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I study nearby star-forming regions using photometric and spectroscopic data and also Gaia. And do theoretical modeling of galaxy-wide stellar populatios.
Key questions:
How star-formation depends on local physical conditons, as metallicity of density?
Can we use observed galaxy-wide propersties of distant galaxies to learn about the way they form stars on small scales? Check out out code: https://github.com/Azeret/galIMF
Is the stellar initial mass function universal? Have a look at the discussion between me and Andrew Hopkins on this topic within the ESO Cosmic Duologues framework.
https://www.eso.org/sci/meetings/2020/Cosmic-Duologues/duologue3.html
The link to the PDF of my talk is here: https://www.eso.org/sci/meetings/2020/Duologues/IMF_ESO_TJ.pdf
And the summary of the discussion can be seen here:
https://www.eso.org/sci/meetings/2020/Duologues/IMF_itw.pdf
A stellar relic filament in the Orion star forming region
A stellar relic filament in the Orion star forming region
Tereza Jerabkova, Henri M. J. Boffin, Giacomo Beccari and Richard I. Anderson, MNRAS
We report the discovery of the oldest stellar substructure in the Orion star forming region (OSFR), the Orion relic filament. The relic filament is physically associated with the OSFR as demonstrated by Gaia DR2 photometry and astrometry, as well as targeted radial velocity follow-up observations of a bright sub-sample of proper-motion selected candidate members. Gaia DR2 parallaxes place the Orion relic filament in the more distant part of the OSFR, approx. 430pc from the Sun. Given its age, velocity dispersion, spatial extent, and shape, it is not possible for the Orion relic filament to have formed as a single stellar cluster, even taking into account residual gas expulsion. The relic filament is also too young to be a tidal stream, since Galactic tides act on much longer time scales of order 100 Myr. It therefore appears likely that the structure formed from a molecular cloud filament similar to Orion A in the OSFR and retained its morphology despite decoupling from its natal gas. Hence, the Orion relic filament bears witness to the short-lived evolutionary phase between gas removal and dispersion due to shears and tides, and provides crucial new insights into how stars are formed in molecular clouds.
When the tale comes true: multiple populations and wide binaries in the Orion Nebula Cluster
When the tale comes true: multiple populations and wide binaries in the Orion Nebula Cluster
Tereza Jerabkova, Giacomo Beccari, Henri M. J. Boffin, Monika G. Petr-Gotzens, Carlo F. Manara, Pier Giargio Prada Moroni, Emanuele Tognelli, Scilla Degl'Innocenti, A&A
Context. Recently published high-quality OmegaCAM photometry of the 3 × 3 deg around the Orion Nebula Cluster (ONC) in r, and i filters revealed three well-separated pre-main sequences in the color-magnitude diagram (CMD). The objects belonging to the individual sequences are concentrated toward the center of the ONC. The authors concluded that there are two competitive scenarios: a population of unresolved binaries and triples with an exotic mass ratio distribution, or three stellar populations with different ages (≈1 Myr age differences).
Aims: We use Gaia DR2 in combination with the photometric OmegaCAM catalog to test and confirm the presence of the putative three stellar populations. We also study multiple stellar systems in the ONC for the first time using Gaia DR2.
Methods: We selected ONC members based on parallaxes and proper motions and take advantage from OmegaCAM photometry that performs better than Gaia DR2 photometry in crowded regions. We identify two clearly separated sequences with a third suggested by the data. We used Pisa stellar isochrones to estimate ages of the stellar populations with absolute magnitudes computed using Gaia parallaxes on a star by star basis.
Results: (1) We confirm that the second and third sequence members are more centrally concentrated toward the center of the ONC. In addition we find an indication that the parallax and proper motion distributions are different among the members of the stellar sequences. The age difference among stellar populations is estimated to be 1-2 Myr. (2) We use Gaia proper motions and other measures to identify and remove as many unresolved multiple system candidates as possible. Nevertheless we are still able to recover two well-separated sequences with evidence for the third one, supporting the existence of the three stellar populations. (3) Due to having ONC members with negligible fore- or background contamination we were able to identify a substantial number of wide binary objects (separation between 1000 and 3000 au) and with relative proper motions of the binary components consistent with zero. This challenges previously inferred values that suggested no wide binary stars exist in the ONC. Our inferred wide-binary fraction is ≈5%.
Conclusions: We confirm the three populations correspond to three separated episodes of star formation. Based on this result, we conclude that star formation is not happening in a single burst in this region. In addition we identify 5% of wide-binary stars in the ONC that were thought not to be present.
Impact of metallicity and star formation rate on the time-dependent, galaxy-wide stellar initial mass function
Impact of metallicity and star formation rate on the time-dependent, galaxy-wide stellar initial mass function
Tereza Jerabkova, Hasani Zonoozi A., Kroupa P., Beccari G., Yan Z., Vazdekis A., Zhang Z.-Y.
The stellar initial mass function (IMF) is commonly assumed to be an invariant probability density distribution function of initial stellar masses. These initial stellar masses are generally represented by the canonical IMF, which is defined as the result of one star formation event in an embedded cluster. As a consequence, the galaxy-wide IMF (gwIMF) should also be invariant and of the same form as the canonical IMF; gwIMF is defined as the sum of the IMFs of all star-forming regions in which embedded clusters form and spawn the galactic field population of the galaxy. Recent observational and theoretical results challenge the hypothesis that the gwIMF is invariant. In order to study the possible reasons for this variation, it is useful to relate the observed IMF to the gwIMF. Starting with the IMF determined in resolved star clusters, we apply the IGIMF-theory to calculate a comprehensive grid of gwIMF models for metallicities, [Fe/H] ∈ (-3, 1), and galaxy-wide star formation rates (SFRs), SFR ∈ (10-5, 105) M☉ yr-1. For a galaxy with metallicity [Fe/H] < 0 and SFR > 1 M☉ yr-1, which is a common condition in the early Universe, we find that the gwIMF is both bottom light (relatively fewer low-mass stars) and top heavy (more massive stars), when compared to the canonical IMF. For a SFR < 1 M☉ yr-1 the gwIMF becomes top light regardless of the metallicity. For metallicities [Fe/H] > 0 the gwIMF can become bottom heavy regardless of the SFR. The IGIMF models predict that massive elliptical galaxies should have formed with a gwIMF that is top heavy within the first few hundred Myr of the life of the galaxy and that it evolves into a bottom heavy gwIMF in the metal-enriched galactic centre. Using the gwIMF grids, we study the SFR-Hα relation and its dependency on metallicity and the SFR. We also study the correction factors to the Kennicutt SFRK - Hα relation and provide new fitting functions. Late-type dwarf galaxies show significantly higher SFRs with respect to Kennicutt SFRs, while star-forming massive galaxies have significantly lower SFRs than hitherto thought. This has implications for gas-consumption timescales and for the main sequence of galaxies. We explicitly discuss Leo P and ultra-faint dwarf galaxies. The IGIMF grid is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A39
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