Star Formation Activity Research Articles

The Size–Linewidth Relation and Signatures of Feedback from Quiescent to Active Star Forming Regions in the LMC

To investigate the effects of stellar feedback on the gravitational state of giant molecular clouds (GMCs), we study 12CO and 13CO Atacama Large Millimeter/submillimeter Array maps of nine GMCs distributed throughout the Large Magellanic Cloud (LMC), the nearest star-forming galaxy to our own. We perform noise and resolution matching on the sample, working at a common resolution of 3.″5 (0.85 pc at the LMC distance of 50 kpc), and we use the Spectral Clustering for Molecular Emission Segmentation clustering algorithm to identify discrete substructure, or “clumps.” We supplement these data with three tracers of recent star formation: 8 μm surface brightness, continuum-subtracted Hα flux, and interstellar radiation field energy density inferred from dust emission. The 12CO clumps identified cover a range of 3.6 dex in luminosity-based mass and 2.4 dex in average 8 μm surface brightness, representative of the wide range of conditions of the interstellar medium in the LMC. Our observations suggest evidence for increased turbulence in these clouds. While the turbulent linewidths are correlated with clump surface density, in agreement with previous observations, we find even better correlation with the three star formation activity tracers considered, suggesting stellar energy injection plays a significant role in the dynamical state of the clumps. The excess linewidths we measure do not appear to result from opacity broadening. 12CO clumps are found to be typically less gravitationally bound than 13CO clumps, with some evidence of the kinetic-to-gravitational potential energy ratio increasing with star formation tracers. Further multiline analysis may better constrain the assumptions made in these calculations.

Large-scale Structures in COSMOS2020: Evolution of Star Formation Activity in Different Environments at 0.4 < z < 4

To study the role of environment in galaxy evolution, we reconstruct the underlying density field of galaxies based on COSMOS2020 (The Farmer catalog) and provide the density catalog for a magnitude-limited (K s < 24.5) sample of ∼210,000 galaxies at 0.4 < z < 5 within the COSMOS field. The environmental densities are calculated using a weighted kernel density estimation approach with the choice of a von Mises–Fisher kernel, an analog of the Gaussian kernel for periodic data. Additionally, we make corrections for the edge effect and masked regions in the field. We utilize physical properties extracted by LePhare to investigate the connection between star formation activity and the environmental density of galaxies in six mass-complete subsamples at different cosmic epochs within 0.4 < z < 4. Our findings confirm a strong anticorrelation between star formation rate (SFR)/specific SFR (sSFR) and environmental density out to z ∼ 1.1. At 1.1 < z < 2, there is no significant correlation between SFR/sSFR and density. At 2 < z < 4, we observe a reversal of the SFR/sSFR–density relation such that both SFR and sSFR increase by a factor of ∼10 with increasing density contrast, δ, from −0.4 to 5. This observed reversal at higher redshifts supports the scenario where an increased availability of gas supply, along with tidal interactions and a generally higher star formation efficiency in dense environments, could potentially enhance star formation activity in galaxies located in rich environments at z > 2.

The Star Formation History in Local Group Galaxies. I. Ten Dwarf Galaxies

The star formation histories (SFHs) of galaxies provide valuable insights into galaxy evolution and stellar physics. Understanding the SFHs enables the study of chemical enrichment of galaxies, star formation triggered by interactions, and the behavior of various stellar populations. This work investigates the SFHs of ten dwarf galaxies in the Local Group (LG), which spans a wide range of types, masses, luminosities, and metallicities. The analysis is based on our new sample of the member stars in the LG after removing foreground dwarf stars by using information from the near-infrared color–color diagram and Gaia astrometry. The sample includes the most complete and pure red supergiants and asymptotic giant branch stars to gain valuable insights into the recent SFHs of the galaxies. A fitting method based on the color–magnitude diagram (CMD) is introduced to measure the SFH. The Padova isochrones are used to generate initial model CMDs, accounting for photometric errors and completeness through star-field simulations to match the completeness and error distributions of the observed CMDs. Subsequently, the SFHs, distance modulus, and metallicity of the ten dwarf galaxies are determined by fitting the CMDs. The results indicate that the star formation rates of dwarf irregulars show a gradual increase, while those of dwarf ellipticals exhibit a gradual decrease from the past to the present. Furthermore, this work shows that the star formation activity in dwarf ellipticals persisted up to 30 Myr ago. A significant increasing feature in the SFH of NGC 6822 reveals star formation activity triggered by an interaction event.

The Host Galaxy of a Dormant, Overmassive Black Hole at z = 6.7 may be Restarting Star Formation

JWST is discovering a large population of z > 4 supermassive black holes (SMBHs) that are overmassive with respect to the stellar content of their hosts. A previous study developed a physical model to interpret this overmassive population as the result of quasar feedback acting on a compact host galaxy. In this Note, we apply this model to JADES GN 1146115, a dormant SMBH at z = 6.7 whose mass is ∼40% of the host’s mass in stars and accreting at ∼2% of the Eddington limit. The host has been forming stars at the low rate of ∼1 M ⊙ yr−1 for the past ∼100 Myr. Our model suggests that this galactic system is on the verge of a resurgence of global star formation activity. This transition comes after a period of domination by the effect of its overmassive black hole, whose duration is comparable to typical quasar lifetimes.

SuperCAM CO(3-2) APEX survey at a 6 pc resolution in the Small Magellanic Clouds

The Small Magellanic Cloud (SMC) is an ideal laboratory for studying the properties of star-forming regions thanks to its low metallicity, which has an impact on the molecular gas abundance. However, a small number of molecular gas surveys of the entire galaxy have been carried out in the last few years, limiting the measurements of interstellar medium (ISM) properties in a homogeneous manner. We present the CO($3-2$) APEX survey at a $6$ pc resolution of the bar of the SMC, observed with the SuperCAM receiver attached to the APEX telescope. This high-resolution survey has allowed us to study certain properties of the ISM and to identify CO clouds in the innermost parts of the H$_2$ envelopes. We black adopted the CO analysis in the SMC bar comparing the CO($3-2$) survey with that of the CO($2-1$) of a similar resolution. We studied the CO($3-2$)-to-CO($2-1$) ratio ($R_ $), which is very sensitive to the environment properties (e.g., star-forming regions). We analyzed the correlation of this ratio with observational quantities that trace the star formation such as the local CO emission, the Spitzer color $ $, and the total IR surface brightness measured from the Spitzer and Herschel bands. For the identification of the CO($3-2$) clouds, we used the CPROPS algorithm, which allowed us to measure the physical properties of the clouds. We analyzed the scaling relationships of such physical properties. black We obtained $R_ 0.02$ for the SW bar and a slightly higher ratio 0.1,$ for N66 in the SMC. We found that $R_ $ varies from region to region, depending on the star formation activity. In regions dominated by HII and photo-dissociated regions (e.g., N22, N66) $R_ $ tends to be higher than the median values. Meanwhile, lower values were found toward quiescent clouds. We also found that $R_ black is correlated with the IR color $ $ and the total IR surface brightness. This finding indicates that $R_ $ increases with environmental properties, such as the dust temperature, total gas density, and radiation field. We identified $225$ molecular clouds with sizes of $R &gt; 1.5$ pc and signal-to-noise ratios (S/N) of $&gt; 3$ black of which only $17$ black are well resolved CO($3-2$) clouds black with S/N $ 5$. These $17$ clouds follow consistent scaling relationships to the inner Milky Way clouds but with some departures. For instance, CO($3-2$) tends to be less turbulent and less luminous than the inner Milky Way clouds of similar sizes. Finally, we estimated a median virial-based CO($3-2$)-to-H$_2$ conversion factor of for the total sample.

The metallicity gradients of star-forming regions store information of the assembly history of galaxies

ABSTRACT The variations in metallicity and spatial patterns within star-forming regions of galaxies result from diverse physical processes unfolding throughout their evolutionary history, with a particular emphasis on recent events. Analysing MaNGA and EAGLE galaxies, we discovered an additional dependence of the mass–metallicity relation (MZR) on metallicity gradients (∇(O/H)). Two regimes emerged for low- and high-stellar mass galaxies, distinctly separated at approximately M⋆ &amp;gt; 109.75$\rm{M}_{\odot}$. Low-mass galaxies with strong positive ∇(O/H) appear less enriched than the MZR median, while those with strong negative gradients are consistently more enriched in both simulated and observed samples. Interestingly, low-mass galaxies with strong negative ∇(O/H) exhibit high star-forming activity, regardless of stellar surface density or ∇(O/H). In contrast, a discrepancy arises for massive galaxies between MaNGA and EAGLE data sets. The latter exhibit a notable anticorrelation between specific star formation rate and stellar surface density, independent of ∇(O/H), while MaNGA galaxies show this trend mainly for strong positive ∇(O/H). Further investigation indicates that galaxies with strong negative gradients tend to host smaller central black holes in observed data sets, a trend not replicated in simulations. These findings suggest disparities in metallicity recycling and mixing history between observations and simulations, particularly in massive galaxies with varying metallicity gradients. These distinctions could contribute to a more comprehensive understanding of the underlying physics.

New Herbig–Haro objects associated with embedded sources

ABSTRACT We continue to present the results of the Byurakan Narrow Band Imaging Survey (BNBIS). The main goal of this survey is to search for Herbig–Haro (HH) objects and jets in Galactic dark clouds. In this work we present the results of the search in the vicinity of infrared sources that are bright in the WISE survey and embedded in the dark clouds. The survey is performed with the 1-m Schmidt telescope of Byurakan Observatory, lately equipped with a new CCD detector, which allows to obtain one square degree images of the sky in various filters. Narrow-band filters were used to obtain H α and [S ii] images, and a medium-width filter was used for the continuum imaging. New HH flows and knots were found near six embedded IR sources, which constitutes a significant proportion of the objects observed. At least two of the newly found HH flows (HH 1226 and HH 1227) lie in isolated dark clouds, thus pointing to active star formation in these regions. Other flows are also located in detached and dense globules or filaments. The length of the HH 1228 flow is about 1 pc; it has also a molecular hydrogen counterpart of the same extension. Coordinates, charts, detailed descriptions and distance estimates are provided. The lower limits of bolometric luminosities of the source stars are typical for low-mass young stellar objects.

Optical- and UV-continuum Morphologies of Compact Radio Source Hosts

We present the first systematic search for UV signatures from radio source-driven active galactic nuclei (AGN) feedback in Compact Steep Spectrum (CSS) radio galaxies. Owing to their characteristic sub-galactic jets (1–20 kpc projected linear sizes), CSS hosts are excellent laboratories for probing galaxy scale feedback via jet-triggered star formation. The sample consists of seven powerful CSS galaxies, and two galaxies host to radio sources >20 kpc as the control, at low to intermediate redshifts (z < 0.6). Our new Hubble Space Telescope images show extended UV continuum emission in six out of seven CSS galaxies, with five CSS hosts exhibiting UV knots cospatial and aligned along the radio-jet axis. Young (≲ 10 Myr), massive (≳ 5 M ⊙) stellar populations are likely to be the dominant source of the blue excess emission in radio galaxies at these redshifts. Hence, the radio-aligned UV regions could be attributed to jet-induced starbursts. Lower near-UV star formation rates compared to other indicators suggest low scattered AGN light contribution to the observed UV. Dust attenuation of UV emission appears unlikely from high internal extinction correction estimates in most sources. Comparison with evolutionary synthesis models shows that our observations are consistent with recent (∼1−8 Myr old) star-forming activity likely triggered by current or an earlier episode of radio emission, or by a confined radio source that has frustrated growth, due to a dense environment. While follow-up spectroscopic and polarized light observations are needed to constrain the activity-related components in the observed UV, the detection of jet-induced star formation is a confirmation of an important prediction of the jet feedback paradigm.

Assessment of SDSS-derived Galaxy Morphologies Using HST Imaging

The Sloan Digital Sky Survey (SDSS) was foundational to the study of galaxy evolution, having revealed the bimodality of galaxies and the relationship between their structure and star-forming activity. However, ground-based optical surveys like SDSS are limited in resolution and depth, which may lead to biases or poor quality in the derived morphological properties, potentially impacting our understanding of how and why galaxies cease their star formation (quench). We use archival Hubble Space Telescope (HST) imaging of ∼2000 SDSS objects to assess the reliability of SDSS-derived morphologies, taking advantage of both SDSS statistical samples and HST’s superior resolution and sensitivity. Single Sérsic fitting and bulge-disk decomposition is performed on HST images for direct comparison with SDSS results. Of the three catalogs of SDSS-derived morphologies considered, none is significantly more accurate or precise than the others. For disk-dominated galaxies (n < 2.5), global Sérsic indices (n) from Meert et al. (hereafter, M15) are preferred. For bulge-dominated galaxies (n > 2.5), Simard et al. (hereafter, S11) and M15 overestimate n by ∼20%, and derived global n from Blanton et al. are preferred. We provide an empirical relation to correct S11 global Sérsic indices. Global R eff from S11 overestimates R eff for the largest galaxies by 0.1 dex. Despite these moderate biases, SDSS-derived single-component parameters are generally significantly more robust than SDSS-derived two-component parameters. The bulge Sérsic index (n bulge) cannot be reliably constrained from SDSS imaging at all, whereas the bulge-to-total (B/T) ratio can be inferred from SDSS (provided that n bulge = 4 is enforced) but has a large random error of ∼0.2.

Probing the interstellar medium of the quasar BRI 0952−0115

Context. The extent of the effect of active galactic nuclei (AGN) on their host galaxies at high-redshift is not apparent. The processes governing the co-eval evolution of the stellar mass and the mass of the central supermassive black hole, along with the effects of the supermassive black hole on the host galaxy, remain unclear. Studying this effect in the distant universe is a difficult process as the mechanisms of tracing AGN activity can often be inaccurately associated with intense star formation and vice versa. Aims. Our aim is to better understand the processes governing the interstellar medium (ISM) of the quasar BRI 0952−0952 at z = 4.432, specifically with regard to the individual heating processes at work and to place the quasar in an evolutionary context. Methods. We analyzed ALMA archival bands 3, 4, and 6 data and combined the results with high-resolution band-7 ALMA observations of the quasar. We detected [C I](2–1), [C II](2P3/2 − 2P1/2), CO(5–4), CO(7–6), CO(12–11), OH 2Π1/2(3/2 − 1/2), and H2O(211 − 202), and we report a tentative detection of OH+. We updated the lensing model and we used the radiative transfer code MOLPOP-CEP to produce line emission models which we compared with our observations. Results. We used the [C I] line emission to estimate the total molecular gas mass in the quasar. We present results from the radiative transfer code MOLPOP-CEP constraining the properties of the CO emission and suggest different possible scenarios for heating mechanisms within the quasar. We extended our results from MOLPOP-CEP to the additional line species detected in the quasar to place stronger constraints on the ISM properties. Conclusions. Modeling from the CO SLED suggests that there are extreme heating mechanisms operating within the quasar in the form of star formation or AGN activity; however, with the current data, it remains unclear which of the two is the preferred mechanism as both models reasonably reproduce the observed CO line fluxes. The updated lensing model suggests a velocity gradient across the [C II] line, suggestive of ongoing kinematical processes within the quasar. We find that the H2O emission in BRI 0952 is likely correlated with star-forming regions of the ISM. We used the molecular gas mass from [C I] to calculate a depletion time for the quasar. We conclude that BRI 0952−0952 is a quasar with a significant AGN contribution while also showing signs of extreme starburst activity, indicating that the quasar could be in a transitional phase between a starburst-dominated stage and an AGN-dominated stage.

A Study of the Merging Dwarf Galaxy VCC322

Galaxy interactions and mergers can enhance or reduce star formation, but a complete understanding of the involved processes is still lacking. The effect of dwarf galaxy mergers is even less clear than their massive counterpart. We present a study on a dwarf merger remnant in the Virgo cluster, VCC322, which might form a triple system with VCC334 and VCC319. We identify a prominent long and straight tail-like substructure that has a size comparable to its host galaxy VCC322. By comparing the color–color (g − r versus r − H) distribution with simple stellar population models, we infer that the metallicity and stellar age of this tail are Z ⋆ ∼ 0.02 Z ⊙ and t ⋆ ∼ 10 Gyr, respectively. In VCC319, we find a sign of isophotal twisting. This suggests that VCC319 may be subject to tidal interaction. An analysis of the Sloan Digital Sky Survey optical spectra of VCC322 indicates mass- and light-weighted ages of about 109.8 yr and 107.5 yr, respectively, indicating an ongoing star formation activity. However, the star formation in VCC322 seems suppressed when compared to other star-forming dwarfs of comparable stellar masses. Our finding of shock excitation of optical emission lines indicates that interaction-induced shock may contribute to the heating of cold gas and suppression of star formation.

GA-NIFS: Co-evolution within a highly star-forming galaxy group at z ∼ 3.7 witnessed by JWST/NIRSpec IFS

We present NIRSpec IFS observations of a galaxy group around the massive GS_4891 galaxy at z ∼ 3.7 in GOODS-South that includes two other two systems, GS_4891_n to the north and GS_28356 to the east. These observations, obtained as part of the GTO Galaxy Assembly – NIRSpec IFS (GA-NIFS) program, allow us to study for the first time the spatially resolved properties of the interstellar medium (ISM) and the ionised gas kinematics of a galaxy at this redshift. Leveraging the wide wavelength range spanned with the high-dispersion grating (with resolving power R = 2700) observations, covering from [O II] λλ3726, 29 to [S II] λλ6716, 31, we explore the spatial distribution of the star formation rate, nebular attenuation, and gas metallicity, together with the mechanisms responsible for the excitation of the ionised gas. GS_4891 presents a clear gradient of gas metallicity (as traced by 12 + log(O/H)) by more than 0.2 dex from the southeast (where a star-forming clump is identified) to the northwest. The gas metallicity in the less massive northern system, GS_4891_n, is also higher by 0.2 dex than at the centre of GS_4891, suggesting that inflows of lower-metallicity gas might be favoured in higher-mass systems. The kinematic analysis shows that GS_4891 presents velocity gradients in the ionised gas consistent with rotation. The region between GS_4891 and GS_4891_n does not present high gas turbulence, which, together with the difference in gas metallicities, suggests that these two systems might be in a pre-merger stage. Finally, GS_4891 hosts an ionised outflow that extends out to rout = 1.5 kpc from the nucleus and reaches maximum velocities, vout, of approximately 400 km s−1. Despite entraining an outflowing mass rate of Ṁout ∼ 4 M⊙ yr−1, the low associated mass-loading factor, η ∼ 0.04, implies that the outflow does not have a significant impact on the star formation activity of the galaxy.

Disentangling the association of PAH molecules with star formation

Context. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous complex molecules in the interstellar medium and are used as an indirect indicator of star formation. On the other hand, the ultraviolet (UV) emission from young massive stars directly traces the star formation activity in a galaxy. The James Webb Space Telescope (JWST), along with the UltraViolet Imaging Telescope (UVIT), opened up a new window of opportunity to better understand the properties of PAH molecules that are associated with star-forming regions. Aims. We investigate how the resolved scale properties of PAH molecules in nearby galaxies are affected by star formation. Methods. We analyzed the PAH features observed at 3.3, 7.7, and 11.3 μm using F335M, F770W, and F1130W images obtained from the JWST. These images helped us identify and quantify the PAH molecules. Additionally, we used UVIT images to assess the star formation associated with these PAH-emitting regions. Our study focused on three galaxies, namely NGC 628, NGC 1365, and NGC 7496, which were selected based on the availability of both JWST and UVIT images. Bright PAH emission regions were identified in the JWST images, and their corresponding UV emission was estimated using the UVIT images. We quantified the star formation properties of these PAH emitting regions using the UVIT images. Furthermore, we investigated the relation between the star formation surface density (ΣSFR) and the PAH ratios to better understand the impact of star formation on the properties of PAH molecules. Results. Based on the resolved scale study of the PAH-bright regions using JWST images, we found that the fraction of ionized PAH molecules is high in the star-forming regions with high ΣSFR. We observed that emission from smaller PAH molecules is higher in star-forming regions with higher ΣSFR. Conclusions. Our study suggests that the PAH molecules excited by the photons from star-forming regions with higher ΣSFR are dominantly smaller and ionized molecules. UV photons from the star-forming regions could be the reason for the higher fraction of the ionized PAHs. We suggest that the effect of the high temperature in the star-forming regions and the formation of smaller PAH molecules in the star-forming regions might also result in the higher emission in the F335MPAH band.

Surveys of clumps, cores, and condensations in Cygnus X

Context. The physical properties, evolution, and fragmentation of massive dense cores (MDCs, ~0.1 pc) are fundamental pieces in our understanding of high-mass star formation.Aims. We aim to characterize the temperature, velocity dispersion, and fragmentation of the MDCs in the Cygnus X giant molecular cloud and to investigate the stability and dynamics of these cores.Methods. We present theKarl G. JanskyVery Large Array (VLA) observations of the NH3(J,K) = (1,1) and (2,2) inversion lines towards 35 MDCs in Cygnus X, from which we calculated the temperature and velocity dispersion. We extracted 202 fragments (~0.02 pc) from the NH3(1,1) moment-0 maps with the GAUSSCLUMPS algorithm. We analyzed the stability of the MDCs and their NH3fragments through evaluating the corresponding kinetic, gravitational potential, and magnetic energies and the virial parameters.Results. The MDCs in Cygnus X have a typical mean kinetic temperatureTKof ~20 K. Our virial analysis shows that many MDCs are in subvirialized states, indicating that the kinetic energy is insufficient to support these MDCs against their gravity. The calculated nonthermal velocity dispersions of most MDCs are at transonic to mildly supersonic levels, and the bulk motions make only a minor contribution to the velocity dispersion. Regarding the NH3fragments, withTK~19 K, their nonthermal velocity dispersions are mostly trans-sonic to subsonic. Unless there is a strong magnetic field, most NH3fragments are probably not in virialized states. We also find that most of the NH3fragments are dynamically quiescent, while only a few are active due to star formation activity.

Star formation histories of dwarf lenticular galaxies

ABSTRACT Star formation histories (SFHs) are essential for understanding galaxy formation and evolution. We present the mean SFHs of 148 dwarf lenticular galaxies (dS0s) derived from the Sloan Digital Sky Survey spectra. These SFHs reveal two distinct periods of active star formation. The first period, concluding approximately 6 Gyr ago, witnessed the formation of predominantly old, metal-poor (Z = 0.0004) stars, accounting for approximately 60 per cent of the stellar mass and 30 per cent of the luminosity. The scarcity of extremely metal-poor (Z = 0.0001) stars suggests pre-enrichment during the reionization era. Star formation gradually waned during this initial phase. In contrast, the second period, ending around 1 Gyr ago, exhibited a peak in the middle of the period, contributing to the formation of moderately old stellar populations with intermediate metallicity. The SFHs of dS0 galaxies show a clear dependence on stellar mass, with more massive dS0s forming stars earlier. However, we find no significant correlation with morphological properties such as outer spiral arms and nucleation. The SFHs of dS0 galaxies share many similarities with those of dwarf elliptical galaxies, suggesting a common origin, mostly not primordial.

Insights into Galaxy Morphology and Star Formation: Unveiling Filamentary Structures around an Extreme Overdensity at z ∼ 1.5 Traced by [O ii] Emitters

We explore the morphological features and star formation activities of [O ii] emitters in the COSMOS UltraDeep field at z ∼ 1.5 using JWST NIRCam data from the COSMOS-Web survey and Subaru Hyper Suprime-Cam. We also report the discovery of large filamentary structures traced by [O ii] emitters surrounding an extremely overdense core with a galaxy number density ∼11× higher than the field average. These structures span over 50 cMpc, underscoring their large scale in the cosmic web at this epoch. After matching the stellar-mass distributions, the core galaxies show a higher frequency of disturbances (50% ± 9%) than those in the outskirts (41% ± 9%) and the field (21% ± 5%), indicative of more frequent mergers and interactions in the innermost ≲1.′5 region. Additionally, we observe that specific star formation rates are elevated in denser environments. A Kolmogorov–Smirnov test comparing the distribution of specific star formation rates of core and field galaxies yields a p-value of 0.02, suggesting an enhancement of star formation activity driven by the dense environment. Our findings underscore the environmental impact on galaxy evolution during a pivotal cosmic epoch and set the stage for further investigation with the increasing larger data from upcoming surveys.

Resolved properties of classical bulge and pseudo-bulge galaxies

ABSTRACT We compare properties of classical and pseudo-bulges and properties of their hosting galaxies selected from the MaNGA survey. Bulge types are identified based on the Sérsic index n of bulge component and the position of bulges on the Kormendy diagram. For the 393 classical bulges and 422 pseudo-bulges selected and their hosting galaxies, we study their kinematic properties including a proxy for specific angular momentum and central velocity dispersion, their stellar population properties including stellar age, metallicity, and specific star formation rate, as well as H i fractions of the galaxies. Our results show that at given stellar mass, disc components of pseudo-bulge galaxies are younger, have more active star formation, rotate more, and may contain more H i content compared with those of classical bulge galaxies, and the differences are larger than those between bulges themselves. The correlations between bulge types and disc properties indicate that different types of bulges are shaped by different processes that may regulate both growth of central components and evolution of outer discs in galaxies. In addition, we propose a stellar mass dependent divider of central velocity dispersion to separate galaxies with classical bulges from those with pseudo-bulges in galaxy mass range of $10.4\lt \mathrm{log}(M_*/\rm M_\odot)\lt 11.4$: $\mathrm{log}(\sigma _0) = 0.23 \times \mathrm{log}(M_*/\rm M_\odot)-0.46$. Galaxies with larger/smaller σ0 can be classified as hosts of classical/pseudo-bulges.

CO outflows from young stars in the NGC2023 cluster

Young early-type HAeBe stars are still embedded in the molecular clouds in which they formed. They illuminate reflection nebulae, which shape the surrounding molecular cloud and may trigger star formation. They are therefore ideal places to search for ongoing star formation activity. NGC\,2023 is illuminated by the Herbig Be star HD\,37903. It is the most massive member of a small young cluster with about 30 PMS stars, several of which are Class I objects that still heavily accrete. It might therefore be expected that they might drive molecular outflows. We examined the whole region for outflows. We analyzed previously published APEX data to search for and characterize the outflows in the NGC\,2023 region. This is the first systematic search for molecular outflows in this region. Since the outflows were mapped in several CO transitions, we can determine their properties quite well. We have discovered four molecular outflows in the vicinity of NGC\,2023, three of which are associated with Class I objects. MIR-63, a bright mid-infrared and submillimeter Class I source, is a binary with a separation of 2 and drives two bipolar outflows orthogonal to each other. The large southeast--northwest outflow excites the Herbig-Haro flow HH\,247. MIR-73, a Class I object, which is also a far-infrared source, drives a pole-on outflow. MIR-62 is a Class II object with strong infrared excess and a luminosity of 7 It is not detected in the far-infrared. The Class I sources have bolometric luminosities of about 20 or lower, that is, they are all low-mass stars. One other far-infrared source, MIR-75, may have powered an outflow in the past because it now illuminates an egg-shaped cavity. The four outflows are all powered by young stars and are located in the immediate vicinity of NGC\,2023. They are at a similar evolutionary stage, which suggests that their formation may have been triggered by the expanding region.

The ALCHEMI Atlas: Principal Component Analysis Reveals Starburst Evolution in NGC 253

Molecular lines are powerful diagnostics of the physical and chemical properties of the interstellar medium (ISM). These ISM properties, which affect future star formation, are expected to differ in starburst galaxies from those of more quiescent galaxies. We investigate the ISM properties in the central molecular zone of the nearby starburst galaxy NGC 253 using the ultrawide millimeter spectral scan survey from the Atacama Large Millimeter/submillimeter Array Large Program ALCHEMI. We present an atlas of velocity-integrated images at a 1.″6 resolution of 148 unblended transitions from 44 species, including the first extragalactic detection of HCNH+ and the first interferometric images of C3H+, NO, and HCS+. We conduct a principal component analysis (PCA) on these images to extract correlated chemical species and to identify key groups of diagnostic transitions. To the best of our knowledge, our data set is currently the largest astronomical set of molecular lines to which PCA has been applied. The PCA can categorize transitions coming from different physical components in NGC 253 such as (i) young starburst tracers characterized by high-excitation transitions of HC3N and complex organic molecules versus tracers of on-going star formation (radio recombination lines) and high-excitation transitions of CCH and CN tracing photodissociation regions, (ii) tracers of cloud-collision-induced shocks (low-excitation transitions of CH3OH, HNCO, HOCO+, and OCS) versus shocks from star formation-induced outflows (high-excitation transitions of SiO), as well as (iii) outflows showing emission from HOC+, CCH, H3O+, CO isotopologues, HCN, HCO+, CS, and CN. Our findings show these intensities vary with galactic dynamics, star formation activities, and stellar feedback.

Observational properties of active galactic nucleus obscuration during the peak of accretion growth

ABSTRACT We investigated the gas obscuration and host galaxy properties of active galactic nuclei (AGNs) during the peak of cosmic accretion growth of supermassive black holes at redshift 0.8–1.8 using X-ray-detected AGNs with mid-infrared and far-infrared detection. The sample was classified as type-1 and type-2 AGNs using optical spectral and morphological classification while the host galaxy properties were estimated with multiwavelength spectral energy distribution fitting. For type-1 AGNs, the black hole mass was determined from MgII emission lines while the black hole mass of type-2 AGNs was inferred from the host galaxy’s stellar mass. Based on the derived parameters, the distribution of the sample in the absorption hydrogen column density (NH) versus Eddington ratio diagram is examined. Among the type-2 AGNs, 28 ± 5 per cent are in the forbidden zone, where the obscuration by dust torus cannot be maintained due to radiation pressure on dusty material. The fraction is higher than that observed in the local universe from the Burst Alert Telescope AGN Spectroscopic Survey data release 2 (BASS DR2) (11 ± 3 per cent). The higher fraction implies that the obscuration of the majority of AGNs is consistent with the radiation pressure regulated unified model but with an increased incidence of interstellar matter (ISM)-obscured AGNs. We discuss the possibility of dust-free absorption in type-1 AGNs and heavy ISM absorption in type-2 AGNs. We also find no statistical difference in the star-formation activity between type-1 and type-2 AGNs which may suggest that obscuration triggered by a gas-rich merging is not common among X-ray detected AGNs in this epoch.