A TREASURY STUDY OF STAR-FORMING REGIONS IN THE LOCAL GROUP. I.HSTPHOTOMETRY OF YOUNG POPULATIONS IN SIX DWARF GALAXIES

AbstractThe dwarf galaxies in the Local Group (LG) reveal a surprising amount of spatial structuring. In particular, almost all non-satellite dwarfs belong to one of two planes that show a very pronounced symmetry. In order to determine if these structures in the LG are dynamically stable or, alternatively, if they only represent transient alignments, proper motion measurements of these galaxies are required. A viable method to derive proper motions is offered by VLBI studies of 22-GHz water (and 6.7-GHz methanol) maser lines in star-forming regions.In 2016, in the framework of the Early Science Program of the Sardinia Radio Telescope (SRT), we have conducted an extensive observational campaign to map the entire optical body of all the LG dwarf galaxies that belong to the two planes, at C and K band, in a search for methanol and water maser emission.Here, we outline the project and present its first results on 3 targets, NGC 6822, IC 1613, and WLM. While no luminous maser emission has been detected in these galaxies, a number of interesting weaker detections has been obtained, associated with particularly active star forming regions. In addition, we have produced deep radio continuum maps for these galaxies, aimed at investigating their star forming activity and providing an improved assessment of star formation rates in these galaxies.

Download Full-text

Sardinia Radio Telescope observations of Local Group dwarf galaxies – I. The cases of NGC 6822, IC 1613, and WLM

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3445 ◽

2019 ◽

Vol 492 (1) ◽

pp. 45-57

Author(s):

A Tarchi ◽

P Castangia ◽

G Surcis ◽

A Brunthaler ◽

C Henkel ◽

...

Keyword(s):

Local Group ◽

Dwarf Galaxies ◽

Radio Continuum ◽

Star Forming ◽

Star Forming Regions ◽

Long Baseline ◽

Planar Structures ◽

Ngc 6822 ◽

Almost All ◽

Transient Alignment

ABSTRACT Almost all dwarf galaxies in the Local Group (LG) that are not satellites of the Milky Way or M 31 belong to either one of two highly symmetric planes. It is still a matter of debate whether these planar structures are dynamically stable or whether they only represent a transient alignment. Proper motions, if they could be measured, could help to discriminate between these scenarios. Such motions could be determined with multi-epoch very long baseline interferometry (VLBI) of sources that show emission from water and methanol at frequencies of 22 and 6.7 GHz, respectively. We report searches for such masers. We have mapped three LG galaxies, NGC 6822, IC 1613, and WLM, in the bands covering the water vapour and methanol lines. These systems are members of the two above-mentioned planes of galaxies. We have produced deep radio continuum (RC) maps and spectral line cubes. The former have been used to identify star-forming regions and to derive global galactic star formation rates (SFRs). These SFRs turn out to be lower than those determined at other wavelengths in two of our sources. This indicates that dwarf galaxies may follow predictions on the RC–SFR relation only in individual regions of enhanced RC emission, but not when considering the entire optical body of the sources. No methanol or water maser emission has been confidently detected, down to line luminosity limits of ∼4 × 10−3 and 10 × 10−3 L⊙, respectively. This finding is consistent with the small sizes, low SFRs, and metallicities of these galaxies.

Download Full-text

The Violent Interstellar Medium of Nearby Dwarf Galaxies

Publications of the Astronomical Society of Australia ◽

10.1071/as99106 ◽

1999 ◽

Vol 16 (1) ◽

pp. 106-112 ◽

Cited By ~ 9

Author(s):

Fabian Walter

Keyword(s):

Interstellar Medium ◽

Gamma Ray ◽

Dwarf Galaxies ◽

Young Star ◽

Stellar Winds ◽

Star Forming ◽

Star Forming Regions ◽

Supernova Explosions ◽

High Velocity Clouds ◽

Ob Associations

AbstractHigh resolution HI observations of nearby dwarf galaxies (most of which are situated in the M81 group at a distance of about 3·2 Mpc) reveal that their neutral interstellar medium (ISM) is dominated by hole-like features most of which are expanding. A comparison of the physical properties of these holes with the ones found in more massive spiral galaxies (such as M31 and M33) shows that they tend to reach much larger sizes in dwarf galaxies. This can be understood in terms of the galaxy's gravitational potential. The origin of these features is still a matter of debate. In general, young star forming regions (OB-associations) are held responsible for their formation. This picture, however, is not without its critics and other mechanisms such as the infall of high velocity clouds, turbulent motions or even gamma ray bursters have been recently proposed. Here I will present one example of a supergiant shell in IC 2574 which corroborates the picture that OB associations are indeed creating these structures. This particular supergiant shell is currently the most promising case to study the effects of the combined effects of stellar winds and supernova explosions which shape the neutral interstellar medium of (dwarf) galaxies.

Download Full-text

Star Clusters in Irregular Galaxies in the Local Group

Symposium - International Astronomical Union ◽

10.1017/s0074180900223425 ◽

2002 ◽

Vol 207 ◽

pp. 94-104

Author(s):

Eva K. Grebel

Keyword(s):

Globular Clusters ◽

Local Group ◽

Cluster Formation ◽

Star Clusters ◽

Open Clusters ◽

High Angular Resolution ◽

Star Clusters And Associations ◽

Star Forming ◽

Star Forming Regions ◽

Irregular Galaxies

I summarize our knowledge of star clusters and associations in irregular galaxies other than the Magellanic Clouds in the Local Group. Surveys affording complete area coverage at high angular resolution are still lacking. Confirmed globular clusters are known only in NGC 6822 and WLM. Very few dIrrs contain populous or sparse open clusters. There is a pronounced deficiency of intermediate-age and young clusters. Apart from parent galaxy mass, the lack of interactions may be a key reason for the lack of cluster formation in the dIrrs. All dIrrs have one or several short-lived OB associations in the star-forming regions in their centers.

Download Full-text

An X-Ray View of Interacting Binaries Outside The Galaxy

International Astronomical Union Colloquium ◽

10.1017/s0252921100151693 ◽

2004 ◽

Vol 194 ◽

pp. 3-6

Author(s):

Andrea H. Prestwich

Keyword(s):

Supernova Remnants ◽

Luminosity Function ◽

Local Group ◽

Spiral Galaxies ◽

High Mass ◽

X Ray ◽

Star Forming ◽

Star Forming Regions ◽

Low Mass ◽

X Ray Binaries

AbstractChandra and XMM-Newton are revolutionizing our understanding of compact binaries in external galaxies, allowing us to study sources in detail in Local Group Galaxies and study populations in more distant systems. In M31 the X-ray luminosity function depends on the local stellar population in the sense that areas with active star formation have more high luminosity sources, and a higher overall source density (Kong. Di Stefano. Garcia, & Greiner 2003). This result is also true in galaxies outside the Local Group; starburst galaxies have flatter X-ray luminosity functions than do spiral galaxies which are in turn flatter than elliptical galaxies. These observational results suggest that the high end of the luminosity function in star forming regions is dominated by short-lived high mass X-ray binaries.In Chandra Cycle 2 we started a Large Project to survey a sample of 11 nearby (< 10Mpc) face-on spiral galaxies. We find that sources can be approximately classified on the basis of their X-ray color into low mass X-ray binaries, high mass X-ray binaries and supersoft sources. There is an especially interesting class of source that has X-ray colors softer (“redder”) than a typical low mass X-ray binary source, but not so extreme as supersoft sources. Most of these are probably X-ray bright supernova remnants, but some may be a new type of black hole accretor. Finally, when we construct a luminosity function of sources selecting only sources with low mass X-ray binary colors (removing soft sources) we find that there is a dip or break probably associated with the Eddington luminosity for a neutron star.

Download Full-text

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.

Download Full-text

Gas accretion from the cosmic web in the local Universe

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316010231 ◽

2014 ◽

Vol 11 (S308) ◽

pp. 390-393

Author(s):

J. Sánchez Almeida ◽

B. G. Elmegreen ◽

C. Muñoz-Tuñnón ◽

D. M. Elmegreen

Keyword(s):

Large Scale ◽

Dwarf Galaxies ◽

Local Universe ◽

Single Observation ◽

Star Forming ◽

Star Forming Regions ◽

Stellar Ages ◽

Gas Consumption ◽

Low Mass ◽

Gas Accretion

AbstractNumerical simulations predict that gas accretion from the cosmic web drives star formation in disks galaxies. The process is important in low mass haloes (< 1012M⊙), therefore, in the early universe when galaxies were low mass, but also in dwarf galaxies of the local universe. The gas that falls in is predicted to be tenuous, patchy, partly ionized, multi-temperature, and large-scale; therefore, hard to show in a single observation. One of the most compelling cases for gas accretion at work in the local universe comes from the extremely metal poor (XMP) galaxies. They show metallicity inhomogeneities associated with star-forming regions, so that large starbursts have lower metallicity than the underlying galaxy. Here we put forward the case for gas accretion from the web posed by XMP galaxies. Two other observational results are discussed too, namely, the fact that the gas consumption time-scale is shorter than most stellar ages, and the systematic morphological distortions of the HI around galaxies.

Download Full-text

Discovery of new dwarf galaxies around NGC4631 with Subaru/Hyper Suprime-Cam

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315007115 ◽

2015 ◽

Vol 11 (S317) ◽

pp. 350-351

Author(s):

Mikito Tanaka ◽

Masashi Chiba ◽

Yutaka Komiyama

Keyword(s):

Local Group ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Outer Region ◽

Absolute Magnitude ◽

Effective Radius ◽

The Other ◽

Interacting Galaxies ◽

Irregular Galaxy ◽

Star Forming

AbstractWe have observed on-going interacting galaxies (NGC4631 and NGC4656) using Subaru/Hyper Suprime-Cam and reduced the data using HSC pipeline and conducted photometry based on DAOphot. Then, we have detected 8 new dwarf galaxy candidates in the outer region of NGC4631 and confirmed the three candidates previously reported by Karachentsev et al. 2014. The 3 or 4 candidates detected in this study may be a star-forming dwarf irregular galaxy and the other 7 candidates may be an old dwarf spheroidal galaxy based on these stellar populations. It looks like that the effective radius - absolute magnitude relation of dwarf galaxies in NGC4631 group is similar to the relation of the Local Group and the other galaxy systems.

Download Full-text

AHUBBLE SPACE TELESCOPETREASURY STUDY OF STAR-FORMING REGIONS IN THE LOCAL GROUP. II. YOUNG STELLAR POPULATIONS IN M31

The Astronomical Journal ◽

10.1088/0004-6256/144/5/142 ◽

2012 ◽

Vol 144 (5) ◽

pp. 142 ◽

Cited By ~ 17

Author(s):

Luciana Bianchi ◽

Boryana Efremova ◽

Paul Hodge ◽

Yongbeom Kang

Keyword(s):

Local Group ◽

Stellar Populations ◽

Star Forming ◽

Star Forming Regions ◽

Group Ii

Download Full-text

Study of the Milky Way's hot coronal gas with its dwarf galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315010443 ◽

2015 ◽

Vol 11 (S317) ◽

pp. 340-341

Author(s):

Stefano Pasetto ◽

Mark Cropper ◽

Yutaka Fujita ◽

Cesare Chiosi ◽

Eva K. Grebel

Keyword(s):

Star Formation ◽

Dwarf Galaxies ◽

Stellar System ◽

Analytical Framework ◽

Host Galaxy ◽

Star Forming ◽

Star Forming Regions ◽

Tidal Forces ◽

Diffuse Halo ◽

Analytical Criterion

AbstractA large amount (5 × 1010 M⊙) of hot gas is thought to exist in an extended (≈ 200 kpc) hot diffuse halo around the Milky Way. We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation of this gravitationally bound systems in this external environment. Ram pressure, Kelvin-Helmholtz and Rayleigh- Taylor instabilities, and tidal forces are accounted for separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment, useful in observational applications as well as theoretical interpretations of numerical results. We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system, thus investigating the detectability limits and relevance of these different effects for future observational projects. The theoretical framework developed has direct applications to the cases of our MW system as well as dwarf galaxies in galaxy clusters or any primordial gas-rich star cluster of stars orbiting within its host galaxy.

Download Full-text