Revealing the formation histories of the first stars with the cosmic near-infrared background
ABSTRACT The cosmic near-infrared background (NIRB) offers a powerful integral probe of radiative processes at different cosmic epochs, including the pre-reionization era when metal-free, Population III (Pop III) stars first formed. While the radiation from metal-enriched, Population II (Pop II) stars likely dominates the contribution to the observed NIRB from the reionization era, Pop III stars – if formed efficiently – might leave characteristic imprints on the NIRB, thanks to their strong Lyα emission. Using a physically motivated model of first star formation, we provide an analysis of the NIRB mean spectrum and anisotropy contributed by stellar populations at z > 5. We find that in circumstances where massive Pop III stars persistently form in molecular cooling haloes at a rate of a few times $10^{-3}\, \mathrm{ M}_\odot \ \mathrm{yr}^{-1}$, before being suppressed towards the epoch of reionization (EoR) by the accumulated Lyman–Werner background, a unique spectral signature shows up redward of $1\, \mu$m in the observed NIRB spectrum sourced by galaxies at z > 5. While the detailed shape and amplitude of the spectral signature depend on various factors including the star formation histories, initial mass function, LyC escape fraction and so forth, the most interesting scenarios with efficient more »
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Publication Date:
NSF-PAR ID:
10352552
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
508
Issue:
2
Page Range or eLocation-ID:
1954 to 1972
ISSN:
0035-8711
We present specific star formation rates (sSFRs) for 40 ultraviolet (UV)-bright galaxies at z ∼ 7–8 observed as part of the Reionization Era Bright Emission Line Survey (REBELS) Atacama Large Millimeter/submillimeter Array (ALMA) large programme. The sSFRs are derived using improved star formation rate (SFR) calibrations and spectral energy distribution (SED)-based stellar masses, made possible by measurements of far-infrared (FIR) continuum emission and [C ii]-based spectroscopic redshifts. The median sSFR of the sample is $18_{-5}^{+7}$ Gyr−1, significantly larger than literature measurements lacking constraints in the FIR, reflecting the larger obscured SFRs derived from the dust continuum relative to that implied by the UV+optical SED. We suggest that such differences may reflect spatial variations in dust across these luminous galaxies, with the component dominating the FIR distinct from that dominating the UV. We demonstrate that the inferred stellar masses (and hence sSFRs) are strongly dependent on the assumed star formation history in reionization-era galaxies. When large sSFR galaxies (a population that is common at z > 6) are modelled with non-parametric star formation histories, the derived stellar masses can increase by an order of magnitude relative to constant star formation models, owing to the presence of a significant old stellar population thatmore »
2. ABSTRACT We study the escape fraction of ionizing photons (fesc) in two cosmological zoom-in simulations of galaxies in the reionization era with halo mass Mhalo ∼ 1010 and $10^{11}\, \mathrm{ M}_{\odot }$ (stellar mass M* ∼ 107 and $10^9\, \mathrm{ M}_{\odot }$) at z = 5 from the Feedback in Realistic Environments project. These simulations explicitly resolve the formation of proto-globular clusters (GCs) self-consistently, where 17–39 per cent of stars form in bound clusters during starbursts. Using post-processing Monte Carlo radiative transfer calculations of ionizing radiation, we compute fesc from cluster stars and non-cluster stars formed during a starburst over ∼100 Myr in each galaxy. We find that the averaged fesc over the lifetime of a star particle follows a similar distribution for cluster stars and non-cluster stars. Clusters tend to have low fesc in the first few Myr, presumably because they form preferentially in more extreme environments with high optical depths; the fesc increases later as feedback starts to destroy the natal cloud. On the other hand, some non-cluster stars formed between cluster complexes or in the compressed shells at the front of a superbubble can also have high fesc. We find that cluster stars on average have comparable fesc to non-cluster stars. This result ismore »
We study a suite of extremely high-resolution cosmological Feedback in Realistic Environments simulations of dwarf galaxies ($M_{\rm halo} \lesssim 10^{10}\rm \, M_{\odot }$), run to z = 0 with $30\, \mathrm{M}_{\odot }$ resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with $M_{\rm halo} \gtrsim 10^{8.6}\, \mathrm{M}_{\odot }$ is populated by a resolved stellar galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field. Our ultra-faint dwarfs (UFDs; $M_{\ast }\lt 10^{5}\, \mathrm{M}_{\odot }$) have their star formation (SF) truncated early (z ≳ 2), likely by reionization, while classical dwarfs ($M_{\ast }\gt 10^{5}\, \mathrm{M}_{\odot }$) continue forming stars to z < 0.5. The systems have bursty star formation histories, forming most of their stars in periods of elevated SF strongly clustered in both space and time. This allows our dwarf with M*/Mhalo > 10−4 to form a dark matter core ${\gt}200\rm \, pc$, while lower mass UFDs exhibit cusps down to ${\lesssim}100\rm \, pc$, as expected from energetic arguments. Our dwarfs with $M_{\ast }\gt 10^{4}\, \mathrm{M}_{\odot }$ have half-mass radii (R1/2) in agreement with Local Group (LG) dwarfs (dynamical mass versus R1/2 and stellar rotation also resemble observations).more »