The interstellar medium of dwarf galaxies: new insights from Machine Learning analysis of emission-line spectra

Abstract

Dwarf galaxies are ideal laboratories to study the physics of the interstellar medium (ISM). Emission lines have been widely used to this aim. Retrieving the full information encoded in the spectra is therefore essential. This can be efficiently and reliably done using Machine Learning (ml) algorithms. Here, we apply the ml code game to MUSE (Multi Unit Spectroscopic Explorer) and PMAS (Potsdam Multi Aperture Spectrophotometer) Integral Field Unit (IFU) observations of two nearby Blue Compact Galaxies (BCGs): Henize 2-10 and IZw18. We derive spatially resolved maps of several key ISM physical properties. We find that both galaxies show a remarkably uniform metallicity distribution. Henize 2-10 is a star forming dominated galaxy, with a Star Formation Rate (SF R) of about 1.2 M yr −1 . Henize 2-10 features dense and dusty (A V up to 5-7 mag) star forming central sites. We find IZw18 to be very metal-poor (Z= 1/20 Z ). IZw18 has a strong interstellar radiation field, with a large ionization parameter. We also use models of PopIII stars spectral energy distribution as a possible ionizing source for the HeII λ4686 emission detected in the IZw18 NW component. We find that PopIII stars could provide a significant contribution to the line intensity. The upper limit to the PopIII star formation is 52% of the total IZw18 SF R.

A physical model for [C ii] line emission from galaxies

“…[OIII] (Inoue et al 2016;Vallini et al 2017), dust continuum (Behrens et al 2018, to constrain D), CO lines (Vallini et al 2018), or even H 2 lines, hopefully becoming available at these redshifts with SPICA (Spinoglio et al 2017;Egami et al 2018). An interesting, and more readily available alternative are optical nebular lines, such as Lyα and C III] , used in combination with machine learning strategies (Ucci et al 2019). The implications of these measurements still need to be worked out fully; we defer this study to future work.…”

“…ALMA has allowed to detect with high resolution and sensitivity line emission tracing the cold gas phases (neutral and molecular) of the ISM in normal star-forming galaxies (SFR < 100 M yr −1 ) at z > 6, that are representative of the bulk of galaxy population at the end of EoR (e.g. Maiolino et al 2015;Capak et al 2015;Willott et al 2015;Knudsen et al 2016;Inoue et al 2016;Pentericci et al 2016;Matthee et al 2017;Bradač et al 2017;Carniani et al 2017;Jones et al 2017;Carniani et al 2018a,b; E-mail: andrea.ferrara@sns.it Smit et al 2018;Moriwaki et al 2018;Tamura et al 2018;Hashimoto et al 2018).…”

ODUSSEAS: a machine learning tool to derive effective temperature and metallicity for M dwarf stars

“…It can be applied to a wide range of studies, with the in-Article number, page 1 of 16 arXiv:2002.09367v1 [astro-ph.SR] 21 Feb 2020 A&A proofs: manuscript no. ODUSSEAS_accepted put attributes being for example the photometric properties of the sources (Das & Sanders 2019;Akras et al 2019;Rau et al 2019;Ucci et al 2019).…”

Challenges in modelling the rest-frame ultraviolet/optical spectra of galaxies at the high-redshift frontier

“…Problems of this type are already acute at low redshifts, for which there are claims that certain very metal-poor galaxies (but at a metallicity above the Pop III regime) display Pop III signatures within specific regions, primarily based on the strength of HeII emission lines (e.g. Kehrig et al 2015Kehrig et al , 2016Ucci et al 2019;Kehrig et al 2018). It is not immediately clear, however, that the discrepancy between the observed HeII fluxes and those predicted by models can be completely detached from the more general problem in explaining the strength of HeII emission in low-metallicity galaxies (e.g.…”