Discovery of two embedded clusters with WISE in the high Galactic latitude cloud HRK 81.4−77.8 (original) (raw)

New detections of embedded clusters in the Galactic halo

Astronomy & Astrophysics, 2016

Context. Until recently it was thought that high Galactic latitude clouds were a non-star-forming ensemble. However, in a previous study we reported the discovery of two embedded clusters (ECs) far away from the Galactic plane (∼5 kpc). In our recent star cluster catalogue we provided additional high and intermediate latitude cluster candidates. Aims. This work aims to clarify whether our previous detection of star clusters far away from the disc represents just an episodic event or whether star cluster formation is currently a systematic phenomenon in the Galactic halo. We analyse the nature of four clusters found in our recent catalogue and report the discovery of three new ECs each with an unusually high latitude and distance from the Galactic disc midplane. Methods. The analysis is based on 2MASS and WISE colour-magnitude diagrams (CMDs), and stellar radial density profiles (RDPs). The CMDs are built by applying a field-star decontamination procedure, which uncovers the cluster's intrinsic CMD morphology. Results. All of these clusters are younger than 5 Myr. The high-latitude ECs C 932, C 934, and C 939 appear to be related to a cloud complex about 5 kpc below the Galactic disc, under the Local arm. The other clusters are above the disc, C 1074 and C 1100 with a vertical distance of ∼3 kpc, C 1099 with ∼2 kpc, and C 1101 with ∼1.8 kpc. Conclusions. According to the derived parameters ECs located below and above the disc occur, which gives evidence of widespread star cluster formation throughout the Galactic halo. This study therefore represents a paradigm shift, by demonstrating that a sterile halo must now be understood as a host for ongoing star formation. The origin and fate of these ECs remain open. There are two possibilities for their origin, Galactic fountains or infall. The discovery of ECs far from the disc suggests that the Galactic halo is more actively forming stars than previously thought. Furthermore, since most ECs do not survive the infant mortality, stars may be raining from the halo into the disc, and/or the halo may be harbouring generations of stars formed in clusters like those detected in our survey.

Two Distant Embedded Clusters in the Outer Galaxy

2000

We report the discovery of two distant embedded young stellar clusters located far in the outer Galaxy. The clusters are resolved in near-infrared images and seen as enhancements in the surface density of IR-excess stars centered close to IRAS 07255Ϫ2012. The clusters are embedded in a molecular cloud containing a CS dense core. The molecular cloud, as traced by CO ( ) is elongated and extends over a region of pc 2 . J p 1-0 15 # 6 From the millimeter observations, we derive a kinematic distance of 10.2 kpc and a Galactocentric distance of 16.5 kpc, making these clusters among the most distant embedded clusters in the Galaxy. The main (richer) cluster is well confined to a region of about 1.2 pc in radius. Down to our detection limit of about 1-2 M at , this distance, it contains at least 30 members. The smaller cluster contains at least five stars. They all exhibit near-infrared color excesses consistent with young stellar objects having circumstellar and/or envelope material. We estimate that the star formation efficiency of this molecular cloud is about 4%-10%.

A new young stellar cluster embedded in a molecular cloud in the far outer Galaxy

Astronomy & Astrophysics, 2007

We report the discovery of a new young stellar cluster and molecular cloud located in the far outer Galaxy, seen towards IRAS 06361-0142, and we characterise their properties. Near-infrared images were obtained with VLT/ISAAC through JHKs filters, millimetre line observations of CO(1-0) were obtained with SEST, and VLA 6 cm continuum maps obtained from archive data. The cloud and cluster are located at a distance of 7 kpc and a Galactocentric distance of 15 kpc, well in the far outer Galaxy. Morphologically, IRAS 06361-0142 appears as a cluster of several tens of stars surrounded by a nearly spherical nebular cavity centred at the position of the IRAS source. The cluster appears composed of low and intermediate-mass, young reddened stars with a large fraction having cleared the inner regions of their circumstellar discs responsible for (H - Ks) colour excess. The observations are compatible with a 4 Myr cluster with variable spatial extinction between Av = 6 and Av = 13.

On the existence of young embedded clusters at high Galactic latitude

Monthly Notices of the Royal Astronomical Society

Careful analyses of photometric and star count data available for the nine putative young clusters identified by Camargo et al. at high Galactic latitudes reveal that none of the groups contain early-type stars, and most are not significant density enhancements above the field level. Two-Micron All-Sky Survey (2MASS) colours for stars in the groups match those of unreddened late-type dwarfs and giants, as expected for the contamination by (mostly) thin disc objects. A simulation of one such field using only typical high-latitude foreground stars yields a colour-magnitude diagram that is very similar to those constructed by Camargo et al. as evidence for their young groups as well as the means of deriving their reddenings and distances. Although some of the fields are coincident with clusters of galaxies, one must conclude that there is no evidence that the putative clusters are extremely young stellar groups.

The Enigma of Star Formation at High Galactic Latitudes

2018

Molecular clouds at very high latitudes ($b > 60^o$) away from the Galactic plane are considered rare and not conventional sites of star formation. Contrary to this, the recent discovery of high latitude embedded Clusters can possibly change our understanding of the Galaxy formation, evolution and dynamics and the role of the halo in the Galactic evolutionary process. This article reviews a study of nine embedded clusters (ECs) reported in recent literature with ages less than 5 Myr and vertical distances from the galactic disc ranging from 1.8 to 5 kpc. It discusses the processes that could cause star formation within low density and extraplanar environments in the halo and discuss the possible origins of these clusters. Are these episodic events or is star cluster formation a systematic phenomenon in the Galactic halo? Two of these objects will be observed by us with Astrosat, so we shall comment on the possible results we expect to get with Astrostat UV and Xray data.

A young double stellar cluster in an HII region, emerging from its parent molecular cloud

Astronomy and Astrophysics, 2008

Aims. We investigate the star formation ocurring in the region towards IRAS 07141-0920 contained in the HII region Sh2-294 (S294). We report the discovery ⋆⋆ of a new young double stellar cluster, and we describe its properties. Methods. High-resolution optical U BVRI and Hα images obtained with ALFOSC mounted on the Nordic Optical Telescope (NOT), near-infrared JHK S images obtained with NOTCam at the Nordic Optical Telescope, and VLT/ISAAC images obtained through the H 2 (2.12 µm) filter were used to make photometric and morphological studies of the point sources and the nebula seen towards Sh2-294.

First Results from the Arecibo Galactic HiSurvey: The Disk/Halo Interface Region in the Outer Galaxy

The Astrophysical Journal, 2006

The consortium for Galactic studies with the Arecibo L-band Feed Array (ALFA) is conducting a neutral hydrogen (HI) survey of the whole Arecibo sky (declination range from −1 • to 38 •), with high angular (3.5 ′) and velocity resolution (0.2 km s −1). The precursor observations with ALFA of a region in the Galactic anti-center reveal numerous isolated, small (a few pc in size), and cold (T k < 400 K) HI clouds at low negative velocities, distinctly separated from the HI disk emission ('low-velocity clouds', LVCs). These clouds are most likely located in the transition region between the Galactic disk and halo (at scale heights of 60-900 pc), yet they have properties of typical cold neutral clouds. LVCs are colder and, most likely, smaller and less massive than Lockman's clouds in the disk/halo interface region of the inner Galaxy. Our observations demonstrate that the cloudy structure of the interface region is most likely a general phenomenon, not restricted to the inner Galaxy. LVCs have sizes and radial velocities in agreement with the expectations for clouds formed in low-temperature fountain flows, although we measure a factor of ten higher HI column densities. Alternatively, LVCs could represent the final stages of the infalling intergalactic material in the ongoing construction of the Galaxy. In the same dataset at higher negative velocities, we have discovered a 'companion' HI cloud located 50 ′ southwest of CHVC186+19-114. CHVC186+19-114 is a typical compact high velocity cloud (HVC) with a well-defined core/envelope structure. The companion cloud has a diameter of only 7 ′ × 9 ′ , and is one of the smallest HVCs known, most likely stripped from the main cloud through the interactions with the halo medium.

Molecular gas and a new young stellar cluster in the far outer Galaxy

Astronomy and Astrophysics, 2009

Aims. We investigate the star-formation ocurring in the region towards IRAS 07527-3446 in the molecular cloud [MAB97]250.63-3.63, in the far outer Galaxy. We report the discovery of a new young stellar cluster, and describe its properties and those of its parent molecular cloud. Methods. Near-infrared JHK S images were obtained with VLT/ISAAC, and millimetre line CO spectra were obtained with the SEST telescope. VLA archive date were also used. Results. The cloud and cluster are located at a distance of 10.3 kpc and a Galactocentric distance of 15.4 kpc, in the far outer Galaxy. Morphologically, IRAS 07527-3446 appears as a young embedded cluster of a few hundred stars seen towards the position of the IRAS source, extending for about 2-4 pc and exhibiting sub-clustering. The cluster contains low and intermediate-mass young reddened stars, a large fraction having cleared the inner regions of their circumstellar discs responsible for (H − K S ) colour excess. The observations are compatible with a ≤ 5 Myr cluster with variable spatial extinction of between A V = 5 and A V = 11. Decomposition of CO emission in clumps, reveals a clump clearly associated with the cluster position, of mass 3.3 × 10 3 M . Estimates of the slopes of the K S -band luminosity function and of the star-formation efficiency yield values similar to those seen in nearby star-formation sites. These findings reinforce previous results that the distant outer Galaxy continues to be active in the production of new and rich stellar clusters, with the physical conditions required for the formation of rich clusters continuing to be met in the very distant environment of the outer Galactic disc.

An intriguing globular cluster in the Galactic bulge from the VVV survey

Astronomy and Astrophysics, 2021

Context. Globular clusters (GCs) are the oldest objects known in the Milky Way, so each discovery of a new GC is astrophysically important. In the inner Galactic bulge regions these objects are difficult to find due to extreme crowding and extinction. However, recent near-IR surveys have discovered a number of new bulge GC candidates that need to be further investigated. Aims. Our main objective is to use public data from the Gaia mission, the VISTA Variables in the Via Lactea (VVV) survey, the Two Micron All Sky Survey, and the Wide-field Infrared Survey Explorer to measure the physical parameters of Minni 48, a new candidate globular star cluster located in the inner bulge of the Milky Way at l = 359.35 deg, b = 2.79 deg. The specific goals are to measure its main astrophysical parameters, such as size, proper motions, metallicity, reddening and extinction, distance, total luminosity, and age. Methods. Even though there is a bright foreground star contaminating the field, this cluster appears quite bright in near-and mid-IR images. The size of Minni 48 is derived from the cluster radial density profile, while its reddening and extinction are estimated from optical and near-IR reddening maps. We obtain statistically decontaminated optical and near-IR colour-magnitude diagrams (CMDs) for this cluster. Mean cluster proper motions are measured from Gaia data. The heliocentric cluster distance is determined from both the red clump (RC) and the red giant branch (RGB) tip magnitudes in the near-IR CMD, while the cluster metallicity is estimated from the RGB slope and the fit to theoretical stellar isochrones. Results. The size of this GC is found to be r = 6 ± 1 , and the reddening and extinction values are E(J − K s) = 0.60 ± 0.05 mag, A G = 3.23 ± 0.10 mag, and A K s = 0.45 ± 0.05 mag. The resulting mean cluster proper motions are µ α = −3.5 ± 0.5 mas yr −1 and µ δ = −6.0 ± 0.5 mas yr −1. We also study the RR Lyrae stars recognized in the field, and we argue that they are not members of this GC. The magnitude of the RC in the near-IR CMD yields an accurate distance modulus estimate of (m − M) 0 = 14.61 mag, equivalent to a distance D = 8.4 ± 1.0 kpc. Such a distance is consistent with the optical distance estimate, (m − M) 0 = 14.67 mag, D = 8.6 ± 1.0 kpc, as well as with the distance estimated using the tip of the RGB, (m − M) 0 = 14.45 mag, D = 7.8 ± 1.0 kpc. We also derive a cluster metallicity of [Fe/H] = −0.20 ± 0.30 dex. Adopting these values of metallicity and distance, a good fit to the PARSEC stellar isochrones is obtained in all CMDs using Age = 10 ± 2 Gyr. The total absolute magnitude of this GC is estimated to be M K s = −9.04 ± 0.66 mag. Conclusions. Based on its position, kinematics, metallicity, and age, we conclude that Minni 48 is a genuine GC, similar to other well-known metal-rich bulge GCs. It is located at a projected galactocentric angular distance of 2.9 deg, equivalent to 0.4 kpc, situating this cluster as one of the closest GCs to the Galactic centre currently known.

Colliding Clouds: The Star Formation Trigger of the Stellar Cluster around BD +40 4124

The Astrophysical Journal, 2006

We present BIMA and SCUBA observations of the young cluster associated with BD + 40 • 4124 in the dense molecular gas tracer CS J = 2 → 1 and the continuum dust continuum at λ = 3.1 mm and λ = 850 µm. The dense gas and dust in the system is aligned into a long ridge morphology extending ∼0.4 pc with 16 gas clumps of estimated masses ranging from 0.14-1.8 M ⊙. A northsouth variation in the CS center line velocity can be explained with a two cloud model. We posit that the BD+40 • 4124 stellar cluster formed from a cloud-cloud collision. The largest linewidths occur near V1318 Cyg-S, a massive star affecting its natal environment. In contrast, the dense gas near the other, more evolved, massive stars displays no evidence for disruption; the material must either be processed into the star, dissipate, or relax, fairly quickly. The more evolved lowmass protostars are more likely to be found near the massive stars. If the majority of low-mass stars are coeval, the seemingly evolved low-mass protostars are not older: the massive stars have eroded their structures. Finally, at the highest resolution, the λ = 3.1 mm dust emission is resolved into a flattened structure 3100 by 1500 AU with an estimated mass of 3.4 M ⊙. The continuum and CS emission are offset by 1. ′′ 1 from the southern binary source. A simple estimate of the extinction due to the continuum emission structure is A V ∼ 700 mag. From the offset and as the southern source is detected in the optical, the continuum emission is from a previously unknown very young, intermediate-mass, embedded stellar object.