Galaxy Evolution with SPICA

SPICA is designed to be a powerhouse for understanding  galaxy evolution. It is now well established that the bulk of the star formation and supermassive black hole accretion in galaxies took place around 10 billion years ago, at a redshift of z~2. Since most of the energy emitted by stars and black holes at the centres of galaxies is absorbed by dust, understanding the physics of star formation and black hole growth at these epochs requires observations in the far-IR.

The build-up of stars and supermassive black holes over cosmic time have roughly similar shapes, with a peak near z~2 and a sharp drop to the present epoch, suggesting that these processes are linked, resulting in the black hole–galactic stellar mass correlation we see in the local Universe. SPICA will trace the co-evolution of Active Galactic Nuclei (AGN) and galaxies with cosmic time. 
Star Formation Rate densities in the FUV (blue points) and in the far-IR (red points) (Madau & Dickinson, 2014; Rowan-Robinson et al. 2016). Note that the bulk of the energy produced by stars and accreting black holes emerges in the infrared; in the IR many more objects than in the UV can be used to establishing this relation. The black hole accretion history from X-ray is shown in green shading) and from the IR in blue shading, scaled up by a factor of 3300, compared to star formation rate history.

Fundamental diagnostics of galaxy evolution

Line Ratios Observed line ratios of [NeIII]15µm/[NeII]12.8µm vs. [OIV]26µm/[OIII]88µm for AGN, LINER, starburst and dwarf galaxies in the local Universe compared to photoionization models. (Fernandez-Ontiveros et al. 2016). The IR fine structure lines provide a clear way to discriminate between the power sources in even the dustiest galaxies.

SPICA will also reveal the processes that regulate the baryon cycle and star formation in galaxies, connecting stellar evolution with the reservoirs of gas and dust on scales ranging from individual molecular clouds to galaxy clusters. Gas accretion, outflows and energetic feedback play crucial roles in the evolution of galaxies.

The evolution of galaxies is regulated by energetic feedback from young stars, SNe and AGN, and the cycling of gas and dust; the underlying mechanisms are poorly understood in detail but effectively probed with IR spectroscopy. Most galaxies evolve through secular processes, such as smooth accretion of metal-poor gas, star formation, and the return of metal-enriched gas and dust into the ISM and CGM. Compression and cooling of the ISM enhances star formation, while outflows from stars, SNe and jets from AGN can heat the gas, destroy or modify the dust, and quench star formation.

The galactic Baryon cycle Schematic illustration of the galactic baryon cycle. Star formation and stellar evolution lead to mass loss and SNe, seeding the ISM with dust, metals and molecules. Starburst winds and jets from AGN provide feedback and launch outflows. Metal-enriched and pristine halo gas eventually cool and accrete in the disk to form new stars and feed the central black hole, starting the cycle again. SPICA provides access to unique diagnostics of atomic and molecular gas and dust, the complete galactic baryon cycle.

Expose the full baryon cycle in galaxies

  • SPICA will measure AGN feeding and feedback in significant samples out to z~1-2
  • Measure key tracers of atomic and molecular infall and outflows of galaxies in the peak epoch of star formation.
SPICA's view of Galactic outflow  Simulated SAFARI OH P-Cygni outflow spectra for a L=2x1012 L. galaxy at z=1, based on Herschel/PACS observations of Mrk231 (Gonzalez-Alfonso et al. 2014). SAFARI will detect outflow and inflow motions in ULIRGs up to z~1-2.

SPICA will quantify the metal build-up in a galaxy population representing up to 80% of the total star formation activity in the Universe. Metals play a major role in gas cooling, cloud collapse, and ultimately the formation of stars and planets. The metallicity in galaxies is determined by the cumulative effects of star formation, outflows, and accretion. By using bright, rest-frame mid-IR spectral tracers unaffected by dust, SPICA will accurately measure the gas-phase metallicity in galaxies over a wide range in redshift. In luminous galaxies, the HI 7-6 recombination line at 12.3μm can also be measured, allowing a direct determination of the abundances of Neon, Sulfur, Nitrogen, and Oxygen.

Metal evolution in galaxies From Fernandez-Ontiveros et al. 2016

Metallicity and Dust

  • SPICA provides an extinction-free means to determine gas phase metallicity for a wide range of galaxies and redshifts.
  • SPICA will also off a new view into the mechanisms of dust formation, processing and destruction over cosmic time.
  • Dust features of high redshift galaxies.

Metal features in galaxies SED fit to the z=4.3 starburst galaxy GN20 (Efstathiou Siebenmorgen 2009) rescaled to L=1012 L at z=3-6. ALMA (10 min.), ELT/MOS and ELT/ MICADO (3 hrs.) detection limits are shown. SPICA will map large areas to the confusion limit 100 times faster than JWST, finding obscured AGN and starbursts at z > 3-5.