scholarly journals Fingerprints of stellar populations in the near-infrared: an optimized set of spectral indices in the JHK bands 0

2021 ◽  
Vol 504 (2) ◽  
pp. 2190-2223
Author(s):  
Elham Eftekhari ◽  
Alexandre Vazdekis ◽  
Francesco La Barbera
Keyword(s):  
Galaxy Formation ◽  
Spectral Range ◽  
Stellar Population ◽  
Near Infrared ◽  
Nir Spectroscopy ◽  
Mass Function ◽  
Initial Mass Function ◽  
Elemental Abundance ◽  
Spectral Indices ◽  
Diagnostic Features

ABSTRACT Stellar population studies provide unique clues to constrain galaxy formation models. So far, detailed studies based on absorption line strengths have mainly focused on the optical spectral range although many diagnostic features are present in other spectral windows. In particular, the near-infrared (NIR) can provide a wealth of information about stars, such as evolved giants, that have less evident optical signatures. Due to significant advances in NIR instrumentation and extension of spectral libraries and stellar population synthesis (SPS) models to this domain, it is now possible to perform in-depth studies of spectral features in the NIR to a high level of precision. In this work, taking advantage of state-of-the-art SPS models covering the NIR spectral range, we introduce a new set of NIR indices constructed to be maximally sensitive to the main stellar population parameters, namely age, metallicity, and initial mass function (IMF). We fully characterize the new indices against these parameters as well as their sensitivity to individual elemental abundance variations, velocity dispersion broadening, wavelength shifts, signal-to-noise ratio, and flux calibration. We also present, for the first time, a method to ensure that the analysis of spectral indices is not affected by sky contamination, which is a major challenge when dealing with NIR spectroscopy. Moreover, we discuss two main applications: (i) the ability of some NIR spectral indices to constrain the shape of the low-mass IMF and (ii) current issues in the analysis of NIR spectral indices for future developments of SPS modelling.

scholarly journals Stellar Population Models

2012 ◽  
Vol 8 (S295) ◽  
pp. 272-281 ◽  
Author(s):  
Claudia Maraston
Keyword(s):  
Galaxy Formation ◽  
Stellar Population ◽  
High Redshift ◽  
Spectral Energy Distribution ◽  
Cosmic Time ◽  
Mass Function ◽  
Initial Mass Function ◽  
Asymptotic Giant Branch ◽  
Spectral Energy ◽  
Massive Galaxies

AbstractModelling stellar populations in galaxies is a key approach to gain knowledge on the still elusive process of galaxy formation as a function of cosmic time. In this review, after a summary of the state-of-art, I discuss three aspects of the modelling, that are particularly relevant to massive galaxies, the focus of this symposium, at low and high-redshift. These are the treatment of the Thermally-Pulsating Asymptotic Giant Branch phase, evidences of an unusual Initial Mass Function, and the effect of modern stellar libraries on the model spectral energy distribution.

scholarly journals Near-Infrared Spectroscopy of NGC 253: Starburst and Surroundings

1996 ◽  
Vol 171 ◽  
pp. 407-407 ◽  
Author(s):  
D. Lutz ◽  
F. Prada
Keyword(s):  
Stellar Population ◽  
Near Infrared ◽  
Velocity Dispersion ◽  
Mass Function ◽  
Infrared Emission ◽  
Initial Mass Function ◽  
Emission Lines ◽  
Lower Mass ◽  
Dynamical Mass ◽  
Near Infrared Emission

Near-infrared longslit spectra of NGC 253 obtained with IRSPEC at the ESO NTT are presented. By analysis of the 12CO 2.29μm bandhead we find that the stellar population in the central starburst region (r ∼ 150 pc) rotates more slowly than the gas, but has a velocity dispersion of 128 km/s, about twice the value found for emission lines from the gas in this region. This implies an about five times higher dynamical mass than previously derived (Rieke et al. 1980), removing the need to invoke a lower mass cutoff in the starburst initial mass function. The peak of near-infrared emission is displaced from the dynamical center.

scholarly journals INFRARED STUDIES OF THE STELLAR CONTENT IN EXTRAGALACTIC SYSTEMS

1981 ◽  
Vol 96 ◽  
pp. 297-316
Author(s):  
Marc Aaronson
Keyword(s):  
Galaxy Formation ◽  
Globular Clusters ◽  
Near Infrared ◽  
Formation Rate ◽  
Absolute Magnitude ◽  
Type Systems ◽  
Morphological Type ◽  
Mass Function ◽  
Initial Mass Function ◽  
Stellar Content

Normal galaxies emit most of their radiation longward of one micron, and many problems related to our understanding of galaxy formation and evolution can be fruitfully addressed with measurements at near-infrared wavelengths. Such problems include the make-up of the red stellar population, the star formation rate, the initial mass function, metallicity effects, and mass-to-light ratio. How these various quantities depend on morphological type, on total mass (or absolute magnitude), on radial position, and on environment is also of great interest. In this review recent infrared observations of extragalactic stars, star clusters, and galaxies having important bearing on these questions are discussed. Particular emphasis is placed on new evidence for the presence of a finite intermediate age population in early-type systems. This evidence comes from observations of intermediate age stars in many Magellanic Cloud globular clusters, observations of such stars in at least one nearby dwarf spheroidal (Fornax), the difficulties of fitting theoretical isochrone models to the red V-K colors of E and SO galaxies, and the differences in the infrared color-magnitude relations for the Virgo and Coma clusters.“It is not very bright to measure a blue magnitude for a red object.”– Vera Rubin

scholarly journals Surface brightness fluctuation spectra to constrain stellar population properties

2020 ◽  
Vol 493 (4) ◽  
pp. 5131-5152
Author(s):  
A Vazdekis ◽  
M Cerviño ◽  
M Montes ◽  
I Martín-Navarro ◽  
M A Beasley
Keyword(s):  
Galaxy Formation ◽  
Surface Brightness ◽  
Stellar Population ◽  
Near Infrared ◽  
Order Approximation ◽  
Mass Function ◽  
Mass Fractions ◽  
Brightness Fluctuation ◽  
First Order Approximation ◽  
High Degree

ABSTRACT We present a new set of surface brightness fluctuation (SBF) spectra computed with the E-MILES stellar population synthesis models. The model SBF spectra cover the range λλ1680–50 000 at moderately high resolution, all based on extensive empirical stellar libraries. The models span the metallicity range $-2.3\le \mbox{$\mbox{[M/H]}$}\le +0.26$ for a suite of intial mass function types with varying slopes. These predictions can complement and aid fluctuation magnitude studies, permitting a first-order approximation by applying filter responses to the SBF spectra to obtain spectroscopic SBF magnitudes. We provide a recipe for obtaining the latter and discuss their uncertainties and limitations. We compare our spectroscopic SBF magnitudes to photometric data of a sample of early-type galaxies. We also show that the SBF spectra can be very useful for constraining relevant stellar population parameters. We find small (<5 per cent) mass fractions of extremely metal-poor components ($\mbox{$\mbox{[M/H]}$}\lt -1$) on the top of the dominant, old, and metal-rich stellar population. These results put stringent constraints on the early stages of galaxy formation in massive elliptical galaxies. This is remarkable given the high degree of degeneracy of the standard spectral analysis to such metal-poor stellar populations in the visible and in the near-infrared. The new SBF models show great potential for exploiting ongoing surveys, particularly those based on narrow-band filters.

scholarly journals The Initial Mass Function of the Massive Star‐forming Region NGC 3603 from Near‐Infrared Adaptive Optics Observations

2008 ◽  
Vol 675 (2) ◽  
pp. 1319-1342 ◽  
Author(s):  
Y. Harayama ◽  
F. Eisenhauer ◽  
F. Martins
Keyword(s):  
Adaptive Optics ◽  
Massive Star ◽  
Near Infrared ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Forming

scholarly journals The stellar population and initial mass function of NGC 1399 with MUSE

2018 ◽  
Vol 479 (2) ◽  
pp. 2443-2456 ◽  
Author(s):  
Sam P Vaughan ◽  
Roger L Davies ◽  
Simon Zieleniewski ◽  
Ryan C W Houghton
Keyword(s):  
Stellar Population ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass

scholarly journals 13C/18O ratio as a litmus test of stellar IMF variations in high-redshift starbursts

2019 ◽  
Vol 15 (S352) ◽  
pp. 234-238
Author(s):  
Donatella Romano ◽  
Zhi-Yu Zhang ◽  
Francesca Matteucci ◽  
Rob J. Ivison ◽  
Padelis P. Papadopoulos
Keyword(s):  
Galaxy Formation ◽  
High Redshift ◽  
Indirect Evidence ◽  
Direct Methods ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Theoretical Ground ◽  
Litmus Test ◽  
The Universe

AbstractDetermining the shape of the stellar initial mass function (IMF) and whether it is constant or varies in space and time is the Holy Grail of modern astrophysics, with profound implications for all theories of star and galaxy formation. On a theoretical ground, the extreme conditions for star formation (SF) encountered in the most powerful starbursts in the Universe are expected to favour the formation of massive stars. Direct methods of IMF determination, however, cannot probe such systems, because of the severe dust obscuration affecting their starlight. The next best option is to observe CNO bearing molecules in the interstellar medium at millimetre/ submillimetre wavelengths, which, in principle, provides the best indirect evidence for IMF variations. In this contribution, we present our recent findings on this issue. First, we reassess the roles of different types of stars in the production of CNO isotopes. Then, we calibrate a proprietary chemical evolution code using Milky Way data from the literature, and extend it to discuss extragalactic data. We show that, though significant uncertainties still hamper our knowledge of the evolution of CNO isotopes in galaxies, compelling evidence for an IMF skewed towards high-mass stars can be found for galaxy-wide starbursts. In particular, we analyse a sample of submillimetre galaxies observed by us with the Atacama Large Millimetre Array at the peak of the SF activity of the Universe, for which we measure 13C/18O⋍1. This isotope ratio is especially sensitive to IMF variations, and is little affected by observational uncertainties. At the end, ongoing developments of our work are briefly outlined.

scholarly journals The origin of very massive stars around NGC 3603

2019 ◽  
Vol 625 ◽  
pp. L2 ◽  
Author(s):  
V. M. Kalari ◽  
J. S. Vink ◽  
W. J. de Wit ◽  
N. J. Bastian ◽  
R. A. Méndez
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
Future Data ◽  
Solar Type ◽  
Stellar Initial Mass Function ◽  
The Universe ◽  
Shed Light

The formation mechanism of the most massive stars in the Universe remains an unsolved problem. Are they able to form in relative isolation in a manner similar to the formation of solar-type stars, or do they necessarily require a clustered environment? In order to shed light on this important question, we study the origin of two very massive stars (VMS): the O2.5If*/WN6 star RFS7 (∼100 M⊙), and the O3.5If* star RFS8 (∼70 M⊙), found within ∼53 and 58 pc, respectively, of the Galactic massive young cluster NGC 3603, using Gaia data. The star RFS7 is found to exhibit motions resembling a runaway star from NGC 3603. This is now the most massive runaway star candidate known in the Milky Way. Although RFS8 also appears to move away from the cluster core, it has proper-motion values that appear inconsistent with being a runaway from NGC 3603 at the 3σ level (but with substantial uncertainties due to distance and age). Furthermore, no evidence for a bow-shock or a cluster was found surrounding RFS8 from available near-infrared photometry. In summary, whilst RFS7 is likely a runaway star from NGC 3603, making it the first VMS runaway in the Milky Way, RFS8 is an extremely young (∼2 Myr) VMS, which might also be a runaway, but this would need to be established from future spectroscopic and astrometric observations, as well as precise distances. If RFS 8 was still not found to meet the criteria for being a runaway from NGC 3603 from such future data, this would have important ramifications for current theories of massive star formation, as well as the way the stellar initial mass function is sampled.

scholarly journals Red Halos of Galaxies – Reservoirs of Baryonic Dark Matter?

2007 ◽  
Vol 3 (S244) ◽  
pp. 17-25 ◽  
Author(s):  
E. Zackrisson ◽  
N. Bergvall ◽  
C. Flynn ◽  
G. Östlin ◽  
G. Micheva ◽  
...  
Keyword(s):  
Dark Matter ◽  
Stellar Population ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Disk Galaxies ◽  
Near Ir ◽  
Baryonic Dark Matter

AbstractDeep optical/near-IR surface photometry of galaxies outside the Local Group have revealed faint and very red halos around objects as diverse as disk galaxies and starbursting dwarf galaxies. The colours of these structures are too extreme to be reconciled with stellar populations similar to those seen in the stellar halos of the Milky Way or M31, and alternative explanations like dust reddening, high metallicities or nebular emission are also disfavoured. A stellar population obeying an extremely bottom-heavy initial mass function (IMF), is on the other hand consistent with all available data. Because of its high mass-to-light ratio, such a population would effectively behave as baryonic dark matter and could account for some of the baryons still missing in the low-redshift Universe. Here, we give an overview of current red halo detections, alternative explanations for the origin of the red colours and ongoing searches for red halos around types of galaxies for which this phenomenon has not yet been reported. A number of potential tests of the bottom-heavy IMF hypothesis are also discussed.

scholarly journals Hα and FUV luminosities from a stochastically formed stellar population

2011 ◽  
Vol 7 (S284) ◽  
pp. 53-55
Author(s):  
Nidia Lugo Lopez L. ◽  
Gladis Magris C. ◽  
Antonio Parravano
Keyword(s):  
Power Law ◽  
Surface Brightness ◽  
Stellar Population ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Low Surface Brightness ◽  
Low Surface Brightness Galaxies

AbstractIt has been observed that the ratio of Hα to FUV luminosity (LHα/LFUV) is lower in low surface brightness galaxies. This behaviour has been attributed to systematic variations of the upper mass end and/or the slope of the Initial Mass Function (IMF) Meurer et al. (2009) and Lee et al. (2009)). However these hypotheses do not explain the observed scatter in luminosity ratio (LHα/LFUV). We present a model for the total LHα and LFUV luminosity arising from a randomly populated IMF following the Salpeter power law and the clustering law of Oey & Clarke (2007).

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