scholarly journals The Nucleus of Our Home Galaxy: A Remnant of an Active or a Starburst Galaxy?

1994 ◽  
Vol 159 ◽  
pp. 351-354
Author(s):  
Leonid M. Ozernoy
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Radiation Spectrum ◽  
Seyfert Galaxy ◽  
Star Formation History ◽  
Starburst Galaxy ◽  
Formation History ◽  
History Of ◽  
Sgr A ◽  
Radio Band

To resolve the above dilemma, two essentially different approaches are undertaken: First, a new, detailed analysis of the entire radiation spectrum of Sgr A∗, from radio band up to gamma-rays, is reviewed, which enables us to put substantial constraints on the mass of a putative black hole. The derived upper limit turns out to be too small to allow the black hole to serve as an ‘engine’ for a Seyfert galaxy. Second, analyses of recent data on the 10 KeV gas in the central 200 pc and on star formation history at the Galactic center both make a star burst the likely episode in a recent past. Taken together, the two approaches seem to indicate that the history of the central part of our Galaxy can be better described as that of a starburst, rather than a Seyfert, galaxy.

scholarly journals The Milky Way’s nuclear star cluster: Old, metal-rich, and cuspy

2020 ◽  
Vol 641 ◽  
pp. A102 ◽  
Author(s):  
R. Schödel ◽  
F. Nogueras-Lara ◽  
E. Gallego-Cano ◽  
B. Shahzamanian ◽  
A. T. Gallego-Calvente ◽  
...  
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Milky Way ◽  
Star Cluster ◽  
Star Formation History ◽  
Central Black Hole ◽  
Formation History ◽  
History Of ◽  
Nuclear Cluster ◽  
Sgr A

Context. The environment of Sagittarius A* (Sgr A*), the central black hole of the Milky Way, is the only place in the Universe where we can currently study the interaction between a nuclear star cluster and a massive black hole and infer the properties of a nuclear cluster from observations of individual stars. Aims. This work aims to explore the star formation history of the nuclear cluster and the structure of the innermost stellar cusp around Sgr A*. Methods. We combined and analysed multi epoch high quality AO observations. For the region close to Sgr A* we apply the speckle holography technique to the AO data and obtain images that are ≥50% complete down to Ks ≈ 19 within a projected radius of 5″ around Sgr A*. We used H-band images to derive extinction maps. Results. We provide Ks photometry for roughly 39 000 stars and H-band photometry for ∼11 000 stars within a field of about 40″ × 40″, centred on Sgr A*. In addition, we provide Ks photometry of ∼3000 stars in a very deep central field of 10″ × 10″, centred on Sgr A*. We find that the Ks luminosity function (KLF) is rather homogeneous within the studied field and does not show any significant changes as a function of distance from the central black hole on scales of a few 0.1 pc. By fitting theoretical luminosity functions to the KLF, we derive the star formation history of the nuclear star cluster. We find that about 80% of the original star formation took place 10 Gyr ago or longer, followed by a largely quiescent phase that lasted for more than 5 Gyr. We clearly detect the presence of intermediate-age stars of about 3 Gyr in age. This event makes up about 15% of the originally formed stellar mass of the cluster. A few percent of the stellar mass formed in the past few 100 Myr. Our results appear to be inconsistent with a quasi-continuous star formation history. The mean metallicity of the stars is consistent with being slightly super solar. The stellar density increases exponentially towards Sgr A* at all magnitudes between Ks = 15−19. We also show that the precise properties of the stellar cusp around Sgr A* are hard to determine because the star formation history suggests that the star counts can be significantly contaminated, at all magnitudes, by stars that are too young to be dynamically relaxed. We find that the probability of observing any young (non-millisecond) pulsar in a tight orbit around Sgr A* and beamed towards Earth is very low. We argue that typical globular clusters, such as they are observed in and around the Milky Way today, have probably not contributed to the nuclear cluster’s mass in any significant way. The nuclear cluster may have formed following major merger events in the early history of the Milky Way.

scholarly journals Metallicity studies of the Galactic center: evidence for a top-heavy star formation history?

2013 ◽  
Vol 9 (S303) ◽  
pp. 252-253
Author(s):  
Francisco Najarro ◽  
Diego de la Fuente ◽  
Tom R. Geballe ◽  
Don F. Figer
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Local Group ◽  
Galactic Center ◽  
Massive Stars ◽  
Star Formation History ◽  
Test Bed ◽  
Formation History ◽  
History Of ◽  
Stellar Properties

AbstractThe Galactic center (GC) region hosts three of the most massive resolved young clusters in the Local Group and constitutes a test bed for studying the star formation history of the region and inferring the possibility of a top-heavy scenario. Further, recent detection of a large number of apparently isolated massive stars within the inner 80 pc of the Galactic center has raised fundamental questions regarding massive star formation in a such a dense and harsh environment. Noting that most of the isolated massive stars have spectral analogs in the Quintuplet cluster, we have undertaken a combined analysis of the infrared spectra of both selected Quintuplet stars and the isolated objects using Gemini spectroscopy. We present preliminary results, aiming at α-elements versus iron abundances, stellar properties, ages and radial velocities which will differentiate the top-heavy and star-formation scenarios.

scholarly journals The Star Formation History of the Disk of the Starburst Galaxy M82

2006 ◽  
Vol 649 (1) ◽  
pp. 172-180 ◽  
Author(s):  
Y. D. Mayya ◽  
A. Bressan ◽  
L. Carrasco ◽  
L. Hernandez‐Martinez
Keyword(s):  
Star Formation ◽  
Star Formation History ◽  
Starburst Galaxy ◽  
Formation History ◽  
History Of

scholarly journals The chemical history of the nearest starburst galaxy – IC10

2009 ◽  
Vol 5 (S265) ◽  
pp. 159-162
Author(s):  
Denise R. Gonçalves ◽  
Laura Magrini
Keyword(s):  
Dwarf Galaxy ◽  
Accurate Determination ◽  
Star Formation History ◽  
Homogeneous Distribution ◽  
Starburst Galaxy ◽  
Chemical Enrichment ◽  
Irregular Galaxies ◽  
Formation History ◽  
History Of ◽  
Chemical History

AbstractThe irregular dwarf galaxy IC10 is located within the Local Group (LG) at a distance of 750 kpc. Although several studies have revealed the existence of stellar populations with a broad range of ages, its star formation history (SFH) and age-metallicity (AM) relationship remain quite unknown. In this contribution we present our spectroscopic investigation of 15 H ii regions, 9 planetary nebulae (PNe) and 1 symbiotic star –so far the farthest known symbiotic binary. Our main goal is to reconstruct the SFH of IC10 and to constrain its AM relationship using young and intermediate-age stars. The direct availability of the electron temperature in our emission-line spectra allows an accurate determination of the IC10 metallicity map at two different epochs. We find a non-homogeneous distribution of metals at both epochs, but similar average abundances for the two analyzed populations. The derived AM relationship shows a little global enrichment, which is interpreted as due to the loss of metals by supernovae winds and to differential gas outflows. Our results bring strong observational constraints to the chemical enrichment history of IC10, the formation of dwarf irregular galaxies and the evolution of the LG as well.

scholarly journals A search for pulsars in the central parsecs of the Galactic center

2012 ◽  
Vol 8 (S291) ◽  
pp. 57-57
Author(s):  
Andrew Siemion ◽  
Matthew Bailes ◽  
Geoff Bower ◽  
Jayanth Chennamangalam ◽  
Jim Cordes ◽  
...  
Keyword(s):  
Distribution Systems ◽  
Galactic Center ◽  
Strong Field ◽  
Pulse Length ◽  
Star Formation History ◽  
Pulsar Emission ◽  
Formation History ◽  
The Status ◽  
History Of ◽  
Green Bank Telescope

AbstractThe discovery of a pulsar or pulsars orbiting near the Galactic Center (GC) could offer an unprecedented probe of strong-field gravity, the properties of our galaxy's supermassive black hole and insights into the paradoxical star formation history of the region. However, searching for pulsars near the GC is severely hampered by the large electron densities along our line of sight and the scattering-induced pulse broadening of the pulsar emission observed through it. As the broadened pulse length approaches the pulsar period, the periodicity in pulsar emission becomes nearly undetectable. Searches extended to higher frequencies, in an effort to reduce scattering, suffer from reduced intrinsic flux, higher system temperatures and increased atmospheric opacity. We are currently attempting to mitigate the challenges associated with searching for pulsars near the GC by employing new wide bandwidth receivers, upgraded IF distribution systems and novel digital spectrometers in a GC pulsar search campaign at the Green Bank Telescope in West Virginia, USA.Our search will cover two frequency bands, from 12-15 GHz (Ku Band) and 18-26 GHz (K Band), during a total of approximately 30 hours of observations, with expected characteristic 10-sigma sensitivities between 5-10 micro-Jy. Our first observations are scheduled for mid-March 2012. Here we will present the status of our observations and initial results.

The Star Formation History of the Local Group Dwarf Galaxy Leo I

1999 ◽  
Vol 118 (5) ◽  
pp. 2245-2261 ◽  
Author(s):  
Carme Gallart ◽  
Wendy L. Freedman ◽  
Antonio Aparicio ◽  
Giampaolo Bertelli ◽  
Cesare Chiosi
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxy ◽  
Star Formation History ◽  
Formation History ◽  
History Of

scholarly journals Is there enough star formation in simulated protoclusters?

2020 ◽  
Vol 501 (2) ◽  
pp. 1803-1822
Author(s):  
Seunghwan Lim ◽  
Douglas Scott ◽  
Arif Babul ◽  
David J Barnes ◽  
Scott T Kay ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Star Formation History ◽  
Test Case ◽  
Numerical Resolution ◽  
Formation History ◽  
Order Of Magnitude ◽  
History Of ◽  
Hydrodynamical Simulations ◽  
Formation Efficiency

ABSTRACT As progenitors of the most massive objects, protoclusters are key to tracing the evolution and star formation history of the Universe, and are responsible for ${\gtrsim }\, 20$ per cent of the cosmic star formation at $z\, {\gt }\, 2$. Using a combination of state-of-the-art hydrodynamical simulations and empirical models, we show that current galaxy formation models do not produce enough star formation in protoclusters to match observations. We find that the star formation rates (SFRs) predicted from the models are an order of magnitude lower than what is seen in observations, despite the relatively good agreement found for their mass-accretion histories, specifically that they lie on an evolutionary path to become Coma-like clusters at $z\, {\simeq }\, 0$. Using a well-studied protocluster core at $z\, {=}\, 4.3$ as a test case, we find that star formation efficiency of protocluster galaxies is higher than predicted by the models. We show that a large part of the discrepancy can be attributed to a dependence of SFR on the numerical resolution of the simulations, with a roughly factor of 3 drop in SFR when the spatial resolution decreases by a factor of 4. We also present predictions up to $z\, {\simeq }\, 7$. Compared to lower redshifts, we find that centrals (the most massive member galaxies) are more distinct from the other galaxies, while protocluster galaxies are less distinct from field galaxies. All these results suggest that, as a rare and extreme population at high z, protoclusters can help constrain galaxy formation models tuned to match the average population at $z\, {\simeq }\, 0$.

Recovering the star formation history of galaxies through spectral fitting: Current challenges

2019 ◽  
Vol 15 (S359) ◽  
pp. 386-390
Author(s):  
Lucimara P. Martins
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Stellar Spectra ◽  
Spectral Fitting ◽  
Formation History ◽  
History Of ◽  
Nearby Galaxies ◽  
Extract Information

AbstractWith the exception of some nearby galaxies, we cannot resolve stars individually. To recover the galaxies star formation history (SFH), the challenge is to extract information from their integrated spectrum. A widely used tool is the full spectral fitting technique. This consists of combining simple stellar populations (SSPs) of different ages and metallicities to match the integrated spectrum. This technique works well for optical spectra, for metallicities near solar and chemical histories not much different from our Galaxy. For everything else there is room for improvement. With telescopes being able to explore further and further away, and beyond the optical, the improvement of this type of tool is crucial. SSPs use as ingredients isochrones, an initial mass function, and a library of stellar spectra. My focus are the stellar libraries, key ingredient for SSPs. Here I talk about the latest developments of stellar libraries, how they influence the SSPs and how to improve them.

Sign in / Sign up

Export Citation Format

Share Document