long-period Variables

Abstract An optical monitoring survey in the nearby dwarf galaxies was carried out with the 2.5 m Isaac Newton Telescope. 55 dwarf galaxies and four isolated globular clusters in the Local Group were observed with the Wide Field Camera. The main aims of this survey are to identify the most evolved asymptotic giant branch stars and red supergiants at the endpoint of their evolution based on their pulsational instability, use their distribution over luminosity to reconstruct the star-formation history (SFH), quantify the dust production and mass loss from modeling the multiwavelength spectral energy distributions, and relate this to luminosity and radius variations. In this second of a series of papers, we present the methodology used to estimate SFH based on long-period variable (LPV) stars and then derive it for Andromeda I (And I) dwarf galaxy as an example of the survey. Using our identified 59 LPV candidates within two half-light radii of And I and Padova stellar evolution models, we estimated the SFH of this galaxy. A major epoch of star formation occurred in And I peaking around 6.6 Gyr ago, reaching 0.0035 ± 0.0016 M ⊙ yr−1 and only slowly declining until 1–2 Gyr ago. The presence of some dusty LPVs in this galaxy corresponds to a slight increase in recent star formation peaking around 800 Myr ago. We evaluate a quenching time around 4 Gyr ago (z < 0.5), which makes And I a late-quenching dSph. A total stellar mass (16 ± 7) × 106 M ⊙ is calculated within two half-light radii of And I for a constant metallicity Z = 0.0007.

On the Impact of Inclination-dependent Attenuation on Derived Star Formation Histories: Results from Disk Galaxies in the Great Observatories Origins Deep Survey Fields

Abstract We develop and implement an inclination-dependent attenuation prescription for spectral energy distribution (SED) fitting and study its impact on derived star formation histories. We apply our prescription within the SED fitting code Lightning to a clean sample of 82, z = 0.21–1.35 disk-dominated galaxies in the Great Observatories Origins Deep Survey North and South fields. To compare our inclination-dependent attenuation prescription with more traditional fitting prescriptions, we also fit the SEDs with the inclination-independent Calzetti et al. (2000) attenuation curve. From this comparison, we find that fits to a subset of 58, z < 0.7 galaxies in our sample, utilizing the Calzetti et al. (2000) prescription, recover similar trends with inclination as the inclination-dependent fits for the far-UV-band attenuation and recent star formation rates. However, we find a difference between prescriptions in the optical attenuation (A V ) that is strongly correlated with inclination (p‐value < 10−11). For more face-on galaxies, with i ≲ 50°, (edge-on, i ≈ 90°), the average derived A V is 0.31 ± 0.11 magnitudes lower (0.56 ± 0.16 magnitudes higher) for the inclination-dependent model compared to traditional methods. Further, the ratio of stellar masses between prescriptions also has a significant (p‐value < 10−2) trend with inclination. For i = 0°–65°, stellar masses are systematically consistent between fits, with log 10 ( M ⋆ inc / M ⋆ Calzetti ) = − 0.05 ± 0.03 dex and scatter of 0.11 dex. However, for i ≈ 80°–90°, the derived stellar masses are lower for the Calzetti et al. (2000) fits by an average factor of 0.17 ± 0.03 dex and scatter of 0.13 dex. Therefore, these results suggest that SED fitting assuming the Calzetti et al. (2000) attenuation law potentially underestimates stellar masses in highly inclined disk-dominated galaxies.

Stellar populations in local AGNs: evidence for enhanced star formation in the inner 100 pc

ABSTRACT In modern models and simulations of galactic evolution, the star formation in massive galaxies is regulated by an ad hoc active galactic nuclei (AGN) feedback process. However, the physics and the extension of such effects on the star formation history of galaxies is matter of vivid debate. In order to shed some light in the AGN effects over the star formation, we analysed the inner 500 × 500 pc of a sample of 14 Seyfert galaxies using GMOS and MUSE integral field spectroscopy. We fitted the continuum spectra in order to derive stellar age, metallicity, velocity, and velocity dispersion maps in each source. After stacking our sample and averaging their properties, we found that the contribution of young SP, as well as that of AGN featureless continuum both peak at the nucleus. The fraction of intermediate-age SPs is smaller in the nucleus if compared to outer regions, and the contribution of old SPs vary very little within our field of view (FoV). We also found no variation of velocity dispersion or metallicity within our FoV. Lastly, we detected an increase in the dust reddening towards the center of the galaxies. These results lead us to conclude that AGN phenomenon is usually related to a recent star formation episode in the circumnuclear region.

Massive stars dying alone: the remote environment of supernova 2010jp and its associated late-time source

ABSTRACT We present late-time images of the site of the peculiar jet-driven Type IIn supernova (SN) 2010jp, including Hubble Space Telescope images taken 2–5 yr post-explosion and deep ground-based images over a similar time. These are used to characterize its unusually remote environment and to constrain the progenitor’s initial mass and age. The position of SN 2010jp is found to reside along a chain of diffuse starlight that is probably an outer spiral arm or tidal tail of the interacting galaxy pair NGC 2207/IC 2163. There is one bright H ii region projected within 1 kpc, and there is faint extended H α emission immediately surrounding the continuum source at the position of SN 2010jp, which has MF555W = −7.7 ± 0.2 mag. In principle, the lingering light could arise from late-time circumstellar material (CSM) interaction, an evolved supergiant, a host star cluster, or some combination of these. Steady flux over 3 yr and a lack of strong, spatially unresolved H α emission make ongoing CSM interaction unlikely. If an evolved supergiant dominates, its observed luminosity implies an initial mass $\lesssim\!{22}$ M⊙ and an age $\gtrsim\!{8}$ Myr. If the source is a star cluster, then its colour and absolute magnitude imply an age of 8–13 Myr and a modest cluster initial mass of log(M/M⊙) = 3.6–3.8. Extended H α emission out to a radius of ∼30 pc reveals a faint evolved H ii region, pointing to recent star formation with at least one late O-type star. Based on these various clues, we conclude that the progenitor of SN 2010jp had a likely initial mass of 18–22 M⊙.

Observing correlations between dark matter accretion and galaxy growth: II. testing the impact of galaxy mass, star formation indicator, and neighbour colours

ABSTRACT A crucial question in galaxy formation is what role new accretion has in star formation. Theoretical models have predicted a wide range of correlation strengths between halo accretion and galaxy star formation. Previously, we presented a technique to observationally constrain this correlation strength for isolated Milky Way mass galaxies at z ∼ 0.12, based on the correlation between halo accretion and the density profile of neighbouring galaxies. By applying this technique to both observational data from the Sloan Digital Sky Survey and simulation data from the UniverseMachine, where we can test different correlation strengths, we ruled out positive correlations between dark matter accretion and recent star formation activity. In this work, we expand our analysis by (1) applying our technique separately to red and blue neighbouring galaxies, which trace different infall populations, (2) correlating dark matter accretion rates with Dn 4000 measurements as a longer-term quiescence indicator than instantaneous star-formation rates, and (3) analysing higher-mass isolated central galaxies with 1011.0 < M*/M⊙ < 1011.5 out to z ∼ 0.18. In all cases, our results are consistent with non-positive correlation strengths with ≳ 85 per cent confidence, which is most consistent with models where processes such as gas recycling dominate star formation in massive z = 0 galaxies.

Transforming gas-rich low-mass disky galaxies into ultra-diffuse galaxies by ram pressure

Faint extended elliptically-shaped ultra-diffuse galaxies and slightly brighter and more compact dwarf elliptical and lenticular stellar systems are common in galaxy clusters. Their poorly constrained evolutionary paths can be studied by identifying young ultra-diffuse galaxy and dwarf elliptical analogs populated with bright, massive stars. Using data mining we identified 11 such low-mass ($2\times10^8<M_*<2\times10^9 M_{\odot}$) galaxies with large half-light radii ($2.0<r_e<5$ kpc) and recently quenched star formation in the Coma and Abell 2147 galaxy clusters. All galaxies happen to have ram-pressure-stripped tails with signs of current or recent star formation. Deep spectroscopic observations revealed rotating stellar discs containing 70-95% dark matter by mass. A large fraction of the disc stars (10-60%) formed in intense star bursts 180-970 Myr ago, probably triggered by ram pressure. Observed global gradients of stellar age corroborate this scenario. Passive evolution in the next 10 Gyr will transform 9 of the 11 galaxies into ultra-diffuse galaxies. If we assume a constant rate of galaxy infall, 44$\pm$16% of the most luminous present-day ultra-diffuse galaxies in Coma must have formed via ram pressure stripping of disky progenitors.

Revisiting the giant radio galaxy ESO 422−G028 – I. Discovery of a neutral inflow and recent star formation in a restarted giant

ABSTRACT Giant radio galaxies provide important clues into the life cycles and triggering mechanisms of radio jets. With large-scale jets spanning 1.8 Mpc, ESO 422−G028 (z = 0.038) is a giant radio galaxy that also exhibits signs of restarted jet activity in the form of pc-scale jets. We present a study of the spatially resolved stellar and gas properties of ESO 422−G028 using optical integral field spectroscopy from the Wide-Field Spectrograph (WiFeS). In addition to the majority ${\sim} 13\, \rm Gyr$ old stellar population, ESO 422−G028 exhibits a much younger (${\lesssim} 10\, \rm Myr$ old) component with an estimated mass of $10^{7.6}\, \rm M_\odot$ that is predominantly located in the north-west region of the galaxy. Unusually, the ionized gas kinematics reveal two distinct discs traced by narrow ($\sigma _{\rm H\alpha } \lt 100 \, \rm km\, s^{-1}$) and broad ($\sigma _{\rm H\alpha } \gt 150 \, \rm km\, s^{-1}$) Hα emission, respectively. Both ionized gas discs are misaligned with the axis of stellar rotation, suggesting an external origin. This is consistent with the prominent interstellar Na D absorption, which traces a $1 \!-\! 3 \, \rm M_\odot \, yr^{-1}$ inflow of neutral gas from the north. We posit that an inflow of gas – either from an accretion event or a gas-rich merger – has triggered both the starburst and the restarted jet activity, and that ESO 422−G028 is potentially on the brink of an epoch of powerful active galactic nucleus (AGN) activity.

Jet‐triggered star formation in young radio galaxies

AbstractEmission in the ultraviolet continuum is a salient signature of the hot, massive, and consequently short‐lived, stellar population that traces recent or ongoing star formation. With the aim of mapping star forming regions and morphologically separating the generic star formation from that associated with the galaxy‐scale jet activity, we obtained high‐resolution ultraviolet (UV) imaging from the Hubble Space Telescope for a sample of nine compact radio sources. Out of these, seven are known Compact Steep Spectrum (CSS) galaxies that host young, kiloparsec‐scale radio sources and hence are the best candidates for studying radio‐mode feedback on galaxy scales, while the other two form a control sample of larger sources. Extended UV emission regions are observed in six of the seven CSS sources showing close spatial alignment with the radio‐jet orientation. If other mechanisms possibly contributing to the observed UV emission are ruled out, this could be evidence in support of jet‐triggered star formation in the CSS phase of radio galaxy evolution and in turn of the “positive feedback” paradigm of host–active galactic nuclei interaction.