To save this undefined to your undefined account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your undefined account.
Find out more about saving content to .
To save this article to your Kindle, first ensure email@example.com is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Star-formation is one of the main processes that shape galaxies, defining its stellar population and metallicity production and enrichment. It is nowadays known that this process is ruled by a set of relations that connect three parameters: the molecular gas mass, the stellar mass and the star-formation rate itself. These relations are fulfilled at a wide range of scales in galaxies, from galaxy wide to kpc-scales. At which scales they are broken, and how universal they are (i.e., if they change at different scales or for different galaxy types) it is still an open question. We explore here how those relations compare at different scales using as proxy the new analysis done using Integral Field Spectroscopy data and CO observations data from the EDGE-CALIFA survey and the AMUSSING++ compilation.
The VISTA Magellanic Clouds Survey (VMC) is a near-infrared survey of the Magellanic system. The VMC data has been exploited to detect and study statistically correlated young groups of stars — also known as “young stellar structures” — in the Large and Small Magellanic Clouds (LMC and SMC). We showcase the ∼ 3000 recently detected young stellar structures in the LMC and their similarity to the fractal interstellar medium. We discuss how their properties indicate their formation mechanisms and that there are no preferred scales of star formation in the LMC.
We report a CO(3-2) detection of 23 molecular clouds in the extended ultraviolet (XUV) disk of the spiral galaxy M83 with ALMA. The observed 1 kpc2 region is at about 1.24R25 from the disk center, where CO(2-1) was previously not detected. The detection and non-detection, as well as the level of star formation (SF) activity in the region, can be explained consistently if the clouds have the mass distribution common among Galactic clouds, such as Orion A – with star-forming dense clumps embedded in thick layers of bulk molecular gas, but in a low-metallicity regime where their outer layers are CO-deficient and CO-dark. The cloud masses, estimated from CO(3-2), range from 8.2×102 to 2.3×104M⊙. The most massive clouds appear similar to Orion A in SF activity as well as in gas mass. The common cloud mass structure also justifies the use of high-J CO transitions to trace the total gas mass of clouds, or galaxies, even in the high-z universe. This study is the first demonstration that CO(3-2) is an efficient tracer of molecular clouds even in low-metallicity environments. This study is published in the Astronomical Journal, entitled “First Detection of the Molecular Cloud Population in the Extended Ultraviolet (XUV) Disk of M83" by J. Koda, L. Watson, F. Combes, M. Rubio, S. Boissier, M. Yagi, D. Thilker, A. M Lee, Y. Komiyama, K. Morokuma-Matsui, and C. Verdugo.
We discuss the first detection of deuterated water (HDO) in extragalactic hot cores. The HDO 211–212 line has been detected with the Atacama Large Millimeter/submillimeter Array (ALMA) toward hot cores N 105–2 A and 2 B in the N 105 star-forming region in the low-metallicity Large Magellanic Cloud (LMC), the nearest star-forming galaxy. We compared the HDO line luminosity (LHDO) measured toward two hot cores in N 105 to those observed toward a sample of 17 Galactic hot cores and found that the observed values of LHDO for the LMC hot cores fit very well into the LHDO trends with Lbol and metallicity observed toward the Galactic hot cores. Our results indicate that LHDO seems to be largely dependent on the source luminosity, but metallicity also plays a role. We provide a rough estimate of the H2O column density and abundance ranges toward N 105–2 A and 2 B by assuming that HDO/H2O toward the LMC hot cores is the same as that observed in the Milky Way; the obtained values are systematically lower than those measured in the Galactic hot cores. The spatial distribution and velocity structure of the HDO emission in N 105–2 A is consistent with HDO being the product of the low-temperature dust grain chemistry.
Ultracompact Hii regions (UC-HII) are the young, very dense cores of massive star-forming regions in dwarf galaxies, where newly formed massive OB stars are surrounded by natal molecular clouds. Thermal energy deposited by mechanical feedback from a cluster of massive OB stars can form a superwind, which may lead to a wind-blown bubble as well as radiative cooling. We investigate the formation of radiatively cooling superwinds in UC-HII using a radiative cooling module in the hydrodynamics program. We built a grid of hydrodynamic simulations to determine the dependence of radiative cooling on the cluster radius, mass-deposition rate, wind velocity, and ambient medium in UC-HII. Our findings could help to better understand star formation in massive star-forming regions, where cool superwinds could trigger the formation of molecular clumpy regions.
We use the AREPO numerical code to model the structure of a Milky Way like galaxy (MW) via a suite of simulations composed of a stellar disc and bulge, a dark matter halo, and a gaseous disc under isothermal conditions. For each model, we produce longitude velocity (l-v) maps of the gas surface densities to extract the skeletons of the main features (arms, bar), and the contours defining the terminal velocities of the gas. We compare these with observations via a number of diagnostic tools, and select the model that best reproduces the main observed features of the Milky Way.
The depletion of CO molecules is observed in infrared dark clouds. However, only few exsamples are found in pc-scale. An NH3 emission is one of good counter parts of C18O because of similar effective critical density. Our NH3 observations of a molecular filament associated with CMa OB1 or KAG 71, which is a target of Kagoshima Galactic Object survey with Nobeyama 45-m telescope by Mapping in Ammonia lines (KAGONMA) project. Although NH3 data shows similarity in morphology with infrared data suggesting no depletion, C18O in the clumps 4 and 6 are weaker than expected based on NH3 data. After examining the dissipation of the high-density gas, photodissociation, and depletion, we concluded that CO is depleted at least in the clump 4. It is a new example of depletion in pc-scale.
We have carried out ALMA observations toward the environments of G333.0162+00.7615 which was considered as a candidate of high-mass young stellar object (HMYSO) in previous studies. Our dust continuum, molecular line emission and radio recombination line emission observations show that this source is not HMYSO associated with hypercompact (HC) HII regions. Instead, we discovered two new hot cores associate with earliest stages of high mass star formation region. We estimated the rotational temperatures of these cores about 270 K from J=14→13 rotational transition of CH3CN ladder. The moment maps show velocity gradients confirming that this cores are rotating.
Galaxies, particularly disc galaxies, show a wide variety of internal structures (e.g. spirals, bars, and bulges). Mapping Nearby Galaxies at Apache Point Observatory (MaNGA, part of the fourth incarnation of the Sloan Digital Sky Surveys), obtained spatially resolved spectral maps for 10,010 nearby galaxies. Many results from MaNGA have collapsed this structure into azimuthally averaged radial gradients, or symmetric 2D shapes, but there is significantly more information about the effect internal structures have on the evolution of galaxies available if we can identify different internal structures. One of the simplest ways to identify irregular internal structures in galaxies is by visual inspection. By employing a citizen science technique to ask this question of N independent volunteers we have obtained quantitatively robust masks (and errors) for spirals and bars in MaNGA target galaxies. In addition to internal features the interface asked users to identify foreground stars and foreground/background galaxies.
To understand the physical properties of the interstellar medium (ISM) in various scales, we should investigate it with pc-scale resolution over kpc scale coverage. Here, we report the sub-kpc scale Gas Density Histogram (GDH) of the Milky Way. GDH is a histogram of averaged density and corresponds to the probability density distribution (PDF) of gas volume density. We use galactic plain survey data (l =10∘− 50∘) at 12CO and 13CO (J = 1 − 0) obtained as a part of the FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45m telescope (FUGIN). With this method and data, we are free from spatial structure and molecular cloud identification. GDH can be well fitted with single or double log-normal distribution; which we call as the low-density log-normal (L-LN) and high-density log-normal (H-LN) components. We found both the H-LN fraction (fH) and L-LN width (σL) along the gas density axis show a coherent structure on the longitude-velocity diagram. It suggests that there is a relationship between the ISM property and kpc scale structure in the Milky Way.
We studied the probability distribution function of the column density (N-PDF) of molecular clouds based on a fit with a multi-log-normal function using the Nobeyama 45-m Cygnus X CO survey data. We identified 124 molecular clouds in 13CO data using the DENDROGRAM and SCIMES algorithms. The N-PDF was constructed for 11 extended (≥ 0.4 deg2) molecular clouds of these identified clouds. We found that every N-PDF is well-fitted with one or two log-normal (LN) distributions. We investigated the distributions of the column density, C18O dense cores, and radio continuum source in each cloud and found that the N-PDF was less correlated with the star-forming activity. The LN N-PDF parameters showed two impressive features. First, the LN distribution at the low-density part had the same mean column density (∼1021.5 cm−2 ) for almost all the molecular clouds. Second, the wider LN distribution tended to show the lower mean density of the structures.
Ultra-luminous infrared galaxies (ULIRGs) are extreme in many ways. The major mergers trigger star formation at very high rates that cause the ISM to be dominated by infrared (IR) photons. We show the ammonia spectra toward the two cores of Arp 220, the nearest ULIRG, in three Very Large Array (VLA) bands (Ku, K, Ka). Typical decay times of the non-metastable transitions ∼ 100 s and are therefore usually difficult to observe. The FIR excitation of Arp 220, however, shows that non-metastable states are widely populated up to a limiting energy of ∼ 1500 K. We assume that this atypical ammonia spectrum is due to the strong FIR field that re-excites the ammonia molecule on timescales much shorter than the already short decay times. The resulting level population causes a break-down of the typical assumptions made for the use of ammonia as a molecular thermometer.
We present maps of the “Survey of Water and Ammonia toward the Galactic center” (SWAG). SWAG was observed over three years (∼550 h) with the Australia Telescope Compact Array (ATCA) and covers the entire Central Molecular Zone (CMZ) at about 26” or ∼1 pc resolution. The observed 21.2–25.6 GHz range contains tens of spectral lines and 4 GHz of continuum. Here, we present some final maps. These include multiple NH3 lines, radio recombination lines, shock tracers like HNCO and methanol (CH3OH), high resolution 22 GHz water masers, and a continuum map. The maps are the foundation for ongoing comprehensive temperature mapping of the CMZ, including the identification of heating mechanisms, the characterization of water maser sources as young stellar objects or AGB stars, as well as chemistry, dynamics, and star formation studies of the ISM in this unique environment.
Following from our recent work, we present results of a detailed analysis of a representative sample of nearby galaxies. The photometric parameters of the morphological components are obtained from bulge-disk decompositions, using GALFIT software. The previously obtained method and library of numerical corrections for dust, decomposition and projection effects, are used to correct the measured (observed) parameters to intrinsic values. Observed and intrinsic galaxy dust and star-formation related scaling relations are presented, to emphasize the scale of the biases introduced by these effects. To understand the extent to which star-formation is distributed in the young stellar disks of galaxies, star-formation connected relations which rely on measurements of scale-lengths and fluxes/luminosities of Hα images, are shown. The mean dust opacity, dust-to-stellar mass and dust-to-gas ratios of the sample, together with the main characteristics of the intrinsic relations are found to be consistent with values found in the literature.
We present an overview of the project “The Physics of Galaxy Assembly: IFS observations of high-z galaxies”, a Guaranteed Time Observations (GTO) programme of the James Webb Space Telescope (JWST). It an ambitious project aimed at investigating the internal structure of distant galaxies with the NIRSpec integral field spectrograph (IFS), having allocated 273 hours of JWST prime time. The NIRSpec capability will provide us with spatially resolved spectroscopy in the 1-5 μm range of a sample of over forty galaxies and Active Galactic Nuclei in the redshift range 3 < z < 9. IFS observations of individual galaxies will enable us to investigate in detail the most important physical processes driving galaxy evolution across the cosmic epoch. More in detail, the main specific objectives are: to trace the distribution of star formation, to map the resolved properties of the stellar populations, to trace the gas kinematics (i.e. velocity fields, velocity dispersion) and, hence, determine dynamical masses and also identify non-virial motions (outflow and inflows), and to map metallicity gradients and dust attenuation.
The discovery of abundant carbon-chain molecules in protostellar cores motivates the development of the warm carbon-chain chemistry. To understand the role of warm carbon-chain chemistry in star-forming regions, we studied C2H and c-C3H2 in 15 embedded protostars in the Taurus molecular cloud, whose evolutionary stages range from prestellar to Class I/II, using data from the Submillimeter Telescope (SMT). We calculated the excitation temperature, column density, and abundance of C2H and c-C3H2 in each source. We compared those properties with evolutionary indicators of the protostars. We also estimated the kinetic temperature using RADEX. Finally, we compared the abundance of C2H and c-C3H2 in our survey with that in the survey of protostellar cores in the Perseus molecular cloud. While we are unable to identify new WCCCs, our results suggest that the abundances of C2H and c-C3H2 could be an indicator to find WCCC candidates.
This work aims to represent the physical properties of a sample of infrared-bright dust-obscured galaxies (DOGs) studied by Suleiman et al. (2022) by fitting the spectral energy distributions (SEDs). Twenty-eight DOGs were examined at redshifts 0.47 ≤ z ≤ 1.63 discovered by combining images of the Subaru Hyper Suprime-Cam (HSC) survey, VISTA Kilo-degree Infrared Galaxy (VIKING) survey, and the Wide-field Infrared Survey Explorer (WISE) all-sky survey, and detected at Herschel Spectral and Photometric Imaging Receiver (SPIRE) bands. The results show a correlation between the star formation rate (SFR) and the dust luminosity of Suleiman et al. (2022) DOG sample, the SFR ranges of the sample according to different redshifts, and a comparison between Suleiman et al. (2022) sample and other samples of DOGs.
We present spatially resolved molecular filaments and clumps in the high-mass star-forming regions N159E-Papillon, W-South, and W-North in the Large Magellanic Cloud (LMC). Our ALMA observations in CO isotopes and millimeter continuum revealed remarkable hub-filament systems with a typical width of 0.1 pc. The most massive clump in the observed regions, N159W-North MMS-2, shows an especially massive/dense nature whose total H2 mass and peak column density are ∼104M⊙ and ∼1024 cm−2, respectively, and harbors massive (∼100 M⊙) starless core candidates. The hub-filamentary clouds in the three regions share a common orientation and have 10–30 pc scale head-tail structures with active star formation at the tips. Their striking similarity proposes a “teardrops-inflow” model, i.e., substructured conversing H i flow, that explains the synchronized, extreme star formation across ∼50 pc, including one of the most massive protocluster clumps in the Local Group.
We present new neutral hydrogen (Hi) observations of the nearby galaxy NGC 2403 to determine the nature of a low-column density cloud that was detected earlier by the Green Bank Telescope.
We find that this cloud is the tip of a complex of filaments of extraplanar gas that is coincident with the main disk. The total Hi mass of the complex is 2 × 107 M⊙ or 0.6% of the total Hi mass of the galaxy. The main structure, previously referred to as the 8-kpc filament, is now seen to be even more extended, along a 20 kpc stream.
We examine the physical conditions required for the formation of H2 in the solar neighborhood by comparing H i emission and absorption spectra toward 58 lines of sight at b < −5∘ to CO(1–0) and dust data. Our analysis of CO-associated cold and warm neutral medium (CNM and WNM) shows that the formation of CO-traced molecular gas is favored in regions with high column densities where the CNM becomes colder and more abundant. In addition, our comparison to the one-dimensional steady-state H i-to-H2 transition model of Bialy et al. (2016) suggests that only a small fraction of the clumpy CNM participates in the formation of CO-traced molecular gas. Another possible interpretation would be that missing physical and chemical processes in the model could play an important role in H2 formation.