PN populations in the local group and distant stellar populations

AbstractOur understanding of galactic structure and evolution is far from complete. Within the past twelve months we have learnt that the Milky Way is about 50% wider than was previously thought. As a consequence, new models are being developed that force us to reassess the kinematic structure of our Galaxy. Similarly, we need to take a fresh look at the halo structure of external galaxies in our Local Group. Studies of stellar populations, star-forming regions, clusters, the interstellar medium, elemental abundances and late stellar evolution are all required in order to understand how galactic assembly has occurred as we see it. PNe play an important role in this investigation by providing a measure of stellar age, mass, abundances, morphology, kinematics and synthesized matter that is returned to the interstellar medium (ISM). Through a method of chemical tagging, halo PNe can reveal evidence of stellar migration and galactic mergers. This is an outline of the advances that have been made towards uncovering the full number of PNe in our Local Group galaxies and beyond. Current numbers are presented and compared to total population estimates based on galactic mass and luminosity. A near complete census of PNe is crucial to understanding the initial-to-final mass relation for stars with mass >1 to <8 times the mass of the sun. It also allows us to extract more evolutionary information from luminosity functions and compare dust-to-gas ratios from PNe in different galactic locations. With new data provided by the Gaia satellite, space-based telescopes and the rise of giant and extra-large telescopes, we are on the verge of observing and understanding objects such as PNe in distant galaxies with the same detail we expected from Galactic observations only a decade ago.

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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

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Very Low Mass Stellar Populations in Star-Forming Regions: Near-Infrared Luminosity Functions and Mass Functions

Symposium - International Astronomical Union ◽

10.1017/s0074180900210358 ◽

2003 ◽

Vol 211 ◽

pp. 91-96 ◽

Cited By ~ 1

Author(s):

Yumiko Oasa

Keyword(s):

Near Infrared ◽

Stellar Populations ◽

Mass Function ◽

High Mass ◽

Star Forming ◽

Star Forming Regions ◽

Luminosity Functions ◽

Low Mass ◽

Stellar Masses ◽

Mass Functions

We briefly describe recent studies of the low-mass young stellar populations including substellar objects and of their luminosity functions and mass functions, especially at lower-ends, in different star-forming regions. The mass function is determined by the technique based on the near-infrared photometry for estimating stellar luminosities and then translating them into stellar masses. We compare the local environmental characteristics of regions in which high-mass stars form with those of regions producing only low-mass stars and intermediate stars. We find that there exist numerous very low-mass YSO candidates including young brown dwarfs and young isolated objects with planetary masses in common. Further, the luminosity functions and mass functions in the star-forming regions might not have a uniform shape below the hydrogen-burning limit.

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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.

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Extragalactic GCs in the near-infrared: genuinely old in E/S0's?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310003017 ◽

2009 ◽

Vol 5 (S262) ◽

pp. 315-316

Author(s):

Ana L. Chies-Santos ◽

Søren S. Larsen

Keyword(s):

Globular Cluster ◽

Stellar Population ◽

Near Infrared ◽

Local Group ◽

Stellar Populations ◽

Age Dating ◽

Early Type ◽

Optical Photometry ◽

Star Forming ◽

Optical Images

Globular cluster (GC) systems are powerful probes to study the evolutionary histories of galaxies, being tracers of major star fomation episodes (Brodie & Strader 2006). They are found around all major galaxies and are easy to see far beyond the local group. Age dating GCs therefore helps pinpoint epochs of major star forming events. Spectroscopic age dating though (Strader et al. 2005) is extremely time consuming and can only access the few brightest clusters. An alternative is to combine near-infrared (NIR) and optical photometry, and therefore have a better chance in lifting the age metallicity degeneracy than with optical colours alone. This approach relies in testing GC colours against simple stellar population (SSP) models. The first studies following this technique showed the possible existence of a high percentage of intermediate age (2-3 Gyrs) GCs in early-type galaxies known to contain old stellar populations from integrated light studies. Two strong cases can be listed: NGC 4365 (Puzia et al. 2002, Larsen et al. 2005) and NGC 5846 (Hempel et al. 2003). In the present study we combine NIR deep photometry obtained with the WHT/LIRIS instrument and archival HST/ACS optical images to determine g(F475W), z(F840LP) and K(2.2m) magnitudes and colours of GCs in 14 early-type galaxies.

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Stellar populations in the highest redshift galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316004877 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 197-198

Author(s):

Andrew J. Bunker

Keyword(s):

Galaxy Evolution ◽

High Redshift ◽

Stellar Populations ◽

Mass Function ◽

Initial Mass Function ◽

Star Forming ◽

Near Ir ◽

James Webb Space Telescope ◽

Large Telescopes ◽

The Universe

AbstractI discuss stellar populations in galaxies at high redshift (z > 6), in particular the blue rest-frame UV colours which have been detected in recent years through near-IR imaging with HST. These spectral slopes of β < −2 are much more blue than star-forming galaxies at lower redshift, and may suggest less dust obscuration, lower metallicity or perhaps a different initial mass function. I describe current work on the luminosity function of high redshift star- forming galaxies, the evolution of the fraction of strong Lyman-α emitters in this population, and the contribution of the ionizing photon budget from such galaxies towards the reionization of the Universe. I also describe constraints placed by Spitzer/IRAC on stellar populations in galaxies within the first billion years, and look towards future developments in spectroscopy with Extremely Large Telescopes and the James Webb Space Telescope, including the JWST/NIRSpec GTO programme on galaxy evolution at high redshift.

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Planetary Nebulae in Local Group Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900093992 ◽

1983 ◽

Vol 103 ◽

pp. 443-460

Author(s):

Holland C. Ford

Keyword(s):

Local Group ◽

Planetary Nebulae ◽

Stellar Populations ◽

Chemical Compositions ◽

H Ii Regions ◽

Helium Abundance ◽

Abundance Gradient ◽

Star Forming ◽

Ic 10 ◽

Ngc 6822

Recent surveys for planetary nebulae have given the first identifications in Fornax, NGC 6822, M33, IC 10, Leo A, Sextans A, Pegasus, WLM, NGC 404, and M81, and extended the identifications in the SMC, the LMC, and M31. Observations of planetaries have established chemical compositions in old or intermediate age populations in 8 Local Group galaxies. The chemical compositions show that i) the helium abundance is higher in planetary nebulae than in H II regions in the same galaxy, and ii) nitrogen is overabundant relative to H II regions by factors of 4 to 100. Planetary nebulae are not a major source of helium in star-forming galaxies, and are a major source of nitrogen. The planetary in Fornax has a relatively high O abundance, and, together with Fornax's carbon stars, establishes the presence of at least 2 stellar populations. The abundance gradient derived from 3 planetaries in M31 is very shallow, and gives high abundances at ~ 20 kpc. By using planetary nebulae as standard candles, upper and lower distance limits have been set for 10 Local Group candidates, and a new distance estimated for M81.

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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.

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Star Clusters in Local Group Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900108551 ◽

1995 ◽

Vol 164 ◽

pp. 181-192

Author(s):

Edward W. Olszewski

Keyword(s):

Stellar Population ◽

Local Group ◽

Star Clusters ◽

Stellar Populations ◽

Cluster Systems ◽

Star Forming ◽

Long Time ◽

History Of ◽

Individual Objects

In this paper I will try to give the flavor of two different concepts of stellar population, namely, the population of cluster systems within galaxies, and the stellar populations within individual clusters. I hope to show, in concert with other papers in this volume, that a generic vision of Population I and II has been outdated for a long time. I believe that it is still proper to talk about populations within individual objects; in the case of galaxies, one might make a correspondence of populations with the important star forming events in the history of a galaxy.

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Sardinia Radio Telescope (SRT) observations of Local Group dwarf galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318000704 ◽

2017 ◽

Vol 13 (S336) ◽

pp. 109-112

Author(s):

A. Tarchi ◽

P. Castangia ◽

G. Surcis ◽

A. Brunthaler ◽

K. M. Menten ◽

...

Keyword(s):

Radio Telescope ◽

Local Group ◽

Dwarf Galaxies ◽

Radio Continuum ◽

Maser Emission ◽

Star Forming ◽

Star Forming Regions ◽

First Results ◽

Ngc 6822 ◽

Almost All

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.

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