Dense Cores of Dark Clouds. XII.13CO and C18O in Lupus, Corona Australis, Vela, and Scorpius

Probing the star formation (SF) activity of cluster galaxies paves an important path towards the understanding of cluster evolution. This thesis presents the study of star formation rates (SFR) in clusters using dustunbiased radio luminosities from the MeerKAT Galaxy Clusters Legacy Survey (MGCLS). Our radio data is complemented by optical data from the Dark Energy Camera Legacy Survey (DECaLS), for photometric redshifts, and also Sunyaev-Zel’dovich (SZ) effect-derived cluster masses from the Atacama Cosmology Telescope (ACT). We present the first statistical study of SFR in clusters using MeerKAT-detected galaxies which takes advantage of MeerKAT’s large field of view to investigate the relation between SF activity and cluster environments out to 2R200. Using radio diffuse emission in the form of haloes and relics as a proxy for cluster merger activity, we divide our cluster sample between disturbed/merger clusters and relaxed clusters. We observe a higher fraction of star-forming galaxies (fSF) in disturbed clusters than in relaxed clusters. Disturbed clusters also have higher masses (M200) and total SFR (ΣSFR) in contrast to relaxed clusters. On analysing the redshift evolution of the massnormalised ΣSFR, we observe a ≈ 4× decline in the SF activity of clusters from the redshift of 0.35 to 0.15, corresponding to ≈ 2 Gyr in look-back time. Our result is roughly consistent with the one from cluster studies that used infrared-derived SFR (≈ 5× decline) at a similar redshift slice as our sample. We use a subsample of double relic-hosting clusters to investigate the relation between cluster SF activity and the time that has passed since the merger started (tmerger) estimated from the relic distances from cluster cores. We observe an anti-correlation between ΣSFR and merger, suggesting that younger mergers have a higher SF activity. However, we see no clear correlation in the mass-normalised ΣSFR with tmerger. We also investigate for differences in the SF activity of galaxies closer to radio relics and those away from the relics and observe no significant differences between the two populations. Iqoqa Ukuhlola kokusebenza kolwazi-bunkanyezi ( star formation -SF) kwesixhobo sezinkanyezi cluster galaxies kucabe indlela emqoka ukuqonda kokukhula kwalamaqoqo (cluster evolution). Lolu cwaningo lwethula ukuhlolwa lwe star (formation rates -SFR) kuma-clusters kusetshenziswa i dust-unbiased radio luminosities kuMeerKAT Galaxy Clusters Legacy Survey (MGCLS). Imininingo ye-radio isebenzisana ne-optical data yeDark Energy Camera Legacy Survey (DECaLS), ukuhlola iphotometric redshifts, ne Sunyaev-Zel'dovich (SZ) nomthelela odalwa yicluster masses esuka kwiAtacama Cosmology Telescope (ACT). Kube sekwethulwa ucwaningo lokuqala lwezibalo lweSFR in clusters kusetshenziswa iMeerKAT-detected galaxies. Kusetshenziswe ithuba lobukhulu bomkhakha lokubonakala kahle kweMeerKAT ukuhlola ubudlelwane phakathi kwe-SFR nemvelo yamaclusters ezinhlobonhlobo zedynamical states. Kusetshenziswe iradio diffuse emission eyizinhlobo zehaloes nerelics njengegunya lokuhlola ukuhlangana kwamacluster , amasampula ama-cluster ahlukaniswe phakathi kwamadisturbed/merger clusters namarelaxed clusters. Okutholakele ukuthi ihigher fraction of star-forming galaxies (fSF) kumaclusters aphazamisekile (disturbed clusters) kunama clusters akhululekile (relaxed clusters). Amaclusters aphazamisekile anama masi aphezulu (M200) kanti isamba sonke siwuSFR (∑SFR) uma eqhathaniswa namaclusters aphazamisekile . Sekucutshungulwa iredshift evolution yemass-normalised ∑SFR, kutholakale ukuthi aphindwe kawu ≅4 times decline ekusebenzeni kwe SF esukela kwiredshift of 0.35 to 0.15, ahlobana ne ≅2 Gyr kwi look-back time. Imiphumela ilinganiselwe ngokuhambisana nezifundo zamacluster kusetshenziswa i-infrared-derived SFR (≅5 times decline) ngokufanayo neredshift slice njengamasampula ocwaningo lolu .Kusetshenziswe elinye isampula esigabeni sesibili ukuze kwenziwe idouble relic-hosting clusters ukuhlola ubudlelwane okusebenza kwama clusters (SF activity) kanye nesikhathi esisuke sidlulile ehlanganiswe (t_merger) kulinganiselwe kusukela ebangeni lerelic distances kucluster ewumsuka (cluster cores). Kutholakale ukungadlelani phakathi kwe ∑SFR ne t_merger, okuchaza ukuthi ukuhlanganiswa kwalawo asemancane kusebenzisa izinga eliphezulu (SF activity). Yize-kunjalo , akubonakali ubudlelwane obucacile kumass-normalised ∑SFR ne t_merger. Kuphinde kwahlolwa ukusebenza okungefani kumagalaxies asondelene neradio relics nalawo aqhelile kumarelics kwase kwangatholakala mehluko otheni kule miphakathi yomibili.

Recent observations with JWST have uncovered unexpectedly high cosmic star formation activity in the early Universe, mere hundreds of millions of years after the big bang. These observations are often understood to reflect an evolutionary shift in star formation efficiency (SFE) caused by changing galactic conditions during these early epochs. We present FIREbox$^{\it HR}$, a high-resolution, cosmological hydrodynamical simulation from the Feedback in Realistic Environments (FIRE) project, which offers insights into the SFE of galaxies during the first billion years of cosmic time. FIREbox$^{\it HR}$ re-simulates the cosmic volume ($L=22.1$ cMpc) of the original FIREbox run with eight times higher mass resolution ($m_{\rm b}\sim {}7800\, M_\odot$), but with identical physics, down to $z\sim {}6$. FIREbox$^{\it HR}$ predicts ultraviolet (UV) luminosity functions in good agreement with available observational data. The simulation also successfully reproduces the observed cosmic UV luminosity density at $z\sim {}6{\!-\!}14$, demonstrating that relatively high star formation activity in the early Universe is a natural outcome of the baryonic processes encoded in the FIRE-2 model. According to FIREbox$^{\it HR}$, the SFE–halo mass relation for intermediate mass haloes ($M_{\rm halo}\sim {}10^9{\!-\!}10^{11}\, {\rm M}_\odot$) does not significantly evolve with redshift and is only weakly mass-dependent. These properties of the SFE–halo mass relation lead to a larger contribution from lower mass haloes at higher z, driving the gradual evolution of the observed cosmic UV luminosity density. A theoretical model based on the SFE–halo mass relation inferred from FIREbox$^{\it HR}$ allows us to explore implications for galaxy evolution. Future observations of UV faint galaxies at $z\gt 12$ will provide an opportunity to further test these predictions and deepen our understanding of star formation during Cosmic Dawn.

We carried out a C18O survey for dense molecular cores in the Corona Australis (CrA) molecular cloud with the NANTEN telescope. We observed 2.2 deg2 at a 2′ grid spacing with a 2′.7 beam, and 1980 positions were observed. We identified 8 C18O cores, whose typical line width, average column density, radius, mass, and average number density were 0.66 km s-1, 1.1×1022 cm-2, 0.13 pc, 18 M⊙ , and 1.4 × 104 cm-3, respectively. We found that Δ Vcomp, 〈 N(H2)〉, R, M, and n(H2) become larger along with an increase in the star-formation activity, whereas the ratio Mvir/M becomes smaller. A comparison of the present cores with those in Chamaeleon, Lupus, Ophiuchus, Taurus, and L 1333 indicates that star-forming cores tend to have a high column density, as well as a smaller Mvir/M ratio.

Context. Cosmic rays drive several key processes for the chemistry and dynamical evolution of star-forming regions. Their effect is quantified mainly by means of the cosmic-ray ionisation rate ζ2. Aims. We aim to obtain a sample of ζ2 measurements in 20 low-mass, starless cores embedded in different parental clouds in order to assess the average level of ionisation in this kind of source and to investigate the role of the environment in this context. The warmest clouds in our sample are Ophiuchus and Corona Australis, where star formation activity is higher than in the Taurus cloud and the other isolated cores we targeted. Methods. We computed ζ2 using an analytical method based on the column density of ortho-H2D+, the CO abundance, and the deuteration level of HCO+. To estimate these quantities, we analysed new, high-sensitivity molecular line observations obtained with the Atacama Pathfinder Experiment (APEX) single-dish telescope and archival continuum data from Herschel. Results. We report ζ2 estimates in 17 cores in our sample and provide upper limits on the three remaining sources. The values span almost two orders of magnitude, from 1.3 × 10−18 s−1 to 8.5 × 10−17 s−1. Conclusions. We find no significant correlation between ζ2 and the core’s column densities N(H2). On the contrary, we find a positive correlation between ζ2 and the core’s temperature, estimated via Herschel data: cores embedded in warmer environments present higher ionisation levels. The warmest clouds in our sample are Ophiuchus and Corona Australis, where star formation activity is higher than in the other clouds we targeted. The higher ionisation rates in these regions support the scenario that low-mass protostars in the vicinity of our targeted cores contribute to the re-acceleration of local cosmic rays.

There appears to exist a conflict between the standard structure formation theory and the existence of the faint dwarf spheroidal galaxies in the Local Group. Theoretical considerations suggest that a cold dark matter universe has been a very hostile place for the formation of small galaxies. In particular, gas would not have been able to cool and condense to form stars inside dark matter halos with a velocity dispersion <10km/s since before the cosmological reionization epoch. In other words, one should not expect to see any major star formation activities in dwarf galaxies with a velocity dispersion <10km/s during the past 12Gyr, according to the current structure formation theory. The real universe, on the other hand, shows that all dwarf spheroidal galaxies in the Local Group have velocity dispersions <10km/s and extended and recent star formation activities are quite common in them. This apparent conflict between cold dark matter models and local observations can be resolved, if one allows the cold dark matter particles to decay relatively recently. The resolution comes about in that the dwarf spheroidal galaxies with a velocity dispersion of \~10km/s seen today were born, in this picture, in a small fraction of halos with a velocity dispersion of ~20km/s, where gas can be retained and is able to cool and contract to form stars. The presently observed lower velocity dispersion ~10km/s of these dwarf spheroidal galaxies is a consequence of the decay of one half of the dark matter in and subsequent expansion of the halos since redshift z~2.

We present deep Spitzer/IRS spectra for complete samples of 46 2Jy radio galaxies (0.05<z<0.7) and 19 3CRR FRII radio galaxies (z<0.1), and use the detection of polycyclic aromatic hydrocarbon (PAH) features to examine the incidence of contemporaneous star formation and radio-loud AGN activity. Our analysis reveals PAH features in only a minority (30%) of the objects with good IRS spectra. Using the wealth of complementary data available for the 2Jy and 3CRR samples we make detailed comparisons between a range of star formation diagnostics: optical continuum spectroscopy, mid- to far-IR (MFIR) color, far-IR excess and PAH detection. There is good agreement between the various diagnostic techniques: most candidates identified to have star formation activity on the basis of PAH detection are also identified using at least two of the other techniques. We find that only 35% of the combined 2Jy and 3CRR sample show evidence for recent star formation activity (RSFA) at optical and/or MFIR wavelengths. This result argues strongly against the idea of a close link between starburst and powerful radio-loud AGN activity, reinforcing the view that, although a large fraction of powerful radio galaxies may be triggered in galaxy interactions, only a minority are triggered at the peaks of star formation activity in major, gas-rich mergers. However, we find that compact radio sources (D < 15 kpc) show a significantly higher incidence of RSFA (>75%) than their more extended counterparts (=15 -- 25%). We discuss this result in the context of a possible bias towards the selection of compact radio sources triggered in gas-rich environments.

We present an unbiased deep [OII] emission survey of a cluster XMMXCS J2215.9-1738 at z=1.46, the most distant cluster to date with a detection of extended X-ray emission. With wide-field optical and near-infrared cameras (Suprime-Cam and MOIRCS, respectively) on Subaru telescope, we performed deep imaging with a narrow-band filter NB912 (lambda_c=9139A, Delta_lambda=134A) as well as broad-band filters (B, z', J and Ks). From the photometric catalogues, we have identified 44 [OII] emitters in the cluster central region of 6'x6' down to a dust-free star formation rate of 2.6 Msun/yr (3 sigma). Interestingly, it is found that there are many [OII] emitters even in the central high density region. In fact, the fraction of [OII] emitters to the cluster members as well as their star formation rates and equivalent widths stay almost constant with decreasing cluster-centric distance up to the cluster core. Unlike clusters at lower redshifts (z<1) where star formation activity is mostly quenched in their central regions, this higher redshift 2215 cluster shows its high star formation activity even at its centre, suggesting that we are beginning to enter the formation epoch of some galaxies in the cluster core eventually. Moreover, we find a deficit of galaxies on the red sequence at magnitudes fainter than ~M*+0.5 on the colour-magnitude diagram. This break magnitude is brighter than that of lower redshift clusters, and it is likely that we are seeing the formation phase of more massive red galaxies in the cluster core at z~1. These results may indicate inside-out and down-sizing propagation of star formation activity in the course of cluster evolution.

We use a kernel density estimator method to evaluate the stellar velocity dispersion in the open cluster NGC 2571. We derive the 3D velocity dispersion using both proper motions as extracted from Gaia Data Release 3 and single-epoch radial velocities as obtained with the instrument FLAMES at ESO's Very Large Telescope. The mean-square velocity along the line of sight is found to be larger than the one in the tangential direction by a factor of 6–8. We argue that the most likely explanation for such an occurrence is the presence of a significant quantity of unresolved binary and multiple stars in the radial velocity sample. Special attention should be paid to single-line spectroscopic binaries (SB1) since in this case we observe the spectral lines of the primary component only, and therefore the derived radial velocity is not the velocity of the binary system center of mass. To investigate this scenario, we performed numerical experiments varying the fractional abundance of SB1 in the observed sample. These experiments show that the increase of the mean-square radial velocity depends on the fractional abundance of SB1 to a power in the range [0.39, 0.45]. We used the 3D velocity dispersion obtained by the dispersions in the tangential directions and the assumption that the radial velocity dispersion is the same as a tangential one to estimate the virial cluster mass and the cluster mass, taking into account the gravitational field of the Galaxy and the nonstationarity of the cluster. These estimates are 650 ± 30 M ⊙ and 310 ± 80 M ⊙, respectively, in substantial agreement with the photometric cluster mass.

We examine the spatial distribution and mass segregation of dense molecular cloud cores in a number of nearby star forming regions (the region L1495 in Taurus, Aquila, Corona Australis, and W43) that span about four orders of magnitude in star formation activity. We used an approach based on the calculation of the minimum spanning tree, and for each region, we calculated the structure parameter 𝒬 and the mass segregation ratio ΛMSR measured for various numbers of the most massive cores. Our results indicate that the distribution of dense cores in young star forming regions is very substructured and that it is very likely that this substructure will be imprinted onto the nascent clusters that will emerge out of these clouds. With the exception of Taurus in which there is nearly no mass segregation, we observe mild-to-significant levels of mass segregation for the ensemble of the 6, 10, and 14 most massive cores in Aquila, Corona Australis, and W43, respectively. Our results suggest that the clouds’ star formation activity are linked to their structure, as traced by their population of dense cores. We also find that the fraction of massive cores that are the most mass segregated in each region correlates with the surface density of star formation in the clouds. The Taurus region with low star forming activity is associated with a highly hierarchical spatial distribution of the cores (low 𝒬 value) and the cores show no sign of being mass segregated. On the other extreme, the mini-starburst region W43-MM1 has a higher 𝒬 that is suggestive of a more centrally condensed structure. Additionally, it possesses a higher fraction of massive cores that are segregated by mass. While some limited evolutionary effects might be present, we largely attribute the correlation between the star formation activity of the clouds and their structure to a dependence on the physical conditions that have been imprinted on them by the large scale environment at the time they started to assemble.

The correlation between fresh gas accretion on to haloes and galaxy star formation is critical to understanding galaxy formation. Different theoretical models have predicted different correlation strengths between halo accretion rates and galaxy star formation rates, ranging from strong positive correlations to little or no correlation. Here, we present a technique to observationally measure this correlation strength for isolated Milky Way-mass galaxies with z &amp;lt; 0.123. This technique is based on correlations between dark matter accretion rates and the projected density profile of neighbouring galaxies; these correlations also underlie past work with splashback radii. We apply our technique to both observed galaxies in the Sloan Digital Sky Survey as well as simulated galaxies in the UniverseMachine where we can test any desired correlation strength. We find that positive correlations between dark matter accretion and recent star formation activity are ruled out with $\gtrsim 85{{\ \rm per\ cent}}$ confidence. Our results suggest that star formation activity may not be correlated with fresh accretion for isolated Milky Way-mass galaxies at z = 0 and that other processes, such as gas recycling, dominate further galaxy growth.

Potassium in the atmosphere of Mercury

We study the links between star formation history and structure for a large mass-selected galaxy sample at 0.05 ≤ zphot ≤ 0.30. The galaxies inhabit a very broad range of environments, from cluster cores to the field. Using Hubble Space Telescope (HST) images, we quantify their structure following Hoyos et al., and divide them into disturbed and undisturbed. We also visually identify mergers. Additionally, we provide a quantitative measure of the degree of disturbance for each galaxy (‘roughness’). The majority of elliptical and lenticular galaxies have relaxed structure, showing no signs of ongoing star formation. Structurally disturbed galaxies, which tend to avoid the lowest density regions, have higher star formation activity and younger stellar populations than undisturbed systems. Cluster spirals with reduced/quenched star formation have somewhat less disturbed morphologies than spirals with ‘normal’ star formation activity, suggesting that these ‘passive’ spirals have started their morphological transformation into S0s. Visually identified mergers and galaxies not identified as mergers but with similar roughness have similar specific star formation rates and stellar ages. The degree of enhanced star formation is thus linked to the degree of structural disturbance, regardless of whether it is caused by major mergers or not. This suggests that merging galaxies are not special in terms of their higher-than-normal star formation activity. Any physical process that produces ‘roughness’, or regions of enhanced luminosity density, will increase the star formation activity in a galaxy with similar efficiency. An alternative explanation is that star formation episodes increase the galaxies’ roughness similarly, regardless of whether they are merger induced or not.

We analyze radial velocities for a sample of 31 Class I and flat-spectrum protostars in Taurus-Auriga, ρ Ophiuchi, and Serpens for evidence of the global dynamical state of extremely young stellar populations buried within parental molecular clouds. Comparing the radial velocity of each protostar to that of the local CO gas, we are able to constrain the one-dimensional radial velocity dispersion of Class I and flat-spectrum objects to ∼2.5 km s-1 or below. This upper limit to the protostellar velocity dispersion is consistent with the velocity dispersions of surrounding CO gas, which we measure to be ∼1.4 km s-1, suggesting that the motions of protostars and local CO gas are dynamically linked and are dominated by the gravitational potential of the molecular cloud. However, the upper limit on the protostellar velocity dispersion could still allow for slightly inflated motions of protostars relative to the local molecular gas. Four of the protostars analyzed appear to have velocities more than 3 σ (7.5 km s-1) away from the central local CO gas velocity while showing spectroscopic indicators of youth and accretion such as H2 emission, H I Brγ emission, or K-band continuum veiling. These radial velocity outliers may represent protostellar spectroscopic binaries or ejected cluster members.

We re-analyse the kinematics of the system of blue horizontal branch field (BHBF) stars in the Galactic halo (in particular the outer halo), fitting the kinematics with the model of radial and tangential velocity dispersions in the halo as a function of galactocentric distance r proposed by Sommer-Larsen, Flynn & Christensen (1994), using a much larger sample (almost 700) of BHBF stars. The basic result is that the character of the stellar halo velocity ellipsoid changes markedly from radial anisotropy at the sun to tangential anisotropy in the outer parts of the Galactic halo (r greater than approx 20 kpc). Specifically, the radial component of the stellar halo's velocity ellipsoid decreases fairly rapidly beyond the solar circle, from approx 140 +/- 10 km/s at the sun, to an asymptotic value of 89 +/- 19 km/s at large r. The rapid decrease in the radial velocity dispersion is matched by an increase in the tangential velocity dispersion, with increasing r. Our results may indicate that the Galaxy formed hierarchically (partly or fully) through merging of smaller subsystems - the 'bottom-up' galaxy formation scenario, which for quite a while has been favoured by most theorists and recently also has been given some observational credibility by HST observations of a potential group of small galaxies, at high redshift, possibly in the process of merging to a larger galaxy (Pascarelle et al 1996).

The velocity distribution of a self-gravitating and time-independent disk-like stellar system is investigated for a plausible mass distribution (Toomre’s [1963] model I), by expanding the distribution function for brevity in a finite double power series with respect to the energy and angular momentum of a particle. Our study is free from assumptions of an ellipsoidal velocity distribution and of small peculiar velocities. However, we consider the particular case in which the functional form of the rotational velocity of the stellar disk is identical with that in the centrifugal equilibrium of the disk except for a constant numerical factor. The results show that in a class of distribution functions, the equifrequency contours for low peculiar velocities are almost elliptical at large radial distances from the center of the disk. The axial ratio of such elliptical contours is nearly equal to B/(B−A), where A and B are Oort’s constants. However, the ratio of the radial and azimuthal velocity dispersions, which are defined by considering stars with high peculiar velocities as well, deviates remarkably from B/(B−A). It is noticed that the radial velocity dispersion in the present models obeys a relation similar to a polytropic one with index 3.