The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star Forming Galaxies
K. Grasha, D. Calzetti, A. Adamo, H. Kim, B. G. Elmegreen, D. A. Gouliermis, D. A. Dale, M. Fumagalli, E. K. Grebel, K. E. Johnson, L. Kahre, R. C. Kennicutt, M… 展开作者
K. Grasha, D. Calzetti, A. Adamo, H. Kim, B. G. Elmegreen, D. A. Gouliermis, D. A. Dale, M. Fumagalli, E. K. Grebel, K. E. Johnson, L. Kahre, R. C. Kennicutt, M. Messa, A. Pellerin, J. E. Ryon, L. J. Smith, F. Shabani, D. Thilker, L. Ubeda
备注：
21 pages, 15 figures, 4 tables, accepted for publication in ApJ
We present a study of the hierarchical clustering of the young stellar clusters in six local (3--15 Mpc) star-forming galaxies using Hubble Space Telescope broad band WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We have identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ~40--60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.
The young stellar population of a star-forming galaxy is the primary engine driving its radiative properties. As a result, the age of a galaxy's youngest generation of stars is critical for a detailed understanding of its star formation history, stellar content, and evolutionary state. Here we present predicted equivalent widths for the H-beta, H-alpha, and Br-gamma recombination lines as a function of stellar population age. The equivalent widths are produced by the latest generations of stellar evolutionary tracks and the Starburst99 stellar population synthesis code, and are the first to fu…
When the cosmic star formation history peaks (z ~ 2), galaxies vigorously fed by cosmic reservoirs are gas dominated and contain massive star-forming clumps, thought to form by violent gravitational instabilities in highly turbulent gas-rich disks. However, a clump formation event has not been witnessed yet, and it is debated whether clumps survive energetic feedback from young stars, thus migrating inwards to form galaxy bulges. Here we report spatially resolved spectroscopy of a bright off-nuclear emission line region in a galaxy at z = 1.987. Although this region dominates the star formatio…
Using the Very Long Baseline Array (VLBA), we have observed the radio continuum emission from the young stellar object HW 9 in the Cepheus A star-forming region at ten epochs between 2007 February and 2009 November. Due to its strong radio variability, the source was detected at only four of the ten epochs. From these observations, the trigonometric parallax of HW 9 was determined to be $π$ = 1.43 $\pm$ 0.07 mas, in excellent agreement with a recent independent VLBA determination of the trigonometric parallax of a methanol maser associated with the nearby young stellar source HW 2 ($π$ = 1.43 …
Star formation in galaxies is a hierarchical process with a wide range of scales from smaller clusters to larger stellar complexes. Here, we present an ultra-violet imaging study of the nearby flocculent spiral galaxy NGC 7793, observed with the Ultra-Violet Imaging Telescope (UVIT). We find that the disk scale-length estimated in Far-UV (2.64$\pm$0.16 kpc) is larger than that in Near-UV (2.21$\pm$0.21 kpc) and optical (1.08 kpc), which supports the inside-out growth scenario of the galaxy disk. The star-forming UV disk is also found to be contained within the extent of H~I gas of column densi…
Recent observations and hydrodynamical simulations of star formation inside a giant molecular cloud have revealed that, within a star forming region, stars do not form evenly distributed throughout this region, but rather in small sub-clumps. It is generally believed that these sub-clumps merge and form a young star cluster. The time-scale of this merging process is crucial for the evolution and the possible survival of the final star cluster. The key issue is whether this merging process happens faster than the time needed to remove the residual gas of the cloud. A merging time-scale shorter …
We report the discovery of BOSS-EUVLG1 at z=2.469, by far the most luminous, almost un-obscured star-forming galaxy known at any redshift. First classified as a QSO within the Baryon Oscillation Spectroscopic Survey, follow-up observations with the Gran Telescopio Canarias reveal that its large luminosity, MUV = -24.40 and log(L_Lya/erg s-1) = 44.0, is due to an intense burst of star-formation, and not to an AGN or gravitational lensing. BOSS-EUVLG1 is a compact (reff = 1.2 kpc), young (4-5 Myr) starburst with a stellar mass log(M*/Msun) = 10.0 +/- 0.1 and a prodigious star formation rate of ~…
Initial conditions for star formation in clusters are estimated for protostars whose masses follow the initial mass function (IMF) from 0.05 to 10 solar masses. Star-forming infall is assumed equally likely to stop at any moment, due to gas dispersal dominated by stellar feedback. For spherical infall, the typical initial condensation must have a steep density gradient, as in low-mass cores, surrounded by a shallower gradient, as in the clumps around cores. These properties match observed column densities in cluster-forming regions when the mean infall stopping time is 0.05 Myr and the accreti…
We present the results of our study of starforming regions in the lenticular galaxy NGC 4324. During a complex analysis of multiwavelength observational data -- the narrow-band emission-line images obtained with the 2.5-m telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University and the archival images in the broad bands of the SDSS, GALEX and WISE surveys -- we have detected young starforming complexes (clumps) located in the inner ring of the lenticular galaxy NGC 4324, and we have established a regular pattern of their distribution…
A large fraction of stars forming in our galaxy are born within clusters embedded in giant molecular clouds. In these environments, the background UV radiation fields impinging upon circumstellar disks can often dominate over the radiation fields produced by each disk's central star. As a result, this background radiation can drive the evaporation of circumstellar disks and lead to the loss of planet forming potential within a cluster. This paper presents a detailed analysis of this process for clusters whose stellar membership falls within the range $100 \le N \le 1000$. For these intermediat…
The interstellar medium (ISM) is turbulent on all scales and in all phases. In this paper, we study turbulence with different tracers in four nearby star-forming regions: Orion, Ophiuchus, Perseus, and Taurus. We combine the APOGEE-2 and Gaia surveys to obtain the full 6-dimensional measurements of positions and velocities of young stars in these regions. The velocity structure functions (VSFs) of the stars show a universal scaling of turbulence. We also obtain Hα gas kinematics in these four regions from the Wisconsin H-Alpha Mapper. The VSFs of the Hα are more diverse compared to the stars. …
We present 737 candidate Young Stellar Objects (YSOs) near the W51 Giant Molecular Cloud (GMC) over an area of 1.25 deg x 1.00 deg selected from Spitzer Space Telescope data. We use spectral energy distribution (SED) fits to identify YSOs and distinguish them from main-sequence or red giant stars, asymptotic giant branch stars, and background galaxies. Based on extinction of each YSO, we separate a total of 437 YSOs associated with the W51 region from the possible foreground sources. We identify 69 highly embedded Stage 0/I candidate YSOs in our field with masses > 5 Msun (corresponding to mid…
We study the degree of angular substructure in the stellar position distribution of young members of Galactic star-forming regions, looking for correlations with distance from cluster center, surface number density of stars, and local dynamical age. To this end we adopt the catalog of members in 18 young ($\sim$1-3 Myr) clusters from the Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) Survey and the statistical analysis of the Angular Dispersion Parameter, $δ_{\rm ADP}$. We find statistically significant correlation between $δ_{\rm ADP}$ and physical projected distance …
The progenitors of super luminous supernovae (SLSNe) are still a mystery. Hydrogen-poor SLSN hosts are often highly star-forming dwarf galaxies and the majority belongs to the class of extreme emission line galaxies hosting young and highly star-forming stellar populations. Here we present a resolved long-slit study of the host of the hydrogen-poor SLSN PTF12dam probing the kpc environment of the SN site to determine the age of the progenitor. The galaxy is a "tadpole" with uniform properties and the SN occurred in a star-forming region in the head of the tadpole. The galaxy experienced a rece…
The nearest young stellar groups are associated with "hubs" of column density exceeding 10^22 cm^-2, according to recent observations. These hubs radiate multiple "filaments" of parsec length, having lower column density and fewer stars. Systems with many filaments tend to have parallel filaments with similar spacing. Such "hub-filament structure" is associated with all of the nine young stellar groups within 300 pc, forming low-mass stars. Similar properties are seen in infrared dark clouds forming more massive stars. In a new model, an initial clump in a uniform medium is compressed into a s…
We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective to locate a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey (2MASS) and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identif…
The determination of chemical composition is crucial for investigating the formation and evolution of star forming galaxies and provides a powerful tool to constrain the effects of galactic winds and accretion from the cosmic web. In this regard stellar absorption line studies provide an attractive alternative to the standard techniques using the strong emission lines of HII regions. We discuss a number of newly developed methods: - multi-object spectroscopy of individual blue and red supergiant stars, the brightest stars in the universe at visual and NIR wavelengths, - NIR spectroscopy of sup…
We compare the mass functions of young star clusters (ages $\leq 10$ Myr) and giant molecular clouds (GMCs) in six galaxies that cover a large range in mass, metallicity, and star formation rate (LMC, M83, M51, NGC 3627, the Antennae, and NGC 3256). We perform maximum-likelihood fits of the Schechter function, $ψ(M) = dN/dM \propto M^β \exp(-M/M_*)$, to both populations. We find that most of the GMC and cluster mass functions in our sample are consistent with a pure power-law distribution ($M_* \rightarrow \infty$). M51 is the only galaxy that shows some evidence for an upper cutoff ($M_*$) in…
We present spatial and kinematic correlation between the young stellar population and the cloud clumps in the Ophiuchus star-forming region. The stellar sample consists of known young objects at various evolutionary stages, taken from the literature, some of which are diagnosed with Gaia EDR3 parallax and proper-motion measurements. The molecular gas is traced by the 850 $μ$m Submillimetre Common-User Bolometer Array-2 image, reaching $\sim$2.3 mJy beam$^{-1}$, the deepest so far for the region, stacked from the James Clerk Maxwell Telescope/Transient program aiming to detect submillimeter out…
Spitzer IRAC observations and stellar photometric catalogs are presented for the Massive Young Star-Forming Complex Study in the Infrared and X-ray (MYStIX). MYStIX is a multiwavelength census of young stellar members of twenty nearby (d < 4 kpc), Galactic, star-forming regions that contain at least one O star. All regions have data available from the Spitzer Space Telescope, consisting of GLIMPSE or other published catalogs for eleven regions and results of our own photometric analysis of archival data for the remaining nine regions. This paper seeks to construct deep and reliable catalogs of…
To investigate how the abundance of N2H+ varies as massive clumps evolve, here we present a multi-wavelength study toward six molecular clouds. All of these clouds contain several massive clumps in different evolutionary stages of star formation. Using archival data of Herschel InfraRed Galactic Plane Survey (Hi-GAL), we made H2 column density and dust temperature maps of these regions by the spectral energy distribution (SED) method. We found all of the six clouds show distinct dust temperature gradients, ranging from 20 K to 30 K. This makes them good candidates to study chemical evolution o…
This is the first paper of a series devoted to the Lambda Orionis star-forming region, from the X-ray perspective, which will provide a comprehensive view of this complex region. In this paper we focus in uncovering the population of the central, young cluster Collinder 69 (C69), and in particular those diskless members not identified by previous near- and mid-infrared surveys, and to establish the X-ray luminosity function for the association. We have combined two exposures taken with the XMM-Newton satellite with an exhaustive data set of optical, near- and mid-infrared photometry to assess …
We present mid-infrared (MIR) observations, made with the TIMMI2 camera on the ESO 3.6 m telescope, toward 14 young massive star-forming regions. All regions were imaged in the N band, and nine in the Q band, with an angular resolution of ~ 1 arcsec. Typically, the regions exhibit a single or two compact sources (with sizes in the range 0.008-0.18 pc) plus extended diffuse emission. The Spitzer-Galactic Legacy Infrared Mid-Plane Survey Extraordinaire images of these regions show much more extended emission than that seen by TIMMI2, and this is attributed to polycyclic aromatic hydrocarbon (PAH…
Gas expulsion or gas retention is a central issue in most of the models for multiple stellar populations and light element anti-correlations in globular clusters. The success of the residual matter expulsion or its retention within young stellar clusters has also a fundamental importance in order to understand how star formation proceeds in present-day and ancient star-forming galaxies and if proto-globular clusters with multiple stellar populations are formed in the present epoch. It is usually suggested that either the residual gas is rapidly ejected from star-forming clouds by stellar winds…
MYStIX (Massive Young Star-Forming Complex Study in Infrared and Xray) seeks to characterize 20 OB-dominated young clusters and their environs at distances d < 4 kpc using imaging detectors on the Chandra X-ray Observatory, Spitzer Space Telescope, and the United Kingdom InfraRed Telescope. The observational goals are to construct catalogs of star-forming complex stellar members with well-defined criteria, and maps of nebular gas (particularly of hot X-ray emitting plasma) and dust. A catalog of MYStIX Probable Complex Members (MPCMs) with several hundred OB stars and > 30, 000 low mass premai…
We present a study of the spatial distribution of the stellar cluster populations in the star forming galaxy NGC 628. Using Hubble Space Telescope broad band WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), we have identified 1392 potential young (<100 Myr) stellar clusters within the galaxy, identified from a combination of visual inspection and automatic selection. We investigate the clustering of these young stellar clusters and quantify the strength and change of clustering strength with scale using the two-point correlation function. We als…
We have conducted a systematic near-infrared circular polarization (CP) survey in star-forming regions, covering high-mass, intermediate-mass, and low-mass young stellar objects. All the observations were made using the SIRPOL imaging polarimeter on the Infrared Survey Facility 1.4 m telescope at the South African Astronomical Observatory. We present the polarization properties of ten sub-regions in six star-forming regions. The polarization patterns, extents, and maximum degrees of linear and circular polarizations are used to determine the prevalence and origin of CP in the star-forming regi…
The mass function of freshly formed star clusters is empirically often described as a power law. However the cluster mass function of populations of young clusters over the scale of a galaxy has been found to be described by a Schechter-function. Here we address this apparent discrepancy. We assume that in an annulus of an isolated self- regulated radially-exponential axially-symmetric disk galaxy, the local mass function of very young (embedded) clusters is a power law with an upper mass limit which depends on the local star formation rate density. Radial integration of this mass function yie…
Star formation is a hierarchical process, forming young stellar structures of star clusters, associations, and complexes over a wide scale range. The star-forming complex in the bar region of the Large Magellanic Cloud is investigated with upper main-sequence stars observed by the VISTA Survey of the Magellanic Clouds. The upper main-sequence stars exhibit highly non-uniform distributions. Young stellar structures inside the complex are identified from the stellar density map as density enhancements of different significance levels. We find that these structures are hierarchically organized su…
Theory suggests that there are two primary modes of accretion through which dark matter halos acquire the gas to form and fuel galaxies, hot and cold mode accretion. In cold mode accretion, gas streams along cosmic web filaments to the center of the halo, allowing for the efficient delivery of star-forming fuel. Recently, two QSO-illuminated HI Lyman alpha (Lyα) emitting objects were reported to have properties of cold, rotating structures (Martin et al. 2015, Martin et al. 2016). However, the spatial and spectral resolution available was insufficient to constrain radial flows associated with …
We explore the evolution of the Stellar Mass-Star Formation Rate-Metallicity Relation using a set of 256 COSMOS and GOODS galaxies in the redshift range 1.90 < z < 2.35. We present the galaxies' rest-frame optical emission-line fluxes derived from IR-grism spectroscopy with the Hubble Space Telescope and combine these data with star formation rates and stellar masses obtained from deep, multi-wavelength (rest-frame UV to IR) photometry. We then compare these measurements to those for a local sample of galaxies carefully matched in stellar mass (7.5 < log(M*/Msol) < 10.5) and star formation rat…
The youngest low-mass protostars are known to be chemically rich, accreting matter most vigorously, and producing the most powerful outflows. Molecules are unique tracers of these phenomena. We use ALMA to study several outflow sources in the Serpens Main region. The most luminous source, Ser-SMM1, shows the richest chemical composition, but some complex molecules are also present in S68N. No emission from complex organics is detected toward Ser-emb 8N, which is the least luminous in the sample. We discuss whether these differences reflect an evolutionary effect or whether they are due to diff…
(abridged) Star formation in the outer Galaxy, i.e., outside of the Solar circle, has been lightly studied in part due to low CO brightness of molecular clouds linked with the negative metallicity gradient. Recent infrared surveys provide an overview of dust emission in large sections of the Galaxy, but suffer from cloud confusion and poor spatial resolution at far-infrared wavelengths. We aim to develop a methodology to identify and classify young stellar objects (YSOs) in star-forming regions in the outer Galaxy, and use it to solve a long-standing confusion with the distance and evolutionar…
We investigate galactic-scale outflows in the redshift range 0.71 < z < 1.63, using 413 K-band selected galaxies observed in the spectroscopic follow-up of the UKIDSS Ultra-Deep Survey (UDSz). The galaxies have an average stellar mass of ~10^9.5 solar masses and span a wide range in rest-frame colours, representing typical star-forming galaxies at this epoch. We stack the spectra by various galaxy properties, including stellar mass, [OII] equivalent width, star-formation rate, specific star-formation rate and rest-frame spectral indices. We find that outflows are present in virtually all spect…
(abbreviated) In the central part of the S254-S258 star forming complex, a dense embedded cluster of very young stellar objects (S255-IR) is sandwiched between the two HII regions S255 and S257. This interesting configuration had led to different speculations such as dynamical ejection of the B-stars from the central cluster or triggered star formation in a cloud that was swept up in the collision zone between the two expanding HII regions. The presence or absence of low-mass stars associated with these B-stars can discriminate between the possible scenarios. We performed a deep Chandra X-ray …
We studied 102 star forming regions in seven spiral galaxies (NGC 628, NGC 783, NGC 2336, NGC 6217, NGC 6946, NGC 7331, and NGC 7678) on the basis of complex spectroscopic, photometric (UBVRI) and spectrophotometric (H alpha line) observations. Using data on the chemical composition and absorption in HII regions, obtained from spectroscopic observations, and using evolutionary models, we estimated physical parameters (ages and masses) of young stellar groupings embedded in HII regions. We found that the gas extinction, A(gas), which determined from the Balmer decrement, does not correspond in …
The luminosities of Type Ia supernovae (SNe), the thermonuclear explosions of white-dwarf stars, vary systematically with their intrinsic color and the rate at which they fade. From images taken with the Galaxy Evolution Explorer (GALEX), we identified SNe Ia that erupted in environments that have high ultraviolet surface brightness and star-formation surface density. When we apply a steep model extinction law, we calibrate these SNe using their broadband optical light curves to within ~0.065 to 0.075 magnitudes, corresponding to <4% in distance. The tight scatter, probably arising from a smal…
[abridged] Unbound young stellar systems, the loose ensembles of physically related young bright stars, trace the typical regions of recent star formation in galaxies. Their morphologies vary from small associations of stars to enormous stellar complexes. Being associated with star-forming regions of various sizes, they trace the regions where stars form at various scales, from compact clusters to whole galactic disks. They have been, thus, the focus of several studies with special interest on their demographics, classification, and structural morphology. Their surveys demonstrate that the cle…
The Massive Young Star Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog (MIRES) and Chandra-based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1,109 MYStIX Candidate Protostars (MCPs) are found in 14 star forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultr…
The origin of the Lyman-$α$ (Ly$α$) emission in galaxies is a long-standing issue: despite several processes known to originate this line (e.g. AGN, star formation, cold accretion, shock heating), it is difficult to discriminate among these phenomena based on observations. Recent studies have suggested that the comparison of the ultraviolet (UV) and optical properties of these sources could solve the riddle. For this reason, we investigate the rest-frame UV and optical properties of A2895b, a strongly lensed Ly$α$-emitter at redshift z ~ 3.7. From this study, we find that our target is a compa…
Strongly star-forming galaxies are prolific in producing the young and most massive star clusters (YMCs) still forming today. This work investigates the star cluster luminosity functions (CLFs, dN/dL ~ L^{-alpha}) of 26 starburst and luminous infrared galaxies (LIRGs) taken from the SUNBIRD survey. The targets were imaged using near-infrared (NIR) K-band adaptive optics systems. Single power-law fits of the derived CLFs result in a slope ranging between 1.53 and 2.41, with the median and average of 1.87 +/- 0.23 and 1.93 +/- 0.23, respectively. Possible biases such as blending effects and the …
We report the discovery of J0121+0025, an extremely luminous and young star-forming galaxy (M_UV = -24.11, log[L_Lya / erg s^-1] = 43.8) at z = 3.244 showing copious Lyman continuum (LyC) leakage (f_esc,abs ~ 40%). High signal-to-noise ratio rest-frame UV spectroscopy with the Gran Telescopio Canarias reveals a high significance (7.9 sigma) emission below the Lyman limit (< 912A), with a flux density level f_900A = 0.78 +/- 0.10 uJy, and strong P-Cygni in wind lines of OVI 1033A, NV 1240A and CIV 1550A that are indicative of a young age of the starburst (<10 Myr). The spectrum is rich in stell…
Aligned and misaligned metallicity gradients in young stars and star-forming regions in the EAGLE discs
Pontificia Universidad Católica de Chile（智利天主教 Pontificia 大学）；Instituto de Astrofísica, Pontificia Universidad Católica de Chile（智利天主教 Pontificia 大学天体物理研究所）；Centro de Astro-Ingeniería, Pontificia Universidad Católica de Chile（智利天主教 Pontificia 大学天文工程学院）
The physical and chemical properties of cold and dense molecular clouds are key to understanding how stars form. Using the IRAM 30 m and NRO 45 m telescopes, we carried out a Multiwavelength line-Imaging survey of the 70 $μ$m dark and bright clOuds (MIAO). At a linear resolution of 0.1--0.5 pc, this work presents a detailed study of parsec-scale CO depletion and $\rm HCO^+$ deuterium (D-) fractionation toward four sources (G11.38+0.81, G15.22-0.43, G14.49-0.13, and G34.74-0.12) included in our full sample. In each source with $\rm T<20$ K and $n_{\rm H}\rm\sim10^4$--$\rm 10^5 cm^{-3}$, we comp…
Spatially resolved studies of high redshift galaxies, an essential insight into galaxy formation processes, have been mostly limited to stacking or unusually bright objects. We present here the study of a typical (L$^{*}$, M$_\star$ = 6 $\times 10^9$ $M_\odot$) young lensed galaxy at $z=3.5$, observed with MUSE, for which we obtain 2D resolved spatial information of Ly$α$ and, for the first time, of CIII] emission. The exceptional signal-to-noise of the data reveals UV emission and absorption lines rarely seen at these redshifts, allowing us to derive important physical properties (T$_e\sim$15…
We report the discovery of [NeV]3426 emission, in addition to HeII4686 emission, in six compact star-forming galaxies. These observations considerably increase the sample of eight such galaxies discovered earlier by our group. For four of the new galaxies, the optical observations are supplemented by near-infrared spectra. All galaxies, but one, have HII regions that are dense, with electron number densities of ~300-700 cm-3. They are all characterised by high Hbeta equivalent widths EW(Hbeta)~190-520A and high O32=[OIII]5007/[OII]3727 ratios of 10-30, indicating young starburst ages and the p…
As deep spectroscopic campaigns extend to higher redshifts and lower stellar masses, the interpretation of galaxy spectra depends increasingly upon models for very young stellar populations. Here we present new HST/COS ultraviolet spectroscopy of seven nearby ($<120$ Mpc) star-forming regions hosting very young stellar populations ($\sim$ 4-20 Myr) with optical Wolf-Rayet stellar wind signatures, ideal laboratories in which to test these stellar models. We detect nebular C III] in all seven, but at equivalent widths uniformly $< 10$ Å. This suggests that even for very young stellar populations…
Context: The formation of high-mass star-forming regions from their parental gas cloud and the subsequent fragmentation processes lie at the heart of star formation research. Aims: We aim to study the dynamical and fragmentation properties at very early evolutionary stages of high-mass star formation. Methods: Employing the NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30m telescope, we observed two young high-mass star-forming regions, ISOSS22478 and ISOSS23053, in the 1.3mm continuum and spectral line emission at a high angular resolution (~0.8''). Results: We resolved 29 cores tha…
The identification and characterization of stellar members within a star-forming region are critical to many aspects of star formation, including formalization of the initial mass function, circumstellar disk evolution and star-formation history. Previous surveys of the Lupus star-forming region have identified members through infrared excess and accretion signatures. We use machine learning to identify new candidate members of Lupus based on surveys from two space-based observatories: ESA's Gaia and NASA's Spitzer. Astrometric measurements from Gaia's Data Release 2 and astrometric and photom…
We have measured the multiplicity fractions and separation distributions of seven young star-forming regions using a uniform sample of young binaries. Both the multiplicity fractions and separation distributions are similar in the different regions. A tentative decline in the multiplicity fraction with increasing stellar density is apparent, even for binary systems with separations too close (19-100au) to have been dynamically processed. The separation distributions in the different regions are statistically indistinguishable over most separation ranges, and the regions with higher densities d…
We present a $40\,$ks Chandra observation of the IRAS$\,$20126+4104 core region. In the inner $6^{\prime\prime}$ two X-ray sources were detected, which are coincident with the radio jet source I20S and the variable radio source I20Var. No X-ray emission was detected from the nearby massive protostar I20N. The spectra of both detected sources are hard and highly absorbed, with no emission below $3\,$keV. For I20S, the measured $0.5-8\,$keV count rate was $4.3\,$cts$\,$ks$^{-1}$. The X-ray spectrum was fit with an absorbed 1T APEC model with an energy of kT$\,=10\,$keV and an absorbing column of…
We present a detailed clustering analysis of the young stellar population across the star-forming ring galaxy NGC 6503, based on the deep HST photometry obtained with the Legacy ExtraGalactic UV Survey (LEGUS). We apply a contour-based map analysis technique and identify in the stellar surface density map 244 distinct star-forming structures at various levels of significance. These stellar complexes are found to be organized in a hierarchical fashion with 95% being members of three dominant super-structures located along the star-forming ring. The size distribution of the identified structures…
We compile a sample of about 157,000 spaxels from the Mapping Nearby Galaxies at the Apache Point Observatory survey to derive the average dust attenuation curve for subgalactic star-forming regions of local star-forming galaxies (SFGs) in the optical wavelength, following the method of \cite{Calzetti1994}. We obtain a $D_n(4000)$-independent average attenuation curve for spaxels with $1.1\leq D_n(4000)<1.3$, which is similar to the one derived from either local starbursts or normal SFGs. We examine whether and how the shape of the average attenuation curve changes with several local and globa…
