A 2MASS ALL-SKY VIEW OF THE SAGITTARIUS DWARF GALAXY. VII. KINEMATICS OF THE MAIN BODY OF THE SAGITTARIUS dSph

The possibility of a gaseous halo stream which was stripped from the Sagittarius dwarf galaxy is presented. The total mass of the neutral hydrogen along the orbit of the Sgr dwarf in the direction of the Galactic Anti-Center is 4 − 10 × 106 M⊙ (at 36 kpc, the distance to the stellar debris in this region). Both the stellar and gaseous components have negative velocities in this part of the sky, but the gaseous component extends to higher negative velocities. We suggest this gaseous stream was stripped from the main body of the dwarf 0.2 – 0.3 Gyr ago during its current orbit after a passage through a diffuse edge of the Galactic disk with a density > 10−4 cm−3. The gas would then represent the dwarf's last source of star formation fuel and explains how the galaxy was forming stars 0.5-2 Gyr ago.

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Dissecting star formation in the “Atoms-for-Peace” galaxy

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832705 ◽

2018 ◽

Vol 614 ◽

pp. A130 ◽

Cited By ~ 2

Author(s):

K. George ◽

P Joseph ◽

P. Côté ◽

S. K. Ghosh ◽

J. B. Hutchings ◽

...

Keyword(s):

Star Formation ◽

Dwarf Galaxies ◽

Initial Conditions ◽

Dwarf Galaxy ◽

Main Body ◽

Star Forming ◽

Uv Imaging ◽

Star Forming Regions ◽

The Galaxy ◽

Tidal Tails

Context. The tidal tails of post-merger galaxies exhibit ongoing star formation far from their disks. The study of such systems can be useful for our understanding of gas condensation in diverse environments. Aims. The ongoing star formation in the tidal tails of post-merger galaxies can be directly studied from ultraviolet (UV) imaging observations. Methods. The post merger galaxy NGC7252 (“Atoms-for-Peace” galaxy) is observed with the Astrosat UV imaging telescope (UVIT) in broadband NUV and FUV filters to isolate the star-forming regions in the tidal tails and study the spatial variation in star formation rates. Results. Based on ultraviolet imaging observations, we discuss star-forming regions of ages <200 Myr in the tidal tails. We measure star formation rates in these regions and in the main body of the galaxy. The integrated star formation rate (SFR) of NGC7252 (i.e., that in the galaxy and tidal tails combined) without correcting for extinction is found to be 0.81 ± 0.01 M⊙ yr−1. We show that the integrated SFR can change by an order of magnitude if the extinction correction used in SFR derived from other proxies are taken into consideration. The star formation rates in the associated tidal dwarf galaxies (NGC7252E, SFR = 0.02 M⊙ yr−1 and NGC7252NW, SFR = 0.03 M⊙ yr−1) are typical of dwarf galaxies in the local Universe. The spatial resolution of the UV images reveals a gradient in star formation within the tidal dwarf galaxy. The star formation rates show a dependence on the distance from the centre of the galaxy. This can be due to the different initial conditions responsible for the triggering of star formation in the gas reservoir that was expelled during the recent merger in NGC7252.

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The curious case of the companion: evidence for cold accretion onto a dwarf satellite near the isolated elliptical NGC 7796

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732241 ◽

2018 ◽

Vol 620 ◽

pp. A133 ◽

Cited By ~ 1

Author(s):

T. Richtler ◽

M. Hilker ◽

K. Voggel ◽

T. H. Puzia ◽

R. Salinas ◽

...

Keyword(s):

Galaxy Evolution ◽

Dwarf Galaxy ◽

Broad Band ◽

Hii Regions ◽

Diagnostic Tools ◽

Strong Line ◽

Main Body ◽

Surprising Result ◽

Star Forming ◽

The Galaxy

Context. The isolated elliptical (IE) NGC 7796 is accompanied by an interesting early-type dwarf galaxy, named NGC 7796-DW1. It exhibits a tidal tail, very boxy isophotes, and multiple nuclei or regions (A, B, and C) that are bluer than the bulk population of the galaxy, indicating a younger age. These properties are suggestive of a dwarf–dwarf merger remnant. Aims. Dwarf–dwarf mergers are poorly understood, but may have a high importance for dwarf galaxy evolution. We want to investigate the properties of the dwarf galaxy and its components to find more evidence for a dwarf–dwarf merger or for alternative formation scenarios. Methods. We use the Multi-Unit Spectroscopic Explorer (MUSE) at the VLT to investigate NGC 7796-DW1. We extract characteristic spectra to which we apply the STARLIGHT population synthesis software to obtain ages and metallicities of the various population components of the galaxy. This permits us to isolate the emission lines for which fluxes and flux ratios can be measured and to which strong-line diagnostic tools can be applied. Results. The galaxy’s main body is old and metal-poor. A surprising result is the extended line emission in the galaxy, forming a ring-like structure with a projected diameter of 2.2 kpc. The line ratios fall into the regime of HII-regions, although OB-stellar populations cannot be identified by spectral signatures. The low Hα surface brightnesses indicate unresolved star-forming substructures, which means that broad-band colours are not reliable age or metallicity indicators. Nucleus A is a relatively old (7 Gyr or older) and metalpoor super star cluster, most probably the nucleus of the dwarf, now displaced. The star-forming regions B and C show younger and distinctly more metal-rich components. The emission line ratios of regions B and C indicate an almost solar oxygen abundance, if compared with radiation models of HII regions. Oxygen abundances from empirical calibrations point to only half-solar. The ring-like Hα-structure does not exhibit signs of rotation or orbital movements. Conclusions. NGC 7796-DW1 occupies a particular role in the group of transition-type galaxies with respect to its origin and current evolutionary state, being the companion of an IE. The dwarf–dwarf merger scenario is excluded because of the missing metal-rich merger component. A viable alternative is gas accretion from a reservoir of cold, metal-rich gas. NGC 7796 has to provide this gas within its X-ray bright halo. As illustrated by NGC 7796-DW1, cold accretion may be a general solution to the problem of extended star formation histories in transition dwarf galaxies.

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The Distance and Dynamical History of the Virgo Cluster Ultradiffuse Galaxy VCC 615

The Astrophysical Journal ◽

10.3847/1538-4357/ac35d9 ◽

2022 ◽

Vol 924 (2) ◽

pp. 87

Author(s):

J. Christopher Mihos ◽

Patrick R. Durrell ◽

Elisa Toloba ◽

Patrick Côté ◽

Laura Ferrarese ◽

...

Keyword(s):

Dwarf Galaxy ◽

Hubble Space Telescope ◽

Virgo Cluster ◽

Cluster Center ◽

Main Body ◽

The Galaxy ◽

Orbit Modeling ◽

History Of ◽

Red Giant ◽

Distance Estimator

Abstract We use deep Hubble Space Telescope imaging to derive a distance to the Virgo Cluster ultradiffuse galaxy (UDG) VCC 615 using the tip of the red giant branch (TRGB) distance estimator. We detect 5023 stars within the galaxy, down to a 50% completeness limit of F814W ≈ 28.0, using counts in the surrounding field to correct for contamination due to background sources and Virgo intracluster stars. We derive an extinction-corrected F814W tip magnitude of m tip , 0 = 27.19 − 0.05 + 0.07 , yielding a distance of d = 17.7 − 0.4 + 0.6 Mpc. This places VCC 615 on the far side of the Virgo Cluster (d Virgo = 16.5 Mpc), at a Virgocentric distance of 1.3 Mpc and near the virial radius of the main body of Virgo. Coupling this distance with the galaxy’s observed radial velocity, we find that VCC 615 is on an outbound trajectory, having survived a recent passage through the inner parts of the cluster. Indeed, our orbit modeling gives a 50% chance the galaxy passed inside the Virgo core (r < 620 kpc) within the past gigayear, although very close passages directly through the cluster center (r < 200 kpc) are unlikely. Given VCC 615's undisturbed morphology, we argue that the galaxy has experienced no recent and sudden transformation into a UDG due to the cluster potential, but rather is a long-lived UDG whose relatively wide orbit and large dynamical mass protect it from stripping and destruction by the Virgo cluster tides. Finally, we also describe the serendipitous discovery of a nearby Virgo dwarf galaxy projected 90″ (7.2 kpc) away from VCC 615.

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Metal-poor nuclear star clusters in two dwarf galaxies near Centaurus A suggesting formation from the in-spiraling of globular clusters

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937120 ◽

2020 ◽

Vol 634 ◽

pp. A53 ◽

Cited By ~ 2

Author(s):

Katja Fahrion ◽

Oliver Müller ◽

Marina Rejkuba ◽

Michael Hilker ◽

Mariya Lyubenova ◽

...

Keyword(s):

Globular Clusters ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Star Clusters ◽

High Resolution Spectroscopy ◽

High Signal ◽

Main Body ◽

Host Galaxies ◽

Low Mass ◽

The Masses

Studies of nucleated dwarf galaxies can constrain the scenarios for the formation and evolution of nuclear star clusters (NSC) in low-mass galaxies and give us insights on the origin of ultra compact dwarf galaxies (UCDs). We report the discovery of a NSC in the dwarf galaxy KKs58 and investigate its properties together with those of another NSC in KK197. Both NSCs are hosted by dwarf elliptical galaxies of the Centaurus group. Combining ESO VLT MUSE data with photometry from VLT FORS2, CTIO Blanco DECam, and HST ACS, as well as high-resolution spectroscopy from VLT UVES, we analyse the photometric, kinematic and stellar population properties of the NSCs and their host galaxies. We confirm membership of the NSCs based on their radial velocities and location close to the galaxy centres. We also confirm the membership of two globular clusters (GCs) and detect oblate rotation in the main body of KK197. Based on high signal-to-noise spectra taken with MUSE of the NSCs of both KKs58 and KK197 we measure low metallicities, [Fe/H] = −1.75 ± 0.06 dex and [Fe/H] = −1.84 ± 0.05 dex, and stellar masses of 7.3 × 105 M⊙ and 1.0 × 106 M⊙, respectively. Both NSCs are more metal-poor than their hosts that have metallicities of −1.35 ± 0.23 dex (KKs58) and −0.84 ± 0.12 dex (KK197). This can be interpreted as NSC formation via the in-spiral of GCs. The masses, sizes and metallicities of the two NSCs place them among other NSCs, but also among the known UCDs of the Centaurus group. This indicates that NSCs might constitute the progenitors of a part of the low-mass UCDs, although their properties are almost indistinguishable from typical GCs.

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A wide angle chemical survey of the Sagittarius dwarf Spheroidal galaxy

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006804 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 42-45

Author(s):

L. Sbordone ◽

L. Monaco ◽

S. Duffau ◽

P. Bonifacio ◽

E. Caffau

Keyword(s):

Milky Way ◽

Dwarf Galaxy ◽

Main Body ◽

Wide Angle ◽

Chemical Abundances ◽

The Galaxy ◽

The Status ◽

Ongoing Project ◽

Detailed Chemical

AbstractWe present the status of an ongoing project to map the detailed chemical abundances of stars across the main body of the Sagittarius dwarf Spheroidal galaxy (Sgr dSph). The Sgr dSph is the closest known dwarf galaxy, and is being tidally destroyed by its interaction with the Milky Way (MW), leaving behind a massive stellar stream. Sgr dSph is a chemically outstanding object, with peculiar abundance ratios, clear center-outskirts abundance gradients, and spanning more than 3 orders of magnitude in metallicity. We present here detailed abundances from UVES@VLT spectra for more than 50 giants across 8 fields along the major and minor axes of Sgr dSph, and 5 more outside the galaxy main body, but possibly associated to its stellar stream.

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Actin filaments in two spermatozoa of crustacea decapoda

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100157899 ◽

1990 ◽

Vol 48 (3) ◽

pp. 70-71

Author(s):

E. Dupré ◽

G. Schatten

Keyword(s):

Electron Microscopy ◽

Actin Filaments ◽

Low Voltage ◽

Active Role ◽

Main Body ◽

Robinson Crusoe ◽

Decapod Crustaceans ◽

Actual Participation ◽

Voltage Scanning ◽

Scanning Electron

Sperm of decapod crustaceans are formed by a round or cup-shaped body, a complex acrosome and one a few appendages emerging from the main body. Although this sperm does not have motility, it has some components of the cytoskeleton like microtubules, which are found inside the appendages. Actin filaments have been found in the spike of penaeidae sperms. The actual participation of the crustacean decapod sperm cytoskeleton during fertilization is not well understood. Actin is supposed to play an active role in drawing the penaeidae shrimp sperm closer to the egg after bending of the spike. The present study was aimed at the localization of actin filaments in sperm of the Robinson Crusoe island lobster, Jasus frontalis and in the crayfish Orconectes propincus, by fluorescent probes and low voltage scanning electron microscopy.

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Review of Prelabor Rupture of the Membranes: Pathophysiologic Concepts and Novel Therapeutic Strategies

Current Women s Health Reviews ◽

10.2174/1573404816999201026223954 ◽

2020 ◽

Vol 16 ◽

Author(s):

Saadia Ghafoor

Keyword(s):

Management Strategies ◽

Signs And Symptoms ◽

Cochrane Library ◽

Main Body ◽

Scientific Publications ◽

Timely Diagnosis ◽

Narrative Literature Review ◽

Contemporary Management ◽

Online Library ◽

Novel Therapeutic Strategies

Background:: Prelabor rupture of membrane (PROM) refers to the breakage of fetal membranes before the onset of labor, resulting in the leakage of amniotic fluid. PROM affects approximately 3% and 8% of preterm and term pregnancies. Because of associated high maternal and perinatal mortality, correct and timely diagnosis together with effective management is highly recommended to prevent adverse fetal and maternal outcomes. Objective:: To provide an overview of the novel concepts in the understanding of PROM including etiology, pathophysiology, risk factors, complications, assessment, diagnostic modalities, and contemporary management strategies for PROM at preterm and term. Methodology:: This narrative literature review was conducted through a literature search using the Cochrane library and electronic databases including PubMed, Web of Science, Medline, Scopus, Crossref, Google Scholar, Wiley online library, ScienceDirect with specific search terms in scientific publications published from March 1980 to March 2020. Main Body:: Preterm PROM has the potential to cause prenatal morbidity and mortality. It is imperative to monitor the signs and symptoms of an impending infection due to the risk of infectious morbidity with PROM at preterm and preterm. PROM at preterm and term requires prompt diagnosis followed by an appropriate management strategy. Conclusion:: The correct and timely diagnosis of PROM is essential for efficacious management. Furthermore, it can reduce avoidable emergent health care visits and related costs in a clinical setting subjected to pregnancy with suspected PROM. Further studies are needed to fill the gaps in identifying better diagnostic predictive tools in high- risk pregnancies.

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